Hi all.
The equipment:
Classic 150 running 12V nominal
The situation:
I am in the process of building the solar RV conversion, and have been giving the classic rectified input from a transformer, powered by the grid to maintain the batteries, test consumption, etc, yada. This is in lieu of 800W of PV that is to go up top side soon.
The classic is set for hydro mode, manual MPP. Voc is ~110VDC according to the classic, with the MPP around 95V or so.
I had it limiting input @ 3A, as the transformer runs a bit warm even with a fan on it above that.
In addition, I've been limiting the output current at 15A, so the input limiting wasn't tripping.
All has been going along well for a few months now like this... There have been no excessive heat events, and only on rare occasions had the fans cycled during charging. Everything was working exactly as expected... until last night.
To exercise the batteries for whatever reason, I have a switch that kills the grid going to the transformer, at which point the classic would go into resting, and I run from battery.
When I turned the switch on last night, the display changed to bulk MPPT, but the relay did not engage. I had seen it do this before once or twice, where there was a brief delay, and then it engaged, but this time, nothing.
After attempting to wake it up by cycling the grid power a couple of times and seeing the same results, I reset it by turning off the battery disconnect. Upon reengaging the batteries, it came up as it always had, so I again applied power to the transformer. Again, nothing, with one exception... A faint periodic "chirping" about once every 2 seconds or so could be heard coming from within, likely the cores of the inductors as the buck circuitry attempted to start and restart.
At this point I removed the cover, looked for anything obvious, saw nothing that appeared out of order, no heat anywhere etc, so I reconnected the front panel and put the screws back in.
Cycled the battery one more time, same behavior, chirp, chirp, chirp, etc and no output. The display this entire time showing "resting", and no relay clicks.
I figured that there was nothing to lose at this point, so I again disconnected the power input, cycled the battery, and did the hard reset on it (the two arrow key function). It came up, I again set it for 12V, hydro, etc... then applied the grid.
*Bang* - I heard the MPPT relay engage and then the fuse on the primary side of the transformer (6A) vaporized immediately.
I checked the rectifier bridge suspecting possibly the worst, but there were no shorts. Working my way down stream, I found the input connection is dead shorted going into the classic.
The classic still powers up and runs on the battery, the only noticeable difference (other than it obviously won't charge anything) is the "IN" voltage now reads 0.0 instead of floating around between 6 and 8V when in rest mode with no input.
So, how bad is it you think, and what's it gonna take to get it back up and running?
I'd also like thoughts on whether or not I caused it, if so, what it was, as I'd rather not repeat it. :-\
Thanks,
Steve
MS 267, don't know on what you did but I am thinking the stepdown is a hefty one and may be too much for the transformer...
In the mean tme do you have an automotive charger you can use to keep you batteries up. Not necessarily the best but will do in the pinch...
Quote from: Westbranch on January 10, 2015, 12:54:22 AM
MS 267, don't know on what you did but I am thinking the stepdown is a hefty one and may be too much for the transformer...
In the mean tme do you have an automotive charger you can use to keep you batteries up. Not necessarily the best but will do in the pinch...
Hi Westbranch
I do indeed have an alternate charging system in place as part of the design that goes around the classic... using the transformer with the classic is really just a temporary thing as it does a much better job. The "backup" charger is meant primarily for grabbing a desperately needed charge when the need arises and doesn't do an "absorb", but definitely is better than nothing.
I too wondered about such a step down, but the manual says it should do it... and the currents are nowhere near the limit... so I dunno. That's why I come to you guys :-\
When the PV goes up, the voltages will be lower... set up as strings of 72 cell/24V nominal.
If the voltage is indeed too much from the transformer, I can change it over to center tap instead, it's just that it runs cooler at higher power levels at the higher voltage.
Steve
Hi MadScientist,
First, this type of input power for MPPT CCs is generally not recommended by the CC manufacturer.
On this Forum, it has been stated that it is not a very good idea, due to the risks of damaging a MidNite Classic, for example.
As you may know, almost all MPPT CCs will be damaged, if the PV + input becomes grounded to the PV in -- . Believe that this blows up some transistors.
It has also been stated, here I believe, that adding a series resistor at the output of the external power supply, to increase its output impedance, limiting the current available should something go wrong.
Know that you were using Hydro Mode, and some Hydros might have a fairly low output impedance ... and so on.
I do wonder if the output of the external power supply became shorted, and that this might have toasted some transistors in the Classic.
Another thought, regards weather you have filter capacitors on the output of the rectifier. The Classic (and most other MPPT CCs) have capacitors on the Vin terminals to help the stabilize the PV input voltage.
FWIW, Guessing over for now. Vic
Hello Vic,
I'd like to mention my own results using a transformer ( not the best of the best home-brews but effective ) and the classics. I was using one transformer and two classics at one time and the only issue I had was using two classic with one power source. In an IRC which boB is a contributor in on occasion, we discussed using the classic on a transformer and he explained why I was having trouble trying to use two classic with the one power source. That was not a good idea but diodes would have eliminated the issue I was having. I chose not to connect the two classics to the one power source and the problem was solved. However, he never mentioned it being a bad Idea to use such a power source and in fact just commented about it being an interesting use of the classic. I was tying to condition an older forklift battery and was somewhat successful. I'm only mentioning this because I use this setup quite regularly.
How can this be any different from rectified power from a wind turbine? He limited his input to ~350w
(http://i261.photobucket.com/albums/ii74/Chevy_l88/20130813_013628_zps1d4bdaa6.jpg) (http://s261.photobucket.com/user/Chevy_l88/media/20130813_013628_zps1d4bdaa6.jpg.html)
Hi Watt,
Believe that we have had a conversation about this ...
I have used a Home Brewed AC-in DC charger with the Outback MX-60, for many years as an auxiliary charger. Have never tried using a Classic instead of the MX.
Also use a different one that uses a Variac (c) on the input, and Auto Jumper Cables on the output, so a single battery or cell can be charged/EQed. It uses NO CC. I am the CC, by varying the Variac output to control current/voltage. This does work quite well.
Perhaps, I mis-spoke when saying that it was described, here, as a bad thing to do. At the least, it was said to be not recommended, due to a risk to the CC's health. The series R was mentioned as something that could help reduce some of the risk. Believe boB did say that if one did DC PS into the Classic thing, that having the DC input voltage not much above the battery voltage, should help reduce the risk to the CC ... from distant memory.
And, way back when, there was a MN team member that was using rectified AC line voltage, to a Classic 200, IIRC. This was described here, but then, probably due to added risks on having no isolation (transformer) from the AC line, it was noted as not a good idea.
The one thing about using a CC with a DC power supply on its input, is that many DC PSes can deliver a lot of fault current. PV modules cannot. CCs were primarily designed to work with PVs. Some CCs can be used to charge a battery from another higher voltage battery, consult the CC manufacturer before doing these types to things, and so on.
FWIW, YMMV. Vic
Hi all
Just to clarify:
This shouldn't be seen by the classic as anything other than a single phase hydro alternator with full wave rectification, running at a constant speed.
There are no caps externally connected
The grid is fully isolated via the transformer, and fault current is(was) limited to 6A, on the primary side, yielding a theoretical 720W of input.
The rectifier bridge rectifier still checks out as good, so there was never an AC component to the input.
Whatever happened appears to have been a cascade event... power on was briefly clear (the small delay between application of power and when the classic changes modes), then the sound of the relay engaging, followed by the fuse immediately popping.
There had been no sign of any input related issues before this when it simply wasn't changing modes (eg it was showing the usual input voltage etc), and nothing wiring-wise was messed with during this time.
After it was all said and done, I did then disconnect the classic from the rectifier to determine which one was the source of the short - it was indeed the classic.
Hopefully this helps with any thought processes along these lines.
Steve
Thanks Vic, for the clarification.
I'd like to add too about another member of this board and others, who direct charge batteries from Rectified AC voltage from a small diesel generator ~170vdc through a classic 200. This has been done for a year or so at around 3KW into a 48vdc battery bank. This is mainly done for proper equalize charge once a week as that battery bank has proven too big for proper care from solar and wind available.
I'm sorry I don't remember that topic regarding previous talk of this setup. If what you say is true, we may have to come up with a bit of filtering to continue using these methods of maintenance charges. I'm certainly open to following proper use of this classic.
I do realize staying closer to battery voltage helps with charge efficiency. I also realize that with a larger input voltage to battery voltage spread heat at the classic is greater but, I'm also under the impression that this range is well within the tolerances of the classic. Honestly, that spread is what has made me lazy and gives me the comfort of just throwing near what I want at it so long as I stay within current limit, under Hyper VOC and above the highest battery voltage required for eq. I also realize some of the difference in charging from a wind turbine and from the mains. I've just never had issue at this point and the one Classic that has been used the most on this mains transformer of mine has been clicking along fine for years on solar and transformer.
Thanks for your input Vic.
Hi Mad ..
Regarding the fuse; fuses usually are not installed in circuits to protect equipment, but to protect wiring from excessive heating. And in the case of your power supply, perhaps to help protect the transformer from being toasted. Am sure that you have looked at the curves for fuse opening a circuit plotting time and the amount of current in excess of the fuse's rating.
The device that probably limited the current into the Classic input was most probably the transformer. And depending on its design, the Classic could have seen many times the fuse's rating for a short period of time.
Regarding the discussion on this Forum, regarding using a Classic connected to a DC power supply ... Believe the stated reason for working to keep the DC supply output voltage only a small amount above the battery voltage, was to try to limit the Classic's output current, should the Classic be a bit slow in regulating the output voltage/current (from distant memory).
Watt, perhaps you were not in the previous discussion on the topic of using a DC PC on the input of a Classic to charge a battery from the AC line or generator.
The thing about adding filter capacitors to the output of the rectifier on such a setup, is to try to keep the Classic's input filter capacitors from being "worked" excessively -- from the 120 Hz (usually) ripple voltage on the output of a simple rectifier. This working can cause heating of the caps, and might not allow the Classic to find a Max Power Point, as the voltage is fairly rapidly changing. PV modules have a nice pure DC output, and a constant load current,, unlike the output of a full wave rectifier without its own fairly large filter capacitor bank. Such a large filter, could create its own problem for the MPPT CC, as sequencing might be an issue ...
I am no expert on MPPT CC design. And, I may not be characterizing what the MN crew, including boB, had to say on the topic. Just my recollections.
FWIW. Good Luck, Vic
Quote from: Vic on January 10, 2015, 10:51:06 PM
Hi Mad ..
Regarding the fuse; fuses usually are not installed in circuits to protect equipment, but to protect wiring from excessive heating. And in the case of your power supply, perhaps to help protect the transformer from being toasted. Am sure that you have looked at the curves for fuse opening a circuit plotting time and the amount of current in excess of the fuse's rating.
The device that probably limited the current into the Classic input was most probably the transformer. And depending on its design, the Classic could have seen many times the fuse's rating for a short period of time.
Regarding the discussion on this Forum, regarding using a Classic connected to a DC power supply ... Believe the stated reason for working to keep the DC supply output voltage only a small amount above the battery voltage, was to try to limit the Classic's output current, should the Classic be a bit slow in regulating the output voltage/current (from distant memory).
Watt, perhaps you were not in the previous discussion on the topic of using a DC PC on the input of a Classic to charge a battery from the AC line or generator.
The thing about adding filter capacitors to the output of the rectifier on such a setup, is to try to keep the Classic's input filter capacitors from being "worked" excessively -- from the 120 Hz (usually) ripple voltage on the output of a simple rectifier. This working can cause heating of the caps, and might not allow the Classic to find a Max Power Point, as the voltage is fairly rapidly changing. PV modules have a nice pure DC output, and a constant load current,, unlike the output of a full wave rectifier without its own fairly large filter capacitor bank. Such a large filter, could create its own problem for the MPPT CC, as sequencing might be an issue ...
I am no expert on MPPT CC design. And, I may not be characterizing what the MN crew, including boB, had to say on the topic. Just my recollections.
FWIW. Good Luck, Vic
Thanks Vic for the update.
Can you explain how the classics work so well with wind turbines as input sources? I understand your comment on the frequency but a 120hz ripple out of a wind turbine would not be hard to duplicate. Just trying to see the difference Vic, not trying to be complicated. I don't want to trash such great charge controllers. At the same time, I have some experience with this scheme and also have not had issue.
The problem with running MPPT charge controllers in this way is that using the grid and especially with a step down transformer,
the MPP voltage can be too close to the Voc and this is where the CC has trouble.... It expects the input source to be
a limited source but to the Classic (or other MPP CC's), it can seem like Hoover Dam. A wind or hydro turbine
is not the same ! They are current and power limited and max power occurs far enough below the Voc that
the CC has a bit of a "buffer" to adjust and limit the current by raising the input voltage when it reaches the max
current (or user limit). Some users get lucky and have a "soft" input source. I bet your source (Steve) is
just too "stiff". It may not be and you just got UN-lucky after a while ?
What I recommend is to add a series power resistor of a couple of Ohms between the rectifier output
and the input of the CC.
Others at Midnite will say don't do any of this. I would say that you just better know what you are doing
in these cases. An added resistor can make it work by giving it that input buffer voltage from Voc (0 amps)
and MPP voltage (max current). Some are lucky enough to have soft source impedance.
Also, I'm not sure what tracking mode you were using but solar is not the mode for these situations...
Legacy or Hydro mode is usually better.
Sounds like you are going to need an RMA for your Classic. Sounds like it is now dead. Gone to meet
its maker... Or, needs to go to visit its maker again.
boB
Quote from: boB on January 11, 2015, 02:56:30 AM
The problem with running MPPT charge controllers in this way is that using the grid and especially with a step down transformer,
the MPP voltage can be too close to the Voc and this is where the CC has trouble.... It expects the input source to be
a limited source but to the Classic (or other MPP CC's), it can seem like Hoover Dam. A wind or hydro turbine
is not the same ! They are current and power limited and max power occurs far enough below the Voc that
the CC has a bit of a "buffer" to adjust and limit the current by raising the input voltage when it reaches the max
current (or user limit). Some users get lucky and have a "soft" input source. I bet your source (Steve) is
just too "stiff". It may not be and you just got UN-lucky after a while ?
What I recommend is to add a series power resistor of a couple of Ohms between the rectifier output
and the input of the CC.
Others at Midnite will say don't do any of this. I would say that you just better know what you are doing
in these cases. An added resistor can make it work by giving it that input buffer voltage from Voc (0 amps)
and MPP voltage (max current). Some are lucky enough to have soft source impedance.
Also, I'm not sure what tracking mode you were using but solar is not the mode for these situations...
Legacy or Hydro mode is usually better.
Sounds like you are going to need an RMA for your Classic. Sounds like it is now dead. Gone to meet
its maker... Or, needs to go to visit its maker again.
boB
Thanks boB for your answer and explanation. Got my confidence back....
Bob,
You most certainly hit the nail on the head with the stiff supply thing methinks... it's only a small-ish transformer, a little bigger than my fist, and doesn't really like to pass more than about 300W without getting on the warm side... BUT... it's incredibly close to the classic... about 3 ft as the electrons flow... by your description, things certainly make a lot more sense than they did...
I was indeed running in hydro mode, manual MPP... I was rather excited to find that combination and found it very useful... maybe a little TOO useful..? I can confirm that for anyone else wanting/needing to go this route, that "solar" is indeed not the setting to use; you'll witness squirrelly things that even made me squirm (not always easy to do LOL).
Best theory that had come across any table in my mind involved inductive kick, even tho there were a couple holes in it. Thank you for clarifying. I appreciate your response, middle of the night on a weekend and everything... You guys have more ethic than the collective that I've worked with over the course of my entire life. It doesn't go unnoticed.
I guess now the burning questions of the hour...
What happens next, and how bad is it going to hurt? :-\
Thanks again,
Steve
Hmmmm....... If it is a small-ish transformer, then I am wondering how much power you were able to get out of the
whole thing ? And how far below the Voc did you get that power ?
Seems that with a small transformer that you SHOULD be one of the luck soft ones.
00
During a brief curiosity thing, I was able to pull about 375W out of it, around 90-95V, with the Voc being somewhere in the 110V range... both fluctuated a little because of line variations (I'm at the end of a 100 ft extension), as well as some shifting that appeared to be associated with temp. The latter isn't entirely clear.
Steve
Quote from: boB on January 11, 2015, 02:56:30 AM
The problem with running MPPT charge controllers in this way is that using the grid and especially with a step down transformer,
the MPP voltage can be too close to the Voc and this is where the CC has trouble.... It expects the input source to be
a limited source but to the Classic (or other MPP CC's), it can seem like Hoover Dam ...
Thanks boB for the detailed description of how MPPT CCs work in this situation.
73, Vic
Quote from: MadScientist267 on January 11, 2015, 05:27:22 PM
During a brief curiosity thing, I was able to pull about 375W out of it, around 90-95V, with the Voc being somewhere in the 110V range... both fluctuated a little because of line variations (I'm at the end of a 100 ft extension), as well as some shifting that appeared to be associated with temp. The latter isn't entirely clear.
Steve
This amount of "cushion" should be fine. Not sure why it died ?
I'm hoping some answers come out of the bench... It's not something that I'd like to see repeated. There's a few plans that hinge around the hydro mode for this project, and of course I'd like to implement them safely. Any insight from the autopsy would be greatly appreciated; hopefully there's something to hear in the next few days, as it's on its way there as I write this.
Steve
Ok, I've made some changes, done a lot of experimenting with trying different things...
I received it back from repair, and was charged for them because the unit had gone overvolt.
I have some proof that the previous high voltage input involved, while not helping anything by giving margins, was not the cause.
The classic is generating these dangerously high voltages (to the unit), internally.
My findings are reproducible (at least on this unit), and I have discovered that if the classic goes from absorb to float, either by force or automatically, the voltage skyrockets into potentially destructive levels.
If the voltage reaches 150, it goes into resting, and the voltage then begins to drop. If it does not, more of an RC type curve is revealed; the rate of climb slowing as it nears its highest, then will begin to fall. All of this occurs over the course of several seconds.
In addition, I decided to put some resistance across the input to see how hard and for how long the classic was driving power into it. It peaked out at ~35V into a 150R 10W. Remember, this was with *NO external input power*, just the classic still connected to the battery. This persisted for 15 or 20 seconds or so, and the resistor was getting very hot. Finally, it began to decline and settle in closer to the battery voltage, where it then let go upon entering resting mode.
I have video that captured a 129.3V excursion... Tho it should be done over as I was clearly a little irate while recording it.
Someone let me know if you really need to see it happen, I'll film it again, with and without the resistor, for your viewing pleasure.
I don't know if it's just this unit and there's something that is supposed to be inside protecting against this and it has failed, or if it is software causing a problem, but there's *absolutely* no doubt in my mind at this point that the same phenomena is what killed the MOSFETs the first go around.
At least the resistor can protect it, albeit not an ideal method.
Steve
Mad..,
Am not an MPPT CC Designer,
But would ask you to NOT place any "load" on the input of any Buck MPPT CC.
At some point, seems to me, that this will become no different than shorting the PV+ input to the PV -- input, and you might be back in the territory of having damaged your CC. At least, it seems quite possible to me.
You mentioned some behavior of the Classic when it transitions from Absorb to Float. What is the source of input power to the CC when it was in Absorb?
Opinions, FWIW, Vic
First, the resistor was eventually placed there to keep the voltages from skyrocketing. I paid a fair chunk of change to get it fixed and returned over something "I caused". I'm calling it "insurance".
Second, a full wave rectified transformer, Voc ~22V, Vmp ~15V. It has nothing to do with the voltage shooting off scale.
The classic is effectively operating as a boost converter for about 15 or 20 seconds after going into float mode. I either A, soak it up somewhere or B, let it run off the chart again and get stuck with the next repair bill.
Which do you think I'm going to choose, hmm?
OK, fine...
But, would seem that it would be safe to either use an AC-operated battery charger (and not involve an MPPT CC), or perhaps use real PVs into the Classic, and perhaps not run the Home Brew DC PS, that you appear to still be using.
However, you do get to choose. FWIW, GOOD LUCK, Vic
There will be real PV.
And I bet it does it with that too.
Been there done that with the "AC powered battery charger"... I brought it back because it would have caused problems that don't exist.
This entire project requires thinking outside the box. I expect cookie cutter thinking from experience with cookie cutter installations.
What I need is for those involved in designing the unit to bring their expertise to the table so that this can be hashed out and resolved.
So the Classic was damaged by over voltage ???
Just looking at the photo of your transformer and diode rectifier, I can take a good guess why you are having problems.
First the recification is leaving a good ac ripple in place, this is usually smoothed out somewhat by using some suitable power caps plus a few noise suppression caps. This is probably not effecting the Classic too much but nevertheless should not be there.
Second, the reason you are seeing some sharp rises in the voltage input to the Classic, as the Classic regulates input from Absorb to Float and Bulkmppt to Absorb is IMHO caused by Inductive Kickback. (google this) This will be your primitive transformer/rectifier design because of the lack of proper AC ripple removal and the complete absense of a snubber circuit.
This kickback is the quickly rising voltage and its likely the Classic has been exposed to over voltage before it's Hyper VOC detection could react.
Reading your recent postings it would appear you are definitely doing things to the Classic that it was not designed for, I suspect its on the way to being rubber-ducked again.
WHy not just get the solar panels and connect them then do your mad scientest stuff?
dgd
FWIW, the Classic does allow some reverse (boost) current out of the PV input, but it is limited to around 9 amps or so.
This is common with MPPT charge controllers with synchronous buck converters. Anything over that and it should
go to Resting immediately. But you can draw some power from the input side for about 90 seconds. The voltage
that it goes up to should also be limited based on the previously measured Voc before it turned on the first time.
IIRC, that is around 10 volts over Voc.
Sorry Steve that we charged you for this. I had forgotten all about this.
boB
Steve, I have a question if you have the answer... I'll also ask Jose in Warranty.
What was the high voltage reading of the input to your Classic ? How high over
150V did it go ?
I saw your IRC post also and saw that you noticed it go to high voltage when transitioning
from Absorb to Float... I will look into this right away.
The input voltage (PV) ~should~ be limiting itself to about 10 volts above Voc... But maybe
it did not see any reverse current because there was not PV connected to the input ?
Will do a sanity check today. Or, insanity maybe.
boB
Quote from: dgd on March 04, 2015, 02:28:50 AM
Just looking at the photo of your transformer and diode rectifier, I can take a good guess why you are having problems.
First the recification is leaving a good ac ripple in place, this is usually smoothed out somewhat by using some suitable power caps plus a few noise suppression caps.
I witnessed a great deal of discussion about this in IRC between Steve and Bob.
As I recall it, the recommendation was specifically *NOT* to put big filter caps on it, because this may make the supply too "stiff" and actually cause damage! I believe the original supply DID have filters (was a fairly grunty commercial supply) but deemed "unsuitable for this use".
So while your comments may be right in a general sense, please don't just assume that you're right and everyone else is wrong, without the benefit of hindsight and/or detailed discussion with the manufacturer about these quite specific issues.
Ross,
I did say that the ripple probably did not effect the Classic.
I most certainly did not assume everyone else was wrong and I was right, I have no idea who everyone else is anyway as I comment only on the forum postings NOT some previous off forum discussion I did not participate in.
Too 'stiff', yea right, got to be better than the existing non-stiff AC component on the DC being supplied to the Classic.
My main point was the rising voltage at Classic regulation steps. Unless the laws of Physics have changed that transformer/rectifier combo is
voltage spiking due to inductive kickback. Is the design of the Classic capable of dealing with these? Methinks not hence the broken Classic sent back for repair.
dgd
Quote from: dgd on March 04, 2015, 04:06:56 AM
Too 'stiff', yea right, got to be better than the existing non-stiff AC component on the DC being supplied to the Classic.
As I understand the discussion, the whole "stiff" issue was a serious consideration - the ability of the transformer / rectifier and any filter caps ability to deliver "substantially more current" than the classic would see from a normally fairly "soft" PV installation, including the comparatively long supply cables.
In discussion, Steve chose to use a modest transformer, with significant current limiting, to prevent the issue happening again.
Quote
Unless the laws of Physics have changed that transformer/rectifier combo is voltage spiking due to inductive kickback.
But riddle me this... with a bridge rectifier between the classic and the xfmr, and the primary of the xfmr unplugged, how is there going to be any inductive kickback? If the output of the classic is positive voltage, the diodes in the bridge will be reverse-biased, and no current could flow to the xfmr secondary, so there can be no inductive kickback, surely?
I'm talking out of turn, I'm not privy to the entire setup, but from what I have seen go past on the screen, it's quite clear that it isn't an "ordinary" situation. (There was also a video posted earlier today - volts were stable about 17V or so with the transformer connected. Then the classic was put to float mode and the volts rapidly climbed. At about 70V (WELL above the open-circuit output of the transformer), the input to the xfmr was removed, yet the volts CONTINUED to climb to almost 130V. I don't know what's going on, but I can't explain it.... but I think it's quite clear it ISN'T just inductive kickback from the transformer!)
OK, like you I'm not privvy to all of the previous discussions.
So the stiffness issue is when the Classic regulates then possible inrush of current due to power caps could damage the Classic.
I leave this discussion to those with full knowledge of the situation.
As for kickback and the bridge rectifier diodes, the issue here may be those rectifier diodes may be too slow to deal with fast rising spikes
and they may be rated for much lower peak voltage.
Anyway, don't know but I personally would not 'test' a Classic with that power source or connecting a load resistor between the PV inputs.
...back to interesting stuff now s my Cubie arrived today Yay!
dgd
Quote from: boB on March 04, 2015, 03:08:36 AM
Steve, I have a question if you have the answer... I'll also ask Jose in Warranty.
What was the high voltage reading of the input to your Classic ? How high over
150V did it go ?
BoB -
The number given to me was 177.3V
Since being returned, the highest I've seen was 150 (and possibly some tenths, can't recall because the 150 and rate of rise was making me panic.
When it hit 150, it immediately went to rest, and the voltage began dropping, about as quickly as it was rising. Presumably this was hyperVoc engaging, as the relay let go at that 150V mark. After the voltage reduced to about 105V or so, it reentered float, but at that point I had disconnected the source, so it continued to fall until eventually it went back to resting.
I've witnessed it doing this three times now, personally. The first one was what started all this. Neither of the first two were captured. The first was also a "natural" mode change into float. The subsequent mode changes were forced, but the behavior is exactly the same.
Video of the third "hyper Voc" event:
https://www.youtube.com/watch?v=bWa_JXjgK7Q
I was able to get it to rise well over 100V time after time, like clockwork. One of them I caught on video as well, reaching 129.3V before topping out and then slowly falling back down again.
I did two resistor experiments to see if the voltage could be suppressed to help protect the unit.
My first was with a 150R 10W, from PV + to ground. When the test was run, the voltage climbed quickly and held at about 35V for around 20 seconds, then dropped back down to less than a volt, with the classic returning to resting mode. The resistor got quite hot during that time frame.
The second resistance test, I doubled the resistance to 300R/20W (2 x 150R/10W in series). During this test, the voltage rose to ~51V, again holding this level for 20 seconds or so. When I went to record the video of the 300R test, the voltage didn't go much higher than 42V or so, but did hold there with similar timing and the like.
Video with the 300R:
https://www.youtube.com/watch?v=PxH3A0gMDvI
As of right now, there's no "problem", meaning it hasn't resulted in damage. However I very strongly believe that it was an event similar to these that caused the damage to the original MOSFETs, as the software had been acting strange just before I did the factory reset and the big bang occurred. I can't help but wonder if one of the effects of that software glitch was that possibly it didn't catch hyperVoc and disconnect the way this is doing at this point, resulting in a voltage that just kept rising, silently killing them.
Other circumstances surrounding this:
While it appears that it will rise somewhat without heavy loading, this is when it rises the highest.
It seems it needs to be in bulk for a few minutes, then transition to absorb to be most prominent. I typically leave it in absorb for a couple of minutes to ensure that it isn't going to bounce back out to bulk. The effect can be seen at any point after having been in bulk followed by absorb... anywhere from the beginning of absorb, to the end, by forcing a float, or left to it's own where it naturally switches over (via timer or end amps).
Hopefully it's a little clearer now with the video of the events. I don't know what the best solution is, but at least the resistors help keep it in check by not allowing it to rise to potentially destructive levels.
Steve, what are you using for an input source here ?
Maybe you could do a short video to show what you have connected and your complete setup there.
I think that may help explain this.
If the classic is holding the battery at Float voltage or Absorb voltage, you must have some kind of input voltage source.
Also, why would the input voltage be right above battery voltage ?
Try replacing your source with a real solar panel.
What version of software ? I have not seen this input voltage rise happen, at least not in a very long time
and certainly not with a solar panel connected to the input rather than the grid.
Didn't you originally connect a rectified grid to the input before using a transformer ? That would explain the 177 volts maximum input reading.
The software will always disconnect when the input voltage goes above 150 volts.
boB - on the solar panel... I'd absolutely *love* to... I simply don't have a practical means to do it, especially at the power levels where it seems to be the worst.
I *strongly* believe that the transformer has nothing to do with the issue we're seeing here. Inductive kick would be there, and gone... It wouldn't last *seconds* and continue to push a basically regulated current thru resistors like it does. It simply cannot be the problem. I'm involving you guys because I'm trying to work this out. That was a relatively expensive "mistake" that you can imagine I wish to avoid a recurrence like the plague.
Without a schematic of the grunt section of the classic, I can't do anything but speculate based on behavior. What I *think* is happening is the software is giving the converter some kind of arbitrary signals that cause it to run "in reverse" as a boost converter. As you know, unregulated, a boost converter can run away, and I truly believe that's what's happening here. The resistors provide somewhere for the power to go so that it doesn't just build up and go out of control.
One thing that puzzles me is the load vs voltage rise, as well as how hard it pushes into the resistors... There's *some* correlation, more load means more power/higher voltage, but if one were to plot it, I would hazard to say that it would not follow a curve, line, or anything else... very erratic.
The other aspect to this is that the software can "intercept" at 150V, is there a possibility that it could let the relay go sooner?
Another thought just crossed my mind, I'll have to run a few and see if I'm right: the /length/ of time it pushes against the resistors /may/ correlate with the batteries settling into the float set point. I'll run a few and report the findings.
The transformer is from a 900VA APC UPS unit, the Voc on it is ~22V, and I'm not sure where it's absolute maximum is, but at about 15V I am pulling ~300W through it. Using this transformer was based on the discussion about keeping the transformer as close to battery voltage as possible. As you pointed out basically, raw math would keep it from passing much more power than that, but both it and the classic are happy working with it, no unexpected heat, etc. It does just fine *except* for this transition to float issue.
I you aren't using the Aux 1 or 2 terminals, you could set Aux 1 to go high when it goes over some PV
input voltage an drive Aux 2 from that. Then set Aux 2 to turn the Classic off (Resting) when its input
goes high. Set Aux 1 PV on High for whatever voltage you want to see it turn off at.
Doesn't really solve the problem except in an indirect way but still something you could do.
What firmware version do you have again ?
boB
Firmware - MNGP=1933, Classic=1923
Sorry about that, got lost in trying to provide details and forgot one of the questions...
Aux 1 is controlling the fan for the transformer, using waste not low I believe... Still experimenting with that.
[EDIT] - Aux 2 has the WBJR on it
I'm working out how to do a temporary setup to do tests with actual PV. It's a logistical issue, but I'll get around it. There's always a way, right? Haha
The *real* solution to that aspect would be to actually do the real install, but some lengths of odd shaped extruded aluminum are standing in the way... gotta make some phone calls and get the metal guy back on the ball I guess now that the weather is starting to show signs of being favorable.
It might take a bit... This weekend is a possibility, have to see how it plays out.
I'd like to find a way to reproduce this for you in your shop so you can gather a better idea of what's happening. My tests will be with 4x 100W @ 12V nominal (72 cell) PV in 3 configurations... 4s, 2s2p, and 4p. The latter most will be the closest to this transformer.
There's a difference as well between the other transformer that was connected when the MOSFETs went... That was in full wave config, this is connected as center tapped half wave on either leg. Theoretically *shouldn't* be a difference, but throwing it out there just in case. I know you've got to be as curious as I am about what's happening here... I don't care about right or wrong *nearly* as much as finding the answer.
You mentioned video of how this is all connected... not sure what anyone would be able to really infer from it, but I suppose I can shoot some as well as draw some schematics... they need to be done anyway LOL
Here are a couple pics along with pertinent schematics...
As you can see, pretty straight forward.
I'll do the real PV tests as soon as I'm supposed to be getting a clear day... other than that, this is about all I can offer up besides the descriptions and video in the other posts.
My theory about it pumping in reverse until the battery sinks to the float set point was indeed correct. It appears it'll push until the cows come home if something were to hold the battery above it. I'm throwing a link to the video I shot earlier where it pushed against those resistors for 3+ minutes, over 100V, until the battery settled to the set point. This was a natural mode change, triggered by the absorb timer. There doesn't however seem to be much rhyme or reason (yet) as to how hard it pushes. :-\
https://www.youtube.com/watch?v=fFgClMw44K0
And the pics of the implementation...
Looking at the video, I wonder what happens if you do the same thing BUT unplug the transformer
right when it goes from Absorb to Float and don't hook up your resistor.
Instead of unplugging the transformer from the wall, disconnect the positive output of
the diodes (cathodes) from the PV input of the Classic right after the transition.
ALSO, when doing this, go to the RFR screen from status by holding the Left-arrow key
and pressing the ENTER key. I would like to see those 4 + and - numbers in the middle
which will show all of the current sense numbers. Video that too if you can.
boB - As requested... I wasn't sure if you'd want resistors or not looking at the raw current readouts, so I did a video both ways. Hopefully these help a bit. I'm still looking for a correlation with the peak voltages... I tried a few more things before posting, looking for a connection, but still not lining up with anything that's visible.
The videos:
Bridge disconnected immediately after mode change, No resistors, Status display:
https://www.youtube.com/watch?v=SGje_sBXDCM
Bridge disconnected immediately after mode change, No resistors, RFR display:
https://www.youtube.com/watch?v=zbcmYDfA5I8
Bridge disconnected immediately after mode change, With resistors, RFR display:
https://www.youtube.com/watch?v=HPduZ-Hke38
Ok, I know there's been a little curiosity going on, and here are my findings over the last couple of days.
I'm 100% positively sure, with no doubt in my mind, that it is coming from inside the classic, and no chance whatsoever that it's coming from anywhere else. At all. Period. To wit, the recent development:
The rise can be triggered simply by forcing bulk then forcing float while battery is above float voltage.
The rise will occur with *nothing* connected to the input at all whatsoever.
I was satisfied that real PV would not trigger it... as I was only seeing minimal rises, just a few volts. There was a blocking diode between the PV and the classic, so there could not have been any loading by the panels. I had more or less resigned to the idea that in some form or another the transformer was at fault, so the PV tests ended early.
But then...
After disconnecting the PV, I let the batteries drain, then charged them again via the transformer. I was trying to catch the peak with the daily "hi pv" register, when it became apparent that this was a product of "yesterday". So I set out to confirm it by letting the batteries discharge for a full 24+ hour window. Sure enough, all it caught was the transformer's Voc at the beginning of the discharge when it was disconnected from the grid: 22.5V
Tonight, I set out to catch any anomaly in disconnecting the transformer, and found the above instead - there was no rise, so I just forced it into float (with no input) so as to avoid the spike, and then *would* have turned the transformer back on. I didn't make it to reconnecting power, as I had then gone back to the status screen, to see it in excess of 65V!
As a sanity check, I went back to tweaks, hit force bulk, and returned to status, it was then sitting at 16.5V (the MPP set point), but of course not actually doing anything since there was still no input.
Back to tweaks, force float, then status, and it shot up again, this time only reaching 27.1V
So I disconnected everything completely from the input, and repeated the bulk/float tests. Same exact results!!! The behavior didn't stop until the float voltage set point was reached, at which time it returned to the 16.5V, and about a minute later, the relay kicked out and it went to rest, voltage falling to ~7.5V
Ross hinted that I should maybe see that with a lower float set point, would it also jump. The answer is yes. Float set to 12.0, battery sitting at 13.0, nothing connected to the input whatsoever, force bulk, force float, rose to 27.1V once again. Another run with the same settings produced 26.6... With the float voltage set at 10.5, input rose to 26.1
I'm STILL not sure what decides how high it goes... but it always jumps... the delta appears to be mostly related somehow to the amount of time spent in absorb... or now even simply bulk? It's very unclear, and temperatures still don't really appear to mean anything. The relationship with time, if there is one, is non-linear.
With the float point set at 10.5, I left it a bit while throwing the basics of all this out on IRC, which took several minutes. It held that voltage (26.1) in float mode, and seemed likely would stay that way until the battery reached the float set point. For what that's worth.
If that's all the further it ever shot up, who cares right? Unfortunately this is just not the case, and now I have no idea what to do. I can only put the resistors on it to help keep it from rocketing :(
Something is also way out of whack with the daily "hi pv" or *something*... it's calling the last high peak 118.4... and I know it didn't rise that high on the status screen - I was watching intently during the disconnect, and it was still rising for each of the subsequent observations... so either it's measuring it independently, or simply not pulling the data from the right place. All I know is, by my count, it should be holding a value of approx 65V, but it's much higher.
With 22 volts Voc the Classic input WILL go higher and 26 volts is not high at all.
PV V is allowed to go higher than measured Voc because if Vbatt is above the set point,
the Voc may have changed since the last Resting period and so it has to be allowed to
go a bit higher at least. Going from 22 Voc up to 150 V or even 118 Volts to reduce
the Vbatt would be right out of course.
I am not sure why you would have seen 118 Vpv high but were you watching the MNGP
all day ? You would have to log that every couple of seconds or be staring at it to
notice usually. That high Vpv voltage logging does require it to be there for a
while, at least a couple of seconds before it logs it IIRC. I will take a look though
and make sure nothing has changed.
Quote from: boB on March 10, 2015, 08:35:47 PM
With 22 volts Voc the Classic input WILL go higher and 26 volts is not high at all.
I'm in agreement there... if that's the furthest it ever shot up (or even double that), I wouldn't be concerned.
Quote
PV V is allowed to go higher than measured Voc because if Vbatt is above the set point,
the Voc may have changed since the last Resting period and so it has to be allowed to
go a bit higher at least. Going from 22 Voc up to 150 V or even 118 Volts to reduce
the Vbatt would be right out of course.
I never put it into solar mode during the PV tests, because I was trying to keep from changing too many variables at one time. It stayed in manual hydro the entire time (and I adjusted the MPP accordingly so conditions could be met).
I'm not entirely sure what you mean by "Going from 22 Voc up to 150 V or even 118 Volts to reduce the Vbatt would be right out of course"... can you elaborate/clarify?
Quote
I am not sure why you would have seen 118 Vpv high but were you watching the MNGP all day ?
No, however it should have stayed in resting mode... I timed everything so that immediately after the midnight reset, I turned the transformer off, and was running from battery while I wasn't able to babysit it (specifically out of recognition that the logging wasn't frequent enough to catch it elsewhere)... :-\
Quote from: MadScientist267 on March 10, 2015, 10:33:51 PM
I'm not entirely sure what you mean by "Going from 22 Voc up to 150 V or even 118 Volts to reduce the Vbatt would be right out of course"... can you elaborate/clarify?
The classic raises the input voltage to reduce charging current and/or battery voltage so if your Voc was 22V it wouldn't need
to go very high of V pv.
Quote
I am not sure why you would have seen 118 Vpv high but were you watching the MNGP all day ?
Quote
No, however it should have stayed in resting mode... I timed everything so that immediately after the midnight reset, I turned the transformer off, and was running from battery while I wasn't able to babysit it (specifically out of recognition that the logging wasn't frequent enough to catch it elsewhere)... :-\
I wonder if that log was simply from the previous day ?
Ok found the problem with the hi Vpv... for whatever reason, "Day 1" was reading data from mid February... Bumping it to Day 2 caused it to find itself and going back to Day 1, it's realigned. The voltage in question (~65) is logged as 69.2V.
So THAT part is at least cleared up.
On to the other parts...
OK, good deal on the Logs... Next...
Next time you catch the input voltage rising above, say 40.0 or 50.0 volts,
press the STATUS button twice and get to the screen that shows Voc and
note that number to see what the Classic thinks the Voc is.
Or, how about watching that screen for a little while or better yet, video that
third status screen if that number happens to be changing or moving around
while actively in Hydro mode and not resting.
Haven't gotten that far yet, but wanted to note that I took a peek just for curiosity... It's been floating at least since today's reset @ midnight... at present, it's got Vin at ~19.2V, and has the Voc registered as 16.2V. Found that rather peculiar.
I'll also do a run here shortly to see what it says at various points. Just wanted to make a note of that for posterity.
Quote from: MadScientist267 on March 11, 2015, 08:37:54 PM
Haven't gotten that far yet, but wanted to note that I took a peek just for curiosity... It's been floating at least since today's reset @ midnight... at present, it's got Vin at ~19.2V, and has the Voc registered as 16.2V. Found that rather peculiar.
I'll also do a run here shortly to see what it says at various points. Just wanted to make a note of that for posterity.
Do you log certain registers ?
You can also check modbus address 4121 which is another form of Voc. (Register 4122)
There is also modbus address 4223 (register 4224) which is Voc before actually coming out of resting.
And address 4230 (register 4231) which I think is what is displayed on the MNGP.
Steve, try this.... Tap/push (lightly-ish) on the top of the PCB while watching the PV input voltage.
Use an insulated somethingOrOther like a pencil eraser. You don't have to have it running or
even have an input source... It should provide around 2/3 of battery voltage reading all by itself
with the input disconnected. See if the input voltage changes/rises/lowers.
The components here would especially be the input voltage divider resistors (part of it anyway)
to the left of the microprocessor (100 pin IC), R20, R21.
R86 and R24 are also in the circuit but they are series and not shunt to negative so would cause an
opposite effect of there is a bad solder joint.
Thanks,
boB
My apologies for the slow response...
It held 7.2-7.3V the entire time :-\
From the sounds of other communications, I guess that's that then eh? I'll jump in the email loop shortly.
Thanks for all the assistance.
Steve
Quote from: MadScientist267 on March 17, 2015, 11:41:41 PM
My apologies for the slow response...
It held 7.2-7.3V the entire time :-\
From the sounds of other communications, I guess that's that then eh? I'll jump in the email loop shortly.
Thanks for all the assistance.
Steve
7 to 8 volts is about what it should measure on the input terminals when there is no input connected except for the 12 volt battery