Engine Hacks: Homebuilt Solid State Ignition Module

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[Dan] wanted to learn a bit about solid state ignition in engines; to get started he needed a test subject, so he decided he would upgrade his old 12 horsepower lawnmower.

Originally the lawnmower engine used a magneto coil ignition system, magnetos are simple and very common in lawnmowers. The magneto is designed to produce a high voltage spike when influenced by a magnetic field. A magnet is attached to the engine’s crankshaft to time the voltage spikes, these spikes are fed directly into the spark plugs to cause ignition, this is why you don’t need a battery. [Dan] explains how the solid state ignition works on his site as he goes through the build details. Essentially it uses a hall effect sensor to detect a spinning magnet on the crankshaft for timing, and a transistor and battery to fire the spark plugs for ignition.

Once he got his circuit up and running on a breadboard, he fitted the entire system into a neat plastic box and fixed it to the front of the lawnmower, as if it was meant to be there all along.

43 thoughts on “Engine Hacks: Homebuilt Solid State Ignition Module

  1. dont like it
    its good for a proof of concept, but nothing more
    no timing control = either trouble starting, or no power at high rpm
    not to mention the way he “tuned” it by hand, I guess the criteria was “oh, it works, lets drill holes here and bolt that thing”

    1. @rasz: You stand corrected by me. It has lots of power and no trouble starting. I also used the TRA12D service manual’s recommendation of 18 degrees before TDC to establish the bolt holes. Thanks hackaday for the review.

    2. @rasz this has the “timing control” that original would have. On the original the points serve as a crank position sensor of sorts. The Hall Effect sensor is replacing the points as a crank position sensor. Manually searching for the optimal position to mount the Hall Effect sensor shouldn’t be a big deal.

    3. LOL Jim the builder only mentioned “advance” in the context of the simplicity of small engine ignition systems. Some how that got twisted into meaning that small engines have spark advance mechanisms. Small engine magneto are pretty trouble free, I really doubt I’d go through the trouble to replace it with a battery power ignition. In the event I where to I’d use the original points as the crank position sensor. When you get down to it it that’s all the points, and the crank lobe that opens them are. They already come from the factory designed to fire the spark plug at the optimum moment.

    4. This is almost the perfect hack. He did something non-trivial, that he has no formal training in. He actually got it to work, which is no small feat.

      What timing could he possible need, other than the hall switch and magnet?

      1. Engines require different ignition timing depending on the load and engine speed. By “require”, of course, I mean “it would be nice to have if you want maximum torque output”.

        As you said, it’s a good hack in the sense that he got it to work. It does add complexity however, and without variable timing it doesn’t really give much benefit. But once it’s on there and working it’s not a big feat to add other cool stuff.

    5. As far as I can recall from the last small engine I took apart, there isn’t a whole lot of what you’re talking about in a magneto system to begin with. There’s no mechanical or vacuum spark advance to speak of so I think this hack is just fine, especially if the parts are cheaper than an actual magneto(around $50), even more so since the last magneto I replaced that was supposed to be a perfect fit, wasn’t which caused my tiller to die every 5 minutes or so.

    6. In a magneto system like that there is no timing advance of any sort. My aunt has an old generator with the same setup. The ignition coil is mounted to the pickup itself, which is mounted above the flywheel. The magnet goes by, charges the pickup and fires the coil. End of story. Troll elsewhere.

      On a related note the coil on her generator just died, I may have to copy this for her!

      1. there’s a governor of sorts on some lawnmowers, basically operating the choke and throttle, with a longer spring than the primary throttle spring, letting it rev up a little under load.

    1. Exactly. The only regulating functions for small engines seem to revolve around adding a bit of extra fuel if the RPMs get a little low. Otherwise I’ve never seen a lawnmower engine with spark advance or otherwise.

      1. Agreed. Never heard of such a thing myself either, I saw this hack and thought, hell yeah this will work great if you set it up right.

        Then you get all these assholes trolling in here about how it won’t fire right at high loads or whatever, people, I have a small engines certificate I spent 4 months training for to get from a college. If I say there is no such thing as spark advance on a small engine, THERE IS NO SUCH THING AS SPARK ADVANCE ON A SMALL ENGINE, FINAL STORY.

        Half the people making comments here have probably never even pulled the carberator apart on their push mower, which is probably the only small engine they own.

        1. You spent 4 months get that cert, and know everything? Hate to break it to you, but I been doing this going on 35 years, and I have in fact worked on plenty of small single cylinder gas engines with spark advance.
          is it required to run correctly, no not in most applications. In those that is designed into, you can tell a difference when is disabled

  2. I like the classic magneto system better… also many magnetos don’t simply feed the voltage generated directly to the spark plug, but instead charge up a capacitor as it rotates, and releases the spark at a specific point.

  3. So nobody else caught how he described the Hall Effect as an actual hall? It’s called that not because the electrons are marching down a hall, it was named after Edwin Hall who discovered the effect.

    1. @mike d no this can be use to set ignition timing for more power, deviate to far from the optimal setting here you will weaken the strength of the spark to the point of no ignition at all.

  4. A classic magneto system is much simpler, of course, but the point of this hack was to see if he could use a hall effect device to control spark timing, and he did that. Bravo! Regarding the comment that it doesn’t provide variable timing, true, but then neither does the original magneto system. The next step in this electronic ignition project possibly would be to work out when to fire the coil based on engine rpm (variable timing), perhaps using the hall effect device as a crankshaft position sensor and then develop another circuit to make a spark at the right time. Interesting. Thanks!

  5. Hey guys! There’s a whole lot of misinformation afloat here! The old magneto ignition has a mechanical switch, which used to be called “the points” in car talk. The sliding cam follower wears and ignition timing undergoes undesirable change. The engine flywheel must be removed (with a custom pulling tool) to service this wear prone part. The “solid state” ignition uses a coil (not a Hall effect device) to switch a transistor which replaces the old wear-prone “points” of a magneto. Presto, no more timing drift, more reliability. Despite what is said in the intro, there is no battery involved. The “solid state” ignition is still a magneto, driven by a moving magnet, just without the wear prone points.

    1. uh, not on a lawnmower. there’s no contact points at all, just a magnet flying past a coil.
      I think you are talking about a distributor for engines with more than one cylinder?

      I agree that this particular hack did not improve performance and added complexity. And it needs batteries now?? Adding fuel injection seems like a much better deal, plus spark timing from the ECU would provide the benefits that this setup could be providing. I beleive there was an EFI conversion recently posted actually..

      1. Ok guys you got me to pull out my Briggs & Stratton Service and Repair Instructions (part# 270962-3/92)and open to section 2. Depending on how old the engine he has it will have what they call “breaker points”. They will be housed either between the engine and fly wheel or in a box off to the side. In either case they are mechanical and driven by a cam in most cases milled into the crank shaft. I know they are there because I have fought with a 1968 engine with a stripped keyway for the fly wheel and part of the repairs I did was to replace and set the breaker points for the ignition system. I wish I could find a diagram of how this Magneto and points system works. And thank god we have solid state ignition now. No more pulling that F flywheel to adjust dwell and no more 6 to 10 pulls to start the engine. I never thought of just replacing the ignition system with electronics. For the more modern ignitions systems here is a site with some diagrams http://home.earthlink.net/~edstoller/id9.html

      2. uh, no. if you look underneath the flywheen you will find the points, capacitor and otherwise. its there on my tecumseh 1577, and most brigs and straton. the only part you see on the outside is the coil

  6. Something to note is that for the past 10+ years small engines have utilized electronic ignitions that have the same physical appearence and fixed mounting as simple magneto systems. In fact, it’s the ONLY type used now so it’s not usually even advertised as a new feature any longer. However, you will see such claims as Easy Start and Single Pull Crank. The new systems are actually pretty complex. They still use the magneto (strong moving magnet and coil) to generate the electrical power but that’s where the simularity stops. Beyound that point it is a completely electronic CDI (capacitive discharge ignition) system with varible timing. There are no contact points with the elec systems either. Although their position was not adjustable, the points were what controlled the timing on mag systems. Note that the earliest systems that were referred to as electronic only replaced the mechanical points with a semiconductor circuit. Conversion systems are still sold for DIY. These are not fully CDI systems with variable timing. The new fully Electronic systems are completely self contained with the only connection being a kill wire to cut power. The physical unit is mounted so that the flywheel magnet passes by it to charge the circuit way before piston TDC (top dead center). This situation allows the unit to delay the spark until the built in timing map calls for it. Engines need to spark near TDC to make for easy cranking but quickly need the spark to occur advanced of TDC to compensate for the speed at which the piston is traveling. Combustion is not instantanious when the spark occurs so the spark is set to occur just before the piston gets there so that max explosition power occurs just as the piston PASSES TDC. If max occurs before TDC, it will try to push the piston down before it’s reached TDC and therefore pushing the crankshaft in reverse. The higher the RPM the more advanced the spark needs to occur. Varible speed engines, such as car engines, need to provide power and efficiency at many RPM ranges during use. Small engines typically run at a constant goverened RPM. They also don’t have any other sensors to indicate air density or engine load so the timing curve programmed into the unit is simple and is set for average conditions at the engines goverened RPM. Since air density is directly related to altitude, the manufacturer must program the timing so that the engine will run anywhere in the region it’s being sold in. In the USA, that’s a huge range so the users near sea level and in high altitudes are not getting peak performance. But obviously the sys works well and MUCH better than old fixed timing non electronic systems. Also, for anyone wondering how the sys detects RPM, it uses two hall effect sensors and measure the time it takes the flywheel magnet to pass from one to the other. It would seem that simply replacing an old mag unit with a new unit would give the engine an updated high tech ign system. Well it would almost work since the mounting brackets are similar and you could probably find a new unit that would fit with little to no modification. The problem is that the new unit must be mounted at a specific point way before TDC but the old units were mounted much closer. I have made the conversion by using the new style unit from a doner engine where I could measure how many degrees in advance of TDC the unit was mounted. I then had to fab a new mount for the old engine. The target was an old garden tiller that would bring a grown man to tears just trying to get the dang thing cranked. It now cranks within the first 3 pulls. FYI my knowledge and experience on this subject comes from working with 2-stroke weed eater type engines used on RC boats so that timing can be varied based on fuel octane, air density, temp., and such. Also, new style elec units also have a rev limiter built in. The record maker engine builders are getting around 17HP at 19,000 RPM from a 30cc engine that would make around 1.2HP at 7,000 RPM on your weed whacker.

    1. yea all you guys are smart …. but the main reason this is a good fix is because orig parts for most of the older engines do not exist any longer or are very expensive….

  7. Anybody got a guess to the age of that engine? Looks pretty old especially with that starter hooked to the engine with a v-belt. I assume it also works as the generator to charge the battery. From my experience with a 1968 single cylinder engine, on a tiller, there are a number of reason I could see saying screw this to the old system and creating my own. I almost did on that engine. So I like this hack. It brings an Old engine back to life. In my case the engine still runs but I have repairs to make to the gear box for the tiller. But if I have timing problems again with it I will consider converting it.
    Thanks for the inspiration.

    1. I totally agree..I think that makes us trolls though..

      I’ll be the one with the balls to say there is too much marketing and too little original ideas/imagination in this scene. How many arduino based lighting or boyscout projects are we going to see?

      1. No, enjoying a hack doesn’t make you a troll. Being a jerk about the others does. As we’ve said over, and over, we’re bringing hacks of all different levels. No need to be negative to those that are simpler than what appeals to you.

        If you want to be the one with the balls, please do(or find) some awesome, not beginner, hacks and send them in. We really do appreciate the tips.

  8. @aztraph, @keville
    Sorry for the long paragraph. Didn’t seem that long until I saw it AFTER clicking submit.

    I’ve been acused of having diarrhea-of-the-mouth. Guess it “runs” over to the keyboard too. But still better to have diarrhea-of-the-keyboard than diarrhea-on-the-keyboard! The latter is a real $hitty situation. Makes your typing stink too. This response is an example.

  9. The comments are very entertaining!

    One of my welders has a Wisconsin engine in it and finding parts in my area is troublesome; I could understand someone implementing a solution like this.

    The great thing about situations involving engines running at a single governed speed(literal thinkers/nitpickers, please don’t embarrass yourselves by arguing the academic issue of governor hysteresis) is that you don’t really need adjustable settings; at least not dynamically. You tune it to run optimally at that that RPM and put it to work.

    @Dan: Congratulations on getting off your rear and doing something; it’s more than I can brag about lately…and I don’t just say that because I have a seat at my workbench.

  10. It’s a TRA-10 or 12D Wisconsin. Wisconsin’s foray into low-deck short piston & rod engines to sell more for gargden tractors. Not many were made. Better than anything else ever made exept for the old tall Wisconsins. Parts for these things got outrageous after Continental Teledyne (aircraft engine people) bought them out. Killed ‘ em as manufacturers, in fact. Finally, Robin, good japanese engine people bought ’em. Then Subaru, a division of Fuji Heavy Industries bought the lot. If I had to fix a no-fire TRA Wisconsin, and it had a battery – I would use a FoMoCo “TFI-IV” ignition module and the Wisconsin’s breaker points without the condenser. I just love HOT sparks at ZERO RPM! (You’d have to use Ford’s “E-Core” coil, also. That’s how I’d do it – if you had a battery.

    1. Yes, it’s a Wisconsin TRA-12D. Still running great. Never had breaker points that I know of. Starting is great, I start it with a rope now, a few years back the starter/generator broke and I never bothered to fix.

  11. It was my understanding that when the cdi came out in the 80s ,u could buy one for any of the briggs and stratton flat head engines of that era ,so it was an upgrade for about $20. But, my Question is, “Does this cdi. Unit give any spark advance? And if it does, how much does it give?” Also if it does give advance, it seems like it would increase hp bye at least 20-30% with a retrofit right?
    Please email me if u know the answers or have some good ideas cuz im buiding some 6700 rpm 5hp Tecumseh engines with billet rods that should put out 8.8 hp .

  12. The hall effect is used on most single cylinder motorcycle engines i have worked on to send signal to the cdi. It is the cdi which advances or even retards ignition in relation to rpm which allows us to map the engine for a controlled power curve.
    The lawnmower hack described has no real need for a cdi or ecu because it has a low maximum load which is why this type of engine lasts so long so the only real benefit of playing with the power curve would be fuel economy unless you plan on building a go kart.

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