Cold battery volts

[PaulMel]

I'm trying to evaluate two 12v 180ah floor scrubber batteries. These are connected in series. They are cold 32 degrees F in my garage.The two batteries are in parellel.I fully charged to 15.5v and held there for 4 hours. Then connected to a 1000w inverter. The voltage of the battery dropped to 11.6v within 30 seconds with 800w load on the inverter. I know this is probably drawing close to 100A, but shouldn't a large battery like this hold above 12v with this load? The two together should be about 300ah. Is the cold doing it? I know capacity at 32F will be reduced by 20%. Still, I thought the voltage with this load would stay up longer.

What do you think?

[RP]

I'm not sure about your particular batteries but usually the amp hours of a battery are at a 20 hour rate.  In your case that means they should deliver 9 amps for about 20 hours.  An 800W load on the invertor is probably near 1000watts on the battery side due to inefficiencies in the invertor so you are trying to pull ~83 amps from a battery designed to give 9 for a long period.

Remember these are likely deep cycle batteries and are not designed for giant peak loads.

[Clifford]

If your batteries are truly 180 AH...   and you have two of them.  Well, you should be able to draw 100 AMPS (1 KW or so) for over an hour.  Your voltages also sound really low.

Have you tried desulfating the batteries?  I haven't done it yet myself, but it sounds like it is relatively easy to do.

[ghurd]

Also, as the load goes up, the amp-hour rating goes down.

The company website may give a AH rating for 5 hours (or another brand's site for a similar battery).

I believe a draw of more than C/10 is hard on them.

G-

[wpowokal]

In summary,

You are asking too much of your batteries.

You are sending a boy in to do a mans job.

You will kill them in short order.

They will warm up and give more freely when under load but heck by then they will be flat.

By comparison my 24V system when place under 1kW load with little incomming amps will droop to 24.7V and stay there, (12.35V equivelent).

But my storage capacity is a little larger, 5800Ah, its normal for volts to droop under load.

Think of it like you are driving along foot steady on the gas, you reach an incline the vehicle slows until the motor(battery) can ballance the load. Go over the incline and the speed(volts) increases as the load  on the motor(battery) decreases.

http://www.homepower.com/magazine/downloads.cfm

Click on bateries, this info may help you understand your batteries.

hope this helps

allan down under

[rich2741]

Paul,

Your biggest problem is you are subjecting the batteries to freezing temperatures (32 F). That is a major no-no.