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Re: [OM] More on the 12 volt SLA battery

Subject: Re: [OM] More on the 12 volt SLA battery
From: Jez Cunningham <jez@xxxxxxxxxxxxxx>
Date: Fri, 18 Sep 2009 13:25:16 +0200
Just doing a few back-of-envelope calculations for fun...
Two Bees at 360Ws = 720Ws
They recharge in 3s so they draw 720/3=240W - at 12V that's 20A
Now take some guesses at efficiency of the inverter and the Bees, say 80%
each and now we're approaching an average 30A.  But they'll charge
exponentially such that the AVERAGE is 30A, starting with an initial peak
that will be several times larger (limited by the internal resistance of the
battery, the connecting leads and the inverter circuitry) and decaying
towards zero.

It's gonna be hard to test what the battery could deliver: a 55W headlamp
bulb will take 4-5A so you'd need quite a bank of them to load it at
30-100A!

I think your tests show it's not in bad shape, but having the spare is
always good!

Jez

On Fri, Sep 18, 2009 at 12:51 PM, Chuck Norcutt <
chucknorcutt@xxxxxxxxxxxxxxxx> wrote:

>
> I finally checked the specs on the
> inverter and found that the low voltage warning is issued at 10.5 volts
> so obviously the two lights (which, together, recycle in about 3 seconds
> from a full dump) are putting a large drain on the battery and drawing
> the voltage way down.
-- 
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