Thursday, Sep 21, 2006 at 21:39
Sorry Mike, you are wrong. You should have kept reading the next few paras.
if we now split the battery bank into two 200 amp hour battery banks we find that 5 amps for a third of the time gives us 49 hours to flat, which is 24.5 hours to 50% state of charge, but again this is for a third of the time so 3 times this is 73.9 hours.
In the first example, calculated correctly using the actual current draw, as opposed to the average current draw we got 181 hours run time from the 400 amp hour battery bank.
In the second example, using the same calculation we got 74 hours run time, for the same equipment, from the 200 amp hour battery bank.
So if the battery bank was split in two, then each bank used for the fridge, and fridge alone, we would get a total run time of 148 hours. Whereas from the full 400 amp hour battery bank we would have got 181 hours.
And all intermittend loads will work the same way.
In effect, splitting the battery bank into smaller banks gives a smaller total available battery capacity and therefore a shorter run time.
All due to Peukert's effect. But the effect doesn't become apparent in calculations unless the actual current draw, calculated on a cyclic basis, is used for each item of equipment as opposed to the average current draw of all the loads combined.
Also consider that the very fact that the battery banks have been separated means that each battery bank will, in all probability, be discharged to a lower state of charge. This shortens the life of the batteries (see the 50% rule).
Ian
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