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Posted by Dave on March 9, 2009, 2:29 pm
There are commercial testers which work by applying a (modest) known load
and measuring the before and after voltages. I assume they work by looking
at the change in battery voltage after a defined quantity of charge has been
removed ...
Dave
John O wrote:
>> On Mon, 9 Mar 2009 10:50:45 -0400, "John O"
>>> I was just yakking with an engineer/programmer of some skill, who
>>> was telling me that a simple voltmeter is probably a bad way to
>>> measure the charge remaining on a pair of 12V lead acid batteries.
>>> At least, it's not an
>>> accurate way to do it.
>>> And here I was thinking my robot battery gauge project was going to
>>> be simple. :-)
>>> What say you? Can a simple meter do an adequate job of telling me
>>> the relative charge remaining in the batteries? I'm not looking for
>>> 65-segment accuracy...10% increments would be perfect, 20%
>>> increments fine, and 25% increments will work.
>>> -John O
>> You probably need to look at the discharge curves for the battery
>> you are using. If you don't have a curve, then generate one by
>> putting the battery under load and measure its output voltage
>> over time as it discharges.
> Yes, I have that curve.
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> telling me that a simple voltmeter is probably a bad way to measure the
> charge remaining on a pair of 12V lead acid batteries. At least, it's not an
> accurate way to do it.
> And here I was thinking my robot battery gauge project was going to be
> simple. :-)
> What say you? Can a simple meter do an adequate job of telling me the
> relative charge remaining in the batteries? I'm not looking for 65-segment
> accuracy...10% increments would be perfect, 20% increments fine, and 25%
> increments will work.
> -John O