Wiring VFD controls through drum switch
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  1. #1
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    Default Wiring VFD controls through drum switch

    I picked up a Clausing Colchester 13" lathe today. I'm looking to wire a VFD to the motor, and use the lever controls on the front of the machine to operate the lathe. So, that means I need to use the existing switches as 12v control switches. I think the on/off switch should be relatively simple to do.

    However, this lathe has a 2 speed motor, along with FWD/REV positions, so a total of 4 positions. The plan is to not mess with switching between high and low on the motor, but just run at a lower frequency for low speed which will have the same effect. So, I will have: FWD/60hz, FWD/30hz, REV/60hz, and REV/30hz.

    I believe I can switch between the 4 described operation modes with the VFD, but need to determine how to wire the drum switch up to switch between the 4 different modes.

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    20210723_202647.jpg

    20210723_202636.jpg

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    Disconnect wires from the drum switch, hard-wire the motor for high speed mode, and connect it to the VFD. Direction is irrelevant at this point, pick one and do it.

    Use the drum switch's contacts to control the run-stop-direction signal control connections for your VFD. If the motor direction is opposite from your handle, just swap two of the three wires on the VFD motor output terminals.

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    I think my main issue is that I'm just not sure which contacts in the drum switch to wire things to! I am not an electrician so I am having trouble reading the diagram lol

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    If you have a dual speed motor then you would wire it for a single speed, and which speed connections you use would be based on the type of motor if it is a constant Hp or constant Torque type. So post a picture of the motor plate. The speed change would be with a speed pot connected to the VFD and not switching the motor windings. The VFD is directly wired to the VFD output, and you need to connect the motor leads at the motor. You are probably better off just replacing the drum switch with a 3 position rotary switch, FOR-OFF-REV and adding a speed pot. The issue is not that the drum switch could not be used, but the contacts are usually burnt from the high voltage and are poor contacts for low voltage signaling. Some people will recondition the contacts, but I have seen intermittent issues using drum switches for switching the VFD inputs, and also you have two extra drum switch positions that would not be used. You would also remove the power contactor and thermal overloads that were previously used for the motor.

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    I know people say not to put a switch between the VFD and motor, but as long as the motor isn't actively drawing current when the switch is actuated it wouldn't be an issue, would it? I'm thinking I could save myself a lot of headache if I just wire the VFD output though the existing controls and use both the high/low speed on the motor. Only issue then I think is that the VFD may not be configured properly if I switch between high and low. Since in high it operates at 3hp and at low, 1-1/2hp

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    Quote Originally Posted by Domodude17 View Post
    …wire the VFD output though the existing controls and use both the high/low speed on the motor.
    That’s exactly what I did with my mill (BP clone). I kept the H/L drum and used an extra (never-before used) set of contacts on it for low-voltage signaling to the VFD. My VFD (Automation Direct GS20) can use an external input to select from multiple motor configurations, so the drum switch changes the motor wiring between 4- and 2- pole, and the VFD uses the appropriate parameters for each. I do not switch when the motor is energized. It seems to work fine. I run the VFD up to 90 Hz, so there keeping the 2-pole configuration gives me a little more on the top end if I want it. Mostly, I wanted to experiment a bit. I use separate, new controls for speed and direction.

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    There is limited advantage of switching the motor windings from high to low vs. using the stock motor in a single speed configuration and turning down the speed pot 50%, the Hp rating will be the same in this case, the torque would be less in the latter (but a non-issue with a lathe multi-speed gearbox). You need to program the VFD for two separate sets of motor parameters and use an additional VFD input to tell the VFD which set of motor parameters to use. You cannot use the current drum switch to start/stop and switch motor parameters while the motor is running. Having done a number of 2 speed motor VFD installs, I have typically have had poor success with such two speed switching arrangements and no longer do them. Basically a lazy mans approach to something that should be done properly in the first place. You can buy an RPC box and find a 7.5 Hp for not much and make your own RPC for probably under $400. If a 2 speed motor was a constant Hp, then I run them on the higher pole setting and run them to 2X their base speed. On most VFD lathe installs I have done where there was a 2 speed motor, typically I replaced the motor with a single speed inverter/vector type motor running to 2X its base speed or more. Hopefully your 2 speed motor is better than the Asian ones I have dealt with.

    A typical 2 pole motor the maximum rated speed is 1.25X base speed, unless it is a vector type motor. If it was a constant Hp motor then I connected it at the higher pole connections and run it to 2X its base speed.

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    So are you using 12v for signal control to switch between high and low? I unfortunately don't think my drum has any unused contacts.

    The only other way I thought to do this: the drum switch is 5 position, with the middle position being an "off" position, so if you were changing from forward to reverse you need to move through this off position. I might be able to set up the off position as a momentary switch to change between fwd/rev, and keep 1 position on each side for 30hz and the other position for 60hz, without a direction assigned to them.

    I'm assuming your GS20 has the ability to change between different preset speeds, do you know if you can assign a rotation direction to those speeds? I'm not at all opposed to going with a different VFD if it'll get me where I need to go (just as long as it's not a Chinese one!)

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    Quote Originally Posted by Domodude17 View Post
    I picked up a Clausing Colchester 13" lathe today. I'm looking to wire a VFD to the motor, and use the lever controls on the front of the machine to operate the lathe. So, that means I need to use the existing switches as 12v control switches. I think the on/off switch should be relatively simple to do.

    However, this lathe has a 2 speed motor, along with FWD/REV positions, so a total of 4 positions. The plan is to not mess with switching between high and low on the motor, but just run at a lower frequency for low speed which will have the same effect. So, I will have: FWD/60hz, FWD/30hz, REV/60hz, and REV/30hz.

    I believe I can switch between the 4 described operation modes with the VFD, but need to determine how to wire the drum switch up to switch between the 4 different modes.
    This is the corrct approach. You want to use the preset speed options on the VFD to achieve two-speed operation. Your manual will tell you how to do that.

    Consider replacing the drum switch with a simple center off toggle and a potentiometer to change speed - you could just put two lines on the box - slow, fast.

    If you have your heart set on emulating the drum switch operation:

    Hard-wire the motor to the high speed.

    Pick a set of contacts in the switch that will be used for forward and rev switching. Common switch lead will go to the high VFD line for forward in both high and low, and to reverse VFD line in rev hi and lo.

    Then pick the contacts that go to the VFD preset speed lines, drum switch will have contacts that connect in high and lo switch positions - tie the two low contacts together and the two high contacts together.

    For most VFDs the common will be just one logic wire for all the functions so that will simplify the wiring - common, fwd, rev, speed 1, speed 2. Basically 5 logic wires.

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    I have a similar setup, but my lathe speed was a separate rotary switch.
    WAS.
    I rewired the drum switch to control the VFD for forward / off / reverse.
    The drum switch is a big robust thing integrated into the lathe and me, so using it makes life easy. No need to look away from the work, my hand knows where it is.

    My speed control is a potmeter in a box on the wall. I added a disk and wrote hz output on it, because I still have 3 gears so spindle speed may differ.

    I wouldn't bother with your 2 pre-existing speed settings; use a potmeter for a wide speed range.
    I go from 15 to 100hz. For high torque use I use low gear range but for threading to a tight spot, the low motor speed is great. the VFD will brake the motor quickly.

    I use the same VFD for my drill press.vfd-instalation.jpg

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    So I had one of my buddies come over who programs VFDs and does industrial controls for a living and take a look. There are a grand total of 14 contacts, so we went through and found contacts we can use for the two 60hz positions and the two 30hz positions. We also found contacts we can tie together to provide a signal to the VFD to tell it which way to rotate. So I think I should be good. Checked the resistance across the contacts and it was an ohm or less, but i'm going to clean them up anyways.

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    We modified our 3 layer drum switch.

    Removed the cross wires so it now is a 3 conductor, on-off-on switch.

    Using basic 3 wire control with separate pot.

    Bent the contacts on ONE conductor so it makes before the other 2.

    The "STOP" wire goes here.

    One of the remaining 2 makes on both sides for "RUN"

    The last only makes on One side for"REVERSE"

    VFD responds as it should

    Sent from my SAMSUNG-SM-G930A using Tapatalk


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