Help with cob light build

[catoblepa]

Hello everyone,
First of all i apologize for my not so good english
I recently built a grow light (actually 2) using 18 Citizen CLU038-1205C4-403H7K4 cobs (datasheet
https://www.digikey.it/htmldatasheets/p ... h-cri.html), powered by 2 Meanwell XLG 240-L-AB (datasheet https://www.meanwell.com/Upload/PDF/XLG ... 0-SPEC.PDF) and kept in place by these holders: https://www.te.com/commerce/DocumentDel ... ng=English.

Let me explain my situation:
After some research i calculated that for each lamp, 9 cobs @0.7A would set approximately 38V each for a total of 342V when wired in series.
That is my full power setting so that I can stay below that point through the dimmer.
So, after setting everything up i plug the driver in and nothing happens.
The output voltage is always around 377-378V with the internal screw turned all the way to the left and i also notice a slight buzzing noise from the driver; same result with the driver disconnected from the cobs.
By playing with the screw and the dimmer i can change the output voltage but the cobs never fully turn on, actually 1 or 2 slightly lighten up when i check the total voltage across the lamp with the tester.
What am i missing?

[Shimbob]

Have you triple-checked that the polarity with every cob is correct?
As a diagnosis step, try leaving the negative voltmeter probe connected to the driver's negative, and measure the voltage at each cob's positive terminal, measure your way down the series.

[PeteR_1]

Hello everyone,
First of all i apologize for my not so good english
I recently built a grow light (actually 2) using 18 Citizen CLU038-1205C4-403H7K4 cobs (datasheet
https://www.digikey.it/htmldatasheets/p ... h-cri.html), powered by 2 Meanwell XLG 240-L-AB (datasheet https://www.meanwell.com/Upload/PDF/XLG ... 0-SPEC.PDF) and kept in place by these holders: https://www.te.com/commerce/DocumentDel ... ng=English.

Let me explain my situation:
After some research i calculated that for each lamp, 9 cobs @0.7A would set approximately 38V each for a total of 342V when wired in series.
That is my full power setting so that I can stay below that point through the dimmer.
So, after setting everything up i plug the driver in and nothing happens.
The output voltage is always around 377-378V with the internal screw turned all the way to the left and i also notice a slight buzzing noise from the driver; same result with the driver disconnected from the cobs.
By playing with the screw and the dimmer i can change the output voltage but the cobs never fully turn on, actually 1 or 2 slightly lighten up when i check the total voltage across the lamp with the tester.
What am i missing?

If you are measuring 377 Vdc on the output then the driver will not work, it’s rated max output volts is 342 Vdc...

You can do a simple test and remove one of the series wired cobs to power only 8 in series, if your wiring is correct and Vf is below 342 Vdc it should light and work.

Note the internal pot only adjusts the Watts from ~ 50 - 100% or ~ 120 - 240 Watts... The optional 100K Ohm Pot Wired to Dim (Purple and Grey Wires) can then adjust the output from ~ 0 - 100%.
But the Vf (forward Volts) of the Connected COBs has to be between 228 - 342 Vdc (Rated cc region) to get the rated 240 Watts output.

The Vf of the COBs or Strips is sensed by the LED Driver’s circuitry and Vdc output is automatically adjusted. The internal pot and external Dimming pot only adjust the output Watts. The output volts Only varies slightly, Automatically.

[catoblepa]

Thanks for your replies.

Have you triple-checked that the polarity with every cob is correct?
As a diagnosis step, try leaving the negative voltmeter probe connected to the driver's negative, and measure the voltage at each cob's positive terminal, measure your way down the series.

I checked again the polarity of each cob and unfortunately they're all correct. Also tried to measure their voltage as you said but it's always 0. The tester reported some strange values between -2 and +2 V so i also used an analogic voltmeter and it says 0V.

If you are measuring 377 Vdc on the output then the driver will not work, it’s rated max output volts is 342 Vdc...

You can do a simple test and remove one of the series wired cobs to power only 8 in series, if your wiring is correct and Vf is below 342 Vdc it should light and work.

Note the internal pot only adjusts the Watts from ~ 50 - 100% or ~ 120 - 240 Watts... The optional 100K Ohm Pot Wired to Dim (Purple and Grey Wires) can then adjust the output from ~ 0 - 100%.
But the Vf (forward Volts) of the Connected COBs has to be between 228 - 342 Vdc (Rated cc region) to get the rated 240 Watts output.

The Vf of the COBs or Strips is sensed by the LED Driver’s circuitry and Vdc output is automatically adjusted. The internal pot and external Dimming pot only adjust the output Watts. The output volts Only varies slightly, Automatically.

I don't understand why the driver without dimmer always outputs around 380V like it was disconnected, in fact its open circuit voltage is 370V. With the dimmer i can change the output voltage value to the constant current region but still no light. Actually when checking (more like experimenting) with the tester (keeping one pin on the + and moving the other on the contacts of the other cobs) one of the cobs turns slightly on, but not more than one at a time.
The wiring should be correct, the + of one cob with the - of the next and the driver connected with the remaining 2 connectors (+ with + and - with -).
Forgot to say i already tried to connect 8 or less cobs to the driver but the result doesn't change. It's like there's no current passing through the cobs.

[PeteR_1]

Thanks for your replies.

Have you triple-checked that the polarity with every cob is correct?
As a diagnosis step, try leaving the negative voltmeter probe connected to the driver's negative, and measure the voltage at each cob's positive terminal, measure your way down the series.

I checked again the polarity of each cob and unfortunately they're all correct. Also tried to measure their voltage as you said but it's always 0. The tester reported some strange values between -2 and +2 V so i also used an analogic voltmeter and it says 0V.

If you are measuring 377 Vdc on the output then the driver will not work, it’s rated max output volts is 342 Vdc...

You can do a simple test and remove one of the series wired cobs to power only 8 in series, if your wiring is correct and Vf is below 342 Vdc it should light and work.

Note the internal pot only adjusts the Watts from ~ 50 - 100% or ~ 120 - 240 Watts... The optional 100K Ohm Pot Wired to Dim (Purple and Grey Wires) can then adjust the output from ~ 0 - 100%.
But the Vf (forward Volts) of the Connected COBs has to be between 228 - 342 Vdc (Rated cc region) to get the rated 240 Watts output.

The Vf of the COBs or Strips is sensed by the LED Driver’s circuitry and Vdc output is automatically adjusted. The internal pot and external Dimming pot only adjust the output Watts. The output volts Only varies slightly, Automatically.

I don't understand why the driver without dimmer always outputs around 380V like it was disconnected, in fact its open circuit voltage is 370V. With the dimmer i can change the output voltage value to the constant current region but still no light. Actually when checking (more like experimenting) with the tester (keeping one pin on the + and moving the other on the contacts of the other cobs) one of the cobs turns slightly on, but not more than one at a time.
The wiring should be correct, the + of one cob with the - of the next and the driver connected with the remaining 2 connectors (+ with + and - with -).
Forgot to say i already tried to connect 8 or less cobs to the driver but the result doesn't change. It's like there's no current passing through the cobs.

You're welcome...

The LED Driver has maximum output Vdc with no "Load" (no LEDs) connected; measured Vdc, bare wires at LED Driver...

It appears that you may have an open (Series) circuit, loose or disconnected wire and or possible damaged COB...
Recheck all your wire terminations, check that they all have adequate exposed wire (removed insulation) and check individual COBs... Good luck.

[catoblepa]

UPDATE
Everything works! I bought a 30W driver to test every single cob and found out the problem was the lack of contact between cobs and holders' pins.
I bent them just a little in the right direction and everything is working fine.
Thanks everyone!!