Checking COB for broken connections in LES. Handling COBS

Just some random info. Please feel free to correct me or post anything

To summarize
1) Handle COBS with care while installing cob and while removing glass lens. Good to read read these if you doing first DIY
AN 31 Bridgelux handing Vero
Cree CX Soldering and handling
2) If you bought a new COB light or made your own and see a cob that is less bright. It is pretty easy to take pics of Light Emitting Surface (LES). I use my phone camera and put my sunglasses in front of the phone camera.

A typical single diode LED, which has a hard epoxy case. They are pretty tough and don't go bad if you drop them.
However it is pretty easy to damage COB LES (Light Emitting Surface). The yellow phosphor resin area or the LES can easily get damaged if you drop anything on it. The LES has tiny connections that connect the multiple diodes within the COB. These connections can break due to stress or impact. The impact of a small M3 screw falling from an inch height may not be enough. However its best to avoid any stress on LES for maximum reliability and longer life of COB.

In this example we see how a string connection was broken after I accidentally dropped a glass lens from a height of about 1 inch on the LES. The side of the lens hit the LES breaking the string connection. Such damage can happen if you are not careful during your DIY build or if the manufacturer of your light was not careful. When you turn on the light you cannot see these broken strings until you dimm your light to a very low current or take photo.


The COB still continues to perform however the efficiency goes down. I dropped the lens again on the other side to keep it symmetrical... just kidding. Will toss this COB out soon.


An interesting observation was that i did not see any noticeable change in current/ power. Indicating that the other strings were probably running at higher than average current, which would cause a decrease in efficiency. I measured this Vero 29 4000K COB(with 2 strings broken) against another Vero 29 4000K cob with PAR meter and saw about 10% less light with the damaged one. Veros are not binned and each Vero may differ from other in their output flux. Still 10% gives an idea.

Here is a pic from SDS post with welding mask glass. Perfect COBS

These arrays are parallel strings, makes sense why the cob continues to operate and why the power usage remains the same.

Hard to see in the pic, are those Veros mounted with holders? I see a while line around one of the mounting screws, just trying to figure out what that is.

@Rahz
No those Veros are not mounted with any special holder. Just Vero 29 cob with 4x M3 screws. I am not sure about the white line. I do not see it but could be some camera issue as the light was too bright.

Ahh, looks like the screws have a flange, was just a little brighter in one pic.

I've been lucky so far with no damaged cobs. My first lamp is going on 2 years now, 23 Vero 18s running above 50C and still going strong. I have played around with the LES a bit and the material isn't hard, a bit tacky actually. After running almost 2 years with no lenses the surface is still clean to my eyes. Maybe photons repel dust?

Rahz said:

Maybe photons repel dust?

Click to expand...

I think so. Radiation pressure

I find that welding glasses work best for close-up LES inspection...I even have the viewpiece from a Welding mask that I use for LES pics

Very nice.

This got me thinking, it's maybe worth looking into number of strings and diodes of different cobs, maybe there is good information on which ones might be the most durable overtime ..

I'm thinking more and smaller strings would be better ... why are the dies not all in parralell then ? Build simplicity ... cost reduction or some technical aspêct i'm overseeing ?

Thoughts anyone ?

excellent thread..gracias

Dimming makes photos easy to check die as well

Thanks for posting! I need to check one of my COBs now.

When I was screwing down the COB onto the heatsink, I had it in one of the IDEAL holders. It popped out of place momentarily and I didn't realize. I continued to screw down the IDEAL holder and I may have damaged it.

I don't really like the IDEAL holders, they're a bit tricky until you can figure them out.

The spring on ideal holders doesn't do a great job but at least you can secure the cob before applying the wires. Try pasting a cob and soldering, then screwing a holder down. Vero is a much better design IMO.

I've been playing around with brackets for holding 3070. They are small enough and simple enough that they can be cut with hand shears so no fancy tools are required. Two brackets per cob, each bracket straddles a corner. Two screws secures each bracket.

Have I tested it and does it work? Yes and yes. Cheap too.

Rahz said:

I've been playing around with brackets for holding 3070.

Click to expand...

If possible share a pic. I am not a fan of ideal holders either and do not know what else to use with 3590

EfficientWatt said:

Very nice.
This got me thinking, it's maybe worth looking into number of strings and diodes of different cobs, maybe there is good information on which ones might be the most durable overtime ..
I'm thinking more and smaller strings would be better ... why are the dies not all in parralell then ? Build simplicity ... cost reduction or some technical aspêct i'm overseeing ?
Thoughts anyone ?

Click to expand...

All COBS are durable. We just have to be careful not to move them or change lens or mess around with them too often. And just a little care while assembling the DIY light.
The smaller LES could be little more durable. 36V 3590 might be little more durable than 72V just because of more parallel strings.
Dies all in parallel would be tough because then you will have a Vero 29 that needs 3 Volts and 28 Amps instead of 40Volts and 2.1 Amps. 28 Amps is a big problem. Cant put no 16 gauge wire all packed in a small die.
Manufacturers decide parallel and series strings (I don't know what else to call it) based on optimal voltage and current. If all in parallel too much current. If all in series, dangerous high voltage(250+Volt DC) and if one fails all fail.

These particular brackets for the 3070 are aluminum and 10mm x 25mm, holes placed 15mm apart. The mounting holes should be positioned in a 15x36mm square. Cob is buttered and placed. The brackets are loosely screwed in and then all the screws come down together til snug. At this point the metal begins to bend so there's a lot of room to tighten down without excessive pressure. The screws can be further tightened until the bracket wants to start bending back on itself between the screw and cob.

I originally had the idea as a way to hold 3590 rather than design a whole new lamp for a larger lens. Then last night I was building one with 3070 using the plastic holders, trying to solder a cob slipping around on paste and then getting the holders screwed down. Grr. Then I noticed the thick wire jacket coming off the HGL driver prevented the holder from sitting correctly. Arrgh! So these same size brackets should work with 3590 and allow 78mm lenses though I don't know yet how it will affect the beam angle.