Ford 600 ignition coil

My 1955 Ford 640 has been converted to a 12 volt system. There is no resistor installed from the ampmeter to switch or to the coil. The coil has no markings on it. Should I install a ballast resistor in the line from the ignition switch to the coil? How can I test the coil to see if it has a built in resistor?
 
Is the tractor running well? If you aren't burning up points and it runs well, don't worry about it. There should be some words on the very top of the coil that says no resister required.
 
Thats my problem, Its not running well. Starts up runs a little while then shuts off. I'm replacing the ignition switch, points and condensor. My coil has nothing printed or embosed on it. I'm thinking when it was converted to a 12 volt system a resistor wasn't installed or this coil might have changed to a built in resistor.
 
Check resistance between + and - posts. 1 1/2 ohms requires a 1 1/2 ohm resistor for 12 volt. 3 ohms is direct 12 volt and needs no added resistor.

NAPA IC14SB or equivalent is 3 ohm direct 12 volt no resistor replacement
 
(quoted from post at 11:35:13 12/10/20) Thats my problem, Its not running well. Starts up runs a little while then shuts off. I'm replacing the ignition switch, points and condensor. My coil has nothing printed or embosed on it. I'm thinking when it was converted to a 12 volt system a resistor wasn't installed or this coil might have changed to a built in resistor.

Consumer-grade Volt Ohmmeters are known for not being very accurate at low Ohms values.

A better test is to use an Ammeter that is capable of reading 5 or ten AMPS and checking the current draw of the ignition system, battery fully charged, engine STOPPED, breaker points CLOSED.

You are looking for 3 to 4 Amps.

If the draw is over that range it indicates a primary resistor needs to be added or (possibly) that the coil has some shorted "turns" and is drawing excessive current.
 
I removed my coil this morning and using my digital multimeteer set at 200 I get a reading of 1.4 ohms between the + and - posts. That would mean I have a 6 volt coil. You said I need a 1.5 ohm resistor. I have a new .6 ohm ballast resistor. Will this work? I read that on a 12 volt system that less than 3.0 ohms to use a resistor.
 
(quoted from post at 11:00:29 12/11/20) I removed my coil this morning and using my digital multimeteer set at 200 I get a reading of 1.4 ohms between the + and - posts. That would mean I have a 6 volt coil. You said I need a 1.5 ohm resistor. I have a new .6 ohm ballast resistor. Will this work? I read that on a 12 volt system that less than 3.0 ohms to use a resistor.

It depends upon exactly what sort of .6 Ohm "ballast" resistor you have.

Some are "PTC", which means their value increases as they warm up under a load. If you have that type and it's resistance increases to somewhere near 1.5 Ohms after the engine runs a minute or two it should work.

If it is just a straight resistor and remains at about .6 Ohms in use it isn't right for your use.
 
It is a resistor I found online to be used in a conversion from a 6 volt to a 12 volt charging system. 6 volt generater to 12 volt alternator.
 
(quoted from post at 14:33:33 12/11/20) It is a resistor I found online to be used in a conversion from a 6 volt to a 12 volt charging system. 6 volt generater to 12 volt alternator.

Depends on what on-line site you got it from and how reliable they are.
 
The P/N is 8NE10306 and I got it from a reliable after market parts dealer. I've bought a lot of parts from them and never been disappointed.
 
(quoted from post at 12:26:23 12/11/20) The P/N is 8NE10306 and I got it from a reliable after market parts dealer. I've bought a lot of parts from them and never been disappointed.

That part number really doesn't mean anything, it has been stuck on a wide variety of parts made and sold by many different outfits, many likely from "The Land of Almost "Right".

GOOGLE the number and click on "images" and you will see what a wide variety are sold under that number.

If you are ACCURATELY measuring it's resistance and it happens to not be of the "PTC type" it's resistance is about half what you need.

Your best bet is (as I told you before) to measure the AMP draw of the primary circuit.

That will tell the tale.

If it's actually a "PTC" resistor the measured current will steadily decrease over the first minute or so to the 3 to 4 Amp range, and it's OK to use. If the current is much higher than that it's not what you need.

Don't continue the test for much more than a minute or so because of coil and breaker point heating.
 
Your best bet is (as I told you before) to measure the AMP draw of the primary circuit.

Just curious... How do you get an accurate measurement of the DC amperage of a circuit that's constantly a switching on and off and inducing an AC component due the switching?
 
(quoted from post at 17:54:21 12/13/20)
Your best bet is (as I told you before) to measure the AMP draw of the primary circuit.

Just curious... How do you get an accurate measurement of the DC amperage of a circuit that's constantly a switching on and off and inducing an AC component due the switching?

READ my earlier reply to this thread.
 
(quoted from post at 22:10:37 12/13/20)
(quoted from post at 17:54:21 12/13/20)
Your best bet is (as I told you before) to measure the AMP draw of the primary circuit.

Just curious... How do you get an accurate measurement of the DC amperage of a circuit that's constantly a switching on and off and inducing an AC component due the switching?

READ my earlier reply to this thread.

OK, I read it, so you're saying to let it warm up and then measure the current with the engine off. Wouldn't it be simpler to let it warm up and then measure the resistance? Measuring amps requires breaking the circuit and inserting the probes of the meter in series with the break point, and then you would have to bump the engine until the points close to get current to flow. Letting it warm up and then measuring the resistance is a lot less work. Heck, since he hasn't installed the resistor yet, wouldn't warming it up in the oven and measuring the resistance be even easier?
 


Sean, what would the resistance of the current detector or meter be,, in the circuit? .2 ohms?? .5 ohms?? 1 ohm??? Could be enough that it would alter the current enough... especially since we are talking about very low resistance to begin with. I agree that it would be more common to have an amp meter and easier to do..However I have two dc amp probes now that clamp around the wire and measure dc current without inserting .5 ohms ....into a 1.5 ohm circuit and distorting the readings..

Maybe a voltage drop across the coil and then the resistor while the points are closed might be a less evasive way to check the resistance. When both drop 6 volts each... and the coil is 1.5 ohms,,, your pretty much there????

just thinking of the error factor on a low ohm circuit....
 
(quoted from post at 10:32:51 12/14/20)

Sean, what would the resistance of the current detector or meter be,, in the circuit? .2 ohms?? .5 ohms?? 1 ohm??? Could be enough that it would alter the current enough... especially since we are talking about very low resistance to begin with. I agree that it would be more common to have an amp meter and easier to do..However I have two dc amp probes now that clamp around the wire and measure dc current without inserting .5 ohms ....into a 1.5 ohm circuit and distorting the readings..

Maybe a voltage drop across the coil and then the resistor while the points are closed might be a less evasive way to check the resistance. When both drop 6 volts each... and the coil is 1.5 ohms,,, your pretty much there????

just thinking of the error factor on a low ohm circuit....

Most current meters introduce a very very small amount of resistance which shouldn't affect the current reading.I believe a good amp meter should be down around 1/1000th of an ohm or less.
 

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