Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 02-27-2020, 10:21 AM   #1
wbs
Senior Member
 
Join Date: Nov 2013
Posts: 309
Default 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?
wbs is offline   Reply With Quote
Old 02-27-2020, 11:46 AM   #2
katy
Senior Member
 
katy's Avatar
 
Join Date: Jun 2015
Location: Red Deer, Alberta
Posts: 5,011
Default 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.
Attached Files
File Type: pdf Model A Starter Motor assembly.pdf (122.4 KB, 53 views)
__________________
If you don't hear a rumor by 10 AM, start one!.
Got my education out behind the barn!
katy is online now   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 02-27-2020, 11:52 AM   #3
Kurt in NJ
Senior Member
 
Kurt in NJ's Avatar
 
Join Date: May 2010
Location: on the Littlefield
Posts: 6,140
Default 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,
Kurt in NJ is offline   Reply With Quote
Old 02-27-2020, 12:14 PM   #4
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Posts: 2,332
Default 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.
30 Closed Cab PU is offline   Reply With Quote
Old 02-28-2020, 08:17 PM   #5
wbs
Senior Member
 
Join Date: Nov 2013
Posts: 309
Default Re: starter motor

thanks as always to those that reply-i will take any advice to heart
wbs is offline   Reply With Quote
Old 02-29-2020, 07:36 PM   #6
barkleydave
Senior Member
 
barkleydave's Avatar
 
Join Date: Oct 2014
Location: Kentucky
Posts: 502
Default Re: starter motor

Sponsored Links (Register now to hide all advertisements)
Amp draw is more informative. You can expect minimum of 60+ amps starting draw on a 6 volt system. Now your starting draw does not go through your amp meter it would burn it up quick! Cold morning start can easily exceed 100+ amps. Now you can reduce the amp draw by half if using a 12 volt system.
barkleydave is offline   Reply With Quote
Old 02-29-2020, 08:10 PM   #7
Synchro909
Senior Member
 
Synchro909's Avatar
 
Join Date: Jun 2014
Location: Melbourne, Australia
Posts: 7,472
Default Re: starter motor

Quote:
Originally Posted by barkleydave View Post
Amp draw is more informative. You can expect minimum of 60+ amps starting draw on a 6 volt system. Now your starting draw does not go through your amp meter it would burn it up quick! Cold morning start can easily exceed 100+ amps. Now you can reduce the amp draw by half if using a 12 volt system.
This was a topic that came up in a recent thread. I pointed out and still maintain that when you convert to 12 volts, the amperage doubles, not halves.
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.
__________________
I'm part of the only ever generation with an analogue childhood and a digital adulthood.

Last edited by Synchro909; 03-01-2020 at 04:55 PM.
Synchro909 is offline   Reply With Quote
Old 03-01-2020, 08:38 AM   #8
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Posts: 2,332
Default Re: starter motor

Syncro - Also insure/upgrade to modern Bendix, or is the old style Bendix OK with this modification of field wiring?
30 Closed Cab PU is offline   Reply With Quote
Old 03-01-2020, 10:05 AM   #9
CT Jack
Senior Member
 
CT Jack's Avatar
 
Join Date: May 2010
Location: Hebron, CT
Posts: 430
Default 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.
CT Jack is offline   Reply With Quote
Old 03-01-2020, 10:31 AM   #10
The Master Cylinder
Senior Member
 
The Master Cylinder's Avatar
 
Join Date: Aug 2012
Posts: 875
Default Re: starter motor

Quote:
Originally Posted by Synchro909 View Post
This was a topic that came up in a recent thread. I pointed out and still maintain that when you convert to 12 volts, the amperage doubles, not halves.
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.
While I understand what your saying what I don't understand is if the draw is doubled why do 12v systems use smaller gauge wire?

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.
__________________
The Master Cylinder

Enjoying life at the beach in SoCal...
The Master Cylinder is offline   Reply With Quote
Old 03-01-2020, 12:16 PM   #11
katy
Senior Member
 
katy's Avatar
 
Join Date: Jun 2015
Location: Red Deer, Alberta
Posts: 5,011
Default Re: starter motor

Quote:
While I understand what your saying what I don't understand is if the draw is doubled why do 12v systems use smaller gauge wire?
Because they're designed for 12 volts. Using 12 volts on a 6 volt system is a whole different kettle of fish.
__________________
If you don't hear a rumor by 10 AM, start one!.
Got my education out behind the barn!
katy is online now   Reply With Quote
Old 03-01-2020, 04:53 PM   #12
Synchro909
Senior Member
 
Synchro909's Avatar
 
Join Date: Jun 2014
Location: Melbourne, Australia
Posts: 7,472
Default Re: starter motor

Quote:
Originally Posted by 30 Closed Cab PU View Post
Syncro - Also insure/upgrade to modern Bendix, or is the old style Bendix OK with this modification of field wiring?
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.
__________________
I'm part of the only ever generation with an analogue childhood and a digital adulthood.
Synchro909 is offline   Reply With Quote
Old 03-01-2020, 04:54 PM   #13
Synchro909
Senior Member
 
Synchro909's Avatar
 
Join Date: Jun 2014
Location: Melbourne, Australia
Posts: 7,472
Default Re: starter motor

Quote:
Originally Posted by katy View Post
Because they're designed for 12 volts. Using 12 volts on a 6 volt system is a whole different kettle of fish.
Katy, you are dead right. The starter designed for 12 volts has a higher internal resistance than one designed for 6 volts.
__________________
I'm part of the only ever generation with an analogue childhood and a digital adulthood.
Synchro909 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 07:34 PM.