I have a 4-7 x 1w led CC driver but it does not work right. When I test 5 1W led's, 4 are bright and 1 is dim and it burns out the middle led. I tested the voltage without any load and it is 32VDC. The 1W LED's I am using are 3.2V, so 32V seems way too high. Is a no-load voltage test valid with a CC driver?

 

post the real specs or part number of the CC driver?
I suspect its an Ebay Chinese cheap junk model and failures are VERY common with them.

What is its rated output current?
What is its rated output voltage range?
What is the rated current for the LEDs?
Are you wiring them in series or parallel?

 

I have a 4-7 x 1w led CC driver but it does not work right. When I test 5 1W led's, 4 are bright and 1 is dim and it burns out the middle led. I tested the voltage without any load and it is 32VDC. The 1W LED's I am using are 3.2V, so 32V seems way too high. Is a no-load voltage test valid with a CC driver?

If you could post the circuit, test circuit and model numbers of the LEDs. You will get answers that are more accurate.

 

Is a no-load voltage test valid with a CC driver?

No. It should be putting out a constant-current, so here is how I would test it:

Connect a 10Ω 2W resistor in place of the LEDs. Since it is a 1W/LED driver, it should be putting out I = P/Vf = 1/3.2 = 0.312A.

0.312A thru 10Ω is E= IR = 0.312*10 = 3.12V.

A second test with a 100Ω resistor would prove that it is delivering the right current near its max. output voltage: E=IR = 0.312*100 = 31.2V. The resistor would have a power rating of P=IE = 0.312*31.2 = 10W. If you don't have a 10W 100Ω resistor, you can immerse a 100Ω 1W resistor in motor oil for a quick test.

If one of the LEDs went bad, it is either because you bought crappy Chinese LEDs, or you forgot to put them on a heatsink. Heatsinks are required under 1W LEDs.

 

No manufacturer
No part number
No schematic
No idea.

ak

 

Here are the parts: LED's are in series

http://www.ebay.com/itm/12142366387...49&var=420360538808&ssPageName=STRK:MEBIDX:IT

http://www.ebay.com/itm/50pcs-Brand...1-Watt-/191217602967?var=&hash=item2c85751197

I did not include a link in my OP, since I was just asking a generic question:
" Is a no-load voltage test valid with a CC driver?"

Thanks for your detailed reply Mikeml - I'll try that test.

BTW, I have used these LED's and drivers to light my entire shop (8 work stations) for 5 years, and to date, I have had ONE failed LED bead and zero driver failures.

 

Here are the parts: LED's are in series

http://www.ebay.com/itm/121423663878?_trksid=p2057872.m2749.l2649&var=420360538808&ssPageName=STRK:MEBIDX:IT

...

These need to be mounted on a heatsink. How did you get the heat out of them?

 

Is a no-load voltage test valid with a CC driver?

Depends on what you want to know. With no load, a CC output will rise to its maximum output voltage, called its compliance. In your application, his can tell you the max number of LEDs you can have in a string. Alternatively, a short circuit current measurement will tell you the CC setting. It takes both numbers to fully characterize a CC output.

ak

 

These need to be mounted on a heatsink. How did you get the heat out of them?

I use aluminum discs or HDD platters

 

Depends on what you want to know. With no load, a CC output will rise to its maximum output voltage, called its compliance. In your application, his can tell you the max number of LEDs you can have in a string. Alternatively, a short circuit current measurement will tell you the CC setting. It takes both numbers to fully characterize a CC output.

ak

 

I think they were mis-labeled. The driver works with over 5 LED's, voltage is correct (Ledcount x ~3.2) and current is 300ma

"With no load, a CC output will rise to its maximum output voltage"

If this is true then the max LED's would be 10 since I measured 32v w/o load. This would make them 6-10 drivers.

Thanks for the help!

 

Check the datasheet. It might have a different opinion of its max output voltage under load.

ak

 

Output voltage is stated as 12-25VDC
So as long as your LED forward voltage range is greater than 12VDC and less than 25 VDC it should regulate the current properly.

I would also check to make sure you don't have a short to the heatsink. sometimes that happens when soldering to those pads.

 

Hello,

As for the led driver, It should be able to drive 4 (4X3.2 = 12.8) to 7 (7X3.4 = 23.8) of your leds.
As for the leds, do you use heat conductive compound between the leds and the plate?
Also what is the temperature of the disk after some time?
Power leds must be cooled to have a long life time.

Bertus

 

It was specified to drive 4-7 LEDs but as I said in my OP, it does not work with 5 or less, 6 is the minimum it will work with.

I have tried both thermal compound (ie: cpu thermal paste) and epoxy. No significant diff in temps, both were approx 95F after 20 mins, measured on the surface of the HS within 1/8" from the LED. Some of these LED's have been on for 4-5 years 12+ hrs/day

 

I don't see an answer to your original question: a CC power supply without a load with increase its output voltage in order to reach the expected current. And there's the rub: cheap power supplies will ramp up until they burn themselves out; good ones will reach a voltage limit and hold it there. If your power supply has a voltage rating (ie- 32volts) it means it will ramp up to 32v to try and push the rated current. If it succeeds, fine, if not (because there's no load there), see first sentence