If you have a current meter, you can add a dummy load and measure the current.


If you can get your hands on a .1 ohm resistor 1%. The voltage measured across it measured in millivolts x10 is equal to your current in mA. You can use a 1 ohm too but I am too lazy to do the math.

A voltage reading will be more accurate because of the high frequency PWM of the device.

 

oh also, how could I test it's current output and if it's constant? I don't have a 50W DC load.

Do you have an incandescent light bulb?

 

Do you have an incandescent light bulb?

what are those??

But seriously, no I actually don't and can't believe how good of an idea that is.

a 50W bulb would be a perfect dummy load would it not???


Anyway, I have my LED hooked up to my power supply right now and am just watching it's current draw.

On startup it was about 850mA

after running for about 2 mins now my power supply is telling me it's drawing 1.23 amps.

my DMM backs this up.

 

1.3A.

And I imagine it's getting pretty hot now.

 

what are those??

But seriously, no I actually don't and can't believe how good of an idea that is.

a 50W bulb would be a perfect dummy load would it not???


Anyway, I have my LED hooked up to my power supply right now and am just watching it's current draw.

On startup it was about 850mA

after running for about 2 mins now my power supply is telling me it's drawing 1.23 amps.

my DMM backs this up.

Were you able to set your current limit on the supply????? You should have just set it there and turned it up slowly.

 

Do the specs have a current rating or just wattage?

 

so after running for a while it's dropped down to 1.07-1.08A

it looks like I'd need to dissipate probably 600 or 700mA from the driver if it's constant current.

so if I'm not mistaken a 15Ohm 10W resistor would drop the current enough to run the LED from this driver, IF this driver feeds the LED 1.7A?

 

Do the specs have a current rating or just wattage?

I posted the specs a couple of posts ago. And yes, it's my own fault for not actually looking at this beforehand. It's really very obvious stuff I should have seen before..... I'm an Electromechanical Engineering Technician you know.....

Driving power: 50w
Model: 10 series 5 in parallel
Input Voltage: 85V~265V
Output Voltage: 32-34V
Current:1750mA
Efficiency > 88%
Power Factor >0.98
Operating Temperature: -20~80
Size (L * W * H): 110mm * 32mm * 23 mm

also, the listing.

http://www.ebay.ca/itm/221319884864...eName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

 

1750 is 1.75. About what you are measuring. You have the wrong driver if you expect less. Adding a resistor will be awfully inefficient.

 

And you do have these LEDs mounted on heatsinks right? If you have the stars that might not be enough. You really should mount them on some aluminum stock to provide additional cooling.

 

no heat sink yet, I was planning on stuffing this LED into an old flexible desk lamp housing.

initially I thought using a computer northbridge heatsink would be sufficient, and would fit in the space of the reflector on the desk lamp, but now I'm having second thoughts.

I can't measure the temp of the LED being held in my "third hand" because my infrared thermometer has a dead battery, but considering the cost of a 10W resistor and it's inefficiencies, I may just drop another $12 and buy the 30W driver.

I could easily use this 50W driver to power some other LED's and it might be easier to string a ton of LED's together than trying to step this driver down to what I need.

Considering that I've just recently purchased this power supply, and LED, this is a good test of both the LED and my power supply so I'm going to leave it running for a while at 120mA

before I turned it down the LED seemed to steady out at 1A.

 

To hell with it, even though I can't afford the $10 is just cost me, I went ahead and ordered the 30W driver.

Knowing me, I would have easily spent far more than that and far far more time trying to make this 50W driver work.

problem solved I'll regret it in the morning lol.

 

(see attachment)
I'm using this arrangement for a 40W round shape LED (almost same as yours) and it is working fine. I got all parts from a TV board from junk. You may use a 5k or 10k variable.

 

what transistor did you use? I'll play around with that circuit too just for fun because I may have the parts on hand.

 

This is sort of like building an atomic bomb and then putting a thicker shell on it so that it doesn't cause as much damage...

 

This is sort of like building an atomic bomb and then putting a thicker shell on it so that it doesn't cause as much damage...

well I'd like to think there is less damage done....but whatever floats your boat


In CC mode, I'm getting 0.87A @ 12V., and its jumping around a little. 0.85-0.87 or so.

 

Ok, so there's a small discrepancy in what my PSU says and what my DMM says,

PSU says 0.95A and my DMM says 1.08A ,,,,,, not sure which to believe, although my cheap Chinese PSU may be more accurate than my broken and fixed DMM.....

when I switch configuration I get 13.39V on my DMM and 12V on my PSU (current on PSU says 0.99A, I'd need 2 DMM's to test both configurations.)

Not sure which to believe but my PSU is a Mastech HY3005F-3 and my DMM is a UNI-T UT51 that's had the battery wires resoldered and usually needs to be pressed together for a diode/continuity reading.

 

what transistor did you use? I'll play around with that circuit too just for fun because I may have the parts on hand.

I have used 2SD1710 transistor. A power transistor used in chines TV power supply. Most general purpose power transistors like this would work fine. D1710, D1047 etc. I got it from junk too .
If you have some low pawer rating transistor, even put two or more in paralal would work fine. Good Luck.

 

I have used 2SD1710 transistor. A power transistor used in chines TV power supply. Most general purpose power transistors like this would work fine. D1710, D1047 etc. I got it from junk too .
If you have some low pawer rating transistor, even put two or more in paralal would work fine. Good Luck.

so I could use any general purpose NPN? like a 2N3904?

I'd need something much larger for dimming this LED though, I think. It's pulling more than 1A when it runs.

 

Should have just ponied up the extra $10 and bought the proper "dimmable" meanwell driver..