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On Tue, 24 Jul 2007 12:09:20 -0400, Jeff wrote:

* wrote, On 7/24/2007 11:10 AM:
The problem with the amp hour meters is (I suspect) they aren't very
accurate. I admit that I've only read the manual on a couple of
different makes but they both talked about initializing the meters and
then later into the manual they mention that you need to re-initialize
(or maybe they said "zero") the meters from time to time..

They are quite accurate in a sense, but I think mine gets confused by
the number and variety of charge sources and sinks. This leads it to
automatically adjust its concept of charge efficiency poorly.
Recently I realized it was using 73% when a better choice was 87%.
However, if you understand that is happening, its easy to compensate.
In my case, I knew that it was losing about 15 Amp-hours a day. A
few hours of charging, as when powering through Wood's Hole is enough
to reset the meter. On a day by day basis, when my alternator charge
rate drops down to around 40 Amps, I know the 450 Amp-hour bank is at
about 90%.

I quite like the basic idea but given that as the battery ages the
charging time changes I cannot see how the meter can be absolutely
accurate and if it is only approximately then I can envision problems
although it certainly seems to make things simpler.

Its better on the usage side than on the charging side. But still,
its infinitely better than nothing.

Well, yes. The output side is just amps times time but when you start
charging it gets difficult as depending on the battery's age you may
need to put back 110% - 125% - ???% of the amp hours that you have
used. This was the part I never could figure out how to compensate
for.

For the moment I use a volt meter and keep a watch on the voltage. I
guess it is sort of a mental gage but I wish someone would invent one
that maybe measured S.G. and compensated for that, automatically
compensate for the ageing battery bank.

Bruce in Bangkok
(brucepaigeATgmailDOTcom)

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