50 with a 6 volt coil

[Kerry50]

I have researched and read the threads about this. I just want to make sure I understand it.
I had a professional rewire my 50 a few years ago. Lately it got to where it wouldn't start by cranking. I could pull start it and it would fire right up. I checked the fire to the points and nothing. So I by-passed the ballast resistor and it fired right up. Checked the resistor and it was burned in two.
What I have: 6 volt coil that says on it no external resistor needed.
So my question is, do I do away with the resistor and keep the coil I got or do I need to buy a different coil and new resistor?

 

[Kerry50]

 

[wore out]

Your 6 Volt coil does NOT need an external resistor when used in a 6 volt system.

But your tractor has a 12 Volt system and a resistor IS needed to use the 6 Volt coil on the 12 Volt system. (Nothing wrong with that setup.)

The oddity here, though, is that it couldn't have started, even when pulled, if the resistor was completely burned in half.

It must have been barely functioning and completely broke when you removed it/handled it/examined it.

This post was edited by wore out on 10/25/2023 at 08:38 am.

 

[Kerry50]

Wore out, it is odd that it would start
when pulled. I agree with you that it must
have had some contact but not all the
time.
So, if what I got is fine, I wonder what
caused the resistor to burn out?

 

[wore out]

''I wonder what caused the resistor to burn out?''

Perhaps it was made in ''The Land of Almost Right''?

If the ignition was ever left ''ON'' with the engine not running, breaker points closed, the resistor will get red hot, as well as the possibility that the breaker points and/or the coil will got HOT and may get damaged, as well.

 

[John T]

Good afternoon Kerry, first here's some general information for you:

On a 12 Volt tractor you can use EITHER a full true 12 Volt coil (around 3 ohms resistance) no added external ballast required orrrrrrrrrrrrrrr a 6 volt coil (around 1.5 ohms) PLUS an external series voltage dropping (12 down to 6) ballast resistor........

If 12 volts was applied to a 6 volt coil it would overheat and until such time the points can overheat also. If 6 volts is applied to a true 6 volt (around 1.5 ohms) coil NO BALLAST SHOULD BE USED or the spark will be weak..

To your specific questions:

1) Lately it got to where it wouldn't start by cranking. I could pull start it and it would fire right up.

I've seen that happen if the battery is weak (or bad connections or grounds dropping voltage) and/or the starter is drawing excess current which drops coil voltage too low.

2) I checked the fire to the points and nothing. So I by-passed the ballast resistor and it fired right up.

That could possibly happen if the ballast or its wiring was bad (incorrect resistance) or totally an open circuit

3) Checked the resistor and it was burned in two.

See the above

4) So my question is, do I do away with the resistor and keep the coil I got or do I need to buy a different coil and new resistor?

DO NOT keep a 6 volt coil and run it non ballasted at 12 volts it will burn up !!!!!!!!!!!!!!!!!!

You can EITHER use a 6 volt coil PLUS a good working voltage dropping (12 down to 6) ballast resistor orrrrrrrrrrrrrr a full true 12 volt coil no ballast required

NOTE many 12 volt tractors that used a 6 volt coil PLUS a ballast also used a starting ballast by pass to improve cold weather starting AS ORIGINAL EQUIPMENT

Hope this helps and answers your questions

John T

 

[Kerry50]

John T thank you for your response. I went to NAPA and got a new ballast resistor. As you can see in the pics, the old resistor has no backing leaving the resistor exposed. The parts guy said maybe it got water on it and thats what caused it to burn out. Well, I do power wash this tractor quite a bit for tractor rides and parades. I'll bet thats what happened. Take a look at the new resistor from NAPA. The resistor is covered and not exposed. Good deal. Also, the wire in the resistor was not burned in two. Maybe that had something to do with it not starting by cranking.
One last question, why use a 6 volt coil with a resistor? Why not just use a 12 volt coil and do away with the resistor? You say a 6 volt coil with ballast helps in cold start. How does that work?

TY again

The ballast resistor I took off the tractor

Showing the old resistor with the wire still intact.

New ballast resistor with the resistor enclosed. A much better ballast resistor in my opinion.

 

[Pete in MD]

What is the NAPA # on your new resistor?

 

[John T]

Hi again Kerry, your latest question:

One last question, why use a 6 volt coil with a resistor? Why not just use a 12 volt coil and do away with the resistor? You say a 6 volt coil with ballast helps in cold start. How does that work? TY again

In situations where a 12 volt tractor uses a 12 volt coil, when cranking to start in cold weather, battery voltage (and therefore coil voltage) can drop significantly which yields a weak spark WHEN ITS NEEDED THE MOST....to start in cold weather..

However, if the 12 volt tractor uses a 6 volt coil PLUS the external series voltage dropping (12 down to 6) ballast resistor AND ITS EQUIPPED WITH A BALLAST BY PASS WHEN CRANKING FEATURE,,,,,,,,ONLY when cranking the ballast is by passed thereby reducing 12 volt battery voltage (say its down to 9 to 11 volts??) direct to the 6 Volt coil by passing the ballast FOR A BRIEF HIGHER ENERGY SPARK when its needed the most. Its (9 to 11 volts) ONLY present long enough to insure a good strong spark yet not over heat the coil or damage the points....Once cranking stops, you're back to closer 12 battery volts with 6 dropped across the ballast leaving 6 for a 6 volt coil

SURE many/most 12 volt tractors use a 12 volt coil no ballast required and start in cold weather and still work fine DUH.. Also, a tractor that came OEM with a 6 volt coil and ballast by pass when cranking can be converted to a full true 12 volt coil NO MORE BALLAST OR BALLAST BY PASS can still work fine no problem ITS JUST THAT THE 6 VOLT COIL WITH BALLAST AND BY PASS WHEN CRANKING has the POTENTIAL (especially in extreme cold or a weak battery or faulty starter) for improved cold weather starting. Don't anyone have a calf, 12 volt tractors and 12 volt coils (NO 6 volt coils and ballasts) are fine...

Hope this answers your question

John T

 

[Kerry50]

John T, ty sir. You answered my questions.

 

[John T]

Great, glad to help

John T

 

[Kerry50]

Here ya go Pete.

 

[Pete in MD]

Thanks.