MTFCA Forum

Steve,
LEDs run on D.C. but the magneto is A.C.
You could create a rectifier with four diodes but...
LEDs do no like a variation in voltage, changing from 8v to 20v?

Was wondering if this would work. Magneto to Buck Converter then one to power each bulb circuit depending an amp draw if necessary
Supposedly a buck converter will provide constant out voltage

A simple answer is best for my poor little brain. "No" answers my question adequately.

No.

"You need to enter at least 10 characters." Sorry, Steve, the Forum will not let me give you a simple answer.

I dont drive at night, but I do have LED bulbs powered by the magneto. There should be some old forum posts on the subject. Some LEDs will light up on a/c.

Jeff
Ledlight.com sells a headlight bulb that will work off 5 to 30 volts a/c or dc non polarity. Need to wire headlights in parallel instead of series. single pin contact bayonet base. Technically according to the specs it should work off model t mag. Unit has a built in voltage regulator so light output should be rather constant from low to high rpm ? I don't know. Haven't tried it. But might be worth investigating.
LED Headlamp 5 to 30 Volt CSP
One product per package unless otherwise stated.
BA15S LED Headlight 5 To 30 Volt Single Filament Non Polarity
Product Code: 68432
USD Price: 19.99
Could not post photo.
Novice

To clear up some details here, and probably cause confusion.
LED bulbs will run on AC power but...
They are diodes at heart so will only light on half the cycle. Not that anyone notices this.
DC is measured at steady voltage, also known as peak voltage.
AC is measured as RMS (equal power to DC) voltage. Example; at 60 Hertz 120volts AC is 170volts peak.
The reason this matters is it is easily possible to exceed the maximum voltage limit forward or reverse voltage rating. These limits are buried in the spec sheets and often overlooked. It is always best to ask if not confident that it is the correct application. Or just take your chances on turning them into flash bulbs.

I love LED's for the old cars and have them in mine. The lower power with brighter light is a win win in my book. I dont have any magneto light ones, that is a gap in the fleet.

In summary: LED's work fine on AC if within the rated limits. If unsure ask the seller or manufacturer.
If someone tests them I am curious how they work. I might need them someday in the future.

Mike

Mike. You are correct on half cycle operation of a single led. The unit I described is a complete led lighting unit with many leds in the array. unit has a build in bridge rectifier and voltage regulator. So it works on both positive and negative a/c pluses from Model T mag. With the voltage regulator its brightness is some what constant with low and high engine rpms and varying mag
frequency and voltage.

Jim,

The DC and AC discussion was in reference to post #2 in this topic where it was stated that LED’s run on DC and not AC.
Then they went on to discuss using a rectifier with 4 diodes making a bridge rectifier.
It is an often repeated mistake about LED’s and AC power.
As long as it is within product limits it works fine.

That said, ALL of the LED bulb assemblies ready to install contain multiple parts and usually not just LEDs inside.
Depending on what components were used and how it is hooked up it can become almost anything.
There is a huge variety of bulbs out there so pick what you want and if unsure talk to the seller and verify it is right for your use.

The bulb that you referenced is very interesting and might work.
[image] I have not tried them and do not have a mag headlight car. I skip from brass to starters in my fleet.
Here is my opinion on them, I do have a few concerns/questions about them.
Brightness, current, lifetime, color, size and materials all look good.
The double sided construction is good but it has to be rotationally aligned for the proper light pattern. Did the pins on the base get aligned correctly?
It uses the stock reflector, does it place the light at the correct depth to be able to have a decent focus?
The socket (Part #6574X) will have to be changed to install this. I do not know of a BA15S socket with screw tab to install in the headlight bucket. Not sure how to solve this without creating custom parts. I have installed single pin bulbs in dual pin sockets with mixed results. No matter what the stock wiring MUST be reworked to avoid shorting the magneto and burning out the wiring.
It has a wide voltage range with a built in voltage regulator and this is what is needed for a magneto bulb. But I believe the stock dimmer assembly will produce a car with 2 high beam settings. This may or may not be a problem.
I am concerned about the comment in the listing about maybe needing a resistor to fix a flickering issue or poor low beam operation. I don’t know enough about this to make judgment here.
I am also concerned about burning out the bulbs when running high speed with a hot mag. The rating is up near the voltage limit so it should work. But the magneto power is noisy power, there might be garbage and spikes that will damage the bulbs? I don’t know how strong they are at the upper limits. I worry about this because I have burned out several electronic things on my car due to this including my Arduino GPS Speedometer. It worked great on my modern cars for many hours and Rusty (my 26 touring) smoked it dead in about 1 block.

I would love to be able to recommend a good solution to the headlight problems on the Magneto bulb cars. So far all I can recommend for high quality long lasting light is to convert to the battery light setup. Like Steve hinted at, the magneto bulbs you get today are not very good.

In reference to Steve’s original question: There is no drop in, no modification replacement LED bulb for our Magneto headlight cars that I have ever seen or heard of. I wish there were, but things are evolving so in the future, maybe.
I hope someone will report about these bulbs or document how to install them in a magneto car.
They have me curious and I would like to know how they work.
I am also curious if there is something else out there that might work that I don’t know about.

Other references:
https://www.mtfca.com/discus/messages/8 ... 1531884556
and
viewtopic.php?t=41086

Mike

I have had a conversation from a tech person but for the life of me I cannot remember where. It was claimed the the LOGO LITES led head lights were rated up to 25 volts AC as well as DC voltage. I have no experience but that was the topic of the conversation. There are some 1157 leds that are rated for AC and DC.

Question I have is......some LED bulbs don't care about polarity but isn't AC just reversing voltage but really fast? For lack of better word.


Brian

Ok, here is some voltage theory.
A.C. = Alternating Current it is a voltage source that rises and falls in a cyclical pattern called a sine wave.
It can be thought of like a crankshaft rotating and the piston going up and down, plotted over time the piston position is a sine wave pattern. if you use the center of the crankshaft as zero you can see that you have both positive and negative pulses. See the enclosed picture. Rarely is AC all positive or all negative so we will not discuss this special situation.

In a crude way AC is just reversing DC really fast.

Some LED bulbs don't care about polarity because they are built to light either way with back to back parts.
Ir they don't care about polarity they will light at the positive and negative pulses.
If the bulb cares about polarity will only light on half the cycles and just put out less light
On polarity sensitive LED bulbs on AC make sure the voltage maximum in reverse is good enough in addition to forward voltage.

The 1157 bulb is mention but it can not be used because the 1157 pins are offset and the Model T uses parallel pins.
The magneto bulb power comes in one contact and out the other not using the shell in the circuit. This is how the bulbs are wired in series.
The battery bulbs use the same base but in one pin for low and the other for high with both using the shell as a common ground. These bulbs are wired in parallel.
See the enclosed picture as to the differences between the bases and how they are hooked up.

So many details have to be correct when choosing the correct bulb for your application.