I have been lerking here for quite a while now. Ever now and then I see a thread about magnetos. I just don't understand. Other than in an effort to rebuild the car just as it was, is there any good reason to spend the kind of money it takes to get a magnito working? If you have a timer, coils and a battery, you don't absolutely have to have a magneto do you? What are the advantages? A new magneto ring is like $150 and the magneto anther $100 right? Is it necessary to spend the money?
It is not absolutely necessary to use the magneto, but Model T ignition timing using original coils is far superior using the internal magneto than running on a 6 volt battery.
You can install a 12 volt battery and help coil performance somewhat, but along with that 12 volts comes some other issues.
Ron the Coilman
Here is a link to an article that explains this in more detail.
More on Model T Spark Timing
Ron the Coilman
A model T running with coils runs much better on the magneto. A 6 volt battery will run the car, but the mag puts out a higher voltage that just makes the car run better.
Mark, The magnito will produce 20-30 VAC if working correctly. This produces a very hot spark at the spark plug which makes the car run much better. A 12V battery will produce much the same results but will eventually damage your starter bendix and spring. A 6V battery will significantly reduce engine performance due to a lower spark level. 6v will operate the engine just fine but the difference in performance versus 12V or the magnito is very noticable. I always use the magnito and find it well worth the added expense.
When I switch from coils to the mag,it feels like you turned on the nitrous. More power, more speed and better milage.
Mark, there is a noticable difference in the performance of the T engine running off the mag compared to 6 V. I start my car on battery (out of an old habit) and then turn the ignition switch to mag. Occasionally I'll forget to turn the this switch to mag and after taking off and building up RPM's, I realize the engine's not pulling the same as usual.
If you know someone with a T and working mag, have them take you for a ride and show you the difference. The mag ring is in the $150 range but if your magnets are OK all you need to do is recharge them and that cost can be free to minimal. Read the articles that Ron suggested as those will enlighten you more on the mechanics of the mag ring and coils.
my two cents with a penny back in change. My dad restored two cars in the sixties, one a 24 coupe and one a full body 25 pie wagon. Both cars he had the mags rebuilt. He still has the coupe and I now have the Pie Wagon. Both electric start, 6 volt. The mag in the Pie Wagon has never work since he had it built, thinking it was not set right. (the rebuilder long since dead). I have owned and run the Pie Wagon for the five years. I can only run it on battery (6 volt). With the full enclosed body made of wood, this car has to be one of the heaviest model T's going. Even though it was rebulit in the sixties, the engine has less then 500 hours on it. It is electric start, 6 volt system, new coils at rebuild and it starts and runs fine. I have given thought to having the mag checked but I have a hard time letting it sit long enough to have someone look at it. So for what its worth, this racer i'm building does not have a mag and will be
6 volt. Just a voice of experence.
This posting is not for the purist, but a model "T" will run very good on a distributor or solid state ignition made for model "T"s.
You do not need the mag ring or the coils.
I have two cars on distributors and a few earlier cars on coils. They both have their good and bad points.
I just need to point out that your are incorrect in stating that the T coil puts out a lower spark level on 6V versus 12V. You are correct that the T runs better on magneto or 12V than on 6V but it has nothing to do with SPARK LEVEL output but has EVERYTHING to do with timing. The magnetic field builds up until the points are pulled open and magnetic field is determined by amps and turns of wire - not voltage. Voltage affects how FAST the current will build up. THAT is the reason the T runs better on mag or 12v Battery.
One of the ironic things is that coils that are setup CORRECTLY (using an HCCT or Strobo-Spark) will run worse on 6V Battery than they do on 12V Battery or magneto. If you setup the coils for a lower current draw they will appear to run OK on 6V since a T coil that fires off prematurely (or even double sparks) will oddly enough run better than a properly setup coil when BOTH are running on 6V Battery. With a coil setup properly, the time delay to fire the coil when powering it off 6V is too long and causes poor and sluggish performance of the engine at the higher RPMS. The higher magneto voltage does NOT produce a higher spark voltage but DOES cause it to happen much SOONER since the coil DELAY is much much shorter with magneto voltage or 12V battery than it is with 6V battery. Whether powered by 6V, 12V or magneto, the coil fires when its points OPEN and those points are pulled open by the coils magnetic field. The strength of that magnetic field is determined by the current in amps multiplied by the number of turns. The voltage applied has NOTHING to do with the amount of current since the points control that but rather has EVERYTHING to do with how quickly the current rises to the point of where the magnetic field is strong enough to pull the points open. Higher applied voltage makes the T coil FASTER to fire after the timer closes. The amount of spark is determined by the magnetic field which is always the same amount since that is the point where the points are pulled OPEN.
Theoretically if you double the voltage applied to the coil, the time to fire it is cut in half but there is a limit to the speed with which the points can be moved and thus increasing the voltage ever higher does NOT result in the coil firing ever faster. A point is reached when further voltage increase does not affect the coils ramp to fire time and only produces HEAT in the coil winding and OVERSHOOT of the proper magnetic field amount necessary to fire the coil. Coils will not last very long if operated in this region.
I have successfully rebuilt 3 mag coil rings following the instructions in the club book "Electrical System" They will last indefinately when the fiberglass tape and boat resin are used. This will take some labor, but cost less than buying one rewound. This part is internal and the insulation cannot be detected from outside the car. They both work better on mag than on battery. The timing is in sync because it fires when the magnets pass the coils and if the coils are adjusted properly it will work on both mag and battery. The battery is used for starting and it is switched to magneto. Any kind of distributor setup or electronic device which fits into the coil box is going to cost you a lot of money, and they can all be seen upon inspection. They will run good on them, but will not run any better. Another thing about using the coils, you can always carry one or two spare coils, and if the car starts to miss, just plug them in and find out which coil is not working. If you use after market parts such as distributor you will not be that lucky, and you might not find the parts when on the road. Just a thought. It's your car and I don't criticize most people, unless they do something radical like putting in a chevy engine or something like that.
Thank you john for pointing it out that the car on battery does not run top notch at high speeds. My car never gets off city streets. can you just take a guess why my mag does not put out? The coupe which was rebuilt by the same person does run on the mag. Should I check the output at the mag pickup? Maybe change the pin to see if maybe a bad pickup? Or should I get out the manual and start reading?
hey, reading thru your posts i got to checking my mag out today. put out 9 to 10 volts at idle and 31 volts at full speed. same voltage with ignition on mag or battery. mine seems to run about the same on mag or batt. i tend to think, with some automotive experience, that if you look at the trace on an osciloscope of the voltage needed to fire the plug it peaks at that point and needs to rise no further, and will decrease due to the ionization of the spark path. it would therfore make me think that if a car runs much better on mag, then the ignition system needs a bit of clean up. my experience with the ts is short, so i am very open to learning about them. john
I think Glen was refering to running 6v and 12v absent the use of the magneto as a separate option. Because Glen has spent 35+ years as an electronics engineer, I suspect he knows what he is taking about.
dear mark, yes i reread some of the posts above and the one explaining the build up or saturation time of the coil and opening the points sooner is interesting. thanks, john
Sorry but I respectfully suggest he has it simply wrong and it doesn't matter how many years we both been at the engineering bench. Electricity really doesn't care what anyones experience is - it works the same for everyone. Not that it matters but I have been an electrical design engineer too for 38 years now. He IS referring to running on 6V versus 12V and the spark VOLTAGE or POWER is the same but the TIMING is what is radically different and makes all the difference. If you read Ron Patterson's tech article you will see some timing diagrams (scope traces) of some tests I ran for him to demonstrate this very thing.
Your scope is showing you spark VOLTAGE and that is not the issue. The problem is that with incresing RPM, the T coil starts to lag in timing because the coil firing event STARTS with the timer closing and the firing of the thing then occurs later after the coil RAMPS UP TO FIRE. Later point/coil ignitions work differently and that is where the confusing usually starts. With a T coil the RAMP TO FIRE TIME only gets shorter when the applied voltage gets higher. Thus with increasing RPM you need the spark to arrive sooner or it will be retarded based on a fixed RAMP TO FIRE TIME of the coil. The magneto delivers this just fine. Higher RPM give higher VOLTAGE and the timing is locked to the magneto pulse so the engine has good power and smooth. With 12V battery the coil ramps up fast enough that the engine seems smooth enough and powerful enough so that works OK too however the timer is NOW the item which determines timing accuracy since the coil is beginning its RAMP TO FIRE time cylce based on timer position rather than magneto pulse position. With 6V battery the coil takes twice as long to RAMP UP and fire and with higher RPM this lag in timing is what causes sluggish engine performance. Spark Voltage is basically the same since the Voltage is determined by the strength of the magnetic field when the points open and the points open at a predetermined field strength defined by the tension on the vibrator. The magnetic field is determined by the CURRENT through the coil (not the voltage applied to it) since as soon as it gets big enough the points open up and the source voltage is disconnected. With 12V the operate current is arrived at in much less time (half) than at 6V.
So I'm a new T guy, and this has always confused me...and I may be wrong, but from what I understand, when running off battery, you have an infinite spark adjustment. When running off magneto, the spark advances a certain number of degrees at a time (17.5 degrees? I can't remember for certain). Wouldn't it be advantageous to have infinite timing adjustment instead of having large increments to adjust the timing? After reading the posts above, it sounds like, to put it simply, the spark timing is delayed when running off battery when the coils are set up properly. If the timing could keep up while running of battery, would the infinite timing adjustments offer any advantage, or is the timing of the mag accurate enough?
Sorry Mark, I don't mean to take your thread off topic!
The old STS (stupid timing steps)? Check your e-mail since I'm not discussing it here - purists get irrational in a hurry. Been there, seen too much of that.
It is important to remember that one of the key original design criteria for the Model T Ford was to have a self contained internal power source for the ignition system. They did not want the Model T to rely on batteries to power the trembler coils as automobiles up to that time had to do.
Here is an article explaining how the Model T ignition system works.
The Model T Ignition System and Spark Timing
To understand more about what happens with Model T spark timing on battery versus magneto you can also read the article in the link I posted above.
Unless you plan on racing a Model T having a suitable power source that would allow infinite timing adjustment simply offers no advantage over the internal magneto.
Ron the Coilman
john f. regan, thanks for the understanding reply and i also saved ron's link to read latter. i understand what you are saying and on my drive today i switched from bat. to mag. a few times. it might be a bit smoother on mag at higher speeds, but not by much. do you call the magneto 8 pole or 16? my ign. switch needs to be cleaned up on the mag. connections as sometimes i kill the engine when switching. once again thanks for the informatiom, very interesting car them ts are! john
I'm not sure here, but I think everyone's missed the question...
From what I get out of Mark's original question is that he doesn't understand what kind of magneto the Model T has. It seems to me that he's thinking the Model T has the kind we most often think of on a speedster; where the generator normally goes. There were several of them; Bosch is the 1st that comes to mind.
Mark, the Model T was built with 2 sources to power the coils; a battery to power the coils for starting the car, and the magneto to run the coils after the engine is running. This keeps the battery from having to power the coils and running down. (On the original non-generator cars.) The magneto is a vital part of the original ignition system; not an after market performance piece like the Vertex you would find lounging comfortably on top of a 351 Cleveland or 429 Boss.
Or did I read his question wrong; and I'm the one all washed up...?
Oh well; happy motoring!
Actually, yes, what you asked was part of my confussion. I was told by a local guy that the mag coil was wired to a bosh mag. I understand now that was wrong. But I also wanted to know if the car would run as well with just a battery as with the mag. This thread has just been FULL of great information. I think I get most of it.
The magneto puts out 8 complete cycles of AC per revolution. The T coil will fire on EITHER the positive half cycle or the negative half cycle. Thus the T coil has 16 positions per revolution where the T coil ideally should produce one fat spark. As you increase the RPM the AC voltage increases in both frequency (cycles per second) AND amplitude. This just happens to be exactly what an inductive load like the T coil needs in order to provide a faster spark with increasing RPM to thus not lag in timing. This is why the T runs poorly on 6V - the voltage does NOT increase with increasing RPM so the effect is that the timing starts to lag with increasing RPM. If the coils are set up to fire at substantially reduced current (whether on purpose or due to misadjustment by "feel") then the engine might seem to perform somewhat OK at the higher RPM even with 6V but the spark energy will be reduced from the "correct" amount as usually set up at 1.3 Amps setting of the T coil. The T coil will run fairly fast when powered by 12V and the performance at that voltage is similar to the performance achieved on the magneto. The advantage of running on 12V is continuous timing variation while the advantage of the magneto is more exact timing (assuming the coils are properly setup to run on mag). When running on Battery, either 6 or 12, A really good TIMER is more important since it alone determines the beginning of the ignition timing event. When running on Magneto, even a so-so timer will usually run very smooth because the timer is now merely selecting which pulse from the magneto that the coil will fire on. The actual firing event is controlled by the magneto current pulse event. The timer can be somewhat sloppy when running on magneto.
In my experience, folks who have a working T magneto and good coils rarely opt to swap out the magneto for 12V battery system since the T runs pretty sweet on magneto. Most folks who opt for the 12V either have a dead magneto or can't seem to get it to run and give up on it. Still others opt for a distributor at that point.
Why do I hear folks saying they start on battery then switch to magneto? Does the magneto require that you turn the engine faster than some care to in order to generate a spark? I know there were plenty of T's out there that had no battery of any kind, so I know that it's possible to start on mag.
From our experience with "Free starts" we know that the engine doesn't even have to be turning to start on battery, just be in the right position under the right circumstances. When people are interested in my truck, I sometimes let them crank it with the crank, after ENSURING that the spark is retarded. I've had kids crank it by just barely turning it until the timer made contact.
I wish my magneto worked. Maybe I would know the answer to this question. My assumption is that you have to turn it over pretty fast to start it on mag and some folks can't or don't want to. I know when my back is bothering me, I wouldn't care to pull that crank. Am I on the right track?
I aint fiqured out on a electric start T why you would need to start on battery.Mine cranks great and easyly on mag.
I can say this to.Danged if I will ever put another 1 together without fixing the mag.They run much better on mag with the coils than just battery.
A cheap,half dead 12 volt battery in my TT was giveing me a fit last fall.I would have to jump it off.Once started the truck didnt run to suit me.I put a new battery in my pickup and stuck the old,but good battery in the TT,it was like tradeing T's.Runs better.Now to try to the in car magneto charge on the TT.
If I were to install a distributar in a T,it would also get the Petronix ignition.It was installed in my 300 I6 that is in my 66 ford.I didnt think much of it at first,as I had never used it,but this was a rebuilt engine and it ran good in the other truck that the sheep,oops,owner, wanted a v8 in.But 6 years later,I can just bump the key and it barly turns over and it is started,even in cold weather with the choke pulled.It is worth the money.And the points can be installed on the roadside if need be.
Starting on battery is easier but not as safe as starting on mag.
It is easier for two reasons:
1. the engine doesn't have to be cranked nearly as fast.
2. there are many sparks produced in the roughly 1/4 turn of the crankshaft while the coil is grounded.
At a cranking speed of 120 rpm (or 2 rps), the 1/4 revolution of the crankshaft takes 125 milliseconds. During that time, a coil can produce 30 to 40 sparks even on a six volt battery - plenty more on 12 volts. On magneto you'll get FOUR! Lots of sparks really helps on a cold day when gasoline is stubborn about vaporising. Lots of sparks not many degrees after TDC will get you going when two where you need them won't.
Starting on battery may not be as safe though, again for two reasons:
1. on mag you have to spin it faster. When spinning it faster, the stored energy in the flywheel helps keep the crankshaft turning in the correct direction.
2. on mag, the sparks are timed with crankshaft position, meaning, that if the spark lever would allow firing at 10 before TDC on battery (because you forgot to move it all the way back up), you won't get a spark until about 4 after TDC - and no resulting kickback.
To all of you that are tired of showing off by cranking on mag and are going to add a battery to improve your life, PLEASE use that battery to make sure that with the spark lever all the way up, that no coils buzz before top dead center!!!!!!!!!
(Marshall, do you hear me?)
Others may disagree with my thinking and I'm sure they'll tell me.
I am sure there are many technical reasons that Model T's run better on the Mag than on a Battery. For those of us whose expertise does not include electronic therory & practice the test is simple: drive down the road at a constant speed with the switch on Batt & change to Mag & with even a moderatly well maintained Magneto you will notice an increase in RPM's. Unless the mag is dead & an engine R&R is in order stick with the Magneto. If my memory is working well a magneto is an Alternating current generator & I seem to remember something about a battery(direct current) being hard on the points on the buzzer coils, another good reason for using the Mag. Perhaps John or Ron can expand on this a bit &/or correct any errors I may have made in the preceeding analysis.
Seths observation on safety are well worth remembering. On more than a few occasions On y 23 Roadster I inched the spark lever down too far to get a quick start & got a nasty reaction from the crank handle. Don't trust to luck !!
Edward R. Levy
Ed you are correct. Ford called the Model T's self contained flywheel power unit a "low tension magneto" because that terminology was common at the time for this type of device.
A modern engineer would likely call it a "single phase permanent magnet AC generator".
In any case the Model T "Magneto" puts out somewhere between 10 and 30 volts AC when working properly. Its design is both remarkably sophisticated and remarkably simple in terms of operation and maintenance respectively.
My grandmother had no trouble hand cranking the family's 1915 Touring in sub zero northern Minnesota winter weather. Dad says they never owned a battery but always used Prestone.
Answering the question from a different perspective - It depends on what you want, and the answer is different for different people. Reasons to have a functioning magneto in no particular order:
1) You want to experience your Model T as it was built.
2) You want to know you Model T is as built. (Not quite the same as 1.)
3) You believe a Model T runs better on magneto than battery.
4) You like the challenge of hand-crank starting on magneto.
5) You like the extra fiddling of starting on battery and switching to magneto. Many folks like the contrast of driving a Model T to a modern car.
6) You want to be able to start and run the car with a dead battery.
7) You like the clicking of the coils when running on magneto.
As with most things in life, I think the truth lies sort of in the middle of the two extremes.
This thread was originally about why to use a mag over a battery. Here is my take:
A six volt battery can produce a somewhat inconsistent spark. I believe this is due to number of issues.
1. When operating on six volts the relative timing differences between the four coils is exacerbated. That is, if the point tension, drop, and gap is different between the various coils it will have less effect on mag or on a twelve volt battery than on six volts.
2. The spark can be retarded on six volts and continues to be further retarded as the engine speed increases. This is also true on twelve volts, but to a lesser degree. This problem could conceivably be overcome by advancing and manipulating the timer, although the initial timing may be too advanced to easily start the car. *(see note below)
3. There is less voltage output from the coil on six volts than from twelve volts or more. The reason for this is that the coil amperage ramps up higher when operated on higher voltage. The reason for this is largely due to inertia of the coil points. The mechanical lag allows the coil to saturate more. Please see the article I wrote for the Montana 500 newsletter that shows this.
* One year in the Montana 500 my mag went out. I ran on battery and was running 3rd when I left the race due to a different issue. The point being that a T can run well on battery and six volts.
The best thing that I liked about using the mag was that almost everytime you switched over you got a big bang. Now I don't have to keep buying mufflers.
If you switch it when idling, it won't bang. If you have to do when driving, push the pedal into neutral and push the gas up before you switch it.
john regan, again thanks for your time and explanation. after reading your post and ron's two articles, i think i am understanding this coil ignition system much better. you all have answered the questions i had about spark timing and the ign. again, thanks, john c.