More on magnetos

My Lister D has fired up since refurbishment, but I wasn't there to see it!!
While I was indulging another hobby yesterday, my son decided he should try to get it going. I had been waiting on a new spark plug, which arrived Friday. While I was away, he fitted it, and wound her up. It seems it went but a bit rough, missing a bit. The spark wasn't bad, but still missed a bit.
So he pulled the magneto coil out again and investigated a bit more. Seems it is open circuit on the secondary winding, but despite that it fires most of the time. This could be the spark jumping the break in the winding.
The magnetor is the normal Lucas RS1 (?) that this Lister model normally seems to have. On the coil there's a live side of the primary winding, an earthed side, and that's in common to one side of the secondary, and the other end of the secondary is the little brass button in the middle of the coil that contacts the brass leaf which connects to the plug lead inside the cap.

The secondary winding is a very fine wire of many many turns. A crude measurement of the wire shows it to be about 0.07mm dia (70 microns) including the enamel. That indicates the number of windings might be perhaps of the order of 10,000.

Anyone tried to re-wind one of these coils themselves? Or is there a better way?
I have many sizes of enamelled copper wire available, but am unsure how many turns it should be.
It would certainly be easier to just aquire another magneto, or just a coil, but not so challenging.

Any suggestions?

I checked on one website and for about £80 or so, they'll rewind the coil. But that's to double the value of the whole engine!!

edit. Corrected typos and added some details.

Wow it sounds as if your son knows what he's doing. Sorry I can't help with your mag as I get a bit lost with electrics. Hopefully someone will give you the answer (Nuts might know) so you can sort it rather then having to buy another mag.

Good luck,

Stu.

I had a thought today on a lower cost solution for this issue.
How about using the primary winding to produce a low voltage impulse and feed that into an old standard 12V car ignition coil, or perhaps a motorbike coil and then the HT from that to the spark plug?
Think that'd work?

Would there be a timing issue in respect of two coils being involved, and so the flux collapse time one after another might introduce delay. If so could perhaps be comensated for by advancing the timing on the magneto drive chain?

There,s a few threads on this subject that will help out as Stu says Nutgone is the most practiced at this heres a post that may help http://www.stationaryengineforum.net/t6186-more-ignition-experiments

There isn't enough turns to use the primary as a charging coil for what is basically an energy transfer system, it would work at engine speeds but probably wouldn't fire at starting speeds (although I could be wrong, it might be worth an experiment with a 6v canister coil, they're only about £13 brand new off eBay). Your best bet would be to remove the coil from the centre bar with a sharp wood chisel & wind on your own coil of about 500 turns with something like 22 gauge wire (you'll need to check my other thread for the wire size as I'm kind of going by memory here).

Winding your own full coil by hand (I'm talking primary & HT side here) would be a very difficult task indeed. Each layer of the coil needs to be separated by a layer of insulating material, preferably special paper soaked in electrically insulating varnish. It would be a very difficult job & you'd probably get in a right mess & the wire is quite easy to break as well. The main problem with hand winding full mag coils is space. It really needs to be done by machine to get it tight & neat enough, otherwise you'll find yourself running out of space before you've got enough copper on there to produce a good spark. (I attended a talk by a magneto restorer recently & learnt quite a bit, this is basically what I'm passing on here).

If you don't mind hiding a motorcycle coil under the mag somewhere, then have a look at my thread (I think Ray linked to it above, PM me if you like as I now have it all done in an easier to follow format elsewhere) & wind yourself a charge coil, you'll basically end up with the energy transfer system commonly used on bikes in the 60s & 70s. It's very reliable & very kind on your points.

Last night I completed removing the primary winding. There must be thousands of turns to that one, many layers of very fine wire, lots of turns per layer.
Anyway as well I did, the bottom layer was corroded right across its width, and obviously useless. Just green gunk.

The primary looks to have too few windings (as noted above, thanks Nutgone), so tonight I'll remove that- it looks to be a single layer of about 40 turns- and wind on a new winding putting perhaps a couple of hundred turns. Could even use a slightly smaller diameter wire I think. I didn't measure the primary but it looks nearly a mm dia.

I'll take some pix to chronicle the journey.

You'll need more than a couple of hundred turns for a normal magnet rotor magneto. Around 200 turns worked for a 6v coil on a flywheel mag, but that won't translate to a normal mag, flywheel mags give a hotter spark & they rotate a lot faster at starting speeds. The Lister D has a geared starter though, which will help a bit.

Don't worry about doing too many turns, it's practically impossible, I doubt you'll ever damage a car/motorcycle canister-type ignition coil.

I think 0.7 mm is about right

I can get them done for £65 including postage .

alot cheaper than other people and alot better IMO .

Winding isnt the problem as long you can stand winding all the tuns of wire , and its better if a shallac coating on outside . but i dont know how you go about winding the two windings .... do you go oposite ways ... and is there a insulator between them ...

Matt

braydh wrote: I think 0.7 mm is about right

Not sure what you meant here Ray. About right for what?

I measured the original primary winding wire diameter at 0.9mm, and the secondary at 0.07mm dia. (very fine)

I've started re-winding the coil to be a single winding, with a view to producing enough power to feed a second coil from a car that will produce the HT spark voltage.
I'll post that for info with pix as I go. Might be interesting to complement that very good thread started by someone on this same topic. (Thanks for pointing me to that whoever it was!)

Geoff

matt86 wrote:I can get them done for £65 including postage .

alot cheaper than other people and alot better IMO .

Winding isnt the problem as long you can stand winding all the tuns of wire , and its better if a shallac coating on outside . but i dont know how you go about winding the two windings .... do you go oposite ways ... and is there a insulator between them ...

Matt

No one uses shellac any more Matt, it's the reason these old mags are giving up. There are far better things available.

Winding mag coils is practically impossible to do by hand, unless you're prepared to bodge it. But with the right machinery & with lots of training & practise you could wind one in about 2.5hrs. That's with a proper coil winding machine, which would cost a few grand.

Ok, here's the promised pictures.

I took the coil and stripped the old windings off. The secondary (on top) was hundreds of turns per layer and about 15? layers (I didn't count).
This left the steel inner, with the formers edges on it.



I used wire that's 0.4mm diameter, from this coil of wire I had lying about in my shed.



Here's my winding setup. Its a toy lathe. I put the four jaw chuck on it, didn't mount the demountable motor (too fast), and now I have a winding unit.



I put the spool of wire on a screwdriver shaft in the vice.



Putting a few layers on, I put insulation in like this..



Eventually I had a lot on there, didn't count, but estimated 500 turns.



So I sealed it up with self amalgamating tape, and set it in the magneto body.



Here's an oscilloscope trace of the output of the coil alone, no capacitor, no points.

In this trace I have a 10x attenuator in the probe, so the 1V per division is actually 10V. So here I recorded 13.2V

I decided this wasn;t enough, so put another 500 turns on. It ended up like this..



Here's the measurement.

In this case I have the 10x attenuator in line still, and using a 2V/division scale, so the indicated peak of 6.8V is actually x 20, so thats about 130V.

Assembling it all it looks like this.


So, now to make the lid fit, find a way to feed the voltage out, and lead that to a car ignition coil. That should give me some ignition spark I reckon.
Its enough to see a tiny arc on the points anyway!! That might be a problem, but I'm hoping the voltage will drop with a bit of load on it.
We'll see.

I see you've put one end to earth, but I don't see why you've put the other wire to the condenser? It should go to the + terminal on the coil, then a wire from the - coil terminal back to the points/condenser.

You might have gone a bit over-kill on the turns, as it only needs to be a few volts AC to pulse through the (normally DC) car type coil, but you'll be guaranteed a good spark at starting speeds I guess, but it won't be quite so kind to your points (although should still be kinder than if it were a normal mag set-up).

Also, it's worth soldering some flexible cable onto the coil ends & burying the connections under your outer insulation. The single stranded enamelled copper wire is very prone to work hardening & snapping with movement & vibration. If it were to snap off you know sod's law would dictate it will snap at a point where you'll have to uncover it all again to make a repair.

Sorry should have said for wire diameter but you have done a good job there am looking forward to seeing it all working .

I think I have too many turns and too small a diameter of wire on this first attempt.
I now have a car ignition coil, and in attempting to use the magneto as a generator to supply that coil, I'm not getting a spark on a spark plug.

So I measured the voltage across the ignition coil, in circuit, using an oscilloscope (so as not to load the circuit with the measuring device), and only get a couple of volts.

Thanks for the correction Nutgone about connections. I had just set it up for a picture, not thinking that my new circuit would be different.

So, I figured that the magneto coil that I'd rewound as a single coil, has too high a resistance, such that the current is insufficient.
To start with I took off the 500 or so extra turns I'd added, and tried again. Some improvement, but still only about 4V across the ignition coil.

Next step is to take the winding off completely and start again with fewer turns and heavier wire to reduce the resistance (impedance).
I'll see if I have some 1mm dia wire or thereabouts, similar weight to the original primary winding, and wind as many turns as fits (probably 500 I'd guess), and see how that works.

More pix as I do that later, maybe over the weekend?

It's good to see some of you know what your doing and talking about

Great work Geoff, hope you can sort it out.

Stu.

Don't worry too much about what voltage you are getting across the coil. Someone else who did this measured his voltage on a scope & found it was only a few volts (this was while the engine was running, so it was working). It's the fact it's an AC pulse that gives you your spark, as the car type coil usually works on a DC system.

But, you could be right, it may be the wire gauge. I think you might be better off with something around the 20swg size (I think that's about 1mm in diameter).

If you want a chart with all the wire sizes (swg & awg) & what they all correspond to in millimetres I know where there is a good one. It's on an ebook in PDF format, but I have the link. Best thing to do is save it the first time you go to that page, otherwise every time you click on the link you are downloading the complete PDF each time, which uses up broadband (although it doesn't use much, but best not to keep clicking on it every 5 minutes). Here's the link, it should be on page 1....

http://www.free-energy-info.com/Appendix1.pdf

Thinking about it, it probably is to do with the wire gauge, so it's really a case of current rather than volts. You really don't need much voltage to make this work. I put this "home made energy transfer" system up on a couple of other forums (including an American based one) & invited anyone interested to PM me, well I got quite a few PMs saying they had measured voltage & were only getting a few volts, I had to tell them to basically ignore their voltage readings as they were largely unimportant, & just proceed. As far as I know they were all successful. With mine I even put the output through a rectifier & tried to measure it as a DC voltage, but still it was only around 1 volt at starting speeds (that's a rope starter flywheel mag). I was using a 6v coil though, which probably helps a bit.

Matt,

I think you're right about voltage, but its was the relative voltage I was really thinking about, (but didn't explain well in the post). If the voltage was high without load, then very much lower under load (load being the ignition coil), then the resistance might be too high, and that in turn means the current probably not flowing. All that pointed (in my eyes) to too small a wire gauge.
I chose that size mostly thinking about number of turns, in hindsight was too quick to use it. Also prominent but unacknowledged in my thinking was that the spools of that size wire were full (not going to run out), could be freely unwound (no tangle), and were on the shelf (free).

I'll have a rake about in my copper wire box and see what I've got. Must be something better about.

That's the trouble with copper these days, it's expensive.

& it's heavy, so any postage is expensive too.

I need to get some more in myself. I usually use Brocotts eBay shop, they're pretty good, but still it ain't cheap.

you need to rectify your AC output to DC, stick something like a 1N4007 on your output to form a half wave rectifier (if your feeling plush go for a full wave bridge)
your coil then needs to be as the battery is here:

I made that diagram for this thread HERE

if you don't rectify the supply the field will not build in the coil, after all its the collapse of the field you rely on to give you a nice fat spark.
Andy

But you don't need to rectify it for this purpose Andy. As the magneto produces the AC pulse at exactly the right time. I only rectified it to get an accurate reading on a multimeter. This is very much like (actually the same as) the "Energy Transfer" system used on bikes & small engines back in the 60s & 70s. I've certainly not rectified mine & Paul found he didn't need rectification on his.

It is still wired up as per your diagram, where the hand wound coil in the magneto replaces the battery in your diagram. No need for rectification though, especially as we're dealing with very small voltages, & a diode will only lose 0.7v of that.

nutgone wrote:But you don't need to rectify it for this purpose Andy. As the magneto produces the AC pulse at exactly the right time. I only rectified it to get an accurate reading on a multimeter. This is very much like (actually the same as) the "Energy Transfer" system used on bikes & small engines back in the 60s & 70s. I've certainly not rectified mine & Paul found he didn't need rectification on his.

It is still wired up as per your diagram, where the hand wound coil in the magneto replaces the battery in your diagram. No need for rectification though, especially as we're dealing with very small voltages, & a diode will only lose 0.7v of that.

mmmm ok, does depend on the diode though,
I do wonder though if your going to the lengths of stripping down a coil, knowing it has a primary and secondary winding, why not replicate it, ok so you wont know the exact number of turns for the secondary winding, but using the same gauge wire you can get it pretty close being careful loading it on evenly, and my estimation is the exact number is not highly critical, the primary winding would be easier being heavier gauge and far fewer turns.
Just a thought

I've just answered my question
http://www.brufnut.de/WORKSHOP/LUCAS/lucas.htm

It's a hell of a job for a novice Andy, especially without a coil winder. Each layer must have some form of insulation in there & ideally the whole thing needs to be soaked in some kind of insulating varnish, right to the centre, especially with rotating coil magnetos.

I've seen how the pro's do it, & yes you could try & do it by hand, but I reckon even the most patient among us would end up throwing it through the shed window.

Winding an energy transfer coil takes less than an hour. It's thicker gauge wire & a lot less turns.

I do intend to start re-winding magneto coils at some stage though, but not just me. There's another forum member who lives in my area & we're talking about it & between us we are gathering knowledge & equipment. Obviously if/when it comes to anything we'll keep the forum up to speed. I think the intention is to mainly sort our own stuff out & help a few mates out at the same time, moving slowly like, just a sideline to compliment the hobby. Well, at least that's what I think, I can't really talk for others.

blackvanman wrote:I've just answered my question
http://www.brufnut.de/WORKSHOP/LUCAS/lucas.htm

That's a good link but I notice he doesn't show you how he stripped down that armature, he leaves out quite a lot of detail (for which I can't blame him, I mean how far does one go?)

Also, he shouldn't be using polyester in between the layers of the HT coil. If he's satisfied that his vacuum impregnating process is up to scratch he should be using something absorbent. The polyester is plastic based. You need the impregnating lacquer to penetrate right to the centre, especially with a rotating coil mag, otherwise things will move when it's spinning. Of course you could paint on a lacquer at each layer as you load it, but I'm told if you did you would get in a right mess (I still think it could be done that way, but would require a good steady hand & lots of patience).