Front mount coil more

[grandpa Love]

We own 5 fords, 6 if you count my dad's
N mutt. Everyone came to us in various
states of 12 volt conversion. None have
a OEM ballast resistor. On all the other
fords I have totally rewired them. They
all work great. They all have a 12 volt
coil,no resistor anywhere. I would like
to understand what the OEM ballast
resistor does,why it's needed, and why
does this site sell a 6 volt and 12 volt
coil for a front mount distributor. If
you have to wire them up the same what's
the point of using the 12 coil?
Electrical is not my strong suit,
explain it in simple terms, or it will
go right over my head. Thanks.

 

[jimtrs]

(quoted from post at 07:13:05 07/16/21).....I would like
to understand what the OEM ballast
resistor does,why it's needed, and why
does this site sell a 6 volt and 12 volt
coil for a front mount distributor. If
you have to wire them up the same what's
the point of using the 12 coil?

Calling @Bruce(VA)


I'll try briefly

The ballast resistor provides less resistance cold (when starting), for easier starts. Then provides more resistance as it heats up to protect the fragile front mount coil, once running.

12 volt front mount coils can be used during a 12v conversion, eliminating the need for an ADDITIONAL ceramic resistor to keep the amperage in line for the 6 volt coil.

 

[TheOldHokie]

(quoted from post at 07:13:05 07/16/21) We own 5 fords, 6 if you count my dad's
N mutt. Everyone came to us in various
states of 12 volt conversion. None have
a OEM ballast resistor. On all the other
fords I have totally rewired them. They
all work great. They all have a 12 volt
coil,no resistor anywhere. I would like
to understand what the OEM ballast
resistor does,why it's needed, and why
does this site sell a 6 volt and 12 volt
coil for a front mount distributor. If
you have to wire them up the same what's
the point of using the 12 coil?
Electrical is not my strong suit,
explain it in simple terms, or it will
go right over my head. Thanks.

The OEM ballast resistor changes value as the tractor runs. At cold startup it is low resistance and provides full voltage/curreny for improved starting. As the tractor runs the resistor warms up and resistance increases to reduce current flow going to the coil. This is needed for coils that cannot handle full current for sustained periods of operation. They overheat and fail. If the construction of the coil is such that it can handle higher currents without damage there is no need for the ballast resistor.

Simple enough?

TOH

 

[grandpa Love]

Wow.....well. I dunno what to think. My dad has used this tractor for several years after we got it running. No OEM ballast resistor, just a ceramic one in line to coil. He uses the tractor a good bit and never had an issue, until last week. I wouldn't start. Didn't have a test light or anything with us ,but pulled a spark plug and saw that it had no spark. Took distributor off and filed points, cleaned them with a piece of paper and put it back on. Still no spark. Been 3 plus years, so we ordered points, condenser, plugs, and coil. Tractor is 12 volt so that's the coil I ordered. Assuming ( wrongly??) That means it was designed to handle 12 volts like the round coils on our 640, 840,950,960........ Nothing is as simple as I think......

 

[Bruce (VA)]

ALL front coils require the oem ballast resistor; doesnt matter if they are 6v or 12v. Thats because technology & materials being what they were in the 30's, that square coil would melt if it ran on much more than 4 amps for any length of time. (see tip # 38 for an example). In order to get a hot spark at the same time the starter was drawing max current from the battery, a ballast resistor was added in the ignition circuit. What that did was add about .3 ohms of resistance in the circuit, added to the 1.5 ohms of the coil. That got you 3.5 amps or so at start up. As the voltage increased when the engine was running to about 7.5 volts, the resistor heated up, adding more resistance in the circuit. 1.0 ohms hot, plus 1.5 ohms of the coil got you down to 3 amps or so to keep from melting the coil. The same rule (actually, Ohm's Law) applies to a 12v circuit. I= E/R. Current equals voltage divided by resistance.

The oem Ford front coil had an internal resistance spec'd at 0.470 to 0.510 ohms . That resulted in a rather quick coil meltdown w/o a resistor. Newer 6v coils spec out around 1.5 ohms and the 12v coils can get to over 2 ohms. So the higher internal coil resistance will allow for greater current w/o a resistor before they melt. Some folks have gone years w/ no oem ballast resistor on a front coil. The problem is that the coil will eventually break down under load......usually a mile from the barn w/ 3 acres of hay down and a storm coming.

If the above isn't TMI for you, click on the link for an N News Article I wrote a few years ago.

https://www.facebook.com/photo?fbid=10215359717820415&set=pcb.1050758781754071
75 Tips

 

[Bruce (VA)]

just a ceramic one in line to coil.

What that got you was a fixed resistance ( of some unknown value......usually 1.5 ohms) that never changed as it heated up. So, you had that same high resistance on a cold start.

It will not handle 12 volts like a round coil because it is not designed like a round coil.
75 Tips

 

[grandpa Love]

Bruce, thanks I will check it out. I guess I will need to see how it's wired up and post back here so y'all can tell me where the ballast resistor wires in. My dad drives the tractor often, but usually never more than 15-20 minutes at a time. Maybe that's why everything worked for 3+ years as it was?

 

[Bruce (VA)]

Google wiring diagrams JMOR and it will show you a complete schematic. It goes between the ignition switch and the coil.
75 Tips

 

[Jim L WA]

Just to add to this, even vehicles from the 50s and 60s used some sort of resister bypass while starting. G.M. vehicles, for instance, ran with a resistance wire to the coil. But when the solenoid closed during startup it shot 12 volts directly to the coil.

 

[TheOldHokie]

(quoted from post at 13:05:12 07/16/21) Just to add to this, even vehicles from the 50s and 60s used some sort of resister bypass while starting. G.M. vehicles, for instance, ran with a resistance wire to the coil. But when the solenoid closed during startup it shot 12 volts directly to the coil.

Ballast bypass systems were used into the 90's if not longer.

TOH

 

[Darryl 2Ms]

Hi guys, I'm going to jump in on this one! I just put a 12 volt round can conversion coil on my 9N. Made by Pertronix, eliminates the front mount. I kept the points for now, and
mounted the condenser on top of the distributor. I have a new OEM ballast resistor in place, and before i converted i also had the ceramic resistor. Can i eliminate the ceramic
now? The other day while test running it, it died. Took the 2 wires from the ceramic resistor, touched the together and it started. Hooked up the ceramic again later and it was
ok. Can you say frustrating??!! So with just the OEM by itself, the points will live? I didn't go with the electronic ignition for now, because i see a lot of guys frying them.
Sooo? one resistor? Thanks .... Darryl

 

[Smokeonthewater]

Pertronics should have included instructions to answer this but I suspect that the included coil likely doesn't require any resistor

 

[TheOldHokie]

(quoted from post at 21:10:46 07/16/21)
Pertronics should have included instructions to answer this but I suspect that the included coil likely doesn't require any resistor

The Pertronix instructions are quite clear. They provide the actual internal resistance of all Flame Thrower coils and direct you to remove all ballast resistance in both 12V and 6V installations. If you are using a non-Pertronix coil you are on your own.

TOH

 

[47fivewindow]

Darryl, the electronic unit needs a minimum 8 or 9 volts. The 6 volt starter needs only 5v to spin the tractors motor. If the starter draws the battery below 8v it spins but doesn't fire. Sometimes when you release the starter they will start before it stops spinning. A multi meter will tell the story, put it on DC volts and hook it to the - side of the coil. It is spinning, so I know it has voltage doesn't work here.

 

[47fivewindow]

I reread your post and see you still have the points. I would eliminate the extra resistor.

 

[Darryl 2Ms]

Thanks for the advice. I had a feeling to get rid of the ceramic resistor. 47 five window?? As in chevy pickup? Seems we all have gearhead disease. I have a couple of 54 3/4 tons myself. Just three windows though. Take care.....Darryl

 

[Tim PloughNman Daley RIP]

Only the Ford Front Mount Distributor uses the OEM Ballast Resistor. You don't say which 5 models you have.

Tim Daley(MI)