Running two different spindle motors from a single VFD?

I have seen several threads in the past on this but am struggling to find anything useful atm.

I have a 2.2Kw 3000RPM spindle and a 2.2Kw 24K RPM spindle requiring different settings in the VFD (Mitsubushi D700), I am not concerned about the automation of the VFD changes, I think the VFD even has a second motor setting (set) so both can be toggled between by a single change.

If power is cut on the mains it seems that there is a risk of a relay opening before the VFD looses its residual current and certainly before a spindle stops turning.

Are there contactors/relay blocks that hold their state if there is power loss? Do they have a name that I have not thought of?

I am tempted to start with a mechanical rotary switch between the spindles and the VFD but am open to suggestions and links to any relevant threads.

Thanks,

Jon

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Originally Posted by JonS

I have seen several threads in the past on this but am struggling to find anything useful atm.

I have a 2.2Kw 3000RPM spindle and a 2.2Kw 24K RPM spindle requiring different settings in the VFD (Mitsubushi D700), I am not concerned about the automation of the VFD changes, I think the VFD even has a second motor setting (set) so both can be toggled between by a single change.

If power is cut on the mains it seems that there is a risk of a relay opening before the VFD looses its residual current and certainly before a spindle stops turning.

Are there contactors/relay blocks that hold their state if there is power loss? Do they have a name that I have not thought of?

I am tempted to start with a mechanical rotary switch between the spindles and the VFD but am open to suggestions and links to any relevant threads.

Thanks,

Jon

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I'm not really following you on what you are asking about. Are you asking about using a single VFD to switch between and operate two different spindles or are you asking about switches? Are you trying to run two spindles simultaneously?

If you have a VFD that can toggle between two settings, it seems pretty simple after that to run two head independently. There is no way to run them simultaneously that I can think of. I had an SCM that used a single VFD to run two spindles, so I can tell you roughly how it worked. In that case, they were the same spindle, so no need to toggle between settings. Basically, the VFD was the first component after the power supply to the head. There was a contactor (call it C1) that was actuated by a relay which supplied the power to the VFD. The power then went from the VFD to two more contactors (call them C2 and C3), basically wired in parallel. Each of these contactors was also actuated by a relay. C2 provided power from the VFD to Spindle 1 while C3 provided power from the VFD to Spindle 2. Each Spindle, in this case, had a magnetic sensor that detected if the head was in the correct position to be operated. If Spindle 1 was not in position, for example, the relay that would actuate C2 could not operate, which prevented the spindle from being able to turn on. Same system was true for C3/Spindle 2, so only the correct spindle should operate at any point in time, while the other one (in position for a toolchange in my situation) could not operate.

When changing between Spindle 1 and Spindle 2, it did not matter if Spindle 1 was still winding down. Spindle 2 would start while Spindle 1 continues to wind down, but since the contactor (C2) was disconnected from the VFD, the spindle does not deliver power back to the VFD (I think this was your concern?). The main thing, I think, is to provide a safety system via wiring the relays to prevent both spindles from operating at the same time. You could do this by using both the NC and NO sides of a single relay (NO goes to Spindle 1 contactor, while NC goes to Spindle 2 contactor), or any other number of methods to ensure they can't both function. Hope that helps.

mmoe thanks for your quick response.

I understand using multiple contactors, my concern is regarding a power cut event and how this would effect a circuit based on relays and if any damage could result that would not have happened if the VFD and motors were wired directly.

Interesting that your system had a spindle coasting whilst another came under power and that was one of my concerns.

Quote:

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Originally Posted by JonS

mmoe thanks for your quick response.

I understand using multiple contactors, my concern is regarding a power cut event and how this would effect a circuit based on relays and if any damage could result that would not have happened if the VFD and motors were wired directly.

Interesting that your system had a spindle coasting whilst another came under power and that was one of my concerns.

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It's getting a bit beyond my expertise, which is mostly just keeping my machines working properly and retrofitting machines that are somewhat already configured mechanically, but I would guess that NOT using contactors would be far more likely to cause damage than using them in the event of a power outage type event. When the contactor is between the spindle and the VFD, the spindle's generated current on coast down should not be able to get back to the VFD because it acts like a cutoff switch. If the spindle is wired directly to the VFD without a contactor and the power is cut, the spindle will send current back through the VFD and lord knows where else, which is where you could get some damage I'd think. You would probably want to incorporate some sort of breaking resistor in any case, but I've never had to replace mine and couldn't tell you how a person chooses the correct resistor for a new application.

Here's a video of the SCM with two spindles. While you can't quite tell in this video, the spindle that goes to the tool change position is usually still spinning slightly right up until just a moment before the tool rack moves to grab it (there is a speed sensor on the spindle that it's waiting for to tell it the spindle is no longer moving, then it moves to grab the tool). The overlap is slight between these two, but really it's because the time it takes to rotate the heads is most of the spin down. If there was no rotation, it would start the second spindle up sooner since it's waiting for the single from the position sensor before the contactor can actuate. Since the spindle gets 100% disconnected from the power supply, I believe it's the same as if it's not even there whether it's spinning down or completely stopped. It's just removed entirely from the circuit by the contactor and no longer relevant.

https://www.youtube.com/watch?v=dEpYuvojixA

A few precautions when using dual motors/contactors on the VFD output, Ideally the motors would have the same characteristics, at least the same pole count.
A reversing contactor pair could be used as these are not only mechanically interlocked, but can be electrically interlocked.
When operating the contactors, the particular contactor coil swap should only be enabled by setting a VFD output (by para) to sense At-Zero-Speed.
This output would be wired into the contactor coil logic.
Any contactor on the input side for E-stop purposes should have a contact to the VFD Stop Input, this turns off the power devices.
Any motor on a VFD when motoring, i.e. winding down does not harm the VFD or if the output power is disconnected at this point.
The biggest concern is if a motor was connected or swapped while the VFD was outputting a speed rate.
Al.

Excellent thank you gentleman, "reversing contactor pair" seems key, special order item unfortunately but should not take too long :)

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Originally Posted by JonS

"reversing contactor pair" seems key, special order item unfortunately but should not take too long :)

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Plenty on ebay and elsewhere.
I usually go with Telemecanique.
Al.

Al,

I acquired a reversing interlocked contactor that seems to be 100% functional.

I use a Mitsubishi D700 VFD which seems very configurable, however as I have worked through the enormous manual for it I have discovered some frustrations with it, for example the second motor options are limited and interestingly the analog voltage input for frequency overrides the "minimum frequency" setting. The 24K RPM spindle is not meant to be run under 50Hz, minor issue as I am the only user.

There are VFD output circuits I can test to see if there is an error status and if there is any frequency output and I am able to make logical decisions based on this as to being safe to switch..

However the reversing contactor pair LP5 K0910BW3 does not work as I had hoped it would, I was (naively perhaps) thinking that it would lock in a state, however it merely prevents the second contactor from being brought live at the same time.

This is all fine unless I loose my 24V that drives the coils, in this scenario, I fear that I will have introduced an expensive failure mode :(

I could put a second little 24V PSU in parallel to mitigate this risk, did I get the wrong reversing pair contactor or is this an inevitability of trying not to use a second VFD for the second spindle?

Thoughts appreciated.

Jon

A reversing contactor has simultaneous pick up prevention done both mechanically (built in) and electrical interlock via N.O. contacts, retaining of the coil has to be done by the circuit that energizes the coil.
It sounds like you are operating a High speed spindle, what is the nature of the other?
You can drop a contactor out while the VFD is outputting, it is picking up while output power is in effect that cannot be done.
http://static.schneider-electric.us/...0140CT9201.pdf
Al.

It is an RF45 mill with a 2.2Kw motor that is very happy at about 60Hz/3000RPM, it is the gearbox that is attached that is the concern with high speed, I am sure the main motor would run nicely at 100Hz.. The second spindle is a little 24K RPM water cooled unit. It seems that I will just have to get over my concerns or put in a rotary switch ;)

Cheers Al.

The problem as I see it you have two widely different motors and are trying to run of the same VFD, which can cause problems in trying to set appropriate parameters.
Al.

Indeed, I should have said sub spindle motor runs at 400Hz. !

Well the inevitable loss of power to the interlocking relay happened... the 400Hz spindle was running at the time, the VFD showed 400Hz still and the motor coasted slowly to a halt.... , I stopped the VFD before re-engaging the spindle and cannot see any problem with spindle motor or VFD :) I don't want to test the main spindle motor with the same failure.. but hopefully it will have the same result should it happen.... :)

There is also magnetic latch/unlatch relays that retain their state, even with loss of power.
P&B among others make them.
Al.