Thread: VFD switching on a Hercus 260

Thanks fellas. Looks like oversizing the VFD doesn't cause any major problems, which is good as there are heaps of 1.5kW units on eBay. I just need to confirm that I can easily reconfigure my motor to delta before I buy a VFD. If it has to come out and go to a motor rewinder it ain't happening.

take the top off the motor wire connection box if its got 6 terminals with jumpers your probably in luck check under the lid it usually shows you the jumper positions either Y or delta
john

Great, thanks John.

Originally Posted by jack620

Thanks fellas. Looks like oversizing the VFD doesn't cause any major problems, which is good as there are heaps of 1.5kW units on eBay.

Whoa! No you can't conclude that, and some VFDs are specific to the motor size. For example my SEWs allow one frame size above and below the nominated size. That's it. It could well be that the particular ones you're looking at will allow a much greater variation in motor size, but don't presume that will always be the case.

What needs to be remembered are these are actually motor controllers. They output a square wave and rely on the natural inductance of the motor coils to form the other half of the circuit and simulate a regular mains voltage sine wave. It's the reason, for example, you shouldn't run a VFD with switches between the controller and the motor.

Pete

OK thanks, I'd better have a look into frame sizes too. The 0.75kW VFD is looking like the safest bet.

Originally Posted by jack620

I'd like to mount the VFD in the area behind the control panel. How hot do these VFDs get?Chris

There is sufficient cooling in the cabinet cavity behind the control panel. The steel cabinet walls act as heat sink. Just needs a small fan to help circulate the air inside the cavity.

Have a look at this older thread for some ideas. I am very happy with the control panel on top of the headstock, I would not want the controls anywhere else.

http://www.woodworkforums.com/f189/2...roject-125170/

Chris

PS: the wheels uder the lathe were only whilst working on it for moving it around without a chainblock - they were since swapped for adjustable legs.

Chris did you find the fan was necessary? I have 4 machines running VFD and haven't used a fan in any of them. It may however depend on the brand, heatsinks are very expensive, so it's an area I would expect some cheaper brands to skimp on.

Pete

Originally Posted by Pete F

Chris did you find the fan was necessary? I have 4 machines running VFD and haven't used a fan in any of them. It may however depend on the brand, heatsinks are very expensive, so it's an area I would expect some cheaper brands to skimp on.

Pete

Pete, no it is not strictly necessary. But:
- in an enclosed cabinet, it is always good practice to add a fan instead of relying purely on convection
- that particular VFD (Omron Varispeed V7) just has an oversized heat sink, and no fan on it's own. Most other VFD's do have a tiny fan built into the VFD.
- My workshop does get quite hot in summer. VFD's are rated for something like 30C ambient temperature, and must be derated by some 10-15% for every 10C above this temperature.
- As ambient temperature rises, all modern VFD's will automatically de-rate themselves, first by reducing the chopper frequency (= more audible noise), then by reducing motor current (less power output). This is why if installed in a cabinet, it is recommended to buy the VFD one or two size larger than the motor.
- for every 10C ambient temperature above 30C, you can about halve the expected life span of a VFD. VFD's perish whether switched on or not, design life is about 8 years (or about same as a TV set).
Chris

Ok fair enough. My workshop doesn't vary much in temperature summer or winter so I sometimes forget that some are sweltering it out in a shed in summer. As I said, I haven't noticed much of a temperature rise in mine whatsoever, however they have quite large heatsinks and I guess they're not there for decoration, so they must dissipate a bit of heat.

Pete

Originally Posted by cba_melbourne

Have a look at this older thread for some ideas.

Thanks Chris. I remember that thread. Looking at the pics of the electrics panel I'm seeing more bits than I thought were required. I assume the perforated black box is part of the VFD? Is that a circuit breaker or a contactor next to the VFD? Are the two white devices furthest from the VFD circuit breakers? One each for active and neutral input? And the two black fuse holders on the ali mount- what are they for?

Any chance you made a circuit diagram at the time you could post here?

Chris

> I remember that thread. Looking at the pics of the electrics panel I'm seeing more bits than I thought were required.

That is only because I wanted a fan, a "zero volt" release, contactors and fuses, separate spindle rpm display...

> I assume the perforated black box is part of the VFD?

No. This is a 12V DC power supply (salvaged from a previous life). It feeds the fan, and the RPM display in the top box.

> Is that a circuit breaker or a contactor next to the VFD?

That is a contactor. Together with the two (original Hercus) pushbuttons in the front panel, they make the "zero Volt" circuit, eg if mains fails one must press the start button again to power up.

> Are the two white devices furthest from the VFD circuit breakers?

Yes, salvaged too from a previous use....

> One each for active and neutral input?

Yes (you can see I originally come from Europe. With this setup it does not matter if the neutral and the phase were reversed, both are treated as if they were live phases. Its standard practice for equipment to be sold internationally. It is in my opinion safer, regardless in which country it is used).

> And the two black fuse holders on the ali mount- what are they for?

If I remember well, one is for the 240V input to the 12V power supply, the other for the 240V to the zero volt circuit contactor. I took the pics before assembling and labelling...

> Any chance you made a circuit diagram at the time you could post here?

I will check tonight.... but the way I know myself, it would be only pencil sketches....

Chris

Thanks for the answers Chris. I probably don't need a circuit diagram now that I have that info.

Originally Posted by cba_melbourne

That is a contactor. Together with the two (original Hercus) pushbuttons in the front panel, they make the "zero Volt" circuit, eg if mains fails one must press the start button again to power up.

I'm surprised VFDs don't have a zero-volt function incorporated into the logic. Or is yours an additional "fail-safe" circuit?

Also, re the 12V PSU- Most VFDs I'm looking at have a 24VDC or 30VDC aux output. My tacho will run off 30V, so I can probably dispense with an additional PSU.

I'm now heading out to the workshop to check the terminal box on my motor.

Chris

My motor can be configured for delta. That's good news.

I've included a pic of the electrical panel. I guess the two white components are zero-volt dropout and/or a circuit breaker. Can anyone clarify? Given that this is a 3 phase machine, can they be incorporated into the post-VFD electrical wiring?

Chris

Hi Chris,
The lower "white thing" with the red square is an overload. That wont be needed. IF you end up using that contactor it will be switching the VSD controls not the 3 phase motor wiring. Same goes for the fwd/rev switch.
Is there a power supply for the controls or do they run on mains V?

I wouldnt be so sure about the "output" on the VSD's, while you maybe correct they may in fact just be terminals on a relay to switch a V source you supply.

Stuart

> I'm surprised VFDs don't have a zero-volt function incorporated into the logic. Or is yours an additional "fail-safe" circuit?

The VFD can be programmed to either restart (or not to restart) automatically after a power failure. But that does not relly remove power from the VFD or from ancillary circuits such as the fan or the power supply for the RPM meter, the machine light, or the outlet for the tool post grinder, or the outlet for a future coolant pump. I like to be sure that after a power failure, or after pressing the red main off button, nothing can suddenly restart by itself.

The emergency stop switch on the control panel is of course wired directly to the VFD - this is important to quickly stop the spindle using dynamic braking. By just removing power to the VFD, the spindle would leisurely coast to a halt, not what you want in an emergency.


> Also, re the 12V PSU- Most VFDs I'm looking at have a 24VDC or 30VDC aux output. My tacho will run off 30V, so I can probably dispense with an additional PSU.

Normally the 24V from the VFD are only intended for a very low current - just enough to operate the inputs and outputs, plus maybe a microscopic small cooling fan of about the size used in laptop computer. In my case I choose a larger fan. And I use the the 12V DC for the RPM meter and its inductive proximity pickup sensor at the left end of the main spindle. I just like the idea having a separate power supply for this, just think what could happen to the expensive to replace VFD, if the cable for the proximity sensor was accidentally chewed up between the gear train. I bought this VFD NOS on eBay France for ridiculously low money, I could not afford to replace it with the same at new price (this is an industrial grade VFD that sells new for about $800 from Farnell last time I looked - Omron VFD's are actually the same as Yaskawa, just slightly different software). Chris