6D Mag Rechargeables

[Tekno_Cowboy]

I'm looking at putting a Cree Q5 in my mag and driving it at about 1A.

I was looking at 4 F-cell NiMH, 6 D-cell NiMH, 3 DD-cell NiMH, 3 DD-cel Li-ion, AA adapter with NiMH in Series or series/parallel. If there's something I missed, please let me know.

My question is this: Without boring out the battery tube, what combination of reghargeable batteries will give me the longest runtime?

 

[Mr Happy]

To figure this out you need to look at the available watt-hours of a given battery combination, and then look at the efficiency of the chosen LED driver for the expected power level and input voltage.

To give you an example calculation, suppose you use 6 D-cell NiMH of good quality 10 Ah rating. Assuming an average output voltage of 1.2 V, that would be 6 x 1.2 V x 10 Ah = 72 Wh.

Now suppose that the LED driver is very efficient and draws about 4 W at a 7.2 V input voltage. That would give you a run time of approximately 72 Wh / 4 W = 18 hours. (For example. Allowing a margin of error you might say 15 hours.)

You can juggle the numbers with other combinations and figure out what appeals most.

 

[jcvjcvjcvjcv]

Five low-quality handgrenades a.k.a. 32650 Li-ion

Total 18.5 Volt x 5 Ah = 92,5 Whr.

 

[Tekno_Cowboy]

Thanks Mr Happy, that's some great info. Seems I've forgotten most of my electronics classes
One thing I'm not sure of though, is how to determine the watts that will be drawn. I should really pull out my textbooks and study up I guess

 

[mdocod]

how many watts will be drawn depends on how hard you drive the LED, the Vf of the LED, and the efficiency of the driver.

If the Vf@1A is 3.8V, and you drive it at 1A, then it's 3.8W, then figure maybe an extra 15% for driver losses, 4.37W.

 

[Tekno_Cowboy]

So Vf x A = W and add 15% to that. Now I've just got to make a spreadsheet and make it crunch some numbers

:thanks:

 

[marschw]

On a practical note, it's possible you'll be limited by the voltage that the driver you're using can take. That's why I had to go with 4x F NiMH for my 6D mag project. 6D Li-ion at full charge would be 26.2v, not a lot of drivers can handle something like that.