I have been working the electrics on my T this past week... break light went dead found the loose wire. The horn went dead... again another loose wire, so I went through the whole T making sure everything was nice and tight.
But it got me thinking, if I ever need to redo my mag why should I? What if I just leave the key on battery if I have a generator keeping the battery charged.
Is it because the generator can't keep up with the battery discharge and thus you would have a dead battery eventually and no spark... the drain would be even quicker at night.
Just curious (I think I answered my own question but just wanted to make sure)

There should be no discharge of Battery if key is in "off"position. The mag puts out a lot more power when using it. You can audibly tell this when switching from battery to mag on your switch.

Yeah, Jack is right. Certainly, you could just run on the battery and generator indefinitely, but you'll find it runs better with the higher voltage put out by the magneto.

The magneto runs your coils on AC power, which gives longer point life. Additionally the voltage increases with RPM giving a hotter spark with in creased engine speed. Finally the ignition timing is much more accurate on MAG since the discharge of the coils is directly related to the magneto output. This explains why a Model T runs so much better on MAG compared to battery.

Thank you for the lesson!

Robert, Here is another lesson. There is a lot of conjecture, misinformation and total BS spewed on this site as total gospel fact.

Model T engine performance using properly adjusted coils operating from 12V battery function as good or better than the same coils operating on magneto. Here is the actual measured data taken using the same professionally rebuilt and adjusted coils using a specially designed data acquisition system that recorded the vehicle velocity and engine RPM as a function of time for each run of the different methods of powering the coils; 6V battery, 12V battery and magneto. Running the coils on 6V battery was the only notable performance degradation compared with 12V battery and magneto operation. The reason for that performance degradation is due to the longer coil dwell time to fire spark when coils are operating on 6V battery. The timer spark advance range is insufficient to compensate for the longer dwell time to fire spark at higher engine RPM when the coils are operated on 6V battery.



The legend:
Pro - professionally adjusted coils
6V, 12V or Mag - source of power for the performance test
V - Velocity MPH
R - Engine RPM

You can maintain the battery by charging it from the generator as many do. Several folks also successfully recharge their battery from their magneto using a simple diode/1156 light bulb charger. The battery drain will absolutely be quicker at night when operating headlights and will likely require additional overnight charging if used for extended periods.

Bob, there are ignitions systems available that allow you to simply run your car on 6 volt exclusively if you want. Or, Like Mike Kossor says you can run your coils off of 12 volt and get perfectly acceptable performance (but generator amps output wont be as high on 12 volts as 6 volts, and your starter bendix might take a beating). These systems are particularly nice if your magneto output is poor or absent entirely, and you don't have time or resources to rebuild it. I am running electronically fired 6 volt coils in my car and like them. My magneto also works fine though and I can reverse the system easily to the original set-up. It is your car and your choice. Choose which ever system meets your needs and driving preferences.

There is one more thing to consider when facing a suddenly dead magneto - what was it that failed?

There are several ways a magneto can fail, many of them mostly harmless for the engine, but some of the fail modes may call for immediate pull down to avoid even worse carnage. Sometimes a bronze screw holding a magnet clamp on the flywheel fails, letting the clamp hit a coil, shorting it. Even if the clamp finds a safe resting place, there's still danger that the now loose ends of a couple of the magnets may vibrate until they crack from fatigue and flies towards the hogshead..

This can be checked through the starter hole - if it's a starter era engine.

...and it will run just fine on 6V too. Possibly with slightly less performance, but in most cases, you won't see the difference. As in any case, you need good coils, adjusted properly.

With a good generator, set correctly, you should have no trouble keeping the battery charged.

(Sorry if any of this is BS Mike.)

Totally disagree that 12 volts is as good as running on MAG. Nonsense.

Here is an authoritative article written by the acknowledged experts on this subject. It is what you need to know, with no BS that you don't need to know.

http://www.modeltcentral.com/ignitionarticlepage.html

The reason to fix the mag is to see what damage has it not working in the first place. You can run distributors, magic coils and magic timers all day but it doesn't address the mechanical soundness of your engine.

The car that this flywheel came out of actually ran well on battery. Not sure how much longer before it came apart with force. Usually when that happens you can count on $ for fix it. Now, factor in what ever ignition "fix" you have to allow it to run and you can see the $350 distributor to fix you problem just became $600+

I agree with Royce. Fix it and run them on AC.

Here is more measured data of Model T engine horse power performance versus coil power source which substantiates my statement: Model T engine performance using properly adjusted coils operating from 12V battery function as good or better than the same coils operating on magneto.



This is independent engine dynamometer test data. You can read the full article here: http://www.mtfca.com/discus/messages/257047/267230.html?1329528704

Royce, Please present your data that substantiates your claim that what I stated is "Nonsense" and "a Model T runs so much better on MAG compared to battery." The article you cited is a wonderful reference on magneto operation but does not substantiate any of your statements about 12V battery operation at all; did you read it?

Regarding magneto mechanical defects; another repair option some folks choose is to completely remove the magnets and keepers and replace them with oil slingers. Then run on 12V battery to enjoy comparable engine performance, save $600+ on repair costs and have piece of mind knowing a magnet and/or keeper will never break lose and surprise you coming through the floor boards while you are out for a ride.

(Message edited by mkossor on March 08, 2017)

WOW Gary T! THAT one is about as close to explosion as I have ever seen! And I have seen a few of them.

Having run my T on 6V for the last 14 years on 6V, I might offer some words of experience.
A Model T will work very well with its coils powered from 6V if attention is paid to correct coil set up and operating conditions, and in this regard I set for equal time to fire (e.g. by using an ECCT).
The initial timing should be set so the coil buzzes just as the piston leaves TDC, so as to give maximum range of timing adjustment.
Then the timer needs to be a good one because of the longer dwell time required - timers prone to contact bounce are to be avoided as the current may be interrupted whilst the magnetic flux is still building up in the coil core. The best mechanical type I've found is the TW, but ultimately the E-Timer is my timer of choice - it eliminates any mechanical limitation.
It should also be borne in mind that with the generator charging, the coil supply voltage will be closer to 7V than 6V, which provides further improvement at speed.
As for point contact life, I'm up to about 34,000km on my original points, and they still look pretty good.
In fact I found 6V performance to be so acceptable that when I did have the option of rebuilding the magneto a few years back, rather than continue to worry about magnets flying off, etc., I replaced it with paddles. The noticeable reduction in flywheel weight also made me feel a lot better about 3rd bearing wear.


(Speed is in km/h)

Here's a reason I doubt most of you have thought about, except maybe Burger. He has an odd way of thinking that I can appreciate.

When the impending zombie apocalypse finally happens, I like the idea of having backup plans. If my T is going to be my primary mode of transportation in such a cataclysm (and it will be, since I can't ride horses), it's nice to know that if my battery and/or generator decide to punt in the middle of an escape attempt I can flip the key to MAG and still outrun the undead.

Probably the least likely reason to ever use the magneto, but when a herd of walkers are after your brains you'll be glad you have options.

The original post was asking why fix the mag? Answers were given before the usual infomercial.

If I were buying a T with the magnets removed I would deduct $1000.

Simple answer to the original question: Because that is the way a T was intended to run.

If you are one of these who don't give a $#!+ if your car functions as it was originally intended and just want to be seen driving some cool sheet metal around, then by all means, do as you wish. Distributor, E-timer, original system on 12v (I have to disagree with Jerry on 6 volt performance. There is a MARKED increase in performance with 12V over 6V in the only car I ever tried it on anyway). 6 volts....whatever floats your boat.

If you want to "Experience" your Model T rather than just ride in some cool sheet metal, then make your Magneto work as it was intended. Otherwise, your T is just another antique car. A Model T is SPECIAL! It is UNIQUE! Very few other antique cars function like a Model T. VERY few! Most would have a hard time naming another car that has no fuel pump, no water pump and no oil pump and can run with no battery. A Model T is more than just some cool looking sheet metal. Embrace it for what it is rather than try to turn it into something it is not.

Hal, that was very well stated - especially the last sentence.

Hal,

Having run on 6V for several years I can state that the car ran as fast as I wanted it to, (I like to cruise at about 40-45), and did all that I asked of it. I will admit that I never tried it on 12V, so maybe I was really missing something. Apparently I was... Anyway, like you say, whatever floats your boat. No worries. Have fun guys!