[AT] question on use of resistor on coil

[Dudley Rupert]

I took a Digital Fluke 73 Series II Multimeter out last night and took some
measurements:

I measured the resistance of four coils: the readings were all in the 1.2 to
1.4 ohm range.
    1 coil was new (still in the box), another was used (came out of a 6
volt tractor) and
    2 were in 6 volt tractors (with no external resistors other than wire).

I measured the resistance of one new ballast resistor (still in box):
reading was 1.2 ohm.

My conclusion (may be flawed) on coils/external resistors is this:
  6  volt coil systems need a total resistance of 1+ ohms and
  12 volt coil systems need a total resistance of 2+ ohms.

If this conclusion is correct (??) and if suppliers only want to stock one
coil type then they only need to stock coils of the 1+ ohm internal
resistance type. As several have already commented, however, this sure could
be made clearer on the coil itself.

Cecil, if you have a coil that says 12 volts on it I would be curious as to
what its' internal resistance is if you can readily take the measurement.

You also stated that the voltage at the coil dropped to under 5 volts when
you checked it with the ohmmeter -- I am not sure what you meant by this.
  I connected my meter to the coil (and to the tractor frame) on my T035 and
turned the ignition on and read 6.1-6.2 volts on the meter.  I then hit the
starter and, while grinding, the voltage reading dropped to just under 5
volts.  Is this anything like what you did?

Dudley
Snohomish, Washington

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com]On Behalf Of Cecil E Monson
Sent: Sunday, October 24, 2004 4:15 AM
To: Antique tractor email discussion group
Subject: Re: [AT] question on use of resistor on coil


>   For a fact, the 420 ignition system is the same as the 40 ignition
system as

stated in the 420 service manual.  6 volt and uses the Delco Remy No.
1115379 coil.

  No resistors in the ignition system.  Only in the lighting system for "dim
lights".
>     My engines that sit, be them John Deere, Willys, Wisconsin, etc.
almost always

give me starting troubles until I clean the points.  Often I clean them by
installing

new.  Sometimes touching up with a file will work.  I have had corrosion in
the

primary wire and also at the switch contacts which set up a resistance that
ruined

or completely eliminated a spark.  Making more cleaning and replacing
necessary.

Moisture induced problems, I think.  On engines that are used constantly,
this
never

seems to be a problem.  You could give me the 420C and I would see that it
runs
more

often.<g>
>
> Ron Cook
> Salix, IA

> In 6 volt systems the external ballast resistor is normally not used.  The
> current though the coil, which is approximately 6 amps, is the same both
> when starting the engine as well as when running the engine.  A current of
6
> amps through a one ohm coil results in approximately 36 watts of generated
> heat which the coil should be able to dissipate.
>
> Hope this doesn't cause any confusion -
> Dudley
> Snohomish, Washington



	Ron and Dudley, thanks to you both. This was what I suspected and being
as I respect the opinions of both of you, I am now sure that these coils are
all
6 volt coils. If they have an internal resistor, they will be marked 12
volts, I
am sure.

	FWIW, Ron, this coil has "12 volts" painted on the side of it in white
paint even though the box says "resistor must be used" so it could be a 12
volt
coil and would account for the yellow spark if the points are OK. I have
several
other good coils that I know are 6 volts and if I get a chance, I'll
substitute
one of them and see.

	Being as I could feel a gritty side to the points with the little "point
file" I got from Sears, I am pretty sure there is heavy pitting on the one
side
and will just put in a new set of points.

	I have suspected corrosion in the ignition switch and erratic operation
in the past but have not been able to prove it. On the crawler, it is almost
impossible to get to the switch without removing the entire loader frame
which
weighs just about a ton by itself. It's one of the pleasures of owning a
loader/
crawler. :-(  The dash has screws that hold it in place but with the loader
frame in the way, you need 4 foot long arms with extra joints to work on it
once it is loose.

	Dudley, It seems to me the voltage at the coil dropped to under 5 volts
when I checked it with the ohmeter. It could indicate an internal resistor
when
going by your comments.

	Thanks again to you both and Ron, if I decide to junk the 420, I'll
bring it out to you. ha ha ha ha

Cecil



--
The nicest thing about telling the truth is you never have to wonder
what you said.

Cecil E Monson
Lucille Hand-Monson
Mountainville, New York   Just a little east of the North Pole

Allis Chalmers tractors and equipment

Free advice

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