Constant current LED driver repair or replacement - Page 1
Forum section: electronics / repair

author: axero
author_rank: Regular Contributor
timestamp: October 26, 2017, 03:04:49 pm
content: I have a wallwasher with an LED driver that appears to start to give up the ghost. I have noticed that the lamp is starting to blink on occasion and the LED driver gives off a high-pitched noise.I could choose to find a replacement driver but I have a hard time finding matching voltages. It is rated for 38W, and a nominal voltage of 43V. More specifically, it's voltages ranges over 36-43V while maintaining a current of 0.9A +- 5%. I measured up a voltage of 38.7V with a multimeter. It looks like so;https://ibb.co/mNwXWRAnother option could be to replace all electrolytic caps and transformer circuits. While caps may be easy to come by, proper transformers with the right number of windings may not be so easy to find. If I take it apart, I'm not sure as to whether it will maintain its IP67 rating. It is sealed with glue, not silicone gaskets.

author: Gregg
author_rank: Super Contributor
timestamp: October 27, 2017, 12:56:57 am
content: I ran across a similar problem when converting a light box to LEDs. The fleaBay LED driver was overdriving the LED modules but I grabbed some nichrome wire and with some clip leads found the proper length for the needed resistance to limit the current to the desirable level. Then I tinned the ends of the nichrome with 3% silver lead free solder and acid flux and soldered copper leads with the same solder (but not the acid flux). Then I enclosed the nichrome in a fiberglass spaghetti tube which I strung around the edges of the light box using silicone sealant in small blobs every 50 to 60 mm. I think the nichrome tested to about 2.3 ohms cold. The flexible fiberglass mesh tubing allows the heat to escape from the nichrome wire.

author: sokoloff
author_rank: Super Contributor
timestamp: October 27, 2017, 01:35:52 am
content: I did not think transformers "wore out" or were a particularly likely component to fail.

author: axero
author_rank: Regular Contributor
timestamp: October 28, 2017, 01:11:29 am
content: Apparently a Chinese transformer is likely to fail prematurely. I have a china made lamp that had the power supply fail on it. It was a complex circuit with unmarked components but after googling for the voltage controller IC, I saw a "recommended configuration" in the datasheet that looked exactly like the circuits in the PS. So now I knew how the components were supposed to behave. It turned out that it was the transformer inside the circuit that had failed. I could not find a replacement transformer anywhere. So I bought instead a new MeanWell PS and fed the voltage from it directly into what I believe must be some kind of constant current driver circuit. I knew from the datasheet that the voltage is supposed to be 12V. That was a lot cheaper than if I would have to buy the components. It is still working, and if the PS should fail, a small 12V replacement will not be hard to find.Now this LED driver is a bit trickier because, 1. space is rather limited unless I'd let the PS be outside the lamp and 2. the current PS is sealed with some kind of glue that looks impossible to take a part without destroying it.I don't know much how LEDs operates, but it seems that voltage doesn't matter to the LED. What does matter is the current. That makes me look upon electricity and voltage from a slightly different perspective. But that confuses me a bit as I believe that even LEDs are sensitive to ESDs. So I'm not entirely sure how it all fits into the equation.But I guess what matters here is that the amperage is 900mA ± 5%. For that to be achieved, 38.7V was measured over the circuit. That would make me assume that the impedance, or resistance of the load is 43\({{\Omega}}\).Now, this is a bit tricky because since the driver maintains a constant current and if that current is too strong and I choose to drop the voltage with say a series resistance circuit, then the power supply will try to drive up the voltage to compensate for that load. So I guess that I will have to match the amperage.When thinking about it, maybe a parallel resistance may help drop the current. Kirchhoff says so. I found for example an "LED power supply 50W 6-48V 1050mA ; MeanWell, LPC-60-1050". It most likely is too big to fit but let's use it for calculational purposes. We know that the voltage should be 38.7V, at this voltage we want to deduct 150mA from the circuit. So the parallel resistor should be 258\({{\Omega}}\) and be able to handle a power of at least 0.6W. A resistance like that may be hard to achieve, so then we have the question of what amperages can the LEDs tolerate? Perhaps it is better to hit a lower threshold than a higher. I guess that the more current you drive through the LEDs, the lower the life span.

author: Gregg
author_rank: Super Contributor
timestamp: October 29, 2017, 03:12:39 am
content: When I put a constant current LED power supply in the light box, I got one rated for 40 watts because I was using 4 of the 10 watt COB LED modules in series. When I connected it all together it was drawing over the specified amperage of the LEDs. 5 of the LED modules in series wouldn’t light at all. So I tried the nichrome wire in series and slid a clip lead along it until the correct amperage for the LEDs was obtained and then gave it a little more length to ensure long LED life. The resistor in series did reduce the amperage.The Chinese LED drivers are inexpensive, give one a try and if it works, buy a spare.

author: axero
author_rank: Regular Contributor
timestamp: November 01, 2017, 09:45:49 am
content: I don't understand this. If you add a resistance in series with a load that is connected to a power supply with aconstant voltage, then yes, you will get a lower amperage the higher the resistance in series.With aconstant currentpower supply otoh, if you add a resistance in series, then the supply will increase the voltage to compensate for the changed load in order to maintain the constant amperage. If it doesn't, then either it isn't working or it is not a constant current driver, or it is maxing out at the upper end of its voltage range.

author: SparkyMarky
author_rank: Newbie
timestamp: August 06, 2019, 10:18:26 pm
content: Consider giving Universal's Everline LED driver's a try. They are universal out of the box, and can be programmed to mimic any of the OEM LED driver. The best part is you don't have to wait for it, your local electrical supplier should have them in stock.https://www.willowelectric.com/led-driver-replacement/