Ignition coil

[Leckster]

I am not getting a good spark (if any) to the plugs and when testing the electrical system on my motor I noticed that the coil was warm. I went to the store and bought a brand new coil hooked it up (positive battery to positive coil, Neg coil to distributor just like the manual states) and again this one became very warm within a few minutes.

Is it normal for the coil to get warm to the touch?
or do I have another problem going on here?
(Maybe a Short)

Don

 

[John T]

Often when a coil gets so hot you cant hold your hand on it, its cuz youre using a 6 volt coil on a 12 volt system AND NOT USING ANY NECESSARY SERIES EXTERNAL VOLTAGE DROPPING (12 TO 6) BALLAST RESISTOR.

This a 6 or 12 volt tractor??

The coil a 6 or 12 volt??

Is there any series external Ballast Resistor after the ignition switch but before the coil??

Is the battery connected Pos or Neg ground cuz the coil wiring should match the tractor battery polarity??

I need to know this stuff so I can betetr advise you, if the ignition is on very long tractor not running its normal for a coil to get fairly hot but not so hot it almost burns your hand

John T

 

[Walt Davies]

I don't know but the Experts on the ATIS list got all over me when I said that the Coil case did not have to be grounded so you might look into that. Giggle.

I'm sure that the coil should not ever run above ambient Temp but if it is close to something hot it may be from that.

And like the previous note said make sure that you are using a Balance Resister if its a 12 volt system.
Walt

 

[John in Nebraska]

If the points are closed, and the key is on, the coil will get hot, because it is discharging the battery. Before electronic ignition, "I left the key on" was a common cause for a dead battery. Since you have little spark, and the coil is warm, I would check the points very carefully, double check the point gap. And you can check the secondary wire at the coil by snapping the points with a screwdriver, should throw a good white spark. If not, try again with another coil wire, before condemning the coil.

 

[KEB]

Assuming the ignition switch is on, there will be current flowing through the coil whenever the points are closed. Engines normally stop with the points closed as one piston is coming up on a compression stroke. If the engine isn't running, its normal for the coil to get warm, but not so hot that you can't touch it.

Whether or not the coil case is grounded is immaterial. The return path for the high voltage pulse is through the condenser and the wire to the distributor. The ignition coil and condensor form a resonant circuit which results in a higher voltage spark than just a simple coil. There is no electrical connection to the case of the coil.

First thing I would do is replace both the points & condensor. Its a cheap way to eliminate a couple potential problems. A bad condensor will cause a weak spark, since the circuit is no longer resonant. Look carefully at the points, the contacts should be smooth. If there's a mound of metal on one contact and a corresponding crater on the other, the condensor is either bad or the wrong value. If both contacts are black and pitted, there's too much current flowing through the points, probably because you're using a 6 volt coil on a 12 volt system without a ballast resistor.

By the way, never clean ignition points with sandpaper. It'll leave abrasive particles embedded in the contact surfaces & cause early point failure. If you can't find an actuall point file, a metal nail file will work. If you have to file points, they're on their last legs anyway & you might as well replace them.

As John T noted, if you have a 12 volt system you either need a coil that's marked for 12 volts or a ballast resitor between the ignition switch and the + side of the coil. If its a 6 volt system, you do not need a ballast resistor, and should make sure you use a 6 volt coil.

Keith

 

[old]

Yes on all systems coils do get warm. Weak spark can be caused but a good number it things. Bad cap, rotor, points, or condenser. And thats just a few of the things that can/will cause weak spark.

 

[Walt Davies]

Keith, sorry I new that it was a joke because of the fact that I was kicked off the list for saying just what you are saying. They have college professor on the list who is an expert on everything and if you don't believe me then just ask him.

Walt

 

[John T]

Walt, I sure dont understand why anyone would be all over you by your claiming "the coil case did NOT have to be grounded" The coils low voltage primary winding terminates out its lil + and - terminals, whle its high voltage secondary winding terminates out the top high voltage tower where the coil wire is inserted, and NEITHER winding (unless shorted) has any connection to the metal case. THEREFORE I SEE NO REASON OR IT MAKES NO DIFFERENCE IF THE OUTER METALLIC PROTECTIVE CAN IS GROUNDED OR NOT

I.E YOURE CORRECT IN MY OPINION.....

While Ive heard tell of some coils manufactured that used the outer metal case as a connection/termination (in which case it would have to be grounded) Ive never seen or used any on these older tractors.

Im unsure what "experts" youre referring to on ATIS?????????????

Take care, fun discussion

John T Retired Electrical Engineer

 

[John T Country Lawyer]

Keith, I know youre an electrical kinda guy and like you (see my reply to Walt below) Ive never seen or used any coils that had either winding connected to the outer metallic case, although Ive heard tell (may be an old wives tale lol) some were made that way. The way I explain the condesnor action to lay people is that if theres no capacitance at all (or its sized way too small) she will still fire BUT A WEAKER SPARK and the points will burn up rapidly. If theres too much capacitance she wont fire at all, but hey the points wont burn up lol. Its just that right size of condensor that allows a higher energy spark plus extends points life thats needed (an engineering balance trade off). I explain to people it sort of controls the rate of stored energy discharge from the coils primary so the maximum energy gets inductively coupled over to the high voltage secondary versus it getting wasted as heat.

Yall take care now

John T Retired Electrical Engineer

 

[KEB]

Walt,

I knew it was a joke, but you'd be amazed at how many people take things like that seriously, so I stuck something in. I'm a principal engineer at a large aerospace corporation, and am constantly running across pHd's who can't think their way out of a paper bag.

Take care,

Keith

 

[Leckster]

I have a 12 volt negative ground system. There is no external resistor. The owners manual does not state there is an external resistor nor do any of the diagrams of the electrical system. The coil states it is a 12v and no external resistor.

The coil only gets warm and not hot and from all the great posts I have received this is normal. next step is to replace the condensor, rotor and points. The condesor does not look to be in good shape.

The tractor was idling a month ago when it suddenly stalled after that I could not get it started. That is when I checked the spark. I get a weak spark on the first rotation and then there is no more spark. If I let it sit for a few minutes and try again I get the same result, a weak spark on the first rotation and then no more spark.

 

[Walt Davies]

John I sure could have used you when arguing with those so-called experts on the ATIS list. I have been a working mechanic for over 40 years and I have never run into anyone like this guy who says that he has a PHD in Engineering sometime its Electrical and sometimes its Mechanical depending on what he tries to shove down someones throat. Them we have the other guys who get mad at me for disagreeing with him and then I get mad and then they kick me off the list. 3 time now, working on new record right now.
The only coil that I know where the case is grounded is in a Magneto and the reason for that is because it does two things creates the primary voltage and the secondary Voltage. I have worked hard on these systems to get those darn metal plate to clean up and ground so you can get a primary voltage.
You should go to ATIS.NET and sign on just to see what you can learn from them. Be prepared though.
Sound Guy on this list came to my aid and almost got shot down for doing it.
I could go on forever here but I think you get the point.
Walt