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Re: Is this motor synchronous?/Motor Types


From: 	Barton B. Anderson[SMTP:mopar-at-mn.uswest-dot-net]
Sent: 	Thursday, January 01, 1998 8:39 PM
To: 	Tesla List
Subject: 	Re: Is this motor synchronous?/Motor Types

Chuck, I just wanted to say "good job" and "good info" on motors. You used very
simple laymans terms to clarify and it really does help. I especially liked the
application explanations. Again, great stuff and thanks for posting.
Bart

Tesla List wrote:

> From:   Chuck Curran[SMTP:ccurran-at-execpc-dot-com]
> Sent:   Thursday, January 01, 1998 4:57 PM
> To:     Tesla List
> Subject:        Re: Is this motor synchronous?/Motor Types
>
> Hello All:
>
> I thought it might help to offer some specifics on single phase motor types
> and typical uses.  since we make about 4600 per day, I do have enough
> contact to provide certain descriptions relative to single phase motors!  A
> little more information might make it easier for all when trying to select a
> motor for a spark gap, or a cooling fan.
>
> Shaded Pole:  This type of motor has low starting torque, low cost, low
> efficiency and NO capacitors.  It would typically be found running a small
> fan, like in the ceiling vent in a bathroom.  It would be of little use for
> anything associated with Tesla applications other than running a small
> cooling fan.
>
> PSC (Permanent Split Capacitor):  These motors are one notch up the ladder
> from a Shaded pole.  They will always have a run capacitor in the circuit at
> all times.  They will have higher efficiency, higher horsepower capability,
> 50-60% less current draw than an equal shaded pole but limited starting
> torque too.  They can be used for shaft on fans for example but not a belt
> drive because of the poor starting torque.
>
> Split Phase:  O.K., here we now have a motor with moderate starting torque
> (100-125% of full load) high starting current, NO capacitor, but it will
> have a starting centrifugal switch.  The switch drops out the start winding
> at about 75% of full RPM.  Here you can use a belt drive due to the improved
> starting torque.
>
> AC Series (Universal):  This type is commonly used in your electric drill or
> other tools that require a high starting torque and a small size too.  It
> can run on either AC or DC, resulting in the Universal tag.  The field
> winding is connected in series with the wound armature through a pair of
> carbon brushes and a commutator.    You can see speeds over 30,000 RPM with
> the universal motor.  They are used in most vacuum cleaners sanders, any
> portable tool no doubt contains a AC series motor.  The means to identify
> this type is to simply look for the sparks arcing off the commutator and
> brushes when you run it from the 120 VAC wall plug.  Or better yet,  just
> look for the commutator and the pair of carbon brushes.
>
> Capacitor Start:  Now we are getting closer to a real motor!  This type can
> be identified by seeing the presence of both a centrifugal starting switch
> and a single capacitor.  It is probably one of the most common motors made
> in between 1/4 HP and 3 HP.  Here you will have high starting torque, up to
> 300% of full speed torque and at the same time moderate starting current.
> This is the type of motor most of us will no doubt find for spark gaps.
> This motor will have a single "Dog House" mounted on it that contains the
> capacitor.  If I were looking for a motor I'd suggest this as a first
> choice, however, it will be more expensive.  Nice motor to consider for a
> synchronous modification too.
>
> Capacitor Start-Capacitor Run:  Pretty much identical to the above motor but
> seen at horse powers above 3 HP.  The run capacitor is added and left in the
> circuit at all times to improve the running efficiency.
>
> The capacitor start, capacitor start/capacitor run and the split phase
> should not be used with a auto transformer to vary the RPM.  If you run it
> below the centrifugal switch pull in point, you will very quickly over heat
> the start winding and create a rather unpleasant cloud of smoke.  That's
> really why I chose a universal motor, the Carter many of us bought about 16
> months ago.  This type can be run at different voltages and change the RPM
> rather easily.
>
> One other item that may help clarify things.  Many posts have mentioned the
> topic of milling flats on the "armature" to create a synchronous AC motor.
> Just for information, a more accurate term would be "rotor".  An armature is
> a associated with a DC motor and contains a winding on a stack of
> laminations, while an AC motor uses a rotor which is a stack of laminations
> with a series of aluminum bars and end rings cast into/onto the lamination
> stack using a high pressure aluminum die caster.  Call it whatever you like,
> just wanted to share the industry terminology!
>
> Chuck
>
> -----Original Message-----
> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Date: Thursday, January 01, 1998 12:22 PM
> Subject: Re: Is this motor synchronous?
>
> >
> >From: FutureT[SMTP:FutureT-at-aol-dot-com]
> >Sent: Wednesday, December 31, 1997 12:56 PM
> >To: tesla-at-pupman-dot-com
> >Subject: Re: Is this motor synchronous?
> >
> >In a message dated 97-12-31 03:32:13 EST, you write:
> >
> ><<
> >> My 1725 RPM motor didn't have a cap, although I'm suspecting I might have
> >> been successful had I removed less material.  How does one determine _by_
> >> _observation_ if a motor is a capacitor start/induction run type of motor
> >> vs an induction start/ induction run or capacitor start/capacitor run
> >> type, short of having a spec sheet?
> >
> >> Thanks again for the help.
> >
> >> Gary Lau
> >
> >  >>
> >
> >Gary,
> >
> >I ground my flats for the 1800 rpm motor 1 1/8" wide for a 2 7/8" dia
> >armature if I remember correctly (I posted this info in the past).  I got
> >good results, so I suppose this ratio is OK.  I have no idea if there is
> >a better ratio.  My motor was a 1/4 HP washing machine motor with
> >no capacitor.  IMO, a .65 amp motor is somewhat weak for use in
> >a sync-gap.  A 1/25 HP motor is probably a practical minimum unless
> >the rotor is tiny.
> >
> >Cap start motors have a centrifugul switch inside, as do induction
> >start motors.  I think cap run motors tend to be small, less than
> >1/4 HP.  This is a rough guide as I'm not an expert on these various
> >motor types.
> >
> >Hope this helps,
> >John Freau
> >
> >
> >