Bad EB Strip?

I just finished a build of two roughly 2ft x 2ft lights, each with 9 Bridgelux EB strips (22 inch) run off a Meanwell HLG-120H-C700B. The first one, no problems. When I fired the second one up for the first time this morning, only two LEDs on one of the end strips lit. Strange. As soon as I realized what was going on (call it 1 or 2 seconds at most), I unplugged it. Then, with no better idea, I tried it again. It's a bit of a blur, maybe it happened again. But then I plugged it in and it was fine -- all the LEDs on. Very strange. Except no -- looking again, two of them -- probably the same two that were on originally -- were dead. Bummer. I tried it again, my mistake -- 3 are dead. So I cleaned up, did some chores, and then took a few pictures to post here (coming right up) -- 4 LEDs are dead.

Backing up, my first thought when only two LEDs lit up was that I fucked up the wiring somehow. But then, how could that be? I mean, if two are lit, that means the current is making the complete circuit (the strips are wired in series). And that's pretty much the sum total of my responsibility as the electrician here...

Another comment: Can I swear only two LEDs lit up and not 3 or 4? No. Damn things are bright, and I wasn't staring too long. (I did have them dimmed all the way down to look, though, as I do in the photo below). And can I swear 2 were out, then 3, now 4? No. But I think it's true. Now I have the photo to prove the 4, so if it goes to 5 I'll know I'm in trouble.

But maybe that's what's really happening, and I should stop plugging it in -- at the moment I have one strip to replace; don't want to make it 2 or 9.

The LEDs that are giving trouble are at the end of the "last" strip -- the one where the negative lead from the driver plugs in. (I'm using the poke-in connectors near the solder pads; the problem is at the other end of the strip.)

Too late to make the long story short, but to shut up already (almost), I think I have a bad strip. I doubt I can ask DigiKey to replace it -- they can't know I didn't fuck it up myself (and maybe I did). The cost of the strip is no big deal; hurts to have ti pay the shipping again, though. Should have bought a couple of extra.

What do you think? Pix:

Thought about it some more and called DigiKey -- what the heck, I bought 18 strips from them, and one has 4 LEDs out. They were great and are shipping me a replacement.

If anyone thinks there could be anything about my configuration that's at fault, please let me know before I do more damage...

Two of 8 EB strips (1120mm) I got from Digikey were damaged. Several of the quick-connect caps were broken off and were not in the packaging. Four or 5 chips toward the center of each strip would not light. The strips were very well packed and there was no damage to the box in which the strips were sent. Apparently, the strips were handled roughly before packing for shipment.

Digikey was great about sending replacements. The only questions they asked were directed toward preventing future occurrences of the damage, so it is disappointing to hear it happened again. I will still buy from Digikey without hesitation.

I feel the same way about DigiKey -- a real pleasure to deal with; the two people I spoke to had brains, senses of humor -- nothing like the typical customer service rep. As far as my bad strip goes, there was no evidence of any mishandling, and I'd just as soon believe that it was bad when it left Bridgelux. Or maybe I damaged it myself applying thermal paste. In any case, I'm not inclined to blame DigiKey.

algebraist said:

I feel the same way about DigiKey -- a real pleasure to deal with; the two people I spoke to had brains, senses of humor -- nothing like the typical customer service rep. As far as my bad strip goes, there was no evidence of any mishandling, and I'd just as soon believe that it was bad when it left Bridgelux. Or maybe I damaged it myself applying thermal paste. In any case, I'm not inclined to blame DigiKey.

Click to expand...

So you're running nine strips at 700 ma and each one draws about 44.2 v at 50 C? When you first turn them on and they're cold it's probably more like 45-48 v. Your driver voltage output is 107-215, adjustable I assume. Okay so 9 x let's say 45 v to be on the low side. That's what, 405 v? You didn't actually specify the strip model, you just said 22" strips. Maybe I missed something. Is it one of those drivers powering nine 44.2 v strips or are they actually lower power strips. You need to be more specific when you write the first post, meaning actual model numbers.

It does seem odd that only some LEDs were out though. Actually I doubt they're straight series wired. Probably made so that if a few burn out the rest stay on.

Maybe it's the 22.1 v strips. It's still at least 200 v, pushing the driver hard, probably hard enough to fail to light all LEDs on startup since you're also running max current. Or could just be a bad strip. Maybe try running that strip with only enough others to get up to the driver's minimum voltage output, so like 4 others.

BobCajun said:

Maybe it's the 22.1 v strips. It's still at least 200 v, pushing the driver hard, probably hard enough to fail to light all LEDs on startup since you're also running max current. Or could just be a bad strip. Maybe try running that strip with only enough others to get up to the driver's minimum voltage output, so like 4 others.

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Yeah, the strips each draw 22.1 volts at 700 mA. I didn't specify the model number because all the 22 inch strips have the same power requirements (the only difference between them is the color temperature; these are 3000K). 9 strips at 22.1 volts each is 198.9 volts, which I think is far enough under the driver's 215V top end to be reasonable.

BobCajun said:

Actually I doubt they're straight series wired. Probably made so that if a few burn out the rest stay on.

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Reasonable; what I meant was that my strips were wired in series, so -- since something lit up -- I must have had a decent circuit from start to finish.

BobCajun said:

probably hard enough to fail to light all LEDs on startup since you're also running max current

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The 22 inch strips have a max current of 1400 mA, so there's no problem there.

Guess it must really be a defect then. Did you try running it with 8 strips, including the questionable one, just to make sure there's plenty of juice to go around?

BobCajun said:

Guess it must really be a defect then. Did you try running it with 8 strips, including the questionable one, just to make sure there's plenty of juice to go around?

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Good idea; haven't tried that. But I built two, same components, and the other one is working fine, so I don't really think that's the problem. Anyway, for now I am sitting back and waiting for the replacement to arrive; if I have problems when I install that one, then I'll start thinking about troubleshooting.

Well just looking at the data sheet again I did find this. The second part number would be yours, I assume. Now look at the figures in the last column on the right, v max cold. For 700 ma it's 25.6. Nine times 25.6 is 230.4 v. At 700 ma that would be 161.28 w, the driver's max output is 150.5 w and 215 v. See you can't go by the "typical" voltage, because that's not the cold voltage, meaning right when you start it up. That's after it's running and heated up. Just settle for an 8 strip rack and you're good. In fact the table says the cold max is at 40 C, so the actual room temp voltage would be slightly higher. BTW a multimeter comes in handy for seeing how much voltage something is drawing.

Actually I missed that the cold temp was minus 40, rather than 40. Still, it's probably best to use those figures as a guide. Most LED data sheets have a graph where you can see the voltages over all temps but this one just has that table so it's less accurate. I would use a multimeter across the output leads to see how much voltage 8 draw when first turned on. Then you could work out if it could power 9. You said you had one running already so it could be just on the borderline of too much and that particular strip may have been higher enough to put it over.

BobCajun said:

Actually I missed that the cold temp was minus 40, rather than 40. Still, it's probably best to use those figures as a guide. Most LED data sheets have a graph where you can see the voltages over all temps but this one just has that table so it's less accurate. I would use a multimeter across the output leads to see how much voltage 8 draw when first turned on. Then you could work out if it could power 9. You said you had one running already so it could be just on the borderline of too much and that particular strip may have been higher enough to put it over.

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Hate to say it, but that makes sense to me. I'll put the multimeter on it when the replacement comes in and I'm working on it again. The coldest it's likely to ever get in my grow tent is maybe 60F, so hopefully that's warm enough to keep the voltage requirements under 23.8V per strip (which is roughly 215 / 9) at 700mA. Otherwise I have trouble. (On the other hand I think there's reason to be optimistic -- -40C is pretty damn cold.)

algebraist said:

Hate to say it, but that makes sense to me. I'll put the multimeter on it when the replacement comes in and I'm working on it again. The coldest it's likely to ever get in my grow tent is maybe 60F, so hopefully that's warm enough to keep the voltage requirements under 23.8V per strip (which is roughly 215 / 9) at 700mA. Otherwise I have trouble. (On the other hand I think there's reason to be optimistic -- -40C is pretty damn cold.)

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You're actually better off running drivers a fair amount below their rated power anyway, because they'll last longer. They get quite hot when run at maximum, at least mine does.

Ugh. The short story: I replaced the "bad" strip, and got just about the same behavior.

I tried to measure the voltage across a strip at startup, but it's tricky -- you have to be quick, because the strips heat up fast, and you're trying to look into a multimeter that is essentially backlit by the sun -- the damn things are bright. So the best I got was somewhere around 22V, which should be fine.

First I tried that with my known "bad" strip in place. After maybe 2 seconds I heard the horrible "zzzzt" of electricity shorting out; here is that strip now:

There was a screw in that hole; the gray you see is Arctic MX4 thermal compound, which is supposed to be non-conductive.

So then I replaced the strip, and saw it light up with two dead LEDs:

Notice that two more further down seem excessively bright. Shutting it off, those other two glow a little longer than the rest:


and then they don't light up so brightly anymore:

So, where to go from here. Do we really think it's a matter of not enough voltage from the driver -- would that cause these kinds of problems? These pictures are with the strips dimmed down, so they aren't using anywhere near the max capacity of the driver (since the required voltage decreases with a drop in the current), but I also had them turned all the way up at various times, so maybe that did damage. As far as not running the driver near its maximum capacity, Meanwell's data sheet for the driver shows that it runs most efficiently near the maximum capacity, so I thought that was pretty much the goal... But I can rebuild the lights to have 8 strips if I need to. Could it be a grounding issue -- my solder connections are buried under electrical tape, but I could cut that away and take a look if that sounds like a possibility.

Sorry to hijack this thread...

I have two questions:
- what is this white spot on my COB? COB is working normal.



- is this COB dead (look at - side) or it can be powered up?

DirtRunner said:

Two of 8 EB strips (1120mm) I got from Digikey were damaged. Several of the quick-connect caps were broken off and were not in the packaging. Four or 5 chips toward the center of each strip would not light. The strips were very well packed and there was no damage to the box in which the strips were sent. Apparently, the strips were handled roughly before packing for shipment.

Digikey was great about sending replacements. The only questions they asked were directed toward preventing future occurrences of the damage, so it is disappointing to hear it happened again. I will still buy from Digikey without hesitation.

Click to expand...

Same for me and my 1' strips. But replacement arrived just two days later!

algebraist said:

First I tried that with my known "bad" strip in place. After maybe 2 seconds I heard the horrible "zzzzt" of electricity shorting out; here is that strip now:

There was a screw in that hole; the gray you see is Arctic MX4 thermal compound, which is supposed to be non-conductive.

Click to expand...

For me, that looks more like a damaged cable (a 215V spark jumping on the screw), than a problem due to MX4, it's definitly not electrically cunductive.

Serva said:

For me, that looks more like a damaged cable (a 215V spark jumping on the screw), than a problem due to MX4, it's definitly not electrically cunductive.

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Interesting. I suppose the spark could have come from the wire -- it's 18 AWG solid wire, and you can see in this picture (copied from above) that it is relatively close to the screw:



I had assumed that it came from the strip itself, but I'll look more closely at the wire for damage. Thanks.

Looks like you may have broke the solder mask, shorting across those two copper planes, which provided the full/higher voltage to those LEDs?

Also, I would only use the screws near the edge for mounting. If you look at the copper it is pulled back around those for this reason. The hole that shorted might be for optic attachment.