Hi guys,
I have a problem with my Classic, yesterday during a particularly hot day we noticed the air con turn off for no reason. I went to the shed to check on things and noticed my battery voltage was around 74v (48v system) The inverter had shut down showing over volt.
The charge controller was showing 67c at the FETS, 55c PCB. The fans had stopped and all LEDs were blinking slowly inside and out. All numbers were 0 except for in and out volts they were both at 74v.
I shut down the panels, and reset the inverter to drain the excess charge and removed the CCs case, after this the temp quickly reduced after which all fans started and all lights back to normal. All numbers have remained at 0 except for in and batt volts. Inside I see there is scorching on the PCB beside the middle three FETs but nothing else obvious.
After a few measurements it appears that the charge controller has cooked itself and connected the panels directly to the battery's so they have pulled the panels volts down to battery volts and then just kept filling the battery trying to bring it up to panel volts.
What has happened to cause this and can it be fixed or is this controller now a bin job ?
Bump this one... I heared about this on a local Australian forum and it's got me worried to.
Having his charge controller short his panels directly (unregulated) to his expensive lithium battery and overcharge it to the point of swelling up and cooking - damaging all his near new lithium cells has me very concerned about connecting my two classic 150's up to my new $10,000 worth of lithium cells (though fortunately i have over voltage protection) I thought the classic wouldn't allow this by design even in a failure event?
Guys how could this have happened (to me its like total brake failure on a car) very serious!
Kurt
The normal failure mode for all charge controllers is as stated by Robin in one of his posts. I'm not sure I understand the panel to battery issue or why the breakers didn't trip. Maybe boB over Ryan can shed some like on this.
Robin's post:
"Breakers are sized to protect wiring, not electronics. You can adjust the Classic to do many things, but make sure the breakers and wiring is adequate to protect. When a charge controller breaks, they typically short internally from battery plus to battery minus. This condition puts a direct short across the battery bank. You need a breaker that will trip to keep the wires from burning up. By the way, all controllers work this way."
I guess you can take comfort in having had an abnormal failure ?
Perhaps short was the wrong word.
The issue was his controller failed internally and some how allowed is Pv to continue to feed power into his battery's but the power flow was unregulated ( like having the pv directly connected to your battery) with high voltage array ( or any array above normal charging range things get overcharged real fast.
Kurt
To resthome,
If the charger had of failed in this manner it would have tripped the HRC fuses and saved the battery.
Because there was no short, or excess flow of current it just kept going.
It was as though the Classic got hot and bothered then just threw its hands in the air, and said "screw you guys I am going home" then just left all the other components to keep going without it :)
To Mike, the only thing that I can be thankful for is that it happened while I was home and was aware enough of my system to recognise something was wrong and check it quickly enough to shut it down.
Had it not happened like it did the controller would no doubt have continued to increase volts in the battery to the point of catastrophic destruction, possibly taking the rest of the shed with it.
As I stated in the OP it would be good to get an idea of what could have gone wrong and if it can be fixed.
Yes, count your stars that you were there and caught what was going on. Hopefully your batteries were not damaged. ~ks
I see you said that only Volts were showing, but nothing else... What is your amperage (configuration) potential from your array?
QuoteYes, count your stars that you were there and caught what was going on. Hopefully your batteries were not damaged. ~ks
His cells reached 4.8v per cell 76.8v (20v overcharge) for a 48v bank. They hit 48.7c and swelled up like a balloons there is defiantly some damage.
Kurt
My array is 5.7kw, so has a potential of around 100amps depending on charge state. However because it is a multi orientation array. It's actual peak is 4kw.
Just before the incident it was on float at 700w. The batteries where already full.
Is offgridQLD and wrt talking about the SAME thing ? Or are they different ? If FLA batteries that would be
74V/24 = 3.1 V per cell... Or if 4.8V for Lithium ?
I am not sure what happened.... I would have said that the processor went nuts or crashed but you (wrt) mentioned
some scorching near the middle FETs. One reason I tend to think it was the processor is that
if an input FET shorted AND the relay stuck, the FETs will usually ALL short out and would trip the battery breaker.
That is how most MPPT charge controllers fail.
This is the first time I have heard of THIS happening, BTW, so this would be extremely rare, luckily.
Was it a Classic 150 ? How long has it been working ? What serial number or when was it built ?
I would hope that we hear from you, WRT tomorrow at least for RMA info. Were the batteries hot ?
If this did not go on for too long, then the batteries I would think would be OK. Nonetheless, this
is scary !
boB
Hi Bob, we are both talking the same incident, they where LiFePo4 pumped to 4.8v. Just about to leave for work so will post a pick of the FETs when I get home and figure out how to. The barcode on the side of the unit is CL02868. Not sure if that is the number you are looking for.
Will post again in 9hrs when I get home. Am driving to Melbourne tomorrow for the distributor to inspect.
Quote from: wrt on January 04, 2015, 09:43:46 PM
Hi Bob, we are both talking the same incident, they where LiFePo4 pumped to 4.8v. Just about to leave for work so will post a pick of the FETs when I get home and figure out how to. The barcode on the side of the unit is CL02868. Not sure if that is the number you are looking for.
Will post again in 9hrs when I get home. Am driving to Melbourne tomorrow for the distributor to inspect.
Thank you ! Yes, that was the number I was looking for. It is older but still not good.
Any charge controller can do this if they break but we all try to make this particular failure mode as rare as possible.
We have now shipped tens of thousands of Classics and yours (AFAIK) is the first and only one to have shown
this particular problem. Also, 67 degrees temperature is nothing for the FETs... they can actually run past 100 degrees C
for a long time but we shut them down before then. I AM curious how hot the batteries got though ?
Usually, the BMS should protect for over-voltage since there is an active control system. Did this happen ?
Hi Bob,
Yes I was talking about WRT's indecent I had some backround on the insedent from another posting of his on a local forum. His cells are Lifepo4 lithium with a nominal voltage of 3.2v pr cell and he uses 16 cells (typically the cells sit around 3.3v - cell 52 -53v for 16 cell bank) When charging you usualy pull the pin and drop to float at around 3.5 -3.6v pr cell . 3.8v - 4v pr cell is usually when you should shut things down and see what went wrong befor you kill something. His cells got to 4.8v pr cell. The cell casing start to swell up like a balloon and typically this turns out to be total loss or reduced capacity (that's if you can successfully clamp the cells flat again)
this is what his cells look like now all puffed up and swollen.
(https://forums.energymatters.com.au/resources/image/thumb/1557)
BMS or BCU systems tipically do have large contactors and individual cell monitoring units that pull the contactors in low and high voltage events for any cell. (The BCU system I am installing on my lithium has both high and low) Though WRT's didn't have a high voltage protection he was just trusting the charge controller. (I was thinking of doing the same at first) The classics have been 100% reliable for me for several years and rock solid voltage regulation.
I just mentioned to WRT's to let you guys now about it as it did look like a rare event and one that is worth investigating.
My own personal interest in WRT's event is I run two classic 150's similar climate (though a little lower extreems in the part of Australia where I am) I run a similar largish system (4000w) of pv on each classic and one of my classics has 3s configuration so high VOC and I notice that unit runs a lot hotter than the other classic with 2s panels and lower voltage to down convert to 48v. After this event I am considering reconfiguring the pv to 2s to help that classic run cooler (that's if WRT's classic failure had anything to do with heat) I'm also about a week away from upgrading my old lead acids to 16x 400Ah lifepo4 lithium cells the same as WRT was using so some interest stemmed from there in the event. (lets just say I had a few nights ofter hearing his story when I woke up in a cold sweat and my wife mentioned I was mumbling something about swollen- pregnant lithium battery cells and possessed classic 150's ;D.... ;)
Kurt
Quote from: offgridQLD on January 05, 2015, 01:48:55 AM
Hi Bob,
Yes I was talking about WRT's indecent I had some backround on the insedent from another posting of his on a local forum. His cells are Lifepo4 lithium with a nominal voltage of 3.2v pr cell and he uses 16 cells (typically the cells sit around 3.3v - cell 52 -53v for 16 cell bank) When charging you usualy pull the pin and drop to float at around 3.5 -3.6v pr cell . 3.8v - 4v pr cell is usually when you should shut things down and see what went wrong befor you kill something. His cells got to 4.8v pr cell. The cell casing start to swell up like a balloon and typically this turns out to be total loss or reduced capacity (that's if you can successfully clamp the cells flat again)
this is what his cells look like now all puffed up and swollen.
(https://forums.energymatters.com.au/resources/image/thumb/1557)
BMS or BCU systems tipically do have large contactors and individual cell monitoring units that pull the contactors in low and high voltage events for any cell. (The BCU system I am installing on my lithium has both high and low) Though WRT's didn't have a high voltage protection he was just trusting the charge controller. (I was thinking of doing the same at first) The classics have been 100% reliable for me for several years and rock solid voltage regulation.
I just mentioned to WRT's to let you guys now about it as it did look like a rare event and one that is worth investigating.
My own personal interest in WRT's event is I run two classic 150's similar climate (though a little lower extreems in the part of Australia where I am) Irun a similar largish system (4000w) of pv on each classic and one of my classics has 3s configuration so high VOC and I notice that unit runs a lot hotter than the other classic with 2s panels and lower voltage to down convert to 48v. After this event I am considering reconfiguring the pv to 2s to help that classic run cooler (that's if WRT's classic failure had anything to do with heat) I'm also about a week away from upgrading my old lead acids to 16x 400Ah lifepo4 lithium cells the same as WRT was using so some interest stemmed from there in the event. (lets just say I had a few night when I woke up in a cold swett and my wife mentioned I was mumbling something about pregnant lithium battery cells and possessed classic 150's ;D.... ;)
Kurt
I/We are very interested in what exactly happened here. One thing I was thinking was that if something like this were to
happen again, a noise maker/buzzer or additionally even a relay/contactor of some sort could be connected
to the to one of the Aux outputs in a mode that would turn on when the battery voltage got above some preset
value for at least a second or two or three. That would keep the plumping from happening.
I am also very interested in the one poster's comment about compressing the plumped battery to get it to
work right again. The attitude there was that it does work but I have not had enough experience with those
LiFePo batteries to know how well that works. Might be that is works great ?
67 degrees C is just not very hot. Remember that the die inside the FETs are rated for 175 degrees C
or 150 C.
boB
QuoteOne thing I was thinking was that if something like this were to
happen again, a noise maker/buzzer or additionally even a relay/contactor of some sort could be connected
to the to one of the Aux outputs in a mode that would turn on when the battery voltage got above some preset
value for at least a second or two or three. That would keep the plumping from happening
The issue I see with that is wouldn't you still be relying on the classic to activate the Aux output. If a rare total meltdown system failure has the PV connected unregulated to the battery and the brains of the unit all upset. Then I'm not sure you could trust the Aux output would be functioning correctly.
I think double redundancy like I have controlled by a external device is the only way to safe guard 100% (well not 100% as that could fail to but you have to draw the line somewhere). Rare events like this just show how important it is . Lifepo4 is reasonably forgiving and a safe chemistry. You need something dramatic abuse to upset it and some extra hard abuse to make it vent or go pop. Though they are are not as forgiving as flooded lead acid when it comes to chronic overcharge as they wont just boil away and makes bubbles like the FLA's. That said even 48v FLA being fed unregulated full output pv at 76v in 40C ambient weather could end in flames.
Kurt
Hi Bob,
I have got the photo I promised of the FETs. The unit was purchased late 2012. The battery temp at shutdown was 48.7c. Whle this does not appear warm it needs to be noted that these cells rarely approach 2c over ambient.
A few of the posters have expressed concern about how dangerous it may have been that the battery reached 76v. I think the scary thing is that they reached this voltage in the time it took me to head out to the shed and pull the fuses on the array after the inverter shut down.
It needs to be considered that my array is around 120voc and the controller would have kept driving the cells to this had I not been home.
The other thing worth noting is that the unit had already shut all its fans OFF by the time the FETs reached 67c temp, therefore removing any heat protection it had. They only came back to life after the temp had reduced into the high 50s and the LEDs stopped flashing.
The place I am driving to tomorrow is called DC solutions in Melbourne. They are the Victorian distributor for Midnite products, and the repair agent. It's a five hour trip but at least I know it won't be lost in the post :)
WRT, I don't see anything weird in the FET picture. At least I don't see any scorching.
The Classic now has battery over-temperature shut down but is normally disabled. Your version
probably didn't have that but even with the latest, it is hidden in the modbus until the new firmware
coming up in a few days.
I think you said that the MNGP display showed the high voltage on its display ? If so, the Aux output would
have worked to show over-voltage before it crashed or whatever happened.
Are you using your own BMS ? I think I saw something about that ? There is a Classic Aux 2 input mode
that is made for a certain LiFePo BMS where it tells the Classic to shut off when going high or low as well.
Can't remember the particular BMS though. Let us know how the visit with DC Solar goes so we can
fix you up if that doesn't pan out.
boB
The marks that have only recently appeared are the dark stains between the metal tabs that overlay the white background on the edge facing the camera. These were not there last time I checked inside and looked to my untrained eye to be scorch marks, as I have seen these before on other electrical items.
Hopefully the trip went well. After a fruitless discussion about warranty periods and my retailer stepping in for me they are looking to repair it under warranty unless they find something that voids it.
They have no idea of a time period yet as they have no way of knowing what parts are needed or how long it will take to get them, I am happy happy with that.
I have requested that they note what went wrong with the unit and what was required to repair it so I can share with you.
As for the BMS, as offgrid has stated, I had yet to fit a hi voltage cutoff to the system and was relying on the Midnites reputation for reliability until I got it done. It was just bad luck I got caught out by an unknown fault. I am happy to share what I can though so we all can learn :)
Ahhh yes !!! I DO see that mark in the picture. that is definitely where the smoke came out of the FET. That FET is probably
split in two.
So, what will happen, I am pretty sure, is that your Classic (in the picture) will come back to us from DC Solar and they
will do something to satisfy you. I am not sure exactly how that works ? Or, at least I can't remember, but I have
a feeling we will see your unit. I would like to know what came first... A blown FET or bad processor or both or just
one of them ?
Thanks for the information ! The more info is always better.
boB
Am I seeing it right, that there may be as many as 4 FETs involved, going by the dark marks?
If the input is shorted, this usually means at least 2 dead. Takes 2 to short. Pretty much the same for most mppt CCs.
First off, truly sorry to hear of your experience. I know how much work goes into planning and setting things up...
QuoteThe issue I see with that is wouldn't you still be relying on the classic to activate the Aux output. If a rare total meltdown system failure has the PV connected unregulated to the battery and the brains of the unit all upset. Then I'm not sure you could trust the Aux output would be functioning correctly.
I think double redundancy like I have controlled by a external device is the only way to safe guard 100% (well not 100% as that could fail to but you have to draw the line somewhere). Rare events like this just show how important it is.
Kurt, I know with wind systems it is pretty common for folks to employ an alternate means of protection for overvoltage (from the turbine); as the risk is high. We're using an inexpensive voltage sensing relay - still unproven in our case, but it's based on a design used effectively by Rob Beckers on grid-tied systems with his Aurora inverters. You may find it of interest. If you search the OP board you'll find more.
QuoteIt was just bad luck I got caught out by an unknown fault. I am happy to share what I can though so we all can learn :)
This is a rare, and remarkably positive attitude given your circumstances. From my opinion these guys have some of the best customer support out there. There will be something to have learned here that, may benefit many others. All too often there's finger pointing and nothing learned from the fact that sometimes, despite our best human efforts, things go south.
Good luck with it.
~ks
+ 1 about wrt's calm attitude . If my new lithiums had been fried. I wouldn't have needed to get on the forum to share it. As my screaming fit of rage would most likely make international TV news ;D ...headlines (man destroys city in a godzilla like fit of anger over swollen batterys)
Yes I have always admired the open and honest attitude that the Midnite crew have maintained even as they grow. Try and find another company there size that involves there customers so much in there products on a personal level. Only good things and a ever improving product can come from that. I sure am keen to find out how the rare even was triggered even if it just turns out to be bad luck and a 1 in a million component falure....might help midnite employ was to protect against it happening again
Ok now the brand loyalty speech is out of the way ;)
QuoteKurt, I know with wind systems it is pretty common for folks to employ an alternate means of protection for overvoltage (from the turbine); as the risk is high. We're using an inexpensive voltage sensing relay - still unproven in our case, but it's based on a design used effectively by Rob Beckers on grid-tied systems with his Aurora inverters. You may find it of interest. If you search the OP board you'll find more.
Yes when I purchased my 16x400ah lithium cells they came with 16 individual cell monitoring cell top boards and a BCU box that has two large 200A contactors inside it (one for charge power in and the other for loads out) the electronics in the BCU box pull the appropriate contactor based on if its a HIGH voltage event or LOW voltage event signal sent from the cell top boards. The box also has a small lcd display with capacity meter, SOC, AH IN , OUT and load - charge values (not really needed now I have the (WBJR). Not a bad little unit covers all bases. (I did a small over view of the BLUE EVpower brand BCU in my youtube channel)...link below in my signature.
Kurt
Hi guys,
Just a quick update on what is happening with my classic.
I have phoned the AU distributor to find out what is happening with the CC.
They state that the problem was caused by one FET overheating, failing, then causing a cascade down the other FETs as each took on an ever increasing load that they could not handle given their already stressed state. All but two failed.
The only problem I have with this diagnosis was the system had been on float for an hour and was running at ~700w I would think the remaining FETs should have no problem accommodating 700w without failure. Although this does link with the fact that the higher the voltage difference between panels and battery, the higher the temp developed within the unit (120v on float compared to 90v under heavy charge output)
As for warranty, the tech stated they are considering sending out a new replacement, however the boss is away until Monday so this cannot be confirmed until then.
As for those discussing my attitude toward the situation...My opinion is that more people need to use logic and common sense when attributing blame to product failure. I believe that any company can have something unexpected happen. They should not be judged by this because it is usually not predictable, they should be judged by how they handle it.
Although the failure of the midnite product did result in the damage to my battery, I had not taken the precautions that should reasonably be expected of someone running LiFePo4 cells against this occurrence, therefore the damage to my battery is in no way Midnite's responsibility or problem.
The failure of the midnite itself, installed to spec, is something they are responsible for and I am very happy with the way it is being handled and with the effort they are making to both rectify my situation and continue improvement to make their product the best available.
To Bob, if this unit does end up coming back to you for a look, I can PM you my details so you know who it belongs to and you can feel free to ask anything you think will help in identifying the cause of failure.
WRT
Please ask your contact at DC Solar to email me ryan@midnitesolar.com I will give him the OK to send out a new one asap
Ryan
Thanks WRT. Yes, if you don't get results with DC Solar (which I'm sure you will though), we will back you up as well of course.
What happens in 99.9% of cases when one FET shorts is this... That FET, that WOULD normally connect the PV input to
the battery terminals through the RELAY contact, would then short the BOTTOM FET and from the almost un-limited
battery current going back into the bottom FET that turns on, that bottom FET will then short, turning OFF your
battery circuit breaker and stopping any more bad things from happening.
In addition, (99.9% of the time), when both top and bottom FETs have shorted out the PV input, the PV will
be at 0.0 volts because of that short circuit of PV + to PV - So if this did not happen, this is extremely
rare.
Normal operation is (at 25 kHz) the TOP FET turns ON and then the TOP fet goes OFF and the bottom FET turns ON.
then the bottom FET turns OFF and the TOP FET turns ON.... Repeat 25 thousand times per second, two cylinders.
So, both of the converters are actually in parallel. If one "cylinder" shorts, the other cylinder should operate
but if one cylinder is shorting the PV plus and minus, the remaining cylinder cannot run. Even if only two
FETs in one cylinder are shorted, the other two cannot operate with their co-horts shorted... UNLESS the
blown FETs actually OPEN up. This would be that 0.1% of blow-ups but we rarely, if ever see that
happen.
Then, in addition to all this, even if a FET goes OPEN, the software should see that the battery voltage
is way over voltage and shut things of. In addition, there is a RELAY... If that relay happens to
not be able to open up, or the contacts weld together (also very rare), then what happened could
happen. There is quite a bit of redundancy and along with over-current protection by way of
the battery circuit breaker, you would think that would be enough.
So much for the department of redundancy department.
Waiting to see what exactly happened, circuitry wise on this one.
boB
Thank you Ryan, I have phoned and passed on the info to the tech, though from his non committal response I don't think it will make too much difference to his decision to wait fir his boss's go ahead :)
On the subject of the cause of the problem, I am interested in the temp limits of the classic, what temp does it shut down at? What temp would you normally see on the FETs on a35c day, or even on the odd 40c day (we get up to 7 days a year at this temp)
I guess what I am asking is, under normal circumstances should the classic have no problems under these conditions with panels putting out up to 120v or will I need to have my array rewired for 2s and maybe the classic string tool be altered to reflect this for future customers. Something along the line of 3s only for climates where max ambient is 30c. Above this, limit to 2s.
It should be noted I have never had temp problems under big charge loads where input volts are lower, only float/low charge rates where they rise.
Or perhaps non of this makes a difference and I was just unlucky to get a crook FET that was waiting for the right combination of high temp and volts to fail.
Obviously I don't want to have to reconfigure if it will no difference to the classics lifespan :)
WRT, with PV output normally rated at 25* C, as the temps rise what amount of de-rating (volts) are/were you observing?
My personal preference is to keep below that 80% of Vmax for the Cl150, and I see you are at 120V/80%...
Mine will be stepped down from nom. 48V to 24V, I see you re going from 120V to 48... maybe too big a stepdown...??
add: for clarification: nom.
The volts on mine vary with load as well as ambient temp. They range from around 120v on low load and a cool day to around 90v on a hot day with a big load.
FET temps vary under the same conditions. Cool day and big load they hover around the 48c. Cool day and light load they will rise to around the 52c mark. On a hot day and big load they are around 52c with this rising to around the 56c mark as the load drops off.
I note that your panel volts are at 48. Keep in mind my volts are at actual out put, not nominal, if you are using 2s x 24v nominal rated panels you may find that they actually run around 70v-80v in practice, and your step down to 24v is greater than mine.
I am running 3s x 24v nominal panels down to 48v
I see what you are doing , an interesting idea. What uses 120V DC?
My panels are 140W 12v panels, not 24 so I will have 4S array configuration for 48V.
In winter time I expect to see upwards of 90V as we can see overnight temps dip to ~ - 40*C
The CC is in the basement so a bit of heat then is a good thing... :) when it is that cold outside
QuoteI see what you are doing , an interesting idea. What uses 120V DC?
His battery bank is 48v . His talking about his charge controller input from the PV array is 120v at times (3 series panels of around 40v at times)
I'm starting to have the same thoughts about reconfiguring one of my arrays back to 2s from (3s now) just to give the classic a easier life I I to have noticed it runs way hotter at 3s than 2s. Keep the input voltage closer to the battery voltage (yes more loss in the wires but I prefer that to loss in the charge controller = heat locked in the little aluminum box ;))
Kurt
Actually Kurt, in this circumstance I am not sure you would have more loss in the wire with 2s.
Usually having higher volts is considered advantageous because you have less amps to carry.
In this case you are reducing the panel count in the string, therefore amps remain the same while volts decrease. The remaining panels are distributed over more strings so you have a higher copper count to send the remaining amps and volts on. Probably not too big a loss at all.
The more strings part is the main reason I am reluctant to reconfigure unless it is clear that the classic needs it to live well in our climate. In my case I have to run 5 extra strings of cable + conduit + fuses +enclosure, bus bars, glands, MC4s, assorted racking and time. It all adds up quickly.
Quote from: wrt on January 09, 2015, 02:32:23 AM
The more strings part is the main reason I am reluctant to reconfigure unless it is clear that the classic needs it to live well in our climate. In my case I have to run 5 extra strings of cable + conduit + fuses +enclosure, bus bars, glands, MC4s, assorted racking and time. It all adds up quickly.
It sounds like each of your strings needs a long cable to the combiner... usually the combiner is at the array and a single cable makes the home run to the controller. If this is the case, the home run cable will have higher losses when you reconfigure to more (lower voltage) strings. On the other hand, the increased cable losses MAY be more than compensated by the increased efficiency of the controller.
Every case is different and the optimal solution depends on knowing the distance, the cable size and length, the panel specs and their configuration. When you design a system, it is usual to use the full power rating of the panels to calculate the voltage drop and power loss in the cable. The power loss in the cable goes as the square of the current, and the current is seldom at the rated specification. In other words, with NOCT conditions the power loss in the cable will be much less than calculated at STC conditions. On the other hand, reducing cable loss by making fewer (higher voltage) strings will cause the controller to be less efficient at all power levels. Here is an example with some numbers calculated:
http://midniteforum.com/index.php?topic=2008.msg18796#msg18796
wrt,
I'm not really sure how your 5.7 kw array is configured... why do you need so much more conduit, cable, racking, etc to reconfigure into more strings?
--vtMaps
My combiner is on the switchboard, each set of three panels has its own string back to its own fuse. At this point I have 10 separate strings, all are contained in conduit.
Running multiple combiners on the roof may seem like a better solution, and probably is in most cases where all panels are in the same area. However in my case the savings are not huge as my array is spread over the 15 meter width of the shed.
By the time multiple waterproof enclosures with the same amount of fuses in them are placed on the roof and wired back to the panels, Plus the heavier cable to run the higher amps from them back to the switchboard are accounted for I doubt there would be a huge costing difference.
As for the racking this again comes down to configuration, each set of 3 panels is on its own set of tilts to take advantage of winter sun, except for 12 which lay flat on the roof, these sets of tilts are equally distributed across the four different facets of the shed roof (the style of roof is called an American barn) this helps to spread generation across the day.
Because of this I only ever see a peak of around 4kwh out of the array, however it produces this for a long time.
I am probably making it sound more complicated than what it is but hopefully it clears things a little :)
The string configuration here is essentially identical to wrt's -- strings of three real 24 V PVs STC Vmp of 106-ish V and Voc about 132 V.
Have run this off-grid system for the last 9 + years. First with the MX-60 CC, and more recently, using MN Classic 150s.
When in the later part of Absorb, and in Float, with light loads, the Vin to the CC often runs 120 Vdc or more, as PV loading is reduced, the string voltage approaches Voc.
It was initially surprising how much less efficient the CC is delivering 200 Watts output with 122 Vin, vs delivering, say, 1500 W with 100 Volts input to the CC. This efficiency reduction is certainly not linear -- there is some exponent involved.
Even the venerable, efficient MX-60 would have its tongue hanging our, frequently running its fan (200 W out, 122-ish Vin), verses essentially never running its fan at 1500-ish W out and 100 Vin.
Did choose this string config, because it laid out well -- strings of two wasted roof space, racks of four PVs were mechanically weak, and a wind concern, and, trying to rack three PVs and wire them as two per string was a real inefficient mess. Also wanted the ability to try heating water directly from the DC PV, rather than AC, and 106 V was better for this than 71 V would be.
My "solution" to the hot CC issue, was to Air Condition (A/C) the Cargo Container Power Room, with a 6,000 BTU window A/C. This works well, and the MX stopped running its fan, ever, And the Classics are happier, as well. But in a hot climate with these high input voltages, without A/C, would bet that most any CC would be very thermally taxed.
The other main reason for A/C in the power room, is to try to keep the batteries as cool as possible, and this has also worked out well.
Just understand, that STC string voltages and losses in the CC, increase by a surprising amount, as the loading on the PVs decrease during Absorb and Float. Working to keep the PVs loaded with heating/cooling and other opportunity loads will help reduce the Vin, and CC heating.
As we all know, heat is not good for most electronics.
This is stating the obvious, but just a reminder. FWIW. Good Luck wrt! Vic
Echoing what Vic said, here even running strings of two 72 cell modules the classic does get hot in float. I have no idea why but it does. The batterys are charged, very light loads on the system, and yet the fan will be running. ITs counter intuitve, but vics explanation of the high input voltage is about as close of an explanation as ive heard.
So it is clear from the feedback received on this thread that 3s is a known problem for generating excessive heat within the controller.
As part of the solution to this problem and continual product development I understand it would not be viable to develop this out of the product, perhaps, as I had posted earlier, better education for users would be an economic solution?
Perhaps adapt the Midnite sizing tool to show a clear warning to avoid this configuration where ambient temp regularly exceeds 30c. Maybe a sticker on the display WARNING: GREATER THAN TWO PANELS IN SERIES MAY REDUCE PRODUCTS LIFESPAN IN HOT CLIMATES. Maybe warnings on the front page of installation manual. Bury it I the manual and the average installer will never see it :D
It must be said here that I sought advice from two separate professionals when I reconfigured and expanded the system last. Both advised to change from the 2s that I was running to the 3s that I now have now. Both could not understand why I would have only 2s when 3s "was so much more efficient" and result in less cable runs.
Edit: As a curiosity, the sizing tool tells me I am fine to step 120v all the way down to 24v as long as I stick to 4 strings ;)
This is a disturbing thread.
I replaced 1000AH of AGM cells early last year with 16 x 300AH LFP (LiFePO4) cells. So far, everything has been very good.
I'm saving to put a second set of LFP....
I have six solar arrays, individually metered. They are geographically diverse - 4 on 2-axis trackers, 2 on single-axis, but all spread across about 50 metres (160'). Each array runs inside on its own feed cable and into the metering, protection and combining (via diode isolation). Arrays are 6 x 100W/12V (nominal, about 17Vmp), for a nominal voltage of 100V.
I have a Flexmax FM80, and a Midnite 150 (I can switch between one, the other, or a mix of both).
Summer temperatures are often 45C here, although my battery room is underground and ambient temperature rarely gets over about 30C.
As I've never seen, (or until now even heard of) failures going overvolt, I chose not to introduce another point of failure with high-voltage disconnect. I'm now worrying about the potential implications of that decision!
I have mitigated it SLIGHTLY with my battery cell monitoring system, which will alarm if any cell gets more than about 50mV above or below the string average, and/or if the total bank voltage gets above or below my preferred limits, but if I am away from home I'm now getting concerned!
(Graph looks a little furry, this is still a "work in progress" and I haven't calibrated the boards carefully, they're "near enough" but not "exactly right")
(http://ranges.albury.net.au/tomw/CellVolts.gif)
DC-rated Normally-closed breakers in the current/voltage range I want are hard to come by (and expensive).
I really don't want to blow the extra watts on an "always on" contactor - not to mention, the reliability issue.
I considered a sacraficial breaker across the input to the classic as a crowbar, but the breakers to the PV won't be tripped by it, because the PV won't make enough current to trip them! Blowing the 100A DC fuse on the input to the classic if I detect overvoltage is an expensive (and scary) step.
Replacing the breakers with solenoid-operated switches? A solenoid to turn it "on" (pulse only), and another to turn it off? Like a mechanically-latching relay? Sounds expensive, large and of questionable reliability. (Granted, it wouldn't get operated more than a few times a year, if that)
Anyone got any other thoughts??
There are a few point here that need to be looked at. As you stated before you have never seen or heard of overvolt failure. Midnite have assured us that this is an extremely rare way for this CC to fail (0.1% of FET failures result in this)
Your power room rarely gets above 30c. mine has seen at least 10 days this year at 35c and 4~5 at 38c
I think even though it is introducing another point of failure. Automatic hi and low volt disconnects are necessary to protect from the rare things in life (says the man with the bolted horse ;D)
Maybe if it is economical reduce the input volts as the others have been suggesting. Although I am waiting for Bob to read my post on the last page to find out whether these higher operating temps really matter.
It sounds like you are about to have around 15k worth of battery, a few hundred extra for control and latching contactors would be good insurance.
Quote from: wrt on January 09, 2015, 03:20:48 PM
So it is clear from the feedback received on this thread that 3s is a known problem for generating excessive heat within the controller.
Well its forum wisdom that the greater the voltage dropped by the controller, the less efficient the controller operates. You probably know that even a couple percent differnce, when you are running 4kW ammounts to a lot of heat. This applies to any brand of mppt controller. Outback publishes effciency curves for the flexmax, and these are a good guide to horse trading pv cable losses against controller losses. If midnite could publish simialr curves for the classic that would a good help in this regard, however given the two products common heritiage we generally assume similar curves for the classic. ie approx 2% extra loss for each step up in string voltage.
Midnite do publish a power graph, which does suggest inefficiency as the input volts rise feeding a 48v bank. However it does not make the same point at lower voltages (the step down theory) the difference between 70v and 120v stepped down to 48v is around 11% loss.
When you look at the difference between 70v and 120v all the way down to 12v the loss is only around 5% you would think the efficiency losses would be massive from 120v to 12v.
Given the heat generated by stepping down from 120v to 48v you would think stepping from 120v to 12v would be unsurvivable in the coldest climate.
It needs to be considered that not everyone possesses forum wisdom untill they have a problem and start googling the problem or join the applicable forum (in this case Midnite solar) and in my case I was actually advised by my local Solar guy that seeing that I was mounting panels anyway that I should take the opportunity to change from 2 to 3s for the increased efficiency. Clearly they do not possess the forum wisdom either ;)
WRT, I like to think of it as the cautionary principle needs to be applied when heading for the upper limits of any electronic device....
that's when that guy Murphy steps in ....
http://www.murphys-laws.com/murphy/murphy-laws.html
Quotethe difference between 70v and 120v stepped down to 48v is around 11% loss.
11%? I take it your referring to 11% of the initial loss of say (2%) so 11% of say 80w = about 11w more loss.
I hope its not 11% of 4000w = 440w...thats a heck of a lot of heat to dissipate in a tiny enclosure.
I have 4000w of pv on one classic and 4200w on the 2nd classic . I would be keen to know how much energy (watts) in heat they both have to dissipate during worst case scenario conditions.
The 4200w array is the 3s range from 90 - 120v depending on loads conditions.
The 4000w array is 2s (different brand of panels to) ranges from 65 - 80v depending on loads,conditions.
Kurt.
Quote from: offgridQLD on January 10, 2015, 11:28:24 PM
Quotethe difference between 70v and 120v stepped down to 48v is around 11% loss.
11%? I take it your referring to 11% of the initial loss of say (2%) so 11% of say 80w = about 11w more loss.
I hope its not 11% of 4000w = 440w...thats a heck of a lot of heat to dissipate in a tiny enclosure.
I have 4000w of pv on one classic and 4200w on the 2nd classic . I would be keen to know how much energy (watts) in heat they both have to dissipate during worst case scenario conditions.
The 4200w array is the 3s range from 90 - 120v depending on loads conditions.
The 4000w array is 2s (different brand of panels to) ranges from 65 - 80v depending on loads,conditions.
Kurt.
Yeah, the Classic isn't going to dissipate 400+ watts. ~maybe~ 100 watts at worst case and that would
be REALLY hot.
boB
I may perhaps not understand the graph properly, I was referring to the maximum output available at 48v with various inputs, 70v input will give you a maximum output of 5022w 120v input drops this figure to 4438w.
Kurt provided your panels are oriented roughly the same you are in a perfect position to judge the difference in output.
Sorry one array north east and the other north west. and different tilts to.To try and spread the power throughout the day and year.
I have questioned the same graphs you are referring to but It sounds like to much heat. over 400w would be like a blow heater on low all the time . Thinking now a classic working full tilt at 4000w output and high voltage input sure can pump out some heat from that front grill. Kind of similar siting in front of a portable domestic fan heater on low (500w) setting :o
Though I don't think so it just dont sound correct. I just know one classic runs so much more cooler than the other. Its not just the fets Especially around the area of the top inductor at idle loads high voc. and that radiant heat from that cant help the fets trying to cool in the same case. I was mucking around with a liquid cooling system but in the end its treating the symptoms rather than solving what creating the symptoms.
So Im going to bite the bullet and just rewire that new array at 2s it's just got to be better for the longevity to be running much cooler.I only need to do it once and enjoy the benefits for years.
Kurt
Quote from: offgridQLD on January 11, 2015, 07:25:38 AM
So Im going to bite the bullet and just rewire that new array at 2s it's just got to be better for the longevity to be running much cooler.I only need to do it once and enjoy the benefits for years.
Another option (that also costs time and money, but perhaps less of one or both) is to buy another controller (maybe a kid?). Reducing the watts through each controller will make them run cooler.
--vtMaps
Yes it will somewhat though . As I mentioned before even when the classic is just idling along in float with say 100w being produced and a high voltage ..120v input . The top inductor is throwing out so much heat that it still runs reasonably hot. I have my classic mounted so I can feel the back of them the one at 80v is not even warm in float 100w or so and the 120v one (the back where the inductor is imbedded in the case is like holding a steaming hot cup of coffee in your hand
Classics in Australia (and almost every product under the sun) Is considerably more expensive than in the US. so I would be looking at perhaps only $200 for extra cable, conduit and higher rating main breaker but $1200 or so for another classic $1100 for a lite or $500 for a kid + more wire and fusing to install it .
Though I am coming to the US mid year for a holiday so perhaps I can smuggle one home in my carry on :)
Kurt
Unfortunately not in this case vtmaps, part of the problem is the less load on them the higher the input volts go and the more heat they generate. Mine was at its hottest when on float ;)
QuoteUnfortunately not in this case vtmaps, part of the problem is the less load on them the higher the input volts go and the more heat they generate. Mine was at its hottest when on float ;)
While you can see I totaly agree with my post up the page reflect that. There is some thought in my mind that by the time the cells are on float the charge controller has done some hard work getting there. So already heat soaked somewhat. Then by the time they are on float Is usually the hottest part of the day. bulk and absorb where done in the early morning.
Again I agree just idling that inductor dropping the voltage is a real toaster but some consideration to the time of day it's on float (ambient temps at midday) and heat soak from getting the cells to float before hand. Vs a fresh cool charger at 7am getting the batteries to float for a few hrs.
I beat around the bush trying to convince myself there was a better way to solve the issue than just going 2s. water cooling, extra fans, diversions loads so it wont sit in float for long periods. In the end the answer to the issue is kind simple (2s)
Kurt
Kurt, since you have 2 Classics is it feasible to swap the inputs to see if it is just that classic or a common-to-all issue?
Quote from: wrt on January 11, 2015, 07:50:27 AM
Unfortunately not in this case vtmaps, part of the problem is the less load on them the higher the input volts go and the more heat they generate. Mine was at its hottest when on float ;)
To keep the battery voltage low (float V) the input voltage has to rise higher than it does when it is MPPT'ing...
And, IF you have large loads while in Float, that is a lot of DC output current at the Float voltage and the
input voltage will be just slightly higher than it is during MPPT Float so that might make one Classic
get hotter ?
boB
Yes I guess I could do that but given that others have had similar findings due to similar configurations. I think I would be barking up the wrong tree.
Regarding large loads while in float I think WRT was saying his controller is hottest under light loads during foat not heavy loads.
My experience has been light loads say 150w and high voltage input = hot inductor and radiated heat through the case builds up . Heavy 3500w loads in float = lower voltage input and heat from the fet area as expected.
So what feels odd is to go up to a charge controller on a mild day that's sitting in float producing 50w output from 120v input and hase the fan running and what feels like 80w of heat radiating from the upper rear left of the case.....inductor location area.
Kurt
Hi guys, on the day my unit broke, Maximum bulk charge built from 1kwh at 8am to 3kw at 10am. 3kw was only evident over one 15 min logging block befor dropping to float and a constant 700w The max load for at least one hour prior to the incident was 700w @ 54.4v battery and 118v-120v input the input varies constantly between the two.
Quote from: wrt on January 11, 2015, 06:20:29 PM
Hi guys, on the day my unit broke, Maximum bulk charge built from 1kwh at 8am to 3kw at 10am. 3kw was only evident over one 15 min logging block befor dropping to float and a constant 700w The max load for at least one hour prior to the incident was 700w @ 54.4v battery and 118v-120v input the input varies constantly between the two.
When you say "charge built from 1kwh at 8am to 3kw at 10am." do you mean kW-Hours (kWh) or power (kW) ?
Sorry Bob, because I am on a phone at work, sometimes spellcheck will choose what it wants.
Both should read kW, this is the charge rate being fed to the battery as displayed on the classic. I was also taking a constant 700w load from the inverter.
Quote from: wrt on January 11, 2015, 07:50:27 AM
Unfortunately not in this case vtmaps, part of the problem is the less load on them the higher the input volts go and the more heat they generate. Mine was at its hottest when on float ;)
True, but if you have two controllers, each with half the array, then only half as much heat needs to be dissipated by each controller.
Quote from: offgridQLD on January 11, 2015, 05:55:58 PM
Regarding large loads while in float I think WRT was saying his controller is hottest under light loads during float not heavy loads.
My experience has been light loads say 150w and high voltage input = hot inductor and radiated heat through the case builds up . Heavy 3500w loads in float = lower voltage input and heat from the fet area as expected.
So what feels odd is to go up to a charge controller on a mild day that's sitting in float producing 50w output from 120v input and have the fan running and what feels like 80w of heat radiating from the upper rear left of the case.....inductor location area.
So, if you want to transmit high voltage to your controller, you should try to match your load to the size of your array.... a large load (relative to the array) pulls the PV voltage down to a more efficient operating voltage.
One way to match the array's (potential) power output to the load, is to disconnect strings from the array when they are not needed. This can be automated. As far as I know, there is no good plug and play solution to do this, but it is coming. There is new emphasis in the NEC on rapid remote shut down of modules and strings, and Midnite and others are developing products to do this.
Other than disconnecting an entire string, there's another way to control array size with switches... I recall seeing a discussion over at wind-sun where someone had six or seven 12 volt panels in series, with a high string voltage that would, in winter, exceed Vmax of his controller. He put a switch across one panel in each string, and each autumn when he set his winter tilt, he shorted out one panel in each string.
--vtMaps
Quote from: offgridQLD on January 11, 2015, 07:58:25 AM
I beat around the bush trying to convince myself there was a better way to solve the issue than just going 2s. water cooling, extra fans, diversions loads so it wont sit in float for long periods. In the end the answer to the issue is kind simple (2s)
So what happened to your water cooling scheme? It looked like it was resolving your heat issues to some extent. Was the ambient temperature and heat being produced just too much for it to be effective?
Strange effect with greater heat in Float, this is something I just do not see with my 150 working 70+ amps, PV in of about 90v and battery at 28v then float at 27.4v PV in at 108v and under 20a the classic runs on the same temperature.
The only addition I have is the classic mounted on an 8mm thick aluminium plate 400 by 250mm.
It all get warm but not coffee cup hot.
Dgd
Dgd,
that aluminum plate most likely wicks a lot of heat out of the case. Mind you if you don't have access to the rear of your classic you might not be able to feel the heat. My units I can put my hand around the back of them. While the front feels warm the top left rear is where it's hot. The left side - top is reasonably warm to. Any where that inductor can radiate heat from the location where its imbedded in the case.
As for the liquid cooling. I think it would stop the thing totally cooking but how I was testing it the thermal contact wasn't good enough to wick a moderate heat away from the case. Milling a flat section along with a O ring slot so that liquid could actually make contact with the case would be best. The other issue is it's another dynamic device that could fail and then you have no additional cooling if your relying on it.
It boiled down to the effort involved in getting it to perhaps do the job. It was less effort to just rewire the array to 2s and have it all work nice and cool on its own (well as cool as a classic typically is = internal fans come on occasionally)
I guess in my view anyhow the classic will function at the high voc and low bat voltage (gap) with big arrays but is it happy doing so? A bit like your car might have a 2 ton towing capacity (max) but it's much more comfortable with 1 ton if doing it regularly.
Then again perhaps I am to pedantic about temperatures and what I call hot isn't anything to worry about all all and as little to no effect on the components or service life.
Kurt
Hi guys,
I am back on solar power again, albeit in a limited fashion. The distributor looked after me after my retailer stepped up on my behalf. I now have a nice new one on the wall.
To Bob,
On the subject of the cause of the problem, I am interested in the temp limits of the classic, what temp does it shut down at? What temp would you normally see on the FETs on a35c day, or even on the odd 40c day (we get up to 7 days a year at this temp)
I guess what I am asking is, under normal circumstances should the classic have no problems under these conditions with panels putting out up to 120v. Perhaps non of this temp business makes a difference and I was just unlucky to get a crook FET that was waiting for the right combination of high temp and volts to fail.
Obviously I don't want to have to have my system reconfigured if it will no difference to the classics lifespan, but will if needed.
WRT, please add a system description to your Signature line in "Profile/Forum Profile / Signature" .. after 61 posts all I can remember is a hooped LiFePo4 Battery :'( :'(
BW Have been delving into what Winston/Balquon have to say and separating out the chaff.. Mostly good as far as I can see, just need the cost to drop a bit.
QuoteBW Have been delving into what Winston/Balquon have to say and separating out the chaff.. Mostly good as far as I can see, just need the cost to drop a bit.
I think you will find that the cost of the chinese lifepo4 batteries wont really come down. There is bugger all profit in them as it is. As it stands they are already less expensive than quality lead acid batteries with lots of benefits. Considering you cant really include the cost of cell management systems as thats a once off purchase.
Kurt
Quote from: Westbranch on January 27, 2015, 11:41:36 PM
WRT, please add a system description to your Signature line in "Profile/Forum Profile / Signature" .. after 61 posts all I can remember is a hooped LiFePo4 Battery :'( :'(
I have inserted the information you requested, though a quick read through my first three posts of the thread will soon jog the memory :)
Quote from: wrt on January 27, 2015, 09:24:07 PM
I guess what I am asking is, under normal circumstances should the classic have no problems under these conditions with panels putting out up to 120v. Perhaps non of this temp business makes a difference and I was just unlucky to get a crook FET that was waiting for the right combination of high temp and volts to fail.
Yes, under normal circumstances the Classic should have no problems.
I have just had two weeks of hot weather, 30 degrees C days and my Classic 150 with 90 to 110v PV input and output to a 24v battery bank. FET temps has been around 53, from 47 to 55
I would agree that you were probably just very unlucky to get a dud FET.
I'm sure that if this was a more common occurence then we would have heard more about it on this forum.
Also this recent trend here, where getting input voltage closer to battery voltage = longer Classic life, is IMHO just nonsense and unproven.
In normal use input voltages up to the Classic's rated voltage should not be a problem.
dgd
QuoteAlso this recent trend here, where getting input voltage closer to battery voltage = longer Classic life, is IMHO just nonsense and unproven.
In normal use input voltages up to the Classic's rated voltage should not be a problem.
Well the trend that most would agree with is cool power electronics = longer life. And the for me anyhow considering I have two identical classic 150 charge controllers with the same size array on each but the only difference is one array is 3s 90 - 120v the other is 2s 70 - 80v. One runs a little hot and fans come on and off regularly + the case is soaked in heat from the inductor cooking away even under light loads . The other runs just warm with minimal fan time.
So the only question is how much less service life will I get out of the hotter classic .....time will tell ...actually it won't as I am switching it back to a lower voltage.
There is a big difference between 30c and 40C day .
Though I agree that a total failure due to running the classic at its upper voltage limits in hot weather must be rare. Though I still think it could reduce its life.
Kurt
Kurt,
I don't disagree with anything you say but I think normal circumstances was the issue.
I do not doubt that the extreme ambient temps you get and hot Classics are a concern AND that the lowering of input voltage WILL work for you.
However, I see your situation as exceptional and probably outside what would be normal for the Classic. I think it was Vic that said keeping the Classic in an air-conditioned room would resolve the situation as lowering ambient temp was the best way to go.
That was why I keenly followed your Classic cooling experiments :)
However, I would not see it as normal solution for an overheating Clssic to reduce input voltage. Lower the ambient or get a cooling system onto the Classic
dgd
Yep I can agree with that. :)
Perhaps I should put my view another way as I didn't want to go around trying to scare people away from running high V input (it can be a handy option sometimes) just worth considering that if you're pushing the limits and or in a demanding environment its going to work against you when it comes to heat. Particularly if your controller is going to spend a lot of time idling along with a big array at its disposal that won't have its voltage pulled down much.
I mentioned my concerns to a electronic engineer friend of mine and he mentioned "I suppose if they use a passive freewheel diode, its losses would dominate, and they would increase with increasing array voltage. But I imagine that super-efficient MPPTs like the AERL models, would use another MOSFET to freewheel the inductor, and their losses might not be any different at high or low array voltages.
all went way over my head but he seemed to be confident in his idea.
Kurt
The Classic will start current limiting if the FET temperature rises too fast in a couple minutes.
It will also limit current when the FET temperature rises to the high eighties degrees C.
The 250 starts current limiting at a wee bit lower temperature. More like the lower eighties.
That might just be the 250KS though.
boB
Thanks Bob, handy to know.
Going by that it sounds like we are perhaps being a bit to pedantic about how hot our controllers run.
Kurt
Thank you indeed boB,
Given that Midnite chooses not to start limiting till the 80's I take this to mean that as long as my temp stays somewhere in the 50's it should be well within it's design parameters and would not have been a contributing factor in it's failure :)
Hopefully you do get a look at my unit. As you could imagine I am keen to find out what went wrong and do what I can to prevent it from happening again.
To dgd,
Giving it a little thought, I might lake a leaf from your book and move the unit a half inch out from the power board. I can do this with half inch thick ally mounting washers. This will allow the rear of the unit to convect heat adding a fourth surface.
Too simple not to do and has to achieve at least something :)
Quote from: wrt on January 28, 2015, 05:41:31 PM
Thank you indeed boB,
Given that Midnite chooses not to start limiting till the 80's I take this to mean that as long as my temp stays somewhere in the 50's it should be well within it's design parameters and would not have been a contributing factor in it's failure :)
Hopefully you do get a look at my unit. As you could imagine I am keen to find out what went wrong and do what I can to prevent it from happening again.
To dgd,
Giving it a little thought, I might lake a leaf from your book and move the unit a half inch out from the power board. I can do this with half inch thick ally mounting washers. This will allow the rear of the unit to convect heat adding a fourth surface.
Too simple not to do and has to achieve at least something :)
Yes, 50s and 60s in temperature is just nothing
I can take a look at your unit when it arrives. Let me know if it is already here.
boB
My Classic 150 has been running with FET temp of 49 and pcb temp of 55 or thereabouts for the last few weeks.
ON Saturday I removed the top cover and secured it with one top bolt off to one side while re-routing some cabling. I noticed after an hour or so the FET temp was down to 46 and the pcb to 42 even though it was a normal summers day with ambient 30.
So after finding some longer bolts and making four 1cm thick plastic standoffs that the bolts go through, I replaced the top cover.
So yesterday and today the temps are FET 45, PCB 40, ambient 29.
I can feel the warmish airflow out the gap at the top of the Classic.
Interesting experiment but will go back to normal setup soon as dont want insects or dust inside.
Might be useful if there was an alternate top cover available with easier airflow over the PCB.
Time now for cool beer at 3 degrees C :)
dgd
Interesting experiment.
I think where the thermocouple for the PCB is placed might play a big roll in the temps shown. Often I have BCB temps that are higher than my fet temp Say 45c FET 50c PCB. The issue with that I guess is that the fans are triggered by fet temps. So no matter how high the pcb temp are the fans wont come on unit the fet temp gets to 48c or 58c for turbo fan.
When I see PCB temps higher than the fet temps is when the inductor is wicking heat into the case under little load and high pv volts in . So the fetts aren't really doing much but the case is getting hot on the other side .
It's not like the classic is bug ,dust,insect proof in stock form. As the front cover has lots of open slots in it . Though I'm not sure how having a spacer stand off and a gap between the cover could affect the designed fan air flow path. That said when the fans are off ...(under 48c fet temp) with a space between the cover it would most likely help get trapped hot air out.
All interesting.
I run mine 8mm -13mm off the back wall , & have noticed it is running coolin running due to fans are less heard. plus I can feel the back side also