MTFCA Forum

I had to replace this “voltage regulator” as they call it on my riding mower. Inside or underside of the flywheel contains what is like a mini Model T magneto. There are field coils mounted to the block and magnets around the inside diameter of the flywheel. This only serves to recharge the battery. The high tension electricity to fire the plugs comes from 2 separate coil assemblies and a magnet on the top/exterior of the flywheel.
There are 2 wires coming from the field coil under the flywheel that plug into the yellow wire. It is AC current, then the red wire sends DC current to the positive terminal on the battery.
It seems like I could wire this same part to a Model T magneto with the same results, but I’m not that good with how electricity works, like why there are 2 wires going in, instead of one coming from a T magneto post.

WHY?? You already have a magneto. why add another one. use your t magneto to charge a battery.
I have a diode charging system on my '14. it charges a 12v battery @ 4 amps. i can run on magneto or battery.
makes no difference in running performance with or without charging. i do primarily run on battery for the infinite spark advance/retard.

He is not suggesting using the magneto shown. He is asking about the regulator in the 2ed photo and if it could be wired up to charge a battery using the existing T magneto.

ok mark g. that makes more sense. my answer would be maybe? if that regulator is rated for the kind if output from a magneto.
say 40 volts & 10 amps for safety. if its cheap enough, try it. it could be a great discovery.

i went looking for one. b/s 18-24 hp. 10-16 amp system. under $10 delivered. i am thinking it should work! go for it & let us know.

You can buy one ready made from the vendors or make this one by Steve Jelf.
http://dauntlessgeezer.com/DG102.html.

I may try it, I think maybe one of the two wires is an output from the mag and the other is grounded through the aluminum housing that holds it onto the side of the motor. I just don’t want to zap my mag with 12 volts but it has to prevent that somehow or the battery would zap the mag on the mower.
I got the idea because when my mower stopped charging and I figured out how it made the electricity, I thought about making one of those chargers for it with the diode and light bulb. It must charge pretty well because there’s an electric clutch on a zero turn that is engaged while mowing and it will run the battery down to where the motor won’t start after an hour of mowing.

Corey,

I had a quick look to see if there was any data around the regulator, or possibly a useful wiring diagram, but nothing came up in the brief time I had.

So please take this as uninformed opinion, however:

- The Briggs regulator may not be able to handle the voltage input from the magneto. You should be cautious around this *.
- It's unclear if it's a series or shunt regulator. If the latter you should NOT use it on the magneto! *
- Just in case - whatever you (or anyone else) do don't use it on a Model T or A generator until it's determined it IS a shunt regulator.

* I would, at least initially, connect the regulator to the magneto with say a 24V bulb in series, and not rev the motor too much. The reason for this is that the bulb in series will limit the available current so that if the regulator shorts, or turns out to be a shunt regulator, you can't fully short out/damage the magneto.

While the latter is unlikely it's not impossible, and even with a bulb the 'system' would still probably charge to some level (dependant to some extent on what's inside the regulator).

Until I was certain of the regulator capacity and type I'd be inclined to leave the bulb in circuit for a while - and if/when I removed the bulb I'd consider first going to a higher wattage/lower voltage bulb, then fitting a fuse in place if that worked ok. Necessarily it'd need to be a fairy low current fuse IMV.

Those technically aren't "regulators", they just dump excess voltage over 14 volts or so. Most of those small engine and power sports stators don't put out over 20 volts. The Model T magneto does, so plan on replacing lots of them. I have thought about adapting one for a generator since the Fun Projects ones are "unobtanium". Some European mopeds had two wire regulators that might work on a generator, because you can control the output through the third brush. With the light bulb regulator there's no need for that since the light bulb acts as a variable resistor.

Not certain about Briggs engines but 18, 20, 22 etc horse Kohlers should put out a max of 30 volts AC at the stator but will charge nicely at about 25 volts AC on that output.
The only issue I'd see is the AC voltage from the T magneto is one wire. The Briggs stator is nicely isolated with the two wires giving the regulator/rectifier the AC it needs. I thought the reg/rec body should be grounded in its usual home but don't know if it'll like using ground as one leg of the AC power. Maybe it won't bother the reg/rec at all.
Luke tells about HOW these reg/recs regulate/are wired internally and to watch out for them. I sure never knew how they regulate/were wired internally either when I was working with them.
Interesting!