[habeeb]

Hi guys, trying to get this LED unit fixed, so it doesn't go in the garbage..

I tried to PM knna , but no reply?


here's what I know might be the problem, problem is I don't use soldering irons, so I need to know what to tell someone..


"I talked the other day again with EVO's designer, he told me currently they use 24V strings and that it avoid the problem of current unbalancing. It happened on the first batch which uses 12V drivers, the unit of Habeeb, especially when some final solder points were cold."

"With low voltage strings, small absolute differences in Vf does a large difference in percentage. At about 7.7V each string, just 0.1V difference is about than 1.3%. Small differences in percentage leads to large differences in current. Over 3% is difficult to manage and the problem aggravates as the lamp gets hotter.

I've noticed the brightest string is the closer to the input wire, so there is the possibility the problem is the final solder points between the 3 pieces are not well done. It is very plausible because those solder points are done when the lamp is already mounted on the heatsink, so it is difficult to get the area hot enough. You can check easily if it contributes to the problem. Just take a voltmeter (or a multimeter on V on DC position) and put the pointer at each side of the two solder points. A cold solder point might add electrical resistance. If so, you will see some value on the display (it should show 0.0V if the solder point is good) and depending of the value, it may explain the problem and would be very easy to repair (just rework the solder point).

If not, I would ask for a change for a unit working fine. If I understood well the designer, now they use 24V strings and it should minimize the problem. Anyway, I will call him tomorrow or on Monday and suggest him to add a current balancing system ASAP. It is sad a good unit fail from a problem which can be solved cheap and easily. "

discussion

[rives]

Habeeb, I remember the thread that this was posted in, but I don't recall seeing if you ever got the voltage measurements. If cold solder joints are the problem, the joints simply need to be melted again so that the solder can reflow and rid themselves of the structural disruptions that result in cold solder joints. This can be difficult because they are attached to the heatsink, and of course, it's function is to move the heat away from where you want it. This requires a relatively powerful iron (with a grounded tip so the device doesn't get power from the iron applied to it) that can apply more heat than the sink can quickly move away.

Cold solder joints are usually fairly easy to spot - they don't have the shiny appearance of a good joint, and sometimes you can see that the exposed grain structure looks coarse rather than smooth.

[habeeb]

^ rives, thank you for the comments.. much appreciated.

would you mind looking at the points and seeing if they need re-done? the problem ot me, is why are both LED's doing it, it must be something else then the solder points, no ???

voltage measurements, I can get, please just tell me how to check them, as I am horrible with meters, electronics are not my specialty.. do I use the meter while the light is on? does it matter the red or black probe what is touching what connector?

problem is while these work, there basically junk, as I want a light that actually is balanced.. I just don't want to throw it away, as it feels like there's some value to it.. also my stress levels need to stay down, and the main point is, what do I do with the piece of junk I don't know how to fix..



( pics in al ittle, server not liking my pictures )

I'm not clear what is wrong; are one (or more) of the LEDS actually completely dark, or is it a balance issue, I mean is one lamp or array brighter than others?

This lamp uses a single output supply to drive parallel strings which is amateurish at best and destined to fail. Your best bet is to find someone who is a tech or has a lab at work to check the power connections and reflow the solder. It should work as before. Note if you don't have experience and the proper tools, iron, hot air, you can damage the LEDs easily.

If you aren't trained in basic DC circuits it is impossible to explain how to troubleshoot with a voltmeter over a forum, sorry. I would say to start at the input to the board where the 2 wires from the Power supply connect and measure here. You are expecting 6-12V or so (I think you mentioned 7.7V), so set the meter on the appropriate range (if not autoranging). Leave the negative probe here on the ground wire and use the positive one to work your way down the power distribution of each array (cluster) and find where the voltage drops. If no joints are bad each array will have full 7.7V and all the grounds will be close if not dead on 0V.

I hope you get it going but if not I'd pitch it and get a better light. Maybe its worth fooling with by modding it, but I wouldn't waste my time, honestly. It really is a piece of crap IMO. Sorry.

[Hammerhead]

Im not sure what array you have 12? 24? I would check ea string make sure you have 24v on ea string. If you have a solid 24v on ea string. You might have some leds that have cold solder joints or other components gone bad. Like said very difficult to troubleshoot when its not in front of me.

The pic shows a single Meanwell ELN-60-12D supply which is a single output supply 6-12V 5A if you look it up. SO he ain't gonna have 24V anywhere.

[Hammerhead]

He mentioned that they use 24v now I dont know if they sent him a new one of those??. I think this is not the first time this unit had issues ?? But same troubleshooting would apply. Pics are from 9/2011

[rives]

Originally Posted by habeeb

^ rives, thank you for the comments.. much appreciated.

would you mind looking at the points and seeing if they need re-done? the problem ot me, is why are both LED's doing it, it must be something else then the solder points, no ???

voltage measurements, I can get, please just tell me how to check them, as I am horrible with meters, electronics are not my specialty.. do I use the meter while the light is on? does it matter the red or black probe what is touching what connector?

I think that the only way that I might see anything in a picture is with a macro lens (maybe). Strat did a good job of explaining the test procedure - keep the negative (black) lead on the input connection, and probe your way through the circuit with the positive (red) probe. Cold joints could cause the problem in both led's if they had something faulty in the manufacturing process and the problem was common to both units. No, it doesn't matter which probe goes where, it is just easier to keep things straight if you keep the color and polarities straight.

Strat, if I remember correctly, he was getting a wide variation in the output of the leds over the length of the fixture - I think that they dimmed substantially the further you got away from the power connection.

[Hammerhead]

Does that 12v power box have any caps in it??

[Shafto]

While bad solder joints could contribute to this problem I think that the cause for issue is the voltage drop along the power rails. They're probably much too small on a 1oz board to carry 5A.

Could also just be imbalance from the LED strings.

Depending on the problem there might be a couple things you can do to help, like soldering on some wires in parallel to the power rails to beef them up, but if it's bad string imbalance, you can't do anything but completely rebuild it with proper constant current drive of separate series strings of LEDs.