BobCajun
Well-Known Member
There's a type of high bay that's widely available now from Cree, the 240w CXB. I have a couple of them and the other day one of them started flashing off and on. Took it apart and found that one COB had burnt out completely and a couple others had much of their "dice" burnt out. The other 9 were functional. I did the test by using alligator clips to link a few together at a time and powering them up with the driver, while also having the dimmer leads shorted so it would be at 10% current.
So anyway, turns out that Cree was wiring them with 2 COBs in parallel and each of the 2 COB units wired in series. They're actually 36v COBs so 12 of them is 432v if they were all in series. By pairing them they cut that voltage in half because two 36v COBs in parallel are still only 36v, just that they're splitting the driver current, which in this case is 1050 ma.
What I had to do was wire 6 of the functional COBs in series. They're now each running at the full 1050 ma and putting out similar intensity to the 12 when they were running in pairs, though slightly lower due to decreased efficiency. I also put PC fans on both of the heat sinks. Apparently, fans are more important than you might think, even when the lamp is supposedly passive cooling. The passive cooling isn't that great, like barely adequate.
I guess if I had another small driver I could run the other three good COBs too and get 50% more light out of the lamp. BTW, I had to tear out the circuit board thing that was around the COBs, connecting them up. Fortunately it was very weak and easily broken and removed. With those connections removed I was then able to wire the 6 up with short pieces of solid copper wire and a soldering iron. I was surprised I was actually able to get the thing working again actually. Had to stick some 40W CFLs in the chamber during the fixing.
One good thing that came out of this is finding out that you can get twice as much light from the 240W CXBs (apparently 240W total, including driver overhead, because the driver says max 220w) by simply rewiring them and adding a second driver. The COBs are 2530s btw. No way to remove the COBs from the heat sink though. They're permanently cemented to it apparently. Must have used a thermal paste that hardens into cement.
So anyway, turns out that Cree was wiring them with 2 COBs in parallel and each of the 2 COB units wired in series. They're actually 36v COBs so 12 of them is 432v if they were all in series. By pairing them they cut that voltage in half because two 36v COBs in parallel are still only 36v, just that they're splitting the driver current, which in this case is 1050 ma.
What I had to do was wire 6 of the functional COBs in series. They're now each running at the full 1050 ma and putting out similar intensity to the 12 when they were running in pairs, though slightly lower due to decreased efficiency. I also put PC fans on both of the heat sinks. Apparently, fans are more important than you might think, even when the lamp is supposedly passive cooling. The passive cooling isn't that great, like barely adequate.
I guess if I had another small driver I could run the other three good COBs too and get 50% more light out of the lamp. BTW, I had to tear out the circuit board thing that was around the COBs, connecting them up. Fortunately it was very weak and easily broken and removed. With those connections removed I was then able to wire the 6 up with short pieces of solid copper wire and a soldering iron. I was surprised I was actually able to get the thing working again actually. Had to stick some 40W CFLs in the chamber during the fixing.
One good thing that came out of this is finding out that you can get twice as much light from the 240W CXBs (apparently 240W total, including driver overhead, because the driver says max 220w) by simply rewiring them and adding a second driver. The COBs are 2530s btw. No way to remove the COBs from the heat sink though. They're permanently cemented to it apparently. Must have used a thermal paste that hardens into cement.
