Vfd's And Contactors

[JimDawson]

I am pretty sure this feature is also built into the VFD, I am just not seeing it.

Are you using a GS2 or GS3 VFD?

 

[joshua43214]

Are you using a GS2 or GS3 VFD?

I will be using a Hitachi WJ200-015SF
This is the unit that Matt sells for my PM1340GT, and it is in transit as we speak.

One option that appears to work is using the big red button to provide power to the VFD (via a contactor of course), then just using the normal inputs for the carriage mounted for/off/rev switch. It would mean having to wait for the VFD to start back up after using the button, but it would give me proper e-stop functions, including controlled braking via regenerative power.
It seems to me that I should be able to hook the big red button to the VFD directly and program the VFD for a simple logic gate that says both switches must be off before a run command is accepted.
The most likely function is to use option code 21 (STP) on the input code configuration with one of the programmable inputs.
see page 3-86 and 3-83
http://www.hitachi-america.us/supportingdocs/forbus/inverters/Support/WJ200_Instruction_NT325X.pdf

 

[JimDawson]

Installing a contactor with a 2 button control ahead of the VFD is probably the best way to insure a fail-safe system. Requiring a control power button push to start up, That's the way my mill is set up. Power fail or E-stop drops the main power to the drives, Requires an Enable button push to restart.

Take a look at 3-85, option code 13, USP. That may prevent startup if the FOR or REV carriage switch is closed. Not exactly sure how that reacts. I'm pretty sure that the VFD is programmable to do what you want.

 

[uncle harry]

Are you using a GS2 or GS3 VFD?[/QUOTE

GS2.......I think that the safety concerns of OSHA & others regarding hard wiring safety circuits still apply. (Yes there are safety qualified PLCs.....) but, for simple reasons that I gave, all of the given safety interlocks are accounted for in the original equipment, To me, the use of these & the isolation of signal to the VFD with the ice cubes is all encompassing. But, I wonder what the GS3 has as other features, considering your question.

 

[JimDawson]

The reason for my question was just to look at a manual that I have. The GS3 is a vector drive, and does have a few more features, but I don't think that there is much difference in the control functionality. Both of the GS drives will pretty much work like joshua wants. The control power relay with 2 button control is still really the safest IMHO

 

[joshua43214]

After more consideration, I have decided that the big red button should be an e-stop. Psychologically, that is the best function for it to have. If for some reason I get caught in the machine, it would be that button I would be frantically trying to hit. Wanting to be able to use it as a simple stop button along with the for/off/rev switch is not sensible.
As such, I will wire it to a contactor before the VFD, and use the built in controlled braking that runs on regenerative power when it is activated or the power fails.
I have a fused 30A switch that I will use as a disconnect, adding a magnetic switch seems redundant since the VFD itself can be programmed with regards to length of power failure and what to do in the event of one. I might still order one just because I prefer a two button switch over the big spring loaded disconnect switch. I think I will also wall mount the unit such that it can be easily removed so the lathe can be moved around for service.
This seems to be the simplest solution. I will be able to use the factory 24v transformer to run the contactor and the lamp, and I will use one of the factory contactors for VFD power. The remaining contactor will be left in place and used for coolant if I decide to install a pump.

After spending even more time on websites from manufacturers, distributors and blogs from people who install these things for a living, I have come to the conclusion that interlock systems to control a manual machine are redundant. The only professional installs I could find that use complicated interlock and relay systems are those that also use PLC's. Complicated interlock systems were used on older VFD's, modern ones have all the controls and the like built into them. For manual machines, they just add an extra layer of complexity and could make the system less reliable, and certainly much harder to diagnose problems. I found some pretty derogatory comments about the use of these systems alongside modern VFD's, mostly aimed at engineers who are not able to let things work as intended, but insist on "improving" everything that comes near them.

I want to thank you all for your help and comments. It really helped get things straight in my head.
-Josh

 

[mksj]

The only professional installs I could find that use complicated interlock and relay systems are those that also use PLC's. Complicated interlock systems were used on older VFD's, modern ones have all the controls and the like built into them. For manual machines, they just add an extra layer of complexity and could make the system less reliable, and certainly much harder to diagnose problems.

Amazing statement for one who has never installed a VFD. This would make every manual VFD equipped Grizzly and their South Bend lathe models obsolete and less reliable based on this observation, as they all use power contactors and relays for the spindle controls/safety interlocks. Your stock PM1340GT uses a DC power interlock relay and the contactors are interlocked so only one can be activated at a time. As there are many opinions and ways to do things, each to their own path.

 

[uncle harry]

The reason for my question was just to look at a manual that I have. The GS3 is a vector drive, and does have a few more features, but I don't think that there is much difference in the control functionality. Both of the GS drives will pretty much work like joshua wants. The control power relay with 2 button control is still really the safest IMHO

I don't know what lathe Joshua has and if the original wiring has interlocks. My Harrison already has interlocks including prevention of startup if the for/rev lever is engaged. The lathe won't restart by resetting the detented e stop. So in my case the isolating relays translate the for/rev contactors function to the VFD while preserving
all of the original safety functions. In essence this agrees with your best safety 2-button latch solution. The for/rev lever replaces the 2 buttons.

 

[mmprestine]

They are designed to be used in the industrial world and that world demands safety standards typically which are defined by the NFPA 79 and UL. The levels for safety circuits are specified in class 0-4. Class 1 would be typical for what you reference and class 0 would be as you desire, the wiring or control I/O on the VFD. Typically all new higher level of VFDs have a genuine relay built in to control the high voltage, this is referred to as Safe-Off in the industrial world.

 

[mksj]

Do you have models of VFDs with this function built in? I am mostly familiar with separate modules such as the Minotaur MSR9T, many safety requirements specify redundancy. https://www.ab.com/support/abdrives/powerflex70/Interfacing_Safety_Relays_Rev04.pdf

The WJ200 can be programmed to prevent restart via input terminal assigned 13USP:Unattended Start Protection), the designs I use when the power relay is tripped (no power) it connects "ON"the input to assigned to this function. The machine requires a new run command to operate which requires the power relay to be reset (spindle switch to off).

I was just reviewing the schematic for the Jet Elite EVS 1236 lath which uses a VFD contactor power E-Stop interrupt after the main power switch. It is a bit controversial as to whether the E-Stop stops the VFD quickly with braking (Category 1) and then prevents restart, or just kills power to everything and the VFD freewheels the motor to the stop (Category 0). In both cases there are dual relay contacts used serially for the reset. I assume these are the relays you are describing which would be part of the low voltage circuit (safe off option) or are you describing output relays to the motor? All these options would seem to require a separate gate guard unit.