[DML] Re: How to figure battery life

["Elvis" <elvisnocita@xxxxxx>]

Well first you need to know - what capacity has your battery ?
(that's the number before the "Ah" - called Ampere-hours)

then you need to know how much current you are sucking out of the 
battery. Just from the number of LED's alone you still don't
know how much they draw - You can drive a LED with 1, 10 or 
even 1000mA. Then it's the question - are they in series
or in parallel ? -> easiest way is to measure the current
you draw from the battery.



Then there's another not so simple question: how much charge
does the battery need to still be able to crank the car ?
10% 20% ? 30% ? (we leave the temperature problem out here
as it would make it even much more complicated).

Example:
you have a 50Ah battery fully charged (we assume it has no
tolerances...which is impossible...)

You draw continuously 1A

We assume you need 20% charge to still be able to start the car
50Ah * 20% = 10Ah -> you have 40Ah left for the LEDs.

40Ah / 1A = 40h - > 40 hours.

Headlights on: 2*55W / 12V = ~10A
40Ah / 10A = 4 hours and you have to push the car (or even 
less as I was only calculating the H4 low beams without the rest)

just the doors open with bulbs -> 5W/ bulb = 30W/12V = ~3A
40Ah / 3A = ~13h 

Doors with LED's that draw 20mA each -> 6*20mA = 120mA
40Ah / 120mA = ~300h

Hope this helps to calculate your own figures.

Elvis & 6548



> I'm trying to figure out how long a fully charged battery will 
last. 
> What is the mathmatical formula for doing it? All my lights (except 
> headlights) are LEDs. The tail & front market lights have 45 
diodes, 
> the side markers have 3 diodes, license plates have 6 diodes, door 
> markers (assuming I keep the doors open) have 6 diodes.
> 
> So with doors open and parking lights on (headlights off) how long 
will 
> my batter last from a full charge?
>




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