K2F magneto info

rayswadling · Post by **rayswadling** » Sun May 16, 2010 7:51 pm

Hi,

I'm checking out the K2F magneto fitted to my G12 engine (it's actually a K2FC). Already it looks like there is play in the bearings, but the original problem was no sparks.
Does anyone know what the impedance of the winding should be? I'm measuring from earth to the slip ring contact and getting 4.5Kohms.
I'm planning to get the mag reconditioned for the bearing issue, but trying to find out if the windings are shot too.

Cheers,

Ray.

SPRIDDLER · Post by **SPRIDDLER** » Sun May 16, 2010 9:42 pm

Try this:

http://archives.jampot.dk/Technical/Ele ... 2F_KVF.pdf

Groily · Post by **Groily** » Sun May 16, 2010 10:18 pm

Not certain Ray, but the HT coil on one standard K2F that works and is on my bench shows 7.5K ohms across the ends of the actual coil (which should be the same test subject to the fit of the HT wire into your slip ring, and the state of the earth brush/other routes to earth in your scenario). That's just one mag and it's not gospel, but it looks good, smells good and above all it actually works!
If you find out a definitive resistance reading for a K2F HT coil, be it C or standard, please do share it - I'd love to know!

rayswadling · Post by **rayswadling** » Mon May 17, 2010 9:14 pm

Thanks for the replies, at least the HT coil seems "normal". I've measured across the points when they are open, and I'm getting a dead short. This is just with a DVM, but I would have expected some sort of resistance there.
I believe that in a magneto there is a low voltage coil connected across the points so that the opening points break the circuit to drive the HT spark from the other coil.

I'm going to send it off anyway for a rebuild, and when I get it back I'll take some more readings and see how they compare.

Cheers,

Ray.

Don Madden · Post by **Don Madden** » Mon May 17, 2010 9:56 pm

The low voltage coil is across the contacts but the resistance is very low. You must have a sensitive meter to read it & zero it out before taking a reading. Cheers, Don.

Groily · Post by **Groily** » Mon May 17, 2010 11:49 pm

You won't get much resistance across the points when they're open Ray even if things are OK because the LT winding goes from the fixed point to the mag's body via the condenser - and the LT coil has very low resistance - while the moving point is earthed anyway via the screw that holds the spring. Certainly not enough resistance to make a bulb go out, or even go dim when the points open.
Have been thinking about HT coil resistance since yesterday- and it's actually hard to say what it 'should' be. Impedance includes sorcery beyond bog-standard electrickery, so it's not a straight case of Ohm's law. Spriddler's reference yesterday stated somewhere that the LT coil's max amperage should be 1.2A - which would become b****r all on the HT side when divided by the turns ratio. Just as well given how fine the HT windings are.
If you can be bothered,
http://en.wikipedia.org/wiki/Magneto
might also be of interest if you haven't already been there . . . Wish I truly understood the finer theory behind some of this, as it's actually interesting. Probably incidentally explains the meaning of the universe or something . . .