Sparton field coils

[Slowplane]

My Sparton horn worked, for a while. It quit and, after I let the smoke out of it, I see one coil is cooked. I've read up on rewinding the field coils, and have in hand 80 feet of 20 AWG magnet wire (200C).
The procedure seems straight forward (stripping, 48 wraps, opposite direction, soldering, etc.) tho' I've never done this job before.
My questions are, "is there anything in particular that I need to be aware of, and should I do both coils while I'm at it?"
Thanks for any input from the barners'; its greatly appreciated, Jeff

[Tom Wesenberg]

I've had to rewind a few field coils. I just measured the length and number of turns in the old wire, then measure the gauge of the wire and use the same length and gauge for the new wire. Draw out on a sheet of paper the direction you need to wind the wire, and then start winding. You may come out a turn or two different than the original coil, since it's hard to wind exactly as the factory did.

No need to do both coils if only one is bad. It's been some years since I wound one, but I seem to recall about 20 feet per coil.

[MAG]

Pay particular attention to Tom's comment:
"Draw out on a sheet of paper the direction you need to wind the wire, and then start winding."
This establishes the direction the armature turns. If the armature turns the wrong direction it can cause the nut on the armature shaft to loosen. Some brand horns ( I don't recall which) have left hand threads on the armature shaft. So, it is important that the coils be wound in the correct direction.

[Slowplane]

Thank you, Tom and Mag, for your suggestions on my coils. I'll give 'er a go tomorrow.
Jeff

[Ron in Quincy]

A friend of mine who is in the business of re-building original horn motors, gave me the following information for the field coils:

6 Volt

(1) The 2 field coils are wound in opposite directions.
(2) Original field coil wire is 20 gauge.
(3) a. 45 turns using coated wire.
b. 6 to 7 turns per layer, not perfect is OK
(4) After completing, spray with varnish or epoxy insulating enamel.

12 Volt

(1) Same as above.
(2) Use 24 gauge coated wire.
(3) a. 100 turns
b. 6-7 turns per layer, not perfect is OK
(4) Same as above.

Ron Rude

[MikeK]

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Just to throw a little GEEK in here, the number of turns in a motor winding is far more important than the exact wire length. The magnetomotive force, "MMF" measured in Gilberts, Gauss, or by Hopkinson's law or Rowland's law is a function of amperage and complete turns about an axis.

Getting back down to earth, if you rebuild any motor it is important to count the number of turns you remove. Don't worry about the exact length having a miniscule difference in resistance, especially in a series wound DC motor like a horn.

If you re-wind an original 45 turn coil to just 3 turns more, or 3 turns less, you will change the MMF about 7%.

[Slowplane]

Thanks everyone for your tips and suggestions. I've disassembled one coil. it appears to be original. 20AWG, 40 wraps, but its only 9 feet of wire. my new wire is also 20AWG. mic'ed out as the same diameter (0.343). I'd read that its approx. 20 feet per coil, but its half that. Could it be 20 feet (approx) total for both?
Thanks, Jeff

[BILL WILLIAMSON]

Originally Posted by Tom Wesenberg

I've had to rewind a few field coils. I just measured the length and number of turns in the old wire, then measure the gauge of the wire and use the same length and gauge for the new wire. Draw out on a sheet of paper the direction you need to wind the wire, and then start winding. You may come out a turn or two different than the original coil, since it's hard to wind exactly as the factory did.

No need to do both coils if only one is bad. It's been some years since I wound one, but I seem to recall about 20 feet per coil.

Tom,
Advice, please: I bough a beautiful NEW tack hammer, with a Hickory handle & the MAGONET DIED! How many feet uf wire will I need to RE-MAGONIZE IT??
THE poor THING won't HOLD A TACK, EVEN IF I spit ON IT!! I' a-tryin' to hang up my 2 calendars, whut day & month is it??? wHEN WILL April Fool's Day be? I hope we're not past April 10th, if so, I MISSED Butch's BIRTHDAY Are the dates the same in ARKANSAW?
bILL w.

[Tom Wesenberg]

Yep, I must have remembered 20 feet for both coils, and not each coil as I earlier posted.

Bill, just stroke the hammer with a rare earth powerful magnet.

[BILL WILLIAMSON]

Originally Posted by Tom Wesenberg

Yep, I must have remembered 20 feet for both coils, and not each coil as I earlier posted.

Bill, just stroke the hammer with a rare earth powerful magnet.

OH, that's EASY
I once made a shop coil for magnetizing everybodys' screwdrivers, if you zapped it with 12 volts, with the WRONG polarity, it'd SHOOT the screwdriver CLEAN across the shop
Bill W.

[JohnLaVoy]

A&L sells the complete horn replacement. But they will sell the motor components separately so you can keep the original horn and have a new motor assembly to run it. The cost of the motor is about $100 I understand.

[Slowplane]

Thanks to all that offered their suggestions and advice. It turned out to be an easy job (with the help you all gave me)

[Goldhardt]

Originally Posted by Slowplane

Thanks to all that offered their suggestions and advice. It turned out to be an easy job (with the help you all gave me)

Have you tried it out yet? Be sure and let us know how it's working!

[Slowplane]

Its on the car, and workin' AHHOOOOGA!!!!