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I've got a lawnmower engine on a hovercraft and I'd like to power the headlight on it without a battery. I understand there isn't an "alternator" per se in these engines, but there's a magneto that provides power to the ignition coil so that the distributor points can create a spark. I vaguely remember reading about harvesting power from the magneto to power (very small) accessories, but I can't find the source.

Is it feasible to pull power from the engine as a source? The LED headlight I have pulls less than an amp, and has its own internal regulators and driver, so the noisy power should not be an issue (it can tolerate up to 40v, I can't imagine the magneto is more than 10-12 volts on the low voltage side.

As an aside - it seems some snowblower engines come with an alternator equipped - I'm not sure if it's just the wiring harness that's not broken out, or if there's actually a part missing. On the off chance someone has been inside one of these:

  • The lift motor is a briggs vertical shaft 6HP engine, I can't find specifics on the exact model because it's been rebranded and the stickers have long gone.
  • The thrust engine is a briggs 1650 (which seems to sometimes come with an alternator), however the engine I have does not seem to be specced with the alternator feature.
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From what I can gather from different sources (including this Wikipedia article):

A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current.

It also produces an output of 50v or higher. This forum post suggests that older B&S magnetos produce 6-8v while pull starting, but 300-400v when running.

I don't think your magneto would be a good way to go. If I were you, I'd get a small deep cycle battery and use it as a power source for your LED light. Something which will take recharging quite readily and do so many, many times without issue.

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  • Thanks. I am trying to reduce weight as much as possible but it looks like a battery might be the way to go
    – Brydon Gibson
    Feb 7 at 13:11
  • @BrydonGibson - If the light is LED, it shouldn't have that large of a draw on a battery. You wouldn't need a huge car battery to get the job done. I definitely understand the need for weight savings, though.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Feb 7 at 13:36
  • @BrydonGibson - Another thought might be to just attach an alternator/generator into the drive system of one of the engines. I doubt it would take much power to run it if it's only going to be used to power the LED.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Feb 7 at 13:38
  • @BrydonGibson - Even another thought along the same lines. I couldn't find much in the way of generators I thought looked robust enough to do the job, however, I did find DC motors which are. IIRC, DC motors, when spun, create power just like a generator (or are a generator for that matter). You'd just have to spin it at fast enough speed to produce the amount of voltage which would work for you. These motors are quite small, so wouldn't add too much of a weight penalty. Much smaller of one than a battery, I'd think.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Feb 7 at 15:29
  • Yeah, that's another option - thinking I can swap the belt tensioner out for an alternator. I was just hoping to minimize part count, complexity, etc etc
    – Brydon Gibson
    Feb 7 at 16:39

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