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Author Topic: Size of batteries needed?  (Read 1257 times)
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« on: December 06, 2009, 09:12:01 PM »

I want to power a 800W submersible water pump using batteries charged by wind (I am looking at a 200w or 300 w turbine at a very windy site). The running time is only 10 minutes twice a day. Am I right in thinking that 2 X 100aH batteries would be adequate? I have read that the start current might be too much, any comments gratefully received.
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« Reply #1 on: December 06, 2009, 10:45:22 PM »

That looks to small to me.

You only want to have a drain current of about 10% of total bank capacity. Its not just about total available power but how fast you use it. The bigger the load is in relation to the bank the harder it is for the bank & will give a shorter working life.

Small banks with high loads dont last long.

Your looking at 64amps ish drain (plus start up loads). So a bank of 600ah would be better.

You also need to have enough reserve to cover non windy days. Normally about 3 or 4 days is used.

So each day you will be using

64amps for 20 mins so roughly 21ah per day. Plus inverter losses (will the inverter be on a timer or on 24 7?).
(if on 24 7 then you will have about another  20ah per day to account for as you will need a big inverter to start a 800w pump)
(my 1000w bore hole pump is started by a 3000w inverter)
You should never discharge lower than 50% & higher will give a longer bank life.
With the 600ah bank you could have about 10 days (5 with inverter losses if on 24 7) with no wind & it will still work.

You also want to look at the size of the turbine & if you really have 4 hours per day of full power producing wind.

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