After all the talk about electric motors today, I went and found a couple universal motors I have kicking around. One was marked 'seized', so I took it apart, forced the armature out, then did a belt sand around the armature to remove the melted plastic. The windings didn't look burnt in any way, so I put it back together and it runs perfectly.
So there it is running from my dc power supply at about 20 volts. It's probably turning at a good 2000 rpm or so, not that it matters. Then I'm wondering how much of the voltage is used by the field and how much remains for the armature- turns out there's about 1 volt across the field and the rest across the armature ( these are in series as in every universal motor I've had apart).
I wonder if the same will be true running it on ac? Probably not, but my main thought here is if I turned it into a permanent magnet field, what voltage would the armature then need in order to turn at some appropriate rpm? After I get back from dinner I think I'll hook it up to ac and see if I can get some ideas. The other option is to separate the wiring and power the field and armature separately. I would first try to power the field to about the level that permanent magnets would give, then see what armature voltage and rpm figures would be like. I'd like to try to use these armatures as is, since they are well balanced already and have a large number of comm segments, making them suitable for 'high' voltage operation. With luck, maybe I can get a motor that will run well from rectified 110 vac, and with rpms down in the low k range.
I know that neodymium magnets aren't cheap, but there would not be many needed, only about $30 worth I'm estimating, and the result could be a motor that's nearly ideal for things like Lane is working on, where you want small size, good torque, and induction motor-like rpms.
All comments welcome.