First of all my T doesn't have a magneto so my coils have to operate on 6 VDC. As coils perform better with a higher AC voltage I was wondering why not use a converter (or inverter, whatever) to provide this AC to the coils?
Coils work on voltage pulses generated by the magneto. It's not AC like you use in the home. What's needed is enough electric power to charge up the coil rapidly enough to make it spark strongly at the right time. This can be positive voltage pulses, negative voltage pulses or just adequate DC. The Model T magneto generates pulses which are alternately positive and negative, and as you have already discovered, go well above 6v. A good magneto at high speed will peak at 30v or more. What's just as important is that as the pulses are generated by magnets rotating with the flywheel, they are timed to give a spark at the right time.
An inverter would just give you 60 pulses/second.
As you haven't got a magneto, the next best is just a 12v DC supply. The easiest plan is to convert the car to 12v - new bulbs and at least some adjustment to the generator. It is a bit hard on the starter Bendix though. (Some will disagree)
When I got my T it was like yours - no magneto; just 6v electrics. After a couple of years I fitted a magneto - what a difference!
Interesting electronic proposition Gary. My limited electronic knowledge would suggest that a converter or inverter would be very inefficient in the process of supplying the necessary AC current to your coils. The E-Timer that I am Beta testing uses square wave AC (Pulsed DC) to fire the coils for a discreet time interval based on voltage so as not to "cook" the coils. This system ,when in production, would be a logical solution to your situation. Improved performance would be also be realized thru precise timing and full-time automatic timing advance. Lets hear from the EE, John Reagan or Ron Patterson on your proposition.
As Chris pointed out the current pulses produced by the Model T magneto are "directly" tied to (synchronous) crankshaft travel (as opposed to an asynchronous signal you suggest) and this produces the spark timing based on spark lever position when running on magneto. Perhaps this diagram will help to explain this commonly misunderstood feature.
The E-Timer provides a ground to each coil just like an original timer does. The power to the coils is the normal DC provided by the battery. This same DC also supplies the power for the E-Timer electronics to develop the timing of the ground to each coil.
Ron The Coilman
As a T owner with no magneto, I can assure you coils can work quite well on 6V provided everything is set up correctly. Certainly no problem achieving the often quoted 40mph, and more.
There was a thread on this about 6 months ago where we found the reason why some cars run well on 6V and others didn't. It was mainly due to timing, coil settings, and the fact the voltage at the coil box input is more than 6V with a generator equipped car.
To answer your question, the main reason why an inverter won't work properly is because its output is not synchronised to the flywheel. Apart from that, you won't find any modern inverter that operates off 6V.
If one feels the need to, it is possible to run the coils off a higher DC voltage without ruining the rest of the car's electrics (i.e. converting to 12v).
Magneto Fig8.pdf (48.5 k)
Thanks Chris and Will. Come to think of it I have heard of the timing provided by the magneto but didn't pay much attention as I didn't have one. An inverter/converter can produce anything from DC to square wave to sinewave at various frequencies but I see the point. I do have a DC to DC converter 6 V to 12 volt that I bought to use in wife's 55 Crown Vic (6 volt) to run a 12 volt sound system. I may try it to provide 12 VDC to the coils so I don't have to convert everything else. That won't be till spring though. Ah well, nothing ventured.....
Thanks to Ron and John also. Your posts showed up after my reply.
As others have pointed out - the timing of the pulses is what it is all about when running off magneto.
Is that why the crankshaft position sensor on my Brides Oldsmobile Aurora costs $900 to replace?
Perhaps the Model T had a bettered idea?
You said, "The E-Timer provides a ground to each coil just like an original timer does. The power to the coils is the normal DC provided by the battery. This same DC also supplies the power for the E-Timer electronics to develop the timing of the ground to each coil."
I don't think that is quite correct. With the E-Timer the points on the coils are shorted closed all the time. This makes them act similar to a new distributor/coil system where the removal of the ground is what causes the coil to fire. The difference is that there is a coil for each cylinder. So the timing of the E-Timer is when the ground is removed and not as with the original timer where it is timed to fire when the ground is made.
At least that is what I understand.
The E-Timer mimicks the time to fire of the coil when using original points. I.E. The E-timer grounds the coil timer terminal for a calibrated period of time so the coil current reaches 3+ amps and disconnects. Then the coil fires.
Ron the Coilman
Maybe there are different methods to use the E-Timer.
Mike Kossor said, "The beauty of the E-Timer is that it requires no modification to the car or its wiring. In the event an E-Timer does fail, the operator would proceed exactly the same as if any timer had failed them; reach under the seat to fetch the spare stock timer it replaced and simply swap timers to restore original operation. The only minor added detail is to remove the jumper wire form across the all coil points."
(from the E-Timer Performance Report thread)
With the jumper wire the points are disabled the coils fire when the ground is removed. This eliminates the points entirely from the system and would likely make it much easier to maintain.
I think were close to the same page. The E-Timer sets the dwell which could be around 45 degrees if similar four cylinder distributor systems. As long as it is long enough for the coil to charge up everything works ok. I assume that the E-Timer only fire once when the ground is removed.
I wonder if the E-Timer sets the dwell by angle of rotation or time.
Everyones description of the E-Timer operatiom is accurate but incomplete in itself which is the reason for the confusion. The E-Timer does ground each coil primary at the appropriate time as detected by the respective vane window afixed to the cam; but it only grounds it for a discrete interval until it opens the ground connection,firing the spark (the coil points are shorted). This occurance repeats at a periodic rate to mimic original coil operatiom for as long as the vane window remains active (about 35 crank shaft degrees of revolution) hence the reference to squarewave actuation. There is another detail that also causes confusion. The duration thje E-Timer charges the coil for the first spark firing (the one that results in combustion) is longer than all subsequent firings. This is done to conserve battery life and be less stressful on the coil and E-Timer. That should help clarify operation.
Quite an interesting dodad.
to answer Gary's original question, since he is running 6 volts and the magneto doesn't work, and he wants better performance, he could run a 12 volt deep cycle battery hooked up to the magneto wire and grounded to the frame. He could charge it once a month and still likely have plenty of juice to drive. If it goes dead, he can still run off his 6 volt system. 12 volts gives a quicker ramp up time for the coils and, although not quite as good as a magneto, will likely work well for him. It's simple, quick, and not very expensive. Especially if he has a deep cycle battery hanging around.
Your mention of 6-12V converters is interesting.
I did actually do experiments with these devices back when I first had the car and discovered the faulty magneto. There was no way a 12v battery or distributor was going anywhere near it. As typical 6-12V converters provide about 1.5-2A output they will actually run the coils. However, due to how the coils operate (spiky inductive load) it's essential to have a large capacitor, say 4700uF 25V, across the output of the 6-12V converter.
I never pursued it beyond the experimental stage once I discovered that 6v was fine for my coils but it did work.
When you say, "...hooked up to the magneto wire..." I hoping you're not suggesting tying the 12V battery into the magneto coil ring circuit. Even if the magneto isn't working, that could still do some damage. Maybe you mean the magneto wire entering the coilbox, while the other end of said wire is disconnected from the magneto terminal? If so, just connect the battery to the traditional battery terminal on the coilbox.
Jerry Remember, Gary has no Mag.
6 volts, isn't too bad. I can hit 40 mph in my coupe with a passenger. Which, is pretty darn fast.
I can see Noels point, 12v one side of the key and the origional 6v on the other.
John H. Your right about not using my converter on coils. A little research on my SR-700-6 "Step Up Regulator" stipulates it's not for use on coil applications. Also remembered it was a positive ground input model. It is a nice converter as it has continous output capability of 10 amps. I see it's no longer available. Maybe I'll just go with a dizzy. It's a speedster so what the heigh.
This thing is kinda neat