Lead acid capacity in freezing temps

mountainman · January 2018

My batteries specs are 208 amp hr but only 50% at 0 degrees. Question since at 50% on capacity do I charge on 10% of 208 or 104 amp hrs. One more thing which is worst on a battery bank discharging to 50 soc and charging at c10 or discharging to 75% soc and charging at c 5. On cloudy days charging with generator at c8.

mike95490 · January 2018

Cold temps slow down the chemical reactions in the battery ( Li batteries go downhill fast below +40F)

But I know of nobody who changes charge rates with temps. The BTS (battery temp sensor) with many high end charge controllers, adjusts the charging setpoints + & - according to temps, but not the amps. So I dont think I'd worry about it.

mountainman · January 2018

So keep it at as is. Any thoughts on which is worse on battery bank daily 75% soc at 5% charge rate. Or 50% soc at 10% c rate?

BB. · January 2018

Probably not a huge difference.

Some have argued that both of those are 1x charging cycle. So, from a pure $/ah cycle cost, a 50% discharge is supposed to be more cost effective.

Personally, use the system the way you need it. Don't drive yourself nuts trying to be perfect.

Bill

softdown · January 2018

0 Freedom or 0 Canadian?

Estragon · January 2018

> @mountainman said:
> So keep it at as is. Any thoughts on which is worse on battery bank daily 75% soc at 5% charge rate. Or 50% soc at 10% c rate?

A 75% SOC is probably marginally better, BUT there are other factors to consider. Assuming a cold bank (0°f?), sulfation will take much longer than it would with a hot bank, so going to 50% may not be so bad as long as it doesn't stay there for long (like many days/weeks). Also, charging with a generator from 50-80% or so can be more fuel efficient that charging from 75-100%.

IMHO, you should give a cold (FLA) bank all the current it will take, assuming voltage is compensated for temp by a RTS. The only reason I limit current is to prevent overloading the generator in use. I don't change the limit based on reduced winter capacity.

mountainman · January 2018

Thanks everyone. In reviewing my battery specs at 75 soc they should last around 7 years but at 50 soc roughly 3 years so from a money stand point 75 soc would be better. So im gonna add 2 more batterys. On cloudy days in early morn I run a 2000 watt generator on a bulk of c6 35 amps with what I have now or c12 with 4 batteries from a dumb car charger for 2 hrs or so. Until the volts reach 14.8 then let solar take over Even on cloudy days I'll get about 2.2 amps.

mcgivor · January 2018

Yes the batteries will last longer but will require a larger bank to supply the same Ah as a smaller bank discharged to 50%, that's where the $/Ah comes in, when calculated the actual energy cycled is close, but replacement means they will be new more often, you pays your money and makes your choices, basically a matter of opinion, I'll keep mine to myself.

706jim · January 2018

My experience with cold batteries is that it doesn't take much to knock them down.

And not much to bring them back up.

FLA at about 0F.

mountainman · January 2018

With the larger bank I'd be able to go a cloudy day without using the gen. I think the gas savings tips the scale for me.

mcgivor · January 2018

With a larger bank the PV needs to be able to recharge after a cloudy day, if currently you have the need to run a generator, the need will be still there, only for longer periods, albeit less often.

mountainman · January 2018

I understand what your saying larger bank. Needs more pv and longer gen charger time even more gas!!! I'm maxed out on a 30 amp controller so more panels more racking more wire another controller.200 amp hrs in winter isn't enough for me

mcgivor · January 2018

Having a 12V system restricts expansion going 24V would allow double the PV on the same conductors, same controller, if compatible, but would require an inverter change, inverter chargers are better than using a car charger, in terms of efficiency. Battery wise, less parallel connections smaller conductors and fuses/breakers. All comes down to needs and of course budget.

mountainman · January 2018

I'm in a rv so guess I'm stuck with 12 volts. I use 75 amp hours per day. My panels bring in 100 or so on a good day. But my batteries in these temps are giving 50.My thoughts were with 400 amp hrs I'd be able to get my 75 and still have enough solar to recharge in a day?

Lead acid capacity in freezing temps

Comments