rewiring 3 phase thermal overload switch to single phase w/VFD

[ching0n]

I've got a new-to-me machine that I'm currently refurbishing. All the wiring looks to be in decent shape and routed in a way that would make sense to repurpose. I've bypassed the current wiring provisionally to test out the motor w/a VFD. The 3-phase setup uses 3 buttons, FWD, REV latching buttons and a stop button that pops either out.

As far as I can tell, Power goes to thermal overload switch, goes to buttons, buttons back to motor windings. I want to remove the buttons and install the VFD there; the button wiring is already wired identically to how I'd wire the VFD. I'd like to use the thermal overload switch.....which I'm guessing acts as a circuit breaker w/the advantage of not having to go to the breaker panel to reset it (am I correct?)

2 of the phases are connected to "L1" & "L2" up top, the 3rd one is nutted to wire '3'. 1,2, and 3 go to mechanical buttons.



A) How do I rewire this thermal switch for 120 single phase? (I've got a 120v VFD)
B) How do I rewire this thermal switch for 240 single phase? (I've got a 220v VFD)
C) Same question as B, but If I wanted to use 4 wire 240 (to use the wire already there and get 120V at the machine for lights and auxiliary 120v)

 

[Bert_]

The vfd has overload protection built in. You don't need that thermal switch.

 

[OccupantRJ]

You should also not have any switches breaking the power between the VFD and the motor.

 

[fitter30]

Standard vfd unless its labeled for single phase to three phase vfd size has to be doubled in hp size at a minimum. Need to check full load amps of motor. Want the vfd same voltage as the motor.

 

[ching0n]

The vfd has overload protection built in. You don't need that thermal switch.

I'm guessing this thermal switch is what's currently built into modern motors? How do VFDs deal w/thermal shutoff built into modern motors?

edit: upon further reading, it looks like 3 phase motors don't customarily come w/built in thermal overload protection

I am also considering using a single phase motor (no VFD) in place since the machine has a reeves drive for variable speed. I haven't checked my 1 phase motor to see if it has built in thermal protection, how would I go about wiring it for this task? Would the contactor buttons function the same as a reversing barrel switch here (it's labeled 3-pole ac-reversing switch and it's rated for 1 & 3 phases)?

 

[Bert_]

Many 1ph motors have internal overload protection. If you needed to use that overload you would need to put the right size heater in it based on the amps of your motor.

Without pictures of the reversing buttons it's hard to say what you have or how to wire it.

 

[wyliesdiesels]

I'm guessing this thermal switch is what's currently built into modern motors? How do VFDs deal w/thermal shutoff built into modern motors?

edit: upon further reading, it looks like 3 phase motors don't customarily come w/built in thermal overload protection

I am also considering using a single phase motor (no VFD) in place since the machine has a reeves drive for variable speed. I haven't checked my 1 phase motor to see if it has built in thermal protection, how would I go about wiring it for this task? Would the contactor buttons function the same as a reversing barrel switch here (it's labeled 3-pole ac-reversing switch and it's rated for 1 & 3 phases)?

Ive never seen a 3Ø motor with integral O/L protection....

 

[wyliesdiesels]

as stated above, you do not wanting ANYTHING between the VFD and the motor. opening the circuit between the VFD and the motor while its running can cause nasty consequences on the VFD

 

[walta]

How do VFDs deal w/thermal shutoff built into modern motors?

edit: upon further reading, it looks like 3 phase motors don't customarily come w/built in thermal overload protection

I am also considering using a single phase motor (no VFD) in place since the machine has a reeves drive for variable speed. I haven't checked my 1 phase motor to see if it has built in thermal protection, how would I go about wiring it for this task? Would the contactor buttons function the same as a reversing barrel switch here (it's labeled 3-pole ac-reversing switch and it's rated for 1 & 3 phases)?

When you program the VFD you enter the max current number from the motors tag and the service factor number. If and when the motor draw to much current the VFD turns off the motor and displays an error code for over current.

I think it would be a mistake to install a single phase motor when you want variable speed. Have both the VFD and the reeves will give you better control.

Walta

 

[ching0n]

Many 1ph motors have internal overload protection. If you needed to use that overload you would need to put the right size heater in it based on the amps of your motor.

Without pictures of the reversing buttons it's hard to say what you have or how to wire it.

It's a cutler hammer; stop switch (middle) just throws the latch on either forward/reverse, there's busbars bridging both at the middle contacts which are also wired (yellow) go to thermal switch, the end contacts are jumped with wires and the bottom contacts (reverse) go to each phase of the motor....it's a fairly clean/simple setup but I have no 3-phase & don't want to deal w/a phase converter. sadly google sux now so can no longer find old literature or wiring diagrams to go by:

as stated above, you do not wanting ANYTHING between the VFD and the motor. opening the circuit between the VFD and the motor while its running can cause nasty consequences on the VFD

I was thinking more along the lines of repurposing it as a thermal circuit breaker at the machine (pre-VFD) so I don't have to walk to the panel if it 'pops'. I considered wiring the reverse switches after the VFD but as you said, it's apparently a no-no. I could rewire to the VFD inputs but kind of defeats the switch amp ratings.

When you program the VFD you enter the max current number from the motors tag and the service factor number. If and when the motor draw to much current the VFD turns off the motor and displays an error code for over current.

I think it would be a mistake to install a single phase motor when you want variable speed. Have both the VFD and the reeves will give you better control.

Walta

I hear you. I just like the 'aesthetics' of the original equipment too and would hate to see it go to waste. I'll see how the reeves performs once I swap those petrified belts w/something pliable.

 

[Bert_]

There's a good chance that overload is not big enough to power a single phase motor of the same horse power. You would have to look at the rating.

If it's rated high enough on single phase you would have to replace the heaters to reflect the higher amp draw of a single phase motor.

I would not expect to be regularly tripping a properly sized breaker. If you overload the machine you the vfd will fault on overload and will need to be reset at the vfd. If you do manage to trip the breaker back at the panel I would expect it to be because of shorted wiring or some other major problem.

 

[aquinob]

I understand what you are trying to do but not quite sure about the switch you are working with. Is that switch a low voltage control switch (uses a magnetic relay to hold the contacts closed) with remote contacts or is it a conventional switch with a separate current limiter?

Ive done a couple of conversions using an LVC and if the switch used heaters, they need to be swapped out for ones that have a bit higher current limit since the current on each leg of 3 phase is lower than single phase.

As others have noted, you want the VFD hardwired to the motor and you are using the vintage switch to turn the VFD on and off. Depending on which VFD you get you can program in the parameters appropriate to your motor.

If you swap out to a single phase and want to use the current switch, then you also need to address the thermal limits (heaters) if it has them since the new motor will have higher current on each leg then the old 3 phase.

I like 3 phase motors, very simple, almost bulletproof.

 

[OccupantRJ]

I liked the look and tactile feedback of the original switches on my lathe and mill because I ran similar machines at work for 30 years, my brain was programmed for it and it was less expensive and simple to use them. The original machine switches were used to control the VFD auxiliary low voltage input/outputs of each machine. If there are other limit switches or such they can also control the VFD as normally open or normally closed. All other wiring was stripped off the machines for neatness and simplicity. I added a pot onto the side of the Bridgeport mill drum switch for speed control. Switch> Vfd> motor. The lathe has one low voltage control cable and one power cable in the machine that are each 3 feet long.

 

[ching0n]

I understand what you are trying to do but not quite sure about the switch you are working with. Is that switch a low voltage control switch (uses a magnetic relay to hold the contacts closed) with remote contacts or is it a conventional switch with a separate current limiter?

Ive done a couple of conversions using an LVC and if the switch used heaters, they need to be swapped out for ones that have a bit higher current limit since the current on each leg of 3 phase is lower than single phase.

As others have noted, you want the VFD hardwired to the motor and you are using the vintage switch to turn the VFD on and off. Depending on which VFD you get you can program in the parameters appropriate to your motor.

If you swap out to a single phase and want to use the current switch, then you also need to address the thermal limits (heaters) if it has them since the new motor will have higher current on each leg then the old 3 phase.

I like 3 phase motors, very simple, almost bulletproof.

The buttons are big honking units so if I were to guess, they're mechanical contactor buttons (I'm guessing there was such a thing back in the day). To me it resembles a tumbler switch but in push button form. I believe I may have to reprogram the VFD to understand the latching switches instead of it looking for a single input from a non latching type button.

I think I'll pull/save the original button and thermal switch wiring for now and feed new wiring for the VFD. I'll play w/the old wiring to try to understand it better and see if I can make it work w/the single phase motor I have off the machine.

Looks like import static phase converters aren't that expensive but reading another forum the push button wiring would also have to be redone plus it looks like it has to be loaded to equalize the current draw:

 

[American Locomotive]

The simplest thing to do is just connect a VFD directly to the motor, hide the VFD somewhere, and then just use the original switch (since you like it) to go to the VFD's enable pins, to turn the drive on/off. It doesn't matter that the switch is "heavy duty", it will work the same.

 

[ching0n]

The simplest thing to do is just connect a VFD directly to the motor, hide the VFD somewhere, and then just use the original switch (since you like it) to go to the VFD's enable pins, to turn the drive on/off. It doesn't matter that the switch is "heavy duty", it will work the same.

yeah, that was the original plan all along

 

[wyliesdiesels]

you dont want a static phase converter...

 

[aquinob]

Just keep in mind that VFD's aren't big fans of dust as they have a small fan in them for cooling and will **** a lot of dust in and it won't all get out. And they do need air circulation for cooling so if you are going to enclose it, it has to be large enough for said cooling to occur.

You could probably get away with using your original switch to power the VFD on and off. Leave the thermal part out of the equation.

Right now I have two machines running with VFD's, a big bandsaw and a RAS. Since the Bandsaw benefits from the variable speed, I used the existing mag switch to power the VFD and then used the VFD buttons to start and stop the saw and the rotary control to speed it up or slow it down. That VFD was mounted in the column.



On the RAS, I also used an old mag switch off a Unisaw to power the VFD but used some remote buttons to start and stop the motor. VS not needed but I needed to control the saw without taking my hand off the saw carriage.

 

[OccupantRJ]

you dont want a static phase converter...

I agree they are not the optimum these days with newer and better technology available. I have a static, a shop built rotary, and three VFD units. The static is reserved for testing out of small hp three phase machines or motors, the rotary sits lonely in storage, and the VFD units get used. The choice of dynamic braking, speed control, and other selectable parameters are another plus. Neither my lathe nor mill have external braking resistors, but can be reversed on the fly for power tapping which is a main requirement for me. I am using the Teco L510 series units and have thoroughly enjoyed them.

 

[ching0n]

I agree they are not the optimum these days with newer and better technology available. I have a static, a shop built rotary, and three VFD units. The static is reserved for testing out of small hp three phase machines or motors, the rotary sits lonely in storage, and the VFD units get used. The choice of dynamic braking, speed control, and other selectable parameters are another plus. Neither my lathe nor mill have external braking resistors, but can be reversed on the fly for power tapping which is a main requirement for me. I am using the Teco L510 series units and have thoroughly enjoyed them.

That's what I ended up installing, an L510. I started testing it out w/a sub-30$ Chinese mini VFD prior. The L510 isn't as ready to go out of the box (needing to go thru menus to set the knob as default for instance) but the manual is a lot better and there's plenty of videos out there for setup.

For on-the-fly reversal, what switching mechanism do you use? If I repurpose my current switches, I'd have to go to 'stop' as an intermediate step as there's a mechanical lockout before changing direction.

 

[alfredeneuman]

You should also not have any switches breaking the power between the VFD and the motor.

Besides a required disconnect.

 

[OccupantRJ]

That's what I ended up installing, an L510. I started testing it out w/a sub-30$ Chinese mini VFD prior. The L510 isn't as ready to go out of the box (needing to go thru menus to set the knob as default for instance) but the manual is a lot better and there's plenty of videos out there for setup.

For on-the-fly reversal, what switching mechanism do you use? If I repurpose my current switches, I'd have to go to 'stop' as an intermediate step as there's a mechanical lockout before changing direction.

I am using drum switches, so seemingly the same process except for the time involved. I can slam the switch to reverse in one motion or I can pause in the off position before actually switching to reverse. I normally do it on about a 1-2 count depending on the tap size and whether it is a blind hole or through hole.

 

[ericm]

Besides a required disconnect.

Between the VFD and the motor?

 

[wyliesdiesels]

I am using drum switches, so seemingly the same process except for the time involved. I can slam the switch to reverse in one motion or I can pause in the off position before actually switching to reverse. I normally do it on about a 1-2 count depending on the tap size and whether it is a blind hole or through hole.

youre using drum switches between the VFD and the motor?

 

[wyliesdiesels]

Between the VFD and the motor?

no, on the line side of the VFD

 

[OccupantRJ]

youre using drum switches between the VFD and the motor?

Nope, using them for the low voltage control trigger functions on the VFD. See post #13.

 

[mattthemuppet]

For on-the-fly reversal, what switching mechanism do you use? If I repurpose my current switches, I'd have to go to 'stop' as an intermediate step as there's a mechanical lockout before changing direction.

pretty sure that's what's called a 2 wire set up - 2 wires to one side of the ON-OFF-ON switch, 2 wires to the other side. Forward is when circuit is connected on one side, reverse is the opposite. Off is in between. You can go straight from forward to reverse as the VFD will handle the ramp down and up depending on the parameters you set for braking and acceleration.

 

[OccupantRJ]

pretty sure that's what's called a 2 wire set up - 2 wires to one side of the ON-OFF-ON switch, 2 wires to the other side. Forward is when circuit is connected on one side, reverse is the opposite. Off is in between. You can go straight from forward to reverse as the VFD will handle the ramp down and up depending on the parameters you set for braking and acceleration.

Mine is a three wire control. A low voltage common goes to the machine drum switch, then contact is established and maintained if the switch is moved to the forward position. Off in center, then established and maintained if moved to the reverse position. These modes trigger the low voltage controls of the VFD. The S1 and S2 low voltage terminals are used for this on the L510 Teco.

 

[alfredeneuman]

no, on the line side of the VFD

If the VFD is remote, as in the case of a rooftop blower with VFD mounted on the 1st floor, it's required to have a disconnect within sight and 50' or less of the motor, what then? There is a disconnect required before the VFD and another on the roof.

 

[LopezBart]

If the VFD is remote, as in the case of a rooftop blower with VFD mounted on the 1st floor, it's required to have a disconnect within sight and 50' or less of the motor, what then? There is a disconnect required before the VFD and another on the roof.

If the disconnect can be locked open, it does not need to be in sight of the powered device.

 

[ching0n]

pretty sure that's what's called a 2 wire set up - 2 wires to one side of the ON-OFF-ON switch, 2 wires to the other side. Forward is when circuit is connected on one side, reverse is the opposite. Off is in between. You can go straight from forward to reverse as the VFD will handle the ramp down and up depending on the parameters you set for braking and acceleration.

Yes, I'm aware I can do that via VFD, my push buttons have a literal physical lock out when in FWD or REV that gets disengaged w/the 'stop' button (via spring/lever) so can't exactly do it w/o going through stop.

I am using drum switches, so seemingly the same process except for the time involved. I can slam the switch to reverse in one motion or I can pause in the off position before actually switching to reverse. I normally do it on about a 1-2 count depending on the tap size and whether it is a blind hole or through hole.

Interesting. If I may ask, does machine coast to a stop when "off" or do you have it brake? I guess it doesn't matter if you switch back fast enough to the other direction as that will achieve the braking.

 

[OccupantRJ]

Yes, I'm aware I can do that via VFD, my push buttons have a literal physical lock out when in FWD or REV that gets disengaged w/the 'stop' button (via spring/lever) so can't exactly do it w/o going through stop.


Interesting. If I may ask, does machine coast to a stop when "off" or do you have it brake? I guess it doesn't matter if you switch back fast enough to the other direction as that will achieve the braking.

Ask away. It is set for braking, but it could be set for coast down as well, depending on the machine and the desired effect. I am good with either. Since I am using quick forward/reverse for threading or tapping the braking gives me a bit of wind down reaction time relative to the tool to make timing it all easier by reducing the *** cheek clenching.
Actions are also different if the machine is in back gear. The over run of the spindle is less because it is slower, and things are more casual for the operator (me). I ran a Bridgeport and lathe for 30 years so I am pretty comfortable at it in general, whether it is through hole or blind hole tapping.
Disregarding any VFD involved, the action of slamming a 3 phase motor into reverse is known as plug reversing. I had production machines at work that had flip-flop motor starters on them that had the motors doing that hundreds of times per day doing tapping operations.

 

[ching0n]

Thanks all, & a heads up:

120V/1hp Open Box L510 TECO/Westinghouse VFDs ~100$​

 

[ching0n]

I pulled these diagrams from an old manual & think are useful for posterity (non-VFD, reversing drum, 115& 230v, single and three phase with and w/o load switch, with and without mag switch). If the pros feel they're no longer code compliant, please chime in.