[RE-wrenches] Best Off-Grid Equalize Charging Method

[Allan Sindelar]

Jeff,
I agree with you about most arrays being too small to sufficiently overcome
internal resistance and get voltage high enough to effectively equalize. I
won't advise either (early or late) approach to running the generator. Most
homeowners won't understand the variables and subtlety involved in
determining when and how to EQ. Rather, I will often advise that the
homeowner considers the gennie as the only tool to pump enough amps into the
batteries. I'll suggest that equalization be done during the day when the
sun is shining, and that both array and generator are used together. This
maximizes the C/rate and has the greatest likelihood of reaching full EQ
voltage and holding it there. Flooded batteries can handle up to around a
C/7 rate if in good condition.
Allan at Positive Energy

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jeff Yago
Sent: Thursday, October 23, 2008 2:55 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Best Off-Grid Equalize Charging Method


I know this has come up before but wanted to see if anything new available. 

Unlike on-grid battery-based systems, off-grid systems require a different
equalize charging strategy to reduce generator run-time and save fuel. The
problem arises when you have a large battery bank and a not so large solar
array. 

You can first run the generator early in the morning at a high bulk rate to
shove as much charge into the battery as possible, then take over charging
with the solar charge controller set for equalize charge and hope you have
enough sun-hours and current to take the generator-charged batteries past
their normal voltage and start gassing, 

OR, 

You can do the reverse and solar charge all day and then at the end of the
day use the generator with the inverter set for equalize charge and continue
charging while hoping this will not require too many hours of fuel usage. 


Of course the size of the solar array verses the size of the battery bank
may favor one method over the other, but are there any actual tests or
studies that make one method always the better choice?

I have found that small arrays have a real hard problem ever getting a large
battery fully charged, let alone provide an equalize voltage for several
hours, yet I have also found most inverters supplied by a generator tend to
back-off the charging current as soon as the battery nears a fully charged
state then tries to stop the generator. I also have found that some
deep-cycle batteries sold for solar applications require charging voltages
and re-charging times that are almost impossible to achieve unless you have
grid power available.

Any documented testing out there?

Thanks,

Jeff Yago




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