Calculate device/battery run time

[Rivermonsters]

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

 

[telectrix]

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.

 

[Deleted member 26818]

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.

 

[telectrix]

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.

 

[DPG]

Remember that car batteries should not be flattened completely. You would need a deep cycle battery (aka leisure battery etc).

 

[Deleted member 26818]

I measured some 7Ah batteries at work the other day, they measured 11Ah.
New last year.