By on February 21, 2020


TTAC’s own Ronnie Schreiber writes:


How many spark plugs do you think a Model T “trembler” ignition coil can fire simultaneously?

I’m foolishly trying to make a spark plug-based Chanukah menorah (candelabra), so I need to have as many as nine plugs sparking at the same time. I could use individual coils but those run about $100 each and I don’t want to spend a thousand bucks on this project.

Yes, I know the voltages are dangerous.

Sajeev responds:

I’m not surprised you asked me this, and let’s not dwell (sorry) on the imminent danger of an ignition system-based menorah.

Henry Ford’s possible objections notwithstanding, using Model T tremblers for a spark plug menorah is doable. But since the Model T needed one trembler for each plug, you could need 9 of them. While I can’t find the trembler’s specs, judging by the YouTube videos, they sure look powerful (and dangerous).  Maybe one could power two plugs!  But while they are cheaper than full retail on a modern coil, they ain’t cheap.

Unless you have used tremblers lying around, what’s stopping you from buying used coil-on-plug units? They are under $40 at my nearest junkyard, but I guess it won’t look as cool as nine big boxes mounted remotely from the menorah.

I’d probably just stick with candles.

What say you, Best and Brightest?

[Image: Ford]

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41 Comments on “Piston Slap: Henry’s Spark Plug Menorah?...”

  • avatar

    What in hell are we suppose to make of this? :(

    Everyone knows Chanukah was over weeks ago

  • avatar

    I have no suggestions. This is uncharted waters for me.

    TTAC, Sajeev,

    If Ronnie is successful, can you run a short blurb with a few pictures? Id like to see the finished product.

  • avatar
    Mike Beranek

    You’re not going to need the same amount of current in this use as you would in a working engine. The spark produced in an ICE engine has to survive the onslaught of compression, which snuffs out less-than-fully-powered sparks.
    In the open air, at 1 bar, the sparks will not need as much juice.

  • avatar

    How about a nice NIXIE menorah?

  • avatar

    Can be done.
    You need a small neon sign transformer and you’ll have to wire the plugs in series and insulate them for 10kV, which is not as bad as it sounds – just don’t get too close and don’t leave it unattended. You’d have a continuous arc, and a pleasant smelling ionization to the room air! Wouldn’t cost much.

  • avatar

    The only purpose to using Model T parts for a menorah is to have Henry Ford spin in his grave to be remotely involved in celebrating a Jewish holiday.

  • avatar

    Instead of automotive coil(s), consider starting with the transformer from an old microwave oven (see “Jacob’s ladder” projects on youtube). Continuous vs. intermittent sparks could open a whole religious debate (but intermittent would lose).

    With multiple air gaps, series vs. parallel is a potential question but has a predictable answer (some say).

    DANGER symbol: Don’t die.

    WARNING or CAUTION symbol (which to choose?): Don’t start generating large amounts of ozone.

    Dust off your gap tool.

    • 0 avatar

      Extra credit:

      a) GFCI won’t save you – or could it?

      b) AFCI won’t power this device – or would it?

      c) Isolation transformer at the head of the chain – any benefit?

    • 0 avatar

      Update: Did some more ‘research’ (starting from zero lol) into trembler coils and I now understand your intent.

      The trembler coil generates a continuous series of sparks – no timing signal needed.

      Watched a trembler cross a ~1 inch gap, so yes it should cross 9x spark plug gap if wired in series. Question now is would the resultant sparks be of equal intensity so as to provide maximum aesthestics – and hypothesized answer is “yes” if the respective gaps are managed properly.

      • 0 avatar

        Update to the update: The resulting sparks might be equal in intensity regardless of the respective gaps – see the *video* here (multiple gaps in series across one spark plug):

        If this is correct, you could manage the brightness of the whole device by adjusting only one spark plug gap (larger gap = brighter).

    • 0 avatar

      Definitely avoid using a microwave oven transformer for this type of project! MOTs output around 2.2-3.5 kV at 200-400 mA, which poses a fantastically high risk of electrocution. Also, because of the high current capability the arcs will be VERY hot (extreme overkill for this purpose, and a fire hazard) and will produce sufficiently copious ozone to trigger acute respiratory problems in many individuals. Finally, the amount of RFI this would likely generate could lead to someone filing a complaint with the FCC!

      In theory, one could mod a MOT and add some external circuitry to tame the beast a bit and reduce the risk, but I’d still steer clear.

      A somewhat safer approach would be to use a neon sign transformer, which typically output roughly 6-18 kV at 15-30 mA (depending on the specific unit). This will produce a nice arc but will not likely source sufficient current to maim, burn, or kill (however, if you go higher than about 20 kV @ 30 mA the risk of sending at least 50 microamps through the heart and causing a lethal shock increases significantly). Unfortunately, all NSTs made since the early 90s feature current-limiting and ground-fault protection so they are unsuitable for generating arcs.

      The safest approach by far (but most complex) would be to build a circuit to drive a flyback transformer, which would give enough voltage for a nice blue-purple arc but would be limited to a few mA at most. A shock from this would certainly get your attention, but not be much more dangerous than a vigorous static discharge.

  • avatar

    If the plugs are wired in parallel, only one will fire, whichever has the narrowest gap. When this plug’s gap wears another plug will take over and so on. Wiring the plugs in series, as Imagefont suggests would solve this problem but is more complex to implement.

  • avatar

    You can’t fire more than 2 plugs with one coil simultaneously. If you hooked them all up to a single coil you would have one that sparked, as the electricity will take the path of least resistance. So head to the wrecking yard and grab some Ford waste spark coil packs. One from an early 4.6 and one from a later Vulcan. Each coil will fire 2 plugs, one in the standard center electrode to side electrode and the other from the side electrode to the center electrode.

    That is why those cars left the factory with one part number for the spark plugs for bank 1 and one for bank 2 as they just put the platinum on the electrode that the spark “leaves” from.

    Since you’ll have 5 coils you’ll have to pick one for a “bye” and connect one of its terminals to ground.

    The next problem is each coil will need its own circuit to fire it.

    • 0 avatar

      Oh and I’m not sure why you think you would spend $1000 on doing it with individual coils. Coils are cheap, no where near $100 each.

      Here is a 10 pac of genuine Motorcraft coils and plugs. For $156

      Or if you don’t mind white box parts you can get a 10 pack of coils by themselves for under $50.

  • avatar

    When I was a kid, I heard stories about home made car anti-theft devices using a Model T “coil box,” must have been a trembler. A nasty experience for anyone touching a metal part of the car. And being stupid teenagers we’d laugh about a dog taking a whiz on a hubcap. Never saw one, don’t know if it was real, or just an apocryphal story told by teenagers.

  • avatar

    Sajeev and Ronnie, now this is quality content.

    Is there an electrical engineer in the house?

  • avatar

    Cause a simple AC circuit and flickering bulbs is just too easy.

    Never underestimate human capacity to over engineer while waiting the needle swing back to simplicity.

  • avatar

    What an interesting project .

    ‘T’ Model coils (“buzzer boxes”) require _very_ low current as they were operated by 4 (IIRC)1.5 volt CD door bell batteries until the engine started and the magneto in the flywheel began to produce current .

    Yes, the anti – theft stories are true as well as using these coils on toilets to shock the living hell out of anyone pissing or sitting….

    No one died from the low current .

    I hope this gets built and a photo or link to one is posted .

    Using the modern Ford coils and a vintage wooden boxed one in view would work very well , kinda cheating but the desired result would be the same in the end, use only OEM Ford branded coils of course .


  • avatar

    At atmospheric pressure, you can probably daisy chain them together in a “waste spark” configuration and then just use a regular coil.

    The problem is more on how are you going to keep them all fired up at all time without burning out anything.

    • 0 avatar

      Daisy chain might work.

      But whatever you do, I think you might want to consider lampshades on each plug. I don’t think unshielded arc light is a good idea for the eyes of your family.

  • avatar

    Level I (safer than candles): Get a 10-light LED “chaser light” soldering kit; relocate 9 (or 8) of the LED’s to the inoperative spark plug gap spaces. Enjoy the [silent and safe] “Knight Rider” effect.

    Level II: Obtain one (and only one) trembler coil. Obtain and assemble a “Velleman K8044: 10-Channel Light Effect Generator Kit” and link 9 (or 8) of the relay outputs to the spark plugs (each lead to each relay, common ground). Enjoy the “Knight Rider” effect but with sparks instead of lights. Since the plugs fire sequentially, the original question of ‘how many can fire simultaneously’ is moot, and the duty cycle on the single trembler coil will be as per original design intent.

  • avatar

    Why not tesla coils?
    “Anything worth doing, is worth doing right.”

  • avatar

    Is this the first question asked by an official Schmuck?

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