Put LED's in cluster, insta-blows #1 fuse - PeachParts Mercedes-Benz Forum

jgilroy · #1 04-17-2010, 11:26 AM

I swapped just the two illumination lights in my cluster with LED's from LEDLight.com (these: http://www.ledlight.com/t10-wedge-5-ultra-bright-smt-led-light.aspx)

My #1 fuse insta-blew with the LEDs in. Replace fuse, poof again. Put the old incandescent lights back in, and so far it's fine.

Any ideas? Thanks.

4x4_Welder · #2 04-17-2010, 11:30 AM

Check the resistance of the LED lamp vs the incandescent lamp. One or both may be shorted

Matt L · #3 04-17-2010, 11:41 AM

If it looks shorted to an ohm meter, the LED is bad. However, because it does not look like a short does not tell you that it is good. Modern ohm meters present a fixed current and measure the voltage. A diode has a forward voltage drop, so it will look like a resistance to the ohm meter (rather than the semiconductor that it really is). Ohm's Law, I=V/R, does not apply to the diode, as the diode is not ohmic.

okyoureabeast · #4 04-17-2010, 12:15 PM

Make sure the leads on the LEDs match that of the original incandescent bulbs. When I got mine they were bent all the way back and I stupidly burned out my rheostat.

jgilroy · #5 04-18-2010, 08:36 AM

My meter has a "diode" setting and I believe they are reading good. With the leads connected in either polarity, the reading is the same as with the leads held apart. I don't know if that's good, but I know it's not a short.

I'll try to apply 12V to them outside the car and see if they glow, but if they're just "bad" and not shorted, could they blow a fuse?

barry123400 · #6 04-18-2010, 11:59 AM

Just in case you are not aware. You have to use a dropping resistor with leds operating from a twelve volt supply. I assume if you did not they should be toast now.

cewyattjr · #7 04-18-2010, 12:07 PM

Also check the contacts on the LED. I had this same thing happen (instant short out) and it was because the LED contacts aren't a match with those in the cluster. There were four contact wires on the LED component, a pair on each side of the "fin." I had to fiddle with those LED contact wires and remove one specific "lead" on each side to keep it from shorting out. Do you think this could be the issue?

Chuck

jgilroy · #8 04-18-2010, 12:20 PM

thanks barry. i didn't hook them up to 12V yet. i guess i won't do that.

i'll have to pull the cluster again to see what the incandescent leads look like. if i can explain the leads on the leds.. it's like one long lead comes out on each side of the "wedge" and wraps around the wedge base and up the other side. they are nowhere close to touching.

cewyattjr · #9 04-18-2010, 12:26 PM

Yeah, I'm pretty sure that it is the configuration of that lead wire that is causing the problem, and that you need to modify it slightly in order for the polarity to "match" rather the directly connect the +/-.

JimSmith · #10 04-18-2010, 12:28 PM

I have not dug into the dash lights for a while, but some things I would check are the Watt ratings of the bulbs you took out. Are they significantly different than the ones you are putting in (1.5 Watts each)? Also, check to see if the bulbs you bought have a built-in resistor. Most LEDs work at 2-4 Volts, and the bulbs have to have a means to drop the voltage from 13.8 or so to under 4 Volts. The manufacturer suggests it is rated for 13.8 Volts, and the kind that have an integrated resistor should work directly. Seems odd though that you blow the fuse if the lamp is not defective.

There may be another issue, that the current rise with an LED is much faster than the incandescent bulb and the fuse may be blowing based on current rise (they turn on faster). You might try turning down the dimmer a bit to add some conventional drop to the system to slow it all down.

Jim

JimSmith · #11 04-18-2010, 12:32 PM

Quote:

Originally Posted by jgilroy

thanks barry. i didn't hook them up to 12V yet. i guess i won't do that.

i'll have to pull the cluster again to see what the incandescent leads look like. if i can explain the leads on the leds.. it's like one long lead comes out on each side of the "wedge" and wraps around the wedge base and up the other side. they are nowhere close to touching.

You have to look at how the socket is configured. If there is a broad contact on each side, then you have a chance at connecting both sides together, outside the LED itself, which will blow the fuse. Kind of like you have a wire connecting the socket terminal on one side to the socket terminal on the other side. Maybe two, actually.

Jim

4x4_Welder · #12 04-18-2010, 01:18 PM

Those led clusters are designed to operate on 12v, so no worries about blowing them. If they ohm'ed out as good, then it's probably bridging the contacts.

jgilroy · #13 04-18-2010, 04:07 PM

thanks everyone! pulling the sockets out again armed with this guidance made it obvious what was going on. i tried to take pictures, but it was hard to get the details in focus. anyone looking to do this in the future should make sure that the lead doesn't wrap around the wedge. straighten the lead and cut it off before it wraps around the bottom. you should only see one lead on each side of the wedge.

cewyattjr · #14 04-18-2010, 04:16 PM

Right, I recall that. They just are assuming a totally different physical location for voltage contacts, so they come "booby trapped" unless you mod them. Enjoy the brightness!

JHZR2 · #15 04-18-2010, 04:49 PM

So what car was this for? What is the benefit? I find it somewhat funny to replace incandescent bulbs with an efficient LED and a ressitor, which just wastes electricity to heat anyway...

But if this is a fix for notoriously bad w123 lighting in the cluster, hey that's great.