Perhaps it would be a good time to return to engines ;-)
Some months ago "Nick H" wrote :-
Worried about the direction of rotation of the dynamo I mentioned in the Maytag thread, I had a look at it and there appears to be nothing to indicate which way it ought to go. It is a two pole machine with fixed brushes on the neutral axis between the main field poles, on which basis it should be equally happy in either direction. There are however two smaller interpoles in line with the brushes, I believe these assist spark free commutation - does their wiring determine the correct rotation?
"Kim Siddorn" wrote :-
Suck it and see, Nick. Rig it up with your lathe and see what kind of output you get.
"Nick H" wrote :-
I'm over thinking again aren't I :-(
KISS - Keep It Simple, Stupid!
"Brian Bailey" wrote :-
Nick, The interpole magnetomotive force neutralizes that portion of the armature reaction within the zones of commutation and produces the proper flux to generate an EMF in the short-circuited coil that is equal to but opposite to the EMF of self-induction. Thus, little or no sparking occurs at the brushes.
The important thing to remember is that an interpole always has the same magnetic polarity as the adjacent main field pole ahead of it IN THE DIRECTION OF ROTATION. Note: this is for generators only --- DC motors are just the opposite, with the interpole having the magnetic polarity of the main pole BACK of it. So if you can figure out the internal wiring you should be able to figure out the direction of rotation.
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Well, with the engine up and running I though I'd better get around to trying the dynamo. It turned out to be quite resolutely anti-clock with practically no output when driven in the other direction - not what is required for the Maytag at all! Investigating further I found that there were two jumpers in the terminal box and after dibbling about with the AVO for a while I concluded that these connected the rheostat and shunt field to the brush / series field / interpole, circuit. Thus by reversing these connections I should be able to reverse the rotation of the machine. Success, at 1380 rpm on the lathe it lights a 100w 240v light bulb with all the dazzling intensity one would expect from a 125v dynamo running 20% slow! Regulation doesn't seem that good with the voltage rising by about 5v when the load is removed - but I wasn't quite sure what to expect in that respect anyway.
Now how to mount it? The proper Maytag Light wore its dynamo over the engine, supported by plates on the cylinder holding-down bolts, (did anyone save pics of the one on ebay recently, the best I can find at the moment is this
1/4KW, the GE dynamo I have is quite a large and heavy lump and 'showing it' to the engine indicated that the top mounted position would not work. Underneath looked a bit more promising, but would make the dynamo vulnerable to fuel spillage and require a certain amount of gymnastic ability to operate the kick start. Then I noticed that the hole spacing on the dynamo was actually the same as that on the engine and moving it to one side to share holes with the long end of the base, the two suddenly looked like they'd always been together!
Shame I don't rally, it'll make a nice little display ;-)