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Halogen to LED conversion help

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Unread postAuthor: MrCrowley » Fri Feb 17, 2012 8:47 pm

Sorry I should have clarified; it was a spare LED with the exact same specifications as the one I'm intending to use on the circuit. The only difference is that it was a 'warm' white LED while the one I intend to use is cool.

Thanks guys.
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Unread postAuthor: dewey-1 » Fri Feb 17, 2012 9:50 pm

What is the actual power pack voltage?
I am guessing it is about 15 volts if you are getting 12 volts out of the module.

If it is actually 12 volts in and 12 volts out, then the module is shorted internally. This would explain your damaging of the "spare" LED.

You could also try installing a 10 Ohm 2 Watt resistor in series with the LED to at least limit the current.
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Unread postAuthor: MrCrowley » Fri Feb 17, 2012 9:54 pm

The actual voltage is about 15V even though it says 12V 500mA on it. Doing some fiddling round, I can get the pot. to control 0-6V. If the power pack actually delivered 12V, this would be 0-4V, I'm guessing.

So it seems like I may just need some more resistors to drop the 6V down to 4V or so?

I can also get 0-2.5V by connecting the 10K resistor to ground on the pot and then connecting the wiper to both pin 2 (analogue) and pin 4 (ground) on the module.

Edit:

I've got 0-4V by connecting the ground from the power supply to a 2K (found on the original halogen circuit), 660R and 630R resistor that grounds on the pot. The wiper then connects to the 10K resistor which connects to both Pin 2 and Pin 4. The positive wire from the power supply then connects to the other terminal on the pot as well as Pin 1 on the module.

Edit 2:
Removing all the resistors with the wiper still connected to Pin 2 and Pin 4, the voltmeter gave a reading of 0-11V and this dropped to 0-3.5V when the LED was connected. For some reason, it stopped working after that so I assume it doesn't like when I connected Pin 2 and Pin 4 together. Module still appears to be working fine though.
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Unread postAuthor: dewey-1 » Fri Feb 17, 2012 11:57 pm

Here is how it should be wired. Basically what Tech said originally.
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Unread postAuthor: Technician1002 » Sat Feb 18, 2012 2:50 am

Thanks Dewey. I didn't have the resources handy to draw it up. That is exactly right.
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Unread postAuthor: MrCrowley » Sat Feb 18, 2012 11:37 pm

Thanks again for the help guys. The diagram is indeed the very first setup I had tried (the diagram I linked on the other page was the second setup I tried) but the reason it didn't work the first time seems to be due to a faulty pot, LED and voltmeter. The pot has a terminal slightly loose so it can either work correctly, not work at all or just provide full brightness. The spare LED that blew seems to have been faulty in the first place as I'm not sure why it blew on this circuit when I first tried it the other day and the voltmeter was giving strange readings on the 10V scale but correct readings on the 50V scale, so I ended up using the divider and working on a 25V scale barely able to see the fluctuations from the pot adjustments.

So it seems to work now that everything's been worked out, I have an even better LED dim range than the circuit I made back in August or whenever. This one only dims the LED to about 50-60% brightness which is the lowest I would ever need it.

Cheers guys.
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