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Old 05-30-2018, 08:03 PM   #1
woofa.express
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Default question. simple starter motor conversion to 12v

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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Old 05-30-2018, 08:38 PM   #2
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Default Re: question. simple starter motor conversion to 12v

Replace the starter drive to a modern Bendix https://www.snydersantiqueauto.com/modern-starter-drive
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Old 05-30-2018, 09:23 PM   #3
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Default Re: question. simple starter motor conversion to 12v

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.

You can buy new 12V configuration starter field coils to make the conversion from the vendors. With the starter motor fields rewired from parallel to series, (making it a 12V starter) the average converted starter will still show almost 2X the power, but not so much as to severely abuse the drive.

As far as 'barrel' drives go, they are not without their own problems. The can and do fail and are extremely difficult to change on-the-road unless you carry a special tool to compress and expose the shrouded set screw.

When a barrel drive fails and locks in the extended position because the much finer helix shatters from excessive motor torque and poor off-shore manufacture and heat treating, the rear of the drive often cannot be compressed, even with the special removal tool, to access the set screw. It becomes hack saw and abrasive cutoff wheel time.

The motor field conversion is the only way to go. If you continue to slam the flywheel ring gear with a 6V starter on 12V you risk walking the ring gear off the flywheel.
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Old 05-30-2018, 09:26 PM   #4
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Default Re: question. simple starter motor conversion to 12v

Quote:
Originally Posted by woofa.express View Post
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
The "6 volt field coils" get replaced with "12 volt field coils". That's it. It's actually pretty easy to do. If you have a good automotive starter and generator/alternator rebuilding shop near you (we have a couple in Houston) they can do it for you. You get the field coils from a Model A parts supplier, like Bratton's. If you have a good soldering iron to solder the field coils in, you can do it yourself.

Check your initial spark timing. That's will break starters.
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Old 05-30-2018, 10:22 PM   #5
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Default Re: question. simple starter motor conversion to 12v

I once bought a set of those 12v coils. Never again. I convert using the original ones. It is as simple as rearranging them so that they are all in series rather than two sets of two in series each connected in parallel. Thatís not easy to put in words but I hope you get it. This gives a field coil resistance 4 times what it was and reduces the power and torque to about the equivalent of running the in modified stater on 8 or 9 volts, I estimate.
Another way is to reduce the voltage getting to the starter. Iíve seen this done a number of ways including using a Bendigo spring in the +ve cable (I assume you converted to negative earth). Another way is to go to a wrecker and find a set of leads from a really small car - the ones that are not much thicker than a pencil. The longer the better. The small cables have a higher resistance and will cause a voltage drop, making life easier on the starter. There are several ways to go - these are just a couple for you to consider.
PS. Have you collected that gearbox yet? All Good?
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Old 05-31-2018, 11:39 AM   #6
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Default Re: question. simple starter motor conversion to 12v

I've been running 12v on a stock starter since 1960, never broke anything except 1 Bendix spring.
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Old 05-31-2018, 04:35 PM   #7
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Default Re: question. simple starter motor conversion to 12v

I agree with Jim Brierley. I've also been running a completely stock original 6 volt starter on 12 volts for many years without a problem , I did the same with Y block engines with good results . Back in the day 1954-55 six volt starters were to kill for .
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Old 05-31-2018, 04:40 PM   #8
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Default Re: question. simple starter motor conversion to 12v

Ran the 6 volt starter on 12 volts for many years without any problems.
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Old 05-31-2018, 04:44 PM   #9
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Default Re: question. simple starter motor conversion to 12v

I'm running a 6 volt starter on 12 volts with a modern Bendix drive and so far no problems. It's spinning a modified motor with 7:1 head
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Old 05-31-2018, 05:10 PM   #10
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Default Re: question. simple starter motor conversion to 12v

I also run the modern starter drive with good results for the past 12 years .
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Old 05-31-2018, 07:01 PM   #11
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Default Re: question. simple starter motor conversion to 12v

I'm totally new to Model As, in fact I finally drove the '31 Coupe I bought last Summer for the first time today. I promised myself to finish a number of other started projects before I would do anything on the A. I'm now at 2.1 miles and counting.

It might be considered heresy that my plans are to do some hot rod type things like might have been done in the 40's or 50's but I'll give it a go anyway. I plan to retain the stock engine with mild mods and drive the car as much as possible so I want bright lights and reliability.

Since my question is starter related I thought I'd ask it here rather than starting another thread. I'm considering converting the car to 12V (I know - not 40's stuff) and since it is an older "survivor" car I'd plan to rewire everything on the car. While changing the starter to 12V, is there any big deal to convert to negative ground while I have it at my local starter/generator shop? I was afraid I messed up something today when I was getting the car started. I absent-mindedly hooked a 6V battery charger up as if it was negative ground. I finally realized my error and hooked it up correctly. With that little deal it made me think it would be nice to have it 12V negative ground just like everything else I own.

Thanks, in advance. Next I'll be asking about leaks that appear to be coming from both the front and back crankshaft seals.

Lynn
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Old 05-31-2018, 07:59 PM   #12
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Default Re: question. simple starter motor conversion to 12v

With respect, the fact that some of you have run 12v on a 6 v starter for years doesnít alter the fact that Woofa has broken 2 in a short time. I run 12 v on my cars but Iíve played with the starter too to prevent what has happened to Woofa. Iíve made my suggestions and answered a query from him by email. Letís see how he goes - hope he reports back.
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Old 05-31-2018, 08:36 PM   #13
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Default Re: question. simple starter motor conversion to 12v

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Originally Posted by Synchro909 View Post
With respect, the fact that some of you have run 12v on a 6 v starter for years doesnít alter the fact that Woofa has broken 2 in a short time. I run 12 v on my cars but Iíve played with the starter too to prevent what has happened to Woofa. Iíve made my suggestions and answered a query from him by email. Letís see how he goes - hope he reports back.


yeh, that's all correct mr Synchro and thankyou. however I must correct you. you see Woofa is my hound and can be viewed on my page. Woofa. express is my log on site. I say Woofa is my dog. Well that's not quite correct. Woofa was my dog until he was sadly retired by a Nissan Patrol. Never liked Nissan's since.
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Old 05-31-2018, 10:02 PM   #14
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Default Re: question. simple starter motor conversion to 12v

If you want to run negative ground, first reverse the battery cables to negative ground. reverse the wires at the coil and at the ammeter and you will be wired negative ground . The starter doesn't know the difference between negative or positive ground . if you feel that it is necessary go ahead and have 12 volt field coils installed in the starter or install them yourself if you can . you will either need to install a ballast resister at the coil or change to a 3.0 OHM coil . For the brightest head lights you will need to install at least a 60 amp alternator . change out the headlamp bulb to the 60-55 watt halogen bulbs The original type wiring harnesses will work just fine with the wires switched as mentioned above . the larger gauge wire will carry the higher voltage and amps with no problem . All of the parts are available in the common model A parts catalogs . If you choose to use a three OHM coil instead of a ballast resistor , you should be able to get one at NAPA . For better performance , I use the Pertronix flame thrower coil . I hope this helps .
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Old 06-01-2018, 05:49 AM   #15
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Default Re: question. simple starter motor conversion to 12v

That's the info and advice I was hoping to get. Thanks, Purdy Swoft!


Lynn
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Old 06-01-2018, 08:04 AM   #16
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Default Re: question. simple starter motor conversion to 12v

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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Old 06-01-2018, 09:23 AM   #17
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Default Re: question. simple starter motor conversion to 12v

I have converted several starters from 6V to 12V using both rewiring the original coils to Series and buying new 12v coils. Either way is OK. The last 4 I converted I used new coils because I was in a hurry.
I have had the starter gear pushed off or starting to push off the flywheel on 3 cars. One was mine. But like some of the others, I ran them for years with no problem. My thinking is those that come off may be replacement starter gears. My car had a replacement gear.
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Old 06-01-2018, 10:09 AM   #18
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Default Re: question. simple starter motor conversion to 12v

I had a 6v starter that I ran on 12v with no problems BUT being the tinkerer that I am (I have been told more than once "You have too much time on your hands") and having two spare good 6v starters laying around, I combined the two to make two 12v starters buy swapping one sets of field coils from each starter and putting them in series. No cost but time (except for replacement brushes and "modern starter drive).
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Old 06-01-2018, 11:53 AM   #19
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Default Re: question. simple starter motor conversion to 12v

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Originally Posted by lake_harley View Post
That's the info and advice I was hoping to get. Thanks, Purdy Swoft!


Lynn
Lynn , you are very welcome .
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Old 06-01-2018, 11:58 AM   #20
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Default Re: question. simple starter motor conversion to 12v

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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Old 06-01-2018, 02:56 PM   #21
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Default Re: question. simple starter motor conversion to 12v

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Originally Posted by Bob Bidonde View Post
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.


Hi Bidonde. they have long been disposed of. cheers, gary.
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Old 06-02-2018, 01:04 PM   #22
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Default Re: question. simple starter motor conversion to 12v

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Originally Posted by Jim Brierley View Post
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.
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
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Old 07-12-2018, 03:24 PM   #23
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Default Re: question. simple starter motor conversion to 12v

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.
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Old 07-12-2018, 03:46 PM   #24
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Default Re: question. simple starter motor conversion to 12v

yes, I see on the internet a "modern starter drive" is infact a Barrel drive. thankyou MikeK
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Old 07-12-2018, 05:38 PM   #25
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Default Re: question. simple starter motor conversion to 12v

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

Last edited by G Baese; 07-12-2018 at 08:09 PM. Reason: accuracy
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Old 07-13-2018, 09:02 AM   #26
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Default Re: question. simple starter motor conversion to 12v

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Originally Posted by G Baese View Post
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
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.
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Old 07-13-2018, 11:31 AM   #27
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Default Re: question. simple starter motor conversion to 12v

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 !
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Old 07-14-2018, 04:00 PM   #28
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Default Re: question. simple starter motor conversion to 12v

Quote:
Originally Posted by woofa.express View Post
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


I know Model T guys use an old Bendix spring as a 'dropping' resistor, see:

http://www.mtfca.com/discus/messages...tml?1491426436



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Old 08-10-2018, 04:54 AM   #29
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Default Re: question. simple starter motor conversion to 12v

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Originally Posted by M2M View Post
I know Model T guys use an old Bendix spring as a 'dropping' resistor, see:

http://www.mtfca.com/discus/messages...tml?1491426436



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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Old 08-10-2018, 10:21 AM   #30
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Default Re: question. simple starter motor conversion to 12v

My previous A, as I recall, had a resistor installed after the coil.
6v starter, 12v alternator. No problem; worked like a charm.
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Old 08-10-2018, 12:17 PM   #31
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Default Re: question. simple starter motor conversion to 12v

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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

No problem. Hope your A is back together and running soon.
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Old 08-10-2018, 01:52 PM   #32
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Default Re: question. simple starter motor conversion to 12v

" 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???

Last edited by johnbuckley; 08-10-2018 at 01:57 PM.
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Old 08-10-2018, 02:10 PM   #33
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Default Re: question. simple starter motor conversion to 12v

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" 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???
See this link:
http://www.mtfca.com/discus/messages...tml?1467567809

12V, with a Bendix as a dropping resistor:

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Old 08-10-2018, 03:54 PM   #34
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Default Re: question. simple starter motor conversion to 12v

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Originally Posted by woofa.express View Post
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
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.
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Old 08-10-2018, 04:34 PM   #35
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Default Re: question. simple starter motor conversion to 12v

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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.
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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Old 08-10-2018, 04:52 PM   #36
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Default Re: question. simple starter motor conversion to 12v

Quote:
Originally Posted by M2M View Post
See this link:
http://www.mtfca.com/discus/messages...tml?1467567809

12V, with a Bendix as a dropping resistor:

The link in this post has a very interesting discussion. I think it shows, among other things, that this is a reactive circuit and that Ohm's Law (as we know it) is not reliable.
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Old 08-11-2018, 02:50 AM   #37
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Default Re: question. simple starter motor conversion to 12v

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.
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Old 08-11-2018, 07:15 PM   #38
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Default Re: question. simple starter motor conversion to 12v

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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.
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.
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Old 08-12-2018, 02:50 AM   #39
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Default Re: question. simple starter motor conversion to 12v

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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.
If I had known you or any person wished to see this I would have kept them or at least photographed them. gary
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Old 08-12-2018, 03:08 PM   #40
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Default Re: question. simple starter motor conversion to 12v

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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Old 08-12-2018, 03:45 PM   #41
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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.

Yes, mine is going to chew up the ring gear teeth if I don't get it modified.
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Old 08-12-2018, 07:56 PM   #42
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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.
Mike ,
I feel like we're speaking two different but related languages: you, engineering and me, physics (although perhaps somewhat out of date). Perhaps you could answer a question to see if we have some common ground.
Do we agree that Ohm's Law, V=IR, cannot reliably used for circuits with inductance or capacitance elements?
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Old 08-13-2018, 12:30 AM   #43
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Default Re: question. simple starter motor conversion to 12v

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Mike ,
I feel like we're speaking two different but related languages: you, engineering and me, physics (although perhaps somewhat out of date). Perhaps you could answer a question to see if we have some common ground.
Do we agree that Ohm's Law, V=IR, cannot reliably used for circuits with inductance or capacitance elements?
Steve, Good grief, kind of a loaded question. Even what appears to be a simple purely resistive circuit, like a battery, two wires, and a light bulb will have some, albeit near immeasurable elements of reactance/inductance and capacitance. That said, Ohmís law is never an absolute.

Anything that functions on the relationship between electricity and magnetism, like any motor, will be highly inductive and, while running will not simply follow Ohmís law. Case in point: The starter motor in this discussion. If it draws 125A @ 6V while running at cranking speed it WILL NOT draw twice that @12 while running. For most parallel dual field DC series motors that number will be about 1.4X the amperage if you double the voltage. Now, does this mean you will not get 4X the power? Yes and no. While running, no. Stalled, yes. At that point it will draw near 2X the amperage. The motor will transition from 4X ďpowerĒ (actually ~3.8X if you want to set up a dyno on a test bench for the starter in question) to about 2X as the inductive reactance changes in a non-linear relationship with armature rotational velocity. The near-stall speed 4X (OK, ~3.8X) is what imparts the increased momentum energy in the armature/Bendix that creates the nasty Ďcrashí engagement.

On anything Iíve posted on Model A forums Iíve always tried to keep things in perspective of the audience. Not too many engineers here, so I have rarely delved into application of the work of Henry, Farad, Steinmetz, etc. . . for electrical problems. Even if I did, this forum lacks a math editor/font, and if I started posting anything with calc or functions derived from the work of anyone beyond Volta, Ampere, and Ohm Iíd be talking to an audience of one (You!). I spent too many years scribbling that kind of stuff on blackboards in front of wannabe EEís and MEís with blank looks.
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Old 08-13-2018, 11:02 AM   #44
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... I spent too many years scribbling that kind of stuff on blackboards in front of wannabe EEís and MEís with blank looks.
Mike, Okay, that little flashback is a good place to wrap this up. Now I'm picturing years of blank looks staring back at me in P. Chem. classses. I'm supposed to be doing this for fun.
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Old 08-13-2018, 09:22 PM   #45
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Default Re: question. simple starter motor conversion to 12v

I was a blank look once but I am feeling much better now.
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Old 09-25-2018, 09:23 PM   #46
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Default Re: question. simple starter motor conversion to 12v

good day.
I went and put a starter bendix spring in line. it now has slightly less of an impact. Only slightly less but not very significant. I have ordered a new field coil. gary
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Old 09-26-2018, 07:54 AM   #47
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Default Re: question. simple starter motor conversion to 12v

I'm surprised nobody mentioned this:

http://www.qualitypowerauto.com/item...-Flatheads.htm

Not the cheapest, nor original, but probably the simplest solution to convert from 6V to 12V.
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Old 09-26-2018, 10:00 AM   #48
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on anything iíve posted on model a forums iíve always tried to keep things in perspective of the audience.

Not too many engineers here.

Iíd be talking to an audience of one (you!).
Mike I always enjoy your posts. Well thought out and although too technical for some not so for others. I understand them.

Not too many engineers but I'm sure more than 1.

So an audience of perhaps 2.
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Old 09-26-2018, 01:47 PM   #49
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Default Re: question. simple starter motor conversion to 12v

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I'm surprised nobody mentioned this:

http://www.qualitypowerauto.com/item...-Flatheads.htm

Not the cheapest, nor original, but probably the simplest solution to convert from 6V to 12V.
I have mentioned those many times.
I have used those since they came out many years ago.
They can be had for around $100 on eBay if you watch for them.
At one time I even showed how to use a floor type headlight dimmer switch mounted in the original start pedal hole to activate it.

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Old 09-26-2018, 03:54 PM   #50
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Default Re: question. simple starter motor conversion to 12v

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I'm surprised nobody mentioned this:

http://www.qualitypowerauto.com/item...-Flatheads.htm

Not the cheapest, nor original, but probably the simplest solution to convert from 6V to 12V.
I wished I'd purchased that new starter. I did purchase a new field coil and airfreight it hopefully in time for our national meet. the coil cost, in AUD 70 and the freight AUD 99. To airfreight the new starter would have cost me my left you know.
Mostly I get my sons who are frequently in the US to pick up but time didn't permit.
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Old 09-26-2018, 04:15 PM   #51
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Default Re: question. simple starter motor conversion to 12v

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I have mentioned those many times.
I have used those since they came out many years ago.
They can be had for around $100 on eBay if you watch for them.
At one time I even showed how to use a floor type headlight dimmer switch mounted in the original start pedal hole to activate the it.
Pete,

That's interesting. Their contact information for Quality Power indicates they are located in Yucaipa, CA, about 15 miles from my house!

I might stop by and talk to them.

David Serrano
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Old 09-26-2018, 05:50 PM   #52
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Pete,

That's interesting. Their contact information for Quality Power indicates they are located in Yucaipa, CA, about 15 miles from my house!

I might stop by and talk to them.

David Serrano
Wow! I didn't notice that when I posted their link. I'm just a few miles myself.
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Old 09-27-2018, 08:24 AM   #53
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Default Re: question. simple starter motor conversion to 12v

I once took a Pontiac starter apart that someone had cut some of the pole pieces off, trimmed both ends of each pole pieces a bit, and stuffed some plastic in to keep the windings centered. I imagine they were attempting to reduce the efficiency of the starter, by reducing the magnetic field. This would be wastful of battery amps I suppose, but would reduce the slam effect.

In thinking about it, I suppose you could also reduce a starters power output by rotating the end plate a bit one way or the other, so the brushes moved the armatures magnetic force to a less than optimal position, again, this would reduce power output, slow the speed, but not reduce the current draw, so this is not the "best" solution.

However, if I was in Australia, I might be tempted to try one of those "outside the box" ideas rather than pony up for fast shipping if I was in a pinch. Just a thought...
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Old 09-28-2018, 12:17 PM   #54
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Default Re: question. simple starter motor conversion to 12v

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I'm surprised nobody mentioned this:

http://www.qualitypowerauto.com/item...-Flatheads.htm

Not the cheapest, nor original, but probably the simplest solution to convert from 6V to 12V.
This looks very much like the one I have on my pickup, that came from Snyder's.
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Old 09-28-2018, 03:47 PM   #55
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Default Re: question. simple starter motor conversion to 12v

Thankyou all for your help. I value it.


I have a new field coil coming but regret not buying a whole new starter motor. But it's done now. thanks again, gary

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Old 10-14-2018, 06:46 PM   #56
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Default Re: question. simple starter motor conversion to 12v

I took the starter to an old an versatile fellow who is jack of all trades and master of most. he was uncertain and endeavoured to seek help. however he came back without success, perhaps in fear of damaging it.
I ordered a 12V field coil from Snyders which I now have in my possession and will convert with that.
I got various opinions on reducing slam by running power through bendix coil and amp meter showed no reduction nor resistance and auto electrician said it was bull shit. However I did try it and yes it did reduce somewhat but insufficient.
Since all of that an A owner demonstrated his new type, made in UK which engaged prior to rotation. This was most impressive and I wish I had known about it prior to purchasing field coil.
I thank you Corley for your input which has been received with gratitude and all others who likewise gave suggestion. gary.
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Old 10-14-2018, 06:48 PM   #57
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Default Re: question. simple starter motor conversion to 12v

The starter I spoke about is what is illustrated by CarlG number 54 below.
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