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Old 06-04-2014, 03:33 PM   #1
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Random Inverter Shutdown

I am experiencing a random low voltage (11.8V) inverter shutdown, only when not on shore power, this has happened 3 times in about 4 weeks of boondocking.
My setup is: 480 Watt 12 Volt solar -> GoPower PWM charge controller-> 6 x 6Volt AGM batteries, total capacity 1300 Amp/h ->Xantrex Pro XM 1800 msw inverter -> Frigidaire fridge is only appliance running when this happens.
Can't remember the start up draw from the fridge but running it draws ~120Watt from the inverter.
Battery charge shown on charge controller ~13.5 Volt
Battery charge tested on batteries ~12.9 Volt
Inverter never shows more than 12.2 Volt - 12.3 Volt incoming.
Due to the location of the batteries the pos. cable to the inverter is 7' - 8' #2 AWG and the neg. is also #2 but 12' - 13' long, factory/dealer installed.
The message on the inverter readout show E02 11.8Volt at shutdown.
I did check all connections.
It is the line loss between the batteries and the inverter which concerns me but it is not possible to shorten the cables, a 1/0 cable could make a difference but I'm worried that there is more going on.
I would appreciate if someone could point me in the right direction, thanks.
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Old 06-05-2014, 04:00 AM   #2
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A couple of different things to check and some observations...

First, you don't have 1300aH capacity.. unless each of your AGM's is 433ah @ 6vdc or you're wired for for running 36vdc :-) I suspect your 6v-AGM's are in the 200-250aH range each; wired for 12v in a combination series/parallel configuration your total is more like 600-750aH.

Second, the loss difference between #2 and 1/O in 8' is negligible at best with no load. Voltage loss is only going to occur as load (amperage) increases, so the interesting questions are:
(a) What is the voltage measurement right at the inverter DC inputs with absolutely no load (everything including the inverter switched off)?
(b) What is the voltage right at the batteries themselves? In only 8' length with zero load these two numbers should match.

Third, What I find most interesting from your post over anything else you've outlined is your voltage loss between the PWM and the batteries - that is substantial and appears likely where your problem will be found. What AWG did they use to wire between the charge controller and the batteries?

Fourth, inverting from DC power is horribly inefficient to begin with. If memory serves me correctly the basic rule of thumb used for sizing your system is that it takes 10amps of DC to produce 100watts of usable 120v AC through an inverter. With that being said, you can figure your usage and capacity based upon the loads you're applying.

In a perfect situation, batteries fully charged, solar panel turned off, absolutely nothing else running but the inverter and the refrigerator (not even any 12v lights), your unit closed and locked up, at best you'll get 60-65 hrs of run time (approx 2 1/2 days) on your present setup. Obviously there are many variables and I'm sure the boondockers more well versed in this area can chime in as well.
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Old 06-05-2014, 08:55 AM   #3
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Thanks Newmar,
I am sadly aware that I paid for ~650 Amp/h that I can't use, the batteries are wired in series/parallel for 12 Volt.
I did check the Voltage at the inverter when turned off and did not see a Voltage drop.
I have not checked the Voltage on the inverter when the refr. is starting up, that is something I need to do with the assistance of my wife.

I am glad you are pointing at the PWM, I have to check the wire gauge from the charge controller to the batteries, if memory serves me right I guess it looks like #4 or #6.
Could it be that the charge controller itself is the problem, I do not see the 13.5Volt+ on the batteries ever. Is it possible that the charge controller is unable to bring the true voltage up to 13.5? I realize there are more sophisticated cc's available. I could run the generator for a few hours and see if that raises the battery voltage. (typing while thinking)
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Old 06-05-2014, 10:23 AM   #4
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Please read:

RV Electrical


Then check your controller's voltage setpoint and wire size vs distance bwtn the controller and the batts.
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Old 06-05-2014, 02:06 PM   #5
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I guess I have an idea what's happening.
1. Our solar setup is taxed to the max
2. 12 awg wiring from charge controller to batteries
3. Charge controller reduces charge before batteries are 100% charged
in this order.
After running the generator for a few hours (then waited ~10 minutes) I checked everything like I did before and now I have strong 14 Volts on the batteries and 12.8 - 13 Volt going into the inverter.
It looks like I need at least 100 Watt 12 Volt more on the roof, (I will probably double what I have now,) heavier gauge wiring from charge controller to batteries and a larger and more sophisticated charge controller, maybe an MPPT controller.

We had a similar solar system on our previous 5th wheel but with an RV fridge and for a residential fridge it is very hard to find reliable information of what the actual requirements are.

Please correct me if I'm wrong.

Thanks 94-Newmar for pointing me toward the charge controller and thank you BendOr for the link to Jack Mayer's rv electrical site which I had read before but only now that I have issues can connect the dots.
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Old 07-03-2014, 09:33 PM   #6
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Problems solved

We doubled the solar to 960 Watt, upgraded the wiring and installed a 2nd inverter. The batteries are charged by 10 am, the panels pull in ~50 Amps per hour now which is amazing.
Now when we run the MW for a couple of minutes the solar puts the power back into the batteries almost instantaneously and no more Voltage drop due to undersized wiring.
Now I know you can't have to much solar
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