Powering high frequency grinders with a VFD? Also how good are HF tools?

Spotted some high frequency power tools on ebay. Not sure if I will actually buy them (£75 for a 125mm angle grinder? ouch) but it did make me curious.

The tools run on 3ph 300hz 200V power. Standard industrial practice is to have a transformer attached to the 3ph power lead that jumps the frequency up.

Since I have no 3 ph main power or access to a Fein dealer to buy a transformer I was wondering if a VFD would work? I have a 1.5kw capacity one that I bought for £20 a while ago as a just in case. Could set it to 300Hz and mount it in an enclosure on the wall.

Recently broke my Makita. Can either get a new one for £40 or go £75 (ONO) on this Fein. Has anyone here worked in industry and can say whether there is noticeably better performance on Fein/HF tools? I don't do 8 hour shifts with it but its certainly one of the most heavily used tools I own.

A transformer cant alter the frequency and whilst a vfd will work most won't like the load being disconnected whilst the vfd is running

I doubt the Fein tools can be rewired Delta to allow them to be used with an inverter.

It is not a transformer that they use but a frequency converter

A lot of the wood butchers [ joiners​] on sites up here use Fein Tools, especially the saw that cuts very close to a floor ect. Very reliable gear by all accounts although pricey compared to Makita ect. The Fein's do have a fine [ no pun intended] reputation.

Hi Rainbows,

check out the prices of the Hitachi grinder combo on Screwfix.......last time I looked they were about £85 for a 9" and a 41/2"......

sell the 9" and it'll pay for most of the little one.....

I use mine every day and they are about 4 years old now, just waiting for the pop..........hahaha.........

Clogs

It's funny how things go and come back in fashion, in our factory we generated 110v 3phase at 200hz for hand held power tools, this gave a better power to weight and high speed for grinders. Air tools and then battery took over 25 years ago or more. Now with portable inverters for easy frequency changing the hi frequency tools live again.

Mike

First off, the tool won't need rewiring. it's already specced at 200V. Configure the VFD to produce 300Hz, 200V and that's what the tool needs.

Second, It's been many years since VFDs had such poor protection that they would suffer damage sometimes as a result of disconnection (or more often, connection) of a load. If the VFD does release its magic smoke, replace it with a modern one and the problem won't recur.

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If you are seriously interested ... look here: **LINK**

https://fein.com/en_uk/high-frequency-grinding/what-does-high-frequency-mean-t400007/

... also note that there is a drill listed on ebay, which makes your £75 look very reasonable.

MichaelG.

All other factors aside, there should be no need to rewire them if they are already 200v.

Looks like they use a rotary transformer....

That's a motor-alternator set. A rotary transformer won't change the frequency. It may change the phase angle.

Air tools can be great if you're at a factory where they're compressing air anyway and much cheaper per unit cost.

Having said that, it's not without it's problems at times, moisture in the system, pressure drop at peak demand...

Tends to be seen much more in industrial environments, rather than a home workshop, they're noisy and expensive to run and pretty terrible in terms of power efficiency (get the electricity to run the compressor, in order to use a tool rather than just running the tool straight from the power). 

Michael W

Edited By Michael-w on 28/08/2017 00:07:04

That's interesting. I've not heard of these before but the principle is clear - they are using 3-phase induction motors, rather than brushed universal motors, so there are no brushes to wear out and no nasty sparks going on. A 2-pole motor at 300Hz has a no-load speed of 18,000rpm, which is good for die grinders (direct drive) and angle grinders (gear reduction) etc.

I see they also do a couple of portable frequency converters for site work - look like solid state. Bet they cost a few bob...

Murray

Is anyone aware of any solid state inverters which will stand a switched load? (i.e. on/off switching at the load, rather than via the inverter control panel.)

I have some 220v 3 phase 400hz ex-military power tools, which normally run of their own dedicated 2 stroke generator.

It could be useful to be able to run them from a normal 50hz mains supply when I don't want the size and noise of a big generator disturbing the neighbours.

Thanks

Bill

My Danfoss VLT500 series inverter specifically states Unlimited switching on output.

But modern IGBT VFDs with overcurrent protection and flywheel diodes will survive with no problems. In normal operation, the electrical environment at an inverter's output is nasty enough already.

If the manual doesn't specifically state that downstream switching is not permitted, then it will be.

A bit of a side line off the original topic but out of curiosity what brand / model are the ex MOD tools?

They're all over in Sheffield at the moment, but as I recall, are all Bosch.

A fair old setup, which may well be for sale eventually, when I re-unite all the bits and get them cleaned up.

I can't remember the full list, but roughly;

small & large drills, small and large angle grinders, straight grinder, rock drill & compressor, small breaker, large road breaker, submersible pump & 2" layflat hoses, circular saw. I think that's about it, apart from the 5KVA generator. (I'm missing the chainsaw, which would originally been part of the kit)

Unfortunately the genny, and some tools are rather inaccessible at the moment, as they are on loan to a friend for a building project, but last week the house collapsed around them.

Bill

Yikes well thats one hell of a way to lose some tools. Hopefully it all gets picked out again or you might need to start testing out VFDs to replace the generator. My method of muffling generators was going to be a fancy enclosure but in the end piling sound insulation over it in a baffle configuration worked out so well I never made a real enclosure. Come to think of it collapsing a house over it would probably do a pretty good job of masking the noise too.

That sounds like a very fun pile of tools to own, though to buy them when they come up would probably fill my garage and cost more than all its current contents. If you ever sell it all on then a week later find a grinder you forgot about I think I could stretch to buy 1 or 3 of them.

Interestingly I can't find anything on high frequency tools other than grinders. Wonder if the MOD commissioned the rest specially so they wouldn't need 2 generators for different frequencies.

.

Yes, that is odd ... Fein seems strangely silent on HF drills

MichaelG.

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Here's the one I mentioned on ebay:

http://www.ebay.co.uk/itm/FEIN-Bohrmaschine-DS848-750W-200v-3Phase-300Hz-HF-Gerat-Industrie-Profi-mit-MwSt/182337676005?

Edited By Michael Gilligan on 29/08/2017 06:02:29

I suspect it may depend also on what control scheme it's employing. It the thing is using flux vector control and fondly imagines that it knows what machine it is controlling, it may get rather miffed if you suddenly banged a stationary motor on the output. On the other hand, if it's just running constant V/F, it would be much less bothered. Doesn't look as if the VLT series does vector control but many do these days.

Murray