The Ford Barn

FRANK PKNY · 03-08-2011, 10:14 AM

I have been dealing with several very helpful suppliers and rebuilders of coils and parts. I recently installed Franks magneto ac volt meter and have found that my mag is putting out 6 to 20+ volts ac depending the the rpm of course. My question is is 20VAC enough to run the coils without any problem? I am getting conflicting advise! Thanks guys.

CharlieB · 03-08-2011, 10:31 AM

Conflicting advice from whom? A hot shot battery for a non starter car is 6 volts (dc) and was used to start the car if the mag was weak. 6 to 20+ ac volts sounds like a normally operating magneto to me. The coils will definitely operate on this voltage. If your coils don't work properly at that voltage maybe the capacitors are going bad. (not a hard fix) then correct set up with a hand cranked tester or HCCT as it's called. Elaborate if you wish.

FRANK PKNY · 03-08-2011, 11:22 AM

The coils are new and were checked an a tester , (don't know what kind) by Texas T parts. Have not been able to run on the road because of snow and now mud. Mud, Mud. !!!! Seems to run fine on the mag , but I have been advised that I should be getting 20+ volts AC off the mag more like 25 to 30. I just have not wanted to run the engine that many rpm's without a load for fear of busting it apart.

CharlieB · 03-08-2011, 07:14 PM

These figues are from an old Dykes motor manual from the 1920's: RPM-1200
vehicle speed-30mph, mag.output-26.2 acv, amps-9. Again you sound like you're right there. Are you having a problem with the way it runs? Sometimes coils are checked with a buzz box tester. All that tells you is that the coil sparks or operates. An HCCT tester is used to set the coil up so it doesn't "double spark" or produce 2 weak sparks instead of 1 strong one. ( a double spark is half the voltage). There are 2 types of testers that check this . One is the HCCT the other is a modern type called a Strobospark tester. If your coils have not been set up on one of these 2 testers They are not set up correctly. Also: do these coils have new Capacitors?

FRANK PKNY · 03-08-2011, 08:18 PM

Thanks Charlie, the coils are new ones. Soon the weather will improve and I will run it under load on the road. I saw the Strobospark on youtube. Ben from Texas T parts set them up. My mag may be short of 26.2 VAC but it appears to be in the 22 v range which I would think should be sufficient to run the coils. I start on a 12v battery and it runs good on it but I have been cautioned that running on 12 vdc for a long period of time will shorten point life. I don't think I will ever be able to get enough miles on the car to worry about that. I enjoy the T and would like to drive as many miles as I can. Thanks for your help. Frank pkny

CharlieB · 03-08-2011, 10:53 PM

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I don't know if they'll actually last longer but they were made to run on ac current. good luck driving.

Doug Money · 03-08-2011, 11:08 PM

Its the DC current not the voltage that causes the points to wear. Actually what happens is one side of the points give material to the other side. With AC this doesn't happen.

Jack Innes · 03-09-2011, 01:17 AM

I recall reading manuals on some early cars that use dry cells only to run a buzz coil where the manufacturer suggested to reverse the polarity on the system once in a while to save the points. This causes the process that Doug mentioned to reverse. In theory, the material is transferred back to where it came from. What this boils down to is very slowly Alternating Current which explains why AC from the mag is better for the points.

CharlieB · 03-09-2011, 10:27 AM

I'll buy that. Especially since DC only travels in one direction. I remember seeing this transfer on ignition points in more modern cars.

FRANK PKNY · 03-09-2011, 10:37 AM

Yes that is very correct. AC current cycles deposits in both directions.

03-08-2011, 10:14 AM	#1
FRANK PKNY Senior Member Join Date: May 2010 Location: POUGHKEEPSIE NY 12601 Posts: 1,016	Magneto output I have been dealing with several very helpful suppliers and rebuilders of coils and parts. I recently installed Franks magneto ac volt meter and have found that my mag is putting out 6 to 20+ volts ac depending the the rpm of course. My question is is 20VAC enough to run the coils without any problem? I am getting conflicting advise! Thanks guys. __________________ [email protected]

03-08-2011, 10:31 AM	#2
CharlieB Senior Member Join Date: Sep 2010 Location: Toms River N.J. Posts: 515	Re: Magneto output Conflicting advice from whom? A hot shot battery for a non starter car is 6 volts (dc) and was used to start the car if the mag was weak. 6 to 20+ ac volts sounds like a normally operating magneto to me. The coils will definitely operate on this voltage. If your coils don't work properly at that voltage maybe the capacitors are going bad. (not a hard fix) then correct set up with a hand cranked tester or HCCT as it's called. Elaborate if you wish.

03-08-2011, 11:22 AM	#3
FRANK PKNY Senior Member Join Date: May 2010 Location: POUGHKEEPSIE NY 12601 Posts: 1,016	Re: Magneto output The coils are new and were checked an a tester , (don't know what kind) by Texas T parts. Have not been able to run on the road because of snow and now mud. Mud, Mud. !!!! Seems to run fine on the mag , but I have been advised that I should be getting 20+ volts AC off the mag more like 25 to 30. I just have not wanted to run the engine that many rpm's without a load for fear of busting it apart. __________________ [email protected]

03-08-2011, 07:14 PM	#4
CharlieB Senior Member Join Date: Sep 2010 Location: Toms River N.J. Posts: 515	Re: Magneto output These figues are from an old Dykes motor manual from the 1920's: RPM-1200 vehicle speed-30mph, mag.output-26.2 acv, amps-9. Again you sound like you're right there. Are you having a problem with the way it runs? Sometimes coils are checked with a buzz box tester. All that tells you is that the coil sparks or operates. An HCCT tester is used to set the coil up so it doesn't "double spark" or produce 2 weak sparks instead of 1 strong one. ( a double spark is half the voltage). There are 2 types of testers that check this . One is the HCCT the other is a modern type called a Strobospark tester. If your coils have not been set up on one of these 2 testers They are not set up correctly. Also: do these coils have new Capacitors?

03-08-2011, 08:18 PM	#5
FRANK PKNY Senior Member Join Date: May 2010 Location: POUGHKEEPSIE NY 12601 Posts: 1,016	Re: Magneto output Thanks Charlie, the coils are new ones. Soon the weather will improve and I will run it under load on the road. I saw the Strobospark on youtube. Ben from Texas T parts set them up. My mag may be short of 26.2 VAC but it appears to be in the 22 v range which I would think should be sufficient to run the coils. I start on a 12v battery and it runs good on it but I have been cautioned that running on 12 vdc for a long period of time will shorten point life. I don't think I will ever be able to get enough miles on the car to worry about that. I enjoy the T and would like to drive as many miles as I can. Thanks for your help. Frank pkny __________________ [email protected]

03-08-2011, 10:53 PM	#6
CharlieB Senior Member Join Date: Sep 2010 Location: Toms River N.J. Posts: 515	Re: Magneto output Sponsored Links (Register now to hide all advertisements) I don't know if they'll actually last longer but they were made to run on ac current. good luck driving.

03-08-2011, 11:08 PM	#7
Doug Money Senior Member Join Date: Jul 2010 Posts: 350	Re: Magneto output Its the DC current not the voltage that causes the points to wear. Actually what happens is one side of the points give material to the other side. With AC this doesn't happen.

03-09-2011, 01:17 AM	#8
Jack Innes Senior Member Join Date: May 2010 Location: Brooklin, Ontario Posts: 704	Re: Magneto output I recall reading manuals on some early cars that use dry cells only to run a buzz coil where the manufacturer suggested to reverse the polarity on the system once in a while to save the points. This causes the process that Doug mentioned to reverse. In theory, the material is transferred back to where it came from. What this boils down to is very slowly Alternating Current which explains why AC from the mag is better for the points.

03-09-2011, 10:27 AM	#9
CharlieB Senior Member Join Date: Sep 2010 Location: Toms River N.J. Posts: 515	Re: Magneto output I'll buy that. Especially since DC only travels in one direction. I remember seeing this transfer on ignition points in more modern cars.

03-09-2011, 10:37 AM	#10
FRANK PKNY Senior Member Join Date: May 2010 Location: POUGHKEEPSIE NY 12601 Posts: 1,016	Re: Magneto output Yes that is very correct. AC current cycles deposits in both directions. __________________ [email protected]