How can i work out how much current a battery would draw, i know how long it needs to be used and the capacity
Answer:
first: the battery will not "draw" current it will "supply" current.
(draw implies use from another source)
the capacity of a battery will be a rating in Ampere Hours (Ah) (or MilliAmpere hours (mAh), simply divide the rating by the time it is needed for (in hours) (Ah/h=A) (mAh/h=mA).
the trouble with this is that the current is determined by the circuit the battery is connected to, not by the amount of time you need it to last for so if the circuit draws more current than you expect then your battery will not last as long as designed, conversely if the circuit draws less current than you expect then the battery will last longer than designed. This is why it is normal to discover the current drawn by the circuit before specifing which battery to use.
Dear Friend,
Always remember the concept of Ohm's Law which is :-
V = I x R
Again current, I = Q/t
If you know capacity that means you know ''V''
If you know how long it would work it means you know ''t''
So, now our equation would be :-
V = (QxR)/t
Substitute the value of Voltage, V , , and time t, Resistance R..then you can find out the value of charge Q.
Hope this helps.
Thanks.
As stated previously the battery SUPPLIES the power .
The LOAD draws the current
You have to work out the LOAD: that is the devices that are attached to the battery.
Say you have 2 lamps ( at 60 watts each) and a fan at 120 watts
That is 240 watts in total.
Now you need to know the current ( amps) for the voltage of the battery
Volts times Amps = Watts
so A = watts divided by Amps
IF the battery supplies 12 volts then the AMPS drawn is 240 /12 = 20 amps
You need now to divide that into the Amp/ Hours of the battery to tell you how long it will last
If the battery has a rating of 40 amp/hours then the load will last
40 / 20 = 2 hours
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