question. simple starter motor conversion to 12v

Jim Brierley said:
woofa, 12v. wiring does not require heavier gauge wire as the amperage used is less than 6v. If you are interested in performance, e-mail me at jimb4e4@gmail.com for info on my performance how-to book.
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hi Jim.
the vehicle was converted to 12V 30 years ago, with the exception of the starter motor and has worked well since, with the exception of the starter .
thankyou for your helpful offer. gary
 
To MikeK.
Thankyou for that reply which was comprehensive and appreciated. Yes I understand all you have said and now I have a further question for you.
Snyders sell an adapter to attach to starter motor and enables that to handle 12V. See the attached link.
https://www.snydersantiqueauto.com/modern-starter-drive
or is the "modern starter drive" what you are calling a "barrel drive"?


that would be simple and save me seeking professional auto electrical services and thus be much cheaper too. I will modify in accordance with your recommendation.
and thankyou again.
 
OK guys, respectfully, it seems that MikeK and Jim Brierley are contradicting one another. Mike states in post #3 that "The amperage will double for a 6V stater on 12V." Whereas Jim states in post #20 that "12v. wiring does not require heavier gauge wire as the amperage used is less than 6v."

So, Ohm's law states that voltage divided by resistance equals amperage. That would indicate to me that if one uses the original 6V wiring the resistance is constant when changing to 12V. Therefore wouldn't 12V in the system create higher amperage?

Further, if the field coils are wired in series to convert a 6V starter to 12V, hasn't the resistance of the field coils now theoretically doubled? If so, Wouldn't the amperage the starter motor sees be approximately the same?

I Think I'm confused now. Please help me to get this straight.

Kind regards,
geary
 
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G Baese said:
OK guys, respectfully, it seems that MikeK and Jim Brierley are contradicting one another. Mike states in post #3 that "The amperage will double for a 6V stater on 12V." Whereas Jim states in post #20 that "12v. wiring does not require heavier gauge wire as the amperage used is less than 6v."

So, Ohm's law states that voltage divided by resistance equals amperage. That would indicate to me that if one uses the original 6V wiring the resistance is constant when changing to 12V. Therefore wouldn't 12V in the system create higher amperage?

Further, if the field coils are wired in series to convert a 6V starter to 12V, hasn't the resistance of the field coils now theoretically doubled? If so, Wouldn't the amperage the starter motor sees be approximately the same?

I Think I'm confused now. Please help me to get this straight.

Kind regards,
geary
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for the STARTER current doubles. For the rest, except the horn, if you replace a 50 w 6 volt bulb with a 50 w 12 volt bulb, current is half.
 
I use the original type wiring harnesses sold by Brattons for the model A , on 12 volts ... Newer automobiles that run 12 volt systems use smaller gauge wiring . The larger gauge wire that was originally used on the model A will carry the 12 volts with no problem , I figure even better !
 
woofa.express said:
I have busted 2 shafts on my starter motor, being 6v and running 12v system.

I have researched and there seems many ways to convert. The rest of the car has been converted. what is the most simple way. emphasis on simple. that's how I like things and that's why I like Model A's
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I know Model T guys use an old Bendix spring as a 'dropping' resistor, see:

http://www.mtfca.com/discus/messages/708324/742229.html?1491426436
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M2M said:
I know Model T guys use an old Bendix spring as a 'dropping' resistor, see:

http://www.mtfca.com/discus/messages/708324/742229.html?1491426436
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thanks M2M. I'm not really a great mechanic and found the information on that link difficult to understand. However I have given the starter motor to my old friend who is nearly as old as my A to modify.
Don't let that detract from my gratitude of your reply. Cheers,, gary
 
My previous A, as I recall, had a resistor installed after the coil.
6v starter, 12v alternator. No problem; worked like a charm.
 
woofa.express said:
thanks M2M. I'm not really a great mechanic and found the information on that link difficult to understand. However I have given the starter motor to my old friend who is nearly as old as my A to modify.
Don't let that detract from my gratitude of your reply. Cheers,, gary
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No problem. Hope your A is back together and running soon.
 
" I know Model T guys use an old Bendix spring as a 'dropping' resistor, "

How on earth can this work??? What's the resistance of a bendix spring?? I can understand welding wire is a decent resistor (but it gets hot doesn't it!) but a bendix spring???
 
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johnbuckley said:
" I know Model T guys use an old Bendix spring as a 'dropping' resistor, "

How on earth can this work??? What's the resistance of a bendix spring?? I can understand welding wire is a decent resistor (but it gets hot doesn't it!) but a bendix spring???
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See this link:
http://www.mtfca.com/discus/messages/599638/653383.html?1467567809

12V, with a Bendix as a dropping resistor:
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woofa.express said:
I have busted 2 shafts on my starter motor, being 6v and running 12v system.


I have researched and there seems many ways to convert. The rest of the car has been converted. what is the most simple way. emphasis on simple. that's how I like things and that's why I like Model A's


thankyou in anticipation. gary
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If you read the first post in this thread, he wanted it SIMPLE.
I see simple as just changing ONE part with no other modifications.
No special tools or skills needed.
There are 12 volt gear drive starters available for model A's that just bolt in.
No Bendix springs and screws to break.
Positive timed shift so the gears are in mesh BEFORE the motor starts cranking.
They have enough torque to crank 14 to 1 compression if you are so inclined.
 
MikeK said:
There is a reason things are breaking! A 6V starter on 12V will deliver four times the torque, not just twice as much. Power =amperage squared times resistance. The amperage will double for a 6V starter on 12V. When you square that, you get 4X engagement slam force.
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I don't know what the correct formula is but I'm pretty sure this is not correct. Power is not torque (they have different units). Torque is the relevant quantity here, corresponding to "slam" force.
 
Help is welcomed and received with gratitude. Theories are welcome and also received with gratitude but don't miss the forest for the trees.

The long and short of the matter is the starter motor engagement is nasty.

I will be reporting on change following modification which will be some weeks away when my Tourer is again operational.
 
steve s said:
I don't know what the correct formula is but I'm pretty sure this is not correct. Power is not torque (they have different units). Torque is the relevant quantity here, corresponding to "slam" force.
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Steve, torque would only apply to a gear tooth engagement load if the rotational inertia / moment of inertia of the starter armature and Bendix assembly was zero. Since this assembly has mass, and in a specific three-dimensional physical arrangement, it gains rotational inertia as it accelerates. That becomes the "relevant quantity" as the gear teeth crash (moving object meets stationary with a huge inertia component). I should have differentiated as to whether, in this starter motor problem, it was average power, instantaneous power, or mechanical power that I made reference to. All three have a time component, but differ in how that is applied.

In the case of this starter motor problem you are looking at near-instantaneous power with the time factor approaching zero, something in the millisecond range as the rotational inertia of the starter and Bendix is overcome and the angular velocity of the huge, massive flywheel and crank assembly increases. The difference between how many milliseconds to gear tooth engagement (slam!) for 6V vs12V is a function of force, in this case the amperage creating the magnetic field. 4X more amperage will result in faster armature/Bendix acceleration. You will have 4X more rotational inertia (function of RPM) at the point of engagement if voltage doubles.

OK, lets look at this slightly differently, as mechanical power. That is a product of force and movement. Movement will always contain a time element (exception- some particle physics). For a running motor, that's the product of torque on the shaft and angular velocity (RPM). Now, for this "slam" problem, movement instantaneously becomes near zero. The kinetic energy in the rotational mass as the gear teeth crash (moving object meets stationary with a huge inertia component) becomes the primary factor in the mechanical force applied to the gear teeth.

That said, I believe I am correct. Power will be a product of the amperage squared times the motor's resistance, you will have increased kinetic energy in the rotational inertia of the starter, and thus 4X the instantaneous 'crash'.

If you want to look at this a bit deeper, reverse EMF in a motor from a moving armature will decrease the amperage as the motor speed increases from starting (zero RPM). This reduces the power output. This is clearly evident in the MTFCA graph, amperage goes up/down as the starter motor slows (compression stroke) and increases (compressed mix passes TDC). At near zero elapsed time on that graph (X axis) the amperage is purely a product of Ohm's law. At about 25ms you see a strong amperage decline as the armature accelerates and creates an increasing reverse EMF. Then you see the up/down/up/down amperage as the starter runs fast/slow/fast/slow across the compression strokes.

Also on that graph you see an interesting huge 'down' spike in the amperage between T=0 and the few milliseconds to the initial start of motor rotation. That is the reverse EMF created by the buildup of the magnetic field in the iron cored motor armature and field. When the field stops building (max, but motor still not moving) the amperage spikes back up. That graph would be extremely interesting and revealing if a third component, angular velocity of the armature, were shown along the same time line.
 
Bob Bidonde said:
I too have been running the original Model A starter on 12V for many years without any issues / failures. Please post a picture of the busted starter.
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If I had known you or any person wished to see this I would have kept them or at least photographed them. gary
 
The problem I had when running a 6 volt starter on 12 volts was that it engaged with such a jolt that it started chewing up the teeth on the ring gear. I finally switched to a modern starter drive which engages very gently. I love it.
 
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