Re: [pvusers] Battery Time

["Scott Willing" <willing@mb.sympatico.ca>]

On 11 Nov 2002 at 18:18, Michael Welch wrote:

> Unless you discharge them too deeply and they don't get charged up
> again soon, I think 6 years isn't long enough. I would be bummed not
> to get 8-10 years out of a battery. But then, I am one of those folks
> that freaks out when my batts hit under 70% of capacity.

Amen.
 
> >Our batteries are stored in an insulated, but unheated shed, which
> >isn't a problem 99% of the time.  Occasionally, I'll have to run a
> >kerosene heater in there when a nasty front rolls through. Looks like
> >the AGM batteries have a wider temp range, but I wonder what the
> >drawbacks are.  Cost appears to be close enough to consider it
> >(especially after adding the maintenence headaches).
> 
> Freezing is most harmful to any L-A battery when they are discharged.
> Not 100% sure, but I have heard that a full L-A battery will not
> freeze due to the high acid levels. Anyone verify that?

Rough numbers:
State of charge (%) / 	Freezing Temp (degrees F)

100 / -76
 90 / -69
 80 / -62
 70 / -27
 60 / -17
 50 / -11
 40 / -6
etc. (do we care?)

I wonder if Bill's charging system is temperature compensated. Makes 
a big difference - if the batteries are cold they need to be charged 
to a higher voltage. Our batts are in a box in the pantry, which is 
on the cool side especially in winter, but still inside and far from 
"cold" -- perhaps 60 degrees F on average. Temp-compensated C-40 
charger takes the batts to around 15 or 15.1V in the winter vs 14.6 
or so (the basic set-point) in summer.

If charging isn't temp-compensated, it could be the reason for 
undercharging and/or premature retirement.

I'd also want to break that battery bank apart and ensure that there 
wasn't a bad cell or battery somewhere that's pulling down the net 
performance of the bank.

And a kerosene heater in a box full of charging batteries? Hmm...

-=s

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