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Morning all again. I have managed to sort out the powersupply I need… - Software & Hardware Design! [entries|archive|friends|userinfo]
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[Mar. 20th, 2007|12:45 pm]
gadget_design

gadget_design

[crackcat]
[music |DJ Scorch - Vol 1 2007]

Morning all again.
I have managed to sort out the powersupply I need for powering 2/3 Luxeon LEDs.
I have running right now at 730ma (30ma higher than i was expecting, but eh), 2 LED's on a nice sized heatsink.
My problem now, is the 10w resistor I'm using, is cooking!! I was told that a 7w would be good enough for me, so I figured a 10w would be overkill.
Should I be mounting this resistor (standard white ceramic) on the heatsink as well?
SHould I up the wattage even MORE?!

Should I just regulate the current of the powersupply instead of limiting the current, and get rid of the resistor all together?

Thanks!
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Comments:
[User Picture]From: marxmarv
2007-03-20 05:22 pm (UTC)
You're using a parallel connection for the LEDs right now, I take it? If I were you I'd wire them in series and recalculate the resistor for the new voltage drop and current. Assuming a 13.2V supply, that would halve the current and cut the resistor voltage drop by about 1/3, reducing the waste heat power by about 2/3. 18 ohm, 5 W sounds about right.
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[User Picture]From: crackcat
2007-03-20 06:09 pm (UTC)
Nope, they are in series...
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[User Picture]From: dc_al_coda
2007-03-25 07:14 am (UTC)

Hot Resistor

I've tried running a Radio Shack 10ohm 10Watt power resistor at 8.1W (just hooked a 9V supply across it) to see how hot it got with a kitchen thermometer.

The final temperature I can't remember -- but it was well over 100 degrees F!

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[User Picture]From: crackcat
2007-03-25 01:31 pm (UTC)

Re: Hot Resistor

so this is normal? Should I sink it, or let it hang free?
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[User Picture]From: dc_al_coda
2007-04-06 03:35 am (UTC)

Re: Hot Resistor

I think its normal to get that hot -- 8W is a lot of heat for a small resistor -- its like an 8W space heater condensed into a small space!

I would let it hang free and away from other parts if possible. I usually use a resistor rated for twice the wattage I'm expecting at high temperatures -- and its guaranteed the resistor won't burn itself up.
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