02-27-2020, 10:21 AM | #1 |
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starter motor
hello - i am trying to figure out how to check ohms on field windings with just removing the band around motor and not disassembling end plate. probably no one knows the answer but does anyone know if windings are series, shunt or compound?
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02-27-2020, 11:46 AM | #2 |
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Re: starter motor
Going by this starter parts drawing I would say that they are connected in series, but with the heavy winding the ohmage will be very low.
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02-27-2020, 11:52 AM | #3 |
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Re: starter motor
the fields split at the post, each goes through 2 field coils to its brush---through the armature to ground through 2 brushes---it is considered s series wound motor
your meter due to the size of the winding is best used to detect shorts, though I like a 110 volt test light better----the shorted area smokes and usually cleaning and insulating there will return the windings to function ----the 'wire" is so heavy it rarely fails open, shorting to ground is more common, |
02-27-2020, 12:14 PM | #4 |
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Re: starter motor
For a very rough guess 6v/60 amps, windings at the terminals = .1 ohms. Way to low to measure with a meter. Variances in probe connection, lead contact at the meter, etc. will throw readings that small off.
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02-28-2020, 08:17 PM | #5 |
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Re: starter motor
thanks as always to those that reply-i will take any advice to heart
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02-29-2020, 07:36 PM | #6 |
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Re: starter motor
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02-29-2020, 08:10 PM | #7 | |
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Re: starter motor
Quote:
The resistance of the starter motor does not change but the voltage across it is doubled, therefore the amps double and the power goes up four fold. R=V/I. resistance (R) is constant so if you double the volts (V), the current (I) has to double also. P=VxI With both volts and current doubled, the power (P) is quadrupled. That's why an unmodified 6v starter running on 12v will spin so fast. The amps drawn can be reduced by increasing the resistance of the starter. I do that by connecting all of the field windings in series, then taking a lead to the brushes. The effect of that is to quadruple the resistance of the fields but the resistance of the armature hasn't been changed so the starter runs at higher speed but not so much as it would without modification. It runs at about what a 6v starter would on about 8-9 volts, I estimate. Using small, long cables also helps.
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03-01-2020, 08:38 AM | #8 |
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Re: starter motor
Syncro - Also insure/upgrade to modern Bendix, or is the old style Bendix OK with this modification of field wiring?
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03-01-2020, 10:05 AM | #9 |
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Re: starter motor
Synchro909 you are right on mate. The physics and the data say it all. The rule of thumb is keep your engine and system components properly maintained and it will always start with 6 volts. I have a 6 volt solid state ignition system in my A and it usually requires 1 - 2 rev's to start for a cold start.
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03-01-2020, 10:31 AM | #10 | |
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Re: starter motor
Quote:
I read somewhere that one of the reasons car manufacturers went with 12v systems (besides the obvious) is that they would save $$ by using smaller copper wires.
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03-01-2020, 12:16 PM | #11 | |
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Re: starter motor
Quote:
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03-01-2020, 04:53 PM | #12 |
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Re: starter motor
I've used both quite successfully. FWIW, it is the huge impact of the bendix hitting the ring gear that causes trouble when 12v is applied to an unmodified 6v starter. My mod reduces that.
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03-01-2020, 04:54 PM | #13 |
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Re: starter motor
Katy, you are dead right. The starter designed for 12 volts has a higher internal resistance than one designed for 6 volts.
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