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If I know how many DC amp hours at 36V I need to replace into my battery bank, is there a way to calculate the number of AC KW hours my charger will use in order to do it?<br><br>Thanks,<br>Larry

Hi Larry,<br>I beleive the two numbers you have
to find are:<br>Charger efficiency (in %) and
Battery charge acceptance (in %). Normal numbers look
like 15~20% loss at the charger (Heat) and 25% +/- 10%
for batteries (Flooded). Some battery types accept
the charge better then others (AGM and Nicad over
Flooded) As far as converting DC watts to AC watts it's
all the same. <br><br>15 amps X 36 volts = 540 watts
for 10 hours, gives 5.4kw add the 40% (540*.4) loss
of 216 watts = 7.56 Kw.(AC used). This should be
correct if the data comes from your e-meter. If the data
comes from you charger's meter you don't know what got
into the battery, so just use the loss for the charge.
The above is just an example.(try it with your
numbers)<br>Good luck <br>Joe

OK, guys, check my math on this.<br>Thanks for
the suggestion, Joe, although I have the problem that
my charger is automatic and therefore its draw
varies over time and Im usually not able to monitor it
closely enough to determine how long its run anyway. But
how about this:<br><br>If P (power in W)= V (voltage)
X A (amperage) then my 240AH battery bank converts
to (36 X 240) 8,640 watt-hours or 8.64KWH. Assuming
something like 60% charging efficiency, as Joe pointed out,
a full replacement of the bank would require 14.4
KWH. If electricity costs $.06/kwh then a complete
replacement of the bank would cost.$.86. Is that really
right?!<br><br>Based on my limited tests so far it looks more typical
that my boat will cruise most efficiently at about
4.3mph at 1 hp (20.8A). At that rate a 20 mi. cruise
would cost $.35.<br><br>Tell me this is right or at
least close.<br><br>Larry

You got it Larry,<br>When you discharge your
batteries it's hopefully not to 100% DOD, but counting the
losses 240 ah is a good number to use. The rest is
correct and should work out to around a buck your
cost...<br>BTW, ain't it great, we can cruise around for the
whole day on a buck. ICE cost are 10~15 time
that.<br>Joe