Thread: 240V alternator question

Depends on the type of alternator. Does it have a separate automatic voltage regulator (AVR)? This would be a small black box with some wires coming out of it. If it has one, then there will need to be wires connected for the voltage sensing circuit - which could pick up from the back of one of the outlets. If it has no AVR, then it could be a cheaper droop style which will produce maximum volts at no load, and decrease as load is applied. Typically you may see up to 260 volts with no load and down to around 220 volts at full load. Again these wires you have may connect directly to the outlet, but more likely it will be there is something missing between the outlets and the field windings. There could have been an AVR in between that converts the 240 volts to a lower DC output for the field. The 240 volts is used as both sensing and drive for the field, and regulates a DC supply to those wires. Could be in the range of 6 to 18 volts DC - again, depends on the alternator.

Try this - run the machine with those field wires disconnected and measure the voltage at the outlets - you should have some 'residual voltage' and see maybe 20 or 30 volts AC. If you get this, get a 6 volt lantern battery - the type that is used in the old dolphin torches with the spring connectors on it, and with the machine running, briefly connect this to the field wires while monitoring the output. If it jumps up significantly, you have DC field windings, and it will need an AVR. You will have to guess at the polarity to start with - if you get nothing one way, reverse the polarity and try again.

Hope that makes some sense...

If you have some details from a data plate, and the manufacturer I may be able to help more.

Oh, and a quick disclaimer - if your not comfortable or familiar with testing and repairing mains powered equipment, please don't try testing or fixing this yourself... I don't want to hear that someone got hurt or worse trying this.

Safety first please.

There is a round thing like a capacitor that is already hooked up to wires from the coils separate from the 2 wires I am talking about. Guess that must be the AVR. Got a few jobs to do on the engine before I will be firing it up so thinking I will hook them up to where I reckon they go and try a cheapie drill or something like that on it and see what happens Thanks Gav.

Sounds like it could be a capacitor excited unit, in which case those wires could well go where you suggested. Run a few tests, take a few pics and get back to us, and I may be able to confirm it for you.