Battery AH selection for a generator

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Muhammad Umer ansar

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karachi pakisatan
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junior electrical engineer
I have a Three phase 750KVA and a 132KV generator in my factory. I need to buy the lead acid batteries for generator starter. I know that the Generator starter needs 24V Dc Supply. My question is that what Ampere hour(AH) of total Battery do i need for their starters respectively. What are the calculations or thumb rule for its sizing?and what factors needs to be considered for sizing batteries.
Umer
 
The battery's energy rating (amp-hours) isn't particularly important.

What's important is having enough power (cranking amps) to turn the starter motor, plus whatever margins are deemed necessary to accommodate a battery with diminished power due to age, low temperature, standby discharge, or other factors.

The installation/interface documents should list a starter-motor current specification.
If an actual specification is unavailable, my personal off-the-cuff recommendation would be a minimum of about 2 cranking amps per kVA.
In your case, 1500 cranking amps (or cold cranking amps, if applicable) for a 750 kVa machine.

A pair of 8D truck batteries might be marginally adequate. For reasonable margins, you might want four.

For an engine that big, you might consider an air starter.
 
More than KvA rating what is the motor that drives the generator? Is it diesel or gas? Diesel will require more than gas to turn it over to start. What size motor? My guess would be a big 8 or 10 cylinder. Only large one I've ever dealt with, and that was only to look at it, had a huge diesel that had a pony motor to start it, if memory serves me it was a small 4 cylinder pony on a large 10 cylinder diesel CAT engine, would need a ladder to work on it it was so large.
Many times you can get info from a large truck or equipment repair shop if you can identify the drive engine to get a compatible battery system.
 
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