LEDs on trailer not work correctly H.E.L.P.

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Gannon
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Post by Gannon » Wed Jan 19, 2011 5:20 am

When you buy LED trailer lights, you can actually specify if you want positive or negative common. This may be the key to the problem

Can you do a drawing of how you connected the diodes to make it work? I wouldn't have thought that you could use a diode to fix it. (assuming that the lights are wired like i imagine they are)
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steptoe
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Post by steptoe » Wed Jan 19, 2011 3:54 pm

Gees, Sven , don't give up too easily.
If these lights bought from Kmart for $8 each as a clearance item had an earth for each circuit in the stop/tail combo light the problem would not have happened (and no internal bridge or share of that earth)

Gannon, I cannot do those impressive drawings you so easily whip up or borrow from some where. Pics can be tricky as process seems to alter every time I have a go.

Simply that 1N4007 diode went in the POS brake light power line to the stop LED red lead with the silver ring end at the LED end. Still shares common black earth with tail and that also junctions with indickator earth.

Someone once said don't try and understand electronics, just know what does what but not how :)
This diode got spade terminals at each end and just stuck it in the wiring junction box I fitted at rear of each light, heat shrink tubed it and bingo

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Wagonman
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Post by Wagonman » Sat Dec 10, 2011 6:53 pm

Crap.. i may have the same problem. I'm fitting these Chinese Road-boy LED tail lights onto my tyre carrier cos i got them for free :D

They have got the brake and park in the same set of LEDs and a common earth wire.

Everything works when 'bench tested'. However when you hook the LEDs to the car (L series) the park lights dont work at all even with power to them and the brake lights only work when the park lights are switched on (ie have power but arent on)

Correct me if im wrong but does this sound like the same problem steptoe had and just requires a particular diode in the brake feed wire?
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steptoe
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Post by steptoe » Sat Dec 10, 2011 9:42 pm

Bench testing was fine, go the Subaru hook up and went to poop.

Not same problem I had but try the cheapy diodes and see if they can do the trick!

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pitrack_1
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Groundings

Post by pitrack_1 » Sun Dec 11, 2011 1:07 am

Steptoe,

from what I understand from what you've written, originally the brake lights would work but the tails wouldn't. Also that the tails/others are ground-switched and the brakes are power (+ve) switched.

LEDs are Light Emitting Diodes. They allow current to (normally) flow one way, like normal diodes. So polarity is important, they'll only work one way.

It is sometimes the case (I believe) that when a circuit (brake in this case) is not activated it is switched/shorted to ground. Flashers too I think.

If this is the case, then when the tails are active, rather than grounding through the LEDs they may be grounding back through the (inactive, but grounded) brake circuit.

Now the diode you put in the brake circuit fixes the problem because it allows the 'forward' brake light current whilst preventing a 'reverse' current flow grounding from the tails back though the inactive brake light circuit. The reason the fuse doesn't blow is I suspect because of current-limiting resistors in the lamp units.

A multimeter should be able to confirm this.

Ahhh, could-bees, maybes, should-bees....

Similar to the old trailer lamps with festoon bulbs that, when there was a bad ground or connection, the tail lamp/brake lamp would flash when the flasher were on, or the flasher would only work when the brakes were off, or both tail/stop would glow dimly together, etc. as power from one circuit grounded through the other. This used to drive (sorry) me crazy.

Ta also for the ADR reference.
Patrick
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steptoe
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Post by steptoe » Sun Dec 11, 2011 7:20 am

yep. have since found a few other wires in the subies that change gender depending on switching of ignition from off to acc to powr or individual switches and nothin' blows ! So, getting used to it now, checking the behaviour of a wire through all ignition switch functions before using it !

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Wagonman
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Post by Wagonman » Sun Dec 11, 2011 6:10 pm

This sounds good in theory.. But how do i check this with my multimetre? Also are you saying putting that diode in there is the fix?

Thanks for the explanation though! :D
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RSR 555
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Post by RSR 555 » Sun Dec 11, 2011 6:24 pm

IMO the best way for you John is to use the wiring that goes to your towbar plug. As this is a positive feed (then earthed after the lamp on your trailer), so you can use the positive feed through your LED light then earth to the body inside the car somewhere.
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Wagonman
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Post by Wagonman » Sun Dec 11, 2011 8:50 pm

see that dude at the computer in your avatar.. that was me against my rear bumper. lol Ill throw in those diodes when i get them, onto both the park and brake feed wires and go from there.
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steptoe
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Post by steptoe » Sun Dec 11, 2011 9:56 pm

multimeter? who used a multimeter? I just tied the diode into the equation and found which way and where and was sorted.

None of this crap would happen if each circuit in the LEDs had an earth of its own.

Mine is fine, fixd it ages ago - long enough for the Monza lights clear lens to go milky white due to environmental exposure over winter!!

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RSR 555
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Post by RSR 555 » Mon Dec 12, 2011 4:16 pm

Wagonman wrote:see that dude at the computer in your avatar.. that was me against my rear bumper. lol Ill throw in those diodes when i get them, onto both the park and brake feed wires and go from there.
That's why he's there.. it's just representing me working on cars :confused:

Yeah, those diodes sound like the go. Pop into Jaycar and let us know how it turns out.
steptoe wrote:None of this crap would happen if each circuit in the LEDs had an earth of its own.
I'm hearing ya Jonno.. must be designed for sh*t cars like Falcommodores :mrgreen:
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Wagonman
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Post by Wagonman » Tue Dec 13, 2011 7:01 pm

Hooray! Problem solvered.. Got some 25c diodes and put one into the brake feed and one into the park light feed and they are all happy :D as am i lol.

Thanks for your help Steptoe, Paul and pitrack_1
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RSR 555
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Post by RSR 555 » Wed Dec 14, 2011 9:19 am

Wagonman wrote:Hooray! Problem solvered.. Got some 25c diodes and put one into the brake feed and one into the park light feed and they are all happy :D as am i lol.

Thanks for your help Steptoe, Paul and pitrack_1
Awesome John. Can you post the details (where from and possibly part number?) of those diodes, so others can find some if they need then. Cheers
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Wagonman
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Post by Wagonman » Mon Dec 19, 2011 10:51 pm

I went to Jaycar and some 400V 3A diodes part number: 1N5404. A bit over kill for leds in a 12V system but they do the job sufficiently.
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