Hi Again
I want to make a red rear light for my bike using a cree led and would like to ask about driving red cree leds. Do I need a different driver to drive them as they are lower voltage than white led’s or can I use a standard driver?
If they require a special driver can you point me to one please as I have had a look around and not seen anything for red led’s.
TIA
Markendo
With which voltage/battery are you planning and which led?
I use NANJG101 (1.4A) with them (on Li-ion 3.7V) without problems. I haven't used them on high for a prolonged time though.
I drive pt54 LEDs with a standard qlite driver @ 3a from 4.2v 18650 and no problems so far
As for cree LEDs I don’t know but the pt54 are an extremely strong platform
And much brighter then any red cree that I know of
Here’s one, dang, missed them at a Radio Shack sale; they’re on eBay today for $20ish:
“… Radio Shack has the Vellerman Kit , nr K8071RS is on clearance for about $5. This is a current limited LED Driver kit, instead of using a resistor to limit the current delivered to your LEDs. It can drive 4 x 1watt LEDs or 2 x 3 watt LEDs. Powerful stuff. I’m using this to finish my 3rd Brake Light….”
for a rear bike light, I’d go with one of DrJone’s mobydrv drivers. Bike lights, especially rear ones, were one of the main things it was designed for.
a well heatsinked 7135 based driver shouldn’t have any problem dropping the voltage from a li-ion battery to a red LED. If you’re worried about it, you can always wire an appropriately sized diode in series with the LED to drop some of that voltage outside of the driver.
The 7135 drivers work fine for red emitters especially the xpe and xpe2. I have ran them up to 2A, they did not put out a significant increase in throw.maximum is about 1.4A-1.5A on a copper sinkpad, before light output starts to level out. For a bike taillight only around 1a would be needed. still plenty bright. If on ally stars, a good star maybe 1.2a and a crappy star 1A max.
++1 dr jones drivers
@matthemuppet
Thanks for that. I did some more searching and found an older thread explaining about using a diode to lower the voltage before it get to the driver.
You are thinking along the same lines of me, driving the led at about 1amp should give enough light and good runtime.
I’ll look up dr jones drivers.
Is dr jones a forum member on here?
Oh, yes I would like to use Li ion.
Many Thanks
Markendo
tip: I just used a lineair nanjg (105C) driver to drive a infrared led (same problem but worse, Vf=1.5-2V) and they run fine on LiFePo batteries. LiFePo's have a lower voltage, so less heat has to be burned off by the driver (as a bonus: it is a safer chemistry)
Hi djozz
Using LiFePo would be better, but I have access to a supply of 18650’s for free. I work in a media department for a uni (lots of batteries for the cameras and portable lights etc) and we get batteries that fail eg. the balance/protection circuit so they just get binned or should I say they come home with me 
Ta
Markendo
I made a nice on and flashing rear light for my bike. Originally with a white XP-G behind some red reflector plastic at 1.4A, now a triple parallel red XP-E which completely kicks ass. It has a USB charging board built in which is really convenient. Next upgrade is a driver that I can use a momentary switch with as the Judco clicky switches I use seem to flake out over time and are hard to use with gloves on.
A parallel triple, a DrJones driver (1.4-2A), a 18650 and a USB charging board would make a super sweet rear light. Get a few different types of triple optics and see which you like the most for throw vs. side visibility.
Thanks to all, I’ll just order up a few things and play around.
Markendo
Hey. I built a tail light with a 3X 7135, 20mode driver ( has slow blink and fast blink), an osram red LED and an 18650 cell for power. The LED has a little heatsink on it but for some reason, even when on high, it does not get warm… shrug. Sorry, the driver, I’ve had for some years from either DX or KD so don’t know if it’s available now. Something like this is what I use.