LM 338 Driver Problems

[Illum]

If your using resistors chances are numbers won't fluctuate that much.

LEDs actually like being driven at 350ma, it is both most stable and the highest efficiency...CREEs are capable of 1000ma so members here tend to overdrive them. I run my indoor fixed lighting at 350ma max, 700ma for outdoors.

the math doesn't make sense...at all:ohgeez:
The only way this would make sense, assuming your multimeter is correct, is for you to power up 3.6 LEDs in series

Well, the math doesn't have to work for the unit to work properly, but this is way too wild:eek:

 

[Carbon2010]

Well i'm glad i'll be running them more stable. Ill do a bench test today with 3 meters (perks of working at a mechanic shop I guess)

-one measuring voltage at the PS
-one measuring voltage at an LED
-one measuring amps in the chain of three
-I'll also check the temps of the LEDs (with a IR Thermometer) every 30 seconds.


I'll check all my results. The leds will have a fan blowing on them to keep everything cool. I think a 5min run time should give me somewhat good results. If nothing seems crazy i'll move to a 10min ... then 30min.

Keep you posted.

 

[Carbon2010]

Success!!!

I ran the LEDs for 30min straight. I used a 120mm Computer fan I had kicking around propped up on two tissue boxes (high tech:)) There were 3 LEDS running in series putting out 455ish mA. There was no heatsink on the back of the LEDs but the fan was directly blowing on them.

Results for 30min:

Amps: 455-456mA
Voltage: 3.26V
Heat: 24-28*C
Voltage at PS: 12.08V Constant

I'm quite happy with the results. Does it make sense on paper though...NOT AT ALL!!! I still don't understand how this is exactly working? It's not the LM338 700mA circuit I wish worked but it does indeed do it's job? Exactly how, i'm still unsure.

Illum once I get everything hooked up expect some pictures and a little "surprise" on the inside of the light fixture. Thanks again for all your help. I'll keep you posted with update pictures of my process:)

Now to my soldering station!