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I have a three phase 750 kVA and a 132 kV 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.

What ampere hour (Ah) battery do I need for the starters respectively. What are the calculations or thumb rule for its sizing, and what factors need to be considered for sizing batteries?

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A lead acid battery Ah specification is for when you want the batteries to deliver power for hours. It is not physically capable of outputting that capacity in a few minutes. Assuming the starting procedure takes at most minutes, the capacity is not going to be the limiting factor, you need to look instead at the actual current it can deliver for that time.

Car batteries similarly have at least two specifications, the Ah and the CCA (cold cranking amps). However the latter is for 30 seconds with the voltage above 7.2 V, which I suspect won't be enough for your load.

You need to know more about the generator starter specification. What current it will take, for how long, and what is the permissible drop in voltage over that time. Then get a battery properly specified for that service, 750 kVA is not a trivial piece of kit.

The battery capacity may be relevant if the specification includes repeated starts without the opportunity to charge between them.

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  • \$\begingroup\$ Thanks dear. very helpful it is \$\endgroup\$ – Muhammad Umer Ansar Jan 26 at 7:32
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Going by manufacturers' ratings, two 12 V 180 Ah lead acid, starter motor batteries would be required to be connected in series. A matching 24 V battery charger would also be required.

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  • \$\begingroup\$ @winny, Many thanks for the correction and my apologies for the rollback to confirm that. \$\endgroup\$ – vu2nan Jan 20 at 14:17
  • \$\begingroup\$ Starting batteries are generally rated in Cold Cranking Amps, while deep-cycle batteries are rated in Ah. Starting batteries are designed to deliver the high currents needed for starting an engine, but cannot withstand being deeply discharged. The OP needs starting batteries. \$\endgroup\$ – Peter Bennett Jan 20 at 16:57
  • \$\begingroup\$ No worries mate. \$\endgroup\$ – winny Jan 20 at 17:15

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