The Selection, Connection, Reversing and Repair of

Electric Motorsby RobertW. Lamparter

electing a motor and connecting theelectricals are the first challenges

encountered after purchasing that long covetedmachine tool. There are several types of singlephase AC motors in current production in theU.S., but only two types are commonly used inpowering our equipment.

TYPES OF TVlOTORS

For the purpose of clarity I will describe thefeatures of the common types of fractionalhorsepower motors.

Universal or series motors are those havingbrushes and a wound rotor. An example of thistype is that found in a portable drill or aDremel tool. They are also distinguished bytheir noisiness.

Induction or shaded pole motors are the onescommonly used in window fans. They have asoiid (squirrel cageI rotor and start slowly,gradually building up to speed.

Repulsion motors are old and unc.ommon, inmy experience, but they may be encounteredat a yard sale or flea market. Being old, theytend to be on the large size. They have awound rotor and brushes electrically connectedto each other but not to the stator windings.A large motor with brushes (assuming that thenameplate doesn't indicate a DC motor orgenerator) is the tip-off that you are likelyexamining a repulsion motor. This type ofmotor can be reversed by shifting the positionof the brushes. Having seen one of thesepowering a large drill press in a localblacksmith's shop, I can be assured that theyhave enough oomph to drive low powermachinery. I would not recommend investingin a repulsion motor since the remainingtypes of motor to be described will do the jobmuch better.

The final three types of motors are the onesmost suitable for powering home shopmachinery: split phase motor (split phasestart- induct ion run), capacitor start motor(capacitor start-induction run), and capacitorstart-capacitor run motor. All are distinguishedby a solid squirrel cage rotor and an audibleclick when the motor has been turned off and

is slowing down. The split phase motor has nocylindrical hump on the outside for thecapacitor; the other two types obviously do.The capacitor start-capacitor run motor willhave either two capacitor humps or will have acapacitor with three separate electricalconnections. By the process of elimination, itshould seem obvious that a capacitor startmotor will have a single capacitor that hasonly two electrical connectors.

All of the motors described operate on housecurrent, which is single phase. Three phasemotors are commonly found on used industrialmachines and will not run on house currentwithout an expensive rotary phase converter.The solid state phase converters are cheaper,but our local electric motor rewinder intimatesthey have a tendency to bum out. Perhapsanother reader with personal experience withsolid state phase converters could enlightenus. Because of a lack of experience with threephase power/ I have found it best to avoid thesemotors. The maker's plate with the electricalinformation states whether the motor is singlephase or three phase.

RECOA{MENDATIONS ONTYPE AND SIZE OF MOTOR

Capacitor motors have a much greater startingtorque than split phase motors. I prefer to usecapacitor start motors on all tools exceptbench grinders. When the starting load isheavy, a split phase motor will take a longtime to come up to speed. There are twoproblems with this. One is that a great deal ofcurrent is drawn, causing the shop lights todim. The other is that the starting windingsare a lighter gage wire; with repeated two- orthree-second starting periods, the starterwindings will eventually burn out.

Split phase motors are considered to beadequate for easy starting tools, such asgrinders, drill presses, jigsaws, and the like.I have found the % hp split phase motor on myold Delta drill press to be adequate for all butthe higher speeds. I plan to replace it with aVzhp capacitor motor when I find one at ayardsale. If I had an industrial drill press with aNo. 2 or No. 3 Morse taper, I would want a3/q 4 7

or I hp motor. A respected practitioner of ourcraft is quite satisfied with a Vehp split phasemotor on his ?" South Bend lathe but admitsto doing only light turning. I believe themanufacturer recommends a Vzhp capacitormotor. I had a Vzhp capacitor motor onrny 12"Clausing lathe. This never seemed to slowdown even under heavy cuts, but a windingeventually burned out. From this experience,I infer that something more robust than aVzhpmotor is needed for a 12" iathe. I suspect that a7+ hp motor would have been adequate, but a1.5 hp motor was the only used motoravailable when the old oqe burned out.

ADBQUACY OF SHOP WIRING ANDTHE MERITS OF 220-VOLT OPERATION

Next comes the job of wiring the motor. Firstlook on the motor's information plate for theoperating amperage and determine if the shopwiring and fusing are adequate. According toSears and Roebuck's "Simplified ElectricalWiring," the starting currents of motors areroughly three times the operating currentlisted. For practical purposes, unless thestarting time of the motor is prolonged by aheavy load, the operating current of the motorwill determine if the breaker is going to trip.As an example, at I lOv, a typical % hp motorwill operate on 7 amps or less, but will draw 22amps when starting. In my old house whichhad lS-amp breakers, I never overloaded thecircuit with a % hp motor.

If you acquire a piece of equipment thatexceeds your shop's electrical capacity, you'regoing to have to do some wiring. The purchaseof my air compressor presented me with thisproblem. At 110v its operating current wasl7.B amps and the 15-amp breaker would triprather frequently. At the time, I didn't knowhow easy it was to add a circuit breaker andrun a22Ov line, so I tapped into one of the20-amp circuits in the house and used l2-gagewire to run a new I lOv line to the shop.

A few years later, a machinist friend introducedme to the concept of using 220v current for themachines. i had always assumed that heavywire such as that used on dryers and rangeswas needed for 220v work. Not so! Thosewires are heavy because dryers and ranges pullcurrents in the realm of 30 and 50 amps,respectiveiy. Actualiy, a reduction in the wiregage may be enabled by running a motor at220v. When a motor is rewired to run at220v,its operating amperage is halved. Thus, thecompressor that pulled 17.8 amps at l10v onlydrew 8.9 amps at 220v. When I finally ran my220v line to the shop, I used a lS-amp breaker

and l4-gage wire. What a difference it made inhow quickly the compressor started. I used thesame outlet as I was using for I lOv, butpainted a sign on the outlet that labeled it asbeing 220v. I doubt this outlet meets theelectrical code since the special receptacles for220vphysicallyprevent a 110v appliance frombeing plugged in; however, I feel this practrceis acceptable in one's home shop. On motorsthat will operate at either I 10 or 220v, I preferto run them on 220v since there is much lessdimming of the lights and much quickerstarting at this voltage.

For future reference, remember that fuses andcircuit breakers protect the wiring of the housefrom overheating and buming while inside awall, and therefore are sized to be compatiblewith the house wiring they protect - not themachine connected to it. This is why it'sdangerous to just put a larger fuse or breakeron the circuit to your shop without improvingthe wiring. l2-gage wire will carry 20 amps,I4-gage wire 15 amps, and l6-gage wire l0amps. Home wiring is fairly straightforward,but the details are beyond the intent of thisarticle. I refer the reader again to the previouslymentioned booklet sold by Sears and Roebuckfor an expanded description of the procedure.

INTERNAL WIRING CONNECTIONS :CHANGING FROM llOV to 22OV OPERATION

Next we tum our attention to the internalwiring arrangements of split phase andcapacitor motors. They are almost identicalexcept that the capacitor start motor has acapacitor. Both motors have two types ofwindings - starter windings and runningwindings. The starter windings determine thedirection of rotation. They are of a light gagewire since they are only used briefly forstarting and then are disconnected from thecircuit by a centrifugal switch when the motoris almost up to speed. The click heard whenthe motor is slowing to a halt is the centrifugalswitch clicking the starting windings backinto the circuit. The lead numbering systemI present in my diagrams, Figures I through 4,is used in three motors in my shop, all ofwhich are of different manufacture. One ofthem is British in origin. I assume thenumbering system is universal, but I can't beassured of this since I haven't found thesediagrams in print. If there is a wiring diagramon your motor, so much the better; you don'tneed me. If not, I'll give you as many tricks toidentify the leads as I can:

Lead No. 8 is the one usually attached to thecapacitor or centrifugal switch. Leads No. 648

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R = running winding

S - start ing winding

-l F : capacitor

I = centrifugal switch

^nd7 are usually buried somewhere in themotor and aren't seen. If three leads aretwisted together, they probably represent tworunning winding leads and a starting windinglead. According to an article in Model Engineer(Volume 145, Number 3520, November 1979,page 12521, the starting windings have aslightly higher resistance than the runningwindings. On my Brooks 1.5 hp motor/ thestarting windiggs have a resistance of 2.2 ohmsand running windings have 1.2 ohms ofresistance. Take the utmost care in maEifigthese measurements since a dirty contact willalter the measurement. If only four leads cometo the terminal board, two are probablyrunning winding leads and two are probablythe starting winding leads No. 5 and 8. I can'tcover all the possibilities, but that should helpyou in getting started.

Figures I and 3 show the comparison betweena motor set up to run onL2Ov versus one wiredto run at 110v. Note that the starting windings

are connected in series with one of the runningwindings when the motor is wired to run at22Ov. A few years ago when I bought a used 3/q

hp motor to replace the three phase one thatcame in my Hardinge mill, a less thanattentive employee at the motor rewindersinstructed me to connect starting windingIeads No. 5 and 8 to running winding leadsNo. 1 and 4 - in essence, to the fuIl 220v input.The motor ran ff.ne for two months, and thenone time on starting, it smoked, made ahorribly loud vibrating noise, and rotated atonly a fraction of its normal speed. Fortunately,only the capacitor had failed. When I purchasedthe new capacitor, I inquired about the wiringconnection on this motor since it was differentfrom two others in my shop. The owner of therewinding shop instructed me to place thestarting windings in series with the runningwindings so that they would absorb some ofthe current going to the starting windings andcapacitor, prolonging their life expectancy.

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DRUM SWITCH CONFIGURATION22Ov

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Having converted a motor to run on 220v, it isworthwhile to test it at I l0v first. If wiredcorrectly, it will run at a somewhat slowerthan normal speed.

REVERSING THE ROTATIONAND WIRING DRUM SWITCHES

Reversing the rotation of a motor is oftendesired. From Figures I through 4, it is evidentthat reversing the connections of the startingwinding leads No. 5 and B is all that isnecessary. In Figures 5 and 6 are the wiringdiagrams for the terminals in a drum switchcontrolling a22Ov motor. Figures 7 and 8 showthe same switch wired for a 110v motor. Notethat the only difference in the internal wiringof the drum switch between i 10v and 220v rs alink between the terminals on the lower left.Pay attention to the fac,t that in Figures 7 and 8Line 2 is the hot or live wire.

Several years ago, when the previouslymentioned % hp motor in my lathe burnedout, I didn't have a reversing switch but onlythe standard single pole wall switch controllingthe current flow. Thoughtlessiy, I hadconnected this switch to the neutral (white)lead. When the motor started to hiss andsmoke, I quickly flipped the switch off. Muchto my alarm, the motor continued to hiss,smoke, and run! When the winding burned, itshorted to the motor frame and a circuit wascompleted {rom the hot wire through theremaining windings to the ground wire. I hadto dash to the breaker box to shut off mv lathe.

ReverseFigute 6

Forward

Figure 8

(thank goodness I've never tried to save a fewcents by buying electric cord without a groundwire or, in this case/ I might have been theground wire.)

This same flow occurs in the wiring of thedrum switchlot 22Ov since both of the linesare hot {live), and Line I is directly connectedto the motor without an intervening switch. Inmy own shop, I solved this problem with amagnetic starter; more on these later. Figure 9shows an alternate type of drum switchconff.guration which may be encountered. Bynow you should have some idea of how toarrange the connections, so I won't illustratethese. If you're stil l in your salad days andcan't afford a drum switch, an alternative is toutiiize a four-way switch, the type used inhousehold wiring when three or more switchescontrol the same circuit. The electrical connec-tions are illustrated in Figures 9 through 13.

There are two types of four-way switches -

cross type and through type - and you'll haveto determine which type you have with anohmmeter or test lamp. I have illustrated theconnections for a I l0v motor only, but there'sno reason the same setup couldn't be used for22Ov operution. With a four-way switch you'llneed a separate switch to turn the motoron and off.

While we're on the topic of making-do, I'll passon another pearl. Shoe eyelets make niceelectrical connectors. |ust wrap the bare wirc

Forward

Figure 5

50

around the post and crimp. Sometimes a rap inthe hole with a center punch is needed toexpand it so that it will ff.t over a screwterminal. Next you'Il 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 sl" ID clear plastictubing and different colors of 14 or 16 gagemultistrand wire. If the cable isn't toolong, a coat hanger can be used to pull thewires through.

MOTOR PROTECTION AND MAGNETIC STARTERS

Motor protection is often neglected. Thefusebox or circuit breaker does nothing toprotect the motor in case of an overload. Theyiust protect the house wiring so it doesn't startto burn while hidden in a wall.

Dayton sells a single pole fractional horse-power manual motor starter/ stock No. 5X269,that lists for $22. Their two-pole modelNo. 5X270 should be used {.or 22Ov hookupsand lists f.or $25. A heater element matched tothe operating amperage of the motor must bebought separately and lists for $4.

Many used machines come with the motorprotection device still attached. In some casesthey are manual devices and in others they aremagnetic starters. Almost invariably thesedevices are set up for three phase operation, soyou'll have to follow the instructions insidethe lid to make the conversion to single phaseoperation and the proper voltage. You'll haveto buy one or two heater elements to matchthe operating amperage of the motor to beprotected. A list of the part numbers for theheater elements is usually printed inside thelid with the connection instructions. Thesecost about $7 apiece. On magnetic starters,also look at the iabel on the magnetic coil to besure it's the correct one for the voltage youintend to use. The protection device is placedin the circuit between the plug and the drumswitch. Thus, the sequence is: plug and cordleading into protection device, then the drumswitch, and then the motor. Some motors havethermal overload protectors built in. I supposethey work, but I've been less than trusting ofthem since the only motor in my shop to haveone was the lathe motor that bumed out. Iconfess that only the more expensive motorsin my shop are protected.

Before moving on to the next topic, a finalreminder - always include a ground wire in allyour circuits so that if a short develops, youaren't the ground.

RNATE DRUM SWITCH CONFIGURA

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TROUBLESHOOTING

There are only a limited number of things thatcan go wrong electrically with split phase andcapacitor motors. Listing what can go wrong iseasy. Explaining how to isolate the circuits fortesting is difficuit, and you'll have to use yourown ingenuity plus the wiring schemes I'vegiven you. You'll need an ohmmeter or a testlamp to do the testing.

If the motor doesn't even hum when you plugit in, it's either not getting any power at ali orthere's a break in one of the circuits inside themotor. Look at the windings. If one or morelooks blackened and smells burnt, it's probablyburned out. It doesn't seem profi.table formotor repairmen to rewind small single phasemotors/ so if you've bumed out a winding,you're probably going to have to replacethe motor.

If the motor hums but won't tum, there areseveral possibilities, all dealing with the

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51

starting windings. Check to see that all theconnections are in the right place. Look forburned windings. Examine the capacitor. If ithas leaked a few drops of oil, it's no good.Remove the wires to the capacitor and test itwith an ohmmeter set on the 100x or 1000xscale. The needle should briefly swing toward0 ohms and then drift back to the high end ofthe scale. If it doesn't swing toward 0 ohms,short the capacitor terminals with a screw-driver and try the test again; the capacitor mayhave had a small charge that would interferewith this test.

The centrifugal switch normally is closed andpasses current when the motor is stopped. If itdoesnlt, pull the bell ends off of the motorframe and look at the centrifugal switchcontacts. Push the contacts together and testthem with the ohmmeter to be certain they door don't transmit current. Oil or grease fromthe bearings can prevent the contacts fromclosing. Look at the contact surfaces for pittingor burning. If they need it, brighten them upwith a point file or emery paper, taking carenot to get the emery dust in the bearing.

If you don't hear a click when the motor'sslowing down, the centrifugal switch isir't

working. Pull the bell ends off the frame andlook at the centrifugal switch. The weightsshould be moveable although stiff because ofspring tension. If the bearings are extremelyworn, the rotor may touch the frame andprevent the motor from operating. I've neverseen this, but I'd expect to ftnd a lot of play inthe motor shaft and either bright spots orbumed spots inside the frame where the rotorwas rubbing.

If the motor starts but just doesn't seem tohave as much power as it should, look to see ifone of the windings looks burned. Check tosee that all the electrical connections arecorrect and clean. Make sure you don't havethe motor wired to run on 220v when you'reonly using I l0v.

A number of publications have served asreferences to supplement what has flowecspontaneously from my pen, and the readermay find the following references helpful:"simplified Electrical Wiring," Sears, Roebuckand Company; Electric Motor Test and Repairby TAB Books, Inc., obtained from a regularadvertiser in HSM; and Model EngineerVolume 145, Number 362O, pages 126O-1263,and Number 3622, pages 1414-1416.

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Imprcved Atlas6"LotheGeor Cover

by C. M. Luchessa

n/T ost owners of the Atlas 5" lathe willJ- Y lprobably share my dissatisfaction withthe original pulley and gearbox cover assembly.Like myself, they have carelessly ieopardizedsafety at times when the somewhat awkwardmounting and removal procedure wasbypassed in a time-saving tradeoff.

The general outline of an alternate mountingscheme shown in Figure I comes close toduplicating the hinged-type gear guardssupplied with older model lathes whichpermitted easy access to the drive belt and geartrain enclosure. Here (Figure 1) the plasticcover is attached to a swivel post mounted onthe rear lathe bench with a small floor flange.A brass snap spring attached to the front of the

gearbox allows the operator to open and closewith kitchen-cabinet ease.

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CONNECTIONS

I moved to Arizona in spting L995. After attiving I boughta miltldrill, 105'1108 (-1tlO on the nameplate) from Enco'I am told the model number vaties with the package'(l got the stand with it.)

The 2 hp drive motor is dual voltage, 1151230V' I pref errgd -to wire-it to operate on 230V, thus gettingby with #12 AWGwiring. Whili the motor had a connection diagram insidethe tirminal box, therc is nothing said about the reversingswitch. Having worked on motots eailier in life, I had no

problem reconnectinS. It passed the "smoke test" (no smoke)

On a single phase motot like this, the statting winding is

wound for operation on 1'1-0V, The running winding is in twohalves,'ea"i one for 110V. For 110V operation all threewindings ate connected in parallel Fot 220V operation the

two ruining windings are connected in series with the

stafiing wiiding coinected aczoss one tunning winding

For my machine I left wire 5 connected to wfues 2 and 3'I had'the reversing switch connect wite 6 to wire 1 or 4

depending upon the ditection of rotation desired' See my

swit ch co nn e ction di a gt am.

Paul E. Pierce

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Apache function, AZ

NOSMOKINGsEcTIqN

NOTCONNECTEO

230V 1

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iandle it, When I deicribed this concetnwith a subsequent order

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supurse"ding it and is advetised in the cwrent issue of Liue Steam'

Siippng "6tt*ot couttesy of New England Brass, as well'

I immediately accepted this offer and was well pLeased with

iht n"* -od"l when it anived' This js cetainly a case ofgoing the exfta mile to ensure customer satisfaction, and

I cannot overctate my appteciation of the way these folksconduct thefu business.

Terence F. McMillanMapleValley, WA

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1 6 T H E H O M E S H O P M A C H I N I S T