Schmidt hub + dual Cree XR-E LED light

Last weekend I finished putting together the dual Schmdit+Cree LED light. Lorah and I went on a 4 hour night ride and the light output rivals her $400 battery powered HID light. To say I’m never going back to the dual E6 lights would be quite an understatement.

I couldn’t have wished for a better result.

It’s constructed as two completely independent units to simplify the physical design and give me some redundancy.

I started with an aluminum tube and a piece of thick angle iron to use as a backing/heat sink for a Q5 bin Cree LED. The LED has thermal epoxy holding it onto the heat sink backing. I put threads in the backing and it screws to the inside of the tube with heat sink grease. The Lens is a Ledil smooth spot that fits perfectly inside the tube.

The electronics start with a Schottky full wave bridge rectifier, an on/off switch, high/low switch and nFlex constant current controller.

I used a high powered TIP3055 shunt transistor with 27V zener diode to keep the input voltage to the nFlex below its rated 30V. The tube itself works as a nice heat sink for the transistor. In testing I found the shunt kicks in at about 25.5V and at that point the LEDs have been at full power for a quite a while. I’ve run up to 8W though just the transistor on the bench with heat sink and it only gets slightly warm to the touch.

I didn’t use a capacitor to smooth out the rectification since even with a huge 1200uF capacitor I couldn’t see any difference in flicker with or without out. I figure one fewer part to fail on me.

All the internal connections are somewhat sealed and protected with heat shrink tubing so it’s unlikely that a solder join will come free due to it bouncing around. The parts are also packed so tightly inside that I don’t think anything even has room to move in there.

Here’s the schematic

My test rig involved having my wife’s bike and my own upside down with her rear wheel up against my front wheel. I was able to hit 40mph in the living room before my arm got tired.

Total cost for each complete unit was about $75 for parts and materials. Of course, I spent way more than that getting various other parts to test with, and smoked a few items before I got it all right.

At 300mA output each light consumes 1.25W. At 1000mA output each consumes 4.5W. I only see the full 1000mA above about 25-30mph, so I leave them on high and they come up extra bright for descents.

The device should be rainproof. The switch caps are waterproof and the switches are sealed. I used silicone to seal the lens and strain relief, and JB Weld to attach the back cap. I haven’t tried dunking it yet. Maybe after PBP. :)

Update: After 3 days of rain on PBP I can say without a doubt that they’re completely waterproof, which is more than I can say for just about every other part of the bike

The beam pattern is about 15 degrees of solid white light with no hot spots that reaches about 100 feet in front of me. There’s a sharp falloff to the left and right of the beam pattern but there’s still plenty of spillover available to read signs and see around corners. I’d say about 80% of the light hits the pavement so it’s a very efficient pattern.

As with the E6 lights, having it on the fork allows me to see bumps and shadows easily.

I have a Cree helmet light that I used with the E6 lights to see outside its very limited trapezoidal pattern and on descents but with the Cree LEDs I didn’t feel the need to use it all.

Since it’s generator powered I can’t easily do an outdoor shot but here’s a beam shot as well as I could do indoors.

It flickers a bit between 2-4.5 mph and kicks in fully at that point. At 15mph its much brighter than my Light and Motion HID light.

The light is good enough that after PBP I’m going to leave it on and use it instead of my HID.

I was a little worried about it overheating but with the airflow from riding and the cool night air it’s cool to the touch even after long fast descents.

Additional assembly pics I took along the way are at

I’m still going to bring one of the old E6 lights with me in case something terrible happens, but I’m pretty confident that it will work out well.

Bonne route!



19 Responses to “Schmidt hub + dual Cree XR-E LED light”

  1. Andrew Says:

    That’s pretty awesome. I especially love the schematic.

  2. Michael Magin Says:

    Oh, so it’s a shunt regulator to limit input voltage to the LED regulator. (Which is about the same as motorcycle regulator-rectifiers — which are also permanent-magnet alternators).

  3. Brenden Says:

    I love it. I would like to build these lights myself! I can’t quite figure it out from the photos - are the two lights hooked up in series to the hub? I assume that they are but I can’t quite follow where the power cables are wired. Thanks for the great write-up and photos!

  4. jgross Says:

    They lights are in parallel and completely independent from each other in order to maintain redundancy.

  5. Brenden Says:

    Okay, I think I get it. I missed the fact that the phono cables have both + and - wires inside. I’m a little slow when it comes to electronics. Thanks!

  6. Alan Says:

    Congratulations Joe. Great project.
    Am I right in assuming the ciruits are parallelled up on the ac side of the bridge and everything after (bridge, volt regulator, nflex current regulator,LED ) is duplicated?

  7. jgross Says:

    Yes. In fact it’s all parallelized (even the RCA plugs) all the way back to the spade connections on the hub itself. I bought an E6 with me so that if one of them failed for a reason not related to a design flaw I could simply plug the E6 into one of the RCA plugs and keep rolling with two lights.

  8. Ed Says:

    This is great! Thanks for putting it together.


  9. MitchK Says:

    This is phenomenal, Joe. I’m going to build a simplified battery-powered version of this twin setup. I almost regret selling my SON hub.

    Can you clarify the material and sealing method for covering the optics? Did you use plexiglass?

  10. jgross Says:

    The lens has an almost perfect fit inside the tube. I applied some silicone sealant to the sides of the lens before inserting into the tube and then ran a thin seal carefully along the outside edge just to be safe.

    I also put some silicone under the switch caps as well as around the strain relief on the bottom. It’s *probably* airtight, but I didn’t test that.

    I used “GE Silicone II window and door” which I picked up at the local Home Depot.

  11. MitchK Says:

    Thanks, that makes it even simpler. I have some thermally-resistant auto/marine silicone sealant I bought at Ace. I’ve been using it on my recent lighting projects, and it should do the trick.

    Do you recall the inside width(s) of the tubing you used?

    I forgot to say above: Thanks for taking the time to publish the writeup and photos! I share your sense of simplicity and redundancy (and fork-level mounting), so I think this design will work very well for me.

  12. jgross Says:

    (measured without calipers). Outside diameter is exactly 1″. Inside is about 27/32″

    Please take a photo and post a link to your completed light. I’d like to see how it turns out.

  13. MitchK Says:

    Thanks a lot, I appreciate it. I’ll definitely send a photo link when it’s done. Project completion (hasn’t even started yet) is 4+ weeks out, but I won’t forget.

  14. Brenden Says:

    I wanted to let you know that I used your design to make two lights of my own. I’m still finishing up the second light but I put the first one on last night and I just can’t believe how bright it is. With the strobe setting it’s also extremely useful as a commuting light. I just want to thank you for publishing this detailed account of your light construction. These lights are so much brighter than the Busch and Mueller Lumotec Fly that I bought. I’m really impressed. I haven’t messed around with the Current Drive setting yet, it’s still at 350ma. Maybe they will be even brighter if I turn up the juice? We’ll see. Thanks!

  15. jgross Says:

    That’s awesome! I’ve love to see photos.

    I recommend leaving both lights at 1A. The hub is trying to produce constant current and the LEDs are more efficient at low current.

    Since any ‘extra’ current is going to go through your shunt and get wasted I think you’re best off leaving both lights on the highest setting all the time.

  16. MitchK Says:

    A few follow-up questions…

    Where did you get the momentary switches, rubber caps, and strain relief plug?

    With the nFlex/momentary switch setup, do you need to turn the light back on once the wheel stops? (Yes, you’ve got me pondering the possibility of re-entering the dynahub world.)

    Have you used them in strobe mode at all? I’m curious if you can get a very high frequency strobe (>=120 flashes/minute) with the nFlex.


  17. Ride Report: 11.15.07 « Pedalling Along Says:

    [...] There also appear to be home built LED lights that put out alot more and cost a bit less, but I don’t think I have it in me to successfully build one.  Here is one that I found that folks seem pretty excited about: [...]

  18. brotherdan Says:

    Thanks for the post. Your results are impressive and inspiring. I just purchased a dynohub and I’m not too happy with my current lighting setup. I think I’m going to try to emulate what you have done here, but I want to run a set of LED taillights off the hub as well.

  19. Walter Page Says:

    I have the will to build but zero knowledge of electronics. Would it be possible to give a url to the exact parts to buy to build “a Schottky full wave bridge rectifier”? Maybe you could also do the same for the “high powered TIP3055 shunt transistor with 27V zener diode”. I guess I should put one of those in also. I already have the LED’s and a controller. I bought all this stuff last winter in anticipation of PBP, but unlike you, the project never came to fruition. I also bought a TuneCharger. My late Spring experiment, last year, driving an LED light with a Schmitt hub through the TuneCharger emphatically showed that the TuneCharger does not put out the kind of current that Fatman boards like!!!

    I particularly liked your “test stand”. I have an old frame mounted on a trainer which is powered by a 1/4 hp electric motor driving through a number of v-belts and chains to the left side of the bottom bracket. On the right side the normal drive train operates. There is a fork mounted on a hinge which is attached to the seat post and carries the wheel with the generator hub. When it all gets going it is quite scary! I can definitely see that your system, at 30 mph, could be life threatening.

    Thanks, Walter

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