Re: (ET) New here, E15 and E12

["David Roden" <etpost drmm net>]

On 24 Sep 2021 at 13:19, David Roden wrote:

> To calculate the amp hours it yielded, divide the power rating of your
> load in Watts by 120 to get amps, then divide by the efficiency factor
> of your inverter (0.8 for an 80% efficient inverter).  Now you have the
> approximate initial battery current.  

Oops, sorry, slip of the fingers.  Divide the load watts by 12 (not 120) 
to 
get the current at 12 volts, then divide by the inverter's efficiency to 
get the approximate battery current.  

For example: 

750 watt load / 12 = 62.5 amps at 12 volts
62.5 amps / 0.80 efficiency = 78.1 amps battery current

I used this method for years.  In more recent years I've added 
instrumentation that measures current and amp-hours directly, so I no 
longer need to use the clock or do computations.  I found that I'd 
underestimated my inverter's efficiency; it's a surprisingly good 92%.

If you're testing 12 volt marine batteries, reduce the 120 volt load to 250
watts, because their nominal reserve capacity rating is measured at 25 
amps.



David Roden - Akron, Ohio, USA

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