battery Ah question

[thekman]

I hope there's no faq for this, I couldn't find one....If I want to run a 24VDC motor (little over 1 HP) that has an FLA of 60A, for about 10 seconds, and I am using 2 12V deepcycle batteries in series, each with a 100Ah rating, how can I calculate an accurate discharge rate? I assume the 100Ah is a 20 hour rating, giving me only 5A per hour, but I need 60 for 1/180th of an hour...I'm pretty sure I'm not going to get 100A for an hour, but stuck on the math.

 

[raithrovers1]

The only sure way is to get the discharge curve from the battery manufacturer.
If your battery is 100Ah it is important to know at what C rating this is. You have stated that it is 20 hour C rating but you will have to confirm.
Experience has shown that a 100Ah battery at the C20 (20 hour) rating would give approximately 60-70Ah for 1 hour or about 330A for 5 minutes (These are taken from a known VRLA battery curve). Therefore your application should be OK.

UPS engineer

http://www.calibrepower.co.uk

 

[IRstuff]

You are supposed to get something on the order of 1 A for 100 hr. However, in your case, your discharge rate is very high, so even though you are only consuming at a rate of about 1/6 Ahr per discharge, you probably need to derate the performance of the batteries.

Yuasa uses a 10 hr rate capacity, that's 10 A as a discharge rate. Your discharge rate is 6 times that; Yuasa's curves don't go that low, but I'm guessing that your battery will be only equivalent to 50Ahr at that discharge rate, which should still give you about 150 discharge events, using another factor of 2 for margin.

TTFN

FAQ731-376