array drops from 60v to 20v

[ashenash]

Friends
My 24v off grid system has a problem I cant seem to fix.
My array tests ok .(2 -24v in series)
I connect to the Midnite diy3024 everything checks ok
I charge 2 sok 12v in series
I connect a small load
Everything looks good- array pushing around 60v
I walk away for an hour
When I come back the array is pushing only 20 volts
Swapped in a Outback fm60 but get the same scenario
What would cause this ?

I've built about 10 small diy systems but never had any similar issue

thanks in advance
bert

 

[TomC4306]

Bad MC4 connection on a panel. Or full battery.

 

[ashenash]

Batts not full, 25v or so
So, are you saying that a bad mc4 would act like that (working normally then an hour later, not working)
I don't understand how that could happen, a working circuit should continue to work unless disturbed
My mc4 and cables are clean tight and dry and out of the direct sun

 

[Rednecktek]

Could be a flakey panel. 20v sounds like a single panel under load so maybe 1 panel is just bypassing instead of contributing.

Try taking out 1 panel at a time and see if one of them just stops working after a couple hours, and check with a meter to make sure the voltage from the panels is what the SCC is reading.

 

[ashenash]

thanks rednecktek,
that's something to try
though 20v seems low for a 24v panel in in the sun
would it drop that low if its series companion is bypassing ?

 

[Rednecktek]

If it's under load the voltage will drop quite a bit which is normal. That's where the difference between VoC and Vmp come from. You're probably seeing some voltage drop from the bad panel too. Add them up and 20v isn't suprising.

 

[ashenash]

If it's under load the voltage will drop quite a bit which is normal. That's where the difference between VoC and Vmp come from. You're probably seeing some voltage drop from the bad panel too. Add them up and 20v isn't suprising.

good answer, thanks.
anybody else ?
good answers always welcomed

 

[mikefitz]

When it shows 20 volts, what's the current into the batteries? What is the voltage of each battery?
Unless the two batteries are balanced, individually and to each other, charging in series may cause BMS shutdown.
SOC batteries are often supplied unbalanced. You may need to charge each at a suitable voltage/current for the cell balance to become usable.
Individual batteries in series often cause issues.

Mike

 

[ashenash]

When it shows 20 volts, what's the current into the batteries? What is the voltage of each battery?
Unless the two batteries are balanced, individually and to each other, charging in series may cause BMS shutdown.
SOC batteries are often supplied unbalanced. You may need to charge each at a suitable voltage/current for the cell balance to become usable.
Individual batteries in series often cause issues.

Mike

My sok batts were perfectly balanced when I installed
I got the same voltage drops with agm batts
this is a pre battery issue

 

[TomC4306]

, a working circuit should continue to work unless disturbed

Wrong. Current/loading can and often does expose poor connections.

 

[400bird]

I don't understand how that could happen, a working circuit should continue to work unless disturbed

You forget that things fail. Bad crimps, soft seated connectors, overheated connections, solar panels, breakers, etc.
As has been mentioned, test the panels individually, this is also a good time to inspect the MC4 connectors. Also check for a failed fuse or breaker.

 

[ashenash]

all were checked on the last troubleshoot

 

[400bird]

Did you individually test each panel both for open circuit voltage and short circuit current?