How to Convert AC Magneto Output to DC for 12V Toy Motor and Prevent Surges?

I am new to this type of work/construction. I am making an artwork/sculpture and would like to use an old 5 bar phone magneto to power a 12volt toy motor. I don't have the magneto yet but have used some in the past to power small lights. It is in the mail and I will be able to test it to see what voltage it is putting out. My question is how to convert the magneto ac current to DC for the motor. Also do I need resistors or capacitors in line to keep it from surging and blowing the motor or on the other side do I need capacitors to keep a ready supply for the motor to keep it moving smoothly? Thanks in advance.


-Jarrod

Jarrod, those magnetos put out a very spiky AC waveform of about 60 volts peak or more.  For a motor you'd want a fairly steady voltage.  I'd suggest full wave rectifying the magneto voltage, then feeding through a series inductor to a storage capacitor (of a working voltage equal to or greater than the peaks on the magneto waveform).  Play around with that and see how you go. If this does not make much sense to you let us know and I'll post a diagram when I can.

David,I get the idea behind your words, but the jargon might as well be Russian. If you could post a very basic picture diagram of the layout that would probably help quite a bit. Is the inductor to convert ac to dc? and can a capacitor be too large? Thanks for your quick response and help in this matter.-Jarrod

Hi Jarrod-You **may** be able to use a switching power supply intended to operate from 120 volts.Take a look at Mean Well APV-12-12.  Their spec sheet says that require at least 90 volts to operate, but I just pulled one out and tested it, and it starts working well below that.  These are fairly inexpensive, at about $6.50 (US).  It may be worth a try.-Rick

I have purchased the APV 12-12. I will need to see about capacitors.
Thanks

Hi Jarrod... OK you have a bit of  a steep learning curve in front of you :-)Here is a typical magneto output waveform:
This was actually from a Model T ford, but a phone magneto is similar.  It does not have a voltage scale, but for a phone magneto the peaks would be around plus and minus 60V or so.  The thing here is that the average voltage is a lot less than this and could maybe drive your motor directly.  Phone magnetos tend to be even more spiky.Here is a circuit to rectify this voltage for your motor:
You should be able to buy these components in an electronics store.  The bridge rectifier should have a PIV (Peak inverse voltage - the maximum voltage they can take) of at least 100V, but that will be easy.  You don't really need to install C1.  C2 should be around 1000 microfarads (uF) at a rating of something around 60 volts - more if you can, but this might make it expensive.  The inductor could be the low voltage  winding of a small transformer, say about 12-24 volts.You may be able to buy an inductor but a small mans power transformer will be easier to find.Because of the spiky nature of the waveform I am not sure Rick's power supply will like it, but it's a good easy cheap solution - if you've already bought one and it does not work as planned, try the above.

Is there anyway you could show an image of these components or links to a site to purchase online? Thanks

Jarrod - if you are getting an APV-12-12 I would try that first.  You just feed the magneto into the 120V AC wires and you connect your motor to the 12V DC wires.  You don't need any capacitors or anything else. It may work, or it may not.If you get nowhere with that, reply to one of my posts and I will give you some more information.

There is a D6 DIC, as a generator, it has a magneto with a bipolar magnet. On the twentieth, it gives out about 4 volts, at maximum speed ~ 7 volts. It is necessary to adapt the battery there for normal power supply of the headlamp and in the future of self-similarity of the onboard computer. So far, I am inclined to this. I chose 4 volts because up to 6 the voltage rises not so often, and it takes even more than 6 to charge. I can only use 1 half-cycle for charging because the second one ensures the operation of the high-voltage ignition coil. The LED headlight + clearance (~ 300 mA) and the on-board computer (50-100 mA) will be connected to the battery. How to connect such a battery to a magneto? It is clear that through the diode, but nevertheless, how is it right for it to recharge on the move, and in the event of a diode failure, I did not burn the coil in the magneto?