Electrical interference from magneto?

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Model T Ford Forum: Forum 2014: Electrical interference from magneto?
Top of pagePrevious messageNext messageBottom of page Link to this message  By James Elenbaas - Granger, Washington on Friday, May 30, 2014 - 09:23 pm:

On three of my Tís I have installed LED turn signals with the appropriate electronic flasher units. On one of the vehicles I have removed the magnets from the flywheel and the turn signals work great. On the other two the magnets are still on the flywheel but I am not using the magneto because they have distributors. On these two with the engine off the turn signals work properly. Upon starting the engine the flash rate of the signals is erratic and seems to be affected by the speed of the engine. Am I right in assuming that the magneto is creating interference with the electronic of the signals and if so what can be done to alleviate the problem. Is there some sort of shielding that can be used on the wiring or around the flasher? How far away from the magneto would the interference extend?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul Mikeska, Denver CO on Friday, May 30, 2014 - 09:49 pm:

Just a guess but I would ground the mag post and see if that changes anything.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James Elenbaas - Granger, Washington on Saturday, May 31, 2014 - 04:39 pm:

I tried shorting out the mag post and it made it worse. Signals just flickered.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Todd on Sunday, June 01, 2014 - 12:07 am:

The interference may be coming from the distributor ignition system. It's called RFI. Try a set of resistance plug wires and coil wire.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Miller, Sequim WA on Sunday, June 01, 2014 - 12:23 am:

Maybe a Bridge rectifier will try and trap the AC signal if you try using it between the power source an the LED turn signals. Adding a capacitor across the source can help. LEDs don't like transient AC pulses. Make sure all the grounds are in good shape.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Sunday, June 01, 2014 - 01:00 am:

I guess I'd have to ask...what is powering the LED's and what you are using for an electronic flasher?

LED can be a pain in the royal butt if they don't find themselves circuit balanced in use.

First suggestion is to turn one of those lights into a bulb for a test, doesn't even matter if a 12 V lamp on 6V supply. Things come back to normal...its a ballast balancing act on your circuit and you'll need a different flasher or a resistor added somewhere to force enough voltage drop.

Next suggestion since you have things handy is that most flashers, especially the modern 6V ones tend to be absolute c-r-a-p. So take the flasher unit that 'works' on the no magnets car and try it in one of the cars that doesn't work.

My 3rd guess is that you have a ground loop issue somewhere as even with the #550 flasher units, I've hog tied the bases to the Bendix cover on working mags and luckily have never had an RF noise issue!

As Fred Miller points out...solid grounds are absolutely critical for LED use. When I do turn signals...I home run grounds from the lamp housings back through the looms...some say over-kill, I say...never yet have had an instability problem...and...want to see LED light set work reliably and bright on 6V?


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J Williams on Sunday, June 01, 2014 - 08:17 am:

I had the same problem and I figured it was the mag interfereing with the new electronic flasher the led lights
Worked beautiful until I started the engine so I just put an
Incandescent 12 volt bulb and a regular flasher in. The
System and it works great.i just mounted the bulb in an
Inconspicuous place and painted it black
Works for me


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, June 01, 2014 - 02:09 pm:

The low voltage AC from the magneto is also low frequency by itself so unless you have it connected to ignition coils that are sparking or directly connected to your battery in some way via a charger circuit - I don't see how the magneto AC voltage just sitting there disconnected could cause any issue with your electronics. If nothing at all is connected to the magneto then it would take a very sensitive circuit (poorly designed) to be interfered with by such a simple AC source that had only one connection namely to ground. If the problem only happens when the engine is running then ignition noise is the first thing to check off course and T magneto/coils is not the only type of ignition that would cause problems for your electronics. HV needs to be generated for the spark plugs and non shielded plug wires do radiate a ton of RFI (Radio Frequency Interference) even from distributor ignitions and that is probably your source signal for what is disturbing your device. Usually such electronic devices need to be in metal housings that are well grounded and all input and output connections then need to be bypassed (filtered) with capacitors suitable to prevent RFI from getting inside. Most RFI problems in T accessories are that the device (like a bicycle speedometer) was never designed to be used in such an environment. Most bicycles do not have an ignition coil anywhere on them so the device has no need for careful RFI filtering.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, June 01, 2014 - 02:20 pm:

Just a word of caution. Ken Todd's advise to add resistor plugs or resistance plug wires must NOT be used with T coils. Notice he stated correctly and emphatically to do this only with a distributor and modern type coil. Use of resistance spark plug wires or resistor plugs can spell doom to a T coil since it typically causes the coil voltage to rise to dangerous levels that can result in the T coil sparking internally which can permanently wreck a T coil. Kens' advice is good but just be careful not to expand it to include T's that use coils/timer.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Pat Kelly on Sunday, June 01, 2014 - 03:21 pm:

I used a headlight bulb and put each filament in parallel with the right and left LEDs and standard flasher. Works good. The flasher would not work with out the incandescent bulb in the circuit. PK


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J Williams on Sunday, June 01, 2014 - 08:33 pm:

If you have a turn signal switch with an indicator light as most
Do just put an 1156 bulb on that wire the small indicator bulb is too small by itself to make the old style flasher work


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