Battery Pack modification

Djedgar

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Sep 7, 2007
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I am working on LED set up for my bike and made a 2 Cree Q5 bike light to see if that was adequate. I purchased a 7.4 Volt Li-Ion battery pack to drive it through a bFlex. While the light seems adequate for my purposes driving it at 1A I have decided to add a 3rd Q5 and drive it lower for most riding with the option of blasting away at 1A if needed.

My 7.4 V Li-ion (made up of 4 18650s) is not enough to drive the 3 LEDs plus the driver so guess I need to go 14.8 V. Is it possible to cheaply modify my 4 cells to run 14.8 given there are IC protection included plus I would need another charger anyway. I know I would loose mAh in the process so might even have to buy 4 additional cells, but will see. The specs I see on Battery Space for the packs show different IC protection levels.

Guess I could just buy a new pack and charger but what fun is that?
 

StevelKnievel

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Oct 13, 2007
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114
Maybe you should just swap out the bFlex for a boost driver like the maxflex or fatman, you might save some money over a new charger. I have had good luck driving 3 Q5's off a 7.2v 4000mAH NiMH through a fatman driver.
 

znomit

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Aug 1, 2007
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New Zealand
Actually you don't have enough voltage to drive 2 LEDs now (unless you are running them in parallel?). The bFlex uses one volt so you only have 6.4v for the LEDs (at 1A they probably need 3.7volts each).
You might find that given enough voltage your 2 crees will be plenty bright enough.
 

Djedgar

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Joined
Sep 7, 2007
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Good idea on the fatman. Actually though of going that route initally anyway. Just wasn't sure where to get a 50kohm logarithimic taper potentionmeter in a small compact size.

As far as voltage now I realize the pack is labeled 7.4 but it acutally measures 8.4 fully charged. Of course it goes down from there but at least I start out with full brightness to realize what the light can do.

I am new to all this and am learning. Otherwise I guess I would have ordered the 14.8V to start with. Oh well.

Thanks for all the advice so far.
 
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