Strange LED tail light happenings

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james
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Strange LED tail light happenings

#1

Post by james » Mon Jun 20, 2011 2:41 am

Hello to all,
I installed a LED (1154) type light in my tail light. 1952 6 volt system.
Battery voltage 6.40 ok. Turn switch to on, hit brake pedal, brake light works fine, nice and bright even with switch turned to headlights, everything works great. Start the engine, hit the brakes and brake light flashes for a split second then its out. Checked voltage at brake switch, ok, checked all grounds ok, checked for voltage drop none. Engine mounting points to frame are bare metal to metal. All grounds are perfect. Voltage at taillight assembly is the same as all other lights. Voltage is not an issue, max voltage from generator is 7.30 volts. I tried hooking up a trickle charger with the engine not running and the voltage peaking at 7.60 volts and the brake light still works fine as long as the engine is not running.
Reinstalled the 6 volt 1154 bulb and it works fine all the time. Tried another LED tail light bulb and it does the same thing as the other one. Maybe someone has run into this before.
Need an electrical guru here. I'm thinking a diode of some sort. Thanks for any help here.

Jim



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Re: Strange LED tail light happenings

#2

Post by steve_wood » Mon Jun 20, 2011 2:15 pm

Jim:

What is the voltage at the tail light with the engine running?

I wonder if the engine vibration is causing a bad connection somewhere in the tail light circuit.... Any chance you can set up test points so you can quickly check the voltage all the way from the tail light to the ignition switch?

I had a lot of issues with the actual brake light switch and how it interacts with the brake pedal... perhaps take another look at that....

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Re: Strange LED tail light happenings

#3

Post by mbskeam » Tue Jun 21, 2011 5:28 am

you might need a diode on each lead.
one on the runnin light and one on the brake side, LED's like this will bleed back thru....
ask me how I know.

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Re: Strange LED tail light happenings

#4

Post by james » Tue Jun 21, 2011 12:57 pm

Mike,
I'm thinking the same way, so I'll ask
how do you know?

Jim

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Re: Strange LED tail light happenings

#5

Post by FlatHeadSix » Tue Jun 21, 2011 2:21 pm

guys,
The "D" in LED stands for diode, so you already have a diode in the circuit. Diodes are "one-way", current will only flow through it in one direction, so they are sensitive to polarity. Try reversing the leads and see what you get. Some of the automotive LED replacement bulbs will not allow you to do that very easily becasue the bulb base will always be the grounded side and the contacts will always get the "positive" voltage from the battery. The problem is that some of them are not internally wired correctly for our application and you will get the problems you are describing here. If you can't reverse the leads then try a bulb from a different manufacturer.

mike

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Re: Strange LED tail light happenings

#6

Post by james » Tue Jun 21, 2011 3:44 pm

Thanks Mike,
What I don't understand is why does the LED light works fine when I hit the brake key on engine not running. But when engine is running the LED will flash for a split second when I hit the brake. Stays off.

I think I will try another manufacturer, do you know of one I should try.

Thanks again, Jim

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Re: Strange LED tail light happenings

#7

Post by Dave_R » Tue Jun 21, 2011 10:02 pm

If you have a mechanical regulator (one with points and coils), that may be an issue.

Or, possibly back-feed from any coil, including the ignition could cause this?

Could be any number of things, even the generator itself.

Try disconnecting the wires from the generator and run it for a few minutes and see if that narrows it down.

- Dave

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Re: Strange LED tail light happenings

#8

Post by jdpan » Tue Jun 21, 2011 11:14 pm

I never had any luck with LED tail lights so I filed them under J for Junk...

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Re: Strange LED tail light happenings

#9

Post by mbskeam » Wed Jun 22, 2011 7:52 am

so I had bleed thru from the brake side messing up the function of the light.
I could see the diode in the bulb, but as they are ALL made in tiwang. who the hell knows if its even hooked up....
I put a diode in line with each wire. problem solved....

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Re: Strange LED tail light happenings

#10

Post by awander » Wed Jun 22, 2011 8:38 pm

The LED automotive bulbs that I have taken apart are all very cheaply made. They basically light all of the LEDs thru a large resistor when just the taillight is on, and then add additional current to light all of the LEDs more brightly when you hit the brake, through another resistor and a diode. The diode is there to prevent the 2 circuits from feeding back into one another, I think.

It is very possible that the "dirty" voltage you get when the engine is running is messing up the LED circuit. You could try adding 2 small capacitors right at the taillight socket, 1 from each contact to ground. I would try a 1uF or 10uF cap.

Andy

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Re: Strange LED tail light happenings

#11

Post by FlatHeadSix » Thu Jun 23, 2011 12:36 am

wow, all the comments since my last post are very accurate observations, and good information.

LED's operate on direct current, ONLY, and as I said earlier the current will only flow through them in one direction, they are diodes and they are what they are. The "dirty" current in a motorcycle charging system that was mentioned earlier is actually alternating current similar to the 110 volt you have in the house and is usually the result of a mechanical voltage regulator doing its job, that's how they work, and again they are what they are and you can't change or fix that.

As I said earlier one of the things you can do is to try a different brand of LED automotive bulb, as mentioned, some of them have resistors and additional diodes already wired into them, but some don't.

The other thing you can do is to add your own diodes, make sure you have the "direction" correct (polarity) so that the additional diode will allow current to flow through the LED bulb. If it doesn't work the way you have it installed, turn it around and see how it works if installed in the opposite direction.

Watch out when installing capacitors, they function as filters and act very much like rechargeable batteries by absorbing excess voltage, all they do is charge and discharge very rapidly. They are effective in controlling the voltage spikes that occur as the result of the secondary current produced by the coil each time the plugs fire. If you are still running points in your ignition you already have a capacitor in the system to take care of that, if you are running an electronic ignition you may want to add something like a radio-suppression capacitor on your coil.

mike

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Re: Strange LED tail light happenings

#12

Post by awander » Thu Jun 23, 2011 1:52 am

Points igi=nition is very noisy. the condensor or capacitor in the system is not there to get rid of noise, but rather to change the characteristics of the coil (LC) circuit so that it works properly.

A small capacitor at the taillight wil certainly do no harm, and may solve the problem-it is sure worth a shot. The only downside I coud see to it is the light will not go off instantly.

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Re: Strange LED tail light happenings

#13

Post by james » Sat Jun 25, 2011 2:12 am

Ok friday night bulb check, here's what I have so far.
All voltage and ground checks are ok.
All contacts at tail light and brake light ok
No major voltage drop with key on or engine running.
No voltage spikes either way.
Engine running charging at 7.30 to 7.50
Consistent charging rate.
Ground at bulb same as at battery.
Ran seperate ground to bulb socket no change.
LED bulb will stay lit with headlights on engine running.
As soon as you hit the brake pedal the brake light part lights for
a split second and the entire light goes out.
I like the brightness of the LED it really shows.
I will try the diodes inline with the wires before I spend
more money on a different manufacturer LED light.
Those suckers are @ $30.00 so I would like to get them to work.
I'll let you know what happens.
For those of you how would like to try LED lights in you old beast.

Thanks for everyone's thoughts on this matter
Jim

Now since I'm done playing, I'll have a beer while the wife is watching that Casey
Anthony trial and there's more time to sit in the garage and ponder.

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Re: Strange LED tail light happenings

#14

Post by james » Sat Aug 06, 2011 2:21 am

sorry for leaving you hanging on the results to this fix but I have to get a crack fixed at the cam bushing. Don't want to run this engine any more till it's fixed. I'll do more experimenting with the led using your suggestions after the engine is in order.
Thanks for your replys to my light issue.

Jim

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Re: Strange LED tail light happenings

#15

Post by awander » Sat Aug 06, 2011 4:17 pm

james wrote:Hello to all,
I installed a LED (1154) type light in my tail light. 1952 6 volt system.......
Jim
Hi Jim:

Wondering where you obtained this particular 6V LED taillight bulb.

Does it have the Red LEDs facing rearward, and the white ones facing outwards (for the license plate light)?

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