OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Wipac Magister Condenser Discharge Ignition System

I just looked up the wipac magister and it looks like old 2 stroke boat motors used them too. Hope this helps other ppl

Hi Michael, if you read the whole thread, you will see that a lot of people have been researching this mysterious "Magister" over quite a long period. We are aware that it was used on motorcycles, boats, stationary engines and of course Scott Bonnar rotary mowers. We now know how it works and have a schematic (circuit diagram) posted in this thread.
I am just waiting to give Jeffrey the one I have here.

This year I've bought two Scott Bonnar reel mowers on ebay, a Supercut and a Model 43, both with 155cc Scott Bonnar engines and both from the early 1960s. I need a couple of fuctioning Magister Capacitator Discharge Units for these mowers. I tried three old units and none were any good. A friend has the technical background and interest to attempt to build some units. I've attached a letter which adds a little to the great information obtained by a Forum member from Motor Cycle 1963. I've also attached photos of the mowers. I'll let you know how we go with this.
Regards
Grant

Hi Grant, I have merged your post with the original Wipac Magister Condenser Discharge Ignition System thread to keep the archive current and up to date.

Also, you will find the bulk of the well written post by grumpy (post 36972 Page 3 of this topic) has been quoted by your friend in the letter to you and posted above. It is great to see that the OutdoorKing forum is helping people by providing useful information, to help with their projects.

The sad part of Magister saga is that there are no values of the components contained inside this secretive beasty!
Hopefully grumpy might have some ideas for us.

Darryl,
Thanks for reopening the Magister thread. I read Grumpy's post quoted in Ron's letter and remember being impressed by the level of theoretical understanding. However, I didn't recognise that the quote in the letter had come from Grumpy's Outdoorking post. I'd apparently forgotten what the post actually told me! I've reread Grumpy's posts and see that he has given some advice about determining condenser and rectifier values. I would appreciate any further thoughts Grumpy may have on the Magister project.
Regards,
Grant

Hi Grant, it should be possible to duplicate the Magister fairly easily by experimenting a bit. I take it the objective is to come up with a device that has approximately the same component values and the same performance as the Magister, rather than trying to make it better than it was.

If we can duplicate the generator part of the Magister (the original "feed coil" inside the flywheel, and the flywheel itself) on a device driven by an electric motor, that will determine how much electrical energy we have available, and at what voltage. The rectifier that follows would be simply a silicon diode with a Peak Inverse Voltage rating of at least 1000 Volts and a current rating of say 1 amp (vastly more than is required). That kind of diode is readily available in the nearest electronic components shop for a few cents. A condenser (capacitor) is then required, and it must have a voltage rating high enough to withstand the voltage the feed coil supplies, whatever that turns out to be. I would guess that the voltage will most likely be in the vicinity of 300 Volts, but we will not know that accurately until the motorised device is available to carry out a test with an actual flywheel and feed coil. Because it is tricky to measure the voltage directly from the coil (it will be a series of very short pulses, relatively widely spaced), I suggest measuring the rectified voltage across the capacitor. The size of capacitor is not important at this initial stage, and 300 Volt capacitors are uncommon now that vacuum tubes (traditionally called "valves") have gone out of fashion, so it would be a matter of seeing what is available from the shops. I suspect two or three lower-voltage capacitors will have to be used in series.

When the experimental program reaches the point of telling us that voltage, it will be time to move on to the "real" test stage with a coil and spark plug connected to the capacitor. At that point, for early experiments it might be wise to use a very small high voltage DC power supply instead of the real feed coil, to guard against damaging a rare and relatively fragile item.

That is a short overview of the way I think this project could proceed. Of course I'm happy to discuss it in detail along the way.

As usual grumpy, a clear, concise and well written post mate. This will give Grant a plan of attack and the results will be invaluable for this archive. Well done mate.

Hello, are you going to make a coil to produce a certain voltage? (because they are not available)?

Magnetude of induced e.m.f. or voltage = number of turns x the change in flux divided by the change in time.

If you can come up with some values, to plug into this formula.
#Number of turns can be wound.
The flux produced by the magnet, I beleive it is horse shoe magnet embedded in the flywheel.
(Not sure of the amount in webers)
#Change in time? I guess if engine in rotating at 3000rpm, you could work that out.

Just looked up in text book, with just one diode that is called a single phase half wave rectifier.
As Grumpy said, it is choppy dc, diode blocks the negative half cycle of the ac waveform produced.

Voltage across the load coil,(primary coil) would be, 0.45 x ac Voltage produced by your supply coil.

Mark, the coils, though rare, are not nearly as rare as working Magister modules. I suspect Grant will be able to put his hands on a coil to find out its characteristics experimentally - but they are too rare to risk damaging by putting one into an experimental ignition circuit. By connecting the coil only to a diode and a fairly small high voltage capacitor, we can learn what its output voltage is. Later, Grant might be able to physically measure a coil. When we know the dimensions of the wire winding (outside dimensions less core size) and the wire diameter, we can estimate the number of turns so that new coils could be wound. Then a new coil with the same characteristics as an original one, could be used in the actual ignition circuit. This minimises the risk of damaging rare items.

Of course once a working ignition system has been produced and tested, so we know it isn't a coil-killer, it might be feasible to run it from an original coil instead of a reproduction one. The aim here is to duplicate the Magister as far as possible rather than parallel-engineer an equivalent item. Unfortunately there isn't all that much chance of making a physically-accurate reproduction of the module itself, because it is assembled in a specially-designed chunk of Bakelite and encapsulated in epoxy. I suspect we can fairly easily produce a device that performs like a Magister but is actually built in a small tin box rather than a Bakelite housing that looks like a WW2 earphone. Once that is accomplished and the design information posted, somebody may or may not start turning up pieces of Bakelite and trying to make a real one - or a whole batch of real ones, to get a lot of Magister-equipped engines back into operation.

Thanks for your technical input which will help us refine the job. Ron made up the trial Capacitor Discharge Unit shown in the photos using items from his shed. The engine pictured runs well with the unit and ticks over very slowly when idling. However, the spark is not impressive.
You can identify the main items: the coil is from I think a Suffolk 4 stroke with 3 leads from the coil, the condenser [capacitor] is a .22uf normally used in small engines and also a diode [rectifier].
These 3 items are wired up as in the diagram and connected to the original 3 leads coming from the flywheel unit: feed coil, points and earth.
The next step is to assemble a tidy looking unit contained in a plastic box.

Thanks for that progress report, Grant. So you are using the original Magister feed coil? Can you measure and report the voltage across the condenser when the engine is running? Is the 0.22 microfarad condenser a standard Kettering ignition condenser?

Ron's Capacitor Discharge Induction set-up uses the original Magister feed coil and points, and the condenser we used in the external unit is a standard Kettering type. It would be interesting to see a voltage measure across the condenser and I'll see what I can get. Presumably the high voltage pulse through the coil is "stored" in the condenser and this part should be critical for the unit to work effectively and to last. Regarding the high apparent failure rate of the external units, it is possibile that in miniaturising the original unit, the coil itself was too small or fragile for the job.
Regards,
Grant.

G'day Grant,
looking at your ignition diagram, the capacitor would have to be polarised, i.e. have a positive terminal, as it is applied to rectified dc voltage.

I will let you know, this the first time I have been exposed to this set up with a feed coil.

The normal mower set up, the capacitior is applied to ac voltage, so would not be a polarised type.

Just something I noticed.

It will not be an electrolytic capacitor Mark. The Magister is a sort of el cheapo Capacitive Discharge Ignition - the capacitor is the hardest working component in the system, and it experiences wild voltage swings and high currents during each spark event. It may or may not actually have reverse voltage applied, but it covers a wide voltage range. Normally the capacitor is an encapsulated plastic type.

Note also that CDI capacitors typically run at 300 Volts, and very small 300 V electrolytic capacitors are not a common component. This is not the reason electrolytics aren't used (they are filtering capacitors, unsuited to complete discharge and recharge 400 times per second, in the case of a CDI on a V8 at 6,000 rpm) but it would be a problem even if this type of capacitor were otherwise suitable.

Hi to all,
Well yesterday, a milestone was reached when the Wipac Magister was finally handed over to Blumbly for his Model 35 Scott Bonnar rotary. Jeffrey came over to Enoggera in Brisbane to collect it and finally meet in person.
This has been a good adventure for us all, first finding one, (many thanks to Grant (willing worker) )and then get it to Wagga and thence to Brisbane.
to Jeffrey, now on to the restore mate!

G'day folks,
Substantial new info located, so I'll reopen this thread to add it.

The notion to look in patent literature, for info on this system, occurred to me recently. It seemed to me, that it was innovative enough that it might have been worth patenting.
And it had been...

So this looks like the right thread for this information. The diagrams and info supplied by previous posters here has been invaluable, in selecting the most relevant patents.



This is the circuit diagram from US Patent 3037148, class 'Ignition Systems for Internal Combustion Engines', filed 28 Dec 1959, granted May 1962.
Invented by George Gayler, and assigned to Wipac Development Ltd.

The major components here are :
11. Flywheel
12. Feed Coil stator
13. Flywheel magnet
14. Feed Coil ~ 4-5,000 turns
15. Rectifier diode
16. Condenser/capacitor, 0.2 microfarad
17. Primary winding of 18
18. Voltage transformer coil, 70:1 turns ratio
19. Contact points
20. Points cam
21. Spark plug
22. Secondary winding of 18

The three Magister module low tension wires are connections from the feed coil 14 [to rectifier 15], points 19 [to the primary of the transformer coil 17], and chassis earth. This isn't shown very clearly in the circuit diagram as drawn, though. The next patent listed here, 3175122, does a better job of showing 'modular' construction.

Note that the transformer coil shown here is wired a bit differently ['autotransformer' configuration] to the production Magister in grumpy's earlier post, but the patent covers both variants. Production 'Magister' ignitions would very likely have differed a bit in construction detail from the patent examples; these aren't rigid specs. Production units would have been optimised for the mass production processes in use, and the situation they were to be used in.

The essential bits from this patent, summarised:

Operation: The capacitor is charged with the contact points open. When the points close, the capacitor discharges through the primary winding of the transformer coil, inducing a high voltage in the secondary winding and causing a discharge across the electrode gap of the spark plug.

The Feed Coil - details for two examples are given:
Type 1 was 5,000 turns of 36SWG aluminium wire. This generated increasing voltage to a peak of 250V at 2,000rpm, then declining to 225V at 3,000rpm.

Type 2 was 4,000 turns of 34SWG copper wire. This also generated 250V at 2,000rpm, but then kept on increasing, to 325V at 3,000rpm.

The transformer coil - specification of 70:1 turns ratio, and inductance of 20 microhenries measured across the primary winding.

---------------------------

Gayler, and a Reginald Penn as coinventor, filed another patent in this class on the same date, which covers operation of this ignition circuit, and several variants of it, from any AC current source; US Patent 3175122, granted March 1965. The low voltage alternator variants had two transformer coils.

--------------------------------------------------

The construction of the transformer coil is most probably along the lines of yet another patent, also filed on 28th Dec 1959, but not granted until August 1965. Inventor was Reginald Penn, US Patent 3202950, class 'Step-Up Voltage Transformer having High Tension Lead'.

This describes a very compact cylindrical transformer, wound on an insulating tubular former with a ferrite core, and the primary winding wound over the secondary.

In the patent, the 'working example' dimensions of the former tube are given as 0.75" long, 0.13" ID, 0.15" OD. Over this is wound the 47SWG enamelled copper wire secondary; described as one layer of three turns plus 15 layers of 193 turns, with paper insulation between layers. Then the primary winding, of 33 turns of 36SWG wire. This gives a turns ratio of ~88:1.
Again this was a 'concept' example, and not necessarily exactly the same as the production units. But it does look a very good match dimensionally for the known Magister examples.

There was also an article titled 'Magister Ignition system' in the UK 'Automobile Engineer' journal, vol 51 p240 (1961), if anyone can find that one.

Perfect....Thank you gadge,provided the trans coil is obtainable this should be fairly easy.
I dont need to make the feed coil since its already there and looks to be example 2 since mine is copper.
Ill show this to my boy and see what he thinks...if the coil is small enough i may even be able to reuse the original casing and reseal it

Thankyou for your efforts...Outstanding!

Hi all,

I'm not up with the theory on the Magister system or, indeed, that thing 'electricity'.
I'm glad there appears to be a possible solution for failing or failed units.

From a historical point of view, this is one of the curiosities.
I would particularly like to thank Moderator Gadge for that extraordinary research
and summary of the issues, and I hope Blue finds a suitable solution.

All very commendable.
---------------------------------------
JACK.

Thanks Gadge, that has validated the interpretation we had of the Magister (that it is simply a crude capacitive discharge ignition system, with a very small charge capacity and therefore a very small capacitor). More importantly, it has confirmed that it uses a typical charge voltage (about 300 Volts) and has given component values and coil-winding data. There seems no obstacle now to anyone with sufficient enthusiasm, repairing or restoring Magister systems.

I'm a bit doubtful about the wisdom of having used aluminium wire on the first version of the feed coil, partly because it is about three times the bulk of copper for the same conductivity level, and partly because unless it is high purity, it is difficult to protect from corrosion over the long term. However from the restorer's point of view, if the feed coil armature has room for aluminium (as, it seems, it must), there should be scads of room to rewind it in copper.

Personally I'd still like to know more about the physical layout of the encapsulated parts in that bakelite "earphone" housing. It will also be interesting to see whether people find convenient ways to remove the epoxy or whateve that potting material is, without damaging the earphone housing.

Yes its epoxy resin and I heated the unit to get the components out. Casing is fine and ok to reuse,the components are not. My initial thought was an epoxy covering,unfortunately the Whole system is filled. The wires,switch contact and HT screw go in,then the components are fitted and soldered,then the whole unit is flooded with resin.
I can see no way possible for failure due to moisture as initially thought. Instead id be more inclined to say it was due to possible overheating.

anyways im gonna give it a go....Not a job id recomend as far as redoing the original,but ill try anything. I think the manufacture of a new unit by restorers may be a better proposition and could be integrated into the system neatly....