Only two LEDs out of six are coming on

[vresor]

I managed to buy the wrong power supplies, but I do have access to a constant current power supply that I can regulate to 20 VDC and whatever current is required, say 1500 mA. What are the consequences of running the LEDs at less than the right voltage, but still the right current, for two weeks or so until the right power supplies arrive?

[Deleted User 6]

[vresor]

That would suck!

[supernip]

dont worry, that only happens when you divide by zero

[vresor]

Seriously though, Cree shows 3.3 volts for the XR-E at 350 mA. I have six emitters in series, so that's 3.3 x 6 = 19.8 volts. The Buckpuck needs 2 volts (if I'm reading the data sheet right). It's close. I'm going from 72 watts of PC up to LEDs, so my plan has been to acclimate slowly with the pots turned down pretty low at first.

[Haggis]

Don't you risk damaging the buckpuck by supplying too low a voltage? You may get away with it but I think it's asking for trouble as the puck tries to compensate.

[vresor]

Okay, I gave up on the 20 volts thing and wired two 20 volt supplies together in series, adjusted them down to 12 volts DC each, set the current output to 4 amps and wired it up. The photo below shows my set up with the major components labelled. When my temporary switch is closed, only the first two LEDs in each string light. Knowing that's bad, I left them on for just a fraction of a second. I'm thinking that's because I'm really only getting 12 volts thanks to a problem with one of the supplies. Does that make sense?

 

[vresor]

Another update. I figured out the problem with my second power supply and now I have 24 VDC and 4 amps. I think everything is connected correctly. The positive lead on the Buckpuck goes to the positive terminal on the first LED, the negative lead of that LED goes to the positive of the next one, etc. Now that I have the right power, all six RBs come one, but still just the first two in the white string. I confirmed continuity from beginning to end of the white string. What am I missing?

[cptbjorn]

Something is shorted to the heatsink in your white string, look for wire touching/solder bridges to the screws. You can test for it by clipping/holding a meter lead on the heatsink and touching every LED pad with it set for continuity, if you get a beep/reading other than open then there's your problem.

[MadWorld]

Another update. I figured out the problem with my second power supply and now I have 24 VDC and 4 amps. I think everything is connected correctly. The positive lead on the Buckpuck goes to the positive terminal on the first LED, the negative lead of that LED goes to the positive of the next one, etc. Now that I have the right power, all six RBs come one, but still just the first two in the white string. I confirmed continuity from beginning to end of the white string. What am I missing?

 

 

You're not connecting them right, it needs to be like this, as you started with positive to positive .

- BuckPuck + + LED - -LED + +LED - -LED + etc...

[thecowkid]

I see a beep coming up.

[vresor]

I'm pretty sure it's + to - to + to -, but the short to heatsink is a strong possibility. Back in a few.

 

That was it! Soldering iron is heating up...

 

Thanks Captain.

[cptbjorn]

You're not connecting them right, it needs to be like this, as you started with positive to positive .

- BuckPuck + + LED - -LED + +LED - -LED + etc...

 

[vresor]

That was it. Thanks again Captain. My pots dim backwards, but I can live with that. Now to get everything buttoned up and get the lid back on the tank. Stay tuned.

[cptbjorn]

Switch the red wire to the other side and the pots will spin the other way.

 

When it happens to me though I just pretend it was on purpose because I'm left handed lol.