Critique my electronic ignition design - Page 1
Forum section: electronics / projects

author: robzy
author_rank: Regular Contributor
timestamp: November 20, 2020, 01:55:33 am
content: So I've created this electronic ignition design for a vintage British car.There is a lot of power filtering because the car's power supply is very dirty (mechanical voltage regulation, and electronic fuel pump). I've given the option of fully isolating the STM32 Blue Pill so that its a bit safer to connect it to a PC if I want.For those unfamiliar with electronic ignitions - the "points" terminal is connected to a switch in the engine which is normally open, and gets connected to ground periodically. The microcontroller uses the signal from the "points" (aka switch) to decide how and when to charge and discharge the primary coil (L1).What do you think? Are there any clangers that I've missed?

author: pwlps
author_rank: Frequent Contributor
timestamp: November 20, 2020, 06:35:49 am
content: Quote from: robzy on November 20, 2020, 01:55:33 amUnless I missed something it's the opposite: normally closed, opens at ignition ?I imagine there is also a capacitor in parallel with L1 (or Q1) and that Q1 can withstand the relatively high voltage of the primary circuit oscillations (a few hundred V).

author: KE5FX
author_rank: Super Contributor
timestamp: November 20, 2020, 07:02:06 am
content: On the input side, if you can afford 20 ohms of series R, I'd put it ahead of the input LC filter. Depending (mostly) on the inductor Q, the combination of a 1 mH inductor and a 1 uF capacitor will ring to surprisingly high voltages. Looks like you'll be over U4's max input voltage before D3 starts to clamp.

author: floobydust
author_rank: Super Contributor
timestamp: November 20, 2020, 07:44:12 am
content: Just a few thoughts.I think you need higher current through the points, wetting current a hundred mA is historically what is out there, a big fat 47-150R power resistor to 12V. It's a big waste though, not sure the (oxide layer) is really that bad, or people just copied that notion. You could use a tiny capacitive discharge to keep the points clean. The plastic cam wears off so points don't last forever anyway.Because the point's wiring can pick up ign noise or arc if bad rotor I would add a reverse diode across the opto LED. Cranking can be 6V so R3 is a bit large, and R1 better to +3.3V, R2 is too big for 3.3V I/O and only 3mA from the STM32?The IGBT already has two resistors R5, R4 built-in. I think you want the IGBT to switch off very fast, so I use a driver that can sink higher current, as well as source not as much. The Miller capacitance with a 400V spike coupled back to the gate is huge and I think your driver will not switch the IGBT well. It will also need a lot of heatsinking on the pc board. Did you build a prototype and try it?I'd add a tachometer take-off terminal.

author: Circlotron
author_rank: Super Contributor
timestamp: November 20, 2020, 10:14:53 am
content: What coil are you going to use?A 12V one similar to the original?A points coil with a ballast resistor?A modern coil with low resistance primary resistance that needs careful dwell control?

author: CJay
author_rank: Super Contributor
timestamp: November 20, 2020, 10:19:53 am
content: Dump the points/condenser and fit a pickup something like this:http://autocar-electrical.co.uk/lumenition-range/magnetronic-product-guideOr this:http://autocar-electrical.co.uk/products/optronic-ignitions/optronic-fitting-kitsChances are there's even a fitting kit to suit the vehicle/engine you've got.

author: robzy
author_rank: Regular Contributor
timestamp: November 20, 2020, 10:24:55 am
content: Thank you everyone.Quote from: pwlps on November 20, 2020, 06:35:49 amEr, good point, I'm not entirely sure. Either way, my main point was that input from the points is either floating or ground.Quote from: KE5FX on November 20, 2020, 07:02:06 amI wasn't aware that LC filters ringing was an issue. I've done a quick google and couldn't find any information on it. Can anyone suggest any resources to learn more about it? How does an input resistor solve it?Quote from: floobydust on November 20, 2020, 07:44:12 amSo in actuality the coils have been replaced by an AccuSpark electronic ignition (http://www.accuspark.co.uk), but thanks nonetheless!Good point re R3 being too large for cranking. R1 I want to keep at +5V just for simplicity. R2 I thought should be okay with 2mA across it, but I'll bump it up. There are only some pins on the STM32 that are limited to 3mA (The ones with the triangle symbol).Quote from: floobydust on November 20, 2020, 07:44:12 amOh, good point on R4/R5! I just moved away from the STGP30H65F IGBT, and didn't realise that this new NGB8245 had inbuilt resistors.I was basing the design on a Silicon Chip schematic where an MCU drove the STGP30H65F directly through an inline resistor. What is a better simple way to drive the IGBT? Can it just be a transistor, dedicated IC, or does it need to be something more complex?I haven't built a prototype yet, but it's on the way, and I'm conscious about cooling. Tachometer take-off terminal will definitely be on the cards.Quote from: Circlotron on November 20, 2020, 10:14:53 amI'm actually planning to use the coil packs from a Holden Commodore V6 VS/VT/VX. I was planning to 'wing it' with the dwell, but once I find a good spec I should be able to control it in firmware.

author: KE5FX
author_rank: Super Contributor
timestamp: November 20, 2020, 12:14:47 pm
content: Quote from: robzy on November 20, 2020, 10:24:55 amSeehttps://www.analog.com/media/en/technical-documentation/application-notes/an88f.pdffor example. Probably not a huge deal in your case, but the voltages involved can get pretty high if the component Qs are high enough. Series resistance limits the amount of inrush current that might be stored and released during ignition startup transients. Or the resistor could go across the inductor, artificially reducing its Q factor.

author: Renate
author_rank: Super Contributor
timestamp: November 20, 2020, 03:47:29 pm
content: I agree with others, you certainly need more current and lower impedance through the points.You don't want something that sensitive flapping in the (electric) breeze.Your coil is probably ~100 X.The primary will probably see 175-250 V spikes normally.Where does the energy go if the secondary wire falls off? How high does the primary go?You definitely need to throw a "heartbeat" LED on your board (or is there one already?)You should also throw a LED in that runs in sync with the coil.And if you're still using points, maybe jumper(s) to loop the (pre- or post-isolated) points to the (pre- or post-isolated) gate drive for "limp home" if the µP blows?The good thing is, since this is British, the expectations for reliability will be low.

author: rvalente
author_rank: Frequent Contributor
timestamp: November 20, 2020, 03:54:00 pm
content: Yes, modern coils need dwell control, you need to charge them right before the coil saturation and that changes when the coil heats up.Why the photo-couplers? You've the same ground potential, no need. Also, this is a very poor igbt driver, you need a buttload of current to turn on and off FAST otherwise it will heat up.If you can, try to update you distributor with a coil model or hall sensor, better performance and less failure like than the points, that's really old technology that nobody misseshttps://people.physics.anu.edu.au/~amh110/Hall_sensor/Bosch%20dist%20hall%20effect.jpgFinally, i do not see a point in making your own ignition driver, Bosch/Denso/Delphi did that for you decades ago, just get a out of the box mature module and be happyhttps://www.bosch-motorsport.com/content/downloads/Raceparts/Resources/pdf/Data%20Sheet_68570379_Ignition_Module_IM_3.2.pdfOr, if you getting yourself the trouble to make a electronic igniton, just give up totally on the distributor at ALL, go for wasted sparkSpeeduino has everything done for you, just use their code. But, if you wanna learn, automotive electronics can be a great school as things go sideways easily.

author: Miyuki
author_rank: Frequent Contributor
timestamp: November 20, 2020, 04:32:59 pm
content: Quote from: Renate on November 20, 2020, 03:47:29 pmIgnition IGBTs have voltage clampTo burn leakage spike and possibly this situation

author: pwlps
author_rank: Frequent Contributor
timestamp: November 20, 2020, 05:44:02 pm
content: A little comment/question related to this project. A long time ago I have bought and mounted a similar system in my car, however the principle was a bit different : instead of interrupting the current in the primary coil the circuit was charging a capacitor with 200-300V voltage and discharging it in the coil. But I don't actually remember what were the advantages of doing it this way. Less heating of the primary ? Anyway I had it working for many years in my car (it was one of my first cars).

author: Renate
author_rank: Super Contributor
timestamp: November 20, 2020, 06:38:53 pm
content: Yeah, capacitive discharge was pretty hip for a while.One of the advantages is that the preparatory energy storage can be done anytime, instead of back-timed from your ignition point.It seems to me that this would give you a bit of advantage starting out before you've figured out the RPMs.

author: richard.cs
author_rank: Super Contributor
timestamp: November 20, 2020, 06:39:59 pm
content: So, given you've gone for an approach that still uses the mechanical points as the input, and are using a fairly conventional ignition coil, what are you actually trying to achieve here? What benefit do you foresee from this electronics? Are you disabling the mechanical advance on the distributor (both the rpm and the vacuum bits) so the microcontroller does all of that instead? If you're not disabling them then what does the microcontroller do?You'll still have to contend with the timing changing as the plastic cam follower wears. If you're going to the effort of adding some electronics why no do as Cjay suggests and replace the mechanical contacts entirely? They're the weak spot and your current design keeps them.I've considered adding electronic ignition to my car, but to be honest what's there works well enough, I never really have to fiddle with it. I might to tweak the timing when the UK goes from E5 to E10 (as I'll probably switch to buying premium fuel at that point), but otherwise I almost never touch it.

author: Circlotron
author_rank: Super Contributor
timestamp: November 20, 2020, 10:59:53 pm
content: Ignition systems are an interesting area. For capacitive discharge ignitions, the spark duration is often only about 0.12uS compared with 1.5-2 mS for a good inductive setup. What’s more, the energy actually delivered to the spark is surprisingly low. With 100mJ poked into the coil primary only about 35mJ comes out the secondary, given that the voltage across the plug gap is in the order of 1.5kV during the arc. For example, one particular coil I used for test had a secondary resistance of 4000 ohms. The peak secondary current was 400mA so we can see straight away that the secondary resistance loses 1600V in series with the 1500V across the plug gap so half the energy is gone already. And there are plenty of coils with secondary resistances much higher than 4K. Add to that the resistance of plug leads and maybe an internal 5K suppression resistor inside the plug... Of course there are so-called multiple spark discharge CDIs available, but the mere fact that they are available is a recognition of the fact that a single CDI spark is often not good enough. I say stick with inductive ignition.

author: Renate
author_rank: Super Contributor
timestamp: November 20, 2020, 11:14:29 pm
content: Quote from: Circlotron on November 20, 2020, 10:59:53 pmAh, that's interesting.I knew that a regular ignition lasts ~1.5 mS and so it continues while the mixture is burning.It means for one that you have a diagnostic insight into how the mixture burns and even turbulence.It seems a shame that you can't merge the advantage of capacitor storage of energy with a longer spark duration.

author: Circlotron
author_rank: Super Contributor
timestamp: November 20, 2020, 11:53:26 pm
content: Quote from: Renate on November 20, 2020, 11:14:29 pmI did just that some time ago.https://www.speed-talk.com/forum/viewtopic.php?t=45340

author: robzy
author_rank: Regular Contributor
timestamp: November 21, 2020, 12:46:17 am
content: Thanks everyone for your posts! Really great information, and so much to reply to.One thing that a few people might've missed in a later post - the points have been replaced by an electronic ignition module.Quote from: Renate on November 20, 2020, 03:47:29 pmBy "heartbeat" do you mean power LED? The STM32 Blue Pill has one onboard. I've been uhm'ing and uhh'ing about a LED in sync with the coil, but for now I'll leave it off as this is mostly in 'test bed' stage.Quote from: Renate on November 20, 2020, 03:47:29 pm'Reliability'? What does that mean? Is it an English word?Any ignition system that I put on the car will be done so with the assumption that it will be a 5 minute job to revert back on the side of the road.Quote from: rvalente on November 20, 2020, 03:54:00 pmLast night I remembered about the Speeduino project and saw they had a TC4423 MOSTFET driver on their ignition outputs. I'm going to add that to my design to drive the IGBTs.Quote from: rvalente on November 20, 2020, 03:54:00 pmWhere's the fun in that?And it looks like a lot of money to spend on many unknowns, including their internal specs and plug options. An IGBT+driver ought to be good enough for this application.Quote from: rvalente on November 20, 2020, 03:54:00 pmThat's exactly the direction I'm heading.Quote from: richard.cs on November 20, 2020, 06:39:59 pmThis car doesn't even have vacuum advanceAdding vacuum advance is on the 'wish' list. Like I mentioned to the commenter above, this is step 1 in a longer term project.CDI is an interesting option which I looked into, but I think that's slightly too big of a jump to make at the moment. Especially because I suspect that this circa-100 year old engine design will not appreciate a shorter spark duration.

author: floobydust
author_rank: Super Contributor
timestamp: November 21, 2020, 06:49:43 am
content: I think it's good to nail down the scope of project, as these can quickly get out of hand, adding more and more features.Ultimately, are you not are doomed because the old points are not enough resolution to control ignition timing in firmware- you need say a 60 tooth crankshaft pickup.I don't know how many cylinders the engine has but crankshaft speed "wobbles" with every cylinder firing, so what you predict as the firing point for say 10deg. advance can be wrong and ca pow.I think at best you can try control/optimize dwell? GM uses a 2D lookup table with axes battery voltage and RPM to determine dwell. So that would be an extra A/D channel.If your firmware hangs or crashes when the IGBT is (stuck) on, it will quickly roast. You might want to leave the ballast resistor there, or go through-hole for the IGBT.Coil-on plug modules have a built-in watchdog timer to limit IGBT max. on time in case of ECU fault.P.S. are the electrics done by Lucas, Prince of Darkness? Their stuff was pretty scary

author: Renate
author_rank: Super Contributor
timestamp: November 21, 2020, 10:57:09 am
content: Quote from: robzy on November 21, 2020, 12:46:17 amNo, I mean adding something to show that your µC is active.I always put a slowly brightening and dimming LED on stuff so that I can see that it isn't wedged.Another LED electrically or logically on the input or output here will give you a sense that it is actually working

author: xavier60
author_rank: Super Contributor
timestamp: November 21, 2020, 12:44:55 pm
content: I allowed the points to still pass full coil current by placing them in the path between the MOSFET's Source and ground.

author: MartinX
author_rank: Regular Contributor
timestamp: November 21, 2020, 11:18:28 pm
content: I have messed with DIY ignition systems for a long time, since 1989 in fact, time flies.As others already pointed out ditch the fuse and inductor at the power supply input, put the resistor first and you get filtering and ESD protection and no brutal inrush current into the 1µF capacitor, you may not think so but putting low ESR capacitors directly at he input will eat away at the contact surfaces of the ignition switch.About the IGBT, almost all of them designed especially as ignition coil drivers are very easy to use, they are meant to be driven directly from the 5V processor with a 1k gate resistor, that is all you need. These transistors are slow by design and have very low gate threshold voltage, in this case 1.8V. Ignition coils are large with high inductance and high parasitic capacitance, super high switching speed does not improve anything and fancy gate driving arrangements are a waste, in fact clamping the gate hard to ground in an attempt to turn off faster messes with the internal protection built in to the device, the zener between collector and gate will have to conduct higher current before it can raise the gate voltage to turn the IGBT on again and protect itself.If you look in the data sheet you can see all the test conditions are given with Rg 1K and Vge 5V and you will find the same in most other data sheets for ignition IGBTs. And also switching losses are not much of a concern since the switching frequency is only a couple of hundred Hz at most, conduction losses are far higher.If you use the contact points as timing input filtering is neccesary the signal will not be clean. Less than 50mA current through the points will hardly work at all, i used 50 ohms load for a long time and it worked very well. The condenser in the distributor must be disconnected or it will cause a significant delay, i used to disconnected it and tuck the wire away so it is still there if you need it if the electronics fail. My last DIY system in my boat lasted for over 10 years without changing the breaker points, the wear on the plastic cam follower seems to stop after initial wear in as long as you keep the cam lubicated, there is special grease for this, only available from vintage car parts dealers nowadays.

author: robzy
author_rank: Regular Contributor
timestamp: November 22, 2020, 12:34:15 am
content: Quote from: floobydust on November 21, 2020, 06:49:43 amYou're right to note that the old points (or, in this case, electronic ignition) might not be enough resolution with only 2 pulses per revolution. I do plan to add another sensor, but I'm curious to see what I can do with the existing setup.I've actually put a logic analyser on the current setup, and I was somewhat surprised to see that at constant RPM the time between coil fires is very periodic. I wonder why that is...Quote from: floobydust on November 21, 2020, 06:49:43 amHaha, they are Lucas, and they can be finicky!Quote from: Renate on November 21, 2020, 10:57:09 amThat's actually a neat idea. I can't promise that I'll implement it in this early version, but throwing on a resistor and LED just to give me the option would make sense.Quote from: MartinX on November 21, 2020, 11:18:28 pmYour explanation makes sense, but I'm not going to lie, it makes me nervousI guess it would be important to choose the right capacitor in this circumstances, can you give any suggestions? I think I was planning to use a film capacitor usually used for mains.Quote from: MartinX on November 21, 2020, 11:18:28 pmThank you very much for all of your input on the IGBT, it's thoroughly appreciated. Because this is a bit of an experimental platform I might include a footprint for the MOSFET driver, but I won't install it straight away.Quote from: MartinX on November 21, 2020, 11:18:28 pmAs I've mentioned, the points have been replaced with an AccuSpark electronic ignition, which is - mercifully - one less thing for me to worry about

author: floobydust
author_rank: Super Contributor
timestamp: November 22, 2020, 04:00:57 am
content: Um, do you have points or not?The Accuspark system seems to be a variable reluctance magnetic pickup and multipole magnet "trigger ring", in a two-wire module connecting to power and the coil and GND. Just a bit confused.Timing jitter can be caused by free play in the distributor gears and timing chain slack. I had a 1968 Ford with the distributor-shaft bearings worn and it wobbled or cocked to one side so the timing and dwell was all over the place. I found it by accident, when I grabbed the cam lobes and noticed they moved sideways, lots of slop.1964 Chevy had defective (new) points that had a very weak return spring, so they floated above 1,200RPMQuote from: MartinX on November 21, 2020, 11:18:28 pmI'm referring to the 10k+1k resistor turning off the IGBT, I think it's high value. No need for nsec here as I have even seen that damage ignition coils, some people tried using a power mosfet instead. The super fast off-time seems to let the leakage inductance of the coil generate too much of a voltaged spike that destroys the coil's primary winding insulation.I would have push-pull drive with the 1k, like the 5V MCU's are using.

author: Circlotron
author_rank: Super Contributor
timestamp: November 22, 2020, 05:20:24 am
content: Quote from: floobydust on November 22, 2020, 04:00:57 amI've always used a 100nF 630v polypropylene cap across a mosfet. The voltage is a half sine about 20uS duration peaking at about 500V with 8A switched current. Added benefit is if the spark fires about 10uS after the mosfet turns off then the leakage inductance energy that has been transferred into the cap (at this moment at it's peak voltage) is available to be sent through to the coil secondary and on into the spark. If you look at the spark current both with and without this cap in place you can see an additional spike in the current when the spark begins.If you use a generic IGBT and not one meant specifically for ignition coil duty then make sure you put a high voltage reverse diode from collector to emitter. MOSFET body diode takes care of this.If you happen to use a bipolar transistor e.g. BUX80 like was popular back in the day, you can put a low voltage reverse diode from base to emitter instead. A schottky diode would be perfect. Any reverse oscillating collector voltage trying to swing below ground forward biases the collector-base junction harmlessly and the diode protects the consequently reverse biased base-emitter junction.

author: Whales
author_rank: Super Contributor
timestamp: November 22, 2020, 07:07:28 am
content: I literally just finished helping my father tune a replacement distributor and adjust his rocker clearances on his MkII Austin 1800 half an hour ago. Finding this topic on the forums ismostexcellent.If you need circuit diagrams or specs for anything Austin 1800, Morris 1100, Mini or MGB then just ask; more than happy to scan a few pages from one of the dozens of manuals for you (including the conflicting bits).If you need someone to bang your head/ideas against then I might be able to help. I'm used to the prince of Darkness. I'm having a look at your circuit now.Sidenote 1: I can't find any specs for the ignitions coils other than prim & sec impedances. I think I approximately measured the ratio on one once using AC from my siggen, but I don't recall if I was able to get stable results or not. Even from the new after-market suppliers of these coils: everyone is clueless, they just have similar part numbers, size and shape. Just be wary of the R and non-R suffix variants, designed to be used with a series resistance in some models.Sidenote 2: A current project of mine is to add intermittant wiper functionality to an existing one speed system. The wiring is more complicated than I expected, complete with brushed contact mechanisms. I have everything worked out except what switch to put on the dash: can't find anything that's 3 position ON-ON-ONandlooks half-right on the dashandis ergonomicanddoesn't cost something crazy like 100AUD.

author: Whales
author_rank: Super Contributor
timestamp: November 22, 2020, 07:25:40 am
content: From my understanding: you're both (1) replacing the points (with a micro-controlled IGBT or sim)and(2) replacing the distributor rotor + cap (by going micro-controlled full wasted spark).Thoughts:1. I presume you're on a 4-cylinder engine. What model?2. Will wasted spark work across all 4 cylinders at once, or will you have to do them in pairs to avoid sparking cylinders at bad times? If so: it might be easiest to go for two coils rather than to try and redirect the HV. There's probably plenty of space under your bonnet, if you clear out last week's sacrificial goats.3. I'd go for a LOT more capacitance in your circuit. Don't just think of transients, think of brown-outs. You still want your ignition to be stable when: starter motor drags a mostly flat battery down, lucas detects old ladies with shopping trollies at night (dims+flickers the headlights), intermittent shorts due to flasher-can, etc. I would probably want at least 1 second of uninterrupted 5V for your micro to last if the Vsupply completely collapses (which by this point the coil won't be useful anyway). Plan to outlast the existing components rather than underlast them.(4) How are you planning to connect one coil output to multiple sparkplugs? Are HV tension lead Y-adaptors a thing? EDIT: The softdrink-can-style ignition coils that these cars use have a screw hiding inside their top terminal (HV output); youmightbe able to put a longer one in for making a junction or something similar? Albeit removing this screw can cause the oil to leak, so don't do it with old coils that might have PCBs in the oil, and you'll have to work out how to insulate all of this.EDIT2: woops, you say you're not on coils, you have an aftermarket sparking system. This is getting hairy to follow

author: richard.cs
author_rank: Super Contributor
timestamp: November 22, 2020, 11:45:15 am
content: Quote from: Whales on November 22, 2020, 07:25:40 amI don't think Y connections work, whichever plug strikes first will cause the voltage to collapse and the other plug probably won't spark at all. "Wasted spark coils" exist which have two HV outputs, as I understand it they are two ends of the winding so neither side is grounded and the two spark gaps are essentially in series.

author: Renate
author_rank: Super Contributor
timestamp: November 22, 2020, 03:44:36 pm
content: I thought "wasted spark" was when you had too much alcohol in the mixture.Actually, the two spark plugs effectively end up in series (with a double-ended coil in the middle).Sparking in a normal atmosphere is easier than in a compressed fuel mixture so the voltage drop across the "empty" plug is much less.So you don't waste that much.Still, I'd rather use N coils instead of N/2.

author: Whales
author_rank: Super Contributor
timestamp: November 22, 2020, 09:41:36 pm
content: I've re-read the OP's replies, he's not using traditional coils, he's using a 3rd party sparking system.QuoteQ: What are the inputs and outputs of this? Doesn't this mean you don't need an IGBT because you're not driving the coils directly?A diagram of your whole system (from rotation sensors to sparkplugs) would be really useful for us to understand what's going on. A new circuit means nothing on its own, it needs context. A sketch on paper or mspaint would be OK (provided it's well labelled).

author: robzy
author_rank: Regular Contributor
timestamp: November 23, 2020, 12:48:48 am
content: Thanks again for all of your posts, super helpful. Lots of people have asked what exactly I'm doing here, so I'll clarify...Right now the 1949 Morris Minor with a sidevalve engine engine is running totally stock, except for an AccuSpark electronic ignition. This is just a Hall effect sensor in the distributor that fires the stock coil. The distributor is still used to route the spark.I'd love to redo the entire ignition system, and I'm starting by getting two Holden wasted spark (WS) coils, which are going to be controlled by the design in this post you've all been critiquing, which is going to use the AccuSpark module just for timing.I'm aware that there are some obvious problems with that - like identifying which of the two WS coils to fire based only on a single signal - but this is just for testing purposes in the garage. I'll find a way to make it work. Once I've proven the concept I'll find a better way to do the timing.Re the attached table - I'm currently moving between Stage 1 and Stage 2Quote from: Whales on November 22, 2020, 07:07:28 amHave you considered going to a car junkyard and scouring old cars until you find something appropriate? Depending on where you want to install it, will a rotary switch do?Quote from: Whales on November 22, 2020, 07:07:28 amThanks for sharing your experiences, the Austin sounds beautiful. That's a good point re capacitance, but that introduces a whole other host of design considerations, and for now I'm just anxious to get a simple proof of concept working.I haven't read anything about doing wasted spark across all 4 cylinders at once, but my gut tells me its not advisable.Quote from: Renate on November 22, 2020, 03:44:36 pmPerhaps. I wasn't too fussed either way, but the wasted spark coils presented themselves first.

author: robzy
author_rank: Regular Contributor
timestamp: November 23, 2020, 01:08:41 am
content: Wait a second - I just noticed that the NGB8245N has a maximum Gate-Emitter voltage of +-15V.Am I going to run into problems powering it off the nominal 12V battery supply? Should I switch it over to the regulated 5V supply instead?

author: langwadt
author_rank: Super Contributor
timestamp: November 23, 2020, 01:55:13 am
content: Quote from: robzy on November 23, 2020, 01:08:41 amthe gate is zener clamped to 12V so with the 1K resistors it should be fine, but the datasheet uses 5V for all the measuments and it is plenty

author: robzy
author_rank: Regular Contributor
timestamp: November 23, 2020, 04:20:08 am
content: Ah, good point, thanks.

author: Circlotron
author_rank: Super Contributor
timestamp: November 23, 2020, 07:19:03 am
content: Seeing you’ve got a flathead with low compression and low turbulence, after you get it all going don’t be afraid to open up the plug gaps a bit. Provided the coils are driven decently, 1.5mm is a good safe maximum.

author: Whales
author_rank: Super Contributor
timestamp: November 24, 2020, 07:35:49 am
content: Thankyou for the table & info about your coils, this makes a lot more sense nowI presume you're aware of the gotchas of real-time computing (don't alloc memory, keep main loop really predictable & simple, don't perform side-tasks unless they have a definable upper bound on computation time, etc). Scope the existing ignition system vs your system (with its outputs-to-coil floating) to make sure it doesn't have any software hangups.Fuse your coils during testing, just in case your STM32 gets stuck (or sometimes boots) in states where the coil is left fully on. Fuses are much cheaper than coils and much less hassle than molten wires. My father's 1800 blew some wires inside the distributor and melted the 12V supply lead to the coil because the points got stuck shut during some testing -- therewasa fuse in the system somewhere, but it was rated several times the wire's current and commoned across several car systems.As it should be, my good sir.Quote from: robzy on November 23, 2020, 12:48:48 amRotary switch: my current plan, but I'm having to spend a lot of time reading fine details. Sadly most are only well rated for AC (eg 5A AC, 0.5A DC). 4 position is much more common than 3 position (probably due to ceiling fans) but I don't want a dash control with that many distracting states if I can avoid it.Junkyard: hmm, I'm imagining mostly 1990-onward cars there. Not sure if I'd find anything pretty, but might be worth trying.

author: Renate
author_rank: Super Contributor
timestamp: November 24, 2020, 12:22:31 pm
content: Quote from: robzy on November 23, 2020, 12:48:48 amQuote from: Whales on November 24, 2020, 07:35:49 amI put a switch on my vehicle for On-Off-Auto. (Erm, it's only half wired.)I was looking for the kind of switch that you find in a nuclear power plant, but they were too expensive.One parameter that I wanted was a 45° step. Most common rotaries are 30°.45° makes it easier to see what position the switch is from all angles.Just add the 45° to your parameter search.

author: Gyro
author_rank: Super Contributor
timestamp: November 24, 2020, 12:28:11 pm
content: Not hugely relevant, but Big Clive just did a teardown of a cheap capacitor discharge ignition module...

author: richard.cs
author_rank: Super Contributor
timestamp: November 24, 2020, 12:40:07 pm
content: Quote from: Whales on November 22, 2020, 07:07:28 amI had something similar on my car, and in the end I bought a switch that mechanically had the positions I wanted (in my case centre off, normal one direction, spring loaded the other), and then added a relay to generate the contact configuration I needed. For mine I wanted wipers in one direction and wipers + washer on the spring side, but the the relay was needed in order to get the wiper parking to work properly - off isn't off N/C, but instead connects to the parking contacts on the motor.

author: robzy
author_rank: Regular Contributor
timestamp: November 24, 2020, 01:21:12 pm
content: Quote from: Whales on November 24, 2020, 07:35:49 amThanks for the tips. All things I'm aware about, but nice to have a reminder. Admittedly, I hadn't thought about a fuse on the primary side for testing purposes, I'll look into that.And yeah, Gyro, I saw that, and took it more as a lesson of "what not to do"

author: robzy
author_rank: Regular Contributor
timestamp: November 26, 2020, 04:10:23 am
content: And we're off to the races!All of the high current traces are duplicated on both sides of the board.This board is going to connect to two wasted spark coils.: Yes, I've just noticed that there's some silk screen labels placed off the board, oh well!: The more I look at this PCB the less happy I am, but it should do for a proof of concept!

author: mikerj
author_rank: Super Contributor
timestamp: November 26, 2020, 03:12:32 pm
content: Quote from: robzy on November 23, 2020, 12:48:48 am100% not advisable! One of the cylinders will be approaching BDC on the intake stroke (so a cylinder full of lovely fuel/air mix) when the plug is fired on one of the others.Have you ever looked at the Megajolt Lite system? This uses an ignition module (EDIS) from various older Fords that include the drivers for a twin coil wasted spark system and a decoder for a 36-1 trigger wheel. All you have to supply it is a form of serial data to tell it how much advance you want, which is performed by a small 8 bit micro in the Megajolt. The ignition module will even work all by itself, albeit with fixed 10 degree advance. The beauty of this is you are using a OEM grade module which are pretty bomb proof to do all the high voltage stuff, but have the flexibility to control it however you want, and you also get the eliminate all the scatter from the cam chain and distributor drive. My father has had one of these systems on his MGB for a number of years and it performs really well, in particular starting is vastly better compared to the Pertronix points replacement module he used previously.

author: langwadt
author_rank: Super Contributor
timestamp: November 26, 2020, 06:36:16 pm
content: I believe VW wasted spark coils like these:https://www.ebay.com/itm/183016291739only need two 5V/~10mA logic signals, the drivers are build in

author: robzy
author_rank: Regular Contributor
timestamp: November 26, 2020, 10:09:56 pm
content: Quote from: mikerj on November 26, 2020, 03:12:32 pmExactly. I didn't know how likely the mixture was to combust without any compression, but I don't want to be the one to experimentQuote from: mikerj on November 26, 2020, 03:12:32 pmTrying to find prices for the Megajolt Lite is tricky, I haven't found any. At the end of the day, though, half the fun here is DIY'ing it. (That being said, I'm seeing screenshots of their software, and that's making me jealous!).Quote from: langwadt on November 26, 2020, 06:36:16 pmGerman parts in a British car?!I jest. Those actually look pretty cool. If I run into trouble with my current setup I might look into those.

author: langwadt
author_rank: Super Contributor
timestamp: November 26, 2020, 10:13:28 pm
content: Quote from: robzy on November 26, 2020, 10:09:56 pmyou want it to run or just drip oil?

author: robzy
author_rank: Regular Contributor
timestamp: November 26, 2020, 11:37:55 pm
content: If a British car doesn't have an oil leak you better fill it up!

author: Whales
author_rank: Super Contributor
timestamp: November 29, 2020, 08:32:58 pm
content: Never get in a helicopter that's not leaking hydraulic fluid.

author: robzy
author_rank: Regular Contributor
timestamp: December 20, 2020, 04:53:22 am
content: Success!Look at that rotor spin!It backfired loudly at the end because the engine stalled (needed a tad more throttle) and the firmware does not handle that elegantly yet. It charges the coil, waiting for a signal that never comes, and after 1 second dumps all that energy into a couple of spark plugs at a most inopportune time.https://youtu.be/6z-Ez1HlIlI

author: Circlotron
author_rank: Super Contributor
timestamp: December 20, 2020, 07:03:59 am
content: To get around the problem of having the gate drive stuck high and having to go low and making an undesired spark, what I did is drive the gate with a 1uF cap in series and a 1M resistor from gate to ground. Also a 1N4148 across the 1M, arrow to gate. That way, if the gate is high for too long it discharges and turns off the IGBT, and in particular the gate voltage falls slowly enough that it doesn’t make a spark. Foolproof.

author: robzy
author_rank: Regular Contributor
timestamp: December 20, 2020, 07:39:50 am
content: Quote from: Circlotron on December 20, 2020, 07:03:59 amNoted for future!I actually burned up an IGBT in testing because my fake-distributor wasn't sending signals to the uC, and the firmware had the IGBT on continuously for a few minutes. I was thinking I needed a 555 timer circuit, but a cap is an interesting option.