Simple Way to Hook Up a VFD to a 13x40 Lathe
So Jerimy reached out to me last week for help with his Enco 13x40 lathe which is different from mine. His was designed with 3-phase input, and he wanted to be able to use it with the lathe controls and the VFD. But he had a problem; the VFD can't make 3-phase input power to the lathe, because the VFD output power should never be switched.
I spent a few hours trying to track down his lathe wiring diagram, and make sense of the thorough wiring diagram he had traced out from his control box. I found several possible candidates for the diagram, and was going back and forth with Jerimy to see if we could figure out how to make it work. Then it finally occurred to me that it's really easy to hook up a VFD to most ENCO lathes (and probably many other Taiwanese/Chinese lathes. Here's the easy scoop.
1) You need to make sure that you run main power to the control box. If you have a single-phase lathe, that's easy -- just use the two conductors on the line in. If you have a three-phase lathe, you'll need to make sure you get the two conductors that connect to the transformer in your control box. The transformer generates AC (sometimes 110 V, sometimes 24V) that is used to control all of the circuitry. You need to get that transformer hooked up.
2) Now that you have a powered-up controller, look for the normally-open auxiliary connectors on the main contactors. The main contactors are typically on the upper-left hand side of the control box; you can find them by tracing the wires that go to the motor back to the contactors that feed the motor (through a thermal relay -- just keep going back).
One of the contactors will be for running in forward; the other will be for running in reverse. Each of those contactors has three main circuits for running the motor -- usually labeled L1, L2, L3; R, S, T; or U, V, W. Then, on the left side there is a NC (normally closed) auxiliary contact that is used to prevent having both forward and reverse on at the same time. On the right side of the contactor there is NO (normally open) auxiliary contact, usually labeled 3 and 4. This contact is generally not used; there are no wires connected to it.
If you don't have the NO auxiliary contact, or if there are wires going to the NO auxiliary contact, you cant use the simple method; you'll just have to figure out your wiring diagram. But if you do have unused NO auxiliary contacts, you're in luck.
To test the unused auxiliary contacts, attach power to the control box, clear the E-stop, and hit the power switch. Now, use a voltmeter to make sure there is no voltage on either of the NO terminals. When you've verified there is no voltage, set your meter to measure resistance, and verify that there is an open circuit across the NO contacts on each contactor. Then switch the lathe to forward (the motor should be disconnected so the lathe won't run) and measure the resistance across the NO contacts. One set of NO contacts will have a resistance of a few ohms -- that one is the forward contactor.
Now set your lathe to revers, and verify that the other contactor NO contacts now have low resistance.
3) With the forward and reverse contactors identified, you're in great shape. All you need to do now is identify the digital control leads on your VFD. One of them is typically called COM, and the others are typically S1, S2, S3, S4. Hook COM to one side of both NO contacts. Hook S1 to the other side of the forward contactor, and S2 to the other side of the reverse contactor.
4) Program your VFD so that S1 is set to be Forward/Stop, and S2 is set to be Reverse/Stop. See your VFD manual. It's usually not hard to do that. Also, you need to set your VFD so that control is from the external digital control.
5) Once that's done, you should be in great shape. Connect main power to the input of your VFD. Connect the three-phase output of your VFD to the motor. And the lathe should work just like it always has -- forward makes it go forward; reverse makes it go in reverse.
NOTE: If you'd like some help understanding these instructions, leave me a comment and I'll get back with you. Happy VFD'ing!
I spent a few hours trying to track down his lathe wiring diagram, and make sense of the thorough wiring diagram he had traced out from his control box. I found several possible candidates for the diagram, and was going back and forth with Jerimy to see if we could figure out how to make it work. Then it finally occurred to me that it's really easy to hook up a VFD to most ENCO lathes (and probably many other Taiwanese/Chinese lathes. Here's the easy scoop.
1) You need to make sure that you run main power to the control box. If you have a single-phase lathe, that's easy -- just use the two conductors on the line in. If you have a three-phase lathe, you'll need to make sure you get the two conductors that connect to the transformer in your control box. The transformer generates AC (sometimes 110 V, sometimes 24V) that is used to control all of the circuitry. You need to get that transformer hooked up.
2) Now that you have a powered-up controller, look for the normally-open auxiliary connectors on the main contactors. The main contactors are typically on the upper-left hand side of the control box; you can find them by tracing the wires that go to the motor back to the contactors that feed the motor (through a thermal relay -- just keep going back).
One of the contactors will be for running in forward; the other will be for running in reverse. Each of those contactors has three main circuits for running the motor -- usually labeled L1, L2, L3; R, S, T; or U, V, W. Then, on the left side there is a NC (normally closed) auxiliary contact that is used to prevent having both forward and reverse on at the same time. On the right side of the contactor there is NO (normally open) auxiliary contact, usually labeled 3 and 4. This contact is generally not used; there are no wires connected to it.
If you don't have the NO auxiliary contact, or if there are wires going to the NO auxiliary contact, you cant use the simple method; you'll just have to figure out your wiring diagram. But if you do have unused NO auxiliary contacts, you're in luck.
To test the unused auxiliary contacts, attach power to the control box, clear the E-stop, and hit the power switch. Now, use a voltmeter to make sure there is no voltage on either of the NO terminals. When you've verified there is no voltage, set your meter to measure resistance, and verify that there is an open circuit across the NO contacts on each contactor. Then switch the lathe to forward (the motor should be disconnected so the lathe won't run) and measure the resistance across the NO contacts. One set of NO contacts will have a resistance of a few ohms -- that one is the forward contactor.
Now set your lathe to revers, and verify that the other contactor NO contacts now have low resistance.
3) With the forward and reverse contactors identified, you're in great shape. All you need to do now is identify the digital control leads on your VFD. One of them is typically called COM, and the others are typically S1, S2, S3, S4. Hook COM to one side of both NO contacts. Hook S1 to the other side of the forward contactor, and S2 to the other side of the reverse contactor.
4) Program your VFD so that S1 is set to be Forward/Stop, and S2 is set to be Reverse/Stop. See your VFD manual. It's usually not hard to do that. Also, you need to set your VFD so that control is from the external digital control.
5) Once that's done, you should be in great shape. Connect main power to the input of your VFD. Connect the three-phase output of your VFD to the motor. And the lathe should work just like it always has -- forward makes it go forward; reverse makes it go in reverse.
NOTE: If you'd like some help understanding these instructions, leave me a comment and I'll get back with you. Happy VFD'ing!
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