# Vfd's And Contactors



## joshua43214 (Dec 2, 2015)

I have what I hope is a simple question.

I have been reading up on VFD installation for my PM1340GT lathe. The installs I have found seem to be split between complicated relay controls, and just direct wiring the original lathe controls to the VFD.

I am wondering what is actually gained by adding in relays/contactors. The only benefit that I can see is being able to provide better logic over interlocking. At first glance it looks like a lot of money and time spent for little or no gain if the same logic can be programmed into the VFD itself.

For some things, I do not see the need for an interlock. For example, I feel no need to lock out the jog button while the lathe is in use. I also believe the built in jog function is already disabled when the lathe is under power.

On the other hand, there is some interlocking I would like to have. For example, I would like the lathe to stay off after power failure, and I would like the for/rev switch to be required to return to off if the e-stop is used. It looks like it can be programmed to stay off in the even of a power failure, but I am not able to find a clear answer in the manual to how restarting the machine works after using the e-stop.

Thanks,
-Josh


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## JimDawson (Dec 2, 2015)

Depending on the VFD you choose, all of those functions can be programmed in.  If you use momentary contact function to Start, then the lathe will stay off after a power fail or E-stop, or require cycling the switch before restart in the case of a maintained contact switch.


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## countryguy (Dec 2, 2015)

I guess in a quick word- its all about safety  I think?   Do what makes sense w/ cost/labor benefits for you.    Make it safe, and have it watchdog key systems where needed but I get you.   The AjaxCNC (centroid) setup I did really made me gain respect for the level of Interlock's they've setup.  Kinda glad I did it all.  Wowza stuff.      For example: the 240 OVer/under voltage interlock started cutting out.   Turns out my 220 w/ the compressor on it was spiking terribly and the VFD picked up on it.   It then shut down the spindle and faulted.    Good / bad?  depends I guess.   I know I would rather keep my VFD than having it go boom on OV/UV conditions.  So much to learn and miles to go yet for me.  ;-)


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## mksj (Dec 2, 2015)

The machine comes from the factory with similar interlocks, to remove them and do direct control of the spindle control via the VFD is a disaster waiting to happen. Since you add a VHD and no longer use the stock relay(s) and contactors that came with the machine, you need to replace them with a similar setup that replicates the original interlocks on the lathe.  Because the lathe does not use momentary direction buttons, if you hit the E-Stop and then reset it, the machine would restart if the spindle switch is in the run position. Have you given consideration to what happens if you have an intermittent switch or one that fails on, or there is a short in the control wiring. May never happen, but could have severe consequences if it occurred.  On the lathe, I consider it much more dangerous than my mill should there be a glitch or operator error. There are ways to prevent restart on a power outage, but this is based on programming and input command on say something like the WJ200. This is also built into some of the designs I have done. You also need to factor that the VFD capacitors hold charge for quite awhile, so the power may glitch for a short period, but the VFD does not power down. The motor may stop temporarily and then restart if there is no power latching relay.

The single relay setup posted as a design is far simpler than the stock system that comes with the lathe. I would also take note of circuit designs for lathes that come factory equipped with VFDs,  they use numerous safety interlocks and relays (example of ERL-1340 which use multiple relays and interlocks) . You may have certain views on how you want the lathe to work, and so design a specific system around your needs. It is a misconception that because these designs incorporate safety features or lock out the jog while running that it complicates things or adds a significant increase in expense. I beg to differ on say a jog lockout, as it requires one or two wires to be connected differently. Wile you may not want certain features, there are numerous other individuals that have requested many additional features, such as For/Rev jog or different braking, double safety interlocks  to be incorporated in their system designs. If that is what they want, and it can be done reasonably and safely, I see no reason not to design/build a system around their wishes. I also think that as you build/install these systems, your understanding/appreciation for the safety features and system design possibilities becomes more clear without adding significant complexity to the basic design. Otherwise go CNC and that takes you to a whole different level.


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## wrmiller (Dec 2, 2015)

As counterpoint, I didn't use any contactors (relays) when I installed my VFD. My preference, my choice. Dangerous? No. Not if you know what you're doing.


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## Ulma Doctor (Dec 2, 2015)

ultimately it's going to be the OP's comfort level that will be the deciding factor.
my advise to you, is the advise given to me many times KISS.
keep it simple stupid...
(in no way meant to imply that you are stupid)


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## mksj (Dec 3, 2015)

KISS is fine providing you understand the system and are willing to risk the consequences. Manufactures these days design systems around liability issues, just look at cars with all there gadgets, interlocks and warning stickers. Too bad the next generation can't read.  The goal is to design systems that provide the functions desired with the least amount of complexity/failure. Since we are hobbyists, we can choose how we want to setup our machinery based on our experience and comfort level. Not understanding something doesn't mean one shouldn't use something or make it simpler, as we all learn and hopefully improve.  After I completed medical school/residency, I thought I new a lot, but as I get older, I realize how little I know. But it doesn't stop me from exploring and learning new things. Each of us is free to choose our own path, and we are lucky to have this freedom of choice. As I use to say to my patients, there is no black or white answer, there is only shades of gray.


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## Ulma Doctor (Dec 3, 2015)

i agree somewhat,
one point i would like to make is that if one chooses to be over-ambitious and can't complete the project, 
the time would have been better spent on using the machine with possible reduced capacity, than not at all.
i'm not suggesting that anyone not try something out of their comfort zone, just be realistic in their understanding before trying to get too ambitious.
sometimes learning is expensive, especially if you smoke a brand new VFD, because you thought you knew what you were doing.
there are quite a few customers, that have called me to come and clean up their messes, because they thought they knew what they were doing, and it was not cheap.


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## uncle harry (Dec 3, 2015)

joshua43214 said:


> I have what I hope is a simple question.
> 
> I have been reading up on VFD installation for my PM1340GT lathe. The installs I have found seem to be split between complicated relay controls, and just direct wiring the original lathe controls to the VFD.
> 
> ...


I designed an isolating circuit for my Harrison M300 lathe that maintains all of the factory safety features. Basically the circuit retains the functions of the original reversing contactors and the master control relay.  The reversing contactors are disconnected from the motor and input (line) source..  A pair of ice cube relay coils are parallel wired to the rev. contactor coils. Then the isolating relays are interfaced with the VFD logic inputs.  This maintains all of the original safety features and is really a simple wiring solution that can be pre-configured on the bench & then fitted to the lathe control cabinet. The other advantage of this approach is that the circuit can be readily reconnected to the original control operation should you decide to sell the lathe to someone who has 3 phase power. That way you get to keep the VFD for other applications.


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## joshua43214 (Dec 3, 2015)

I do have a great appreciation for safety. That is indeed why I started this thread.
I have just the right kind of stupid to stop the machine with the big red stop button, then turn it back on while forgetting to move the direction switch back to off.

I will relate a story about safety devices.
A long time ago in a land far far away, I was at a woodworking tool show. There was this guy with a new safety device for stopping saw blades. He had a little portable table saw and a pack of hot dogs. As the crowd watched in awe, he would feed the hot dog into the blade and the blade would slam to a stop taking only the lightest bit of skin off. Every one agreed, it was an amazing invention.
But...
He wanted some large amount of money for the system. Every one also agreed that it cost far too much, especially considering that the real danger from a saw is not the blade, it is kick-back.
A short while later, a controversy sprang up over the device. It seems the inventor went to OSHA in an attempt to make the installation of his device mandatory. At that time, many of us where still pretty upset about a requirement for low-voltage controls on some wood working equipment, and had (sort of) adjusted to a requirement for magnetic switches.

I used to work with a guy who always said that the best safety device you could install on a car would be an 12" spear jutting up out of the steering wheel. You either drive safely, or you get impaled.

The point is that safety starts with the operator. Depending on safety devices to keep you safe is in my opinion very mis-guided and is actually less safe than simply working safe. Putting my body in harms way and expecting to be safe because some safety system is in place is a disaster waiting to happen. Imo, most safety systems are redundant to work safety, not the other way around. I work safe, and any safety systems I use are there as a redundancy to my work habits. How many people drive more recklessly knowing that their air bag system will keep them safe?

So, after reading the manual for a second time, and the quick start manual for the first time, I am back to where I started.
Aside, from being able to create an interlock that requires the for/off/rev switch be moved to off after using the big red button to stop the lathe, I am not seeing a single feature gained from setting up a bunch of contactors or relays. I am pretty sure this feature is also built into the VFD, I am just not seeing it. All the other features are programmable in the VFD itself as near as I can tell.

My goal is to prevent myself from doing a stupid act like using the big red button and forgetting to return the run switch to off.


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## JimDawson (Dec 3, 2015)

joshua43214 said:


> 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?


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## joshua43214 (Dec 3, 2015)

JimDawson said:


> 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


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## JimDawson (Dec 3, 2015)

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.


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## uncle harry (Dec 3, 2015)

JimDawson said:


> 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.


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## JimDawson (Dec 3, 2015)

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


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## joshua43214 (Dec 3, 2015)

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


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## mksj (Dec 4, 2015)

joshua43214 said:


> 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.


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## uncle harry (Dec 4, 2015)

JimDawson said:


> 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.


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## mmprestine (Dec 5, 2015)

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.


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## mksj (Dec 5, 2015)

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.


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## uncle harry (Dec 6, 2015)

mksj said:


> 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.





mksj said:


> 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.





mksj said:


> 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.





mksj said:


> 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.



I just opened the Jet Manual PDF and did a casual review of the safety  wiring.  The safety circuit is basically generic and provides hard-wired inter locks to stop the input to the VFD.  The schematic also shows the inclusion of the braking resistor which should insure a rapid stopping of the motor when the safety/run input is opened or disabled.   My Harrison M300 is basically wired similarly but being probably a late 70's issue utilizes interlocked forw/rev contactors for the motor since VFDs weren't available then.


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## joshua43214 (Dec 7, 2015)

This is what I came up with.
It has the advantage of being simple, cheap, and uses a single 8 conductor shielded wire. It also preserves all the factory components in their factory assembled places so if I ever sell the lathe it will be a simple matter to restore it to the factory set up.
The factory wiring is not shielded, so I mounted a terminal block behind the control panel and routed all the switch wires to it. This will put the bulk of the machine between the 3ph electrical and the unshielded 24v control wiring. An 8 conductor shielded wire is then routed back up to the VFD.
The high voltage wiring is handled by the factory control box. This allows me to use the built in thermal protection, and just uses the Forward contactor to switch the 220v line voltage. I added two jumper wires to bypass the direction switch and route power to the contactor so it will close when the big red button is closed. This is the same effect as unplugging the unit, and requires the VFD be programmed for controlled braking in the event of power failure if the circuit is to function properly as an E-stop.

The jogging circuit might be too complicated, but it is simple to keep what is doing what straight when hooking everything up and diodes are really cheap.


The diagram only shows the two 220V hot legs being switched, the contactor is actually switching both hot legs and the neutral so it acts exactly like pulling the plug. Both machine and VFD a grounded at all times.
Once I get a braking resistor and tidy everything up, I will post some pics and revised schematics.


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