Unexpected PV breaker trip

ajw22

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Nov 16, 2018
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Just a report to help others avoid potential troubles in the future.
TL;DR: Install breakers with high enough Amprating to account for higher current during hot weather.


I have 3 solar chargers, each connected to their own oversized PV array, so that I can get enough power on days with less than ideal weather.
Each array is 3180Wmp, Vmp 91.8V, and Imp 34.63A. The solar charger limits itself to at most 2285W, so the draw from the solar panels should never ever exceed 2285W/91.8V = 24.9A, right? And in practice during spring, it was closer to 20A.
So I used 32A breakers for chargers #1 and #2, and a leftover 25A breaker for charger #3. A bit tight, but they don't trip until at least +15% or so anyway...

It worked well for 5 months, buttoday #3 breaker tripped. The weatherwas super hot, so according to the "temperature coefficient" stated in the datasheet and assuming panel temp of 55C, the panels now had a Vmp of just 81.3V (11.5% lower!!). The solar charger compensated by pulling more than 28A. The 40+C heat in the electrical room probably helped set off the thermal trip of the breaker, too.
Solution: replaced the 25A breaker with a 32A.
 
Yeah, a bit tight on the amp tolerances there. I suppose live and learn. At least they actually tripped and didn't cause other issues.
 
Correct. Its common that people underrate solar-breakers wrong. Seen it happen and been there as well :)
 
I had a related situation - doubled the panels going into an existing Midnite Classic 150 (winter time)while I was waiting for the new/additional one to arrive. I have 80a breakers at the control box on the Midnite output. It so happened that I got a perfect day and the Midnite went above 80a... and tripped the breaker.

This was when I discovered that Midnite has the ability to limit the output power... so I set it down from 85a to 80a... to avoid tripping the breaker in the future. Maybe your charge controller has an output amps limit setting? You could use that to make sure it doesn't trip your 25a breaker?.
 
Does limiting the output amps of the charge controller allow an array to be larger than whats recommended for the charge controller?
 
Cheap4-life said:
Does limiting the output amps of the charge controller allow an array to be larger than whats recommended for the charge controller?
I'm talking Midnite Classicspecifically- and I view your question asseperate aspects.

Aspect 1) The Classic is designed to let the user limit output and will throttle or discard the PV input to achieve the user setting. This can run continuously... e.g. the Classic will not shutdown but continue to operate all day....

image_ofseuz.jpg


Here's what the current limitslooks like in the interface of Classic 150 in 48v battery mode:

image_txingm.jpg



Aspect 2) If you exceed the max input design of 4420w and feed in 8000w (as an example) the Classic will protect itself (e.g. it won't burn up or anything)but I think it willshutdown / stop producing output to the battery. However, I'm not sure and didn't find anything to reference in a medium google search. Assuming wiring/breakers are not in the way...maybe its temperature related more than anything else.

Here's what the manual says....

image_utdbcb.jpg
 
An array can almost always be bigger than the controller without limiting further. The controller always have a limiter per default. (Of course check this out first)

As an example. In Sweden most arrays are 10-20% larger than the inverter because its cheaper to do that and have more total power over the day than buying bigger inverter.

Limiting in this sense is to set a limit on the current so you dont trip the system if it isnt properly sized. I recommend to properly size it instead. Though it can be that you want to have more even curve during the day and limitng is cheaper than sizing.

I have not heard of any charger that is damaged by to much total "power" available as long as the Voltage range from the panels doesnt go above the Max voltage on the device.
 
OffGridInTheCity said:
This was when I discovered that Midnite has the ability to limit the output power... so I set it down from 85a to 80a... to avoid tripping the breaker in the future. Maybe your charge controller has an output amps limit setting? You could use that to make sure it doesn't trip your 25a breaker?.

Yes, my charge controllers are set to put out at most 40Amp. That results in 20A~25A on the PV side on typical days.
The problem was that as the panels heat up in peak summer, the panels put out 11.5% lower voltage, and the current increased 11.5%, thus tripping the breaker.



Cheap 4-life said:
Does limiting the output amps of the charge controller allow an array to be larger than whats recommended for the charge controller?

Absolutely, and I absolutely recommend it. I have a +40% larger array than what my charger can handle. Results in more stable max charging output for more hours/day, even with less than ideal weather. Panels are cheap nowadays - put up as many as you can.
 
Thats great! Why do they even have a recommended maximum amount of watts if its only the volts that matter. Outback and midnite both have a maximum amount of watts listed for their controllers. They both also have options to limit the amps they output
 
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