Is the use of a coil of wire , copper tubing, or Bendix spring, a drop resistor or an inductor? If the resistance is measured, there in negligible resistance in ohms.
Doesn't the coil have a limiting effect on the amperage, not the voltage?
The starter still receives 12 volts, but the amperage flow briefly is reduced, slowing down the rotation of the armature?
George, remember voltage, amperage and resistance is all related by E=IR. The extra 'wire' acts as a resistor, and a small resistance can significantly reduce voltage at a high amperage (in the range of 200 amps). The energy is converted into heat, and as a result your 'dropping resistor' will get HOT!
Using that formula E=IR, you can have a 12 volt power supply and only have 6 volts available. Or have low voltage (2 to 9) volts available with excessive amperage. Depending on your resistance.
How about a 6 volt battery and no resistor!
Dropping resistors don't work. See 12 volts spins too fast June 24 at the top of this page.
The problem with the resistor or any other device to drop the voltage, is that they won't do anything to the starter when it is not under load. It only drops the current flow when under load after it makes contact with the starter ring.
Only two methods which will fix the problem. One is to use a 6 volt battery, and the other is to rewind the starter for 12 volts.
I measure 9v using my coil as a dropping resistor.Jerry....
Bob Stoeckly did some experiments using a bendix spring as a dropping device. I never saw the oscilloscope traces, but Bob said that a bendix spring is indeed an effective dropping device. If Bob says it, it is undoubtedly true. There is a huge current draw when the starter first begins to spin, this I suppose, is when the bendix spring does its thing. I would guess that most of the drop is from resistance, but a little would be from inductance too.
You have to remember the starter motors' lowest resistance is when it's at rest, hence, inrush current. Dave in Bellingham, WA
My testing also proved a Bendix Spring is a very effective current limiter, as is a 12 foot #2 gage wire.
There is a large current input until the starter motor turns. Once it turns the back emf generated by the starter motor will reduce the current draw. Of course once it starts to turn the engine the current draw will increase. The problem is not so much as 12 volts on the starter motor as it is the fact that the 12 volts slams the Bendix. As Royce said above this can be overcome by using skinny 12 volt style cables.
There is no argument to win or lose here. If you want to use 12 volts, then you can make it work. If you want to use 6 volts you can make that work also but you don't want any skinny 12 volt cables or dirty connections.
So make a choice and keep that Model T running down the road,
It makes no difference, a starter Bendix spring or a skinny 12 volt cable, neither will drop the voltage fast enough to prevent damage to the bendix. Rewiring the starter for 12v is self defeating because it will then have the same cranking power current as the 6 volt starter. You double the voltage and double the resistance and the current stays the same.
Perhaps this might help to clarify what Glen is saying.
When the starter motor starts to turn and before the Bendix engages, it draws too little current foe any kind of dropping resistor to be effective.
At the moment the Bendix engages the flywheel, the starter motor is seeing nearly the full 12 Volts.
When the Bendix engages the flywheel, it does so with the full force of the 12 Volt battery.
Below is a sketch of the sequence of events.
This discussion has many possible views. If one wants to change the design of how to engage the Bendix, then a search of the literature - in this case the internet - will give various answers for solid state designed motor controls for speed and torque. If 12 volts is used without a controller then there will be a mashing of gears. If you stay with the original 6 volts - yes there will be a mashing of gears - but a a bit slower clash.
A possible suggestion for a solid state controller for speed and torque at 12 volts refer to:
You need to figure out what the rating will be for the four solid state transistors T1-T4.
The question is have you improved the Model T?
The only reason for using 12 volts on a model T that makes sense to me would be if you want to run with coils, but the magneto is dead. Fixing the magneto may take a complete teardown of the engine if in car charging doesn't work, while driving on bat with a 12 v battery would get the coils almost the same high speed performance as on mag. Then you can delay the engine teardown until other problems makes it necessary.
Using the hand crank most of the time saves the bendix, gives good exercise - and it's fun
The starter might still come in handy in emergencies, like if the car stalls halfway in an intersection..
Royce's father came up with the skinny cable hookup for 12 volts. It works. If you want to use 6 volts then use 6 volts. If you want to use 12 volts then use 12 volts. The choice I'd yours.
No Ted, It doesn't work. See Bob's chart above. He is right on and agrees with everything I said. But I've had it . I people don't want to listen and learn from experience they deserve a damages Bendix.
It works on both of my Model T's. I still think it's a matter of choice. I have personal experience and I know the skinny cable technique works.
Others are convinced it doesn't and that's fine with me.
I have no problem with anyone staying with the original 6 volt system.
PS: Don't tell anyone but my 1943 M Farmall starter works fine on 12 volts using the original 6 volt style heavy cables.
Bob, The resistance of the starter motor is at it 's lowest point when the 12 volts is applied, Therefore, the current drawn is at it's highest point. The torque produced is maximum and drives the Bendix hard into the Ring Gear. the voltage drop across the resistor is not instantaneous therefore the voltage drop and drop in current does not occur until the motor is turning and the damage has already been done.
This is a typical Model T forum thread. Royce and Ted insist that the dropping resistor works based on their experience. Bob Stoeckly told me that he did tests that supplied empirical data that a bendix spring actually does lower the starter current at the time of engagement. Glen and Bob Cascisa insist that it can't work based on theory.
I wonder who is right?
When I get some time, I will hook up my 'scope and find out.
Something missed here. Volts are the electromotive force. Amps are the flow of current. The combination of speed & force are what damages the bendix right? If you lower the amperage you will slow the speed down you will also find that the starter will engage much nicer. I you use a low amp battery such as a riding mower battery (180 - 230 cca) you will find this out. Yes I know it doesn't fit but I bet we can figure that out with some 3/4" plywood. the bonus is they are $30 on sale @ Most discount auto parts stores. We tried it a year and a half ago and it seems to work very well. Thanks for letting me get my two cents in.
In theory, reality and theory are the same.
my old 50 chev ton truck worked fine on 12 v for years . i guess they had a better bendix. charley
It's not theory just fact. Apply 12 to a starter with a series resistor. The starter will jump into spinning with instant torque. The Bendix is instantly jammed into the ring gear. After the motort starts spinning the rpm will reduce because the voltage is being dropped by the resistor but it is too late.
Love that quote, Royce! I always thought it was attributed to Yogi Berra, but Wikipedia (gasp!) says no!
If theory and practice do not agree then either theory or practice is wrong.
Glen, Bob, and George are all correct no matter how much resistance you put in the line, 12 volts will be at the ready for use. It is only after you pull the switch that the voltage drops and that first click is the one that breaks the Bendix at 12 volts.
If you test the voltage at a tail light on a long trailer you might get 12 volts but as soon as you turn on the light, the voltage will drop.
I had a bad ignition issue on a T with a distributor. The coil had battery voltage but the wire had 25000 ohms of resistance. We are told not to measure resistance only voltage drop. But in my case there was only one strand of wire left and on a voltage check I got battery voltage to the coil but the coil wire with one strand had too many ohms of resistance to pass the voltage.
So sometimes you have to measure the resistance and not only the voltage drop.
A faulty contact in a switch will cause the same problem.
Frank may be old but he is correct. It is not theory, it is ohms law and practice has many variables. Ohms law does not. 12 volts will eventually break your Bendix Spring or knock off the collar on your drive gear or both. Some may last longer than others but they will all eventually fail.
Ok, I have a few questions that I will throw out:
1. At the time of bendix engagement, will a long 12 volt cable or a bendix spring provide any voltage drop?
2. How much voltage does a six volt battery actually supply to the starter at time of bendix engagement? (Assuming normal sized cables.)
3. How much voltage does a 12 volt battery actually supply to the starter at the time of bendix engagement? (Assuming normal sized cables.)
4. How much longer does it take the bendix to engage when operating on 12 volts as opposed to six? (Assuming normal sized cables.)
5. How much voltage drop would be needed to safely engage a bendix when operating on 12 volts?
It's more complicated than Ohm's law. It has a lot to do with DC motors and their physics as well as Ohm's law. I would like you disbelievers to try some experiments on your own. I think you will be surprised at the results.
I do not think the motor controller circuit posted by George will work. Note how the output transistors are connected. This will present a short circuit across the power source. The motor will never be energized.
Tom, The Bendix is thrown forward as soon as the motor starts to turn. When you apply 12 volts to the starter it begins rotating instantly and here is why. When you apply 12 volts to the starter you do not just have twice as much power to drive the motor , you have four times the driving power.
The ohms law formula for power is Voltage squared divided by the resistance. Assume the voltage is 6 Volts and the resistance is 5 ohms. 6x6=36/5 ohms = 7.2 watts power. With 12 Volts 12x12= 144/5 ohms = 28.8 watts. Hopefully you can see why 12 volts is so bad for the Bendix. After the motor is turning the voltage does drop but it is too late. Just try it on the bench. Apply 12 volts through a bendix spring or skinny 12 volt cable. When you apply the 12 volts the motor will spin at a fast rpm instantly and then slow down as the voltage drops. It is easy to see.
Glen, I understand the concepts. I was hoping folks would speculate or guess or whatever and put some figures to the questions that I posed above.
8 volt batteries are available at many farm and home stores. They will fit in most 6 volt battery holders, I have no data what the increased voltage will do to the bendix. I know it will spin the starter over a little faster and many heavy duty bulbs will take the extra voltage. If not, a small resister like 100 ohm in series with the bulb will work. In many cases nothing needs ro be done to the generator to facilitate charging. Since most cell phone and GPS chargers work on 5 volt, an 8 volt source should work. Are there others beside me using an 8 volt battery?
I know the numbers say it doesn't work, but I broke numerous bendix springs and mangled a bendix or two before I used one of the mangled springs as a resistor. Since then I have not broken one and engagement was noticeably softer. I have driven this T more than 50K miles so there is a long term trial history.
OK, so I took the time to find out what really goes on with 12V and resistors and such.
Here is a T starter with a 6 volt battery:
Here is 12V, no dropping resistor:
Here is 12V, with a Bendix as a dropping resistor:
12V with 8 foot long 12V cable as dropping resistor:
My conclusion: Either a long cable or a Bendix spring is an effective dropping resistor. The Bendix spring seems slightly better.
Nearly identical to what I posted here in 2008. I used calibrated test equipment.
Here's one of the videos:
http://www.bing.com/videos/search?q=youtube+cornydogeater&qpvt=youtube+cornydoge ater&view=detail&mid=6141B11E66C40EA5863B6141B11E66C40EA5863B&rvsmid=6141B11E66C 40EA5863B6141B11E66C40EA5863B&fsscr=0&FORM=VDMCNL
This is the one with the long 2 gage battery cable. Voltage goes just over 8 while the starter is cranking.
So how are you measuring the voltage at the precise moment the Bendox engages the starter ring gear? Oscilloscope, dc voltmeter or digital volt meter. They all have a different time to respond to the voltage applied.
The Bendix is going to engage much sooner with four times the cranking power.; I( don't see that in your graphs
Me? I measured the voltage with an oscilloscope as shown above.
If you replace the floor mounted starter switch with a home made one the 12 volts won't be reached until after the starter has engaged.
Ok, That's good, Now how did you determine when the Bendix engaged. It should have engaged much sooner with direct 12 Volts.
Glen, look at the traces. The second current spike is when the Bendix engages. You keep saying it all should happen much faster on 12V, but it just doesn't. A lot of it goes to Craig Leach's point above. A similar sized 12V battery cannot put out the same current as a 6V battery, all else also being equal.
Thank you for doing the starter tests and presenting your results. Unfortunately, I see something different when I examine the data.
Focusing on the period from startup to bendix engagement, I extracted the average current, average voltage, and time for each of your three tests. The product of those three variables is basically the "work" input to the starter, measured in watt-seconds. The result of that "work" input is the rotational speed and linear velocity of the starter gear. When that gear comes to a sudden stop upon hitting the flywheel gear, the total work is absorbed by the teeth on the flywheel and by the bendix spring.
You may want to double check my numbers, but I found the following watt-seconds of input for each case:
6V battery (stock): 22.8 watt-seconds
12V (without dropping resistor): 50.3 watt-seconds
12V (with dropping resistor): 38.3 watt-seconds
Of course it's the RPM and linear velocity of the starter gear that really counts, and the energy input is just an analogy. The conclusive answer would be to measure the actual speed of the gear upon engagement. But since it's the same gear and the same shaft, I think we can assume that the relative differences in work input pretty much indicate the relative speeds of the gear upon engagement.
So by calculating the percentage differences in work input, we can infer the relative kinetic energy of the gear at engagement.
6V battery (stock): 100%
12V (without dropping resistor): 220%
12V (with dropping resistor): 168%
Conclusion: The dropping resistor does reduce the energy input to the starter gear during the pre-engagement period. But not down to the level of a stock installation. Without knowing the design limits of the bendix spring and ring gear it is impossible to say whether 12V with a dropping resistor is within acceptable limits other than by long term testing.
The long term testing is the hundreds if not thousands of Bendix that have been damages or destroyed by using 12 volts. As I said before the total drive power is four times that of 6 volts with 12 volts. The Bendix has to be thrown into engagement sooner with 12 volts and with four times the fource. I don't see that in the graphs presented. The dropping resistor may help a little but not much.
Dick, I think that your figures are very close. Here is another set of graphs that show a little more. I used the pickup off of my Fender P-Bass to measure the revolutions of the free turning starter. I have calculated the speed of the second revolution, as this is close to when the Bendix would engage. 60000/Ms/turn = rpm.
12V on a free T starter.
12V with Bendix spring dropping resistor.
6V on free starter.
Total kinetic energy = velocity (rpm) squared times some constant. Without knowing the mass of the Bendix, we don't know the constant, but it doesn't matter as we can compare the graphs to each other by squaring the the speed. The Bendix engages a little before the second revolution, so this may be a little off, but probably not much.
1695 squared = 2873025 (6 volt)
2024 squared = 4096576 (12 volt - bendix)
2558 squared = 6543364 (12 volt)
2873025 = 100%
4096576 = 143%
6543364 = 228%
So, while the Bendix spring does not knock it down to the same level as a 6 volt battery, it does knock it down quite a bit. Judging from anecdotal evidence, I still conclude that a Bendix spring is an effective dropping resistor.
If one were to rewire the 6 volt generator to a 12 volt device, would the resultant RPMs, engagement force, and other parameters equal that of the non-modified 6 volt generator?
What is gained by making the conversion?
Dave, I don't understand your question. Did you mean to say generator?
By the way, Glen's theory that the starter on 12V should put out 4 times the force as when powered by 6V is in general correct. I have thought a lot as to why it doesn't hold up in practice. I think the reason is that although the speed is doubled with 12V, the inertia is also increased. Also, the friction increase is a function of speed. As an example, suppose a certain starter (as in our graph above) would spin up to 2510 rpm on 6V. Why does it stop at 2510 rpm? The reason is friction. If you had a hypothetical frictionless starter, it would continue to speed up indefinitely on any voltage. A DC motor reaches top speed when the torque and friction reach equilibrium. So, if you apply 12V to this same starter, you may think it would spin up to 5020 rpm, but in fact, it only goes to 4379 rpm. This is because that although the torque is the same at 2510 on 6V as at 5020 on 12V, the friction is doubled at 5020, so on 12V it never makes it there.
I'm sorry - no I did not mean generator - that's what happens to me when I read the Forum and post something before my caffeine fix.
I meant starter..my faux paux! Wherever the word generator appears, please substitute starter.
So, if the original 6 volt starter was modified to accept 12 volts, would the bendix engagement speed be reduced to the 6 volt value?
Thanks to all for collecting & sharing the data, and for maintaining a civil & rational discussion. I learned a lot. Respectfully, jb
Dave has the same question I have. Thanks Tom for your obvious effort on this subject.
Another question? If 12 volts are "Better," for starting an engine, why did not Ford use 12vdc in the 1917 design? There were a large number of makers gravitating towards electric starters, and 12vdc was available. Cost can not be a factor, if one reviews the size of 6vdc starters of the period, some were better constructed than the T starter, indicating a greater manufacturing cost.
Why not use the starter/generator combination, if the mashing of the Bendix as a concern? Or wasn't it a concern when Ford decided to upgrade? There were patents for such a device in beginning in 1912. Marmon (https://www.google.com/patents/US1171948) had a design that attached to the front of the crankshaft direct. A design that avoided a mashing of the Bendix.
None of that was a concern because 6V worked, and works, just fine. There was most likely no concern about mashing a Bendix if you very simply do not mash it with straight 12V.
BTW, I've got to believe a 12V battery, in 1919, cost a lot more than a 6V.
Jerry, I agree. And that is why I am asking, "Why now add a fifth wheel to the cart?"
As a spare! ;O)
Living within a mile and a half of the Pacific Ocean there is a constant salt air coming in. Even in my heated shop tools will rust. Every few weeks a lawn mower or a modern car has an issue with rust
If I can help my lights by using 12 volts I will-----------our town goes from five thousand to probably twenty thousand every summer with fishing, camping, and lots of boats, RVs pulling some thing with the folks unfamiliar with someone in a vintage car going forty MPH. Its bad enough in a modern car with good lights and good turn signals.
I hope you all switch to 12 volts. It just means I'll sell a lot more Bendix and springs. That I know for sure and I don't need a graph to prove it.
I ran a simple non-scientific imperical test using 12 volts and 12 volts through a Bendix Spring to start a motor. I looked real hard but could not see any difference in time for the Bendix to engage with either test. This tells me that the Bendix was engaging before the voltage dropped when using the resistor. I also noticed a reduction of maximum RPM when using the resistor and a longer time to reach maximum RPM. All of this agrees with what I have said about using a resistor. The voltage drop occurs too late.
Glen, it takes 73 ms for the Bendix to engage on 12V without the dropping resistor and 93 ms with. Did you really really think you could see a 20 ms difference with your naked eye? To put some perspective on this, a car travels one inch per ms at 60 mph. So 20 ms is the amount of time it takes for a car to travel 20 inches at 60 mph.
Glen, please look at the traces. The voltage drop occurs instantly. You're a smart guy and you know stuff about electricity. You have got to know that this is true even without looking at the traces above which clearly show it.
I don't have a dog in this hunt. I don't care if someone runs 12V or 6V. All of my cars are 6V and work just fine, but I would rather see folks using a dropping resistor if they use 12V. I too sell Bendixes and springs, but I would rather folks didn't break stuff unnecessarily. It might not prevent damage to use a dropping resistor, but the evidence sure points toward it mitigating the damage.
"If one were to rewire the 6 volt starter to a 12 volt device, would the resultant RPMs, engagement force, and other parameters equal that of the non-modified 6 volt starter?"
Answer: Yes, pretty much so.
What is gained by making the conversion?
The resultant RPMs, engagement force, and other parameters would equal that of the non-modified 6 volt starter. (nearly)
A good "winter time project" on my list of things to do.
My advice, if you feel you must use 12V on your T for some reason, it to use a starter made for the purpose, such as the one made by Becker. A converted T starter is a compromise and is not as robust (all of the current goes through a single brush wire that feeds both power brushes) as the made for the purpose starters.
Having said that, I know folks that have been using converted T starters for years and years with good luck. The problems I've seen is situations of abuse, such as cranking a tight engine for too long rather than allowing the starter to cool between short uses.
Seem to be unable to contact Darryl...not sure if he is still making them.
Would like the 12 volt system for more choices of lights - directionals...and "accessories" - horns etc. Definitely a vehicle that Larry S would not like...just a "fun" car for me.
Thanks for the advice...
Actually planning ahead....making a list of projects - it will be for a currently non-starter car - for the day when I can no longer turn the crank and will change engines then. With full awareness that Royce's dad hand cranked for many years...and Steve still does. Not all of us are blessed with such great genes!
(Message edited by adave on June 29, 2016)
The time period to engage a starter using either 6 or 12 volts with or with out drop resistance should be limited. During this discussion I have not seen any one state what the engagement time should be. Generally with large motors - diesels for example - 15 seconds is the limit with 3 to 4 minutes between attempts.
I hate to 'put a fly in the ointment', but if one bendix is not sufficient, maybe 2 in series is better!
I couldn't resist.
Tom, This discussion is useless as I know for a fact that 12 volts does damages the Bendix. If the series resistor did drop the voltage in time as you claim what advantage do you have by converting to 12 Volts. Your still cranking with 6 Volts. And you are right, a starter converted for 12 Volts will be no better than a 6 Volt starter. So all of this discussion is useless. Just stay with 6 Volts and make sure you have the heavy gauge wires and good clean connections.
In my '10 I converted to 12 volts to be able to use Halogen headlights. It does not have a starter other than me.
In the case of all my other T's the price of a battery is half what a 6 volt battery costs. Never had an issue with a Bendix failure on any T converted to 12 volts - no flywheel gear damage - nothing - nada - never.
i dont think this discussion is useless. I think it is usefull and informative.
OK 2 cents more. Its obvious that some of us are going to run 12 volts. Either because the mag failed, we like to see were we are going @ night, we couldn't buy a 6 volt battery in the same county our battery failed in or we blew every bulb in our car getting a jump from a modern car because we use the head nights as a diagnostic tool to determine that we had a dead battery. So stay with 6 volts Or every year replace the 5020, 5022, 5023, 5024 & the two 5025's use the old spring for a volt drop. Then go out and enjoy your car & share it with everyone you can before we all have heart attacks over this topic. Besides our new cars will soon be using 24, 36 & 48 volt systems in the near future to give us a royal pain in the you know what. Can you say $700 for a battery?
What is the effect of jumping a 6v bat with a 12v, on the Starter? Does this decrease the 12v and increase the 6v output? I have used 12v batteries and broke springs but not when jumping a 6v. May be lucky. JW
Well it depends if you have help or not. To connect the 12 volt to a 6 volt can be exciting. Sparks. If there should be gases escaping from the 6 volt at the time you connect the 12 volt there may be an explosion.
If you have a helper, they can "touch" the jumper negative to the frame away from the 6 volt at the moment you engage the starter. Yes there are some sparks, but generally no explosions.
Of course if you are luck nothing will happen and the car will start.
Right on George That's the way I do it, holding the 12v ground and making contact after the starter is engaged to avoid jamming the bendix gear into the fly wheel.
Here's what I did 25 years ago after switching 6 to 12v and promptly breaking 3 bendix springs.
1 reduce the wire guage, battery to starter
2 install used bendix spring as a dropping resistor
3 turn on headlights before engaging starter
Haven't broken a spring in 25 years. May break one tomorrow but as of now, nope.
For what it's worth....(probably not much)
Jerry...(love my water pump)
For what it is worth, probably not much to some people, I don't know anyone who has broken a Bendix using 12V and a Bendix spring as a dropping resistor. I know many who have broken a Bendix on straight 12V.
If you do decide to use a Bendix spring as a dropping resistor, it works very well to put it onto the ground cable.
Admittedly, I am challenged when it comes to electron knowledge...
Tom - your advice to put the bendix spring (resistor) onto the ground cable has me stumped...put it between the battery negative post and the frame ? If I do that, doesn't that defeat the purpose of having the full 12 volts to operate lights, horns and other accessories?
Dave, the lights will never notice the difference. The efficacy of a dropping resistor is a function of its load. A starter puts a tremendous load on the system, the lights, not so much.
Another lesson learned today.
I am often amazed at the scientific knowledge shown in this group; this thread is a good illustration of it.
My brother and I came up with this theory of electricity when we were much younger: it is smoke inside the wire tube; a light bulb is a short section of clear tube where you can see the smoke. If the smoke gets out of an electrical device, it's toast. If two different wires cross each other, the smoke blows up!
Usually works for me!
And I know I should be able to understand all them fancy graphs up there, but something in my brain goes "TILT!!" and I go looking for the nice pictures Jay posts. I blame it on my Dyslexia which really screwed up my trying to learn Calculus. (thank goodness for spell-check, or I'd never spell dyslexia right!)
And yes, thank you all for trying to pass on good information. My solution to all this discussion: I'll stick with 6 volts, as Ford intended! (Although my DB is 12 volts!)
I would not worry to much about the mathematics of the electrical system in a Model T.
The infernal magneto and induction coil have their beginnings with the fellow Michael Faraday FRS (22 September 1791 – 25 August 1867). He was was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic induction, diamagnetism and electrolysis.
Faraday was an excellent experimentalist who conveyed his ideas in clear and simple language; his mathematical abilities, however, did not extend as far as trigonometry and were limited to the simplest algebra.
To see what started your Bendix drive to be harsh on starting, see Faraday's magnetic rotation device. It was not created by calculus but by experimentation.