I'm trying to run a rooftop A/C unit that draws 10.5 amps at 120V = 1260 watts.I have a 2000 watt inverter connected to a 430 amp hour battery bank using 18' of 2/0 stranded cable.This should be well within the capacity of the inverter, battery bank, and wire size.However, even with a fully charged battery bank (from 16 100 watt solar panels; batteries showing 13.7V, several days of charging), the batteries drop within seconds to < 11.0V triggering the inverter low voltage alarm.What am I missing here?Thanks!!!

Is that measured while running? Voltage drop is a function of amperage. If the inverter is just in idle mode waiting, there will be negligible amperage draw, so there will be negligible voltage drop. Suddenly ramp that up to 150amps and there almost certainly will be voltage drop. The question is if it's an acceptable amount of drop.

The 2000 watt inverter, just like high quality 2000 generators, is not enough capacity to handle the big spike in amperage draw when A/C compressor calls for power without something like a soft start kit installed on the A/C unit. Look up Micro Air, we have one and it is one of the best upgrades we have done and we run the A/C off our Yamaha 2400 inverter gen. Next culprit I think would be the batteries. You have a lot of capacity, but you are asking a lot of them as well. Others have covered it, more batteries or switch to lithium which suffer less voltage sag under load.EDIT: I just reread OP and realized it said 18', as in 18 feet, of 2/0 cable. That is fat cable, but 18 feet is a long length that I suspect contributes to the low voltage fault at the inverter. Put the inverter as close as possible to the batteries and use as short of wire length as possible.

there is no cable listed that is good for a 36 foot return run that can handle a 2000 watt inverter. I missed that in the initial postto the orininal op, is there any way to move your inverter right close to your batteries then run the 120V output the longer distance? a 4/0 cable used for that distance will give you a 5% voltage loss and you are much smaller than that so I am assuming over 10% loss which means your 12.6V quicly drops to 11.5ish ands then the surge from the batteries will let it drop under the inverter low voltage alarm level. sorry I didn't pick this up at the get go but I like Ewarnusa assumed 18" not feet as no one mounts an inverter that far from the batteries, it even says in the inverter manual to mount as close as possible to the batteries. captdaveo

Your AC may run at 10.5 amps, but the compressor likely “starts-up” at much more than that. You possibly don’t have enough “oomph” for a long enough duration to fully start that compressor and get it running; especially if you have any other loads on those batteries at the time of start-up.

Thanks for the reply, but that's not the issue. The AC will start and run for a few seconds, so it's getting past the startup load. It's that it won't keep running because the battery voltage drops so low -- even though 430 amp hours should be (in my opinion) plenty sufficient to run the A/C for awhile -- even longer with 40 amps of solar dumping into the batteries at the same time.

Running A/C over draws the batteries causing inverter alarm

ewarnerusa
Nomad
Jul 26, 2024
The 2000 watt inverter, just like high quality 2000 generators, is not enough capacity to handle the big spike in amperage draw when A/C compressor calls for power without something like a soft start kit installed on the A/C unit. Look up Micro Air, we have one and it is one of the best upgrades we have done and we run the A/C off our Yamaha 2400 inverter gen.
Next culprit I think would be the batteries. You have a lot of capacity, but you are asking a lot of them as well. Others have covered it, more batteries or switch to lithium which suffer less voltage sag under load.
EDIT: I just reread OP and realized it said 18', as in 18 feet, of 2/0 cable. That is fat cable, but 18 feet is a long length that I suspect contributes to the low voltage fault at the inverter. Put the inverter as close as possible to the batteries and use as short of wire length as possible.
- StirCrazy
  Moderator
  Jul 26, 2024
  there is no cable listed that is good for a 36 foot return run that can handle a 2000 watt inverter. I missed that in the initial post
  to the orininal op, is there any way to move your inverter right close to your batteries then run the 120V output the longer distance? a 4/0 cable used for that distance will give you a 5% voltage loss and you are much smaller than that so I am assuming over 10% loss which means your 12.6V quicly drops to 11.5ish ands then the surge from the batteries will let it drop under the inverter low voltage alarm level. sorry I didn't pick this up at the get go but I like Ewarnusa assumed 18" not feet as no one mounts an inverter that far from the batteries, it even says in the inverter manual to mount as close as possible to the batteries. captdaveo
bid_time
Nomad II
Jul 20, 2024
Your AC may run at 10.5 amps, but the compressor likely “starts-up” at much more than that. You possibly don’t have enough “oomph” for a long enough duration to fully start that compressor and get it running; especially if you have any other loads on those batteries at the time of start-up.
- captdaveo
  Explorer
  Jul 20, 2024
  Thanks for the reply, but that's not the issue. The AC will start and run for a few seconds, so it's getting past the startup load. It's that it won't keep running because the battery voltage drops so low -- even though 430 amp hours should be (in my opinion) plenty sufficient to run the A/C for awhile -- even longer with 40 amps of solar dumping into the batteries at the same time.
  - MNtundraRet
    Navigator
    Jul 20, 2024
    captdaveo wrote:
    Thanks for the reply, but that's not the issue. The AC will start and run for a few seconds, so it's getting past the startup load. It's that it won't keep running because the battery voltage drops so low -- even though 430 amp hours should be (in my opinion) plenty sufficient to run the A/C for awhile -- even longer with 40 amps of solar dumping into the batteries at the same time.
    The first reply was correct. The fact it quit after a few seconds shows the batteries voltage output dropped to far to keep it running.
time2rollagain
Explorer II
Jul 22, 2024
How old are the batteries? Have they been consistently charged to 14.4 to 14.6 volts? I believe the lead-acid batteries may have lost some capacity and while not dead they cannot hold the voltage up.
Otherwise I recommend 600+ Ah of lithium battery as a replacement if expecting to run the A/C for any length of time.
- captdaveo
  Explorer
  Jul 22, 2024
  Brand new batteries. Two sets of deep cycle 6V golf cart batteries wired in series, then the 2 sets in parallel, 215 amp hours per battery. The solar charge controller is set to stop charging at 13.8V, perhaps I should set that higher? Was trying to avoid adding 2 more batteries, but that might be necessary...
  - time2rollagain
    Explorer II
    Jul 22, 2024
    Yes most GC2 will call for a couple hours absorption time at 14.4 - 14.8 volts. Verify with the manufacturer.
time2rollagain
Explorer II
Jul 22, 2024
18' of 2/0 is still a bit far to feed 150 amps to an inverter. Have you checked the inverter input vs voltage at the battery terminals?
- captdaveo
  Explorer
  Jul 22, 2024
  I have, no voltage drop from the cables.
  - valhalla360
    Navigator
    Jul 24, 2024
    Is that measured while running? Voltage drop is a function of amperage. If the inverter is just in idle mode waiting, there will be negligible amperage draw, so there will be negligible voltage drop. Suddenly ramp that up to 150amps and there almost certainly will be voltage drop. The question is if it's an acceptable amount of drop.
StirCrazy
Moderator
Jul 22, 2024
what brand and model is the ac unit?
- time2rollagain
  Explorer II
  Jul 27, 2024
  Dometic 13.5, no easy start, vintage 2006, 30 amp trailer.
time2rollagain
Explorer II
Jul 22, 2024
Also keep in mind 430 Ah is based on a 20 hour discharge rate. The 3 hour rate running the air will be closer to 300 Ah. Another good reason to add the two more batteries.
Compare with US Battery US2200
https://www.usbattery.com/wp-content/uploads/2022/07/usb-ampere-hour-capacity.pdf
StirCrazy
Moderator
Jul 23, 2024
don't know if your checking this post at all, but it is uncomon to be able to run a ac off a 2000 watt inverter thats why I asked what brand and model so I could look up the specs. Part of the problem is you are not starting with with a fully charged battery , close but not full, then the drag down of lead acid batteries, once you put them under a very large load, is dropping the voltage even further to the point of hitting your low voltage alarm.
so how do you fix that, well as mentioned add more batteries, but I would recomend another 4 not just two if it is dropping off that fast, or switch to LiFePO4 which have less of a drop down effect when under load. you just have to do the math and see which is more afordable for one, less weight and better in the long run with any other modifications. I know when your talking about 8 GC batteries space is a premuim as well as weight, but that would get you about 400ah you could use. if you went LiFePO4 you could get the same preformance out of 4 100AH batteries or two 200AH batteries for a total of about 120 lbs as aposed to 560lbs
- time2rollagain
  Explorer II
  Jul 23, 2024
  Yes my Go Power 2000w inverter runs my Dometic 13.5 with ease. For about the same space and weight of my 4x GC2 I DIYed a 1200 Ah LFP battery. Easily holds voltage above 13.0 under extended heavy load.
  Although my 4x GC2 would run the A/C for at least a few minutes while testing. Never tested how long they would run the A/C.
  - StirCrazy
    Moderator
    Jul 24, 2024
    did you add an easy start? i have the gopower 2000watt inverter in my 5th and have never been able to run it.
    I would imagin the age of the batteries could be playign a part also if that is so, to many unknowens and the OP isn't coming back to answer it seams.