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Hello

I am trying to calculate how long a car battery will last for which is 50ah, 12v. Running a 20watt device, 240v, turned on 24hours a day, how long would this battery last?
Any help appreciated
thanks
 
20 watts @ 12V =1.667A.

you should get around 24 hours out of the battery. are you using an inverter? that will cause some loss.
 
20 watts @ 12V =1.667A.

you should get around 24 hours out of the battery. are you using an inverter? that will cause some loss.
50 Ah divided by 1.667A = just under 30 hours.
 
50 Ah divided by 1.667A = just under 30 hours.
i always allow for not letting the battery go completely dead, and if he's using an inverter, that will lose some power.
 
Remember that car batteries should not be flattened completely. You would need a deep cycle battery (aka leisure battery etc).
 
I measured some 7Ah batteries at work the other day, they measured 11Ah.
New last year.
 

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