# lamp runtime calculation help please.



## ljw2k (Dec 4, 2011)

Hi all can someone tell me how to workout runtime please and what calculations i need as i asked a long time ago but totally forgot how to.

Source 12v car battery 
80 Ah 
Lamp 20W


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## JacobJones (Dec 4, 2011)

Watts/voltage=amps.
Amps/Ah=runtime in hours.

Assuming your bulb is 12 volt:

20W/12V=1.66666667A
1.66666667A/80Ah=48 hours runtime.

In reality you won't get that long.


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## ljw2k (Dec 4, 2011)

Thanks alot and i just worked it out about the same rounding the figures up

20W / 12V = 1.6A

80Ah / 1.6 = *50 hrs runtime *


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## FRITZHID (Dec 4, 2011)

never round up runtime, it's almost always shorter than u calculate.


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