Testing a Cree XHP50.2 J4 3A led

The above makes no sense. Do you understand what fins on a heatsink are for?

It’s simply to increase the surface area which allows the air around it to pick up heat. If you fully enclose the heatsink in a box then the fins become useless. You’d be better off not even using the heatsink.

If this were a high powered flashlight that was used in short bursts I’d replace that heatsink with a big chunk of copper. This will allow for a longer turbo time.

Since this is a light that is going to run constantly, increasing turbo time is not important. I’d just let the heat flow through the gold part and heat up the outer housing. Then the outer housing will be exposed to moving air and pull the heat out. With enough surface area in the outer housing and enough moving air the lights temperature should reach an equilibrium within a safe range.

The above is not ideal, but do not say it makes no sense. If the heatsink is going to be enclosed it is still better for it to be finned. You might not be able to understand what is meant by his term heatsink but the rest of us can clearly see the large aluminum heatsink with extruded fins. :wink: And stormrider is correct that filling the air gap with potting epoxy is still not ideal but better than air.

Stormrider: I pot flashlights with a mix of silicone(rtv) and silicon carbide lapping powder. It works well for flashlights but might not be economical for your application? Outherwise you can buy potting epoxy by the gallon for descent price.

Are you able to pot and seal the front of the enclosure and cut some vents or openings around the heatsink fins to let in some air? I think this would give the best performance but maybe a trade off with aesthetics?

@lightrider: BTW, several years ago I tried filling a Pepsi aluminum can with #320 silicon carbide abrasives to cool 3 hard driven XPGs in the center (absurd art objects). Man…it’s heavy :laughing:
But the heat was indeed spread to the can’s surface fairly well. Got better result with damp SiC sands (better than water alone).

Haha! Ya, I guess it would be like a cement brick. A cool brick at least. :slight_smile:

I’m losing my patience and I don’t have time to give you a lesson in thermodynamics.

Basically, empty air or solid chunk of aluminum makes no difference in your application. Do the cheaper, leave it air. You will have the same performance.

I think you are confusing flashlight design with car mounted light design. They are not the same.

Sorry, no more help from me. Let someone else teach you. Your too resistant to learning.

Good luck on the project.

That’s not too bad. Haha:)
With the small power you are going to be using, you wouldn’t need to expose the entire heatsink. But any airflow will help significantly. I understand that this is what JasonWW is trying to say. But with this amount of power, i think you will be fine with potting if that is what you want to do.

I’m not the one to ask something like that as 1) I do not like the XP-G3 emitter and 2) I don’t recall ever putting any light together that pulled such low amperage.

As far as your drawing goes, if you can’t put a heat sink in the opening that fills the opening then you’re falling short of optimization. Cut off the open air portion and leave the heat sink exposed, don’t pot anything. Just because something is cheaper does not make it better, most of the time it’s quite the opposite. If it’s not worth making right, it’s not worth making at all.

Your goals is to give the maximum heat path to the outside of the light. If you have an empty cavity then your goal is to fill in that cavity with metal or worse case potting material / silicone to give the largest heat path to all outside surfaces you can. Adding heatsinks to the inside of an enclosed space will not help you much.

For your goals, if the driver will be external, then sure, go ahead and fill in the back of the light with silicone to optimize the heat path cheaply and easily. Then close it back up for waterproofing.

That light looks like it should handle at least 15-20W without an issue based on the results with similar sized flashlights.

If you’re using a constant current driver then the voltage of your XHP35 won’t be far from 12,7-12,9V at 1,2A. The LED voltage is current dependent. It’s unlikely to get an XHP35 running at 1,2A with 14V vf, unless it’s broken. At higher current the voltage will automatically increase. LED die temperature also affects the voltage: higher temp lower voltage and vice versa.
14V is your input voltage. Using buck driver even under no load the V out will be slightly lower than the V in. All the components inside the driver eat some voltage to work.

Correct me if I’m wrong here =)

- Clemence

I thought about the same things back when I had to mod my bike headlight. Tried to find any driver to drive XPG R5 at it’s max datasheet current (1,5A). As I learnt, it’s harder to design proper passive heatsink if I were to drive all the LEDs to their max rated current. More current = less efficient LED = more heat = more heatsink cooling needed. I ended up using boost driver and cram as many LED as I could and drive them less than 500mA each. Try not to use cooling fan, it has to be a very good long life IP66 minimum to be reliable. If you are using aluminum handlebar such as Renthal you can use it as a heatsink too.

Wait are we talking motorcycle or bicycle here? For bicycle or e-bike, efficiency should be one of your priority too.

triple 3p XPG3 quad 4p XPG3, XHP35, XHP50, or even XHP70 are the better choice if you can get boost driver. Less current - higher voltage - less heat - less power needed. A single boost driver from luxdrive is a good and very reliable driver. You can easily drive up to 40Vout using 12Vin at cooler running 350mA/LED. That will broaden your choice.
Or you can invest more, using hyperboost from Taskled, up to 80Vout with adjustable current up to 3,2A!! This is rather expensive at USD 40 but will unleash your creativity. It’s also automotive rated (withstand “dirty” automotive voltage spikes).
Taskled Hyperboost

EDIT: Don’t use luxdrive unless you sure the DC power source clean from spike and pulsing. I remember I destroyed 2 luxdrive because my older scooter still used half sine DC output. You can check your front light, if it pulsing on very low RPM then it’s half sine DC. With full rectified DC, Luxdrive is OK. Older bike lead acid battery also fluctuates heavily when you starts the engine, or when hard downshifting (hard engine braking). That’s why linear driver isn’t a good choice for bikes

  • Clemence

Closer, bigger, macro pics please…

I did all the reflow with my “deluxe” DIY hotplate or heatgun.

FYI, I have two unused front light LED driver from my old scooter. Both are still working properly. If you want, I can send it to you for free (shipping cost only). Each module has three separate outputs, 3 output per module, I guess. I’ll check it later. You can use the driver and throw the rest. It has fan output too.
Tried to dig into my old post in CPF but looks like it’s deleted by the moderator. I remember modding bike’s headlight is forbidden there.


BTW: Sorry Djozz, looks like we’re hijacking/derailing your thread :stuck_out_tongue:

- Clemence

Derailing threads is a well-respected pastime on BLF.
Carry on. :+1:

Your never going to get a good beam pattern with that big emitter. That looks like an H4 bulb size. If your okay with a cool white color, you can use these bulbs.

They use the Philips Luxeon ZES chips and are much brighter than stock and give a perfect factory beam pattern.

My article on Bikers Oracle isn’t available right now as they are swapping servers. So here’s a few pics. If you want more info, just let me know.

Low beam comparison on my 86 Honda vfr700.

I hope that helps.

Well I guess there won’t be any pictures. Appearantly Photobucket is requiring a $400 a year fee to host pictures effective 6-28-17.

Tested. One channel smoked, sorry…. :stuck_out_tongue:

- Constant current 3 channel buck driver rated for 12-15V I guess…Bought from Ebay somewhere in 2013

- Designed as 2x5watt low beam and 15watt high beam (in high beam all three COBs turned on) per module

- 3 x 6V unknown super low CRI 6500+ K COB LED. Wired for 2 Lo and 1 Hi beam.

  • Each channel outputs 0,87A-0,88A. You can combine all three in parallel to get 2,64A total.

Tried with 3 x XPG 4500K bought from Sedstar (super nice and dirt cheap). Link: Sedstar 4500K XPG
These are good cheap LED with known spec, perfect for testing any project. You can use your fancy LED later

Worked fine with 3 XPG: roughly 9V, 7,9watt/channel. Could be wired for a total 3 x 7,9watt = 23-24watt total.

With 2 x 144AM (6V); roughly 10,56watt per channel the IC smoked less than 10 minutes. So you better limit the output to ~8 watt/channel. With new XPG2/3 or 219C you will get lower output power since the vf of these newer LED are lower but possibly still brighter than the good old XPG. If you can find the same IC it should easy to fix, I think it’s common IC found online.


If you want to use this driver you better cool the inductor, they got very warm (not too hot) with 3 x XPG. Hence the fan.
The fan got very noisy after ~1 year street use. The salty balinese dust sucked rubbed the exposed plain bearing.

@JasonWW: We never wanted to use those badly designed LED engine. I offered Stormrider the driver, not suggesting him to use it as is. It’s an awful kind of LED lamp indeed. I bought it during the dark ages when anything brighter than halogen bulb attracted me. And no, I really hate cool white headlight, no matter what CRI they are.
As for the image hosting, try Flickr. Rather complicated but allows you to store very high quality images complete with copyrights protection and rich features.

Flickr seems popular. I’ll just go around the forum looking for pictures that still show up and see what host they use. :wink:

For me, anything less than cool white looks dingy. Like old style incandescent bulbs. I can’t stand it.

Cool white for me is anything over 5000K. I prefer to work under 5700K high CRI. Driving is another thing, on whitish cement road or behind white painted car, anything above 5000K irritate my eyes. Try tailing a white ambulance with CW HID on a empty twisty country side road (no street lights).
But yes, lower than 4000K everything looks not so good (for driving).

- Clemence

Yeah, like I mentioned in post 229, I have an old 86 Honda vfr700. It’s got LED headlights (and just last week, LED tail lights).

Reminds me of the old pocket rocket: Honda RVF400
Revving up to 15000RPM each upshifting, with 4-1 pipe sounds like a crazy mosquitoe from afar. The whiney timing gear sound also very distinctive. Those were the days…