How can I get this motor to reverse?

J

jrudyk1

Member
Location
BC, Canada
Occupation
Journeyman Electrician
This shop replaced the motor for their lathe and I was sent to hook it up. The lathe has a forward/reverse switch hooked up to a pair of contacters. I am wondering how to hook up the new motor so it works with the existing setup. The old motor has already been discarded so I don't have that for reference. Originally 4 leads would go to the motor from the terminal block. I've drawn up what I think would work and attached some pictures of the motor and schematics. The new motor is not instant reverse so it would have to come to a stop to change direction but that's a compromise they can live with. Motor will be running on 208v.
https://imgur.com/a/zkdEN9J
 
On the nameplate it says to swap T5 & T8 to reverse direction. You don't mention the number of poles on the contactors. Hopefully there are four. Two of the contacts would supply the line voltage, the other two would connect T5 to T4, and T8 to T2 & T3 for one direction. On the other contactor, two of the contacts would again supply the line voltage, while the other two would connect T8 to T4, and T5 to T2 & T3 for the other direction.
 
Greetings jrudyk1

The power feeding this motor is it fuses or breaker?
 
TwoBlocked said:
On the nameplate it says to swap T5 & T8 to reverse direction. You don't mention the number of poles on the contactors. Hopefully there are four. Two of the contacts would supply the line voltage, the other two would connect T5 to T4, and T8 to T2 & T3 for one direction. On the other contactor, two of the contacts would again supply the line voltage, while the other two would connect T8 to T4, and T5 to T2 & T3 for the other direction.
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could still be done with three pole contactors, but one of the line voltage contacts would be eliminated and motor would have one line conductor always energized. Which is code compliant, a motor control only has to interrupt enough lines to interrupt current through the motor. A disconnecting means has to interrupt all ungrounded conductors though.
 
Tommy1776 said:
Greetings jrudyk1

How to wire a 3 phase 208v forward/reverse switch to contactors to a motor

To wire a 3-phase 208V forward/reverse switch to contactors for a motor, connect the power supply to the contactors' input terminals, then use the switch to select which contactor energizes, effectively swapping two of the three phases going to the motor to change its direction of rotation; ensure proper interlock between the contactors to prevent them from energizing simultaneously, which could cause a short circuit.

https://www.electricaltechnology.org/2014/06/rew-for-three-phase-motor-connection-power-control.html
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TwoBlocked said:
On the nameplate it says to swap T5 & T8 to reverse direction. You don't mention the number of poles on the contactors. Hopefully there are four. Two of the contacts would supply the line voltage, the other two would connect T5 to T4, and T8 to T2 & T3 for one direction. On the other contactor, two of the contacts would again supply the line voltage, while the other two would connect T8 to T4, and T5 to T2 & T3 for the other direction.
Click to expand...
These are 3-pole contactors, KM1 and KM2. The original motor had 4 wires going to it from the terminal block at the bottom of the control box photo as also described in the schematics
 
With single phase motors, you either reverse the start winding, or reverse the run winding. Doing so with the motor running, will make it continue the same direction. It will have to come to a complete stop before it can be reversed. The new motor should work and wire the same as the old.
 
jrudyk1 said:
These are 3-pole contactors, KM1 and KM2. The original motor had 4 wires going to it from the terminal block at the bottom of the control box photo as also described in the schematics
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Can't see your picture from post 1. You can reverse a single phase motor running on high voltage by swapping T5 from line 1 to line 2.
 
jrudyk1 said:
These are 3-pole contactors, KM1 and KM2. The original motor had 4 wires going to it from the terminal block at the bottom of the control box photo as also described in the schematics
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Here is the basic concept of doing it with two three pole contactors with the power wiring circuit. I just drew this.1735316390494.png
 
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hillbilly1 said:
Doing so with the motor running, will make it continue the same direction.
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That is dependent on what the motor design is. If the aux winding is totally disconnected by a centrifugal switch after reaching a pre determined speed yes. A PSC or CSCR type motor would have counter force applied when you reverse the aux winding while still running. Typical ceiling fan motors are PSC and an example of something that can be reversed while running, but PSC have low starting torque and is why it takes considerable time for it to come to a stop and then reverse rotating. The typical CSCR motor would not a have a very high (reverse) starting torque until it has slowed down enough to disengage the centrifugal switch.
 
kwired said:
That is dependent on what the motor design is. If the aux winding is totally disconnected by a centrifugal switch after reaching a pre determined speed yes. A PSC or CSCR type motor would have counter force applied when you reverse the aux winding while still running. Typical ceiling fan motors are PSC and an example of something that can be reversed while running, but PSC have low starting torque and is why it takes considerable time for it to come to a stop and then reverse rotating. The typical CSCR motor would not a have a very high (reverse) starting torque until it has slowed down enough to disengage the centrifugal switch.
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But we are not talking about that type of motor.
 
hillbilly1 said:
But we are not talking about that type of motor.
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Likely so. Key factor is that it says general purpose motor, along with the 2 HP rating. 1 HP and below often is capacitor start but not capacitor run. Over 1 HP is usually CSCR.

I have seen up to 10-12 HP PSC motors, but those were not general purpose motors, they were definite purpose motors for fans that didn't need high starting torque.
 
jrudyk1 said:
These are 3-pole contactors, KM1 and KM2. The original motor had 4 wires going to it from the terminal block at the bottom of the control box photo as also described in the schematics
Click to expand...
Yes, it can be done with a 3-pole contactor, as in post #4. Sorry, but I don't see a control box photo nor schematics.
 
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