Cree MCE, 3.7 Li Ion boost/buck?

[jeff r]

Hello, I am trying to put together a light using either a 3.7 Li Ion or 7.4 Li Ion battery with controller (over/under-discharge) and a Cree MCE.
I already have a 3 and 4 cell 18650 of 3.7 volts in parallel and I would like to stay with this setup.
However, I can use a 7.4 4000mA 2 cell series pack as a last resort.

I want the light to go long and narrow for long distance lighting (night riding-road). I basically need a high and low setting.

I have a Cygolite Mitycross 350 mounted on my handlebars and want a long-throw light for my helmet.

I have looked at many of the boost/buck controllers on many different websites: taskled.com, ledsupply.com, etc. But the more I read and see different options and capabilities, the more complex this seems.
4 die Cree MCE - each die 3.4v@700mA max.
I had thought of wiring the MCE as 2P2S - 6.8v@700mA (or would that be 6.8v@1400mA) using a boost controller with the 3.7v batt.
Or, 4S 13.6v@700 using a boost and 7.4v batt.

Anyone have some advice to offer?
Thank you, Jeff

 

[marcopolo]

Because of (usually small) imbalances I prefer to err on the series side rather than go parallel. So it would suggest 4S with a 7.4v battery.

It's usually preferable to go higher voltage less current.

My penny's worth.

You want good throw with your MC-E, easy!!! Trout tested a Ledil Iris and it was superb for throw. (supplied at cutter). It is however 38mm diameter but worth every mm!! A couple of the boom reflectors are good too but nothing trumps the IRIS on the MC-E.

Reda the whole of this thread (beamshots):

http://forums.mtbr.com/showthread.php?t=464544

Marco.