Ignition systems - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: September 30, 2021, 10:24:40 am
content: For some reason I was trying to work out how a car ignition work and found myself stumbling. It doesn't help that automotive people use completely different terms for things, like high tension instead of high voltage, condenser rather than capacitor and coil rather than transformer/inductor?So here's how far I got... a lot of this is probably wrong and left me with questions.In an old engine, you would see a coil of wire on the crank or the housing and a magnet on the other. Each time the magnet passes the coil it creates a pulse of current. That is then stepped up to high voltage and creates the spark across the plug. The questions are, how is it stepped up and is this type of ignition void of "points" or does the condensor/capacitor hold the charge from the coil pulse and then release it when the points close?In a modern engine with CDI ignition I assume the alternator/battery circuit charges the capacitor constantly and electronics decide when to discharge it through the coil to get a spark.This "coil" they refer to, I get the feeling it can be multiple things, like the generator coil on the crank or the step up transformer... or an inductor.Can anyone help clarify for me in more "normal" electronics terms?

author: jpanhalt
author_rank: Super Contributor
timestamp: September 30, 2021, 11:01:04 am
content: The magnet passing a coil is a magneto ignition. Uncommon in most cars today but still used in piston powered aircraft as it will work without a battery. The original Ford model T ignition used a "buzz" box. They are still used today for such things as igniting model pulse jets and giving shocks. There are lots of variations. The attached picture is the one I use for my pulse jet.A brief history:https://www.modeltcentral.com/Model-T-Ford-Electrical-Specifications.htmlhttps://en.wikipedia.org/wiki/Ignition_systemOhioans are proud of Charles Kettering whose system was the standard automotive system for decades. Kettering, Ohio is said to be just outside of Dayton, Ohio (see: Wikipedia).

author: Benta
author_rank: Super Contributor
timestamp: September 30, 2021, 11:01:36 am
content: The "old" ignition system you mention is called a "magneto ignition". It has the advantage that no outside excitation is necessary (eg, battery). It's still used in lawn mowers etc.Since the 1950s it's no longer used in cars. Cars today use ignition coil(s), which is basically a flyback transformer. The primary is energised by the 12 V system, and when ignition is desired, the primary circuit is broken, leading the secondary voltage to peak to around 20 kV.Earlier, you'd have one or more external ignition coils (large cylindrical thingies), today the coils are much smaller and placed directly on the spark plugs, but the principle is the same.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: September 30, 2021, 11:32:57 am
content: When the points are closed the coil primary charges up.When points open there is a large change of voltage on primary which is stepped up in the secondary coil and that gives around 25,000 volts pulse.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 30, 2021, 11:56:40 am
content: In layman terms on points ignition:12V system3 Ohm primary winding of the coil3 mH primary inductance1:100 Transformer ratioWhen the points are closed, 12V is applied to the primary winding and the current slowly increases until it reached 4A12V/3Ohm = 4AAt this time you have stored the maximum energy in the coilW=1/2*L*i^2W= 1/2*3*4*4 =24mJ (Energy)Once the points are opened, the magnetic field collapses and produces a voltage of around 300V peak at the primary windingsThis 300V is transformed with the transformer ratio of 1:100300V * 100 = 30.000 Volts peak secondary high voltageThe reality is a little more complicated but the general picture is correct.

author: Circlotron
author_rank: Super Contributor
timestamp: September 30, 2021, 12:40:23 pm
content: A magneto ignition has many turns of wire on a laminated iron core. Olde timey versions had 1% of the winding short circuited with a set of contacts ("points"). When a magnet on the flywheel moved into position across the iron core the magnetic flux is sort of prevented from entering the core because of the short circuited winding. When the magnet is in the optimum position the contacts are opened and the magnetic flux now rushes through the core and induces a high voltage into the winding that is then fed to the spark plug. Not perfect, but an accurate enough description for this discussion.Some of my ignition experiments:

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: October 01, 2021, 12:28:52 am
content: Pulse generator, 30 VDC power supply, IGBT and ignition coilhttps://youtube.com/shorts/LPxDsCX5UfY?feature=share

author: David Hess
author_rank: Super Contributor
timestamp: October 01, 2021, 03:42:22 am
content: Aren't modern electronic ignitions all capacitive discharge? That would be where a capacitor discharges into the primary with the secondary stepping the voltage up. The advantage over Kettering ignition is that with the energy stored in the capacitor instead of the coil is that much higher power can be achieved.Heathkit used to make a CDI kit which worked on a Kettering system with a switch to change between modes. It only made a noticeable difference when compression was high.Common lawn engines use magneto ignition also, and I assume portable generators as well.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 01, 2021, 04:25:26 am
content: Hyundai/Kia use a two stage conversion design with the first raising the voltage to 300V or so and the second stage is a forward topology boosting the voltage to the final ignition voltage. Not capacitive discharge as such as the bus voltage doesn't fall that much, but it still has the advantage capacitive discharge offers. They were first to market with a midsize car that gets 35 MPG highway without resorting to hybrid technology.Aircraft ignition systems are indeed mostly capacitive discharge, except for the few that use high frequency inverters direct to the spark plug.

author: james_s
author_rank: Super Contributor
timestamp: October 01, 2021, 04:30:36 am
content: I don't know much about the truly modern ones, but most of the 80s-90s solid state ignition systems were not CDI because the CDI ignition was notorious for creating large amounts of RF noise. Instead they worked very much like the old Kettering (points & condenser) system except using a transistor in place of the points and a computer to adjust the timing over a range of operating parameters.The coil in a conventional ignition system can be thought of as a coupled inductor in a boost converter. The switching device closes, placing 12V across the primary which causes a magnetic flux to build up in the iron core. When the switch opens this field collapses resulting in a high voltage pulse (same principal as a boost converter) which is then stepped up according to the turns ratio between the primary and secondary.The operation of magneto ignition has already been covered, it works very similarly except voltage is induced in the primary by the moving magnet rather than from the 12V electrical system in a vehicle. The points (or more recently solid state equivalent) still work the same way, opening up to interrupt the circuit causing a rapid collapse of the magnetic flux and a resulting high voltage spike in the primary that is coupled to the secondary.

author: james_s
author_rank: Super Contributor
timestamp: October 01, 2021, 04:33:12 am
content: Quote from: NiHaoMike on October 01, 2021, 04:25:26 amTurbine engine ignitions, including those used in aircraft work like that. They are very similar to the spark igniters used on gas cook stoves. Aircraft piston engines almost exclusively use magneto ignition of the same basic design as used during the dawn of powered flight.

author: bdunham7
author_rank: Super Contributor
timestamp: October 01, 2021, 04:52:57 am
content: Quote from: David Hess on October 01, 2021, 03:42:22 amNo, actually, coils and their driving transistors have evolved to pretty high energies and CDI really never was all that widespread among OEMs. The only OEM application I can remember were old Mercedes Benz V8s from the late 60's and early 70's. There were probably others, but with low-impedance primary coils and high current drivers, they can make very powerful multi-strike ignition systems using coil-per-plug arrangements.

author: David Hess
author_rank: Super Contributor
timestamp: October 01, 2021, 04:58:06 am
content: Quote from: james_s on October 01, 2021, 04:33:12 amDo all piston aircraft still have dual magnetos with two spark plugs per cylinder for redundancy?As I recall, the test is to change the magneto selector from both to magneto 1 and then magneto 2 and the engine RPM is only suppose to drop by like 100 RPM or something. But I remember reading about US aircraft on Pacific island bases during World War 2 where they said maintenance was such a problem that aircraft often would not even run without both magnetos selected.

author: james_s
author_rank: Super Contributor
timestamp: October 01, 2021, 05:01:08 am
content: Quote from: David Hess on October 01, 2021, 04:58:06 amAll certified aircraft engines that I'm familiar with have dual ignition systems with two separate spark plugs per cylinder. I don't think there has been much development there in decades, most of the engines being made are still the same basic designs developed around the 1950s. There are some non-certified automotive engine based aircraft engines that do not, I'm not sure whether these use a magneto or conventional automotive ignition system.

author: bdunham7
author_rank: Super Contributor
timestamp: October 01, 2021, 05:05:18 am
content: Quote from: David Hess on October 01, 2021, 04:58:06 amAll conventional (old style) piston aero engines are like this, yes, but there are examples of newer systems out there flying around. But they aren't just for redundancy, you lose some power and the engine runs hotter with only one spark plug going. Some old rotary engines were spark plug fouling monsters, so having dual ignitions helps there too.

author: Monkeh
author_rank: Super Contributor
timestamp: October 01, 2021, 05:18:36 am
content: Quote from: bdunham7 on October 01, 2021, 05:05:18 amEven relatively recently, some otherwise normal inline car engines have had dual spark for a cleaner burn, and let me tell you, those plugs go on for a while.

author: Circlotron
author_rank: Super Contributor
timestamp: October 01, 2021, 07:44:16 am
content: I have made ignition systems for a living for the last 27 years.One of the most overlooked issues with a capacitor discharge ignition is it's woefully low efficiency, at least when using conventional coils. The short answer is - a 1uF capacitor charged to 450VDC has 100mJ of energy. Discharge it into a coil primary, and once the spark in a running engine has begun it takes about 1500V to maintain the spark. Under these conditions a modern E-core coil will send about 35mJ to the spark gap. An older points type canister coil delivers about 25mJ. if you ignore plug lead resistance the majority of the losses are in the coil secondary. with a 1uF 450V CDI the coil secondary current will be close to 400mA peak. If the coil secondary resistance is say 6000 ohms then there will be 1500V across the spark gap and 2400V lost in the coil secondary resistance. So right way we can see the efficiency would be only 38.5%. One particular inductive ignition I make delivers a measured 150mJ to the spark gap. This is a huge jump compared to a CDI.I posted a thread about this to a high end car forum about this a while back.https://www.speed-talk.com/forum/viewtopic.php?t=42274

author: Circlotron
author_rank: Super Contributor
timestamp: October 01, 2021, 07:50:46 am
content: Best thing you can do of course is have a CDI initiate the spark and before it goes out have an inductive ignition jump in and maintain the spark.https://www.speed-talk.com/forum/viewtopic.php?f=1&t=45340

author: SteveyG
author_rank: Unknown
timestamp: October 01, 2021, 08:52:59 am
content: Modern coils are just HV generators, and will produce a high voltage the entire time the trigger signal is appliedCoil packs vary in design, but for the most part work the same way, however some will use a wasted spark system whereas others will only fire on the correct cylinderIgnition coil + points are pulsed by the ignition timing system.

author: paulca
author_rank: Super Contributor
timestamp: October 01, 2021, 09:09:53 am
content: Interesting, I thought CDI was more common, maybe because I ride motorcycles. Which use CDI a lot.Quote from: SteveyG on October 01, 2021, 08:52:59 amWas watching a video about Harley Davidsons. They really are a pile of junk. The engineering is many places is, well, really, really poor. It's not even like they evolved and adapted with the times/tech, they don't/didn't. And.... are now dieing.They used a single crank pin for 2 pistons, not because that was a good choice, but because they couldn't be bothered to have two crank pins, balance the engine and have a sane firing interval. They use a 45* firing interval as a result. So BANG, BANG................ BANG BANG. Then because they were cheap skates they decided that per-cylinger ignition was too much effort so they just fire both plugs. This results in the BANG, BANG, POP..... The POP is caused by the engine being so poorly made there is enough combustable exhaust gas in the exhaust strike to ignite!With an unbalanced crank, the bike shakes violently when idleing. So they mounted the engine on rubber.... with a cheap and nasty steel frame that flexed. Resulting in many deaths caused by death wobble oscilations. They added a counter balance (to fix the unbalanced pistons) such that the vibration of the unbalanced mass was forward/back, not up/down, hence the shaking. The only saving grace is that when moving, some of that insane vibration is muted by the road motion.I think the video making summed it up by saying, Harley's, you either get them or you don't. I don't.

author: HighVoltage
author_rank: Super Contributor
timestamp: October 01, 2021, 09:50:38 am
content: Quote from: SteveyG on October 01, 2021, 08:52:59 amI am not aware of such system.Do you have an example of that setup?

author: Circlotron
author_rank: Super Contributor
timestamp: October 01, 2021, 10:31:58 am
content: Quote from: HighVoltage on October 01, 2021, 09:50:38 amI have never heard of such a thing either. I’d like to hear more about this.

author: SteveyG
author_rank: Unknown
timestamp: October 01, 2021, 11:25:24 am
content: Quote from: HighVoltage on October 01, 2021, 09:50:38 amA standard coil on plug is this type, 12V is applied all the time, there is a separate trigger pin. Search coil on plug and you'll see these types.

author: langwadt
author_rank: Super Contributor
timestamp: October 01, 2021, 11:54:24 am
content: Quote from: SteveyG on October 01, 2021, 11:25:24 amthat's a standard ignition coil, the lowside igbt is just moved from the ECU to the coil

author: SteveyG
author_rank: Unknown
timestamp: October 01, 2021, 01:13:39 pm
content: General definition would be the "standard ignition coil" as the large cylinder type which would feed the distributor, not a COP type.Looks like there are various COP configurations though. I think only the 3 pin coils are the type with just a transistor inside.

author: HighVoltage
author_rank: Super Contributor
timestamp: October 01, 2021, 01:13:50 pm
content: Quote from: SteveyG on October 01, 2021, 11:25:24 amThis system has been around for a very long time....They can not "produce a high voltage the entire time", they work the same way as before and have to charge up the primary with energy before producing the high voltage at the output.I am just developing a new ignition coil for an OEM.The difference these days is that we have 30A primary current after only 100us of charge time.And the secondary peak voltage must be >50kV, besides a few other crazy requirements.

author: SteveyG
author_rank: Unknown
timestamp: October 01, 2021, 01:16:19 pm
content: Quote from: HighVoltage on October 01, 2021, 01:13:50 pmI certainly have some in the garage somewhere 5 pin with integral diagnostics, I'll see if I can dig one out later for disassembly, I think they were branded Haldex, but I can't remember off-hand.

author: HighVoltage
author_rank: Super Contributor
timestamp: October 01, 2021, 01:20:45 pm
content: A few years ago, the 2 extra pins have been used to feed the OBD2 system.These days the "intelligent" feedback information is all carried over one input signal wire.

author: Circlotron
author_rank: Super Contributor
timestamp: October 01, 2021, 01:39:37 pm
content: Quote from: HighVoltage on October 01, 2021, 01:13:50 pmHow much energy? Physically small coils don't give you much to work with. And why such high currents and short charge times? What's wrong with say 10A and 3mS? Less time for I2R dissipation in the primary?

author: langwadt
author_rank: Super Contributor
timestamp: October 01, 2021, 02:16:12 pm
content: Quote from: SteveyG on October 01, 2021, 01:13:39 pmby standard I mean like it has been for decades, a coil and a switch to charge the primary. The coil is just on the plug and the switch is a transistor integrated in the coil. I don't think any one has used distributors in a very long time. The reliabilty issue and mechanics to drive it is probably expensive compared to a few extra coils.Some coils are 3-4-5 pins, sometimes it is just extra grounds

author: HighVoltage
author_rank: Super Contributor
timestamp: October 01, 2021, 02:16:20 pm
content: Quote from: Circlotron on October 01, 2021, 01:39:37 pmAlmost 150 mJ Energy in the sustained spark.Short charge time to keep the windings cold30A primary current to get about 300 mA peak current in the spark.And ion measurement is built in as well.There is not much room for error in the dwell time.And you can not trigger these coils with a typical ON signal.1us after the ON signal starts, a signature is transferred to the coil to really turn ON.

author: SeanB
author_rank: Super Contributor
timestamp: October 01, 2021, 02:52:31 pm
content: Going to guess that is for multipulse ignition, for ultra lean operation, so you will have enough spark to ignite the fuel mix, even if the plug area is transiently non combustible, you have enough high energy sparks that the lean mix will strike before TDC and complete combustion to a large degree.I helped my father install high energy inductive ignition, that used a vane that blocked an optical sensor, that then triggered a low resistance (IIRC under 0,8R primary) coil, to provide the ignition pulse. Had to use inductive wound Bougicord leads, as the carbon ones basically melted, and spark plugs had to be special Lodge ones, as the other brands like NGK or Champion would only last a week before misfiring. But was able to run really lean, and provide extra power at the top end of the RPM, even if your 10 000km service was change 4 spark plugs, rotor and distributor cap, as they would all be badly eroded, and not likely to make another service.Big difference, made it a stealth supercar, well capable of beating the common sports models, 3 series BMW, low end Porsche, VW 1st generation GTI. None of them thought an Alfasud 1.5l was capable of beating them stop to stop, or at top end. He kept the stock exhaust as well, so it did not sound any different. Just used to eat gearbox synchros, and brake disks.

author: paulca
author_rank: Super Contributor
timestamp: October 01, 2021, 03:25:52 pm
content: On coils.... related, sort of, but I read something suggesting that on motorcycles, the engine has a stator and a rotor for generation... like 99% of them do, that's our alternator, however they claimed that on some bikes at least, they use different sized coils and power different things from each coil.So there was a larger, heavier coil for powering the ignition, a smaller coil for powering lights and another smaller one, gone through a rectifier for running electronics. Oh and a single neutral. It's like a 6 phase generator with the phases split and used in singles or pairs for different sub-systems. It makes sense to a degree, why pump all the current for the ignition at 17,000rpm through the rectifier and then use it t generate high voltage, reducing the size of the wiring and the rectifier.... and not broadcasting that ignition RF through out the bike, but keeping it close to the engine.I'm just not sure how true this is or how common it is.This video and section 1:33:https://youtu.be/mdOJ717PKRc?t=93

author: langwadt
author_rank: Super Contributor
timestamp: October 01, 2021, 04:40:36 pm
content: Quote from: SeanB on October 01, 2021, 02:52:31 pmsound like a story that gets better every time it is told, adding lots of spark energy isn't going to magically add sginificant power and running lean definitely isn't

author: HighVoltage
author_rank: Super Contributor
timestamp: October 01, 2021, 04:44:40 pm
content: Quote from: SeanB on October 01, 2021, 02:52:31 pmYes, Multi Pulse is another reason to have an ultra fast charge time.To get the combustion more stabilized, the spark current must be increased.Especially for lean burn mixtures, a higher spark current is required.Spark duration has become secondary in modern systems and long spark duration are a relic in the past.

author: Benta
author_rank: Super Contributor
timestamp: October 01, 2021, 04:58:21 pm
content: Quote from: SeanB on October 01, 2021, 02:52:31 pmInteresting. Never heard of this before.I know of multiple pulse direct injection (FSI, TSI, TFSI, whatever they like to call it), where only the immediate area around the spark plug has stoichiometric mix and the rest is lean.Please give an example of a production engine that uses multipulse ignition.

author: LaserSteve
author_rank: Super Contributor
timestamp: October 01, 2021, 05:42:30 pm
content: Yes,We Ohioans love our Kettering, EE.. Except for his love of Tetraethyl Lead Additives..Many of the buildings from his companies still survive in Dayton...Steve

author: bdunham7
author_rank: Super Contributor
timestamp: October 01, 2021, 06:09:18 pm
content: Quote from: Benta on October 01, 2021, 04:58:21 pmI've seen both Ford and BMW products that use multistrike. Ford in particular has been using it for a decade-plus now.

author: james_s
author_rank: Super Contributor
timestamp: October 01, 2021, 07:36:07 pm
content: Quote from: langwadt on October 01, 2021, 04:40:36 pmLean burn is done for fuel economy, not power. It has been a common technique for decades, lean out the mixture as much as possible during light load when it is less likely to ping and the total heat energy is not enough to burn valves.

author: james_s
author_rank: Super Contributor
timestamp: October 01, 2021, 07:45:46 pm
content: Quote from: paulca on October 01, 2021, 09:09:53 amYes, it's clear that you don't. They are not really my cup of tea either, but I do appreciate that they are one product that has had the sense to not mess with a successful formula. A modern Harley is very similar to one that was made 20, 40 or even more years ago and that is a great part of the appeal to people who buy them. I do love the sound personally, and I like the fact that it's essentially a slice of a radial engine. A friend of mine is a motorcycle enthusiast, he has several Japanese sport bikes, an electric bike and a Harley, he rides the latter the least, but he has said that riding it has a very manly feel and he loves it for a cruise on a nice day. It's an iconic vintage classic that you can still buy new.If Harley changed their design to be more modern, they would lose what makes them unique and they would completely alienate their entire customer base while then trying to compete in a market that is saturated by other brands, it would be the dumbest move they could possibly make. They'd lose their existing customers and you still wouldn't buy one.

author: Benta
author_rank: Super Contributor
timestamp: October 01, 2021, 08:33:30 pm
content: Quote from: bdunham7 on October 01, 2021, 06:09:18 pmThis does not sync with my knowledge. AFAIK, only Mercedes is (half-heartedly) following this track lately. Everything else is aftermerket/tuning accessories.

author: bdunham7
author_rank: Super Contributor
timestamp: October 01, 2021, 10:10:06 pm
content: Quote from: Benta on October 01, 2021, 08:33:30 pmI've seen, tested and measured these systems and I assure you they are common in at least Ford products. You can just google 'Ford multistrike' to read about it. This system famously killed a Ford engineer a while back--it turns out that the rapid succession is much better at stopping the heart than single pulses.

author: BrokenYugo
author_rank: Super Contributor
timestamp: October 01, 2021, 10:33:16 pm
content: Quote from: langwadt on October 01, 2021, 04:40:36 pmDefinitely a bit of a "bigger fish" story (though a tuned up Alfasud outrunning a stock Mk1 GTI or 3 series BMW is certainly well within the realm of plausibility), but there is some truth to it. The big deficiency of points ignition is you have a dwell angle energizing the coil, not dwell time, so as revs climb at some point you aren't closing the points long enough to saturate the coil and ignition energy falls off. This is where "dual point" distributors came in, by staggering a pair of rubbing blocks (the cam that operates the points) and points a longer dwell better suited to high RPM operation could be achieved with realistic rubbing block geometries.

author: langwadt
author_rank: Super Contributor
timestamp: October 01, 2021, 11:19:40 pm
content: Quote from: BrokenYugo on October 01, 2021, 10:33:16 pmsure if the ignition system is marginal upgrading it will help, but there's no point is going to plug melting levelsamazing how long it took before they figured out an extra coil and wasted spark was smarter than all the distributor nonsense

author: Circlotron
author_rank: Super Contributor
timestamp: October 02, 2021, 09:26:30 am
content: Probably one of the driving forces for getting rid of the distributor was simplifying engine assembly on a production line. Now no need to get it all synced up. Just attach all the parts and it is ready to run.

author: Circlotron
author_rank: Super Contributor
timestamp: October 02, 2021, 11:59:35 am
content: Quote from: HighVoltage on October 01, 2021, 04:44:40 pmWith older engines at least, long spark duration was considered desirable.What size plug gap is your new coil meant to be used with, and what is present day thinking on this?

author: HighVoltage
author_rank: Super Contributor
timestamp: October 02, 2021, 12:18:27 pm
content: Quote from: Circlotron on October 02, 2021, 11:59:35 amYes, you are correct, it was desired but why?We always believed this myth. But University research out of the early 80s has shown that this is not correct.The longest spark duration I had measured was 3 msImagine an engine running at 6000 RPM = 100 Hz = 36 degree crank angle / msSo, even a 1ms long spark would last for 36 degree crank angle.Lets say that same engine has a spark advance of 30 degree before TDCIf you retard this spark advance only a few degree, the engine looses power dramatically.Only the first few 100 us are responsible for a good ignition process.You can force a long duration spark to stop at shorter duration and it makes no difference for the engine.Even in the old days, with old style ignition systems it was the case.Porsche had a stock CDI in some 911 engines with 500us spark duration and they had full power and no problems. At the same time, GM had the HEI with over 2ms spark duration.I think the inductive system got stronger and stronger with higher currents on the primary and automatically the secondary windings and the secondary inductance increased. And because of the large secondary L, the long spark duration followed as a consequence.On the new coils, the spark gab will stay at 0.8 mm.One important aspect is the ion measurement across the spark gap and the analysis for each spark.There is more software in a modern coil these days as hardware.

author: themadhippy
author_rank: Super Contributor
timestamp: October 02, 2021, 01:11:14 pm
content: Quotedon't know about modern bikes,but it was certainly true on the some of the bikes i had in the past.On my ole z200 it came in handy to get the thing home when the cam bearing started to wear out,turning on high beam made the engine work harder,putting more tension on the timing chain.

author: Benta
author_rank: Super Contributor
timestamp: October 02, 2021, 02:42:11 pm
content: Quote from: themadhippy on October 02, 2021, 01:11:14 pmYour magneto was on the cam shaft? What kind of bike was this? The ones I know of have it on the crank shaft.

author: themadhippy
author_rank: Super Contributor
timestamp: October 02, 2021, 03:58:50 pm
content: Quoteno,the cam bearing was worn,causing the timing chain that drove the points to go slack ,putting more load on the engine, by turning on the headlights , took enough slack out to get me home.I discovered the "cure" when i hit the indicators to pull over as the engine was dying and dam thing started running again,turning off the indicators and the engine started to die.

author: paulca
author_rank: Super Contributor
timestamp: October 02, 2021, 04:16:45 pm
content: Quote from: themadhippy on October 02, 2021, 01:11:14 pmI figured it would be the only way to do it without a battery. And a lot of bikes didn't have batteries or electric starters "back in the days".But thinking back I have had bikes which will not run their head light off the battery. Tail light, side lights, indicators, dash lights, yes, head light no. (I found this out the hardway when I accidentally hit the kill switch while riding through pitch black night, instinctively pulled the clutch and the headlight went out.... at 50mph.

author: Benta
author_rank: Super Contributor
timestamp: October 02, 2021, 04:34:07 pm
content: Quote from: themadhippy on October 02, 2021, 03:58:50 pmThat still makes no sense to me. But never mind, I don't care about bikes anyway.

author: Nusa
author_rank: Super Contributor
timestamp: October 02, 2021, 06:44:40 pm
content: I once had a 1980 Datsun truck that had two coils, 2 plugs per cylinder and a 10-wire distributor (2 in, 8 out). My understanding is both plugs were fired at the same time with the aim of faster and more complete combustion in the cylinder. I passed that truck to family in 1993 when I moved to California. Sitting in a cousins barn in Ohio, last I knew.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 02, 2021, 07:59:09 pm
content: I had an 1985 Nissan truck that also had the dual spark plug per cylinder setup. IIRC the spark plugs were actually timed to fire about 5 (?) degrees apart.

author: David Hess
author_rank: Super Contributor
timestamp: October 02, 2021, 11:52:12 pm
content: Quote from: Circlotron on October 01, 2021, 07:44:16 amYou are absolutely right that the constant current out with variable compliance from an inductive source is more ideal. I suspect in the past capacitive discharge systems did better simply because commonly available Kettering systems were marginal for higher compression engines when only points were available.In principle the capacitor should be replaced with a lumped element transmission line used as a charge line so the peak to nominal discharge current is lowered increasing efficiency, but I have never seen or read of a capacitive discharge ignition which did this and now high frequency high voltage solid state switches allow even better ways.

author: langwadt
author_rank: Super Contributor
timestamp: October 02, 2021, 11:59:54 pm
content: here's an interesting way of doing CDI,https://electrooptical.net/static/oldsite/www.analog-innovations.com/SED/CD-Ignition-Basic.pdf

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 03, 2021, 01:36:53 am
content: Quote from: Circlotron on October 01, 2021, 07:44:16 am100mJ per spark (as measured on the primary side) is only about 7W for a 4 cylinder engine running at 2000RPM. There's much, much greater energy savings elsewhere in the engine.

author: Circlotron
author_rank: Super Contributor
timestamp: October 03, 2021, 02:40:04 am
content: Quote from: NiHaoMike on October 03, 2021, 01:36:53 amThe point was no so much wasted energy as the discrepancy between advertised spark energy and what is actually delivered to the plug gap. As an example, using my standard test gap (pictured) a 100mJ measured-at-the-secondary inductive setup can eventually make the ceramic insulator glow bright yellow at a high spark rate but a "100mJ" CDI hasn't got a hope in the world. That's gotta be the lowest tech method of observing the amount of energy delivered.

author: paulca
author_rank: Super Contributor
timestamp: October 03, 2021, 08:58:01 am
content: Quote from: David Hess on October 02, 2021, 11:52:12 pmOn a 2021 motorcycle the ignition system is called "Computer controlled digital transistorized with electronic advance"Which is Honda speak for a "digital" CDI unit using a SCR under computer control.The unit is usually a box about the size of a cigarette packet, fully potted, the coil is embedded at the base of the HT lead.Hard to find the actual unit on this bike, I expect it's contained in the FGM-TI fuel injection black box or similar.https://www.bike-parts-honda.com/honda-motorcycle/750-MOTO/NC/2021/NC750XAM/Frame/IGNITION-COIL/103806/F_38_20/2/42369