AC generator/magneto voltage regulation


Old 09-23-16, 06:05 PM
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Join Date: Sep 2016
Posts: 2
AC generator/magneto voltage regulation


First time posting here so hopefully I'm doing this right. I'm currently working on a old 70s dual sport motorcycle. The wiring is currently a mess so I decided to try my hand at making my own wiring harness except I've hit a snag.

The current wiring is hooked up to an unregulated magneto.

One coil is rectified and is used for a charging circuit for a 6v battery, this supplies power to the incandescent tail lights and blinkers.

The second coil is unrectified and is used to power the 6v incandescent headlight only.

What I'm trying to do is find out if it's possible to regulate the charging circuit to 12v dc to charge a small 12v battery or a large capacitor and run 12v led blinkers, 12v led tail lights and an incandescent 12v headlight. I would eliminate the ac lighting coil.

How would I determine the output of my magneto so I can pick a voltage regulator? Also how is this thing even work without one?

If I get a voltage regulator can I just wire it into the output of the magneto after a rectifier? The couple I've seen online have a + - input and a + - output although my magneto only has one output wire and the coils ground to the frame inside the magneto. I'm not sure how I would wire one in our am I looking for a different type.

Sorry this is long any help would be great!
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Old 09-23-16, 06:33 PM
PJmax's Avatar
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Join Date: Oct 2012
Location: Northern NJ - USA
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Welcome to the forums.

I moved your thread to the motorcycle forum. The pros will see it here.

If the system is 6vdc you cannot regulate it to 12vdc. You can regulate down but not up.
You could possibly use a 6vdc > 12vdc invertor but I'm not sure how much current your magneto can deliver.

Pilot Dane may have an idea. He'll be by in the AM.

Was looking around and found this......
Industry Grade DC 6V to DC 12V Step Up Converter | eBay
+/- 1 amp of power..... about 18 watts. You'd need to add up the wattage of your lights.
Old 09-24-16, 01:25 AM
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Join Date: Sep 2016
Posts: 2
Sorry I don't think I explained well. The magneto is supplying unregulated ac power which increases with the rpm of the motor. With just a 12v bulb for resistance the output seemed around 10v on idle and would climb to around 25v when I would increase the rpm. The amperage looked to be around 1.5A at idle and climb to around 6A if rpm was increased.

My guess is maybe the resistance of all the stock bulbs was just enough to keep the magneto output around 6v with the battery soaking up voltage spikes.

My thought was if the magneto puts out say 72 watts what difference would it be as 12v 6A our 6v 12A both are theoretically the same amount of power. Our am I just really confused.

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