This information is getting towards my real question.

My inverter shuts off whatever it is powering and starts buzzing to
warn me whenever the battery reaches some pre-set point. Using the
inverter, though it throws a little(?) overhead on top of what the
fan draws, doesn't let the battery deplete the way a direct hookup
does--say a fan or the fridge--by running it to zero volts or near
zero volts.

What that point is where it shuts down, I don't know, but I guess
it's around 10.5 or 11 volts. So the question is not just how many
amp hours are available from the battery, but how many amp hours are
sustainable above say a 10.5 volt window.

Using Dave's example, and assuming that I had the same Sears Diehard
650 CCA battery, could I divide the amps (since we're talking amps
here) of my fan and inverter combo into the eight amps the fridge
draws and get a multiplier for the two hours. For example, Dave
assumes (rightly or wrongly) that 50% depletion from 8 amps happens
in two hours. Does that mean that 50% depletion at one amp will occur
at 16 hours?

jim

On Jun 20, 2006, at 11:58 AM, Dave Vickery wrote:

> A real world example.  A new Sears diehard 650 CCA aux battery will
> last 4
> hours until completely dead running the 8 AMP fridge.  On 12 V the
> fridge
> runs continously pulling 8 amps.  So assume 50% depletion in 2
> hours = 16
> Amps available.
>
>
>> From: Loren Busch <starwagen@GMAIL.COM>
>> Reply-To: Loren Busch <starwagen@GMAIL.COM>
>> To: vanagon@GERRY.VANAGON.COM
>> Subject: Understanding Amp Hours
>> Date: Tue, 20 Jun 2006 08:43:35 -0700
>>
>> The answer to another question here on the list raised this question.
>> Given
>> that we have the amp hour rating for a battery and also given that
>> we don't
>> want to draw it down below about 10.5 volts, about 80%.  Does that
>> amp hour
>> rating assume draw down to the 80% level, or draw down to 'dead',
>> zero?
>> I've always assumed that if I have a 50 amp hour battery that I
>> can draw 1
>> amp for 50 hours before reaching the point that will require
>> charging, or
>> will I only get 20% of that, 1 amp for 10 hours, before reaching
>> the point
>> where I need to recharge?
>