VFD / motor drive advice please

[richardb15]

Hi all,

I know this isn't strictly related to the Acorn, but I want to use the Acorn6 to control a second spindle on my mill to be used as a jig grinder.

I couple of years ago I bought my wife a Hauser No3 jig borer and with it came a mountain of accessories, tooling, cabinet etc. Within all that were 3 grinding head motors which I realised were off a No5 Hauser that was in the same factory, but that machine had changed hands twice and current owner untraceable, so I had these high speed motors available.

Hauser made jig borers but there were options to add grinding heads to them as can be seen in these pics here:
https://www.lathes.co.uk/hauser/page4.html

or PDF here:


If you look at the 5SM, 3SM and 3-SMO they all have a detachable grinding motor on the spindle. I've got 4 of these, all different collet sizes so figured I'd just get them wired up and we are golden.

I don't have any wiring diagrams and haven't been able to find them to know how the Hausers were wired, but one of the motors still has a nameplate:


From taking one apart they are a 3 phase induction motor, and the wiring plug that goes into the motor has 5 connections, 3 have the same resistance between each pin, one is not connected, and one is an earth. The smaller motors are 3.5ohms and larger ones 1.4ohms between phase pins. With that info and the nameplate I figured there were 3ph, 110v, 300W and designed for a 240-440Hz feed. That is a really awkward voltage here in Australia!

Anyway I bought a single phase 240-110v transformer (500W):


and a 110v 1ph to 110v3ph VFD (400W):






So thought that would do the job. I wired it up, turned on the transformer and VFD with all default settings. The Hauser motor ran slowly and responded somewhat to the speed dial, but it would only go up to around 7Hz and seemed to be flickering, not steady. I set parameter 12 from the default 50Hz to 250Hz, being that was what the motor plate said. Turned it on again and poooooofffff, the magic smoke came out.

Not wanting to repeat myself, I figured I'd ask here to those with more VFD experience than me and hope someone can help. Did I just not use a large enough VFD, can you oversize one too far? Anyone know where i could get a Hauser wiring diagram for their early jig grinders, or know how Hauser did the variable frequency back in the 50's and 60's?

Any help or info appreciated, thanks.

[centroid467]

Just to clarify, the VFD released the magic smoke?

I'm not sure what happened there but I can say that the main thing that would happen with oversizing a VFD is that you may reduce the resolution of the current monitoring to a point where the control of the motor suffers. That, of course, depends on the VFD design and how big you go. A size or two up is most likely going to be fine but running a 400W motor from a 15kW drive could have some issues.

[richardb15]

Yes it was the vfd that the smoke came out of. I just wonder if the startup current draw was too much, but I'd have thought the vfd soft start would negate that. More thinking required.

[Muzzer]

Did you set the "rated" motor parameters (P1-00 to P1-05)? These are the "motor plate" values you showed in the photo of the motor. These match the voltage the VFD will apply, depending on the speed at which the motor is turning. For this motor, it should apply around 120Vrms when running at 13,200rpm, at which point it will be outputting 440Hz.

It's possible that you were applying the full voltage at only 50Hz, which would be problematic, as it would likely saturate the stator and overcurrent the VFD in a way it would struggle to protect itself against. The user manual is wonderfully obscure in the way only a Chinese manual can be. However, parameters P1-02 (voltage ie 120V) and p1-04 (rated frequency 440Hz, corresponding to 120V) are particularly critical.

The rated motor current P1-03 limits the phase currents to protect the motor from overheating if you overload it. It's good to get that set about right but won't let the smoke out if it's not correct