Re: Sync Motor Wanted

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At
>I've been selling complete asynchronous rotaries and separate rotors for
>many years now and the reaction from hobbyists on a budget when they ask
>for a price on a 7" rotary can be very interesting. Usually there is a
>longer than normal silence. I charge $650 for a complete 7" asynchronous
>rotary and that doesn't even reflect the true hours of machine and
>assembly time involved.
>
> > After I finish my present giant project, grinding iron sounds relaxing
> > ;-))  But not for a few weeks yet...
> >
>
>Too bad motor armature laminations aren't iron, because that would make
>the job easier. They are silicon steel and are much harder on tooling
>than iron. :^)
>
> > Ok, I guess I am just a little surprised this cool part of Tesla coiling is
> > not a "buy off Ebay" (or anywhere else) part!!!
>
>I guess I'm not, because there's more involved than meets the eye and a
>very limited market.
>
>Ed Wingate RATCB

If one wanted to sell 1/10-1/4 HP sync motors, they'd probably be better 
off finding a good off-shore (china, india) source and reselling than going 
to the trouble of buying induction motors and machining them. The machining 
to make a sync motor is the route you take when you get the motor almost 
free and you have lots of (low-paid) time, which is not the way to run a 
business.

The other approach would be to find a source for big stepper motors and 
build an appropriate controller.  You probably don't want a Slo-Syn type, 
because there's too many poles, although, if you're driving it with a 
feedback controller, it might be ok.

For that matter, some sort of DC servo loop might not be a bad way to 
go.  It's not like you're concerned about power efficiency, so the 
controller could be as simple as a straight Class A thing based on a 2N3055 
running a 24VDC motor.  Drive it with a simple PLL and an optical or 
magnetic pickup to sync to the power line.

I would think that you could do it for around $20-30 in parts (excluding 
the motor, but including the PC board), which is certainly in a reasonable 
range (considering what folks are paying to  build SSTCs, for instance).

In fact, given that the load is fairly constant, one might be able to use a 
3450 RPM AC motor with a phase control type speed controller to run it at 
1800 RPM. Or, a series wound universal motor (as in vacuum cleaners, angle 
grinders, and the like) could be controlled the same way.