Help> driving 3xCreeQ5 with 11.1V lion & Bflex

[heatstroke]

Please check my Maths :
I am stuck with a 11.1V 4400mAhr Lion battery.

I would like to drive 3xcreeQ5 in series with the Bflex at 750mA.

Each LED - vf = 3.42 (x3)
The fully charged Lion is 4.2v (x3)
Discharged Lion is about 2.65.

Am I correct in assuming I can use the Bflex till baattery voltage drops to 3.42 V before it goes into direct drive ? This should still give me about 80% of the battery capacity ?

At less than 1C discharge, how much voltage droop should I expect on the Lion batteries. (18650)

I am building a light for a friend and he does not have access to a 14.4 V lion charger, other wise I would rewire his 3s2p to a 4s1p pack.

Cheers
Rich

 

[Gunner12]

A Cree Q5 is probably 3.6-3.7 at 750 mA drive current(I've read reports of 4v at that current)

The driver, voltage sag, and other stuff, I don't know about.

 

[LEDite]

Heatstroke;

I've built several Triple-Cree lights and the operating voltage is dependent on the final temperature of the LED's.

You should be close with 11.1 VDC and I would just use a resistor to set the current about 15% under where you want to end up.

This will allow for the slight LED voltage reduction after burn-in.

Most regulator circuits will drop ~ 1 volt which may be too much for your LED requirement.

Larry