MAGNETO RE-MAGNETISER
This project was brought about from having taken every magneto apart that I encountered at an early age not realising that this releases the magnetism held within, This resulted in a couple of our engines having starting/running problems which baffled me for a while, At a later stage in the hobby I became wise to this and thought a nice relatively simple project would be to build a magnetising machine from some readily available materials. (GALLERY LINK AT BOTTOM PAGE)
RESEARCH
First step of the project was to crawl the web to look at similar projects to base my design on, after studying many sites I came across this website Magneto Parts Instructional Guides, which included A copy from gas engine magazine of an article detailing how to build a magneto magnetiser, After studying this the I noted the following key points..
Magnetic power = the amount of turns and the current flowing through these turns, this is called ampere turns.
To re-magnetise magnetos you need a minimum of 16000 - 20000 ampere turns
The materials used in the construction of the coil cores and base must be of low carbon steal
MATERIALS
The first stage of the build was to obtain some suitable materials, I managed to get some 1 inch thick low carbon steel for the base about 10x4 inches, some 2.5 inch diameter bar for the core centres and some insulated 1.5mm enamelled copper wire, although this wire is smaller than the instructional guide I felt it would be easier to use a smaller wire at higher voltage (24vdc to batteries in series) to make the coils more compact and due to the machine being operated in short bursts it would handle to current adequately. Also obtained where some 6mm single copper cable for making the connections, a 24vdc contactor, a 0-50 amp car ammeter and some transorbs, the transorb is paced across the supply to the coils to discharge any high voltage spikes which are created when you energise and de-energise the machine, and a big button to make it all work.
CONSTRUCTION
First stage was to turn two coil cores from the solid bar in a lathe about 5 inches long, the ends were faced and two small holes drilled in one end to allow a 6mm thread to be cut, the base piece was drilled two or three times on each end along its length to allow the coils to be moved up and down to suite different magnetos, two pieces of 1" x 3" x 4" steal where fashioned for the pole pieces at the top of the coils, and drilled three times to allow adjustment in and out, all the holes were countersunk to ensure a flush face.
COIL WINDING
Before winding the coil cores where insulated simply with about three layers of PVC electrical tape, then the wire was started with a long tail sticking out and coiling slowly by hand along the length of the coil, when a layer was complete it was covered with electrical tape and the next layer started just slightly in from the edge of the last layer, this was repeated until there was about 120-140 meters of wire on each coil which totalled about 600 turns.
ASSEMBLY
Having completed two coils I made four plastic discs to insulate the coils against the base and pole pieces (but not the core, they need to look like doughnuts) once mounted, two 6mm counter sunk screws where used to fix the coils to the base and the same to fix the pole pieces to the tops of the coils. The ends of the coils where terminated as shown in the diagram on the right, ensuring the correct polarity of the transorb other wise there will be a small fire works display and a nasty smell (personal experience), the contactor is installed to allow rapid switching of the power and is shown as the switch symbol.
Operation
Having wired the unit up, it was time to find out the polarity of the remagnetiser, the battery was connected and the button pressed and the contactor clunked in and the amps went to about 40 amps, this creates some residual magnetism in the iron cores allowing the polarity to be checked with a common compass, now remember that opposites attract, so when bringing the compass close to the core and the north needle is attracted, it means that the core is the south and the opposite should be the north, next the same operation is used to find the north and south on the magneto and marked in chalk, the magneto is placed on the remagnetiser so that the opposite poles are on each other, and some loose pole pieces made from the same 1 inch iron are used to build up either side (see photo gallery),
ZAP !!!!!!!!
Finally with the choice magneto in place (the Petter M B.T.H M1) the button was pressed and held for 3-4 second bursts (about 4 should do), when pressed the armature of the magneto span round as the poles lined up inside and the amps shot up to almost 50. After the magneto was prised from the remagnetiser (and any other metal objects that were in range) it was set up with a spark plug and the difference was amazing , the rpm need to generate a spark was much reduced, and the resistance as turned was defiantly greater. The magneto was quickly back on the engine and when started went straight over to paraffin and ran smoother than ever.
