The stator has two coils - the center connection between them is earthed making it a simple two phase alternator.
This way Tecumseh acieved full wave rectification using just two diodes. As you know, there's no regulation and in the manual, Tecumseh acknowledge that overcharging of the battery can occur - their solution, remove one of the diodes.
If you build the Kohler circuit you'll only be able to use one of the coils (one of the two wires that come out from behind the flywheel) The result won't be a lot better than the one diode you have now that doesn't overcharge. In fact looking at the Kohler ciircuit, the fact that there's a centre tap earth means, I think, you cant use it as it stands on a Tecumseh alternator.
My aim is to improve on this when I get my A-800 project up and running again soon. The circuit I sketched down but haven't built yet looks like this.
Sorry about the quality it was drawn on the back of a bit of card in the workshop. Without getting too technical the diodes are replaced by SCRs. A reference voltage for both halves of the circuit is provided by a zener diode. The SCRs cease to turn on and conduct when the reference voltage is reached so a 14volt zener diode would limit the charge to 14 volts. Although 14 volt zeners are available I was thinking of using say a 6.8 and 7.5 zener in series (14.3 volts) as the tractor isn't going to be run for long periods so it's important that the battery drain from starting it is replaced fairly quickly.
I haven't got round to building a prototype board yet but I've run this circuit on an emulator with 330 ohm resistors and it seems to work fine (in theory at least). The SCRs will probably be BT151 because they're easy to obtain here, the diodes will be whatever I have to hand as long as they can handle say 100 volts as a reasonable safety margin.
Best not steal Mark's thunder, but he can talk you through replacing the zener to make it either adjustable or just accurate to the voltage of your choice rather than the zener voltage.
I'd be interested in Chuck's view if he latches on to this thread.
Edited by wheeledhorseman, 17 April 2013 - 03:22 PM.
A-800 Ranger (1974). B-111 (1979) a future project, C-100 (1977) with 42" SD deck, C-120 Auto (1975) with 42" RD deck, D-200 Auto (1977) with 3-point hitch and 42" RD deck, D-200 Auto (1978), 210-4 (1988) with 36" RD deck, 227-5 (1988) with 42" RD deck and powered grass / leaf collector, 216-5 (1985), 316-8 (1989) with 42" RD deck, 8-25 RER (1994) WH attachments: Dozer / Snow blade x 2, mid mount grader, lawn aerator, garden roller, 5 cu ft dump cart, 10 cu ft dump cart.
Other makes: Agrifab row crop cultivator, Westwood, tipping trailer, dump cart, garden roller. Unknown make boom crop sprayer.
Wheel Horses are like Pringles - one is never enough!