light with 3xR2 on 12V lead accu

Can this setup work?
I will use 3 pcs. of R2 led on stars connected in series, one ohm resistor also in series with leds and fuse 1,5A all connected to lead accu 12v/4.5ah.
leds will be mounted with screws and thermal grease on heatsink(PC chipset heatsink). for reflector I will use 48.16mm 3-LED Reflector for Cree Emitters. leds with cooler and reflector will be glued together with epoxy resin.
will this be enough light for bicycle riding? or must use two of this lamp?

If you plug it all into the LED calculator; 12 volts, 3 R2's in series (≈3.7 volt vf) and a 1 ohm resistor load resistor in series = 900 ma current. It looks like it should work great. If you have a good meter on hand, maybe wire that in series too for your first test. Just to see how much current it really draws.

One light like this should be more than enough for an excellent bike light. Don't forget to mix some 5 micron aluminum oxide in with your epoxy if it's not already thermal epoxy.

Good luck and :welcome:

Al Combs said:

If you plug it all into the LED calculator; 12 volts, 3 R2's in series (≈3.7 volt vf) and a 1 ohm resistor load resistor in series = 900 ma current. It looks like it should work great. If you have a good meter on hand, maybe wire that in series too for your first test. Just to see how much current it really draws.

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of course there will be metering. i saw that R2 can work at 1400mA if heat dissipation is ok.I presume current in my circuit will be cca.1A

Al Combs said:

One light like this should be more than enough for an excellent bike light. Don't forget to mix some 5 micron aluminum oxide in with your epoxy if it's not already thermal epoxy.

Click to expand...

I didn't know that, thank for info! what temperature should I expect at front of led's?

Al Combs said:

Good luck and :welcome:

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thank you! you are the first one who didn't only look at my post,but reply to it!

Sponge said:

of course there will be metering. i saw that R2 can work at 1400mA if heat dissipation is ok.I presume current in my circuit will be cca.1A


I didn't know that, thank for info! what temperature should I expect at front of led's?


thank you! you are the first one who didn't only look at my post,but reply to it!

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I think heat is more the issue than current. The one produces the other. Cree's specs say absolute max rating is 1 amp, but it will go higher. Even so at 1.4 amps your not going to get 50K hours. Another thing you have to consider using resistors instead of a constant current regulator, as temperature rises, forward voltage drops. What you set up with a meter might behave different on the road after it's been running for an hour.

Sometimes guys here use the bleeding edge as a reason down the road to mod some more. Of course on a bicycle with three in series, if one blows you go blind. You can look at the PDF's on Cree's page to give you an idea of their LED's safe operating temperature range. The good thing is being on a bicycle, the wind should help with any heat build up.

How would you use a PC chipset heatsink inside of a waterproof enclosure, or is it? The breeze wouldn't reach the fins of the heatsink. A solid piece of metal to mount the stars on that's in thermal contact with an enclosure that has fins on the outside might be more efficient.

FWIW, here is a CPF list of regulators. If you look in the buck and linear section, check out the Kennan2 just for an example. You can buy 3 of these for ≈10 bucks, one for each LED. Or drive all three LED's on one of them. By default it's output is only 750ma, but there's a link explaining how to mod it to go higher. Really 1 amp is bright enough. Three R2's @ 1 amp is 750 ≈lumens, brighter than a car headlight. Well maybe not an HID.

Al Combs said:

I think heat is more the issue than current. The one produces the other. Cree's specs say absolute max rating is 1 amp, but it will go higher. Even so at 1.4 amps your not going to get 50K hours. Another thing you have to consider using resistors instead of a constant current regulator, as temperature rises, forward voltage drops. What you set up with a meter might behave different on the road after it's been running for an hour.

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i think that chipset cooler will be enough to keep those led's cool
I will drive it at 1A max. and cool them all the time, because bike is moving

Al Combs said:

Sometimes guys here use the bleeding edge as a reason down the road to mod some more. Of course on a bicycle with three in series, if one blows you go blind. You can look at the PDF's on Cree's page to give you an idea of their LED's safe operating temperature range. The good thing is being on a bicycle, the wind should help with any heat build up.

Click to expand...

same thing could happen with lamp with only one led
I have small backup halogen light which is connected to dynohub

Al Combs said:

How would you use a PC chipset heatsink inside of a waterproof enclosure, or is it? The breeze wouldn't reach the fins of the heatsink. A solid piece of metal to mount the stars on that's in thermal contact with an enclosure that has fins on the outside might be more efficient.

Click to expand...

heatsink will not be all covered with resin, only small part of it.I will probably drill some small holes in heatsink so resin can flow in it and make all stronger. fins will be free to air. so when bike is movin' at 20kmph it will keep those leds very cool

Al Combs said:

FWIW, here is a CPF list of regulators. If you look in the buck and linear section, check out the Kennan2 just for an example. You can buy 3 of these for ≈10 bucks, one for each LED. Or drive all three LED's on one of them. By default it's output is only 750ma, but there's a link explaining how to mod it to go higher. Really 1 amp is bright enough. Three R2's @ 1 amp is 750 ≈lumens, brighter than a car headlight. Well maybe not an HID.

Click to expand...

hey, thank for those infos!! this will be very helpfull in future project (P7 led with 2 lion batt. on helmet).
But, for this project, I will stay on serial connection and maybe a resistor.