> From: Chuck Curran[SMTP:ccurran@execpc.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 > Thank You to Gary Lau for asking the question that prompted Chuck's excellent reply! (RWO)