Over voltage warning

[cnetate]

Hey guys. First post here. I've been adding solar to my RVs for years but I'm definitely not an expert and I love learning about this stuff. I've run into an issue as I'm expanding my solar array that can't figure out and am seeking help. Here's what I got.

This is on my 5th wheel rv.

The first is a sting of 5 200w panals rated at 28.98voc and 8.2a. For 144.9 v. I have this hooked up to a 60a 150v epever mppt charger. The most I've seen from this is around 138v and I've never had an issue for the year I've had it hooked up to my 2 Chins lifepo4 300ah battery bank for 600ah. And it does a great job charging.

Now, I just added the same exact string, same panels, charger, wire size etc to the battery bank and I have 2000w total now, but this string is giving me an over voltage warning on my MT50. It's reading around 165voc with no amperage.

So I thought maybe the BMS wasn't allowing the string to charge since they were full. I ran down the battery, disconnected the first string, waited for the voltage to drop on my second string and once it did, it began to charge normally. I connected the first string again and I had a green light on both, indicating they were charging. But I noticed it seem one charger would charge for a few seconds and then stop, them the second string would charge, like they were switching off. I went to check on the array again and I had a over voltage again on the second string.

Both controllers are wired directly to the battery with a 60a fuse.

Charge parameters are the same on both chargers. I used Will Prowse's advise and have 0 temp compensation, charge limit 14.6v, boost 14.4, float 13.6, 0 equalize time.

Can you tell me what's causing the over voltage warning on the 2nd string? I was thinking I could use a common bus bar and wire the chargers to the bar and the bar to the battery? Thanks for any help!

 

[chrisski]

Seems you can only go 4s.

The more each panel works, the lower the voltage. By adding the third string seems each panel works less, and voltage goes up.

Could also be the newer string has a higher and different VOC and VMP. That happened with my newest set of renogy panels.

 

[cnetate]

Hey thanks for the reply. I'm not sure what you mean by only go 4s?

Are you suggesting I add a third string?

I checked the specs and all the panels are exactly the same.

Thanks for your help.

 

[chrisski]

I checked the specs and all the panels are exactly the same.

Have you done the temperature compensated calculations to see how much these panels are supposed to put out? Usually this is in the spec sheet. If its 144 volts, that is probably at 25 C, and voltage should go up bu .26% per 1 C the temp goes down. A chilly day could push the panels above 150 F.

If you are at 144 F, that is a little to close for me for even the cold days we have in Central AZ in the desert where the temp can dip to freezing early in the morning.

If you have 10 panels, I think you have them setup 5S2P, and that pushes the 150 volt limit, so 4 in Series with two of those strings in parallel with two spare panels or 3 panels in series and three of those parallel with one spare panel would take you away from pushing the 150 volt limit.

 

[mikefitz]

checked the specs and all the panels are exactly the same.

There is a tollerence on the panel specification, your new panels are generating a higher Voc.
From the Epever manual for the 60A 150 volt unit,

 

[cnetate]

Yeah I was suspect that the one string would read pretty similarly to the other string. It seems as though the battery won't allow the charging.