24V DC 300watts load works from a Truck battery

Thread Starter

Jonathan Foong

Joined Mar 13, 2021
27
I would like to understand the way of calculating or formula, how long a 24VDC 300watt load could last to function from a 24V DC 170AH truck battery?
Thanks.
 
Last edited:

crutschow

Joined Mar 14, 2008
27,939
Current is P/V, so a 300W load draws 300W / 24V = 12.5A.

The battery is rated at 170AH (ampere-hours) so the maximum life for a fully-charged battery would be 170AH / 12.5A = 13.6 hours.
But for good battery life you don't want to discharge a standard vehicle battery below about 50% of its capacity, so the maximum should be about 7 hours.
For discharge below 50% you would need to use a deep-cycle type lead-acid battery.
 

Ian0

Joined Aug 7, 2020
3,497
That’s not the same answer as “how long would a 300W load run from a truck battery, and the truck would still start afterwards?”
 

Thread Starter

Jonathan Foong

Joined Mar 13, 2021
27
Current is P/V, so a 300W load draws 300W / 24V = 12.5A.

The battery is rated at 170AH (ampere-hours) so the maximum life for a fully-charged battery would be 170AH / 12.5A = 13.6 hours.
But for good battery life you don't want to discharge a standard vehicle battery below about 50% of its capacity, so the maximum should be about 7 hours.
For discharge below 50% you would need to use a deep-cycle type lead-acid battery.
Thank you very much for your detailed coverage reply.
 

Thread Starter

Jonathan Foong

Joined Mar 13, 2021
27
That’s not the same answer as “how long would a 300W load run from a truck battery, and the truck would still start afterwards?”
Thank you for your consideration about this situation, I should make it clear making use of a truck battery (24V 170ah) to run on the load would be charged by a battery charging equipment when it is needed, rather than the truck. Sorry to confuse you.
 

Ian0

Joined Aug 7, 2020
3,497
Thank you for your consideration about this situation, I should make it clear making use of a truck battery (24V 170ah) to run on the load would be charged by a battery charging equipment when it is needed, rather than the truck. Sorry to confuse you.
Didn't want you to get stranded with a truck that won't start!
But as @crutschow says, use a battery that's designed for deep discharge. If you use a SLI (starting lighting & ignition) battery, it will probably last 100 cycles. 300 for a leisure battery, a few more for a deep cycle VRLA battery, or 2500 for a tubular plate battery.
 

Thread Starter

Jonathan Foong

Joined Mar 13, 2021
27
Didn't want you to get stranded with a truck that won't start!
But as @crutschow says, use a battery that's designed for deep discharge. If you use a SLI (starting lighting & ignition) battery, it will probably last 100 cycles. 300 for a leisure battery, a few more for a deep cycle VRLA battery, or 2500 for a tubular plate battery.
Definitely, it is thankful for your consideration concern about my situation, and again, your further information about various types/grades of battery and its rechargeable life cycles is also an added knowledge to fulfill my requirements. Noted and thank you very much.
 
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