In phibìc America, many single phase electric motors motors in the variety of 1 hp come 2 hp canbe rewired to operation at either 120 volts or 240 volts (or 115 vs 230 volts, itdepends top top what voltage is suspect "nominal").Such motors will typically have six leads coming out of the motor to the wiringbox, or few of the connections might be screw terminals.The best means to readjust the voltage top top a motor is to follow the wiring diagram onthe label. But sometimes once you open up a motor, there"s just six wiresand no diagram! This taken place to it is in the instance for the 1.5 hp motoron my old table saw.20 years back I wired it come 240 volts, yet I wanted to switch it ago to 120 volts.for where I relocated it to.
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Internally, the motor has two 120 volt windings, which are in serieswhen the engine is wired because that 240 volts (left, in ~ left).When convert it to 120 volts, the two windings space reconfigured to be in parallel.It would be easier to attach A come C, and also then affix power come B.But this will certainly switch the polarity of the winding in between A and also B, which way windingA-B would certainly be fighting winding B-C. If you climate plugged it in favor that, themotor would certainly draw about 100 amperes, yet it wouldn"t run. If the circuit breakerdidn"t pop ideal away, the motor would begin to smoke within ten seconds.
But it"s no that simple: there is additionally a starter winding
But it"s actually more complex than portrayed above. The motor also hasa starter winding, i m sorry is in collection with a starter switch and also starter capacitor(see red outline at left). The starter winding is only active while the motoris spinning approximately speed.If the starter winding and capacitor likewise needed to be reconfigured for voltagechanges, the wiring would be quite a nightmare!So instead, the starter winding in these electric motors is constantly a 120 volt winding,and the motors two 120 volt windings are supplied as one autotransformer to make the 120volts because that the starter winding. Reconfiguring between 240 and also 120 volts is donethe same way, yet the starter winding stays linked to one of the windings.If friend don"t have actually a wiring diagram, and also the motor is at this time wired for 240 volts,you can identify allude "B" by the fact that the isn"tconnected to either power lead. Utilizing an ohm meter, inspect whichof the 3 wires indigenous B lead to the power lead with just one wireattached come it. That"s the one you need to disconnect and also connect to C.And the winding end at A needs to be carried to B.
After functioning this out, i realized, two decades ago, I relocated the starter capacitor mount onthis engine so that wouldn"t protrude over the table observed table once the blade istilted 45 degrees. And in relocating the capacitor, I ended up mounting it best overthe motor"s brand plate, which likewise shows the wiring.So removing the capacitor cover, I can see the label, complete with wiring diagramand ns was able to check my work prior to I plugged that in.
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Working out the wring because that a 120/240 volt solitary phase engine without in ~ wiring diagramSuppose you have actually a an enig single phase induction motor, 1750 rpm or 3500 rpm(or really close come those RPMs). Over there are 6 leads, or wires coming the end of it.How carry out you wire it up?On part motors, it will certainly be six connections, however some of them might be screw terminalsin the wiring rather of cable leads. I"ll just speak to them leads.If the motor has screw short articles for it is registered the leader to,it will commonly have second screw short article for connecting wires with each other in240 volt operation, yet the screw short article doesn"t attach to something in the motor.Using an ohm meter, find a pair of leader that has less 보다 5 ohms between them.The reading should not adjust as you organize the meter top top those. Label thesewires 1 and also 2. 1 and also 2 shouldn"t have any type of conductivity to any kind of other leader coming out.Now find an additional pair of wires through the very same resistance together 1 and also 2 in between them,Label this 3 and 4. 1-2 and 3-4 are the main windings.
The continuing to be two leader should affix to the starting capacitor, starting switch,and straiting winding in series (with the motor not running, the starting switchwill it is in closed).Label these continuing to be leads 5 and 6.If you measure the resistance in between 5 and also 6, you must see thereading on her meter continually raising (set your meter come something otherthan the shortest ohm range). If youswap the meter probes in between 5 and also 6, the resistance reading will be reduced again,but again go up. You room measuring resistance across the capacitor, and also as it"charges up" from the meter applying current come measure,the resistance analysis will go up.For 120 volt operation, you have to either connect1,3,5 to one strength lead and also 2,4,6 to the various other OR 1,4,5 and also 2,3,6. Yet which one??If you acquire it wrong, you will blow the circuit breaker or damage the motor.Basically, if winding 1-2 is the contrary winding 3-4, very bad things happen.You can, because that a brief time, run the motor turn off 120 volts using just one of the 120 volt winding.So just leave leads 3 and 4 disconnected. Connect one power bring about 1,5, the otherto 2,6, and also plug the in come 120 volts. The motor need to run.Unplug the motor, now include lead 3 to 1 and 5 (1,3,5 and also one that the power leadsall together), and leave simply 2,6 to the various other power lead.Plug in the motor, while it runs, measure up the voltage in between the remaining unconnected command 4 and also the other lead offering power, connected to leads 2,6).If the voltage is much less than 10 volts, climate youcan connect lead 2,4,6 together. Her motor is currently wired for 120 volts.If the analysis is end 200 volts, climate you need to swap leader 3 and also 4.Re-label lead 3 together 4, and 4 together 3, climate repeat the step over and make certain the differencereading is much less than 10 volts.To turning back the motor, swap leads 5 and 6 (the ones that go to the starter winding)To cable the motor because that 240 volts, connect lead 1 come one power leadconnect leader 2,3,5 with each other (without connecting them come either strength lead)Connect the other power result in 4,6.If the motor has actually screw write-ups in the wiring box, there will certainly be an extra screw post,not linked to anything, because that connecting leader 2,3,5 together.And together before, to reverse the motor, swap leads 5 and also 6If this doesn"t work-related for you, it"s possible that the engine is no a double voltagesingle phase motor, or there is miscellaneous wrong with it. Feel complimentary to email me.I probably won"t be able to help you, however it"s useful to understand whereyou run right into problems. That way, if a the majority of folks gain hung increase on the sameproblem, I might be maybe to add some notes around that.And if you punch up a engine or it captures fire, don"t reprimand me!