Starter short problem

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Model T Ford Forum: Forum 2012: Starter short problem
Top of pagePrevious messageNext messageBottom of page Link to this message  By John Housego (United Kingdom) on Monday, May 28, 2012 - 05:33 pm:

Clearly not right, with armature removed from the starter I have a dead short between the casing (gnd) and 2 field coil windings, also short between positive feed terminal and ground! The 2 field wire tails have poor insulation are they supposed to be insulated from there clamps? Both clamps look intentionally connected together unless this happened due to the fault by arcing together?

Wonder if anyone could advise me the correct resistance readings please...
-between two field wires
-field wires to ground
-field wires to positive terminal
-positive terminal to ground

Im confident the positive terminal insulator is not the issue here. Be very interested to hear any advice please. Many thanks in advance.

John (Aylesbury UK)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Monday, May 28, 2012 - 07:27 pm:

John
Sounds like you have a short between the field windings and the starter case which is not normal.
This passage in your message is unclear to me: The 2 field wire tails have poor insulation are they supposed to be insulated from there clamps? Both clamps look intentionally connected together unless this happened due to the fault by arcing together?
Attached is a photo of a rebuilt (series/parallel) Model T starter field, perhaps it will help. .
1
In answer to your specific questions:
-Very low resistance as the field winding is #7 gauge wire and buss bar.
-Ideally zero ohms, but several Mega Ohms will work.
-Same as first answer.
-Same as second answer.
Good luck
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By JohnH on Monday, May 28, 2012 - 07:31 pm:

The readings would be a fraction of an ohm given the windings are a few turns of heavy gauge wiring. A DC ohms test isn't likely to reveal much.
A really rough idea of just how low the resistance is could be obtained from the typical stall current of the starter; 580A. At this current, the terminal voltage at the starter is typically 3V due to internal resistance of the battery, and associated wiring. Resistance in this condition (i.e. starter not rotating) calculates to 0.005 ohms. Just the test lead resistance of a typical multimeter is much higher than that.


Top of pagePrevious messageNext messageBottom of page Link to this message  By JohnH on Monday, May 28, 2012 - 07:35 pm:

I should clarify the above as being the resistance of the individual windings. With all the windings disconnected there should ideally be infinite resistance to the body of the starter.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Housego (United Kingdom) on Tuesday, May 29, 2012 - 09:15 am:

Ron & John, thanks so very much for your input its very much appreciated. I have found that the insulation wrap on the field coils has rotted and shorting to ground in a couple of places so I guess I will look to replacing the field coils.

John (Aylesbury UK)


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