MTFCA Forum

Rather than tacking this onto the other LED thread, I just have a question. I noticed tonight with the 1920 roadster running in a dark garage that there is a very faint, barely perceptible flicker from my LED headlight bulbs with the light switch turned off. This seems to coincide with engine RPM. I notice it in both bulbs, on magneto or on battery. It is too faint to see in the daylight. Is there a potential short or is current being generated in the circuit from an adjacent wire?
The car runs fine.

Some times LED bulbs will glow for a few seconds and gradually dim. Does it stay on all the time when the switch is off? If so, you must have a high resistance connection to the battery when the switch is off. Maybe something in the switch has graphite or some other conductive substance on it.
Norm

I'm guessing your LED lighting is responding to energy radiated by the ignition system or the magneto. Either that, or your light switch has some metal dust in it that allows a very slight leakage of power between the switch terminals as Norm suggested.

LEDs can be very sensitive to small currents that are being "thrown around" by the flywheel magneto, that is also the reason that a digital multimeter is almost useless when working on a Ts electrical system, and an old analog meter works best. The flywheel magneto was a great idea in its time but todays fine electronics have a hard time dealing with the rather crude and unrefined way of generating electric current in Henry's model T.
It sometimes helps to solder a small resistor in the system as a kind of ballast to quench those unwanted flickers in the LEDs

Yes. Mine flickered while running. It drove me crazy. I was told that it was interference from the coils. I took them out and went with magneto bulbs.

The magneto while running puts out such a field that an AM radio within 100' will have static. It doesn't happen with the engine off, even with a radio very close to the car.
Norm

I have had a fluorescent drop light flicker on when it’s not even plugged in if the engine is running. It makes me wonder if that’s why Henry didn’t put radios in the model T. The flywheel magneto would’ve made it impossible to get any reception. L O L.

I believe the ignition would be more likely than the magneto to make the lights flicker.

Probably not related but here goes. I have LED's all around. Headlights, running lights and brake light. The tail light bulb has two contacts, one for running and one for brake. I believe internally there is something that just makes the LED's brighter when power is applied to the brake terminal. My issue was when I applied the brake, the headlights would come on dimly. Following a suggestion from a fellow who has dealt with this problem before, I installed diodes in both the brake and running light circuits (at the rear lamp), so a back feed could not occur. Problem solved.

If you have something that is normally powered on when the engine is running, is there a possible source of a similar back feed?

Noel,

There are a couple of likely explanations for the phenomenon you're experiencing.

(1) LED's are a diode, and diodes will rectify. Consider that when you apply an aerial to a 'crystal set' you typically use a diode to 'convert' a nearby radio signal (RF) into an audio output (AF) that you can listen to.

Model T's produce RF. The wire running from the lamp back to the switch (along with the connection to ground) will act as an aerial of sorts and pickup some of the RF, and the LED's could be simply responding to that.

(2) LED's are a low current device. If you have a leakage resistance, even if it's quite high, in your switch or somewhere in the lighting circuit it could well be enough to light LED's, but not incandescent bulbs. Even without a leakage per se the low current nature of LED's is another reason why they might respond to nearby RF, even if that's fairly low power.

LED's will also respond to changes in supply much more quickly than incandescent bulbs, therefore you could expect to see a 'flicker' if the LED was being intermittently supplied by RF from the coils. If this were the case I'd expect the flicker to change frequency with engine revs.

If it's a problem to you it may be easy to address with a capacitor from the high side of the LED to earth. I'd start with something like a 0.1uf and see if that made a difference. Some 'fault-finding' and/or experimentation may be required, but it's fairly simple stuff and could entertain you for a morning I guess.

Luke.

I think they are hollering, "Get me out of here. I don't belong in this outdated contraption!"'

Allan from down under.

I don't think it's a problem, as the car runs well. I only noticed it in the dark garage at night. I thought my lenses were vibrating and reflecting light until I looked closer.

Noel, recently I had my 11 in my shop for maintenance, anyway when I went to start it the first 1 coil buzzed and the volume on the 1980's boom box in my shop went to wide open, something it's never done before.
Another thing I've noticed is cows and horses reacting when driving by with a T running on coils. There is definitely stray voltage.

I think you need to SEE a doctor.

Aliens may be nesting in the coil box. Like fire ants, tiny Aliens are attracted to electromagnetic radiation. Of course, cows and horses have always been hyper-sensitive to Aliens.

The "modern car" led headlights I sell have extra circuitry to stop the flickering. LED's are just diodes and they are switching on and off at an insane pace. I know this information won't help you with the T bulbs but it's a real thing. Here's the link if you want to see what the bulbs are all about and what is missing from the cheaper ones. I TRIED to get them to make a set for Model T's but they were not interested.

https://www.auxito.com/discount/WTD?ref=sG3Pbc_5Dh__Hy

Tim,

I followed the link you posted. It did not offer any explanation of componentry used in those lamps that might prevent the flickering Noel has identified. It may be that I've missed something, so I wonder if you could post that detail here?

Thanks, Luke.