Please help advise on modding mr-11 bike light

[pbwatson]

I have a couple Performance Viewpoint halogen lights that are a few years old. That I would like to modify to use LED's, I have never done any of this before & would like some opinions of what any of you would do with these lights to get the most light output & good battery runtimes, I would like to get at least 4-5 hours of battery life. Runtimes were never all that great in the first place but now as they age are pretty dismal.

Currently the lights are.
-dual beam handlebar mount; 6 volt. 12 & 20 watt mr-11 halogen bulbs
Runs off 7.2v, unknown amphours waterbottle nimh battery
-single beam helmet mount; 6 volt. 12 watt mr-11 halogen bulbs
Runs off 7.2v, unknown amphours flatpack battery (fits in jersey pocket or camelback)

The dual beam battery lasts about 45 minutes if I only use the 12w beam & maybe 30 minutes with occasionally turning on the 20w also. The helmet mount runs maybe 20-30 minutes. At their best I would get 90-120 minutes out of them depending on how much I use the 20w & less than an hour with all bulbs blazing.

I would like to significantly increase my runtime & still get similar light output. If the mods work I'll buy new batteries in the fall when the days get shorter. I was going to test the modding waters by just doing one lamp first, this way I compare runtimes, brightness, and just see if its worth it to mess around with.

I found a drop in mr-11 at superbrightleds but the light output looked pretty pathetic. They have 12 LED in narrow or wide beam for about $9 ea but light output is only 12 lumens, there is a "high power" 1 watt led for $12 but light output is still only 24 lumens. Also both of these are 12 volt & I dont know how they'll run off my batteries.

After several hours of googling I think I'll have to build my own bulbs to fit in the mr11 space. The good news is the wiring connection on the lamps is not fixed, it is a flexible wire lead that clips onto the bulb connections so I have some flexibility on how I use the space, the diameter is however pretty important to retain a good seal for weather resistance.

Here is my initial idea & build questions after hours of scouring. I found the Parts found at dealextreme
-Cree XR-E Q5 LED emitter on a star shaped board
-800mA Regulated IC Circuit Board
-33mm smooth plastic optical reflector
-33mm glass lens
That all looks like pretty straightforward connections unless I am looking at it wrong. I do however have a few questions

-What about a heatsink, I saw paste. Do I just smear paste on the back of the emitter board to dissipate heat or do I use the paste to affix some piece of aluminum finn type material? My housings are aluminum by the way.
-What about the angle of the beam, how do I adjust this? I would prefer to have a tight long throw beam as this is most useful for constant use. & then later add a second LED that is a flood for intermittent use.
-The Cree Q5 is the brightest I could find, am I right or is there another brighter LED (Q5= 107-114 Lumen at 350mA, 171-182 Lumen at 700mA, 214-228 Lumen at 1000mA) & how will this compare to my current 6v 12watt & 20 watt halogens?

What would you do in modding this bike light?

Thanks in advance for your time
Paul

 

[aljsk8]

hi

the led star needs fixing (thermal epoxy / paste) to some more material
be that be a big chunk of aluminum or copper or to the housing of the light if possible. This is because the star run at 1amp will get hot - hot enough that on its own it will damage the led.

about brightness

12w halogen will be about 200 lumens mabee 250 - but quality of those mr11s varies
20 w halogen will be 300 - 350 lumens (again quality varies)

if you run your Q5 cree at 800ma you will get over 180 lumens

but to compete with the 12w and the 20w halogen you would need 3 leds

heres the main thing tho - running your halogens together you get max 500 - 600 lumens for 32w

running 3 Q5 crees at 800ma you get about 500+ lumens for 10 - 12w

so - similar brightness but will run 3 times longer!

beam patterns are changed by changing the optics / reflector
and this is also important to get right

 

[Szemhazai]

The easiest way to achieve your goals will be wait for MR-11 replacements based on XR-E leds – they are not currently available but if there are MR-16 & Gua10 lamps it is only a matter of time.

 

[pbwatson]

Thanks for the info. I checked with a company that sells single cree mr-11's & multi-cree MR-16's to see if they plan to offer multi cree mr11's. I was told that they will not do it due to cooling problems in such a confined space.

Have any of you tried to cram 3 cree's in such a small space? Would it be possible & how much would the bulb life be shortened?

Maybe I need to just use the single LED to replace the 12w bulb & leave the 20w in place for when I really need to wash the trail in light. At least that would give me a nice long runtime (If I keep my finger off the 20 watt trigger)

Paul

 

[cave dave]

...
12w halogen will be about 200 lumens mabee 250 - but quality of those mr11s varies
20 w halogen will be 300 - 350 lumens (again quality varies)

if you run your Q5 cree at 800ma you will get over 180 lumens...

Halogens may start off that bright but being direct drive they get dim very quickly, and then the efficiency gets even worse. Plenty of good circuits around here to get fully regulated LED light.

Mixing Halogens and LED's kind of sucks, the blue white light clashes with the Yellow light. Its best to stick with one or the other.

Also those MR11s have very wide spill angles. Somewhere over 90 deg. So a lot of light is going into the spill. Not bad for MTB, but not necessary for road riding. I find that a single Cree like in a Fenix L2D, often puts a 10W halogen to shame after about a 1/2 hour of use in the real world.

 

[Christexan]

What you are wanting to do is pretty easy, I think some of your questions have been answered but haven't taken the time to read through it all (don't have the time)...
The "heatsink paste" is just that, a paste to affix the hot unit (whatever it is) to it's related heatsink. These are either a thermal "compound" (simply a semi-liquid that fills in the microscopic (or macroscopic) gaps between the unit and heatsink) or a thermal adhesive, which does the same as above but also provides a mechanical bond (glue) to prevent the part from shifting after it is set.
EITHER of these options should be used as thinly as possible, adn the surfaces being mated should be as smooth and flat as possible, a metal-to-metal contact is tremendously more efficient than any paste in heat transfer terms. In microprocessor circles, the pastes are applied to each surface after polishing (lapping) them mirror smooth, then scraped off with a razor blade or credit card or other smooth straight-edge, and only then are they joined together. Obviously for a simple cheap DIY light, this is a bit extreme, but you get the idea, the smoother the initial fit, the better the paste will work to fill in the gaps without causing too much of a heat barrier.
The heatsink should be as large as reasonable, I have also modded some Performance lights (the Viewpoint Gen3 emitter lights, a pain to disassemble thanks to being tack-glued together, but judicious use of heatgun and prying tools gets them apart eventually (they are threaded as well, to add insult to injury, but they don't use the threads on the LED versions (they do after I mod them though)), using Fraen optics and Cree XR-E LEDs. The existing emitter was thermal-adhesive tacked onto an aluminum heatspreader that filled the cavity laterally edge to edge with "fingers" along the edges to spread the heat to the exterior walls (polymer)... better than nothing but terrible compared to a direct-to-ambient method... anyhow I digress, under the heatspreader was welded an aluminum "slug" about 1" deep and 3/4" diameter to further draw heat from the emitter.
Your halogen probably uses the same housing (polymer) as I have, without the existing heatsink options, or a previous generation (these are rebranded Nighthawk lights if you want to see the different head models used over time).
On my light, I used the existing heatsink, and made an additional sink of about 3/4" tall copper snugly fit to the inside of the housing to raise my emitter to the new optic height (much shorter than the existing luxeon optic), and to provide additional heat transfer away from the LED. The same technique will work for you, a copper or aluminum heatsink (block) cut to fit the housing above the MR-11 base (if you want to keep that you could insert a couple of wires in the pinholes to go to your regulator board), if not, you can remove it and wire directly to the regulator board. Adjust the "heatsink" block to fit the regulator (on the backside preferably, making sure to prevent shorting out) and the emitter and optic/reflector stack on the frontside. Make it snug, I solder my emitters to the copper heatsinks, but if you are using aluminum I'd recommend thermal adhesive (Arctic Silver adhesive) to firmly bond the unit to the heatsink. Test fit everything several times before final assembly, apply thermal adhesive (a tiny amount just big enough to thinly cover the emitter base), and then assemble firmly. Make it so the "stack" is gently but firmly pressed onto the emitter and let sit overnight before handling. If using a three-screw faceplate, make the stack so that the faceplate nearly, but not 100% sits flush with the body (paperwidth maybe) when it starts pressing the optic down (don't overtighten or you can damage the emitter). If using the threaded round style, make it so there is a turn or two left before bottoming out.
Oh, your bezel MAY (or may not) seal properly going from the MR-11 to an optic/reflector, on mine I had to slightly cut the outside bezel ring (the stock optic was slightly smaller than a real MR-11, I did all trimming with an X-acto knife), and had to trim a few "tabs" inside the housing, but with a real MR-11 light that probably wont't be a problem.
Those are my suggestions, others may vary, good luck and have fun!

Oh, and here are my pics of the Performance Gen3 disassembled unit... if you have one of these and want to "safely" disassemble it, the trick is heat it up so that the face ring is SLIGHTLY pliable (it WILL burn and bubble, be careful)... and if yours are like the 2 I've done (likely), there will actually only be 4 solid "gluepoints" which you can feel when it's heated up and soft enough to give slightly by testing around with a very thin screwdriver... insert the small screwdriver while keeping it hot (too hot too touch, but not hot enough to melt), and gently but persistently work the screwdriver in and around those 4 points (not the rest of the bezel, to avoid deforming it excessively)... once you've broken the glue at those 4 places, the bezel will easily come off/unscrew. I marred my first attempt (pictured) much more than necessary before discovering the glue was only in 4 points, not all around.
Oh, the final effort, the original light was a tight spot, not terribly bright (would be a visible brightening inside a halogen beam, but not noticeably so and over a much tighter area) the upgraded light is significantly brighter than my Nighthawk 10-watt halogen, running Cree XR-E P4s at 800mA with a 25-degree optic. (So at around 3 watts, it's brighter than a similar halogen at 10 watts, your runtime would therefore more than triple for the same or better output in an apples to apples comparison like that with the same watt-hour source).

 

[auroreboreale]

While I am running a 12-14V 12W +22W Halogen MR-11 system, this new LED bulb might be of use, as it is rated for 8-30DC volts...

http://www.superbrightleds.com/specs/MR11-WHPx.htm

Reading this thread, I am not convinced it would be as bright as what I have now with a 12V 12W Halogen.

I confess that I have little to no modding skills. From what I gather here, I need to wait for a 3 Cree LED 12V MR-11 drop-in replacements...I still have good Halogen MR-11 spares, so I will keep on biking with them until the consumer technology catches up!

Good luck!

 

[Christexan]

LOL, same thing I posted in the other thread, but to summarize...

Halogen MR-11 vs Cree LEDs...
Calculate halogen lumens at roughly 20lm/watt (actually that's on the high end, but to be safe)... with 10-20% wasted in spillbeam artifacts (rings, etc, outside the usable spillbeam).

Calculate Cree LEDs at roughly 80lm/watt out the front after optics losses.

So to upgrade to LED, the 12W halogen (240lm, say 200 usable lumens after losses), requires 3 watts of Cree LED lumens (rebels, SSC, whatever, all are in that ballpark). A single cree run at around 800mA will meet the bill, and triple your runtime (ignoring electronic losses, that depends on what you get to regulate with).

So for the 20W halogen at 400 lumens, you'll need 5 watts of Cree LED output, or at least 2 LEDs running around 700mA (I'm doing the Vf change calculations on this end to save the extra formulas required). In an MR-11 format, either single, or triple, lenses are available off-the-shelf. For a triple-lens setup, you actually come out better from an efficiency and heat perspective if you run at lower currents. And you can crank the light output up well beyond the 20-watt halogen and STILL use less power by far. Of course at higher power in a triple setup heat looms it's ugly head, but a triple running at 350mA with decent heatsinking (aluminum sink in the back of the package) will more than match the 20W bulb and still be manageable in the heat department. If you can seal the connector end of it and the "light package" (blob of silicone would do the trick on the connection) then you could drill holes in the outer housing for ventilation. This would help tremendously with getting the trapped heat out and allow you to run a triple much hotter, but I wouldn't go above 700mA in a triple-MR11 without an all-aluminum heat path to the housing even with cooling holes, which will be a LOT of light output at that current.

Also, these are all "standard/worst" case numbers, in reality I have a triple-MR11 with Q2 LEDs, that runs 700mA at under 10Vf (actually around 9.6) (or well under 5 watts), when according to the "specs" it should run at around 10.8Vf at that current (3.6Vf at 700mA is a "standard" number). So with that fixture I can blow away a 20-watt halogen for all of 5 watts of power. And this is off a benchtop lab supply, measured at the emitters (well, at the PCB connections which have massive traces to the emitters, basically all-copper PCB surface with only division lines breaking the sections electrically, so negligible loss on the PCB).

Pictures soon to come! (Soon as I have time to mess with them, LOL)

Oh, I do have pics of a Performance Viewpoint "Gen3 Emitter" that I gutted and upgraded with a Cree XR-E and Fraen lenses, took a little trimming here and there but is MASSIVELY improved over 10W halogen and the original emitter (Lux III with spot-optic that was next to useless for biking). Had to make a copper "heatstack" that I AA'd to the original aluminum heatsink to get the emitter to the right height, but was good for extra thermal mass anyhow. Sadly I always forget to take pics of the "assembly" process, but I can disassemble one to show the final results (ugly but works).
http://christexan.com/biking/bikelights/Gen3 Emitter/

 

[WeLight]

If your interested in MR11 retrofit kits we have 2 avail, one using the bflex microcontrolled constant current driver which has 3 user modes including a bike mode(has multi current and flash settings, low battery warning etc) and one based on the fatman boost driver if you want to cart minimal battery pack size

http://www.cutter.com.au/proddetail.php?prod=cut757
and
http://www.cutter.com.au/proddetail.php?prod=cut756

Both kits include a triple MCPCB with Cree Q5 XR-E leds and a 35mm triple narrow optic from khatod
Cheers
WeLight