M Farmall Napa 6v coil update...... Honda parts?

Well I appreciate all the replies from all of you re. my Napa 6v coil experience. For any of you who hadn't caught my last reply in that thread I had returned both of them and with much relief as they cost $43. They have no competition here in Warroad MN so we pay full retail. Neither worked in either of our 6v M Farmalls.

Because the tractor I was working on runs strictly off the battery w/ no generator the only 6v component on the tractor is the starter. After quizzing a few of you in another post regarding the voltage impact (6v vs 12v) on points/condenser it occurred to me that a 12v coil was the better choice. Checking on Ebay I could get a generic forklift coil to my door for about $20. But I didn't know if it would work so shied away from that option.

I don't know why I didn't think of it sooner but I then realized we had a whole pasture full of 12v coils. I picked a Honda and BOOM I'm in business. M runs like a top after sitting for years.

Thanks again for all the input. One last thing though. I will give you an update on the Napa coils. There was a lot of hypothesis in the former thread re. the Napa coils failing to work. None really satisfied me (somehow, an internally ballasted 6v coil just make zero sense to me)

I'll take this up with Napa and get the facts from the horses mouth. I'll let you know.

Glad you got it fixed--without rereading your original post, I think they meant internally ballasted 12 volt coil, not 6.

Okay granted, but honestly again, what would be the point of ballasting a 12 volt coil? Makes no difference to the points/condenser, right ...and why would you want a 6v spark when you can have a 12v spark.

Another note. As i recall the coil said "no external resistor needed." This seems to refer more to issues of radio interference than voltage conversion.

Some allow 12 volts for starting and run on 6 volts; I think 12 volts would fry the condensor. This subject has been gone over many times, I don't remember all the details. But I do know that the 460/560 use a ballast resistor in a 12 volt system.

Dave, Thanks for the update and youre sure welcome, glad we could help..... I thought I explained the whole 6 volt and 12 volt coil thing for you in my other two long posts pretty well, but its hard to put in a paragraph what would take a long article to cover correctly, perhaps this will help. I give 90 minute Seminars on Coil Ignition at several National John Deere shows so it obviously cant be covered here in detail in 5 minutes lol....

1) MANY (not all, read my earlier post) what some people call "internally ballasted coils" dont actually have any internal discrete resistors laying inside them, they have more wire length/coils or higher resitance wire in the primary so the total resistance is like 2.5 to 3.5 ohms for a 12 volt unti and 1.25 to under 2 for a 6 volt unit.....

2) A 6 volt coil has around 1.5 ohms primary resistance while a 12 volt has more like say 3 ohms NOW I BET YOU WONDER WHY LOL

THE REASON IS SO THE POINTS DONT HAVE TO SWITCH MUCH MORE THEN 4 AMPS OTHERWISE THEY WOULD BURN UP TOO FAST

ITS THE SWITCHING CURRENT OF MECHANICAL CONTACT POINTS THATS THE LIMITING FACTOR ADN WHY THERES AROUND 1.5 OHMS PRIMARY RESISTANCE IN THE 6 VOLT SYSTEM BUT TWICE THAT IN THE 12 VOLT

Its the same reason if you use a 6 volt coil on a 12 volt tractor you need the external current reducing voltage dropping ballast SO THERES A TOTAL OF AROUND 3 OHMS (1.5 for coil + 1.5 for ballast) in the primary circuit SO THE POINTS ONLY HAVE TO SWITCH 4 AMPS get it????????

Points arent different for 6 or 12 volt tractors, they are a current switching device (how many amps is whats critical) whose voltage withstand rating is wayyyyyyyyyyyyy higher then 6 or 12 volts anyway.

SOOOOOOOO if you read my two long previous posts plus this one it may (hopefully) help you figure out those coils and the difference in a 6 and 12 volt and the reasons why and why some require an external ballast while others dont.

ONCE MORE if the NAPA coils were 12 volt (which I suspect) they wouldnt work well on your tractor BECAUSE you still had that external ballast (which you shouldnt use with a 12 volt coil) and there was low current flowing through them butttttttttttt if you had tossed the ballast they likely woukld have worked fine becasue you then would have had 12 volts on a 12 volt coil. SIMILAR if you use other 12 volt coils laying around, DONT USE THAT BALLAST. If you use a 6 volt coil USE IT get it??????

Best Wishes n God Bless, if you like e mail me and maybe I can find one of the Ignition articles I had published in Green Magazine and send to you, theres not enough time here to explain what can take years of study to understand so hang in there n keep us posted

John T Retired Electrical Engineer

YES it makes a hugeeeeeeeeeeee difference cuz it determines how many amps the points have to make and break........ I have it covered in my post above....

ALSO theres no 6 volt or 12 volt spark, the coil steps the voltage up to several THOUSAND VOLTS.......

12 volT coils ARENT NORMALLY BALLSTED. Its the 6 volt coils on a 12 volt tractor that need external ballast otherwise the coil will overheat and the points burn up quickly....

What some call 12 volt "internally ballasted" was explained in my previous postings plus above one last time

best wishes now yall take care HOPE THIS HELPS YOU UNDERSTAND

John T

John,
Having read Dave's posts, I'm only guessing that he doesn't have a clue about electricity in an ignition system. I wish him well ingetting his tractors running, but it sure frustrating to try and give advice to someone who won't listen because of preconceived ideas/partial understanding.

Earlier, I had asked on this forum if the points/condenser were affected at all by an increase from 6v to 12v. The consensus there was no, so you bring up a new issue for me stating that an increase in voltage may cause condenser problems.

but this would be the only reasonable explanation for a ballast that i can think of..I mean damage to the condenser.

Anyway i do appreciate the conversation because I would like to clear up the gray areas for myself.

Thanks

John,
Thanks again for the review. I will be spending more time again looking through your explanation of the differences because I DO want to know exactly whats going on.

I did initially power the first coil with 12v (no ballast) In fact, I worried I might damage it so I put the ext. ballast on a bit later in the process. The distributor was working properly when the coil failed to fire. I tested it based on your check list. So, I believe the first Napa coil now was non-op.

The cost for Napa's 12 volt coil is $18.00. Their part number is IC14SB and it does have a ballast resistor built in. Hal

Keep a extra set of points in your pocket becaues you will need them

jimmy

Youre again sure welcome, hang in there I'm sure you will get her up n runnin.

John T

All engines that use a 12 volt system and point ignition use a resistor in the current supply to the coil. Some use a wire in the harness some use the ceramic and some use a coil with one built in. John T explains it perfectly a couple posts up. Points open and close thousands of times a minute. With the higher pressure or amps of 12 volts they will erode or burn themselves up rapidly. That's why the resistor is used to cut the current and greatly extend the life of the points. To sum it up if you have a 6 volt system no resistor is needed, if you have a 12 volt system a resistor is required in some form or points will have a short life. 6 or 12 volts has no effect on the condenser so don't let that confuse you more.

If you do not have a generator or alternator, then you have about 12 volts at the battery. If you have a generator or alternator then the voltage would likely be 13.5 - 14 volts. I would not worry about burning anything up. An external resister should be fine with a 12 volt coil. Actually on my old 4 cyl race car I removed the alternator and the external resistor and never burned up any points or condensers. I am not an expert, just my experience.

> if you have a 12 volt system a resistor is
> required in some form or points will have a
> short life.

The coil will also have a short life. It will overheat at low rpm due to the long dwell time.

(quoted from post at 17:25:42 11/21/08) > if you have a 12 volt system a resistor is
> required in some form or points will have a
> short life.

The coil will also have a short life. It will overheat at low rpm due to the long dwell time.

Click to expand...

I agree with everything except the last eight words. The dwell time as a percentage of each second or minute does not change with RPM, unless you count zero, when it 'dwells' as long as the points are closed to start with. The length of each power cycle is greater, but so is the cool-down time, both being in milliseconds. I would think it would overheat equally at any RPM.

This might be construed as hijacking a post, but my question is how many amps are used in the electronic conversion kits? Barry.

A 12 volt system must be have either an external resistor or internal resistor. In old auto engins the resistor would reduce the voltage over the coil to around 8 volts. This voltage reduction was for the COIL as those of us who lived in that era can testify. Remove or bypass the resistor and the coil will burn up. Points and condensers have always been rather inexpensive and coils more expensive. LMack

(quoted from post at 17:50:01 11/21/08)

(quoted from post at 17:25:42 11/21/08) > if you have a 12 volt system a resistor is
> required in some form or points will have a
> short life.

The coil will also have a short life. It will overheat at low rpm due to the long dwell time.

Click to expand...

I agree with everything except the last eight words. The dwell time as a percentage of each second or minute does not change with RPM, unless you count zero, when it 'dwells' as long as the points are closed to start with. The length of each power cycle is greater, but so is the cool-down time, both being in milliseconds. I would think it would overheat equally at any RPM.

Click to expand...

At high rpm & thus short dwell time, the current may never reach the coil's maximum, since it rises exponentially and at such rpms, the dwell time is shorter than the time dictated by the L/R ratio. HOWEVER, at low rpm, the dwell time being longer, coil current reaches it's maximum & then just sits there, at that maximum, making heat until the dwell period ends (current is lower trace). Even without an oscilloscope (using a simple ammeter) you can observe the AVERAGE current decrease into the coil as rpm increases. The product of this average current times voltage does heat the coil more at the lower rpm/longer dwell time. Because of this, heating increases by a factor greater than just the time, but cooling is just proportional to time.

JMOR--Thanks--I learned something today with that explanation.

I'm glad! After writing it, I was a little concerned that it wasn't clear enough.
Have a good 'un!

I used to work at Napa, the coils will say right on them that a external resistor is required or not, doesn't take a brain surgeon to figure that part out. I always use a new 12v coil with no external resisotr required when I convert a tractor to 12v. I don't like the resistor hanging on the tractor and more wires to come loose, they should be less than $20 and you don't have to worry about it.

(quoted from post at 05:42:54 11/21/08) Keep a extra set of points in your pocket becaues you will need them

jimmy

Click to expand...

Correct-O!
mike

Condensers are rated for 2 to 3 hundred volts.There is enough voltage to shock you across ignition points when they open.You will not find a resistor inside an ignition coil.Theres no room plus the added heat will kill the coil in a short time.I test condensers at 400 volts.