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

Hi All,

I have scanned the article and have attached it. Hopefully this helps to fill in some of the gaps in information about this interesting little magneto setup.

Cheers,

Sir_Chook

Thank you so much for the info, Sir Chook, we can hopefully know more about it and how it actually works...Well done mate! A very interesting article. Now all we need is the values and voltages.

Hi All, Thats an interesting little piece that coil and sorry to say I didnt locate it. It wouldnt be too hard to make a exact replica these days. As long as the right voltages come out and its identical on the outside job done. I just need a non working one to price it up. If there is enough people here interested I would take that on. Well done on the PDF Sir Chook.

Blumby you have done such a good job making me believe that this is a really rare collectable old mower,then you want to buy it

Here is a standard Kettering ignition circuit, as used in pretty much all spark ignition motor vehicles before electronic ignition took over:



Let's compare that with the Magister circuit:


In the Magister, the Feed Coil, Rectifier and Condenser do no more than create a DC voltage source for the coil. After that, the rest of the circuit is the same as the Kettering circuit, except there is no capacitor (condenser) across the points.

So, what advantage does the Magister have? It generates a DC supply that may be at a higher voltage than 12 Volts. However the Magister also has no capacitor across the points, and it only applies its DC voltage to the coil for an instant of time. The Kettering ignition system has that capacitor because it effectively converts the 12 Volt supply to 150 Volts at the moment the spark is developed. The Kettering system also magnetically "saturates" the iron core of the coil by maintaining current through the primary for a substantial period before the points open. When they open, the collapsing flux in the coil's iron core generates a "back EMF" of 150 Volts, and the coil turns the 150 Volts into perhaps 15,000 Volts. There is no saturation of the iron core with the Magister, and as a result the spark generated is of much shorter duration than with a Kettering system. Because of that it is a much lower energy spark - but it may have a very high intensity during its brief duration, depending on the DC voltage applied to the coil primary, and the coil's turns ratio.

The bottom line is that the Magister can fairly be described as a basic form of Capacitor Discharge Ignition system. CDI systems are notable for being able to fire fouled spark plugs. They are also notable for not being able to ignite lean mixtures, or mixtures diluted by exhaust gas due to poor scavenging, or deliberate Exhaust Gas Recirculation, due to the brief low-energy spark. Because port controlled 2 strokes usually have very poor scavenging at light load, I think it is unsurprising that the Magister system was not adopted by many engine manufacturers. However that does not mean that it was a crackpot idea: there was a lot of interest in CDI at about the time it was produced, and fouled spark plugs are a perennial problem with crankcase induction 2 strokes.

Hi Grumpy, Based on your description is there any point trying to make copies of the original or would it be better to hide a modern version in the same case? Got off the track of the original forum here but this is a very interesting little piece.

I don't think it is very practical to try to hide a standard modern CDI in such a small case, and in any case I think you'd have problems supplying it with smoothed 12 Volt power in sufficient quantity. You could reverse engineer the Magister itself - all that is required is experimenting with components, since the circuit is available.

If you have the behind-the-flywheel bits, which are difficult to make, the only requirement is to breadboard the parts that normally go in the round black module until they work. Just by spinning the flywheel, you'll find out what voltage is supplied by the feed coil. The diode was probably a feeble germanium item orginally, but an ordinary modern 1 Amp 1000 Volt silicon diode should be fine. The capacitor has to fit into the space ultimately, and this will determine its capacity, but you can find the required voltage rating by connecting your feed coil and diode to a high voltage-rating capacitor and measuring the steady-state voltage (typically 300 Volts for a CDI). That only leaves the ignition coil to fiddle with. Unfortunately tiny coils with a zillion turns on the secondary are a hassle to produce for experimenters, but once again, you would start off ignoring the size issue and testing to see what turns ratio is required (which depends in large part on what DC voltage you can develop on the capacitor). Many commercial CD units work with standard Kettering coils, which have a turns ratio of about 100:1 AFAIK. Once you know what works on the breadboard, you have to miniaturise, which requires ingenuity and cut-and-try techniques.

Interesting Grumpy. There is one for a rainy day and I do have all the parts mentioned in the shed right now for the bread board. Just need to unhook some of them from the Hydrogen Fuel Cell

Unfortunately, it does not explain the use of the brass strap fitting on the outside of the Magister unit....could it be a switch of some sort?

Why not ask willingworker (since he has one and mows the lawn with it regularly)? Incidentally, having this research split into two threads will be archivally unfortunate.

The brass strap on the Magister condenser discharge unit is an ignition switch, as you suspected.
Grant.

Thanks for that Grant....we now know how it all works...will see what we can do about the archive.....

Can you change the name from Scott Bonnar Query to something like Scott Bonner 19 Model 47 and Magister Coil??

Hi Plymouthbel, the problem is that the Magister issue lies across 2 threads, Blumbly's SB Model 35 and your SB Model 47. Both machines have the Magister in common.

What we have decided to do (which will make for a good archive) is to create a new thread using posts from both the previous topics for just the Magister discussion. This will be contained in an engine forum as it falls into that category, as an ignition system.

This will make it easier for anyone researching the Magister, as being buried in 2 different lawnmower threads would make it harder to find.

Hi to All, this thread is for discussion on the Wipac "Magister" condenser/capacitor discharge ignition system for 2 stroke engines. These units have been fitted to 2 Scott Bonnar rotary mowers that we know of; the SB Model 35 and Model 47.

Gleaning this information has not been easy, as worldwide very little seems to exist...but, with the help of our members, we now know how it works and have a circuit diagram of all components. Many thanks to all that have contributed to the archive.

Hi to All,
Well, we've finally come full circle...this thread was started by Jeffrey (Blumbly) referring to his Scott Bonnar Model 35 Rotary and his quest to find parts to complete his restoration; in particular, a Wipac "Magister".

Just recently, I was doing some SB research and talking to Grant (willingworker) in Adelaide and mentioned that I was anxious to find one of these mysterious little devils, for Jeffrey's Model 35 resto. Grant made some inquiries and found one for me. Many, many thanks to Grant!
It is missing the little brass strap and center brass screw, but the strap can easily fabricated from shim brass and the screw sourced easily as well.

It has made the journey to Wagga safely, and it is here to present to Jeffrey, when he heads this way, prior to his move north.
Now the quest begins to find a metal catcher for it!

Here's some pics....


A good result in the end!

That is excellent Deejay and willingworker, well done. A point of caution: be very careful finding a screw that actually fits that center thread. It might not only be Whitworth, which is interchangeable with UNC in all sizes except half inch (minor difference in thread angle, not usually necessary to worry about in low stress applications), but it could be BSF, or even BA, both of which are very rare these days. It seems unlikely to be either metric or one of the American threads, but anomalies do happen. The main point is that the right screw needs to be found, and it may well be something extremely unusual. Just finding a screw of the right diameter and screwing it in will simply ruin something rare, perhaps almost irreplaceable.

When the right screw is found, please post details here since it will be useful for the archive.

Thanks grumpy, yes mate, it is a great result.
More good news....the center hole in the middle of the "Magister" is not threaded...It is 3/16" in diameter and a clear hole right through. That makes it a bit easier.

Wow is all I can say I didn't think I would ever see one at all.Thanks to all who were involved,I can't thank you all enough.I do know that it will now be the first one to restore after the move.I don't know if we will be as lucky with finding the catcher.Maybe if I could get some details on one I maybe able to make one up.As far as the screws goes it screws into the side of the cowl.I have a glass jar full of old brass screws I'm sure I will have one that will do the trick.I will only need to find a piece of brass to make up the contact point.

Have villiersparts.com got these? They have alot of remanufatctored old coils, points and condensers. I know it's a bit late but may help other ppl out

Hi Michael, thanks for the input...the answer is no, they don't...I have checked all over the world...these are really like hens teeth....very rare! We were just very lucky to find one for Jeffrey.