Voltage Rectifier/Regulator Design for Magneto

[Philip Gustafson]

Hi I'm trying to build a a rectifier/regulator for a very old moped. My magneto is putting out 20-70V AC depending on the engine RPM. I would like to get this regulated down to a solid 4A or more at 13-14VDC. Originally it used some kind of sealed half way bridge rectification and regulation method that is unkown as it was in a sealed unit. I am considering setting it up as with a full way bridge rectifier to optimize output efficiency but really whatever works best is fine. I'm kinda lost at this point so any advice is appreciated.

 

[duke37]

A car dynamo regulates its output by altering the field excitation. It can be damaged by taking too much current so a control box reduces the excitation at at certain current level.
A car alternator is built with a leakage inductance so that the maximum current is safe even with the output shorted.

I have never played with a moped or motor cycle generator but a diagram I have seen appears to control output by shorting it. The current is then limited by the inductance and no power is generated.

To get maximum output from the magneto, you could rectify to a DC voltage and use a buck convertor to drop it to 14V. You could get more output current than input current. There are controllers to take the power from wind turbines and opitimise the load to get maximum output.

Using the generated AC, then a SCR or triac could do the control but will need development.

There may be ground problems between the battery and the magneto if a bridge rectifier is used.

 

[Alec_t]

I'm guessing the magneto has only one (single-phase) winding for powering the lights, but :-
Is the magneto single or multiple phase?
Is any part of its winding(s) grounded?
How many input connections (including ground) did the original rectifier/regulator have?
Does the moped have a battery?
Is the moped wiring positive or negative ground?
Can you post a link to a wiring schematic for the moped?