Scratching My Head On This Farmall H Ignition System

[Farm Boys Way]

So as you can see I have a 12v battery on this tractor, cranks over with keyed switch. The keyed switch provides 12v to coil lead. I cannot seem to find a ballast resistor that will reduce the voltage to 6v, so i can utilize the original 6v coil. All three ballast resitors seen here don't reduce the voltage. What am I doing wrong?

Thanks

 

[n9lhm]

No resistor will reduce voltage until there is current flow through it. Hook up your resistor and then monitor voltage across the coil as you crank the engine slowly and it should go from 0 to approx. 6 volts if everything is OK. My $.02, if you are doing a 12V conversion go get the correct 12V coil instead of using a 6V coil with a resistor. It will reduce the ignition current draw by half, lengthen the life of the points, and eliminate another failure-prone component (the resistor).

Brian

 

[Farm Boys Way]

No resistor will reduce voltage until there is current flow through it. Hook up your resistor and then monitor voltage across the coil as you crank the engine slowly and it should go from 0 to approx. 6 volts if everything is OK. My $.02, if you are doing a 12V conversion go get the correct 12V coil instead of using a 6V coil with a resistor. It will reduce the ignition current draw by half, lengthen the life of the points, and eliminate another failure-prone component (the resistor).

Brian

When I connect 12v to the resistor it doesn't reduce the current coming through it.

I also have this coil unit Napa IC14SB

 

[BarnyardEngineering]

Couple of things you're doing wrong. First you're spending money on resistors for no reason, LOL. Second, you're measuring the voltage wrong.

Measure the voltage ACROSS the resistor. Put the red probe on the left terminal and the black probe on the right. That measures voltage drop across the resistor. It probably won't be exactly 6 Volts, but it will drop the voltage enough to keep the coil from overheating.

Using a resistor is fine. I don't buy the whole "failure prone" bit. They're no more "failure prone" than any other component on the tractor. Why do people draw the line at a resistor on a 75 year old tractor, but jump in their 20XX model pickup truck with computers and electronic gizmos out the wazoo without a second thought?

 

[used red MN]

Is the engine running now or was it? Generally when engine stops the ignition points are closed. This means the lead going into the distributor should have a connection back to batttery negative through the closed points, the engine, the chassis then to the negative battery cable. Maybe I shouldn’t confuse the issue by making a suggestion that differs from 9ns proposal. To confirm the points are working stead of measuring voltage across the coil I measure it to ground. With power to the coil when the points close the distributor terminal should lose power. And don’t comeback saying I show .1? volts anything below 0.5 volts is close enough to zero. If the points aren’t providing a ground for the coil circuit you have to file, sand, clean or replace them so they do provide a ground when closed. I also am a believer in using what you have. The 6 volt coil with a resistor is fine. The majority of IH tractors that had points up through the 70s used this system with minimal problems. They kept the 6 volt coils because they utilized a bypass circuit for the resistor when starting to increase spark voltage. To do this requires a special solenoid. It is usually not needed in your application.
Curious what kind of a charging system are you running? Maybe you have other leads feeding your system off the solenoid. The black wire you have looped up and crimped into the positive battery cable is not heavy enough to carry the current of a charging system.

 

[used red MN]

Is the engine running now or was it? Generally when engine stops the ignition points are closed. This means the lead going into the distributor should have a connection back to batttery negative through the closed points, the engine, the chassis then to the negative battery cable. Maybe I shouldn’t confuse the issue by making a suggestion that differs from 9ns proposal. To confirm the points are working stead of measuring voltage across the coil I measure it to ground. With power to the coil when the points close the distributor terminal should lose power. And don’t comeback saying I show .1? volts anything below 0.5 volts is close enough to zero. If the points aren’t providing a ground for the coil circuit you have to file, sand, clean or replace them so they do provide a ground when closed. I also am a believer in using what you have. The 6 volt coil with a resistor is fine. The majority of IH tractors that had points up through the 70s used this system with minimal problems. They kept the 6 volt coils because they utilized a bypass circuit for the resistor when starting to increase spark voltage. To do this requires a special solenoid. It is usually not needed in your application.

Here is a little more of an explanation of the “Kettering” (points) ignition system. It may repeat things I said above. I have this saved to copy.
The points are just a simple switch that open and close ..turn on and off.. the ignition coil circuit rapidly. Inside the coil the primary circuit that is connected to the two terminal posts on the coil which is an ..electromagnet coil.. is one continuous long insulated wire going around and around. So when you have power to the positive terminal and nothing connected to the negative terminal there is power on both terminals because as I said it is one continuous wire. That is what is making the terminal on the side of the distributor show it has power by the test light. When the points close and are contacting properly you ..ground out.. that side of the coil which makes the light go out. Because the negative battery post has a cable connecting it to the chassis of the tractor and that is where the test light probe is and the distributor base mounts to the engine which is mounted to the tractor chassis. As the points are closed magnetism builds in the primary electromagnet of the coil. That coil is right next to the ..secondary coil.. inside the coil so the primary magnetic field is crossing over into the secondary coil. The secondary winding connects to where the spark output of the coil is. Now the points are pushed open and the primary electromagnet instantly looses its magnetic field. The electrons in the secondary field that where being highly excited suddenly want to find some place to discharge to so they find the exit of the coil by way of the ..high tension.. terminal or socket where the coil spark wire to the distributor cap connects. There are a few more parts to it like the condenser which is sort of a buffer to some of the electrons that come out of the primary coil windings during the opening of the points and helps the contacts surfaces of the points last longer.

 

[Jim.ME]

When I connect 12v to the resistor it doesn't reduce the current coming through it.

I also have this coil unit Napa IC14SB

The NAPA IC14SB coil is a 12- volt coil that does NOT REQUIRE AN EXTERNAL RESISTOR. Why not just use the IC14SB and not have to deal with a ballast resistor at all? You can't be doing a restoration, or you would be keeping it straight 6-volts.

 

[used red MN]

The NAPA IC14SB coil is a 12- volt coil that does NOT REQUIRE AN EXTERNAL RESISTOR. Why not just use the IC14SB and not have to deal with a ballast resistor at all? You can't be doing a restoration, or you would be keeping it straight 6-volts.

My reply was based on the IH “bullet” coil shown in his picture, those are 6 volt.

 

[Jim.ME]

My reply was based on the IH “bullet” coil shown in his picture, those are 6 volt.

Understood as to your reply.

My reply was to the post of Farm Boys Way where he posted he had a NAPA IC14SB coil unit. I may have been off a bit in how I interpreted what he wanted to say but he posted he has an IC14SB and I wanted to be sure he understood that one does not need a ballast resistor. If he has a true 12-volt coil, why chase a ballast resistor for the old coil in his picture? A true restoration would stay completely 6-volts, so no ballast resistor needed. Using the IC14SB eliminates a ballast resistor and a couple wiring connections that just add to things that could cause problems in the future.

 

[Farm Boys Way]

Thanks for all the reply's, reviewing all the info