Outback Flexmax 80A Tripping Battery Breaker

Hi, I live off grid and constantly trying to upgrade my system for improvements. I've been using Outback's Flexmax 80 controller, and recently upgraded to (8) Valence U27-12xp lithiums in a 24v arrangement with (9) 280 watt / 38.5v panels configured 3x3. Mosts of my loads are small 12v and 24v for DC lighting, small DC refrigerator, and water pump. I have a 24v Foshan 3000 watt inverter that is only turned on to run a washer and dryer.

Most of the time my batteries stay at 80% (I keep the FM80 set to charge only to 80% to extend battery life. Over the weekend my wife did three loads of laundry and we brought the batteries down to 63%. A day came and went and I noticed the batteries didn't recharge at all, so today I checked things out and the fuse/breaker was tripped between the FM 80 and the batteries. I reset the breaker, the FM80 came back to life and after a few minutes it tripped again. I lowered the limit on the FM80 to 60 (FM80 was only seeing about 34 amps) and still tripped.

Long story short, I'm off grid so a system malfunction is a major problem for me. I'm using a breaker like this, which I know isn't the greatest. Anyone want to guess whether there is an issue with my controller or if the breaker is just shot? The FM 80 isn't even 6 months old.

Those panels at full power will output over 100 amps what size breaker do you have. You said you set the FM 80 to 60 amps is that 60 amps charging.

The breaker is 80 amps. The 60 amp I referred to is the limiter function, first option on the charger settings, before bulk and float voltage settings.

dp you have a way to meter the power coming out of and or in to the the SCC ? How many amps are going in at what volts and how many amps are going out at 24Volts

98v, 11 amp IN
27.6v, 36 amp OUT

The panels will output over 100 amps at full power in a 3x3 string? I always get confused on series/parallel combinations but I thought a 3x3 configuration would be putting out closer to 21.8 amps and 115.5v?

no the SCC could output that much if the SCC were large enough. I'm willing to bet you have a bad breaker I think the Flex Max would be pretty true to its specifications.

9 280 watt panels wil produce a max of 2520 watts
2520 watts at 24 volts is a little over 100 amps possible.

Craig said:

9 280 watt panels wil produce a max of 2520 watts
2520 watts at 24 volts is a little over 100 amps possible.

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Thanks for the help, Craig. I hope it is just the breaker b/c this is my third charge controller in as many years.

Can you elaborate on your math a little more? Using online tools (the Renogy website) with three series of three panels parallel panels I don't get how you come up with those numbers. I'm not questioning you, I'd just like to understand.

If so, what size breaker would you recommend?

I would say something larger than 80 so a minimum of 100Amp.


My math 9 panels times 280 watts = 2520 watts

the the flex max amp rating is 80 amps at the system voltage. you have a 24v System so the flexmax can put out a max of 24volts x 80Amps which is 1920 Watts which is probably ok since panels rarely produce full power.

If the panels were producing the full wattage and you had a larger or 2 SCC you with those panels could produce a max of 2520 watts / 24 volts or 105 amps.

Usually controllers are rated for input voltage and output amps output amps * system voltage = max watts
or panel wattage / system voltage tells us the amps a SCC needs to process to handle all the power.

Sorry if I'm confusing it all makes sense in my head lol

No, that makes total sense. I’m still confused because my electrician designed the addition of 6 of my 9 panels and calculated ~20 ish amps with “a lot of headroom to expand”. What it sounds like from you and from what I observe from the system’s performance I could probably get away with 6 panels and be at more of an optimum performance for the FM 80.

he is calculating the amps produced by the panels at a higher voltage when they are in series. your panels are probably putting out around 120 Volts at 20 amps. The SCC converts the higher voltage lower amps to whats most efficient for charging. You could drop 3 panels and see if that helps. But I think the flexmax can handle the extra juice and it will be way better on cloudy/rainy days to have as many panels as possible.

Would I be correct in thinking that the SCC was never exceeding the breaker voltage then, just running in float mode, until we ran the battery bank down with the washer and dryer, and when it had to start really cranking out the juice to recharge the batteries that's why it exceeding the breaker limits?

mannytheseacow said:

Would I be correct in thinking that the SCC was never exceeding the breaker voltage then, just running in float mode, until we ran the battery bank down with the washer and dryer, and when it had to start really cranking out the juice to recharge the batteries that's why it exceeding the breaker limits?

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That is exactly my thought. Even if it were in bulk it may not if drawn enough amps

I have two FlexMax 80's and 36x300/310/330watt panels. The FlexMax will limit the current output to what you program so I went overboard on the panels. I originally test the FlexMax on a 12V setup and found no problems as it hit the 80 amp limit...which is why I am now running two and a lot of panels. I would definitely try swapping that circuit breaker. Also using Outback FlexPower 7.2kw pre-wired setup and am very impressed. Just hooked up two AC's this week and 3800 watts all day is nothing.

That's good info, Stiffmeister. Thank you. When I started observing my problem I dropped the limiter all the way back to 60 amps and was still having the issue. Since my initial post I have upgraded the breaker from the cheap marine breaker that I linked to and replaced it with a 100 amp Midnight Solar breaker. Haven't had the problem since... though I haven't drained my battery bank that much since then either.

mannytheseacow said:

Since my initial post I have upgraded the breaker from the cheap marine breaker that I linked to and replaced it with a 100 amp Midnight Solar breaker. Haven't had the problem since.

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Hopefully your wire size is correct for that breaker size. Otherwise the wire will protect the breaker rather than the other way around.

About 2 ft. of 3 ga.

I've been dealing with calculation for the past weeks. How did you end up Manny? Is everything running well? I use the same breaker, the 80A.
Question, was there a 125% factor into the system sizing when the calculations were made? I see a little over run with the numbers there, I think...?
What is the ISC of the panels if I may ask?