macgyver35

Hello all,

Some time back I purchased four Cree XML Bike Lights on Amazon. They are a generic Chinese brand, but VERY bright. The idea is to mod them to attach to the roof rack of my XJ; two in front for long-range lighting, and one in the back with a diffuser for area lighting and auxiliary back-up lighting (can't see crap out the tinted rear window at night) I occasionally need lots of area lighting on job-sites and campsites for extended periods, and normal halogen off-road lights drain the battery too quickly. And, to be honest, the LED offerings from the off-road lighting companies are just insanely expensive. Those that aren't expensive have terrible blueish color to the light they put out. The Cree XM-L emitter puts out a nice bright white light; around 4800K color temperature.

While I have the skills to fabricate mounts, do the basic switch/relay wiring, and some basic soldering, I'm a complete dunce at IC chips/electronic circuits.

I wondered if any of you circuit gurus could tell me if the driver for these lights could be modded to run solely in high mode (it's currently high/low/strobe), and if there is a way I can bypass the switch on the driver and just activate the circuit with a standard spst or spdt switch in the cab of the Jeep. I have hooked the light up to 12V DC at 1 amp and the light seems to run fine on that. Normally, it runs on a battery pack consisting of (4) 18650 cells (3.7 volts each) soldered together.

I tried like crazy to get some decent shots of the driver board, even running to the camera shop to buy a macro adapter for my lens.

Any help would be appreciated. If further info is needed, I'll do my best to find it and report back. Thank you.

http://www.flickr.com/photos/40427356@N05/8532048157/

http://www.flickr.com/photos/40427356@N05/8532047875/

Boker and QPA Pro shown for scale against XML Bike Light

http://www.flickr.com/photos/40427356@N05/8532073797/

5-90

The bluish colour on white LEDs is due to the fact that there is no such thing as a "white" LED - a Light-Emitting Diode is a monochromatic emitter. By definition, it cannot generate white light on its own, there are two ways for it to do so:

- As a UV emitter, it excites phosphours lining the capsule. This is also how a fluorescent lamp works.

- It's not a "single" emitter - it is three balanced emitters, generating RED/GRN/BLU light, which mixes into white.

The "bluish" ones are almost guaranteed to be the first type. The second is somewhat recent, but gives a "purer" white light.

However, if the driver board natively takes 14.8VDC, and runs fine on automotive system voltage (typically 13.0-13.6VDC) or even automotive battery voltage (12.2-12.8VDC,) then why reinvent the wheel? Desolder the battery contacts on it, solder wires to it, you're good!

(typical forward working voltage for an LED is somewhere under 5VDC, running greater voltage through a regulator is part of the function of the driver board. This is much of why LEDs have a longer battery life - as long as the combined output of the cells exceeds the working voltage of the LED, the LED "sees" full voltage from the regulator circuit - and a semiconductor regulator is used because it will always give the same output voltage, as long as the input voltage exceeds that by a nominal factor. Sure, it can be done without electronics - see "voltage divider." Problem is that the output of the voltage divider slides down as the input voltage slides down, which is why they tend to not be used in portable battery-powered applications...)

Seriously, tho - why do work that's already done for you? Just use the driver board, pipe system voltage to it, et viola! - you're there.

macgyver35

Thanks for the response. I actually understand a great deal about LEDs themselves, how they work, and what causes them to emit light. I have a huge collection of high-powered, high-tech flashlights, I'm a member of www.candlepowerforums.com. I have lights that run on Osram Golden Dragon LEDs, as well as Cree QE5, XPE, XP-G R2, XP-G R5, S2, and XM-L T6 and U2 emitters. I have a new one that I just got that has three XM-L T6 emiiters and puts out a whopping 2200 Lumens on high. That's nearly as much output as a pair of H4 60 watt halogen headlights, but in a package the size of a coke can. Granted, there is more to the color temperature of the light emitted from an LED, but for all practical purposes, the end result is that these lights put out what would be classified as "neutral white" light, while many other cheap automotive LED lighting is clearly emitting something in excess of 6000K. At any rate, the color rendering index of lights at or above 5500K begins to degrade at a exponentially rapid pace, and causes objects to appear to the eye to be of much different colors than what they would appear at warmer color temps or natural daylight.

The XM-L T6 emitters in use in these lights have a luminous flux of 280 lumens at 700ma, are rated at 4750K-5000K color temp, and have a CRI index of 75.

Some of my collection:



The stock battery pack for the light puts out a nominal 7.4 volts to the driver of the LED, although, the driver will safely handle up to 14 volts DC. It's not a big issue to just hook up "12v" automotive power to the battery leads. But, just as you correctly stated, the circuitry will regulate the power that actually goes to the LED. I.E., the LED itself will not be receiving a full 12 volts, and attempting to supply 12v directly to those LEDs will fry them. Trust me, I had an extra raw XM-L lying around and tried it, just to see how long it would last. Instant *POOF*!

The other problem comes in the fact that the activating switch for the driver is integrated onto the driver board as shown in the pics. Obviously, I don't want to climb on the roof and manually press the switch on the back of each light every time I want to turn them on. Also, the driver circuitry results in different output modes (high/low/strobe) being selected each time that switch is pressed. The crux of my questions were if anyone knew a way to modify the circuit to eliminate the multiple modes and make the light operate in high mode only, and a way to bypass the need for the switch so that the circuitry would be activated as soon as power is applied to the main battery inputs. As it stands, you plug in the battery pack and nothing happens until you hit the switch on the back of the light, and it goes from high to low to strobe, and then starts the cycle again at each button press.

5-90

Then, since they're switched externally, you can feed them through a relay and use a switch on the IP. The only problem you're going to run into is the "modes" in the driver board - but that can be worked out with switch selection and a use pattern (get an ON-OFF-MOM switch. Push it down twice to cycle through the first two modes, then flip it up for on.)

The problem you'd run into is that most CREE modules (and similar) are surface-mount devices, which are more difficult to solder. And you'd have to design, etch, & build a board. Can be done, but just obnoxious enough to want to avoid for "one-off" parts.

Me? I'd probably have selected straight ON-OFF driver boards, gotten the emitters, and then designed & machined housings out myself. A TIR collimator is easy to find, and lenses are commercially available.

Post Scriptum - While I often throw in detail that the OP may not need, when answering technical questions I do try to explain as much as possible - not just for the OP, but for the benefit of anyone else who may happen to need to know. Please do not assume that I think you don't know what's going on - I don't know what you know, nor do I know what anyone else who happens on this may know...