Falcon 67 rectifier replacement

Hi Gents,
Have a bit of re-wiring to do on a Falcon 67 this weekend. One job is to refit a new modern rectifier. I can work out where the DC connections go but on the AC side I only have one wire from the alternator. Do I connect the other AC terminal on the rectifier to the frame or just leave one wire connected only. Also is there supposed to be a voltage regulator anywhere. I can't see an original one fitted nor one show in the drawings. Cheers
Brent

Hi Brent,

From the information that I have to hand, I would have expected two outputs from the a.c. generator. How many lighting coils does your armature plate have? Does your lighting switch have a "direct" position?
The machines did not have an actual voltage regulator but used three lighting coils to give a crude form of control. One coil is permanently connected for battery charging and the other two (connected in parallel) only switched into circuit, via the lighting switch, when the lighting position is selected.

Regards
Dave

Hi Dave,

The armature plate has two coils and one magneto. The lighting switch has a direct position.

I hooked it all up over the weekend just following the drawing in the 8E manual and everything seems to be running all OK - even with only one wire on the AC side of the rectifier there appears to be current flowing back into the battery (about 1Amp at just over idle).

I am a sparky (not automotive though) and this has me baffled. The only thing I can think of is that the frame is also part of the AC circuit as well as the + earth. Like you I expected 2 wires for the AC input into the coils.

All a bit confusing really.

Cheers

Brent

Hi Brent,

If you have a pair of windings they will be connected in parallel, one end of the two coils connected to earth on the armature plate and the other ends connected together and brought out as a single wire. So, as you said, the return for the rectified (1/2 wave) current is via earth connection to the battery.
This is similar to the 4F/6F engine units but in these cases both ends of the paralleled pair of coils were brought out of the engine via a two way socket and one end earthed directly to the frame.
In your bikes case the full output of the generator is connected permanently and no voltage regulation is provided. So it would suggest overcharging the battery was/is not an issue with the power available from the generator. Out of interest, what charging current do you get at higher revs with lights switched off?

Regards
Dave

Hi Dave,

Many thanks - You have have just cleared all the smoke and mirk - everything now makes sense. It is clearly a half bridge rectifier with the frame as the return path for the coils.

I have the wheels off the bike getting respoked but expect them back early next week. When I get the wheels on I will pop an ammeter in series with circuit advise the charging current with lights turned off.

Really appreciated your input

Cheers

Brent