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Ballast resistor for 12v conversion

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dan

07-04-2001 09:25:23




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I just converted my super c to 12 v and am having trouble with ballast resistors. I tried an ru4, sopposed to drop to 6v, but it didnt drop voltage one bit. then I tried another one from napa and it didnt do anything either. the thing I cant figure out is what is the purpose of a resistor if the voltage going out is the same as it was going in? does anyone have a tried and true part number for one that will drop the voltage to 6?

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dan

07-05-2001 16:45:16




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 Re: ballast resistor for 12v conversion in reply to dan, 07-04-2001 09:25:23  
ya know I was getting in such a hurry trying to fix the tractor that I completly forgot it has to be running to check the voltage drop. that sure makes me feel stupid. I should have known. I have been a mechanic for about 20 years now. it is easy to forget the older simple systems when you got your brain all full of electronics and computers and injection systems. I now work at a case and kubota dealer and boy do I have to ask alot of stupid questionsbecause of all I have forgotten.

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Haas

07-05-2001 06:09:45




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 Re: ballast resistor for 12v conversion in reply to dan, 07-04-2001 09:25:23  
IF you measure the voltage with at voltmeter and the engine not running, it will show no voltage drop because there is no current flow. Not sure what will happen if you measure with the engine running. However, it the resistor is getting hot, it is working.



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Tom Zander

07-04-2001 18:08:48




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 Re: ballast resistor for 12v conversion in reply to dan, 07-04-2001 09:25:23  
The voltage drop you are looking for will not occur unless there is current flow. The ignition points must be closed with the key in the on position to get a voltage drop. In a 12 volt negative ground system the feed from the key is connected to the plus terminal (positve). The minus terminal is connected to the distributor lead that is connected to the ignition points. These connections are reversed on positive grounded systems. The two small terminals are the primary winding of the coil. The ignition pionts connect the primary to ground causing a magnetic field to build up around the coil when current is flowing. When the points open the magnetic feild colapses around the secondary winding which is also in the coil. The secondary winding has current induced into it by the primary windings colapsing magnetic feild (The coil is actualy a step-up transformer). The large wire going from the coil to the distributor cap is connected to the secondary winding and provides a path for the high voltage induced into it to fire the spark plugs.
Ignition coils come in two types, internal and external resistors. Internal types do not use a ballast resistor since they have a resistor built in to the coil. Twelve volt internal coils will measure 3 to 5 ohms acrossed the plus and minus terminals. The external type will measure about 1.5 ohms and require a ballast resistor be used in series with the primary. Using the wrong coil and/or resistor combination will result in burned points, missfire, and plug fouling. Connecting the primary circuit improperly (polarity) will also cause problems.

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Tom Zander

07-04-2001 18:08:42




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 Re: ballast resistor for 12v conversion in reply to dan, 07-04-2001 09:25:23  
The voltage drop you are looking for will not occur unless there is current flow. The ignition points must be closed with the key in the on position to get a voltage drop. In a 12 volt negative ground system the feed from the key is connected to the plus terminal (positve). The minus terminal is connected to the distributor lead that is connected to the ignition points. These connections are reversed on positive grounded systems. The two small terminals are the primary winding of the coil. The ignition pionts connect the primary to ground causing a magnetic field to build up around the coil when current is flowing. When the points open the magnetic feild colapses around the secondary winding which is also in the coil. The secondary winding has current induced into it by the primary windings colapsing magnetic feild (The coil is actualy a step-up transformer). The large wire going from the coil to the distributor cap is connected to the secondary winding and provides a path for the high voltage induced into it to fire the spark plugs.
Ignition coils come in two types, internal and external resistors. Internal types do not use a ballast resistor since they have a resistor built in to the coil. Twelve volt internal coils will measure 3 to 5 ohms acrossed the plus and minus terminals. The external type will measure about 1.5 ohms and require a ballast resistor be used in series with the primary. Using the wrong coil and/or resistor combination will result in burned points, missfire, and plug fouling. Connecting the primary circuit improperly (polarity) will also cause problems.

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BOB[PA]

07-04-2001 12:06:54




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 Re: ballast resistor for 12v conversion in reply to dan, 07-04-2001 09:25:23  
DAN i use the napa brand RU-6 with no proplems on my super a in order to ckeck must have tractor running and with volt meter check wire right at dist. should be what you are looking for. you must reverse the wires at coil and dist + goes to hot wire coming in - wire goes to dist

please post back with any ?

hope this helps bob



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The Red

07-04-2001 13:13:48




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 Re: Re: ballast resistor for 12v conversion in reply to BOB[PA], 07-04-2001 12:06:54  
Bob no need to swap the coil wires. The - stands for the primary winding. The + is for the secondary wiring which should go to the distributor on a 6 volt coil. Delco Remy would have been better off marking those P and S.



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RickB.

07-04-2001 10:16:00




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 Re: ballast resistor for 12v conversion in reply to dan, 07-04-2001 09:25:23  
If you are reading voltage with the tractor shut off, points open and switch on, you will measure 12v on both sides of the resistor. Take voltage reading with tractor running, or points closed; switch on. There is no voltage drop across a resistor without a load applied to it.



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