JMOR, A resistor question.

[Jim.ME]

Why is it that some say the original 0.5-ohm resistor must remain when converting to a 12-volt coil on a front mount distributor? I can see it if using the original 6-volt coil and an addition ballast resistor. Wouldn't the ohm reading of the 12-volt coil determine that the same as it does on any other conversion? Pertronix instructions for 12 volts say to remove the resistor when using a 12-volt coil. The half ohm shouldn't make or break a 12-volt coil working but I have never seen a reason as to why that resistor itself should not be removed from the circuit, as long as coil resistance is correct. The best I have figured is that given the resistor was used with the 6-volt coil, the front mount distributor points should be limited to a lower current than points in a side mount, with either voltage. I can see the resistor assembly staying, as the one terminal stud not connected to the resistor is used a termination point for several power wires. Not looking for an argument, just a sound answer of why some say that resistor must stay.

Thanks,
Jim

 

[HFJ]

i installed a pertronix 4 years ago. and yes, they told me to take the OEM resistor out of the circuit. i did, but the part is still there- like u said, acting as a terminal block.

 

[Jim.ME]

i installed a pertronix 4 years ago. and yes, they told me to take the OEM resistor out of the circuit. i did, but the part is still there- like u said, acting as a terminal block.

Understood and agree, my question pertains to a regular points ignition.

 

[Jim L WA]

Jim.ME it will be interesting to see what JMOR says. But in my pea brain, the ballast resister is there to allow a higher voltage to the coil while the starter in engaged. Once the tractor starts and the resister heats up the voltage to the coil drops. The concept would be the same for either a 6 or 12 volt system.

 

[Jim.ME]

Jim.ME it will be interesting to see what JMOR says. But in my pea brain, the ballast resister is there to allow a higher voltage to the coil while the starter in engaged. Once the tractor starts and the resister heats up the voltage to the coil drops. The concept would be the same for either a 6 or 12 volt system.

If there is a ballast resistor it reduces the voltage going to the coil which in turn means less current flow through the points during normal operation, increasing their life. Some starting systems use a bypass circuit to send full voltage from the solenoid, when engaged, to the coil side of the resistor, bypassing the resistor during starting. The OEM resistor on an 8N does not get bypassed.

 

[wore out]

If there is a ballast resistor it reduces the voltage going to the coil which in turn means less current flow through the points during normal operation, increasing their life. Some starting systems use a bypass circuit to send full voltage from the solenoid, when engaged, to the coil side of the resistor, bypassing the resistor during starting. The OEM resistor on an 8N does not get bypassed.

"The OEM resistor on an 8N does not get bypassed."

It doesn't need to be, as it is a "PTC" (Positive Temperature Coefficient) resistor and has a low resistance when cold, and it's resistance doubles (more or less) as it heats up from current flowing through it.

So, as long as the engine starts within a half-minute or less after primary current begins to flow the system acts more or less the same as those with a "starting bypass".

Not all primary circuit resistors are "PTC", ones used with "starting bypass" setups typically are NOT.

 

[JMOR]

Why is it that some say the original 0.5-ohm resistor must remain when converting to a 12-volt coil on a front mount distributor? I can see it if using the original 6-volt coil and an addition ballast resistor. Wouldn't the ohm reading of the 12-volt coil determine that the same as it does on any other conversion? Pertronix instructions for 12 volts say to remove the resistor when using a 12-volt coil. The half ohm shouldn't make or break a 12-volt coil working but I have never seen a reason as to why that resistor itself should not be removed from the circuit, as long as coil resistance is correct. The best I have figured is that given the resistor was used with the 6-volt coil, the front mount distributor points should be limited to a lower current than points in a side mount, with either voltage. I can see the resistor assembly staying, as the one terminal stud not connected to the resistor is used a termination point for several power wires. Not looking for an argument, just a sound answer of why some say that resistor must stay.

Thanks,
Jim

I do not know why some say keep it. I can give my opinion. They may think it could help save points when key on & stalled, as the resistance more or less doubling to tripling with heat would serve to reduce stalled current, but in this case, would a 20-30% reduction save coil or points? Even cold, it will reduce the coil current during startup, not desirable, but small enough the it may not matter, as cold it is only adding a few tenths of an Ohm to the 12v coils 3.25 Ohms.

 

[Jim.ME]

I do not know why some say keep it. I can give my opinion. They may think it could help save points when key on & stalled, as the resistance more or less doubling to tripling with heat would serve to reduce stalled current, but in this case, would a 20-30% reduction save coil or points? Even cold, it will reduce the coil current during startup, not desirable, but small enough the it may not matter, as cold it is only adding a few tenths of an Ohm to the 12v coils 3.25 Ohms.

That matches my opinion/thoughts. Just like changing a 6-volt "can" coil system to a true (no external resistor required) 12-volt "can" coil, no ballast resistor is used. Given many distributors use the same points for 6 and 12-volts, and in some cases the same condenser, I don't see the OEM resistor saving the points appreciably. I asked you as I see it is included in at least some of your drawings. I understand at least some of those were what people wanted.

Thank you.
Jim

 

[Jim.ME]

"The OEM resistor on an 8N does not get bypassed."

It doesn't need to be, as it is a "PTC" (Positive Temperature Coefficient) resistor and has a low resistance when cold, and it's resistance doubles (more or less) as it heats up from current flowing through it.

So, as long as the engine starts within a half-minute or less after primary current begins to flow the system acts more or less the same as those with a "starting bypass".

Not all primary circuit resistors are "PTC", ones used with "starting bypass" setups typically are NOT.

I agree with you, if a 6 volt coil it being used with a conversion to 12-volts (the extra ballast resistor has to be added with the 6-volt coil as well).

My question was, "Why is it that some say the original 0.5-ohm resistor must remain when converting to a 12-volt coil on a front mount distributor?"

Agreed the PTC resistor acts like a "starting bypass" system used with a ballast resistor and a 6-volt coil in a 12-volt system. I don't know of a bypass system used with a 12-volt coil (a 12-volt coil being one properly wound for resistance to operate in a 12-volt system without an external resistor).

 

[JMOR]

That matches my opinion/thoughts. Just like changing a 6-volt "can" coil system to a true (no external resistor required) 12-volt "can" coil, no ballast resistor is used. Given many distributors use the same points for 6 and 12-volts, and in some cases the same condenser, I don't see the OEM resistor saving the points appreciably. I asked you as I see it is included in at least some of your drawings. I understand at least some of those were what people wanted.

Thank you.
Jim

A lot different with stock 6v system where that PTC resistor can be equal to or nearly twice the coil resistance, depending on temperature.

 

[Jim.ME]

A lot different with stock 6v system where that PTC resistor can be equal to or nearly twice the coil resistance, depending on temperature.

Agreed.

If one is rewiring one of these to a 12-volt system, the entire (A8NN1250B, current Ford/NH part number) resistor assembly could be removed, and the ammeter terminal used as the junction point for the generator/alternator output as well as all loads, as is done on many machines. That could clean things up for some and avoid buying a new resistor assembly just for the junction terminal function. Or the junction block (8NNN-14448) used on later models could be installed if a junction block was wanted.

 

[wore out]

I agree with you, if a 6 volt coil it being used with a conversion to 12-volts (the extra ballast resistor has to be added with the 6-volt coil as well).

My question was, "Why is it that some say the original 0.5-ohm resistor must remain when converting to a 12-volt coil on a front mount distributor?"

Agreed the PTC resistor acts like a "starting bypass" system used with a ballast resistor and a 6-volt coil in a 12-volt system. I don't know of a bypass system used with a 12-volt coil (a 12-volt coil being one properly wound for resistance to operate in a 12-volt system without an external resistor).

At one point in the past the consensus here was that the modern commonly sold aftermarket "front-mount 12 Volt" coils were designed with the idea that the OEM resistor would remain in place.

Of course with the source and quality of today's replacement parts the primary resistance of these replacement coils likely varies considerably.

 

[Jim.ME]

At one point in the past the consensus here was that the modern commonly sold aftermarket "front-mount 12 Volt" coils were designed with the idea that the OEM resistor would remain in place.

Of course with the source and quality of today's replacement parts the primary resistance of these replacement coils likely varies considerably.

Sounds like when one is going to install a square 12-volt coil it would be prudent to check it with an ohmmeter and determine the need for a resistor or not with a given coil. And then if the distributor was modified to use a 12-volt can coil that would not apply.

 

[Tim PloughNman Daley]

I do not know why some say keep it. I can give my opinion. They may think it could help save points when key on & stalled, as the resistance more or less doubling to tripling with heat would serve to reduce stalled current, but in this case, would a 20-30% reduction save coil or points? Even cold, it will reduce the coil current during startup, not desirable, but small enough the it may not matter, as cold it is only adding a few tenths of an Ohm to the 12v coils 3.25 Ohms.

YEP, we've discussed this before. Just easier and best fo rookies to keep it in. So, while we're on topic of the front mount, Ballast Resistor, and 12V conversions, your PICTOGRAMS show both conversions with one keeping the OEM AMMETER in the circuit and the other using a VOLTMETER swap out. Please explain both with pros and cons stated. Is one better than the other and why? There have been many opinions expressed over the years here but few with legit data backup. It seems you would want to see the charging rate on the system with an AMP Gauge. A VOLTMETER just showing the ALT voltage charge means not much to me. FORD did away with the AMMETER in 1957 on the '01 Series changing to an IGN CHARGE IDIOT DASH LAMP for a reason. Ineffective? Also in 1957 were the Diesel Models now using a12V NEG GRN battery but still with a GEN and a VR. The 12V ALTERNATOR did not come into production until the early 1960's, first with Chrysler. As ALT's came in dashes only had an idiot lamp now or with a VOLTAGE charging rate scale - look at your car/truck.

Tim Daley (MI)

 

[Jim.ME]

YEP, we've discussed this before. Just easier and best fo rookies to keep it in. So, while we're on topic of the front mount, Ballast Resistor, and 12V conversions, your PICTOGRAMS show both conversions with one keeping the OEM AMMETER in the circuit and the other using a VOLTMETER swap out. Please explain both with pros and cons stated. Is one better than the other and why? There have been many opinions expressed over the years here but few with legit data backup. It seems you would want to see the charging rate on the system with an AMP Gauge. A VOLTMETER just showing the ALT voltage charge means not much to me. FORD did away with the AMMETER in 1957 on the '01 Series changing to an IGN CHARGE IDIOT DASH LAMP for a reason. Ineffective? Also in 1957 were the Diesel Models now using a12V NEG GRN battery but still with a GEN and a VR. The 12V ALTERNATOR did not come into production until the early 1960's, first with Chrysler. As ALT's came in dashes only had an idiot lamp now or with a VOLTAGE charging rate scale - look at your car/truck.

Tim Daley (MI)

So, the reason to leave the OEM resistor assembly in place when doing a 12-volt conversion, using a 12-volt coil, is because it is easier and best for a rookie.

Ammeter, Voltmeter, indicator light, or nothing, is a personal choice. Here is why I prefer a voltmeter over an ammeter, indicator light, or nothing. A voltmeter shows the charging circuit is producing voltage ("pressure") above the battery voltage ("storage pressure") to push amps ("flow") back to the battery ("storage reservoir"). Since an ammeter shows amps (flow) you can have no amps showing meaning; the battery is charged, or the charging unit voltage is below the battery voltage and unable to charge the battery, or accessories are using all the charging current with a minimal amount possibly going to the battery, or there is a "break" in the charging circuit wiring. What is commonly used to test to see which it is? A voltmeter. Using a voltmeter in place of an ammeter will show charging voltage and battery voltage when the engine is stopped, so you have an idea of battery condition as soon as the switch is turned on.

 

[Tim PloughNman Daley]

So, the reason to leave the OEM resistor assembly in place when doing a 12-volt conversion, using a 12-volt coil, is because it is easier and best for a rookie.

Ammeter, Voltmeter, indicator light, or nothing, is a personal choice. Here is why I prefer a voltmeter over an ammeter, indicator light, or nothing. A voltmeter shows the charging circuit is producing voltage ("pressure") above the battery voltage ("storage pressure") to push amps ("flow") back to the battery ("storage reservoir"). Since an ammeter shows amps (flow) you can have no amps showing meaning; the battery is charged, or the charging unit voltage is below the battery voltage and unable to charge the battery, or accessories are using all the charging current with a minimal amount possibly going to the battery, or there is a "break" in the charging circuit wiring. What is commonly used to test to see which it is? A voltmeter. Using a voltmeter in place of an ammeter will show charging voltage and battery voltage when the engine is stopped, so you have an idea of battery condition as soon as the switch is turned on.

YEP

 

[Hobo,NC]

I do not know why some say keep it. I can give my opinion. They may think it could help save points when key on & stalled, as the resistance more or less doubling to tripling with heat would serve to reduce stalled current, but in this case, would a 20-30% reduction save coil or points? Even cold, it will reduce the coil current during startup, not desirable, but small enough the it may not matter, as cold it is only adding a few tenths of an Ohm to the 12v coils 3.25 Ohms.

Most are not tooled up to get a precision measurement, the safe bet use the original resistor. I have never seen using the resistor be an issue on a square can coil standard are EI ignition.

 

[Tim PloughNman Daley]

Most are not tooled up to get a precision measurement, the safe bet use the original resistor. I have never seen using the resistor be an issue on a square can coil standard are EI ignition.

Hobo: Do you use EI in all your N's?

Tim Daley (MI)

 

[Hobo,NC]

Hobo: Do you use EI in all your N's?

Tim Daley (MI)

I don't own a running front mount. I have a few N's one has not ran in 20 years the other 7. Once I moved up to a Hundred series then replaced them with thousand series I have not needed a N. When customers with Ft. mounts keep having issues with their points ignition I recommend EI. I have only had one that after a few years would not start when I went to check it I put my spark checker on it, it had good spark the fix was replace a dragging starter. I had another (6V) the fix was to replace the coil. On that one I could not find the issue I threw a points distributor on it with the same coil it ran the fix was a new coil. I played with that one quite a bit as I had the hood off I scoped it and ran every test I could dream up all for reference down the road. It had the old style starter drive as soon as the engine hit the drive would kick out. A failing coil can be extremely frustrating I have no problem throwing a new coil at it.

What I learned diagnosing EI is its basically the same test as a points system, EI is not as friendly to a weak/failing/intermediate coil, trust your spark tester. I don't trust my judgment without a spark tester nor do I trust anyone else's. Not every issue is spark related but it can be the easiest one to confirm, confirm it without a doubt and move on.

 

[boler76]

no matter if you have 6v or 12v square front mount coil you need the resistor that changes resistance with temperature , otherwise eventually you will need another new coil, .