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I have a few COB LEDs laying around, but unfortunately I don't know the exact model anymore. Hence I can't read their data-sheet.

However, I would still like to use them. I own a good multimeter, and figured it might be possible to use it to determine some characteristics of the LEDs, so that I can figure out what driver to power them with.

Can you recommend to me a certain procedure to do this, that would allow me to find some "optimum point", where the risk of damaging the LEDs is relatively low, but where I don't have them running way under their potential? When I talk about "risk of damaging", I refer to the risk of damaging them during operation - if I happen to destroy one or two during the initial measurements, that would still be worth it.

I found this thread that treats a related question, but there the topic is LED-panels, and I have COB-LEDs, so maybe there are some differences..

I also know the driver which I used to power multiple of them in series - it was the HLG-185H-C700A - but I don't know the exact number of LEDs I used to power with that driver (might have been btw. 6 and 8 I think). However, what we can conclude is that the operating current of the LEDs is 0.7A. The reason I won't use that same driver again is that I don't want to run as many LEDs as I used to.

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    \$\begingroup\$ Do you know anything about the LEDs? Wattage or operating current? They will turn on and exhibit a strong knee near their operating voltage. \$\endgroup\$
    – K H
    Mar 22 '21 at 8:26
  • \$\begingroup\$ @KH I'm feeling dumb that I didn't mention it.. I edited my question to include info about a previous driver that I used, which includes the operating current. \$\endgroup\$ Mar 22 '21 at 8:39
  • \$\begingroup\$ Buy new ones with a data sheet to avoid disappointment. \$\endgroup\$
    – Andy aka
    Mar 22 '21 at 9:18
  • \$\begingroup\$ Increase the current in small steps until the LED starts to be hot (about 50 degree C). \$\endgroup\$
    – user208862
    Mar 22 '21 at 10:55
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Your current driver is a current control driver, so it will adjust output voltage to produce a 700mA current. If you have a digital multimeter, you can set up a string of the COBs attach them to the driver and measure the voltage across them while they are operating.

You can use a smaller string of LEDs with that driver. Only disadvantage is it's more efficient at max load. It's rated to work from 143V to 286V output. Be careful with it. 286VDC is a nasty zap.

You can hook up roughly the number of LEDs you remember using, check the voltage per LED while they're running and use that to guage if the minimum 143V will work for whatever number of LEDs you actually want.

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  • \$\begingroup\$ The concept of the driver being (approximating) a constant-current-source where the voltage is variable, and the LED being a current-driven device is what caused me some confusion I think. Yours and Damiens answer helped to clarify that. Thanks for the warning as well - in hindsight I would like to slap my earlier self for wiring together about 200V DC with tiny wires.. I had even less of a clue than I have now and fortunately was spared.. \$\endgroup\$ Mar 22 '21 at 9:25
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    \$\begingroup\$ You need to select your wire size based on current and your insulation type based on voltage (and other factors like FT4 rating if necessary). \$\endgroup\$
    – K H
    Mar 22 '21 at 10:02
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COB LEDs are usually current-driven, not voltage.

You can sacrifice one and increase current slowly until failure and step down 30% from that.

You can also count how many LED chips are there, as they are usually visible underneath the phosphor, then check the voltage. That will tell you roughly how many strings in series and parallel, usually they take about 100-150mA per string.

Note that cooling is an important factor in how hard you can drive a COB LED.

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  • \$\begingroup\$ This means that I can supply a higher-than-needed voltage (as long as it's not unreasonable high) to the LED, right? As long as I use a power-supply which approximates an ideal current-source, ie. aims at providing exactly the operating-current of the LED? The note about counting the tiny chips is very interesting! Cooling is handled, I have them mounted on some large star-heat-sinks. \$\endgroup\$ Mar 22 '21 at 8:47
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    \$\begingroup\$ "This means that I can supply a higher-than-needed voltage". COB and LED in general are current-driven device. "higher than needed voltage" doesn't mean much, what matters is the current, not the voltage. You should use a power supply that is current limited. Also be careful because most power supplies have large output capacitor that can kill your LEDs. If you use a Voltage regulated power supply you will need a resistor to control the current. But it may depend, perhaps your COB already has one integrated, but in general it's not the case. \$\endgroup\$
    – Damien
    Mar 22 '21 at 9:28

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