Thread: VSD suggestion

I posted this in the Hercus forum but figure it might get wider attention here.

I was going to just replace the 1/2 HP motor on my Hercus lathe after further consideration I have decided to go the VFD/VSD route.

Does anyone know anything about this SAJ unit?
SAJ 0.75KW VSD VFD inverter 240V variable speed drive | eBay

I have a friendly techo at work who can help me install it

Hi Bob,

Looks pretty good to me, I note there are a couple of things would recommend it.

1. It has vector control, which is much better for low speed torque than the cheaper V/F type drives.

2. It has the frequency control pot on the front of the drive, for a lathe, that's all you need. Just wire the drive digital controls to your existing forward/reverse jog and stop switches.

Nothing wrong with the price either!

Regards
Ray

Originally Posted by RayG

Hi Bob,

Looks pretty good to me, I note there are a couple of things would recommend it.

1. It has vector control, which is much better for low speed torque than the cheaper V/F type drives.

2. It has the frequency control pot on the front of the drive, for a lathe, that's all you need. Just wire the drive digital controls to your existing forward/reverse jog and stop switches.

Nothing wrong with the price either!

Regards
Ray

Thanks Ray - much appreciated.

I see it has FWD and REV buttons on the front of the unit itself. As I plan to locate the unit right next to the lathe, could I just use those?

Also I wonder what happens if it's going FWD and the REV button is hit?

For an emergency switch should it be between the mains and the unit or can a switch be located between the Unit and lathe?

Originally Posted by BobL

Thanks Ray - much appreciated.

I see it has FWD and REV buttons on the front of the unit itself. As I plan to locate the unit right next to the lathe, could I just use those?

Also I wonder what happens if it's going FWD and the REV button is hit?

For an emergency switch should it be between the mains and the unit or can a switch be located between the Unit and lathe?

Hi Bob,

No.. you should wire the VFD directly to the motor, no switching.

For the e-stop you can do it either with a latching contactor upstream of the VFD or some prefer to use the drive itself to stop the spindle.

On a lathe, where you might have a large mass rotating, i think its better to use the drive to control the stop, it will stop faster. (depending of course on the ramp chosen)

As far as switching, I am used to where the position of the levers are on the lathe, so that in operation, you just operate fwd/reverse normally.

I think it would be a bit clumsy having to press buttons on the drive.

Do you have a circuit of the existing control?

Regards
Ray

Hi Bobl,
I'm pretty much with everything Ray has said.
Re "Also I wonder what happens if it's going FWD and the REV button is hit?"
*On my VSD* if you have it set to ramp down, switching from fwd to rev is no problem, it just slows down as normal then starts up as normal in reverse. I haven't been game to try doing that in "free run stop" mode.

Stuart

p.s. In fact if you dont have a camloc spindle it might be an idea to lock out revs and go easy on the braking. Or you might find the chuck rolling towards you(has any one heard of anything like this?)

Yes all VFDs can switch a motor from running from forward to reverse without any problem at all, one of the many advantages with them. What they do is simply decelerate according to the pre-programmed schedule, once they've stopped they simply accelerate back up to speed again with the motor running the opposite way.

I know many people simply use the VFD controls, but I would instead encourage you to tuck the controller away somewhere out of harm's way and instead use switching in to the drive. That's the way they're really designed to be used in industry and it will open up a lot more advantages like emergency stop etc that may not be on the VFD's panel. The panel is just the basics of the controller's functions. The VFD's are an industrial device, and so the wires are exposed to some extent. I'm not a fan of having any form of 230V wiring anywhere where chips/coolant could potentially contact them. The switching wires on the other hand are only 24V so there's no chance of any electrocution, and they are just logic control to the drive, so if one was shorted it would just send a wrong signal to the drive.

Here are a couple of shots of the panels on my surface grinder and my mill. The one of my mill just reminded me I was supposed to powder coat that aluminium knob next time I was doing some, never mind ... next time Anyway, the point is they look pretty much just as they did when running 3 phase.

Pete

Thanks Guys very helpful indeed.

The existing switch box and wiring harness are a bit of a mess. The main switch box is a largish clunky looking rusting metal box that was located on the back of the lathe stand. This switch box has a mains power switch and a Forward/reverse switch. From that box there was a metal conduit around to the front where there was a stop start switch and and simple e-switch in series.

I don't want to put any of that back on the lathe mainly because I don't want to have to get around to the back of the lathe to use the mains power and rev switches. I will make up a more compact panel using the 24V logic lines that can be mounted to the front of the lathe.

Hi BobL,
Making a small switch panel would be a good idea that can have a E/Stop Switch which I suggest that you have controlling a Latched Contactor to the Input 240VAC to the VSD, this way in the event of an emergency you can kill all power to the VSD. You can then have separate Pushbuttons for Stop, Start and a Rotary Switch for Forward/Reverse. You can mount a Rotary Pot for Speed Control. If you have Coolant then also a separate Rotary Switch for that can be added. Put the VSD into an Enclosure and fit a Circut Breaker to the Input 240VAC, make sure to allow 100mm gap arround the VSD as they get hot and like good air-flow, in the Enclosure you can add any other Switchgear that is needed on your Lathe.

Regards,Keith.

Keith an e-stop is generally incorporated into the logic switching of the VFD and not as a separate mains input latch, the drive remains powered. The reason is that it provides protection in the event of a power failure (no volt protection) and allows multiple e-stop switches. The VFD can be allowed to brake a motor much faster this way compared to simply allowing the lathe to coast down. Finally, there is a considerable amount of electronics inside a VFD, and constantly turning it on and off is definitely not a good idea.

Of course some of these factors may or may not be a consideration for the OP's installation, I'm simply pointing out the way it's normally done and why. In our cases, where we're using the drives off a standard switched GPO I can't see any good reason to have a contactor on the input.

Pete

I have convenient wall and GPO right next to the lathe. I'm thinking of mounting the VSD unit at about head height on the wall above the GPO. The shed has it's own set of circuit breaker box.

Finally, there is a considerable amount of electronics inside a VFD, and constantly turning it on and off is definitely not a good idea.

When I leave the shed I usually turn the mains off, are you suggesting that I should leave the VSD on all the time?

Turning the VSD off each night will not do any harm. I think Pete meant removing power from the VSD as a general stop.
I haven't seen any of the cheap ones with this feature (yet) but i used to install a few different drives that had a detachable control panel. With an extension cable, usually purchased seperately, you could mount the VSD in an enclosure and have the full controls anywhere you wanted. They sound like they would be ideal for lathe/mill control (I have neither). I think they were Fuji and Allen Bradley drives.
Sorry for the derail, it just occured to me

Originally Posted by BobL

When I leave the shed I usually turn the mains off, are you suggesting that I should leave the VSD on all the time?

No definitely not. I was just suggesting using the motor drive's emergency stop function instead of completely removing the power to drive in the case of emergency stop. Most of us here have small machines, so it may not be a big factor, but larger machines can take a while to coast down. On the other hand the drive can actually brake a motor, hence stop it faster than if power were simply removed.

Mounting the drive on the wall would work, but as I mentioned it's not what I would do or recommend.

Pete

Pete F,
The placeing of a contactor and in the event of a Category 3 or 4 Installation it would be Two Contactors on the input side of the VSD is what is done in Industry.
In an Industrial Installation a Risk and Hazard Assessment would be done to determine the Control Category as per AS4024.1-2006 then the Stop Category would be determined being Stop Category 0 or 1 as per AS60404.1-2005 and you also have to take account the OHS Regulation 2001 Chapter 5 Clause 92.
Most Drives do not meet these conditions as they are not dual redundant, they would need to conform to AS61508-2005 or AS62061-2006 or EN13849, and generally would not meet IEC61800-5-2.
If you wanted to incorparate a Stop Category 1 into the Lathe Control useing Standards then a Failsafe Controller would be used so an Emergency Stop would signal the Failsafe Controller which would bring the Hazard to rest, this is where ramping and brakeing as found in drives can be used then a complete removal of power would be done according to Stop Category1, but you also have to make sure that the Hazard is removed. If you wanted the Drive to be the point of issolation as said before it has to meet the Control Category as determined by the Hazard and Risk Assesment and at this stage they do not, this is why placeing Contactors at the input side of the Drive is what is done in Australia.
My suggestions for the placeing of a contactor in the input side of BobL's application was to afford him a simple solution as its a Domestic Installation, if BobL is concerned that he needs to stop his Lathe quicker than a free-run to stop then BobL can determine if he needs to make his circuit a Stop Category 2 and can also decide on the complexity of his circuit.

I have worked in the area of Industrial Safety for over 20 years now and design Safety Circuits for Industry, I have trained WorkCover Inspectors, am part of the Standards Committee SF008 and was a participant in the Federal Government Safe Design Project so I do know what I am talking about when it comes to Safety Circuits.

I understand that this a Domestic Installation and as such is not subject to all the requirements that an Industrial Installation would.
I offer suggestions in the Forums of things that should be considered based on my experiances.

Regards,
Keith.

Keith I have no idea of the Australian safety regulations, and can barely recall any of the electrical regs. All I do know is that the drives have e-stop facilities built in, and they require the drives to be powered in order to brake the motor. This is as per the manufacturer's application notes. The circuit to do so is not complex, it is just another logic wire and a $10 switch from Jaycar wired in the same circuit. I use this e-stop function on my mill, on my surface grinder I use 3 wire logic control and therefore has it by default. My lathe doesn't have one and really should, so I will reconfigure the wiring arrangements on this machine in the fullness of time. At the time I was too keen to get it turning and wired it as simply as I could, in hindsight a mistake as I could have preserved the original switch panel, as I did with my other machines.



An emergency stop situation on a lathe is almost certainly going to be mechanical and not electrical, however should electrical isolation be required then one simply turns off the switch on the adjacent GPO. Are you saying that based on your qualifications, to comply with Australian safety regulations, despite the fact that it's plugged in to a switched single phase GPO, a contactor would need to be added to the input supply to additionally electrically isolate the drive, thereby rendering its built in e-stop function useless? IIRC correctly, the fact that coolant MAY be used, to similarly comply with Australian electrical regulations, the switching for this contactor must be low voltage, therefore a transformer would be needed.

If it was hardwired then yes a contactor on the input would definitely be required. I know the regulations sometimes defy belief so I'm now very keen to know the answer as to why they would require a drive's emergency stop facility to be rendered useless, an isolation switch on the GPO ignored, and about a hundred + bucks worth of additional parts in order to pass?

Pete

Hi Pete F,
Sorry I didnt get back to you sooner but I’ll try to explain what I was saying another way.
For the normal operation of the Lathe, Mill or any other Machine you would use the Start, Stop, Jog etc. controls and they would be wired to the VSD as per the relevant VSD Instruction Manual. When it comes to the Emergency Stop this is where you are in trouble and want to turn the Machine off as quickly as possible so you would look at the type of injury the Machine could give and how you would be subjected to it.The Hazard and Risk Assessment I referred to and that is found in the AS4024.1-2006 Standard is used to categorize this. From that you get a Control Category which is how the parts of the Machines Control will react (operate) when you press the Emergency Stop. Attached is an example of the Graph as found in the Standard AS4024.1-2006

From the Graph you then get the Control Category, being from B to 4.
This Control Category tells you how the Safety parts of the Control will react; in this case it’s the Emergency Stop on the VSD.
Most VFD's have an Emergency Stop Input, and if you look at the VSD's Specifications they will refer to what Standard, Control Category or SIL Rating it conforms to, if not stated then you would have to assume it would be a Category B.
If we take the example of a Lathe the Injury can be quite severe and not possible to avoid so you would be looking at a Control Category 3 or even 4.
What the Standard AS4024.1-2006 says for Category 3;
The safety related parts of control systemshall be designed so that asingle faultin any of these parts does not lead to the loss of safety functions.Common modefaultsshallbe taken into account.
Whenever reasonably practicable the singlefaultshall be detected at or before the next demand upon the safety function.
The Emergency Stop input of the VSD would have to conform to this and that was my point that I was making, not all VSD’s Emergency Stop Inputs conform to this so other components would be added to the Machines Control System so when the Emergency Stop is used you can bring the Machine to a safe stop. By placing a Contactor or two Contactors at the Power Input side of the VSD you can be assured that it is isolated, this also where a Safety Controller can be used, it checks that the Contactor/Contactors have indeed functioned. In the Category3 and 4 Circuits one also looks at whether one Contactor is enough to provide the level of redundancy.
Emergency Stops have themselves been given a Category, either Stop Category 1 or Stop Category 2
Stop Category 1 is where you remove all power, Stop Category 2 is where you bring the hazard to rest then remove all power. Stop Category 1 would be where you would remove the power to the VSD if it did not have a suitable Emergency Stop input e.g. in this case a Category 3 or 4 or SIL3 rating.
For a Stop Category 2 you can use the Functions of the VSD to bring the Machine, in this case the Lathe to a quicker stop by DC injection, Fast Ramp Down Time etc. To maintain the Control Category 3 a separate Controller can be used that its self has a Category 3 rating and they have an inbuilt timer so when the Emergency Stop is operated it signals the Controller which sends a signal to the VSD to use the DC injection, Fast ramp Down Time etc. to stop the Lathe then the Controller Isolates the Input Contactor/ Contactors.

So in the case of what has been discussed in the Forums about Emergency Stops and using the VSD/s Functions to bring the Machine to a quick stop I have commented that one should look at what the Emergency Stop input is rated at and look at the control circuit as some extra control gear maybe needed to be considered so that a possible failure in the VSD won’t lead to somebody being hurt.

You made some points in your response, they have E/Stop facilities built in, yes they do but in light of what I have written above it may not be suitable. You also said simply turn off the switch on the GPO, yes that will do it but is it in reach when you are in trouble.

I hope I have made what I was trying to get at a bit clearer, if I have not let me know and I’ll try to explain it. I did refer to a lot of Standards I know, that is what is used when designing control circuits in Industry that Operators are going to use to operate the different types of Machines and by law Designers have to take them into account so Machinery is safe to use. I make my comments in the interest of informing the people like me who enjoy reading the posts on the Forums and share our collective knowledge and experiences.

Regards,
Keith.