Resistor

Farmall B & BN Tractors, 1939-1947
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Tractor Rod
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Resistor

Postby Tractor Rod » Tue Oct 05, 2021 10:39 am

:help:
I bought a Farmall B snd it ran great for awhile and then it stopped. I isolated the problem and it was a bad resistor. It is converted to 12 volt and has the small external porcelain resistor. I bought a new resistor and put it on and it started right up. The next day I tried to start it and it wouldn’t run again so I bypassed the resistor and it fired right up. Can I run the tractor without the resistor or what are the recommendations? I don’t know why it is burning up the resistor? Thanks in advance for your help.

Eugene
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Re: Resistor

Postby Eugene » Tue Oct 05, 2021 12:16 pm

You need the resistor is you are using a 6 volt ignition coil. Use an Echlin, Chrysler, ballast resistor from the auto parts store.

Why the resistor filiment is breaking - unknown. May not be burining up, just breaking - bad luck.

You can run the tractor without the ballast resistor. It will burn the ignition points up if you do.
I have an excuse. CRS.

Tractor Rod
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Re: Resistor

Postby Tractor Rod » Tue Oct 05, 2021 7:53 pm

Thanks. I’ll buy one tomorrow morning.

Eugene
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Re: Resistor

Postby Eugene » Tue Oct 05, 2021 9:45 pm

There are two different Ohm resistors available. It doesn't make any difference which one to choose. Idea is, the resistor drops the voltage across the points to between 6 and 9 volts.

The resistor need to be fastened solid to keep it from flopping around.
I have an excuse. CRS.

Tractor Rod
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Re: Resistor

Postby Tractor Rod » Wed Oct 06, 2021 12:42 pm

Thanks. I believe it is the original 6 V coil that is on it. Does that mean I still need a resistor on the front side to drop the voltage down to 6 before it goes into the coil? Or can it just be wired directly without a resistor not causing a problem?

indy61
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Re: Resistor

Postby indy61 » Wed Oct 06, 2021 3:36 pm

You need to know if your coil has an internal resistor. Many will have it marked on the coil.
A 6v coil doesn't need an internal or external resistor and should read around 1.5 ohms.
A 12v coil needs to have an internal or external resistor and should read around 3 ohms.
Simple enough with a cheap multi-meter connected to the + and - terminals on the coil and reading the resistance.

Eugene
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Re: Resistor

Postby Eugene » Wed Oct 06, 2021 4:03 pm

indy61 wrote:You need to know if your coil has an internal resistor. Many will have it marked on the coil.
A 6v coil doesn't need an internal or external resistor and should read around 1.5 ohms.
6 volt coil needs a ballast resistor when the tractor is converted to 12 volts to drop the voltage at the ignition points to between 6 and 9 volts. The prior conversion to 12 volts already has a resistor.
A 12v coil needs to have an internal or external resistor and should read around 3 ohms.
OK. You can purchase a 12 volt coil with internal resistor. It cost quite a bit more than the ballast resistor.
I have an excuse. CRS.


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