Aux output based on FET temperature

[JerryB]

Hello Midnight!
I have a fairly large solar array on my boat (9, 240 watt panels @ 90 volt nominal) with a Classic 150 located in the engine room. The controller feeds a 1200 AH 12 volt battery bank. When the controller is putting out it's maximum cuurent (~95 amps), the unit will overheat even when the engine room temperature is 70F or lower (internal fan is running fine, no local obstructions). Overheating is defined as throttling back on the max current available as well as a high FET temp reading. An external fan directed at the box solves the problem. It would be nice if the AUX function could be triggered by a user settable FET temperature threshold, thereby allowing control of the fan. Since the FET temp is readable, it would seem to be a straightforward task, no? Thanx for your consideration.

Jerry

[Halfcrazy]

I could see an Aux function "Temperature sensitive" and the user can select between FET, Battery or MNGP temp and then they could set the turn on and off temperatures.

On a side not you say the controller is throttling back do you see it back down from 95 amps to 90 or less? It will always be in current limit with 9 240 watt panels that is about double its capacity so I would expect it to run hot..

[boB]

Jerry, could you please also look at the FET temperature in the TEMPS menu in the Classic ??
I am curious what it is here.   It may just be that you are seeing current limiting because of
the 90 some amps into the 12V battery with such a large array.  Seems like 70 degrees F
is pretty low and should not be a high ambient temperature for the Classic.

If it is just current limiting, then another fan would not help unfortunately.  Check the temps
though and we'll see what is going on there.

Thanks,
boB

[JerryB]

Bob & Ryan,

The controller is throttling back to 80-85 amps,, at least when I looked at it. I did monitor the FET temperature and from memory they were in the 180 degree range. When I applied external cooling, the FETs dropped 20 degrees or more and the current came back up to 95 amps or so. Clearly the classic is limiting at it's design maximum, but the higher temperatures are causing it to further limit (a good design philosophy). My feeling is there is just not enough air passing through the box. Perhaps it's the highly assymetric duty cycle driven by a 90 to 12 volt reduction.

Regarding the 9 panels, these are mounted horizontally (on a boat....). On the best day of the year at high noon, the effective (vertical vector) solar insolation is about 90% of STP. At NOCT (a measured 50-55 degree centigrade) you lose another 10% and I would estimate that the conversion efficiency of the clasic is about 90-93%. Add some wiring loss and you get about a 1/3 reduction of STP output or about 1500 watts. That is about what I see coming out of the classic when everything is cooking in MPPT mode. I designed for the larger array to provide for more daily hours of good output.

Thanx for looking into this. Let me know if I can provide more information.

[boB]

So you have   2160  watts worth of solar on one Classic into a 12V battery ??
That's like  160 amps worth at 13 volts !

The Classic is lower efficiency at 12V output compared to say, 48V so that is
about right.  Sounds like it is limiting OK as well.  You must have converted
from Celsius to F from the display.  That would be in the 80 degree C range
which would be about right for limiting.

Yes, I can add an Aux output based on temperature.  This won't be right away
but I will try to get that in there when we get a chance.

Have you thought about getting a second charge controller ??   One (if that is what
you have now)  will severely limit your output capability even if it was letting
you do 110+ amps continuously.

Thanks,
boB

[JerryB]

Hi Bob,

Thanx for the reply. I didn't consider adding a second controller because the array is pretty well matched right now based on actual available PV power (see above analysis). We're located in the Olympia WA area (Puget Sound), not exactly the sun capital of the world. There are times when the array power does exceed the charging needs, for example when the classic goes into absorb mode and the current drops. In such cases the array voltage increases above MPPT levels and I have implemented a "clipper-like" circuit that diverts array current into the hot water heater. This will only occur if the PV voltage drifts above about 85 volts (adjustable) and is proportional up to 95 volts. BTW this circuit was disabled for all of the cases documented above. If this were a conventional off-grid system, I would NOT be using a 12 volt battery bank, but that is what is needed for a yacht. I will be using and observing the classic much more in about 2 weeks when we take off for 6 weeks of cruising. I should have a wealth of information when we return.

Thanx for your willingness to consider adding the temp feature. I think you'll find folks will use it.

Regards,

Jerry

[niel]

hi jerry,
could you clarify a few things for this land lubber?

1> is this battery bank tied to the starting system on the boat?

2> is the 12v going to an inverter and if so what is the make and model number of it?

3> what does the battery bank actually consist of? specifics please.

[Vic]

Hi Jerry,

As you know warm electronics lead shorter lives.  HOT electronics is not a good thing and can lead to catastrophic failures,  altho the Classic is a tough product.

Personally,  I would try setting an Aux output based on PV voltage,  and have the added fan always run at or above this value.  You could set this voltage fairly low,  say 50 volts or so.   If you can,  make the fan fairly large.  When ambient temps are high in that engine room,  the fan may not do much to cool the Classic.

Adding a second Classic -- the NEW Classic Lite would be a good mate for the existing one,  would help reliability a lot.  With a pair of Classics,  neither one would be stressed,  and there would  be redundancy.
Classic Lite Facts pdf:
http://dl.dropbox.com/u/31975941/Just%20the%20Facts.pdf

I was counciled against relying on one MPPT CC to limit charge currents to safe values at all times using a too-large PV array.  This was with a much smaller OVERLOAD than you are placing on your Classic.

Hope that you are using large enough wire on the output side of the Classic,  and you are using appropriately sized Output (battery) circuit breaker on the Classic.

Know that some boats do not have a lot of extra room for solar hardware,  and adding a second CC could be difficult and so on ... 

Like niel,  noticed the largish battery bank,  and also wondered about the configuration.

Good Luck!  Vic

[boB]

Hi Jerry,

Personally,  I would try setting an Aux output based on PV voltage,  and have the added fan always run at or above this value.  You could set this voltage fairly low,  say 50 volts or so.

The input voltage is almost always going to be above 50V in Jerry's case.  Even when it is off it will be high.
He ~could~  have the fan come on as well when over a certain power output.

That said, both of these methods would work.  What we want to do is to have an aux output function that
lets the aux turn on when one of a selected temperature goes above some specified temp.. i.e.  Either,
FET temp , PCB temp , Battery temp, MNGP temp OR even power output.

boB

[JerryB]

Hi Folks,

Here are some details that were requested above. The battery bank consists of 6, 1200 AH AGM 2 volt cells in series. They are L16 form factor cells  made by Concorde. The pure series configuration is ideal from a current sharing standpoint and I know from experience that series-parallel hookups are trouble even with careful balanced wiring. Yes, they are tied into the starting bank; indeed they are coupled to a starting set when I want them to be. For the record, I spoke with Midnight before I bought the classic and told them what I wanted to do, and they said it would be fine. The output wire from the classic is #6 but it only runs about a foot to the inverter whcih in turn runs 2/0 wire to the battery bank. All is properly set with disconnects and breakers rated for DC service. The inverter is a Magnum Energy sine wave inverter (2800 watts) and is superb. I trashed a Xantrax Freedom model after several years of trouble, 3 repairs and grounding design flaws. I have built a temperature sensing circuit that will moniotr the case temp and turn on a stout fan when it hits 50 degrees C. I'll install that tomorrow. The engine room never gets above about 80 degrees F even when running for hours. Hope this all helps.

Jerry

[Vic]

Hi boB/ Jerry,

boB,  yea,  but it is SO easy to change the V value.  My point is to try to make the LARGE fan run when the sun is up.  Did this fairly early in the life of my MX-60 -- 4-inch fan blowing into the open wiring compartment.  THat was set to 70 V PV in  (and still is),  with a 106 Vmp.   Works fine,  more cooling,  to me is better.   And wondered just why single out the FETs.  Cool the CC as much as you can -- all of it.  But this thread WAS about a Feature Request,  so all of the above is off-target.

Jerry,  sounds like a nice large system,  and done well.  Single strings are the only way to go for large-ish banks.  AGMs may not have the cycle-life of others,  but you prob do not want flooded cells,  and your DOD is prob not that great.  Thanks  Vic

[Halfcrazy]

Jerry
Something I did once was take 2 spare Classic fans and silicone them over two spare knock out holes in the bottom. I then wired them to Aux 1 set for Day Light. Anytime I ran the dc gen-set the fans ran and it really kept the Classic cool. I will try to find a picture.

Ryan

[nigel]

Ryan one assumes they were smoked stained spare fans for you R&D department. Im aware youve smoked more than most

[Halfcrazy]

Yes they may have had traces of that cool smokey smell 

[Robin]

Take a look at our power graph for a Classic 150 running 90 volts max power point into a 12V battery. These graphs are based on a 25C ambient. I do not have it in front of me, but I am pretty sure the Classic is only good for about 1200 watts. You have over 2000 watts. The life expectancy of this Classic will be shortened for sure and you are losing a fair amount of available PV power at times. I am curious about your home brew Clipper. Why is it necessary? It is not wise to add things to the input of any charge controller because it makes them want to blow up. If the load diversion is being done on the far side of a rectifier, it may be ok, but if you are dragging the input voltage down to a heater element voltage, you are asking for trouble. That may look like a short to the input terminals of the Classic. Shorting the input terminals will blow it up. When we do our Clipper, all the load diverting is on the other side of a rectifier, so it does not appear as a short to the input terminals.
I strongly suggest a second Classic if you want a long life out of the Classic. The MAgnum inveerter has very high idle current, so you will want to turn it off when not in use or connected to the dockk for charging.
Oh yeah, that 6AWG wire must be getting hot! Even though it is short. That also heats up the Classic and your breaker on the other end of the wire. Putting a 4AWG wire into our terminal block is a pain, but it can be done. We have already ordered tooling to make a totally new terminal block that will ease the pain of connecting 4AWG wire. We have at least 2000 more terminal blocks to use up though.
Good luck,
Robin