# How to calculate the total time a battery can operate light?

Thanks

hi,I am willing to just use solar panels to recharge my batteries and then to power my garden lights. What I need is how do I know if my battery will be able to power my lights for atleast 24 hours. How do I choose the solar panels to be able to charge the batteries. IF I know how to calculate for atleast one light and battery that should be enough for me to calculate for my whole system.

Thanks

Thanks

active| newest | oldest1 W = 12V x i, i = 1 W / 12 V, i = .083 Amps

Time = (Amp-hours / Amps) / (Safety Factor)

t = (1.3 Ah / .083 A) / 2, t = (15.6 hours) / 2, t = 7.8 hours

You should be able to maintain full brightness for ~ 8 hours depending on how efficient your driving circuitry is and you only run the LED off of the battery.

Do you understand the equations? Try different numbers and make sure you understand how different power lights and capacity batteries will effect the time you get.

can you explain how did you put the value for the safety factor?

It's an arbitrary number really. Mostly it takes into account any inefficiencies in the battery or circuit. It also would help extend the light if you had a couple of days in a row without enough sunlight. You can reduce that number at risk of not having enough power to get the light all the way through until the panels take over again.

Watts are volts x amps.

Battery in watt hours (Storage capacity), light in watts and discharge till the light wont work (About Half to be safe).

You can do the same with amps.

Light in amps, battery in amp hours (Storage capacity) and discharge until the light wont work (About Half)

So a 5 amp light will stop working when running on a 10 amp hour battery in one hour.

Does this help?

Joe