Oberg Die Grinder

My friendly scrap man recently handed me a nice wooden box which he thought might be "interesting". Inside was a beautifully made, high speed Oberg die grinder (VM17 Nr 202) with collets and cable but, unfortunately, no power supply. Not a problem you might think - however, it's 38V, 400W and 900Hz to give a top speed of 54,000 rpm.

Oberg were a Swedish engineering company who made high quality files but I can find very little about the die grinder or its power supply. Has anyone ever used one of these or have a manual or circuit diagram or can anyone suggest what I might need. The plug has 3 pins (I presume the casing is earth) and I wondered whether it is low voltage 3 phase which I might be able to supply from an inverter somehow?

Any suggestions welcome

Put some pictures in an album but can't get them in the query.

thanks

Hi Alexander

Fein make high frequency power tools for industrial use from memory 300 cycle. Maybe if you spoke to one of their agents you may find a source. I have seen a rotary converter set up for driving an entire sheet metal factory, there was a special and separate bus system. to drive the tools. They are very robust.

Regards
John

It'll be a low voltage 3-phase 2-pole motor. Taking the 'synchronous' speed of a 2-pole induction motor at 50Hz of 3000rpm and multiplying by 900/50 you get 54000rpm. I think most standard VFDs go to 400Hz; no idea if you can get ones that go higher.

Andrew

If you want to use a VFD then you need to use transformers to get from 230V to 38V. Each rated at 200W.

Your motor has a "resistance" of 38^2/ 133 = 11 ohms which is not a million miles from 8 ohms of a loudspeaker. So what I am suggesting that a pair of 200W audio amplifiers driven by a variable oscillator which has the phases of its output correct could be another way to go.

Or if you are really clever you build your own VFD

Frank

Hi Alexander

I think this high speed spindels ar sold under the name SPINTEC nowadays.

Check this links.

http://www.ptsintl.com/pdfs/SPVSpintec.pdf

http://shop.spvspintec.se/

Ingemar

I would keep hold of it and see if you can find a use to get it working because if it's anything like the Hi-speed spindles sold by Arc they are quite expensive to replace.

Michael W

This might sound crazy but at that voltage they probably drove it via something a little akin to a 400w RMS audio amplifier although I doubt if it was a hi fi one. It was probably powered from a 110v supply. 38v RMS sounds about right for that as the peak voltage with a sine wave would 2 root(2)*38 which comes out at about 106v . I'd guess it would be driven with something more like a square wave in practice. That way the usual sort of speed control used to keep speed stable under load could be used

John

-

i agree with Frank and John - an old audio amp driven from a simple frequency generator should give you enough power at that frequency.

possibly doesnt need to be that big - depends on what you are grinding i guess, but an old 100 w amp should be pretty cheap, you may be able to parallel the channels.

-russell

If it has three windings, you should be able to run it of a BLDC motor controller - simples.

**LINK**

This will knock you back the thick end of a tenner though.

Neil

I'd guess it's 38v RMS AC Niel not DC.

If some one wanted to try an audio amp the simplest solution would be to drive the channels in anti phase and connect the motor across the outputs of the 2 channels. Trouble is though I'd guess it was driven with a pretty simple switched DC square wave drive and inductance effects might blow an audio amp up.

If it was driven with a switched square wave the arrangement may be similar to the speed controllers used on universal motors. In that case the motor might be 180v and the speed controller has a limited a range of "speeds". The mark space ration is never 50 - 50 it's always less to control the power into the motor. The back emf duration when the drive is off is used to detect that the motor is under load which would normally cause the speed to drop. That's prevented by increasing the mark to space ratio over a limited range. I understand electric model loco's use a similar arrangement and via a DC supply.

John

-

Having said all that I'd guess it would be fine with a 900Hz switched 50v DC supply or somewhat lees so wonder what they did do. I am assuming it's "pre brushless" but if not Neils idea may work out but I suspect it would really need one that will take a higher voltage.

John

-

Apologies for the delay in responding to all the helpful advice. Unfortunately, we had a leak in the kitchen on Friday (at least I became aware of the effect of a long term slow weep from a joint under the sink when the parquet under the lino started to swell and buckle up). You wouldn't believe how far water can spread!

Anyway, many thanks for all the comments - I am always amazed by the breadth of knowledge on this site. Ingemar (I'm guessing from Sweden) identified that Oberg are now Spintec and the site gave lots of information. They still make a VM17 spindle which fits all my information on mine so the die grinder is a 3 phase induction motor powered from a converter. I'm guessing that the power packs they supply will be well out of my price range so I was very interested to read Neil's comment that it may be possible to power it using a BLDC motor controller designed for a brushless DC motor - I can certainly go for a £10 solution (long Scottish heritage). I knew nothing about the technology of brushless motor control but when you read a bit about it, they do appear to be pretty similar to a low volt 3 phase motor although I certainly don't understand all the stuff about different waveforms etc. I did see that brushless motors appear to have Hall effect sensors to feed back motor performance data - will that be a problem here since presumably there won't be any on my spindle. I will probably contact Spintec to see if they can provide any more information but thanks again for all the help.

Might not work with a BLDC controller - these days most don't have hall sensors they use back-emf sensing, but they do normally have permanent magnets so might not work if yours is an induction type. It would probably run once its started, but I doubt it would start.

Hello Thor,

Welcome to the forum. the above posts suggest the WM17 needs a 38V supply so make sure this is programmed into the VFD (it seems that the minimum may be 25V chastotnii-preobrazovatel-sunfar-e300-manual-en.pdf )

Neil

Thor, I have set up my VFD for a conventional 3-phase motor, but I am no expert on high speed motors.

Your do seem right to me but I am no expert.

I would guess a quick try to see if it works should be OK if you have the voltage limited to 38V, but you may want to set a current limit as well?

Good luck - you might want to wait and see if an 'expert' turns up in a bit!

Neil