Reducing 12 volts to the starter

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Model T Ford Forum: Forum 2017: Reducing 12 volts to the starter
Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrett on Monday, April 03, 2017 - 05:06 pm:

I know this topic is controversial, but here goes...
I read a post on the forum a while back that mentioned a way to reduce 12 volts going to a 6 volt starter by using a starter bendix spring as a reducer by splicing it into the starter cable. The car seems to run better on 12 volts, but not surprisingly, I've had to replace the bendix due to the high impact on the bendix when it hits the flywheel.
My questions are:
1). Does using the starter bendix spring actually work as a voltage reducer?
2.) Does it matter where you splice it in - before the starter switch or after.
3). Is there another method to get the same desired results.
Many thanks for the feedback!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Monday, April 03, 2017 - 05:12 pm:

Mike

measure the resistance of the bendix spring and apply OHM's Law.

Yes, I've seen it done, and believe it is the living manifestation of a Wives' Tale

Better to rewire the starter before you cost yourself a ring gear


Top of pagePrevious messageNext messageBottom of page Link to this message  By george house . . .caldwell county, TX on Monday, April 03, 2017 - 05:44 pm:

Mike, to answer the first 2 of your 3 Questions: 1.) Yes. 2.) yes it matters where you splice it in. I have a worn out Bendix spring spliced on top of the starter motor on my T s with 12 volts. You want the 12 volts to go to the starter switch but not the starter. I tested this out with a friend. Ignition off I hooked a voltmeter to the starter motor terminal. Friend pressed the switch down and I get 7.35 volts to the starter. Others will say just use s 6 v battery but when you don't have a mag, a T runs twice as good on 12 v and when you have a distributor too.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gordon Drisko on Monday, April 03, 2017 - 06:05 pm:

Scott, In applying Ohm's law, what is the value of "I"


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Monday, April 03, 2017 - 06:35 pm:

Gordon:
About 160A while cranking, with a good starter

I was a little flippant with my initial suggestion...it would be easier to calculate through a Voltage Drop Calculator on line. Assuming 12V in, the voltage drop is negligible...certainly not in the 6V range.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Monday, April 03, 2017 - 06:40 pm:

Dang...not paying attention...160A at 5-6V


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie Spokane, WA on Monday, April 03, 2017 - 07:17 pm:

I did the tests. The results are in this thread, if you dare to look!

http://www.mtfca.com/discus/messages/599638/653383.html?1467567809


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Rogers - South of the Adirondacks on Monday, April 03, 2017 - 07:22 pm:

Mike- does your mag work? If not it's way better to add a small 12 volt battery under the seat to power the coils.

Don't make the mistake of replacing the 6 volt battery with a 12 volt- it's not necessary and will harm your car.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie Spokane, WA on Monday, April 03, 2017 - 07:24 pm:

If you are using a Bendix spring as a dropping resistor, it doesn't matter where you put it as long as it is in series. I think that the best place to put it on the ground strap (between the ground strap and the frame). That way it won't be prone to shorting, as it may if it is on the "hot" side.

disclaimer: I don't advocate using a Bendix spring as a dropping resistor with 12 volts, as the starter will still engage significantly harder than on 6 volts. However, it is better than using nothing and many people have reported good results using this method.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Manuel, Lafayette, La. on Monday, April 03, 2017 - 07:36 pm:

Tim, if a separate 12 v is used for the coils, how would this be wired?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Davis Houston TX on Monday, April 03, 2017 - 07:50 pm:

Mine reduces 12v to 9v.......Been doing it for 12 years. Never busted a bendix since.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George n LakeOzark,Missourah on Tuesday, April 04, 2017 - 12:05 am:

I'm using a Bendix spring also on my 12 volter. Works well for me.

Geo. n Missourah


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrett on Tuesday, April 04, 2017 - 08:46 am:

Thanks to all for the great feedback. For those who are running a spring, is it possible to get some photos of your setup?? :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Larry Smith, Lomita, California on Tuesday, April 04, 2017 - 09:16 am:

If you run a six volt system like you are supposed to have, you don't need to worry!


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Tuesday, April 04, 2017 - 10:56 am:

John Manuel:

The wire that is connected to the magneto post at the top of the transmission cover (hogshead) should be disconnected from that magneto post and connected to the positive (+) terminal of your small battery. Alternatively you can most likely simply remove this magneto connection wire at the MAG connection on the back of your ignition switch. No harm comes to the magneto if there is nothing connected to the mag post at the transmission cover or if you disconnect it at the other end. Make sure you don't have the battery connected in any way to the magneto post wiring. Connect the battery negative terminal (-) to ground at the car frame or block anywhere. Just about any gauge wiring can be used since the battery drain will be .7 amps (yes less than 1 amp) when the engine is running so a 20 amp hour garden tractor battery (12V) can run the car well over 20 hours before you need to charge it back up but for longest battery life you should recharge it asap after running the car since if you let the battery get discharged and leave it that way - it will deteriorate. The nice part is that you can put some quick disconnect terminals on the battery and thus be able to take the battery out of the car to where the charger is if that is most convenient. This is a way safer (and cheaper) method of running your T until you get the magneto fixed.


Top of pagePrevious messageNext messageBottom of page Link to this message  By george house . . .caldwell county, TX on Tuesday, April 04, 2017 - 11:04 am:

I was waiting for a snarky remark like that Larry. Try to answer his 3 questions. All of us answered the first two. Mike, I can't post photos but - a good Bendix spring will have both 'eyes' in the same plane when viewed. It'll work as a voltage reducer but most guys have sprung Bendix springs with the 2 'eyes' probably 90 degrees off. this is the type that I use. I'm sorry that I can't post pictures but you'll have to grind the interior of one of the ends of the spring(eye), heat it and open it up a wee bit to fit over the starter terminal. Replace the terminal nut and fasten the other end of the Bendix to the cable from the starter switch.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, April 04, 2017 - 11:28 am:

The voltage drop across the resistor while the starter is spinning the engine will not be the same as when the voltage is first supplied. The starter bendix will still slam into the flywheel. You either need to run the starter with a 6 volt battery or rewind the starter for 12 volts.

Another way to accomplish the same results would be to connect two 6 volt batteries in series and use the output of the two in series to supply the ignition and use one battery alone for the starter. It is much easier to run the coils on magneto or to use a 6 volt distributor. You can use any distributor on 6 volts if you use a coil made for 6 volts. Most of the older cars made before the 1950's used 6 volt ignition coils, so they should still be readily available.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Manuel, Lafayette, La. on Tuesday, April 04, 2017 - 12:52 pm:

John Regan: thanks. I was thinking 12 v battery positive to mag post on switch via terminal block where mag post wire would normally go. Start on 6v then switch to "mag" (now 12 v batt) and run coils on 12v. My magneto was removed by the previous owner.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Glen Chaffin on Tuesday, April 04, 2017 - 01:37 pm:

This question has been answered many times in previous posts. There are two reasons to switch to a 12 volt battery. 1. To start the car quicker. 2. To provide a hotter spark to make the car run better. There is no doubt that the car will run better but the improvement is minimal if the coils are adjusted properly. However, 12 volts is fatal for the Bendix. Contrary to what the experts say a dropping resistor will not solve the problem. Power to the starter is determined by voltage times current, or voltage squared divided by resistance. Therefore, when you use 12 volts you are increasing power not by a factor of 2 but by a factor of 4. When you push the starter switch the full 12 volts is applied to the starter jamming the bendix into the starter ring gear . As the motor starts to turn the current will drop because of the resistance but the drop occurs too late to prevent damage. Sure, the voltage drops but the damage has already been done. Rewiring the starter for 12 volts will solve this problem while making the car run a little better but the starter will then have the same cranking power as it did on 6 volts.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Rogers - South of the Adirondacks on Tuesday, April 04, 2017 - 04:43 pm:

No need for a 12 volt battery to start a T quicker. Just take a look at Steve Jelf's video showing him slowly cranking (barley a 1/4 turn) to start his car.

If a T starts hard it has nothing to do with the starter (6 or 12 volt).


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrett on Tuesday, April 04, 2017 - 05:15 pm:

Glen, good explanation of the subject. Actually, I'm fine with the starter having the same cranking power as 6 volts. I have no problems starting with a 6v battery, but I notice better performance when running on 12 volts, (especially since I'm running with a newly refurbed set of Coil Doctor coils!!) so I want to stay with 12v. I'm adding a 12 volt regulator from Lang's to keep the charging under control. The next task is to have the starter modified with new windings to handle 12v.
Keep 'em rolling! :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Lenney Glenn on Tuesday, April 04, 2017 - 09:44 pm:

If your magneto does not work fix it. If your magneto has been removed replace it. If your coils don't work properly send them to Ron or Brent. Just because one is ignorant of the operation of the tee components is not a good reason to reject them. I have never seen a tee with all these "upgrades" perform any better than a well maintained stock tee. Changing to twelve volts is nonsense. Listen to John and Glen. They are correct on all points. I prefer to spend less money keeping my tee in good original condition so as not to hide my poor maintenance behind "upgrades" The only upgrade I would recommend is the miserable brakes.


Top of pagePrevious messageNext messageBottom of page Link to this message  By rick howerton on Tuesday, April 04, 2017 - 10:04 pm:

I got two cars with 12v starters. I`ve been told there is no difference between 6 or 12 I believe there is a deference its the way their wired on the inside the starter. My Bendix use to really slam in , now they do just right. How about going to a smaller gage cables. 6 volt cable is larger allow more amp flow, you might go with 12 volt cable it`s smaller, it slows down the amps, in turn slows down voltage to the starter. six volt cable is equal two welding cable. Try it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By rick howerton on Tuesday, April 04, 2017 - 10:09 pm:

Don` try welding cable , try 12 volt cable from the auto store, hope this helps.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Lenney Glenn on Tuesday, April 04, 2017 - 10:30 pm:

If you must change to twelve volts open your starter and change field coils from a parallel to a series hook up. This is the correct way to relieve the twelve volt stress on starter and thus the bendix. Much easier and simpler than the bendix spring resistor bologna.


Top of pagePrevious messageNext messageBottom of page Link to this message  By rick howerton on Wednesday, April 05, 2017 - 10:58 am:

Back in the old days when jumping a battery, and you wanted more jump power. You took both neg. clamps off both batteries, put each neg. clamp on the pos. clamps that's doubling the size of your pos. cable. Push the two bumpers together, you talk about spin a dead engine over! Your upping your amp flow. It also works in reverse, smaller the cables slower the starter. when I was in high school I worked for a car dealership. We use to do it all the Time. Cables is cheap and easy.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chadwick Azevedo on Wednesday, April 05, 2017 - 11:32 am:

Something not mentioned that I feel is relevant is the engine that is being cranked. Are we spinning some high head cast iron pistons or a high performance overhead with high compression a cut down flywheel etc.

Dealing with a stock engine there is a lot of mass to get moving. When you remove a magneto, lighten a flywheel, and are using aluminum pistons the mass is greatly reduced. Nearly every speedster I've been around is running 12 volts on the stock starter and no mag. Broken springs are unheard of.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Glen Chaffin on Wednesday, April 05, 2017 - 12:36 pm:

You guys just don't get it. It does no good to put any type of a resistor in series with the Started. Whether it be a resistor, a Bendix spring or a 12 volt cable. None of them will drop the voltage fast enough to protect the starter and Bendix. The Starter will not turn unless current is flowing and the resistance will not drop the voltage unless current is flowing, therefore the voltage does not drop until after the current is flowing and the motor turning. In my experience most people complaining about the starter not turning the engine over fast enough are using 12 volt starter cables. When you use the correct large gauge 6 Volt cables and insure you have good solid wire connections you have no problems on 6 volts.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erik Barrett in Auburn Ca. on Wednesday, April 05, 2017 - 02:15 pm:

I'm with Norman and Glen. By the time enough current is flowing for a resistor to be effective, the drive has already slammed into the ring gear. Either use a 12 volt starter or make the six volt system work properly.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Rogers - South of the Adirondacks on Wednesday, April 05, 2017 - 03:25 pm:

It's a myth that 6 volts is not adequate to start a T.

It's also a myth that a T engine has to spin fast to start properly.

If a T does not start properly with the original equipment then something is broke and needs to be repaired- not "upgraded".


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jeff Perkins / St. Croix Valley Mn on Wednesday, April 05, 2017 - 05:07 pm:

I have to say after 40 years fiddling with 9 Model T's I totally agree with Larry Smith and Tim Rogers.


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