Trying to understand why my MPPT burned up.

[Guda]

Okay my bad. 6s-6s-3s in parallel

This shows how I parallel. This is the new setup but all the same parts.

Combiner box build, can electricity jump?

I have more to order & it will only do part of my MPPT's capabilities. Not sure what it cost as I built it from stuff I had laying around. That I bought for a combiner box build. When I am ready to add a lot more pv I'll just buy a prebuilt outdoor model.

diysolarforum.com

Why now? Something to do with how the sun was hitting the PV. When I posted on this before it was when the sun was in the same spot.

My battery will handle 100a in/out.

The 250 was reporting max amps & had a yellow light. All that for what the 250 was saying was 24 amps out.

The voltage was normally about 180v ish

I'll try to login on my phone

 

[Hedges]

Okay my bad. 6s-6s-3s in parallel

This shows how I parallel. This is the new setup but all the same parts.

Combiner box build, can electricity jump?

I have more to order & it will only do part of my MPPT's capabilities. Not sure what it cost as I built it from stuff I had laying around. That I bought for a combiner box build. When I am ready to add a lot more pv I'll just buy a prebuilt outdoor model.

diysolarforum.com

Why now? Something to do with how the sun was hitting the PV. When I posted on this before it was when the sun was in the same spot.

6 x 44.2Voc = 265V at nominal 25 degrees C.
Not knowing your cold temperatures or temperature coefficient of your panels, I use +16% to be conservative (-15 degrees C is 40 degrees below 25, and 0.4%/degree temperature coefficient)
265V x 1.16 = 308V

While a 3s string was in parallel, that sank current pulling Voc of array down to about 133V.
If an MC connector failed open disconnecting the 3s, Voc popped up to 265V (which Midnight can probably handle), but rose higher in the cold.

>>Poof<<

 

[Guda]

6s are not 265w. 3s are

 

[Guda]

My wiring was not the problem except array arrangement.

 

[Hedges]

6s are not 265w. 3s are

6 x 37.5Voc = 225V
250V/225V = 1.11
Those should stay below 250V under reasonably cold conditions, 11% headroom for increased Voc

3 x 44.2Voc = 133V

I would have tried to make the strings closer to the same voltage, but primarily to improve power production.

When SCC isn't drawing current, your arrays would have a bit over 2x Imp from panels in the 6s strings dumping their current into the 3s string.
Properly fused, might or might not blow a fuse.
It does make the MC connector carry 2x normal current (but not more than what we expect it to handle by spec)
It might age the PV cells faster.

I would have wired the 250W panels 4s3p for 150 Voc, and the 265W panels 3s for 133 Voc.

 

[labeeman]

I had a MidNite Classic 250 burn up after 15 ish months. I was at about 180v & 20a ish. The 250 can handle 250v 63a in. I was well below that. Now I am thinking it might have been my pv arrangement. I had 6p-6p-3p. Arrays ideal for summer, winter & east. The reason for that is a few. 1st array was summer on the roof. Making a array at 45 degrees on the roof was not what I wanted to do. 20 degrees was easy & the wind does not grab it at that angle. Next I put up east to get power as early as possible. Then the winter array is mounted so I can get the snow off easy.

The 250 months ago was reporting "max amps" & a yellow light was on. This was strange as I was only putting about 20amps at max. I'm not so sure there wasn't a issue with the 250 as it was a strange version.

I just found a burned connector on a pv from the east array that gets shaded. Although I have ideal diodes & breakers, I think something is going on with the different arrangements. Like the "T" in MPPT is for tracking. So if there is different V & A coming from the pv then the MPPT must not be tracing correctly.

At this point I am on the summer array only. Something is up with the winter array that I need to figure out. I will have another AIO in a couple weeks. When that comes in I'll connect the winter array to it. The east array is just going to do nothing until I get the other 2 AIO.

I am not sure whats going on technically but I am not going to have differently aimed pv on 1 mppt any more.

Replace the burnt connector get a clamp-on dc amp meter, disconnect all loads of the PV at the MPPT check the amps on each array if not 0 you have a wiring problem in your array.

 

[Guda]

I've been reacting to issues for like 20 months. Not doing thinks how I'd like. Wired for the 250, it died. Now my MPPT is 145v 80a lol.... So my 6s becomes 3s2p. Not ideal. But I have a new battery coming & another AIO. I'm not adding the winter array until I can just put it into the new AIO. In the final incarnation of this system I'll have 4 AIO & a mess of PV. I am even contemplating a "solar generator". Think a array 10x bigger than the MPPT can handle. But it only gets turned on in bad weather.

I just got done testing all the 250w pv & their all ok. I'm going to take down the east array & test those at a later date.