Direct Drive Cree Q5 with 18650?

[kasey197]

Folks, been a while but its nice to be back. I've ordered some Cree Q5s from DX (http://www.dealextreme.com/details.dx/sku.2394) to be swapped into some current lights. From the looks of it, would have thought that a direct drive from protected 18650 would be fine (at the expense of some LED life..) but theres some chatter that the Q5s from DX have a very high Vf of around 4.1 V for 1A ? If so, DD would prob only give me 10 mins at best at 1A.....

Any thoughts/experiences with DD-ing this sucker would be much appreciated.

 

[65535]

Chances are you would get a Cree with a nominal Vf of about 3.7 and at 4.2 volts be driving the led at ungodly currents, maybe good for a bright flash for a few seconds, but I seriously doubt you will get any life, or usage out of it, just get a cheap DX regulator.

 

[znomit]

+1
I got 5 Q5s from Dx and they were nowhere near 4v at 1A, more like 3.7.

Edit: actually 10.7v over 3 leds, 3.6v each at 1A (3.4 at 500mA)

 

[kasey197]

cool thanks folks! Will give it a bash with a spare fatman I have lying around to get a handle of the Vf & let you know

 

[TickTack]

As an alternative, what cheap DX regulators do you suggest for running at Q5 on a single 123a?

Two 123as?

A single 18650?

 

[lctorana]

I DD a Q5 with a 17670 in an old Golston, via a 1 ohm resistor.

It's a nice result.

 

[MatajumotorS]

I have tried, dirrect driving q2 cree led from almoust fresh 18650 it was more than 2Amps

 

[lctorana]

Hence the resistor.

 

[glockboy]

The Crees can handle over 2 Amps, just get a good heatsink for it.

 

[brontosaure]

cree Q5 direct drive not possible with 18650 li-ion
you must use 2 resistors in parralel with 1.2 ohm/2WATT valueS
to get 0.85 A. efficiency is not so bad..

 

[Krit]

I think li ion battery is very low internal resistance. Resistor at least 0.5 ohm should be used for safety. Volt from li ion might over to 4.2 or higher after finish charged.

 

[Nils]

Testing my "purple" Q5 star from DX I have problems even reaching the 1A with an 18650.

This is however with the current going through some clamps and my multimeter.

Checking the voltage simultanouesly with another multimeter I seems my specim needs about 3.9V to get 1A...

I can take a fresh protected 18650 from the charger and get about 1.1 A for a few seconds then dropping fast to under 0.9A

Be aware though you will measure about 4.2V on a fresh UNLOADED cell this voltage drops to about 3.9V under load.

I haven't dared connecting the wires from the led DIRECTLY to the cell without any measuring device interconnected. Maybe this will give a little higher values...

To me that's actually a bad thing since I wanted to drive the Q5 with a single 18650... but as I only get about half an amp at 3.6 V = 1.8Watt this is highly unsatisfactory...

Going to try another Q5 from kaidomain and a boost driver...

...the SSC P4 U-bin I have lying around seems to have quite a lower vF... maybe I should give it a try in single cell configuration...

 

[kasey197]

Did the DD with a Q5 star in a KD light body and the bleeding thing is BRIGHT and doesn't emit magic smoke. With fresh protected 18650 batts I measured 3.98 volts across the LED and just over 1 amp between batt negative and torch body. The internal resistance of the torch body/switch/wiring/battery seems sufficient.

Given the lack of regulator its not surprising that the light dims a tad after 10 mins or so but I'll live with that for this cheap and cheerful mod...

Thanks to all for the help n feedback ....