More Ignition Experiments

In the light of recent questions on coil ignition for engines with knackered magneto coils, & Paul reminding us of his experiments with his Villiers engine(s) I have decided to have a go at this with my Tarpen.

Back in September, at the last rally of the season, my original Tarpen generating set decided to stop running. I felt it was an ignition problem, even though we still saw a spark at the plug the engine still wouldn't run.

After dismantling it last week I discovered the coil on the magneto was at fault. The coil was slightly loose on it's laminated metal centre, I had no idea at the time of restoring it, but these coils are supposed to be wedged in. I think it was probably the vibration which got to this one, as it seems the high tension side of the coil has lost it's earth connection.

I can't repair it, & can't afford a rewind, also I can't get another flywheel mag coil with a big enough centre hole, so I have emailed a bloke in America about sourcing a suitable replacement. I remain sceptical, as I've yet to hear back.

So, i thought I would have a go at something Paul (forum member pauldg) tried on his Villiers engine. This is where you wind a coil around the original coil centre (or a suitable replacement) which uses the magnets in the flywheel magneto to generate a small voltage, which should, in theory, be enough to run a normal car or motorcycle ignition coil.

I had a dig around & found a drum end of some 20swg enamelled copper wire (sometimes called "Magnet Wire" it is used to wind coils). I also have some proper coil winding tape, which is a bit like insulation tape but not made from PVC, as PVC isn't an effective insulator with high frequency electronics, not that this should matter in this instance, I'm sure regular insulation tape would suffice, in fact I'm sure even sellotape or masking tape would be just fine.

I've also dug out some motorcycle coils....



The one on the right is a 12v coil from an Indian built Royal Enfield 500 Bullet, the one on the left is a generic 6v coil from a vintage motorbike. I'm told the 6v one doesn't work, but I've taken some readings & it seems fine. Maybe it's a 12v one & that's why it wouldn't work on my dad's old Velocette GTP??? I will post up my readings from both coils later.

Here's what I've got to deal with (ignore my new cordless Dremmel from Lidl)....



The 2 coils & the magneto back plate, complete with coil centre. as you can see the condenser is nice & shiny. I've tested it for both capacitance value & insulation resistance (if you're unsure about a condenser & don't have a megger tester (insulation resistance tester) to test it with, my advice is to fit another & see if that works any better)....



The points have been polished with a fine rubber grind stone & they meet very well, so that's all OK.

I decided to make up a small coil centre piece from card & cover it inside & out with the special insulating tape. Then I started to wind a coil....





A word of advice, before you start winding a coil, make sure you have a piece of tape ready to secure it when it comes to an end, as most times if you put it down & let go of it it can happily unwind itself!

Notice in the pictures I have secured the end of the wire by wrapping it round something. when I was finished & had taped down the other end I went back to this beginning, un-wound it from it's securing place & tidied it all up, so always leave more than you think, as you may want to add a turn or two on this end, as I did....



So, there it is. i have done one layer, which contains about 29 turns. I think i will do at least one more layer, as I would like to finish near where I started, for ease of connections. Also, i don't know how many turns I will need or how much voltage it will produce. It's easier to remove a few turns than it is to add them on later, so I would rather have too many than not enough, so I may even go for four layers (about 100 turns).

I've got ideas about possibly rectifying the supply & maybe regulating it to keep a small pack of batteries charged for easier starting, but that may be a little bit out of my league. First of all I would like to get the engine running.

I would like to ask Paul, or anyone else interested, how many turns do you think I will need???

Also, will an over voltage wreck my coil? Should i perhaps think about incorporating a voltage regulating device? I know you can get very simple little chips with 3 terminals that do this, obviously it would probably need rectifying first. Perhaps I could even use a varistor (I doubt a gas discharge tube would work at these low voltages), to keep the voltage below a certain level & avoid any damage to the ignition coil???

But, there is no need to go to all these lengths. Basically you need no more than I already have here to get an engine running, just a coil centre, some winding wire (anything insulated will do) & an ignition coil from a car or motorbike. I will do the simplest method to get the engine running first, so you can all see just how easy it is (I hope), then I will hopefully go onto the more complicated things later.

Any thoughts?

dont know if this helps Matt but i think villiers coils have three layers maybe four and produces 6v but on testing these there were peaks in voltage i think i have one stripped if you need i can count turns

oh and nice little drill

braydh wrote:dont know if this helps Matt but i think villiers coils have three layers maybe four and produces 6v but on testing these there were peaks in voltage i think i have one stripped if you need i can count turns

oh and nice little drill

Yeah, I think I'm going to need quite a few more layers, especially as each layer has less turns than the last (another thing I learned from the magneto man's lecture the other night, especially with this type of coil, it keeps it neater to taper it slightly).

I've looked & found Paul's original thread where he first experimented with this stuff. It's on page 2 of this thread....

http://www.stationaryengineforum.net/t5208p15-when-will-i-learn

Looks like I will need a fair few more turns, which is a shame, as it makes my hands ache!

Well, to answer a couple of questions (I hope they can be classified as answers - I'm only playing with this myself...)

Rectification

There's no need to rectify the coil output, it does produce AC but it's the part of the cycle you are using that's important - the timing is such that the coil is 'charged' by the rising slope of the waveform which is interrupted by the points. Adding a rectifier will only reduce your available voltage at this point anyway.

Regulation

Again, no need to regulate the supply. An ignition coil is only rated for a voltage if there is a constant DC source - i.e. a battery. There is a good chance that the engine could sit not running with the points closed so the coil needs to be able to dissipate the voltage without overheating - when running you are dealing with EMF's in the kilovolts anyway so to put a regulator in would just likely destroy the regulator.

Number of turns

It is possible to work out exactly how many turns you need, but you need to know a lot of 'stuff' that just isn't practical to find out - wiithout some very specialised equipment anyway. I have been working with the theory of using roughly double the number of layers of LT windings found in the original two-part coil pack. This bit is very much 'suck it and see'. While having more turns will produce a higher voltage, I don't personally think it's possible to physically fit enough turns in to damage the external coil (I could well be wrong about that...) The voltage is also directly related to speed - more speed = higher voltage. At the sort of engine speeds we're dealing with here (<4000rpm usually) I really don't see a problem to wind on as much as you can fit. This might well end up using more wire than is strictly necessary, but the amount of wire here isn't going to break the bank...

As an aside to this, I have joined wire to add more turns without any problems. Just remove a portion of enamel and solder the ends together, side by side. I haven't seen a need to re-insulate it either...

I've seen with standard coil rewinds people mention inter-layer insulation - i.e. adding a layer of tape or card between each layer of windings. I don't think this required for an LT generator coil such as this, unless you are concerned about the quality of the enamel (or other) insulation. I've been using second hand wire from a 240v generator core and it's been fine - maybe running for a long time will show problems but none so far.


Oh, and hand cramp appears to be an occupational hazard with this too - I must come up with some sort of winder...........

Using the ouput as a charging source

I'm not sure... I haven't measured the available current but I don't know if it would be enough. I'm pretty sure you'd have to run the ignition coil off the batteries and in turn charge them from the magneto - I can't see the output being stable enough (what with being buggered around with by the points etc.) to supply an ignition coil and charge a battery. I'm going to have to look at this now


(p.s. The original coil should be tight on the core, but my JAP has the same system fitted and the coil is held in with small varnished wooden wedges which I believe to be original fitment - not that that helps much if the coil itself is dead, but maybe easier to wind your new coil on something like a square wooden former, then slip it on the iron core and wedge in place?)

Cheers Paul. I was thinking about just using this as an independent "lighting coil" affair, rectifying the output, regulating it & using this alone to charge a small pack of NiMH batteries which in turn run the coil, therefore just making this a charging coil. But the more I thought about it, the more I thought that the whole point of this exercise is to try & get away from using batteries at all! It's just over complicating things.

What about the diode on yours? Did you leave it in? I've got plenty of diodes, all different types, some very high voltage ones & some very fast acting ones as well.

Also, do we need to be careful how we stop this engine? I know it's not a good idea to just de-energise coils quickly, but I think this is more to do with DC coils. Is it going to be best to fit a stop switch which earths something out to avoid any large back EMF rupturing anything? (just a thought I had after someone giving me some tips on getting the Homelite to put out a voltage from it's dynamo by putting a battery across the shunt coils, I was warned not to quickly disconnect it, & I remember having to put a reverse biased diode across a MOSFET on one of my HV coil experiments a while back for similar purposes, like is sometimes done with relay coils in high frequency stuff, I think).

In the meantime I've been putting on a few more layers....



& I have now completed my coil. I have used up all the wire from the roll & I think I've got about 8 (+ a bit) layers, but I can't be absolutely sure on that. I ended up with this....



I then stripped the enamel from the ends & soldered on some proper flexible cable (the solid stuff will soon work harden & snap otherwise). i made the joints, covered them in heat shrink & wound them in their respective directions (gaining another few turns) until they met & were both of the more flexible wire. then I finished it off with more of the special tape....



Let it be known that I HATE the special tape! It's horrible stuff to work with & looks very untidy. The only reason I've been using it between layers is to hold the whole thing together. The trouble is this coil has no ends, like a bobbin or spool type coil, so the tape has been applied at the end of each layer simply to hold it all in place. If it were a proper magneto coil I wouldn't use tape anyway, i would use paper & cover it with varnish between layers, like they do with proper re-winds. But it's not a proper magneto, one of those would be practically impossible to wind by hand anyway, once you got onto the HT side!....



So, there it is, fastened onto the backplate. I'm guessing polarity is unimportant? But, just in case I don't get a nice pure sine wave I will leave both ends long enough, so if they need to be swapped over they can be.

This new coil does still come on & off the centre, it's wound on a card former. But it's quite tight on there & the connections are well protected, so I doubt I will wedge it. The other 2 Tarpens I restored had the coils wedged on by the 2 outer most laminations of the core being bent slightly to hold it in place, which is what I was going to do with this one, before I realised it was too late & the coil was buggered!

So, next I will have to rebuild the rest of the engine. It's still in bits, I just need to make up a couple of gaskets & piece it all back together, it's all cleaned up & ready to go, I just wasn't in any hurry & had the other Tarpen to finish first (which I still do, so there may now be a slight delay before this is picked up again).

I'm still anxious for any further input or ideas from anyone. Paul, any thoughts on my couple of points above (the diode & the stopping method). The more I think about it, the less I think it matters about stopping it, as you're not really rapidly de-energising the coil.

Just as an aside, what do you reckon on the idea of using this as a charging coil only, & running the ignition from a small battery pack? (More like a car or motorbike system). Might be a project for the future on a different engine maybe? I quite like the idea of adding my own charging coils into a flywheel mag, to charge a battery or just run some lights or something. When I was younger & found out that some Villiers motorbike flywheel mags had lighting coils I always wanted one for one of my stationary engines, my dad always said "What for?!!" & I said "Well, to run lights, of course!"

Right, I've been piecing this engine back together this evening. I made up a crank case gasket, fitted it. heated up the breaker cam & shrunk it back onto the crank shaft, replaced the magneto back plate, then made up a cylinder base gasket, put the piston & then the barrel back on, eventually followed by the flywheel....



I put a wire onto the points terminal, along with the condenser wire & fed that & the other 2 wires (from my coil) out through a small hole in the magneto backplate (the hole was already there, I didn't do any drilling)....



This way I have all my connections where I can get to them, so I shouldn't need to remove the flywheel again, as long as the coil has enough turns.

So I got my multimeter out & did some testing....



I rigged up a mains powered drill with a 3/8" square drive socket adaptor, followed by a 3/8" to 1/2" adapter, followed by a 1/2" whitworth socket. This would drive the nut on the end of the crank shaft....



I started by testing for AC volts, but I was getting little over 1v, which I thought was a little low. So I got this out....



A home made bridge rectifier I made some time ago. You see most multimeters don't read odd AC voltage very well, so I thought I would use this to turn the AC voltage into a DC voltage, but the readings were still very low, even with the drill going reasonably fast.

But I decided the voltage here was pretty unimportant. What we need is that quick kick of voltage, through the car coil at just the right time, to produce the spark. So I connected it all up with some HT lead & a spark plug....



I tried it with both coils, with much the same result from both of them. I eventually got both coils with some HT lead shoved in them....



This way I could try one, quickly change over some connections, then try another, or try things another way round. But basically I am getting a spark. It's a weak spark & requires quite a rate of revs to get it going, but the drill is a lot slower than the final engine running speed will be, so I may just see about getting it together & seeing if it'll run.

But, TBH I think it needs more turns on my coil inside the mag (the "Charge" coil as I call it for now). If I have the 8 & a bit layers I think I have, then I must have somewhere around 150 to 200 turns on the coil. the trouble is this coil has no spool ends, so it's getting thinner & thinner, each layer has less & less turns. I think what it really needs is to come off, come apart & be wound on a spool with ends which will fit on the centre bar.

But for now I just want to see if it runs. If it does then it's a very easy way to overcome knackered mag coils.

I have actually got 2 proper magnetos, both rotating magnet types, on the bench. One is a WICO A type, the other is a Lucas SR1. Both have knackered coils. I would like to see if this can be done on these types of magnetos. My guess is it will work, but as they generally rotate slower than flywheel mags I reckon it would need a lot more turns, probably something in the order of 500+. Which isn't difficult to achieve, but right now I've run out of enamelled copper wire & can't afford to buy any more. I will have a hunt round tomorrow, to see if I've got any I can "borrow" off anything else.

But for now I can confirm what Paul first said, this does actually give you a spark at the plug, & it's really easily done. What I feel I've done here is make it sound really difficult & complicated, but honestly it isn't, you don't need any special tools or expertise, just some enamelled copper wire & a car or motorbike ignition coil (I wouldn't personally recommend any other type of wire, especially any multi-stranded or flexible cables & plastic insulated wire is likely to take up too much room on the coil).

It will probably be a few days before I can see if it runs though, Ian's got the flywheel nut & starter rope dog over his place, & I will need those to get it going. Although I do have another Tarpen here I could borrow the bits off, possibly.

Ok then, a couple more thoughts...

Stop switch

Put a normal on/off switch in parallel with the points - when it's in the 'run' position you want the switch open, close the swith to stop (effectively the same as holding the points shut). This means there is no possibility of erroneous EMF. The way a coil works is to have a supply interrupted (opening of the points) and the rapid breakdown of voltage induces HT in the secondary - if you just use a switch to 'disconnect' the coil there is a (slight) possibility of causing a mistimed spark at the plug - catch this wrong and it could try turning the engine backwards....

An ignition coil is nothing more than a transformer and they don't work with DC - it's the change in voltage that makes it work.

You mentioned about getting a decent sine wave too - don't worry about that, just so long as there's a voltage it will be in the right place because of the design of the flywheel magneto system. It matters not whether it's a clean sine or a 'steppy' pyramid shaped wave that's as dirty as a saturday night pavement.

Rectifier diode

Pretty pointless having one really, there has been no difference having one or not with the bits I've done - except for a slightly lower energy spark at low speeds...

If anyone wants, I'll sketch what is going on to (hopefully) demonstrate what I've been saying about the timing and the voltages...

Measured voltage

You're very unlikely to get a sensible measurement with a digital multimeter - use an analogue one (with a needle) or an oscilloscope if you really want to measure it. In any event - I have yet to achieve a spark that's visible in daylight yet the engine runs just fine. (Voltage being directly proportional to speed and all that.)

Charging

Running a single coil to charge a battery to run the ignition is usefull only as an exercise in curiosity. Apart from being quite an inefficient use of power the sole reason for using a battery on a car or bike is for lights and starting - most engines that need a very reliable ignition (aeronautical etc.) use magneto systems with no battery interaction. Make of that what you will.

Getting another coil in the housing on the other hand will give you a secondary power source for running stuff like lights, or charging a little battery etc. Again, I'd say it's only worth is experimentation but that's part of the fun.


The fact you're getting a visible (albeit weak) spark as it is now would suggest to me that it'll run just fine, if the rest of he engine is serviceable.

Thanks Paul, so basically we are earthing out the coil to stop the engine (as I suspected) & this one should run.

Ian came round this afternoon with the missing parts, I also ran it again on the drill to show him the spark & I can now tell the 6v coil is giving a better spark than the 12v coil. I doubt it would start if it was a handle start engine, but this is a rope start, so both Ian & myself believe this one will run.

I will put it together tonight & see about having a test run tomorrow. (Am quite excited now , if this runs I will move onto one of the magnetos sitting on my bench, if I could get this to work for a slower mag then I need never have a magneto-derrived non-running engine again )

You might be surprised at how little a spark is actually needed to get an engine to start - One of my 'test subjects' is an atco-villiers kick start cylinder mower. That starts first or second kick...

I see no reason why a self contained magneto wouldn't work - the principal is exactly the same. If you fill the space that was previously taken up by the LT and HT coils then it should be enough. It's not going to be running at less than half engine speed anyway, which is still way higher than you could get it spinning by hand.

Of course, you could always make a Low Tension booster transformer but that's for later.............

pauldg wrote:

Of course, you could always make a Low Tension booster transformer but that's for later.............

Or, you could go the other way & have a ballast resistor, wired through a "Start & Run" switch (if you found the coil was good for starting but too hot for running). I think this system is far less stressful to the coil than how they are designed to run, so they can probably cope with a little extra voltage.

Anyway, I put it all together last night & tidied up the wiring a little. I put a grommet in the magneto backplate & wrapped the wires together....



Then I set to the task of mounting the coil itself. I found some steel brackets I got from Lidl some time ago & modified a small right angle one to fit snugly with the curvature of the auto coil case. Then I wrapped some rubber self amalgamating tape round the coil, to protect it, then secured the bracket to the coil with a couple of jubilee clips....



Here's a couple more pics of it on the engine....





But I have positioned it on the back side of the engine, so when it's at a rally it won't be seen, here's the view of the front of the engine....



& here's the side of the engine which is normally on show when at a rally....





So it can't be seen at all.

I've put a spark plug on there & given it a pull with the rope, I can see a good blue spark there, even in daylight, so it should run. I'm just about to go out there now, put a little fuel into the float chamber & see if she will start. Fingers crossed.

Nuts I hope it works for you sorry I haven't a clue what you've been talking about for the rest of the thread

Only thing I'd say is to move the hose clips round so it tidies it up a bit more and have the screw part of the clips under the coil.

Good luck and I hope it starts and runs.

Stu.

Cheers Stu, what I really want is a pair of hose clips which are more the right size, I will do some more tidying up in that area though.

Well, it works!

I've just been out there, took some 2 stroke out of the Scott tank & filled up the float chamber. I pulled it over a few times, but nothing! Then I realised I'd left the drain plugs out of the bottom of the crank case ( ), I put them back in & she fired up 2nd pull & ran until the fuel in the float chamber ran out.

So, it looks like I can show this engine this season after all. One thing's for sure, I've saved myself a fair few quid . If/when a proper magneto coil does turn up I can fit it & remove all this quite easily. I'm going to have a little experiment with a Lucas SR1 coil next, which also fits inside the WICO A type magneto, but I need to get some more enamelled copper wire first. I've also been told there is another motorcycle coil in the workshop somewhere, it's a different type, not the canister type, but does the same job & is a 6 volt one as well (came off an old Honda I think). I just need to find it now.

I will do a video of this when the engine is back in the Tarpen & it's all back together, which will take a while now as the rest of it is over Ian's place & I can't really get over there very easily at the moment.

Great news shame you lost me with the technical electic stuff but you may be able to help others with ther same problems.
Glad to hear you managed to get out and try it, we are having another snow storm and about an inch has come down in about 15minutes and there saying anything up to 7 inches are forecast. Bloody fed up with the stuff now only 1 day in the last 7 days it hasn't snowed.

Stu.

Our snow was all over in a day down here. I don't like the stuff myself, but I wouldn't mind a bit more of it, as it keeps people away! (I'm a grumpy so&so who likes my peace & quiet. As long as I can get out to the workshop).

Well, I couldn't resist it, I had to have a play with the old Lucas SR1 mag. As I was rather helpfully reminded by someone, I already had a coil of roughly the right wire to do some experiments with, as this mag has an intact primary coil. So, instead of cutting the old coil off this one, I just connected my auto coil up to the wire which used to go to the points.

Here's a few pics....

here's my basic set-up, with the mag clamped in the vice & the 12v coil on the stool beside the bench....







I had to run a separate earth wire for the plug....



But there was no need to drill the mag body, as there was already a hole where the stop switch used to go....



So, I set it all up as before, once again using a known good condenser. I ran it with the drill & got sparks!

I needed to wind quite fast, so I reckon, even with a 6v coil, it would still need more turns of copper in the coil, but it's good to know it works.

Next step is to get some more enamelled copper winding wire & wind a bigger coil. But so far I would say that's a success.

I also ran the Tarpen engine up a couple more times, it starts & seems to run OK, although I think the timing might need some adjustment, but it's difficult to tell, as I'm running it for just a few seconds each time & there's no exhaust, which 2 strokes don't like anyway. I will know better when it's back with the rest of the Tarpen.

Nuts I'm going to have a go at doing this on the villiers marvel engine, the coil is already stripped of the wire. might have enough space, would it be better to use thinner wire if got limited space?

remind me again what is the tape I need called? and what thickness wire would go for?

let me get this right for the circuit, from the points you got an earth then a live feed that go to one side of the charging coil? then the other would go to the + on the auto coil, then would the - go to ground? if I got that right it seems doable.

I will get some pictures up of the engine with coil etc and see what you think

Matt

Matt, wind the coil, as described before, one end goes to a good earth, the other end goes to the + terminal on the auto coil.
Take a wire from the - terminal of the auto coil & feed this to the points, this goes on the same points terminal as the condenser, so could even go to the condenser if easier (this wire is probably already there).
Then it's just the HT lead to the plug

I used enamelled copper wire from Brocott's, they sell on eBay. It's called "Enamelled Copper Wire" (sometimes called "Magnet Wire") & mine was size 20swg, but anything up to about 26swg will do (that's about 0.5mm diameter). This wire is generally sold by weight, I'm not sure if a 100g roll would do, it may well be enough with the thinner ones (25swg & 26swg). A quick search has discovered a 250g roll of 22swg here....

http://www.ebay.co.uk/itm/250G-ENAMMELED-COPPER-WINDING-WIRE-MAGNET-WIRE-22-AWG-/181066932443?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2a286e20db

A word of advice is to use some proper flexible cable to make your connections, just use an old bit of flex off something with the outer covering stripped off, but try not to use single core wires where there will be any movement. So, like I did, at the ends of your coil scrape off the enamel coating from the winding wire (just carefully scrape it off with a stanley knife or even some emery cloth) then solder your flexible cable onto that & wrap the whole thing in tape so the single core wire is completely covered, hidden & not moving. The trouble with single core wire is it's not meant to flex. Over time it can work harden & will snap.

The tape isn't that important, but if you want some I will find a link....

http://www.ebay.co.uk/itm/130-C-THERMAL-ARMATURE-WINDING-ADHESIVE-TAPE-12MM-x-66M-/370742896666?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item5651ffa81a

That's the thinner (12mm) one, but is probably easier to deal with. I used the 25mm one, but that's because it's all I had & was originally bought for much bigger coils.

The neater the wire on the coil is, the better. Try not to cross it over, wrap it nice & snug together, pull reasonably tight, but not so as to damage the wire or it's enamel coating.

I tend to count the turns on one layer, then just keep a count of the layers. You'll want about 250 turns, possibly more for a proper 12v coil, but you shouldn't need more than, say, 350, any more than that would probably be excessive.

When you've made the coil & soldered on your flexible cable ends, keep these flex ends reasonably long, as you may need to swap them over & see which way round gives the best spark. I doubt it will make any difference, but it could. Remember, one is earth, the other is the + supply to the auto coil, so make them both long enough to stretch to the auto coil, try both ways, see which is best, then trim up & make neat.

It's easy stuff really, just very basic soldering, & some coil winding (which will make your hands ache, so always have a few bits of the sticky tape cut off ready. If you need to let go of it, tape it up first, then it shouldn't unwind itself). You don't have to know exactly how it works, & sometimes it's better not to try to think about it, just be happy it does.

Good luck & let us know how you get on. Any problems come back here.

Oh yes, if that coil centre is bare metal & has corners, you may want to wrap a layer of thin card around it first, then start your coil winding on top of that. Metal corners & edges can damage the enamel coating on the winding wire. I just used a bit of cereal box cut to size & taped on. Only needs one layer though.

Go for it Matt, I want to see if someone with limited electrical skills can do the same as Nuts.

Stu.

Well, hopefully those instructions there should be easy enough to follow, but if they're not then just come back for more.

Next time I wind a coil I will take a few more pics, & try to do a step-by-step.

I think he'll do it though, I've got faith in him, as I'm sure we all have.

Good to see my idea works for someone else ***see below***

Also - just like to take the opportunity to say to nuts about the SR1 - told you so Something to try before adding more wire is to compare the spark produced with a known good unit at the same speed, you might just be a little surprised...

As for coil winding - neater is better in that it looks nicer and you get more turns into the space, but random winding is identical electrically so don't worry too much about neatness if you don't want to... 250 turns is a good starting point, but more won't hurt. The rating of the coil is for a constant voltage (i.e. a battery source) and if you work out the average voltage from this sytem you're likely going to be well under a volt at normal running speed.

Taping between layers only has the advantage of allowing you to stop to rest your hands, if it was an HT coil being wound you may benefit from the extra insulation but on the LT it's not essential. If you want to have something to hold it in place to rest, normal pvc insulation tape (or plain old selotape) will work just as well.

As nuts said, if the former/core you are using has any corners or sharp bits at all - cut up a cornflake packet and put that on first. If you don't though and it compromises the enamel insulation the absolute worst that'll happen is you'll electrically lose the first layer. It's not going to blow up or anything.

Cheers Paul.

& I would like to take this opportunity to say a big thank you to Paul. After all it was his idea first. I did remember it from when he first posted it & have thought about it quite a lot since then, but for some reason it didn't come straight to mind when I first discovered what was wrong with the Tarpen. It's not like I've even done anything to his original idea, that's the beauty of it, it just works. (although I do have plans to do some more experiments with lighting coils & possible battery charging).

In my mind this is just such a simple idea, I understand if you're not into electronics at all then it might look a bit difficult, but electrically it is very simple. It's always the simple ideas which are the best though, isn't it? It just needed someone to think of it in the first place, then have a go at putting it to work.

So thanks Paul, your tinkering has saved my Tarpen from early retirement this season. I now fully intend to rally it this year, just to prove to myself (& others) that this is a reliable & long lasting solution for knackered mags & a cheap alternative to expensive rewinds.

Looking on eBay you can buy standard car type 12v coils for as little as £10 including P&P, & 6v classic motorbike style canister coils (like the one I've used) for just a few quid more. A roll of 22swg enamelled copper wire isn't ever so cheap, but certainly less than a tenner delivered for 250g, which should wind a couple of coils. As Paul says, the winding tape I used really isn't necessary (although it withstands much higher temperatures than other insulating tapes), so for around £20 you could have the complete solution, even less if you take the bits from something else, this one cost me nothing.

As for insulating between layers, no it's not necessary with this. But at the lecture I attended the other day by a local magneto rebuilding specialist I found out that you must insulate between layers on a high tension coil, they use paper, which then gets soaked in a special insulating varnish by a vacuum encapsulation process. But that's nothing to do with this method, I just thought I'd pass on a little bit of what I'd learned at the lecture. It was very informative & these blokes do insulate between layers on the LT coil as well, but I can't remember why right now .

stationary stu wrote:Go for it Matt, I want to see if someone with limited electrical skills can do the same as Nuts.

Stu.

excuse me i would say i have a bit of electrical knowledge but is basic 12v wiring that i have self taught . so not a complete idiot

I will order some and give it a go .

Thanks nuts that makes sense , could i not put a layer of tape on the coil center pole instead of card ?

Matt

Think I would go for card, but you could use tape, preferably use a few layers though, not just one. Anything to soften the corners a bit, that's all. This enamelled copper wire is quite susceptible. You see it's the coating of enamel (just a thin coat of varnish) which acts as the insulator, whereas normal cables have a nice thick layer of plastic to protect them, this stuff just has that layer of varnish.

It's pretty tough stuff though. I used a card centre with a layer of the tape to secure it, but I suppose you could use a few layers of insulation tape or something.

Cheers Matt

I have ordered some wire and some tape now , i will have a go once it gets here and once its wound anb back in i can figure out what voltage coil i need 6v or 12 v .

Matt

here you go lads i was looking for ignitor videos on utube but i found this on the way

bit of use full or usless info depends what you do or dont need to know
will defo help matt me thinks with the marvil engine rewiring job
kev