Ignition coil question - Page 1
Forum section: electronics / general

author: Connecteur
author_rank: Frequent Contributor
timestamp: October 11, 2021, 03:56:04 pm
content: I hope this isn't too far off-topic for this forum, but the Model T Ford had a trembler coil type ignition system. When activated by a timer, the trembler coil energized a buzzer. A condenser in parallel with the breaker points and coil formed a harmonic circuit that generated high voltage in the secondary coil which was boosted higher by the condenser and breaker points. As long as the timer (rotary wiper switch) was activating the trembler coil, a high voltage current was sent to the spark plug. Each cylinder had it's own trembler coil assembly.There were two power sources in most cars that drove the ignition, a battery or a magneto. The magneto was AC, so I am curious if AC impeded the performance of the ignition compared to DC. I know some cars had dry cells used for easier starting, and a switch to select the magneto after it was running. After 1919, the Model T got a wet cell battery, generator and a starter, but retained the magneto and trembler coil ignition until 1927.

author: HighVoltage
author_rank: Super Contributor
timestamp: October 11, 2021, 06:18:21 pm
content: Quote from: Connecteur on October 11, 2021, 03:56:04 pmAnd what is your question?

author: Connecteur
author_rank: Frequent Contributor
timestamp: October 12, 2021, 12:20:26 am
content: How effective is AC compared to DC for creating good ignition with a trembler coil?

author: Circlotron
author_rank: Super Contributor
timestamp: October 12, 2021, 04:46:09 am
content: With an AC supply there is going to be repeating dead spots in the supply voltage, and if this occurs at the exact moment you need a spark then things are going to have to wait until the voltage rises high enough to get that buzzer buzzing again. That is not a good thing. But then, neither is the entire ignition setup of a Model T. Except maybe for the continuous train of sparks at cranking speed. Not sure how much spark energy in those things. Any idea how much current is interrupted by the buzzer contacts? Actually, maybe the flywheel magnets are positioned so that the AC zero crossing point doesn't matter. I better go read up on these things.

author: bdunham7
author_rank: Super Contributor
timestamp: October 12, 2021, 05:16:38 am
content: Quote from: Connecteur on October 12, 2021, 12:20:26 amThe magneto is not an AC source for the tremblers, it's a bit more complicated.https://www.fordmodelt.net/downloads/Model%20T%20Ignition.pdf

author: HighVoltage
author_rank: Super Contributor
timestamp: October 12, 2021, 09:12:20 am
content: Robert BOSCH had a very similar system in the early days of the automobil.The basis goes even back further to an guy named Ruhmkorff and he invented the Ruhmkorff / Funkeninduktor, probably the first ignition system ever invented in 1855.https://www.tubecollection.de/ura/ruhmkorff.htm(Sorry, I only have a German link)Even this old inductor and the Bosch system was DC based.But then, I never tested a Ford Model-T ignition system.The old Bosch system was extremely weak in today's comparison.So, I would expect the Ford system to also be very weak.

author: Connecteur
author_rank: Frequent Contributor
timestamp: October 12, 2021, 03:49:56 pm
content: Quote from: bdunham7 on October 12, 2021, 05:16:38 amFrom your reference: "The magneto output is an ac signal of varying voltage, frequency and current with eight complete cycles for each crankshaft revolution."

author: BrokenYugo
author_rank: Super Contributor
timestamp: October 12, 2021, 04:05:25 pm
content: We're talking about a 4 cylinder engine that peaks out around 1800 rpm, with timing controlled by a stick on the steering column, and low enough compression ratio it runs fine on kerosene. I doubt any dead spots or low ignition energy (especially since it's a sort of MSD system) cause much trouble, but I've never messed with one myself.

author: Connecteur
author_rank: Frequent Contributor
timestamp: October 12, 2021, 04:10:51 pm
content: Quote from: HighVoltage on October 12, 2021, 09:12:20 amI don't read German, but I believe most power sources in the early days were DC from batteries. The Ford magneto produced an AC signal of 8 cycles per engine revolution, and a voltage that varied from 4 volts to 30. The buzzer in the trembler would vibrate at around 200 Hz, which would vary depending on voltage. An engine running at 1800 RPM would produce a magneto frequency of about 240 Hz, but a much lower frequency and voltage when hand-cranking the engine.My question would be whether such a variable AC power source might impair the creation of a spark at times, compared to a DC battery source.

author: floobydust
author_rank: Super Contributor
timestamp: October 12, 2021, 06:04:44 pm
content: The Model T magneto is just816 horseshoe magnets and 16 coils, its output is pulsating (ripple) not sinusoidal but a peaky triangle waveform. There are dead spots at certain crank angles where the magneto instantaneous output is too low to generate a spark, so there could be a delayed/retarded spark always happening if the Timer was ahead of a magnet.If the magneto was at a zero cross, there will be no spark possible even though the Timer is commanding a spark to start. Ford was on top of this, the magnet positions were synchronized on the crankshaft and advanced 7 degrees. But still deadspots exist. There's also like 10 revisions to the magneto design.I don't think spark intensity is as much of an issue (beyond cranking) as is timing accuracy.I noticed somebody went full tech and made aModel T replacement Timerwith microcontroller, Hall sensors, IGBT's. It looks good, would people here put one in or use the original buzz coils and timer?Given you can break your arm if the engine starts up in reverse, and nobody likes to hand crank an engine much...edit: it's patentedUS 8662058which gives all the electronics details.

author: bdunham7
author_rank: Super Contributor
timestamp: October 12, 2021, 06:08:38 pm
content: Quote from: Connecteur on October 12, 2021, 04:10:51 pmYou need to carefully reread the reference I posted and then understand the magneto is not simply a power source for the tremblers. There's no trembling in magneto mode. Instead, the magneto pulse is what determines the timing of the spark and the coil/point assembly simply follows the magneto and produces a single spark in response to the magneto current pulse. I suppose you could say that instead of 'trembling' there is a single 'quiver' per spark.

author: bdunham7
author_rank: Super Contributor
timestamp: October 12, 2021, 06:12:59 pm
content: Quote from: floobydust on October 12, 2021, 06:04:44 pmIt's easier to think of the timer in magneto mode as a window or gate--like a distributor--rather than a 'command' as it is in battery mode. The actual sparks and their timing are a product of magneto arrangement, the timer just determines which ones happen and which don't.

author: floobydust
author_rank: Super Contributor
timestamp: October 12, 2021, 06:13:23 pm
content: I thought the vibrator still was operating when under magneto power? As long as sufficient voltage is there for it to oscillate during peaks. I'd have to hear one operating, but say 500Hz bursts at most possible 16 per crank rev?edit2: Then the ignition timing would change - spark(s) when Timer contact closes to instead a siungle spark when it opens. One article says the engine normally speeds up when switched from battery to magneto, I'd think that is more advance but who knows with this old engine that seems to run with way retarded spark timing overall.The vibrator is part of the coil's core so always there I think, once flux builds up the contacts open. Hmm.

author: Connecteur
author_rank: Frequent Contributor
timestamp: October 12, 2021, 07:27:17 pm
content: Research is telling me that most people think that the magneto makes the car run better than on battery, which is counter to what I had expected. I suppose the voltage from the magneto is usually higher than the 6 volts of a battery. Someone suggested that a 12V battery made the car run better. I suppose it proves that a variable AC source doesn't impair the functioning of a trembler coil.I haven't done the math, but I expect that a 200Hz buzzer would deliver many sparks in the part of the cycle where the ignition for that cylinder was active.

author: floobydust
author_rank: Super Contributor
timestamp: October 12, 2021, 08:04:52 pm
content: It's multispark but weak sparks, when the vibrator is running. Really long duration.If it changes over to a single spark mode i.e. Kettering (one strong spark) when running from magneto, then duration is much less, no backfires.Since the vibrator's armature is moved by the coil's flux, there is a limit to the flux density regardless of power source, I think. This would imply it's some timing change that makes them run "better".It must have been unreliable, or the Model T sold huge volumes. There were many companies making Timers and coils, they're all over antique shops and eBay.It's interesting the magneto is axial flux, flat wire edge wound technology.

author: bdunham7
author_rank: Super Contributor
timestamp: October 12, 2021, 08:09:41 pm
content: Quote from: floobydust on October 12, 2021, 06:13:23 pmI don't have much experience with Model T ignition in running cars--and they are a bit unique, but magnetos that use magnets like that typically produce a pulse that reverses, but since the Model T has 8 magnets, the output looks more like a thin triangle. I have not personally connected a scope to one--if I spot a Model T I'll ask if I can throw my ScopeMeter on it! Anyway, the way I've always assumed they work is sort of like a more modern points-free solid-state small engine magneto where the magneto reversal as the center of the magnet crosses the coil is what triggers the primary opening and thus the spark. This is a bit different than the impulse-coupled magnetos that you see on aircraft and old tractors.Quote from: Connecteur on October 12, 2021, 07:27:17 pmAt 600RPM it will have a magneto 'frequency' of 80Hz with a peaky waveform and significant power only in the peak area. I think you're getting one spark, but I'm open to further investigation.

author: Connecteur
author_rank: Frequent Contributor
timestamp: October 12, 2021, 08:56:11 pm
content: I doubt any Model T engine ever turned at 6000 RPM,except maybe that guy who was pulling his house,and had just crossed the Great Divide on his way to Oregon.

author: bdunham7
author_rank: Super Contributor
timestamp: October 12, 2021, 09:09:27 pm
content: Quote from: Connecteur on October 12, 2021, 08:56:11 pmWho is contending that they did?

author: amyk
author_rank: Super Contributor
timestamp: October 13, 2021, 12:16:25 am
content: Quote from: floobydust on October 12, 2021, 06:04:44 pmI'd think most people who have a Model T have one because it's a simple and entirely non-electronic historical artifact, so it seems very odd to put that in it.

author: floobydust
author_rank: Super Contributor
timestamp: October 13, 2021, 02:16:18 am
content: Many car show videos of the Model T's having ignition problems and dying once they get there. We have no idea of how reliable the car was in the first place. They're kinda old now. The Timer is on the lower front of the engine and no fun to access. I would rather augment vintage equipment with modern stuff if it means no more breakdowns.The E-Timer designer is MSc EE, Mike Kossor WA2EBY so it certainly conquers the mechanical issues. Note he kept the ~500Hz buzz (multispark) to drive the coils with.

author: BrokenYugo
author_rank: Super Contributor
timestamp: October 13, 2021, 02:58:28 am
content: I've found that most old car technology with a bad or unreliable reputation actually works quite well (or at least well enough) if you know how to set it up and maintain it. I wouldn't doubt it if the model T ignition system falls into that category, along with drum brakes and air cooled Volkswagen heaters. It's also been my experience that aftermarket "upgrade" stuff for vintage cars is frequently worse than the OE design in some way, if it even fits and works out of the box to begin with, no matter who or where it came from.

author: james_s
author_rank: Super Contributor
timestamp: October 13, 2021, 05:54:36 am
content: The problem is that car parts wear out and you can't get new OEM parts indefinitely. Often even the OEM stuff that is still available becomes cheap and crappy. When parts wear out and you can't get good quality new parts then it becomes difficult to keep something working properly even if you know what you're doing.Modern cars (as in made in the last 40 years or so) are also far more reliable and last much longer than cars used to while requiring less maintenance. I'm just old enough to remember when even fairly new cars still needed frequent tune-ups and a car with 100k miles was getting pretty worn out. Even my 30 year old car doesn't need tune-ups as such, it needs maintenance like any machine but there's nothing to adjust. The fuel mixture is controlled by a computer and the ignition is timed off a crankshaft sensor that reads dimples around the perimeter of the flywheel. It has a distributor but that doesn't adjust the timing. I fixed a lot of small engines from lawnmowers and such that needed the points cleaned and adjusted, newer ones with electronic ignition are much more reliable.

author: Miyuki
author_rank: Frequent Contributor
timestamp: October 13, 2021, 04:01:49 pm
content: Quote from: james_s on October 13, 2021, 05:54:36 amIt is that sentiment because people were young back then and have just good memories.Mechanical distributor with centrifugal regulation and even mechanical contact is something terrible to adjust and worn relative quick.Modern cars tend to be more and more reliable (cars from 2000 have today fewer problems than cars from 1990 had ten years ago)Of course, there are some missteps in design from time to time and some problems caused by pressure on fuel consumption and emissions. Like early plastic thermostats tend to be fair from durable and causing engine destruction.And also modern superdownsized engines like 1.0 with turbo and supercharger in a big car will be pretty worn after 100k miles.btw I was recently servicing a neighbor's lawn mower, it uses a simple magneto, just a coil on the core and directly connected to the spark plug. Super simple system.Also spark plugs in modern engines last forever compared to old ones when you should change them like every 10k or so

author: Connecteur
author_rank: Frequent Contributor
timestamp: October 13, 2021, 04:25:49 pm
content: Henry Ford believed in building something to be the best of its time. Better ignition systems were available in 1908, but one source I read said it would have cost him $140 for a magneto. The trembler box had been around for awhile and tried and true. and he could build them cheaply. But Ford didn't believe in fixing what worked, even as ignition systems became cheaper and more reliable.Even though Ford was promoted to Chief Engineer at the Edison Illuminating Company, he wasn't an electrical engineer. His field of interest was more on engines, both steam and internal combustion. He tended to leave the electrical engineering to others. By 1927, he was still committed to an ignition system that was over 30 years old, and had to be persuaded by family to change.

author: floobydust
author_rank: Super Contributor
timestamp: October 13, 2021, 07:44:48 pm
content: I think Ford was being cheap and practical.Charles Ketteringhad lots of patents 186 (he made leaded fuel, freon too) and ignition system patents back to 1910. Who would want to pay royalties to what became a competitor (Dayton/Delco) ?Kettering had the starter motor on Cadillacs back in 1912 with his prototypepoints+distributorsingle-spark system, filed 1911 patented 1917. But it needed a secondary battery and generator.Looking at the Model T you can see the engineering was not shoddy at all, for the era. Cost was the main priority though.

author: james_s
author_rank: Super Contributor
timestamp: October 13, 2021, 10:29:03 pm
content: That's not surprising. The Model T was engineered from the ground up to be affordable, that was its whole claim to fame. It was not the first car or the best car, but it was the first reasonably practical car that ordinary people could afford to own.

author: BrokenYugo
author_rank: Super Contributor
timestamp: October 13, 2021, 11:10:47 pm
content: The T, and the Ford Motor Company in general, were cheap and practical to a fault. They only quit building Ts and designed the next car when people quite buying them, as everyone else had more or less standardized on the more or less modern car pattern by then, clutch brake accelerate, 4 wheel brakes, H pattern transmission, etc. Ford were also highly reluctant to license any patented technology, you can blame Philips head screws on Henry Ford, they also kept using mechanical brakes long after hydraulic became prevalent.

author: amyk
author_rank: Super Contributor
timestamp: October 14, 2021, 12:05:59 am
content: Personally I think GM HEI is a good balance between fully-mechanical points-type ignitions and fully-computer-controlled ones. It's a simple self-contained unit.