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Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 10:26am 20 Dec 2022
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I'll bet this one is an original.....
I'm trying to think through if it may be possible to get a DC Voltage from the magnet in a small petrol engine used for the ignition.
The coil for the spark has a magnet in the flywheel wizzing round. Would it be possible to make a coil and cut a hole in the blower housing to make use of the magnet to generate a small DC Voltage?
If so I guess a substantial Cap would be needed to reduce flickering and if there would be enough magnetic Field to generate say 3-6W, what would be a ballpark winding for the coil? How many turns of what gauge wire or is there anything that could be easily adapted and Fitted?
I am NOT trying to take power off the spark coil but rather add a coil that takes advantage of the magnet already there on the outside of the flywheel used to generate the spark.
Any clues to the viability or execution of such an idea? Anyone know of any tiny alternators that could be adapted? Just looking to power a small LED light.
As a Curiosity, I have also pondered the Theoretical idea of making a generator on the 23" Flywheel of My old Lister engine.
If a Bunch of magnets were glued around the flywheel with opposing poles, could a single coil be used on a fixed stationary mounting to generate power?
Not concerned with what the power would be, rather If Multiple magnets could be used on a single coil or if Multiple coils would have to be used?
pd-- Senior Member Joined: 11/12/2020 Location: AustraliaPosts: 122
Posted: 11:07am 20 Dec 2022
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Many of the smaller motorcycles do exactly what you are trying to do. Thea have a separate lighting coil opposite the coil used for the ignition. many of them just have a rectifier and battery. if the lights are not on then the battery gets an equalizing charge. This is pritty typical of a lighting coil you would find mounted on the inside of a flywheel
As for the Lister Yes
phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135
Posted: 12:20pm 20 Dec 2022
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The multi magnet idea has been used on some motorbikes for over 80 years. They always fix them on the inside of the rim to prevent them flying off. No rare earth magnets or suitable glue back then so the quenched cast steel magnets were clamped in place with iron polepieces screwed to the brass flywheel. Inverter generators and Fisher & Paykel motors use curved ferrite magnets on the inside rim of the rotor.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 01:15pm 20 Dec 2022
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Pretty sure it is possible Dave.
So from your description, the coil is on the outside of the flywheel.
Can you provide a few photos of the setup and the existing ignition pickup coil.
It depends on the strength and number of the magnet/s.
Eg the coil that pd-- showed would be good for 6V 25W perhaps ... or maybe 12V 35W ... but would vary considerably depending on rpm. And it also would have some substantial magnets in the flywheel surrounding it.
I'm a bit afraid that the setup you're describing would be much lower output ... but 3W is not a lot of power.
Understood ... pretty unlikely to be able to tap any power off the ignition supply coil without totally wrecking the spark production.
Certainly possible in my view, but could add more suggestions with a few pix of the existing setup.
Yes, but not as much power as having multiple coils ... so depends what power out you require
Multiple magnets could be used with a single coil, yes.
Adding more coils will certainly increase the power ouput again, over just one coil.
Depending on the load you want to run, you may be able to wind a coil so it doesn't need a capacitor ... but if the revs are low or vary a lot, a bridge rectifier and cap certainly could help reduce flickering.Cheers, Roger
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 03:01am 21 Dec 2022
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The idea of using the ignition coil magnets came from thinking of a Neighbor.
She has this thing of mowing the lawn in the dark. Lovely woman and bit of a standing joke why she does it. I was going to get her a Bicycle headlight for clamping on the handlebars so she can see what she is doing.
I heard her out there the other Night about 9pm and Grabbed my big battery spotlight and stood at the fence and lit the part of the yard up for here so she could see what she was doing. She came over laughing and said I could see you coming and thought you were going to tell me to shut it off. I said no, I came over to help you see where the hell you are going! Her husband saw the light from inside and came out to see what it was and laughed his head off when he realised.
Just gave me the thought that there is a magnet on the flywheel wizzing round not doing anything for the majority of it's rotation and if it could be put to work for something other than making spark which seemed feasible enough.
I bought some crappy LED " Driving" lights off flea bay which I measured at a Searchlight like 6W. I thought they would be perfect for illuminating 12 Ft in front of a mower and wouldn't need to be recharged or have batteries.
She gets me to service her beloved mower and tells me to spend whatever it needs because " She wants it to last". I looked up the date code on the engine, the thing is 28 years old already! I said I think it has lasted pretty well.
I don't think it will last much longer, getting to a pint of fill up the oil and check the petrol. After I tuned it the thing starts fine and doesn't blow smoke but it's going through that oil quick that's for sure.
next time I get it i'll have a better look and see how practical it would be to mount a lighting coil on the thing.
As for winding coils, is there a formula or a table somewhere that tells one how many rotations and what wire thickness one needs or how is it worked out?
I wouldn't mind having a play with a DIY generator in the new year. Should be a good learning experience. Watched a lot of YT vids where people do their own for wind turbines and always thought running one of a little diesel engine would be much better. :0)
Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344
Posted: 03:50am 21 Dec 2022
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G'Day Davo, As far as the coils go the one coil test done on motor conversions would work and you will lose the rectifier diode voltage of around 0.7 volts so measure the rpm and coil voltage after changing to DC then just multiply coils to get your target output.
Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648
Posted: 05:08am 21 Dec 2022
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Davo, most small outboard engines use a 'charge' coil to do what you want. Originally this was for powering the navigation lights on runabouts that had no battery. Since they were incandescent light bulbs back then, no rectifier was required.
I have fitted a few of these coils as they usually are not standard on small outboard motors. You need to consider that the magnet face width, the magnet distance and the coil pole faces have to be of a specific dimension to get useful power from the flywheel.
Flywheel magnets face to the 'inside' (at least on any I've seen) so the coil needs to be there too. If you try to fit it on the outside you'll get a poor result.
If the flywheel is not designed to accommodate such a coil then your only other option is to fit a pulley and drive some kind of permanent magnet generator/self exiting alternator. This sounds way too cumbersome so why not just make a suitable bracket on which a suitable torch could be clamped to?
phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135
Posted: 07:34am 21 Dec 2022
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Unlike many outboards and motorbikes most lawnmowers with electronic ignition have the magnet poles on the outer rim of the flywheel. It makes repairs much easier as there is nothing under the flywheel. It should make adding a generator coil much easier too. As noted above a simple test coil on suitable core will tell you how many turns will be needed. Making an efficient core may be the issue. Most have a 2 pole magnet, though I have seen a 3 pole one (S-N-S). If you have an old transformer with E - I laminations take the E's and see if the spacing of the middle and outer limbs matches the spacing of the magnet poles. If so the coil can go on the middle limb. Cut the ends of the limbs to match the curve of the flywheel. If it's the outer limbs that match the pole spacing cut away the middle limb, and trim the outer ones to fit the curve. The spacing from the flywheel should be about the same as the ignition coil.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 10:30pm 21 Dec 2022
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Thanks for the feedback.
Yes I realise for the mower it's too hard for the effort and not practical either the way the machine is used. That said. I was wondering about the theory and if it could be used with something else if need be. Got the neighbour a Bike light which should fit in the handlebars.
Interestingly I couldn't find one with a solar panel to recharge the thing from daylight.
Pretty sure the magnet is on the outside of the flywheel which is what made me think it could be possible to put an extra coil for making power.
One of my little Diesels has electric start and does 6 Amps I think it is from an external coil on the fly wheel. Another diesel is electric start but has no charging system so maybe they thought it would be used with a generator. Not much good if it was put on a water pump!
I might look at getting some magnets to put on the flywheel and if I can find any cheap lighting coils as spares for something.
Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648
Posted: 04:12am 22 Dec 2022
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This would be way too risky for me, to stick/ bolt something on a fast rotating flywheel.
You run a big risk to seriously unbalance it.
The risk of the magnets flying off is very great, do not under estimate centrifugal forces.
phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135
Posted: 05:18am 23 Dec 2022
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Experimented with extracting some power from the ignition coil. 1) Find right polarity Connect a 1N4007 diode from "Kill" switch to 470nF 250V AC cap. to chassis. Meter across cap. With cathode to kill sw. my mower gives -320v With anode to sw. gives +12.5V - This is what we want.
2) How much current can be drawn? Adding a 470uF cap briefly kills the ignition. then add resistors till it misfires. Runs fine at 100 ohms, not so good at 82 ohms. Voltage at 100R = about 6.5V Therefore I = 65mA, P = 422mW Might need to add a switch to get max. spark when starting. Need to experiment.
A pair of 1W white LEDs in series give a useful amount of light at that current. Solar garden lights are just a few tens of mW and they are just enough to light a path.
I considered winding some wire on the end of the ignition coil core to see if more power could be had, but the mosquitoes drove me inside. You could try it, much less work than making and mounting a lighting coil.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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