LED COBS in series, large voltage mis-match

Thread Starter

jeffkrol

Joined Dec 8, 2015
32
Setup.. 3 COBS with a V(f) of 34V in series with 5 COBS with a V(f) of 9.4V.
700mA constant current driver with enough voltage to cover the sum.

Any issues?
I know that small differences are meaningless with constant current drivers but thought I read somewhere (which I can't find again) that large differences can cause some sort of current imbalance.

Was it my imagination?
 

Ian0

Joined Aug 7, 2020
6,286
Setup.. 3 COBS with a V(f) of 34V in series with 5 COBS with a V(f) of 9.4V.
700mA constant current driver with enough voltage to cover the sum.

Any issues?
I know that small differences are meaningless with constant current drivers but thought I read somewhere (which I can't find again) that large differences can cause some sort of current imbalance.

Was it my imagination?
Yes. Definitely your imagination.
If they are all in series the currents through them all are identical.
 

BobTPH

Joined Jun 5, 2013
5,743
I think your description is ambiguous. I read it as 3 34V LEDs in parallel, 5 9.4V LEDs in parallel and those two groups in series. But others have read it as all 8 in series. Which is it?

If it is the latter, you are going to need 150V, which is pretty high for a constant current driver, though you may be able to find one.

If my reading is correct, the paralleled ones will not will not share current equally, so that is a problem.
 

Thread Starter

jeffkrol

Joined Dec 8, 2015
32
I think your description is ambiguous. I read it as 3 34V LEDs in parallel, 5 9.4V LEDs in parallel and those two groups in series. But others have read it as all 8 in series. Which is it?

If it is the latter, you are going to need 150V, which is pretty high for a constant current driver, though you may be able to find one.

If my reading is correct, the paralleled ones will not will not share current equally, so that is a problem.
No..all in series..
To some other questions asked here.
The real driver is this:
HLG-120H-C1050AB
74-148V, 525,1050mA adjustable

Or one in the family.


OK so my imagination, I can live with that.

Just had a hard time "believing" one could hook say 2.2V red LED stars in series with the likes of 34 V white COBS with no repercussions.
2.2----34----2.2----34--- ect...

IN REALITY the actual string will be;
9.6----34----9.6----34 -- ect up to the 150 V limit (Or I hit approx 154.4W) @ 733mA
Seems the answer is I am wrong in thinking that.
 
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