Battery Voltage drop under load

Hi,

The load will be closer to 26 amps due to inverter overhead.

The thicker plates do cause greater voltage drop.

brulaz wrote:
Is a voltage drop to 12.0V to be expected with a 21.3A load with a fully charged ~216Ah battery bank?

I've never loaded the batteries that much before, so really have no idea what to expect.

It's a pair of 3 year old GCs, ~216Ah new, maintained by solar: daily charging up to 14.8V then 13.1V float. Haven't checked their sp.gr. recently but it was ok 6 months ago.

When resting at 13.1 float, I turned on the newly installed inverter and then the frig (256W according to the inverter, so 21.3A at 12V), and the voltage at the batteries dropped to 12.0V.

Turning off the frig, the battery voltage went quickly back up to 12.5V or so, and the solar controller was then in mppt.

Thanks all.

It was the voltage at the batteries that dropped to 12.0V.

(The inverter reported 11.9V. 0.1V is about what I expect for cable V drop with that load)

And yes the solar was active at the time but overcast. And I was just using the frig load as a test. No plans to run it routinely.

If the sun comes out, I'll equalize first, then try again with the solar turned off.

The drop is normal but with a 10% load on a new battery-bank that size you have 5 hours run time on the refrigerator (not counting any other loads.

I would suspect your inverter will sound "low battery" warning in about that time frame due to total demands on the batteries.

You did not state how large your solar panels were, but you would never make it through the night with that small a battery-bank.

I would make the battery DC VOLTAGE measurement across the terminal posts first to be sure you are not having any voltage drop due to too small of battery cables...

I use 4AWG cables with properly crimped ring terminals for everything I hook up to my battery setup... My DC VOLTMETER measurements is done at my main BANK 1 and 2 BATTERY SWITCH which is about two feet away from the batteries. I think I usually see about a .1VDC drop when my three 12VDC batteries are running my 600WATT PSW Inverter running at half power which is around 22 AMPS DC current.

I was originally going to use 2AWG ANCOR MARINE GRADE CABLE between all of the battery terminals and the three four position BLUE SEA switches I have setup to control four 12VDC batteries in Parallel. Ordered the 2AWG cable and ring terminals but never installed them.

I would RULE OUT your cabling first before pointing to the low performance of the battery setup. I would also check the terminal connections at the batteries as well. They may not be tight and may need cleaned up some...

0.5VDC voltage drop seems excessive to me for a 21 DC AMPs load measured at the battery terminal posts...

Roy Ken

You need an ammeter to follow the action. The voltage drop you are seeing is a little higher than it "should be" but you also have the solar on which confuses things.

The amps in from the solar would make the amps draw from the fridge net less from the battery and hold up the voltage a bit higher, so perhaps your actual situation is worse (but it is not a calamity, just more than it should be)

You can help by improving the inverter-battery path (fatter wires and tighter connections) but there might also be less capacity in the batteries than you think, since you have not been checking on them all that much and they might need at least a good equalization session to bring their "at full" SG back up some

I get about 0.8 drop with a 70 amp draw on four 6s but that is just my set-up. Others would get more or less than that with theirs. with two batteries instead of four you get more drop. With AGMs instead of Wets you get less drop.

Some inverters are better than others too for amps draw. My older 2000w Vector (now moved to the truck camper from the 5er) pulls 90 amps to run the kettle but my newer Can Tire Xantrex 2000w using the same wires and batteries pulls 80 amps to run the same kettle.

Normal