Subject: electric motor information (long, informative)

From: [email-masked] (Bruce A. Yanagida)
Date: 24 Jan 1995 19:22:43 GMT

Hi, everyone .. the news poster from my company is broken so I am
posting this from a remote account. 

This is an article from a 1987 HSM that I have found incredibly
useful a couple of times including lately. Please note that I
can unfortunately not assume responsibility for typos. The wiring
of electric motors can under some circumstances be dangerous, so
be careful.

Grant Erwin                     | uunet:     ...!uunet!ole!grant
Cascade Design Automation Corp. | Internet:  [email-masked]
3650 131st Ave SE, Suite 650    | TEL:       (206)-649-7613
Bellevue, WA  98006             | FAX:       (206)-649-7600

------------------- article follows

      The Selection, Connection, Reversing and Repair of Electric Motors
      ------------------------------------------------------------------

                    by Robert W. Lamparter

                    reprint from "Home Shop Machinist"

     Selecting a motor and connecting the electricals are the first
     challenges encountered after purchasing that long coveted machine tool.
     There are several types of single phase AC motors in current production
     in the U.S., but only two types are commonly used in powering our
     equipment.

     TYPES OF MOTORS

     For the purpose of clarity I will describe the features of the common
     types of fractional horsepower motors.

     Universal or series motors are those having brushes and a wound rotor.
     An example of this type is that found in a portable drill or a Dremel
     tool. They are also distinguished by their noisiness.

     Induction or shaded pole motors are the ones commonly sold in window
     fans. They have a solid (squrrel cage) rotor and start slowly,
     gradually building up to speed.

     Repulsion motors are old and uncommon, in my experience, but they may
     be encountered at a yard sale or flea market. Being old, they tend to
     be on the large size. They have a wound rotor and brushes electrically
     connected to each other but not to the stator windings. A large motor
     with brushes (assuming that the nameplate doesn't indicate a DC motor
     or generator) is the tip-off that you are likely examining a repulsion
     motor. This type of motor can be reversed by shifting the position of
     the brushes. Having seen one of these powering a large drill press in a
     local blacksmith's shop, I would not recommend investing in a repulsion
     motor since the remaining types of motor to be described will do the
     job much better.

     The final three types of motors are the ones most suitable for powering
     home shop machinery: split phase motor (split phase start - induction
     run), capacitor start motor (capacitor start - induction run), and
     capacitor start - capacitor run motor. All are distinguished by a solid
     squirrel-cage rotor and an audible click when the motor has been turned
     off and is slowing down. The split phase motor has no cylindrical hump
     on the outside for the capacitor; the other two types obviously do. The
     capacitor start-capacitor run motor will have either two capacitor
     humps or will have a capacitor with three separate electrical
     connections. By the process of elimination, it should seem obvious that
     a capacitor start motor will have a single capacitor that has only two
     electrical connections.

     All of the motors described operate on house current, which is single
     phase. Three phase motors are commonly found on used industrial
     machines and will not run on house current without an expensive rotary
     phase converter. The solid state phase converters are cheaper, but our
     local electric motor rewinder intimates they have a tendency to burn
     out. Perhaps another reader with personal experience with solid state
     phase converters could enlighten us.  Because of a lack of experience
     with three phase power, I have found it best to avoid these motors. The
     maker's plate with the electrical information states whether the motor
     is single phase or three phase.

     RECOMMENDATIONS ON TYPE AND SIZE OF MOTOR

     Capacitor motors have a much greater starting torque than split phase
     motors. I prefer to use capacitor start motors on all tools except
     bench grinders. When the starting load is heavy, a split phase motor
     will take a long time to come up to speed. There are two problems with
     this. One is that a great deal of current is drawn, causing the shop
     lights to dim. The other is that the starting windings are a lighter
     gage wire; with repeated two- or three-second starting periods, the
     starter windings will eventually burn out.

     Split phase motors are considered to be adequate for easy starting
     tools, such as grinders, drill presses, jigsaws and the like. I have
     found the 1/3 hp split phase motor on my old Delta drill press to be
     adequate for all but the higher speeds. I plan to replace it with a 1/2
     hp capacitor motor when I find one at a yard sale. If I had an
     industrial drill press with a No. 2 or No. 3 Morse taper, I would want
     a 3/4 or 1 hp motor. A respected practitioner of our craft is quite
     satisfied with a 1/3 hp split phase motor on his 9" South Bend lathe
     but admits to doing only light turning. I believe the manufacturer
     recommends a 1/2 hp capacitor motor. I had a 1/2 hp capacitor motor on
     my 12" Clausing lathe. This never seemed to slow down even under heavy
     cuts, but a winding eventually burned out. From this experience, I
     infer that something more robust than a 1/2 hp motor is needed for
     a 12" lathe. I suspect that a 3/4 hp motor would have been adequate,
     but a 1.5 hp motor was the only used motor available when the old one
     burned out.

     ADEQUACY OF SHOP WIRING AND THE MERITS OF 220-VOLT OPERATION

     Next comes the job of wiring the motor. First look on the motor's
     information plate for the operating amperage and determine if the shop
     wiring and fusing are adequate. According to Sears and Roebuck's
     "Simplified Electrical Wiring," the starting currents of motors are
     roughly three times the operating current listed. For practical
     purposes, unless the starting time of the motor is prolonged by a heavy
     load, the operating current of the motor will determine if the breaker
     is going to trip. As an example, at 110v, a typical 1/2 hp motor will
     operate on 7 amps or less, but will draw 22 amps when starting. In my
     old house which had 15-amp breakers, I never overloaded the circuit
     with a 1/2 hp motor.

     If you acquire a piece of equipment that exceeds your shop's electrical
     capacity, you're going to have to do some wiring. The purchase of my
     air compressor presented me with this problem. At 110v its operating
     current was 17.8 amps and the 15-amp breaker would trip rather
     frequently. At the time, I didn't know how easy it was to add a
     circuit breaker and run a 220v line, so I tapped into one of the
     20-amp circuits in the house and used 12-gage wire to run a new 110v
     line to the shop.

     A few years later, a machinist friend of mine introduced me to the
     concept of using 220v current for the machines. I had always assumed
     that heavy wires such as that used on dryers and ranges was needed for
     220v work. Not so! Those wires are heavy because dryers and ranges
     pull currents in the range of 30 and 50 amps, respectively. Actually,
     a reduction in the wire gage may be enabled by running a motor at
     220v. When a motor is rewired to run at 220v, its operating amperage
     is halved. Thus, the compressor that pulled 17.8 amps at 110v only
     drew 8.9 amps at 220v. When I finally ran my 220v line to the shop, I
     used a 15-amp breaker and 14-gage wire. What a difference it made in
     how quickly the compressor started. I used the same outlet as I was
     using for 110v, but painted a sign on the outlet that labeled it as
     being 220v. I doubt this outlet meets the electrical code since the
     special receptacles for 220v physically prevent a 110v appliance from
     being plugged in; however, I feel this practice is acceptable in one's
     home shop. On motors that will operate at either 110v or 220v, I
     prefer to run them on 220v since there is much less dimming of the
     lights and much quicker starting at this voltage.

     For future reference, remember that fuses and circuit breakers protect
     the wiring of the house from overheating and burning while inside a
     wall, and therefore are sized to be compatible with the house wiring
     they protect - not the machine connected to it. This is why it's
     dangerous to just put a larger fuse or breaker on the circuit to your
     shop without improving the wiring. 12-gage wire will carry 20 amps,
     14-gage wire 15 amps, and 16-gage wire 10 amps. Home wiring is fairly
     straightforward, but the details are beyond the intent of this
     article. I refer the reader again to the previous mentioned booklet
     sold by Sears and Roebuck for an expanded description of the
     procedure.

     INTERNAL WIRING CONNECTIONS: CHANGING FROM 110V to 220V OPERATION

     Next we turn our attention to the internal wiring arrangements of
     split phase and capacitor motors. They are almost identical except the
     capacitor start motor has a capacitor. Both motors have two types of
     windings - starter windings and running windings. The starter windings
     determine the direction of rotation. They are of a light gage wire
     since they are only used briefly for starting and then are
     disconnected from the circuit by a centrifugal switch when the motor
     is almost up to speed. The click heard when the motor is slowing to a
     halt is the centrifugal switch clicking the starting windings back
     into the circuit. The lead numbering I present in my diagrams, Figures
     1 through 4, is used in three motors in my shop, all of which are of
     different manufacture. One of them is British in origin. I assume the
     numbering system is universal, but I can't be assured of this since I
     haven't found these diagrams in print. If there is a wiring diagram on
     your motor, so much the better; you don't need me. If not, I'll give
     you as many tricks to identify the leads as I can:

     Lead No. 8 is the one usually attached to the capacitor or centrifugal
     switch. Leads No. 6 and 7 are usually buried somewhere in the motor
     and aren't seen. If three leads are twisted together, they probably
     represent two running winding leads and a starting winding lead.
     According to an article in "Model Engineer" (Volume 145, Number 3620,
     November 1979, page 1262) the starting windings have a slightly higher
     resistance than the running windings. On my Brooks 1.5 hp motor, the
     starting windings have a resistance of 2.2 ohms and running windings
     have 1.2 ohms of resistance. Take the utmost care in making these
     measurements since a dirty contact will alter the measurement. If only
     four leads come to the terminal board, two are probably running
     winding leads and two are probably the starting winding leads No. 5
     and 8. I can't cover all the possibilities, but that should help you
     in getting started.

     Figures 1 and 3 show the comparison between a motor set up to run on
     220v versus one wired to run at 110v. Note that the starting windings
     are connected in series with one of the running windings when the
     motor is wired to run at 220v. A few years ago when I bought a used
     3/4 hp motor to replace the three phase one that came in my Hardinge
     mill, a less than attentive employee at the motor rewinders instructed
     me to connect starting winding leads No. 5 and 8 to running winding
     leads No. 1 and 4 - in essence, to the full 220v input. The motor ran
     fine for two months, and then one time on starting, it smoked, made a
     horribly loud vibrating noise, and rotated at only a fraction of its
     normal speed. Fortunately, only the capacitor had failed. When I
     purchased the new capacitor, I inquired about the wiring connection on
     this motor since it was different from two others in my shop. The
     owner of the rewinding shop instructed me to place the starting
     windings in series with the running windings so that they would absorb
     some of the current going to the starting windings and capacitor,
     prolonging their life expectancy.

     Having converted a motor to run on 220v, it is worthwhile to test it
     at 110v first. If wired correctly, it will run at a somewhat slower
     than normal speed.

     R = running winding
     S = starting winding

      |
     ___   = capacitor
     ---
      |

      |
      o
       \
        \  = centrifugal switch
         V
      o
      |

          +----------+-----------------------  line 1
        1 |        8 |
          |          |           +-----------  line 2
          |         ___        4 |
          |         ---          |
         (           |           (
          )          o            )
         (            \          (
          )            \          )
         (              V        (
          )          o            )             220 V AC
         (           |           (              Forward connection
     R1   )         (             )  R2
         (           ) S1        (                  _
          )         (             )              .     .
         (         7 |           (              .       .
          )          +            )              .     .
         (         6 |           (                  <
          |         (            |
          |          ) S2        |              Figure 1
          |         (            |
        2 |        5 |         3 |
          +----------+-----------+

          +----------+-----------------------  line 1
        1 |        5 |
          |          |           +-----------  line 2
          |         (          4 |
          |          ) S2        |
         (          (            (
          )        6 |            )
         (           +           (
          )        7 |            )
         (          (            (
          )          ) S1         )             220 V AC
         (          (            (              Reverse connection
     R1   )          |            )  R2
         (           o           (                  _
          )           \           )              .     .
         (             \         (              .       .
          )             V         )              .     .
         (           o           (                  >
          |          |           |
          |         ___          |              Figure 2
          |         ---          |
        2 |        8 |         3 |
          +----------+-----------+

          +----------+-----------+-----------  line 1
        1 |        8 |         4 |
          |          |           |
          |         ___          |
          |         ---          |
         (           |           (
          )          o            )
         (            \          (
          )            \          )
         (              V        (
          )          o            )             110 V AC
         (           |           (              Forward connection
     R1   )         (             )  R2
         (           ) S1        (                  _
          )         (             )              .     .
         (         7 |           (              .       .
          )          +            )              .     .
         (         6 |           (                  <
          |         (            |
          |          ) S2        |              Figure 3
          |         (            |
        2 |        5 |         3 |
          +----------+-----------+-----------  line 2

          +----------+-----------+-----------  line 1
        1 |        5 |         4 |
          |          |           |
          |         (            |
          |          ) S2        |
         (          (            (
          )        6 |            )
         (           +           (
          )        7 |            )
         (          (            (
          )          ) S1         )             110 V AC
         (          (            (              Reverse connection
     R1   )          |            )  R2
         (           o           (                  _
          )           \           )              .     .
         (             \         (              .       .
          )             V         )              .     .
         (           o           (                  >
          |          |           |
          |         ___          |              Figure 4
          |         ---          |
        2 |        8 |         3 |
          +----------+-----------+-----------  line 2

     REVERSING THE ROTATION AND WIRING DRUM SWITCHES

     Reversing the rotation of a motor is often desired. From Figures 1
     through 4, it is evident that reversing the connections of the
     starting winding leads No. 5 and 8 is all that is necessary. In
     Figures 5 and 6 are the wiring diagrams for the terminals in a drum
     switch controlling a 220v motor. Figures 7 and 8 show the same switch
     wired for a 110v motor. Note that the only difference in the internal
     wiring of the drum switch between 110v and 220v is a link between the
     terminals on the lower left. Pay attention to the fact that in Figures
     7 and 8 Line 2 is the hot or live wire.

     (TYPEWRITER ARTIST NOTE: Please bear with me. It isn't trivial to
      pass graphic information through ASCII. The following legend is to
      help the suffering reader to follow the typewriter art.)

        DRUM SWITCH LEGEND: There are 9 connection points depicted. The
        central 3 points connect either to the right 3 points, as shown
        first, or to the left 3 points, as shown second. In Figures 5
        through 8, some of these points are wired together, and some are
        connected to wiring points in the motor. These motor wiring points
        are numbered the same as they were above in Figures 1 through 4.

                                       (o)----------------V
                   (o)                                   (o)

                                       (o)----------------V
                   (o)                                   (o)

                                       (o)----------------V
                   (o)                                   (o)
                          Drum switch: connection 1

                    V------------------(o)
                   (o)                                   (o)

                   (o)                                   (o)
                    ^------------------(o)

                    V------------------(o)
                   (o)                                   (o)
                          Drum switch: connection 2


     line 1                            (5)----------------V
     --------------(1)--__      +------------------------(*)
                          --__ /
                              / __
                             /    --__ (8)----------------V
                  (2&3)-----+         -------------------(*)

     line 2                            (4)----------------V
     --------------(*)-----------------------------------(*)
                          Forward (220v)
                         Figure 5

     line 1         V------------------(5)
     --------------(1)--__      +------------------------(*)
                          --__ /
                              / __
                             /    --__
                  (2&3)-----+         -------------------(*)
                    ^------------------(8)

     line 2         V------------------(4)
     --------------(*)-----------------------------------(*)
                          Reverse (220v)
                         Figure 6

     line 1                            (5)----------------V
     --------------(1)--__      +------------------------(*)
                          --__ /
                              / __
                             /    --__ (8)----------------V
                  (2&3)-----+         -------------------(*)
                    |
                    |
                    |
     line 2         |                  (4)----------------V
     --------------(*)-----------------------------------(*)
     (hot)                Forward (110v)
                         Figure 7

     line 1         V------------------(5)
     --------------(1)--__      +------------------------(*)
                          --__ /
                              / __
                             /    --__
                  (2&3)-----+         -------------------(*)
                   |^------------------(8)
                   |
                   |
     line 2        |                  (4)-----------------V
     -------------(*)------------------------------------(*)
     (hot)                Reverse (110v)
                         Figure 8

     Several years ago, when the previously mentioned 1/2 hp motor in my
     lathe burned out, I didn't have a reversing switch but only the
     standard single pole wall switch controlling the current flow.
     Thoughtlessly, I had connected this switch to the neutral (white)
     lead. When the motor started to hiss and smoke, I quickly flipped the
     switch off. Much to my alarm, the motor continued to hiss, smoke and
     run! When the winding burned, it shorted to the motor frame and a
     circuit was completed from the hot wire through the remaining windings
     to the ground wire. I had to dash to the breaker box to shut off my
     lathe. (Thank goodness I've never tried to save a few cents by buying
     electric cord without a ground wire or, in this case, I might have
     *been* the ground wire.)

     This same flow occurs in the wiring of the drum switch for 220v since
     both of the lines are hot (live), and Line 1 is directly connected to
     the motor without an intervening switch. In my own shop, I solved this
     problem with a magnetic starter; more on these later. Figure 9 shows
     an alternate type of drum switch configuration which may be
     encountered. By now you should have some idea of how to arrange the
     connections, so I won't illustrate these. If you're still in your
     salad days and can't afford a drum switch, an alternative is to
     utilize a four-way switch, the type used in household wiring when
     three or more switches control the same circuit. The electrical
     connections are illustrated in Figures 9 through 13.

     There are two types of four-way switches - cross type and through type
     - and you'll have to determine which type you have with an ohmmeter or
     test lamp. I have illustrated the connections for a 110v motor only,
     but there's no reason the same setup couldn't be used for 220v
     operation. With a four-way switch you'll need a separate switch to
     turn the motor on and off.

     While we're on the subject of making-do, I'll pass on another pearl.
     Shoe eyelets make nice electrical connectors. Just wrap the bare wire
     around the post and crimp. Sometimes a rap in the hole with a center
     punch is needed to expand it so that it will fit over a screw
     terminal. Next you'll need four- or five-wire "cable" to run from the
     switch to the motor. Since cable is not available in my small town,
     I've made my own using 5/8" ID clear plastic tubing and different
     colors of 14 or 16 gage *multistrand* wire. If the cable isn't too
     long, a coat hanger can be used to pull the wires through.

     (*)----(*)                (*)    (*)                (*)    (*)      
                                                          |      |
                                                          |      |
     (*)----(*)                (*)    (*)                (*)    (*)      

     (*)----(*)                (*)    (*)                (*)----(*)      
      Forward                      Off                    Reverse
     Figure 9

     (1&4)----(8)                                       (1&4)    (8)
                            Through-type                  |       | 
                            4-way switch                  |       |
                              110 v                       |       |
      (5)----(2&3)                                       (5)    (2&3)
       Forward                                            Reverse
     Figure 10                                          Figure 11

     (1&4)   (2&3)                                      (1&4)   (2&3)
       |       |             Cross-type                      \ /      
       |       |            4-way switch                      \      
       |       |              110 v                          / \     
      (8)     (5)                                        (5)-   -(8) 
       Forward                                            Reverse
     Figure 12                                          Figure 13

     MOTOR PROTECTION AND MAGNETIC STARTERS

     Motor protection is often neglected. The fusebox or circuit breaker
     does nothing to protect the motor in case of an overload. They just
     protect the house wiring so it doesn't start to burn while hidden in a
     wall.

     Dayton sells a single pole fractional horsepower manual motor starter,
     stock No. 5X269, that lists (used to list) for $22. Their two-pole
     model No. 5X270 should be used for 220v hookups and lists (used to
     list) for $26. A heater element matched to the operating amperage of
     the motor must be bought separately and lists (used to list) for $4.

     Many used machines come with the motor protection device still
     attached. In some cases they are manual devices and in others they are
     magnetic starters. Almost invariably these devices are set up for
     three-phase operation, so you'll have to follow the instructions
     inside the lid to make the conversion to single-phase operation and
     the proper voltage. You'll have to buy one or two heater elements to
     match the operating amperage of the motor to be protected. A list of
     the parts numbers for the heater elements is usually printed inside
     the lid with the connection instructions. These cost about $7 apiece.
     On magnetic starters, also look at the label on the magnetic coil to
     be sure it's the correct one for the voltage you intend to use. The
     protection device is placed in the circuit between the plug and the
     drum switch. Thus, the sequence is: plug and cord leading into
     protection device, then the drum switch, and then the motor. Some
     motors have thermal overload protectors built in. I suppose they work,
     but I've been less than trusting of them since the only motor in my
     shop to have one was the lathe motor that burned out. I confess that
     only the more expensive motors in my shop are protected.

     Before moving on to the next topic, a final reminder - always include
     a ground wire in all your circuits so that if a short develops, you
     aren't the ground.

     TROUBLESHOOTING

     There are only a limited number of things that can go wrong
     electrically with split phase and capacitor motors. Listing what can
     go wrong is easy. Explaining how to isolate the circuits for testing
     can be difficult, and you'll have to use your own ingenuity plus the
     wiring schemes I've given you. You'll need an ohmmeter or a test lamp
     to do the testing.

     If the motor doesn't even hum when you plug it in, it's either not
     getting any power at all or there's a break in one of the circuits
     inside the motor. Look at the windings. If one or more looks blackened
     and smells burnt, it's probably burned out. It doesn't seem profitable
     for motor repairmen to rewind small single-phase motors, so if you've
     burned out a winding, you're probably going to have to replace the
     motor.

     If the motor hums but won't turn, there are several possibilities, all
     dealing with the starting windings. Check to see that all the
     connections are in the right place. Look for burned windings. Examine
     the capacitor. If it has leaked a few drops of oil, it's no good.

     Remove the wires to the capacitor and test it with an ohmmeter set on
     the 100x or 1000x scale. The needle should briefly swing toward 0 ohms
     and then drift back to the high end of the scale. If it doesn't swing
     toward 0 ohms, short the capacitor with a screwdriver and try the test
     again; the capacitor may have had a small charge that would interfere
     with this test.

     The centrifugal switch normally is closed and passes current when the
     motor is stopped. If it doesn't, pull the bell ends off of the motor
     frame and look at the centrifugal switch contacts. Push the contacts
     together and test them with the ohmmeter to be certain they do or
     don't transmit current. Oil or grease from the bearings can prevent
     the contacts from closing. Look at the contact surfaces for pitting or
     burning. If they need it, brighten them up with a point file or emery
     paper, taking care not to get the emery dust in the bearing.

     If you don't hear a click when the motor's slowing down, the
     centrifugal switch isn't working. Pull the bell ends off the frame and
     look at the centrifugal switch. The weights should be moveable
     although stiff because of spring tension. If the bearings are
     extremely worn, the rotor may touch the frame and prevent the motor
     from operating. I've never seen this, but I'd expect to find a lot of
     play in the motor shaft and either bright spots or burned spots inside
     the frame where the motor was rubbing.

     If the motor starts but just doesn't seem to have as much power as it
     should, look to see if one of the windings looks burned. Check to see
     that all the electrical connections are correct and clean. Make sure
     you don't have the motor wired to run on 220v when you're only using
     110v.

     A number of publications have served as references to supplement what
     has flowed spontaneously from my pen, and the reader may find the
     following references helpful: "Simplified Electrical Wiring," Sears,
     Roebuck and Company; "Electric Motor Test and Repair" by TAB Books,
     Inc., obtained from a regular advertiser in "Home Shop Machinist"; and
     "Model Engineer" Volume 145, Number 3620, pages 1260-1263, and Number
     3622, pages 1414-1416.