Re: rotary gaps +- problems

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

Original poster: "R.E.Burnett by way of Terry Fritz <twftesla-at-uswest-dot-net>" <R.E.Burnett-at-newcastle.ac.uk>

Hi Bob,

If that is a DC (universal) motor with brushes,  then I am not sure that
you need to use a start capacitor with it.  Start capacitors are normally
used with AC squirrel cage induction motors.

You should be able to identify the connections to the field (stator)
winding,  and the connections which go to the armature winding via the
commutator.

These can be connected in parallel,  series or seperately driven depending
on what the motor designer had for breakfast.  (Actually gives different
loading characteristics.)

I would start by connecting the two windings in series.  It should run
smoothest and coolest from a DC supply,  but may run OK from rectified
AC or even directly from a variac.  This type of motor can also be well
behaved when a light dimmer is used for speed control.

The following page has some info that may be useful:
	http://www.4qd.co.uk/faq/bmnc2.html
Scroll down to the bit about Series and Shunt wound motors.

I'm sure there must be others on this list using similar motors so it will
be interesting to see what connections they recommend.

							Cheers,

							-Richie,
On Sun, 28 Jan 2001, Tesla list wrote:

> Original poster: "bob golding by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <yubba-at-clara-dot-net>
> 
> HI all,
>     Been having some problems with the motor for my rotary. After designing
> the whole thing around a
> centrifuge brush motor  when I went to fire it up I discovered that the
> electronic controller has died :-(
> after trying to fix it I decided it would properly die as soon as I put the
> coil on anyway. It is a series
> wound brush motor with a start winding on one of the field coils as far as
> I can tell. it has three wires
> coming off it so I assumed that if I put a cap between the two wires coming
> off the field coils it should
> work. It does but doesn't seem to to have much torque. It is rated at 300
> watts and draws around 2 amps at 180
> volts. The cap I am using is 16 uF at 250 volts. It should turn my `12" x
> 1/2" rotor as the centrifuge hub
> that was on it is heavier than my rotor. Should the size of the cap affect
> the torque? I am leaving the cap in
> circuit when the motor is running. Will this make any difference. The motor
> spins up to 5500 RPM with no
> trouble without the rotor on. Help! I don't want to change the motor if I
> can help it as this will mean a
> major redesign.
> 
> cheers
> bob golding