Thread: Fitting VFD to Craftsman Lathe

Hi Bob,

I think Pete has covered it pretty well already, just one point to clarify when you say...

Is it detrimental to these devices to have them powered up but NOT driving a motor?

By that I assume you mean powered up and connected to the motor, with start/stop control via the VFD control terminals. (in this case a foot switch) No problem.

You can switch the output of a VFD, while it is powered up, but only if it's not running. Is that what you meant?

Similarly that "stored" electricity is put back into the circuit when the motor is shut down and can sometimes be seen as arcing in the switching circuit. That's the best layman's description I can manage I'm afraid. The motors being talked about here are much smaller, but of course it's all relative.

Expanding a little on Pete's description, when you break the circuit, the flux in the motor field coils doesn't drop immediately, it takes time, during that time, while the motor is spinning down it acts a generator until the flux through the field coils decays. It can be a problem with fans and pumps that can auto-rotate as well.

In motors of the size we are talking here, it's unlikely to be a problem, just another reason not to switch the output of a VFD while it's running.

Regards
Ray

Thank you for that Pete.

All the operational switching of my VFD is done via the remote switching function ( F10 - 1). No switching occurs on any motor wiring. The motor is wired directly to the VFD.

The Schaublin's main switch controls the mains power to the VFD via the contactor.

BT

"You can switch the output of a VFD, while it is powered up, but only if it's not running. Is that what you meant?"

Ray,

In some ways, no. What I had been initially thinking was, could I run both motors via a single VFD. The motors would be switched separately. What you are saying is that it can be done if you switch the VFD output from one non running motor to the other enabling only the running of a singular motor.

I could never have both motors running simultaneously. Using individual VFD's will overcome that restriction.

BT

As long as the drive is not running the motor at the time you can do all the switching you like, no problem. Just be aware however that if you have vastly different motors the VFD isn't going to like it. In this thread we've seen the last few pages of trying to get the VFD to drive just one motor correctly, now imagine how difficult it is to say to the drive "nah mate, forget all the parameters I just told you about THAT motor, I just flicked a switch and now I want you to drive THIS motor"

In fairness to the VSD, its been used on 8 motors and it ran fine out of the box, unless you count one error running at 5Hz. Other than that its when I have been playing around with the settings that the problems started. On that subject, I've been increasing F_13 today, it sounds fine up to F_13=5, at F_13=6 I think I can hear a difference in the way it starts, it does sound different at F_13=7, it sounds nasty at F_13=8.
Stuart

Yes but in Bob's case he's been talking about a 2 HP motor and a 0.4 HP motor if I recall correctly. A BIG difference in frame size!

Pete

Hi Stuart,

I've been digging further into what F5 and F13 parameters do and how they interact.

First, to clarify what the difference between the 50Hz settings and 60Hz settings are, the difference is that the voltage boost is calculated at 2.5Hz on the 50Hz case, and 3.0Hz in the 60Hz case. (Don't know why they just didn't say 5% of rated motor frequency?) I can't tell the difference between F5=1 and F5=4

Anyway, back to F13, the F13 is the percentage added to the V/F curve. So selecting F5=1

Hz Voltage%

1.0 8% + F13
2.5 10% + F13

So when you pick F5=1 and F13=5 you get (10+5)=15% output at 2.5Hz, which is not quite the same as selecting F5=2, because at 1.0Hz you will have 8+5=13%, wheras F5=2 would be 10.5%

The conclusion, is the same, I think you just have to tune the combination of F5 and F13 to give the required startup. In the case of a mill or lathe, we never start under load anyway, so the tuning isn't all that critical. F5=1 and F13=0 works just fine on the HM52.

Still, I think it's a good argument for a vector control drive if you need the torque at low revs.

Regards
Ray

Ray,
Always takes me awhile to get my head around those graphs each time I look at them. Would it be fair to say that if I am mostly above 25Hz F_13 isn't going to make much differeance?
So If I understand what you said earlier. If there was more load on the motor at start up do you think it wouldnt error with F_13=10

F_05=1 + F_13=0 in the morning.
Thanks
Stuart

Noticed another strange thing with my VSD today. I was boring on the mill in lower gear at 220rpm with an irrupted cut which was giving me a lot of gear noise. So I figured I would take it out of low and run it at 660rpm and 15Hz on the VSD. Started it up and took a cut, it worked just find, then while it was sitting there spinning it shut down with a OL1 error. I tried setting F_13=5 but it ran for a minute or so and then shut down. So it was back to lower gear and 220rpm 50Hz. I *guess* increasing F_18 like the manual says would fix this.
Stuart

Just a tip if you haven't already finished.
It would be quicker to mill out the majority with an end mill then use the boring bar.

Dave

I have. It would have but I hadn't really dicided how deep I was going until I got there. lol
Stuart