Whats the formula to calculate a rough estimate of run time?

bigchelis

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Whats the formula to calculate a rough estimate of run time?

With nickel hydride batteries?
With Lio-ion batteries?

Thanks,
bigchelis
 

SilverFox

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Hello Bigchelis,

If you take the battery capacity and divide it by the load, you will end up with an estimate of run time.

For example, if your battery capacity is 2000 mAh and your load is 500 mA, you should get a run time of around 4 hours.

Tom
 

bigchelis

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Hello Bigchelis,

If you take the battery capacity and divide it by the load, you will end up with an estimate of run time.

For example, if your battery capacity is 2000 mAh and your load is 500 mA, you should get a run time of around 4 hours.

Tom
I remembered reading this before and searched it without success. What if you use multiple cells. In you're example say it was 3 cells would it be 6000 divided by load of 500mAh in which case run time would be about 12 hours right?

1. only add up the voltage when combining multiple cells.
2. only add up mAh if the cells are in parrallel which for my flashlights is never. So, never add up mAh when doing this calculation.
Possible Ex: If the 2000mAh cell is under load at 500mAh draw with 3 cells the extra power allows for the same lumens at less draw.
In youre example say each cell was 4v. With 3 cells it would be 12v. Now with the extra power the 500mAh draw is not needed due to the extra power in voltage available. So, in theory now the draw could be divided by 3=166mAh draw giving me an estimated run time of 2000mAh/166mAh draw=12 hours.

Is this correct?



Thanks,
bigchelis
 
Last edited:

brandx

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Aug 11, 2006
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You are on the right track but maybe missing something.
1) multiple batteries in series = add voltages but same mAh.
eg 3 batteries of 4 v and 650mAh in series (end to end) would give you 12V potential and the same current capability of a single cell = 650 mAh.
2) multiple batteries in parallel = same voltage as a single cell but add the currrent apability. Using the 3 batteries of the above example we get 4 volts but 1950 mAh.
3) you must be careful of what your bulb-LED-driver is capable of handling insofar as voltage is concerned. Some LED drivers cannot handle the 12 volts of the above example, and most incandescents will react adversely to a voltage more than they were designed for = POOF.
 

jerry i h

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Jul 26, 2007
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Berkeley, CA
This is the formula I use:
1) if multiple batts in series, capacity = no change
2) if batts in parallel, capacity = each individual batt added together (note: this set up is very rare and unlikely).

hours of use in hours = 0.80 (accounting for batt conversion efficiency) * (batt capacity in AH's) * (# of batts in parallel; ususally = 1, so ignore) ÷ (torch drain in amps)
 

Lynx_Arc

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you could always do a search on CF to see if anyone has done a runtime graph of the light in mind already
 
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