250 Magneto - Some info.

[marsheng]

Just some info on what I found.

I have the 2 coil magneto. One coil has the one side grounded (Coil1) and the other has both leads coming out (Coil2)

Coil1 at 1000 RPM with no load 5 v
Coil2 9.5 v

Coil2 with a 35W headlamp as a load, @ 1000 RPM gives 6.6 v @ 1.8 amps => 12 watts
At 2000 rpm 8v and 2 amps => 16 watts.

Just for fun I put coil1 and coil2 in series and at 1000 rpm got 9.5 and 2000, 11 v with the same bulb as a load.

So with a few more revs, you may get 12 however with the regulator, it probably approx 1.5 volts lower.

Time for a new magneto. Not sure if a rewind is an option. I need to cater for a 35 + watt 12 v headlight.

[ducwiz]

Seems you did your measurement with a 12V lamp, right?
http://roadandrace.com.au/alternator_conversions.htm offers an alternator rewind for better power output, but still 6 V.
The 2coil alternators came in a 28 or a 40 W version. Imho, it is impossible to get more than approx. 40 W from those weak power sources.
If I had a n/c single I would go for an Electrex conversion kit, https://www.electrexworld.co.uk/cgi-bin/sh000001.pl?WD=ducati&PN=STK%2d160%2ehtml#SID=826. 120W is plenty of power, even sufficient for a H4 lamp.

Hans

[marsheng]

Seems you did your measurement with a 12V lamp, right?
Hans

Yes I did.

I have a stock of small Pit bike magnetos (which I normally use for race bikes) and Ignitech ignitions. The pit bike ignitions have always just powered the ignition which is low so had no problem. There are however no specs on the power. I'll do a test on them and see what they can do. Postage is a killer living here in New Zealand. Most times from the USA or UK, it is over the 50 euro or $50 mark per shipment in the current state and delivery is another problem, Been waiting for 4 weeks for GT250 conrods to even leave the UK and 6 weeks for the bearings from Japan China is very low cost and sometimes even included in the price and quick delivery. 10-15 days.

Cheers Wallace

[marsheng]

The setup.

magneto.JPG

[Jordan]

Nice idea to test your alternator on the milling machine.
What's the max spindle speed?
How do you attach the rotor?

[marsheng]

I can get to 6000 RPM.

It is just clamped onto a slitting saw arbour. I centered it in the lathe.