Magneto voltage question

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Model T Ford Forum: Forum 2015: Magneto voltage question
Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Redelman, Kouts, IN on Sunday, August 09, 2015 - 02:57 pm:

I am checking out everything on an original 1926 fordor and have just replaced the lifters and valves. I removed the hogshead to inspect the trans and replace the bands and to make sure the oil pickup is clean.
My question is when I hand crank the engine I only have 2.9 volts AC, is this about right? Also has anyone tried using a battery charger on boost to recharge the magnets? I have a 250 amp 12 volt charger I could use, I'd rather not remove the battery from my car and truck to do it because of the computers in them.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Sunday, August 09, 2015 - 04:41 pm:

Can you start the car on mag? In that case it's enough :-)
Voltage isn't critical at low rpms as far as I understand, the coils needs amps to ignite.

You can test the output with the engine running on bat, let the magneto pickup power a 1157 bulb and measure the voltage over the bulb with an analog voltmeter.
The bulb should be very bright at higher rpms and may even blow if the magneto is hot.

I think you can recharge the mag with your battery charger - if needed, check it first with the bulb :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Redelman, Kouts, IN on Sunday, August 09, 2015 - 05:55 pm:

Hi Roger, The engine is still partially apart so I can't run the engine. I am just checking everything I can with the engine in the car. I went ahead and used the battery charger today to strengthen the magnets per the diagram that uses a compass to find North, and I indexed the flywheel at every North location which increased the hand cranking voltage to 3.8 volts. My gap is .042 with the crank pushed back as far as it can go and has .012 end play in the bearing. When the engine runs it will be the first time in over 65 years, this car still wears it's original top covering and the only wear in the door dovetails is in the drivers door. Some T enthusiast who have seen this car are amazed at its original condition.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell, Huntsville, AL on Sunday, August 09, 2015 - 10:22 pm:

Steve, you are at about the limit of gap. The manual calls for 0.025 to 0.040 inch. Best at 0.025 inch at the top and about 0.030 at the bottom (measured with the engine vertical, transmission on top). The greater the gap between magnets and coil ring, the less current will be induced.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Monday, August 10, 2015 - 12:32 am:

He is working with an original engine that has .012 end play in the crank so if you subtract that .012 from the .042 you get about .030 clearance part of the time. Steve if you can solder that end play is not that hard to fix.

(Message edited by redmodelt on August 10, 2015)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Garnet on Monday, August 10, 2015 - 12:41 am:

To actually answer your question Steve, there is very little voltage when hand cranking - and you can't really judge the condition of the magneto by hand cranking other than to say yes, there's voltage or no, there isn't. Don't be in a hurry to fix something that may not problematic. Generally, a combination of batteries equaling 36 volts is used when attempting to recharge magnets in-car.

Regards,
Garnet


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