Led driver resistor blow out - Page 1
Forum section: electronics / repair

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 28, 2022, 07:15:25 pm
content: My dad has had some issues with this one particular LED can light and so instead of continuing to buy replacements I wanted to see if I could fix it. I found this what I think is fusible resistor(wire wound) that looks like it got hot and burned out. Anyone know what I should replace it with? The led driver is a 10w ish jobby so I figured like 1440 ohms would be 10w but I'm not an electrical engineer

author: tunk
author_rank: Super Contributor
timestamp: March 28, 2022, 07:33:42 pm
content: Diodegonewild@youtube recently did a modification of an LED bulb, andthe resistor was 10ohm. If you use a 1440 resistor I guess it will have to bea high wattage one.Edit: 10W means that the LEDs are 10W, not that the resistor should be 10W.

author: james_s
author_rank: Super Contributor
timestamp: March 28, 2022, 07:45:31 pm
content: The fusible resistor didn't just blow up on its own. You have to find the failed part that caused it to blow otherwise the replacement will blow up as soon as you connect power. It's probably the driver IC that failed. Your logic on the resistor value is way off, the wattage of the driver is unrelated, the resistor is probably a few ohms at most, just enough to limit the inrush, it is primarily a fuse.

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 28, 2022, 10:14:06 pm
content: I do know that when I put a larger resistor in place of it the light worked but the resistor got hot. It was a 3w I think.

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 28, 2022, 10:16:06 pm
content: My reasoning for the 1440 ohm resistors was just from the fact that the driver was rated for 20w and the whole circuits power goes through the one resistor. I suppose if I think hard enough it makes sense to use a lower ohm resistor

author: abdulbadii
author_rank: Frequent Contributor
timestamp: March 28, 2022, 11:09:50 pm
content: It'll be very very helpful if you try reverse engineer to acquire schematic at least around the fusible R

author: james_s
author_rank: Super Contributor
timestamp: March 29, 2022, 12:30:26 am
content: Quote from: CoopedUp on March 28, 2022, 10:16:06 pmFrankly it sounds like your understanding of electronics is not at a level where you should even be thinking about working on something that is mains powered. I'm not sure where you're getting that number, are you assuming the entire 20W is dissipated by that resistor? The resistor doesn't even matter anyway at this point, you have to find out what caused it to blow up. Resistors don't just blow like that without a cause.

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 29, 2022, 02:19:21 pm
content: Originally I was thinking that the resistor was current limiting the whole circuit but that would make it less efficient I think. The driver is 20w the light is 10w. If I can find what else is wrong with the circuit that would be nice. When it wasn't working at all the voltage at the output would be 20v ish then fall down to about 12 before jumping back up.

author: CoopedUp
author_rank: Regular Contributor
timestamp: March 29, 2022, 02:23:00 pm
content: And now that I think about it I had measured the continuity across that resistor before hand, I wanna say it was 20 or 30 ohms... As nd it didn't blow up until I heated the driver board up and turned it on. It worked for about 45 seconds then blinked a couple times then the resistor blew

author: james_s
author_rank: Super Contributor
timestamp: March 29, 2022, 09:29:40 pm
content: The resistor is a fuse, if it is doing any current limiting it is just the initial inrush when the thing is first switched on and the bulk filter capacitor has to charge up from 0V. The resistor has nothing to do with limiting the current once it's running, that is handled by the driver circuit. In almost all cases it is some form of buck regulator. Get out your multimeter and use the diode test function to look for shorted semiconductors.

author: thinkfat
author_rank: Unknown
timestamp: April 01, 2022, 09:03:48 am
content: I suggest to buy a different brand power supply.I have a feeling, that if you try repairing this one, the next thing we'll hear from you is an "emergency room" story. If anything at all.

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 01, 2022, 09:29:49 am
content: Most probable is the driver went k-boom!.

author: CaptDon
author_rank: Super Contributor
timestamp: April 01, 2022, 02:26:57 pm
content: Heated the driver board up??? Why?? As others have said that resistor is probably between about 3 ohms to maybe 10 ohms for inrush protection and is ABSOLUTELY required to be flameproof and not the typical carbon composition resistor. Reverse engineering still won't give you the original value used by the manufacturer, but seat-of-the-pants prior repair experience on these types of things tells us 'roughly' what value we would expect to see in that functional position of a typical SMPS.

author: simon mugo
author_rank: Contributor
timestamp: April 02, 2022, 02:40:19 am
content: you just said the LED keeps blowing off? For me i think the LED is receiving more current than expected. if the resistor gets hot too, this is another indication that the current flowing in the Circuit is much that it should be. Yopu need to check at all the components that make up this board. Ypu might think the LED and the resistors are wrong but maybe there is another fault such that even if you reolace the LED still it might blow off after some time. Just test the whole circuit to ensure that the circuit has no any other single fault. I had similar trouble and i found that a diode was also faulty.

author: amyk
author_rank: Super Contributor
timestamp: April 02, 2022, 11:58:38 pm
content: Are the LEDs actually being driven at 10W ? What arrangement are they in?

author: CoopedUp
author_rank: Regular Contributor
timestamp: April 03, 2022, 02:40:37 pm
content: The LEDs are in series, I tested just the lights first with my power supply and they turned on around 31v, at 38.5v the LEDs draw 9.8 w I can't remember what voltage the driver was running at now but I think it was in the low 40s

author: james_s
author_rank: Super Contributor
timestamp: April 03, 2022, 06:07:53 pm
content: The driver is a constant current source, it regulates the current and the voltage goes to whatever forward voltage the LEDs have under those circumstances. The voltage will vary significantly depending on the temperature of the LEDs.