Three-phase power for workshop

[Sonic EscapeParticipant @sonicescape38234]

All my machines need three-phase power but unfortunately I have only a single-phase connection. My lathe had an inverter that I used to power other stuff but this was inconvenient. I had to reconnect the wires every time. So I sold it and I bought two Delta VFDs, VFD022EL21A and VFD007EL21A . I need two not because I plan to use two machines in the same time, but the mill has two motors.

This is the electrical wiring that I’m planning to do. Nothing complex, just the bare minimum. There will be two sockets where I’ll plug the machine I want to use in that moment. I’m not decided yet about the controls (start/stop and speed). I think I’ll make one small mobile box with buttons and a long cable for each VFD and I’ll attached it somehow to the machine that is in use. Or one fixed box with a connector for each machine.

I hope the long control wires will not be susceptible to EMI. I’ll add some decoupling capacitors. Also I’ll add a resistor between the analog speed control input and ground to stop the motor in case the cable is disconnected somehow.

 

[Robert Atkinson 2Participant @robertatkinson2]

Not a bad start. I’d suggest a couple of changes:
1/ Use a second relay in the 24V circuit with two contacts one connected to each of the VFD E-Stop inputs Don’t use extra contacts on the existing relay, keep the mains and low voltage control circuits separated for safety.
2/ Unless the VFDs have input filters you need to add a filter at each VFD input.
3/ Use screened / armoured cable e.g. CY or SY between VFD and sockets and plugs and motors

Ideally use outlets with interlocked switches BUT wire the switches to the INPUT the respective VFD (keep your control circuit). This has the advantage that you can’t unplug the motor with VFD on.

Robert.

[Ian PParticipant @ianp]

Your emergency stop will not be instantaneous. Cutting mains supply to the VFD can leave the motor running for several seconds until the DC bus capacitors discharge. Better to use the VFD’s E-Stop feature or at least use the deceleration parameter you have set.

I’m not conversant with the VFD you linked to but ones I have come across have setable options to suit the motor it is driving so ideally the motors you are switching between should have similar ratings.

Ian P

 

 

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

Not a bad start. I’d suggest a couple of changes:
1/ Use a second relay in the 24V circuit with two contacts one connected to each of the VFD E-Stop inputs Don’t use extra contacts on the existing relay, keep the mains and low voltage control circuits separated for safety.
2/ Unless the VFDs have input filters you need to add a filter at each VFD input.
3/ Use screened / armoured cable e.g. CY or SY between VFD and sockets and plugs and motors

Ideally use outlets with interlocked switches BUT wire the switches to the INPUT the respective VFD (keep your control circuit). This has the advantage that you can’t unplug the motor with VFD on.

Robert.

I’m not sure I understood what you mean at point 1. In my understanding this VFD has a N.C. relay output (RB) that by default is signaling a malfunction. I want to add this N.C. contact in series with the 24V circuit. So any fault will cut the supply of the contactor coil.

The input relay is actually a Siemens 3TB41 contactor. It has 3 N.O. and one N.C. contacts. You mean that is not safe to rely on insulation between contacts?

 

This VFD claims to have filters at both input and output.

 

 

On Ian P Said:

Your emergency stop will not be instantaneous. Cutting mains supply to the VFD can leave the motor running for several seconds until the DC bus capacitors discharge. Better to use the VFD’s E-Stop feature or at least use the deceleration parameter you have set.

I’m not conversant with the VFD you linked to but ones I have come across have setable options to suit the motor it is driving so ideally the motors you are switching between should have similar ratings.

Ian P

 

 

I don’t have much experience with VFD’s but I think only when you are using vector control you need to match the motor parameters with VFD settings. In V/f control mode I suppose the VFD doesn’t care about the motor unless it doesn’t exceed its output current.

This VFD doesn’t have an emergency stop input. I think is safer to just cut the power and not to rely on other features. There is an optional breaking module. Is not very expensive but is not clear for me the benefit of a quick stop. So far I never had to quickly shut down a machine.

 

 

 

 

 

 

[Robert Atkinson 2Participant @robertatkinson2]

Hi Sonic,
The arrangement with the NC fault outputs on the VFD is OK. The additional relay is to cover the fact that disconnecting the input supply of a VFD does not result in a rapid stop of the motor (This was also raised by Ian P). Whenever the E-stop is pushed the Stop inputs on both VFDs must be activated. This ensures the motor stops quickly (power is provided by the “DC Link” capacitors inside the VFD and the inertia of the motor and load). The braking is DC for this so you need to set the 8.x parameters.
It is OK to use the auxillary contacts on a contactor for low voltage control circuits as they are adequately isolated. However you need two contacts, one for each VFD Stop input. So an additional relay is required or a contactor with a second auxillary contact.

There is one oddity in your circuit which could catch the unwary. The ON button is at mains potential while the OFF and E-STOP are at 24V. You would not normally expect one to be on mains. This is not good practice.
If you add an isolator switch on the supply (which you should have anyway) You can leave the 24V transformer primary permanently connected and put all of the control switches at 24V.  If you are using the mains plug as an isolator then you would have to switch off at the socket.

Robert.

[Sonic Escape]

On Sonic Escape Said:

On Robert Atkinson 2 Said:

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On Ian P Said:

Your emergency stop will not be instantaneous. …

 

 

…

This VFD doesn’t have an emergency stop input. I think is safer to just cut the power and not to rely on other features. There is an optional breaking module. Is not very expensive but is not clear for me the benefit of a quick stop. So far I never had to quickly shut down a machine.

 

 

 

 

 

 

The benefit of a quick stop is because ‘so far I never had to quickly shut down a machine.’   People who catch clothing or hair in a machine, or who have a whirling rod incident, appreciate the feature.   I make do with a big red button, but foot or belly operated rails are common on new industrial kit and amateurs do fit them.

Safety apart, a machine that stops quickly speeds workflow.  Also braking by heating some big resistors is less wearing than dissipating the energy in the drive train.   Neither of these seem particularly advantageous in a  hobby workshop.

Dave

[EmgeeParticipant @emgee]

You may want to consider fitting a higher fault current RCD if at all 1 is necessary, you no doubt already have RCD protection on your workshop installation.

Even with a 30ma operating current RCD on a VFD supply tripping can be problematic, you will have 2 operating with 1 machine so makes it even more likely you will experience tripping issues.

Bond the protective braid of the SY cable to the incoming cpc (earth conductor) as advised by the VFD manufacturer, some advise connection to cpc at both ends, others only at the VFD end.

Ensure you have an adequately sized cpc conductor connected at the motor casing, even if the braid is connected both ends don’t rely on that as the resistance will be too high.

Emgee

 

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