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6 volt coil in 12 volt system

G

gail brigham

Member
I recently changed plugs, wires, points, coil, etc on my Ford 800 and when I changed the coil out it was a 6-volt , not a 12 volt coil. The tractor had been running but would lose power when it got hot and someone on the YT discussion forum suggested among other things that the coil be changed. In fact, the old coil was corroded mightily inside the connection where the coil wire goes to the distributor but everything still worked. Okay, my question is: Should I go back with a new 6-volt coil? It won"t start with the new 12 volt coil for whatever reason. Thanks again to whomever replies.
 
(quoted from post at 07:48:41 05/28/10) I recently changed plugs, wires, points, coil, etc on my Ford 800 and when I changed the coil out it was a 6-volt , not a 12 volt coil. The tractor had been running but would lose power when it got hot and someone on the YT discussion forum suggested among other things that the coil be changed. In fact, the old coil was corroded mightily inside the connection where the coil wire goes to the distributor but everything still worked. Okay, my question is: Should I go back with a new 6-volt coil? It won"t start with the new 12 volt coil for whatever reason. Thanks again to whomever replies.
Click to expand...

All ignition coils are 6 volt. Some of them have an internal resistor which allows them to be used on a 12 volt system, and others require an external resistor if they will be used on a 12 volt system.

If your coil is labeled for 12 volts, it DOES have an internal resistor, and if your tractor is a 6 volt system that coil will NOT work.
 
You may have a bad coil off the shelf, but I doubt it. Do you have spark from the coil wire? If not, re-check your points and perhaps the new condenser is bad, but not likely. If your coil wire does have spark, check your rotor for correct installation and make sure you didn't forget to put it in. (guess how I know about that one, OOOOOpsy.). Also, check to see if there is a ballast resistor somewhere in the coil wiring. There may well be one with a 6V coil on there. If so, you either need to remove it or go back to a 6V coil. Good luck.
 
Ah but the question is do you have a ballast resister in the system?? If you do then using a 12 volt coil with internal resister will not work and that maybe your problem. If you do not have a ballast resister in the system then you have your points set wrong or a wire loose or you have a short inside the distributor which can happen when installing new points. Point gap by the way should be 0.025, manual says 0.024-0.026
 
I traced the wire toward the battery looking for an external resistor but couldn't find one. I thought it would look like an automobile resistor made of ceramic mounted somewhere along the way to the switch terminal, etc. (nothing on the distributor side for sure). And yes, I probably should check for something else I may have overlooked. By the way, it shouldn't matter which way the distributor locks in right? I did match the #1 wire with the hole in the dist. that is marked with a "1" ..... with the notch in the dist. cap in the right place I should be okay, huh? That's the only other thing I can think of .... points were set at .025 just like the manual prescribes, everything else looks to be okay.
 
Not to make you sound like a dummy, but did you gap the points on the lobe or flat of the shaft??? The reason I ask that is Top Secret.....

Dave
 
I did set it on the high point of the shaft. I also rotated the thing with the starter and found the gap opening and closing to satisfaction............ i.e., all looked well
 
OK. Do you have any spark at the coil wire and/or at any spark plug wires? If so, you should probably find top dead center and check your distributor timing. If not, you must have a wiring/coil/points/condensor issue.
 
(quoted from post at 08:49:25 05/28/10) I traced the wire toward the battery looking for an external resistor but couldn't find one. I thought it would look like an automobile resistor made of ceramic mounted somewhere along the way to the switch terminal, etc. (nothing on the distributor side for sure). And yes, I probably should check for something else I may have overlooked. By the way, it shouldn't matter which way the distributor locks in right? I did match the #1 wire with the hole in the dist. that is marked with a "1" ..... with the notch in the dist. cap in the right place I should be okay, huh? That's the only other thing I can think of .... points were set at .025 just like the manual prescribes, everything else looks to be okay.
Click to expand...

Now you've lost me. #1 spark plug DOES go to the #1 position on the distributor cap, and that cap SHOULD fit on the distributor in only ONE position, but if you've had the distributor OUT of the engine, or otherwise moved the distributor, it is CRITICAL that it be put back in the correct position.
 
No such thing as a pure 6 volt or 12 volt coil. A tractor with a 12 volt "system" starts at 9 volts and runs at around 13-14 volts.

What coil you use depends on how it's wired in. The vast majority of "12 volt" systems with breaker-points use what you are calling a "6 volt" coil.
 
"All ignition coils are 6 volt. Some of them have an internal resistor."

That's COMPLETE nnalert!

If you can show me a common generic ignition coil made in the last 40 years that actually has a resistor inside it I'll buy you a steak dinner.

Actually, a coil made for 12 Volts WITHOUT the use of an internal resistor is simply wound with more turns of wire in it's primary so NO resistor, internal OR external is needed.
 
IF you removed the distributor from the engine and didn't mark where the rotor was pointing when you pulled it and didn't place the rotor pointing to where you mark it. You need to start over.

You need to remove No1 sparkplug near the radiator and bring No1 piston to TDC on the compression stroke by holding your thumb over the plug hole while a helper hand cranks the engine slowly until you feel pressure and until that piston is at TDC. Then point the rotor at the No1 plug tower and install the disributor.

If you didn't remove the distributor you need to use a volt meter to see if battery vlotage is at the coil. With the points open you should have voltage on both small terminals on the coil. Hal
 
Technically speaking a 'coil' is not a voltage device but a CURRENT device. Any resistance applied within the circuit is 'current limiting.'
These 6v-12v conversions take several forms but the conventional form is to reuse the original coil and insert a ‘current limiting resistor’ so as not to overheat the winding in the coil. In some cases the coil is replaced with a ‘12v coil.’ I really don’t know how the construction of the 12v differs from a 6v. Some say a resistor is added some say more windings are added. The point is that design says X# of amperes in the circuit and if you are replacing the old coil with a new one of, probably, twice the resistance sufficient current will not be developed to make an adequate spark.
Verify you have a power resistor in the circuit and remove it and use the new coil or go back to the old coil. Prove the old coil by running the tractor. If it is in fact it’s failing when hot toss it and replace. If not, you saved the price of a coil.
Two things I’ll mention: (BTDT) If you are going to rebuild a circuit replace one part at a time with a like part including the wire. If you’re trouble shooting, change out one part at a time. If you wholesale throw parts you will never know what solved the problem.
Good luck and have fun.
 
I didn't remove the distributor, only the cap. Anyway, I managed to get it to start with the new "12 volt" coil. I really appreciate all the comments on the forum today........... I learned a lot. It still blows me away how useful these discussion forums are and how gracious/helpful people can be.
Thanks to everyone who posted!
Lane
 
(quoted from post at 10:56:01 05/28/10) "All ignition coils are 6 volt. Some of them have an internal resistor."

That's COMPLETE manure!

If you can show me a common generic ignition coil made in the last 40 years that actually has a resistor inside it I'll buy you a steak dinner.

Actually, a coil made for 12 Volts WITHOUT the use of an internal resistor is simply wound with more turns of wire in it's primary so NO resistor, internal OR external is needed.
Click to expand...

????????????????????????????
 
(quoted from post at 16:18:15 05/28/10) I didn't remove the distributor, only the cap. Anyway, I managed to get it to start with the new "12 volt" coil. I really appreciate all the comments on the forum today........... I learned a lot. It still blows me away how useful these discussion forums are and how gracious/helpful people can be.
Thanks to everyone who posted!
Lane
Click to expand...
At the very least, you could reveal to the world what it was that you did to make it start. :roll:
 
Doesn"t this also imply the the number of secondary windings have to increase to get the proper induced voltage in the secondary circuit?
 
I would say yes, to keep their same 98:1 turns ratio. I took apart both an old 6v/0.6 ohm front mount coil and a newer so called 12v/2.5 ohm front mt coil. The primary wire diameter in the 6v was 0.025 inch and in the "12v" was 0.0179 inch.
Wire size difference, while keeping same number of turns, isn't enough to gain the (2.5-0.6)=1.9 ohms, so my conclusion was that both changes were made (more turns & smaller wire), at least for these two examples. No I didn't try to count the 170 (?) primary or 16,500 secondary turns. Nor unwind 75 feet of primary out of those little windows or the 6,000 feet of 0.003 in. secondary wire which has to come off before you can get to the primary. :wink:
 
(quoted from post at 14:46:36 05/28/10) Rusty you just proved you dont know nuthin, you dont even suspect nuthin.
Click to expand...

Have it your way if you want, but I'll keep on selling the internally resisted coils for 12 volt conversions.

47b89c4998811_51089n.jpg
 
Old coils usually have it stamped in the metal underneath "use with resistor".I am inclined to think if it needs a resistor it would say so otherwise I take it they are manufactured to apply to the application.

I just replaced a set of points on my Fergy and it had a fibre washer included which goes between the static and moving part.just something else to watch.
 
There is no room in standard coils for a 3 inch long 30 watt resistor.The heat generated by the resistor would burst the coil.Cut one of the coils you are selling and post a pix of the internal resistor.Coil voltage is adjusted by using wire turns and wire size.
 
The coil DOES NOT say it has a internal resistor. All it says is one is not required externally.

Hack that monster apart with yer hacksaw and take a picture of the resistor in there!

Brad
 
I figured someone would ask what I did but I probably should do like Dave2 said yesterday and say that it is "top secret." Seriously, I had the plug wires in the wrong holes. I used the old cap to make sure I went back just like the old one but screwed up. Funny how I thought it had to be the coil. I learned so much from everyone yesterday-it was a tutorial on coils, resistors, interchangeability, etc.
Again, thanks for the help. This forum is priceless.
Lane
 
(quoted from post at 09:51:13 05/29/10) I figured someone would ask what I did but I probably should do like Dave2 said yesterday and say that it is "top secret." Seriously, I had the plug wires in the wrong holes. I used the old cap to make sure I went back just like the old one but screwed up. Funny how I thought it had to be the coil. I learned so much from everyone yesterday-it was a tutorial on coils, resistors, interchangeability, etc.
Again, thanks for the help. This forum is priceless.
Lane
Click to expand...
Hey, thanks for the follow up. You have to know that it will help someone somewhere along the way. Funny how it is always the last thing that one looks at that fixes the problem! :wink:
 
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