Battery over-discharge warning; how can I fix it?

[WhileyCoyote]

I have 400w panels atop my 35ft bus. They feed into an 80amp MPPT solar charge controller. I have a Renogy 3000w inverter hooked up to a 30amp shore power inlet and 600ah 12v battery bank. Solar panels have never gone over 160w. Volts are 12 to battery bank; 36v for solar panels. All outlets and lights are 120v and 3amps or less. When I turn on all breakers in my distribution box which has a 50amp main breaker, I get an over discharge warning. When I turn on 1 breaker and plug in the fridge and/or the 10000btu portable A/C, I also get the same reading. Every component has an ANL fuse. I don’t have anything running to the bus’ alternator.

How do I get my rig completely off grid so I can run both my a/c and my refrigerator at the same time, all day long?

 

[dcg9381]

do I get my rig completely off grid so I can run both my a/c and my refrigerator at the same time, all day long?

$$$. A lot of $$$.

I've seen one rig setup to to this. It was a Sprinter. It had a lot of lithium, a roof full of panels, and was assisted by a very large alternator.

Is your fridge residential?

HVAC is the huge hit because it's likely to pull at least 12A continuous and require a lot of starting current. Yours may be more efficient as it's not a roof top unit. I am seeing DC power HVAC units in the market which are likely more efficient... They'd be better if they could feed from 24v-48V.


Quick math:
600Ah * 12v = 7.2kWh (total capacity, you've got lead acid, you won't be able to discharge nearly that much power, maybe 50%)
120V * 12A = 1.4 kW (normal draw via HVAC, not surge)
I'm my experience, RV HVAC with soft start usually needs 2500 watts of generator, so you're in the ballpark on the inverter.

Is it the Renology that's giving "over discharge"? Likely what that means is that your battery voltage is dropping below a threshold.
For that inverter to do 2500 watts, it needs to be able to move 208A from the batteries. That's 3/0 copper. Just eyeballing your setup, I'm not sure you've got 3/0 copper?

 

[nadogail]

Your battery bank and cables seem to be undersized for the application.

 

[WhileyCoyote]

They are 2/0

 

[WhileyCoyote]

They are 2/0

 

[dogdog]

more solar panel or less electrical usage ?

AH and Watt Hour are different.
Solar panel Watt and charge controller amp and inverter watt are different ...

This is your scenario right ?

your solar panel is not able to keep your batteries top off (fully charged) and your usage is draining the battery banks down to unacceptable level of 11v or below.

 

[kbeefy]

That 11.1v on the ammeter is no good.


Are you sure the cables are 2/0 and not 2ga? They don't look that big....

 

[kbeefy]

Heres a pretty good forum specifically for Off Grid and solar...

https://diysolarforum.com/

 

[dcg9381]

They are 2/0

Issues I see:

• If you have 400 watts of solar - but your all time high is 175 watts something is likely wrong.. You're not even in the ballpark of being able to sustain power... You're going to need a lot more PV.
• 2/0 might support 195A, but it's going to be VERY HOT. You do not have large enough wire to support a 3000 watt inverter.
• 11.1V means that you've exhausted your battery bank. It might be the batteries, or something in the wiring between them and the 2/0 cable to the inverters. This is why you're crashing the inverter.
• Lead acid batteries cannot sustain high discharge rates (amps) without voltage drop. They will work for a while, but not as long as you'd think.

 

[TractorJeff]

I posted a similar scenario back in June/July/August about a similar issue. Go read what they offered me for insight!