Two short videos of a VFD in action

[Ian PParticipant @ianp]

I am a staunch advocate of using three phase motors and a VFD in the workshop.

I have done two short videos showing the sort of speed range available, but also to debunk the old wives tale that there is no torque at low speed and that motors overheat at low speed.

The VFD display is showing frequency 4.0 to 130.0Hz and the Fobco belt drive is set to give a 3:1 reduction. Spindle speed is 38 to 1250rpm.

Videos are a bit grotty (hand held phone) the first shows a 1/4" drill in mild steel, and the second is a homemade single edged counterboring tool removing 50mm diameter aluminium around a 14mm hole to reduce the flange thickness by 2mm.

 

Ian P

Edited By JasonB on 10/08/2014 20:03:07

[Ian PParticipant @ianp]

on a Fobco drilling machine

[Ian PParticipant @ianp]

Sorry the links I put did not seem to be active, this should be the first one

 

Edit, Oops, maybe they do work

 

 

IanP

Edited By Ian Phillips on 10/08/2014 20:06:27

Edited By Ian Phillips on 10/08/2014 20:06:52

[JasonBModerator @jasonb]

I altered them for you.

[Michael GilliganParticipant @michaelgilligan61133]

looks like that works very nicely, Ian

MichaelG.

[Ian PParticipant @ianp]

Jason, your'e an ace!

I looked at my post, then had another attempt, but by then you had fixed the links.

I read and re-read the instructions on the YouTube button (in this edit box) but I must not have followed them properly. Thanks anyway.

Ian P

[JasonBModerator @jasonb]

When adding them to your post it does look like they have not worked as you just get a box with "Iframe" in the middle, once you add the post it will look right.

J

[Oompa LumpaParticipant @oompalumpa34302]

"I am a staunch advocate of using three phase motors and a VFD in the workshop."

Ian, so am I. If you had asked me six months ago I wouldn't have had an opinion, secretly I believed they might be a bit of a waste of money. All this changed when a friend gave me a small three phase motor and VFD for one of my machines.

It was transformed and I am now wanting to change my other machinery to VFD and three phase too. I am rebuilding a drill press right now that will be three phase and with similar characteristics as the one you show above and I am hopeful that this week I can get one of the VFD drives I have been sent working with the new motor I have because the old drill press has now been collected by it's new owner!

If you haven't experienced a Variable Frequency Drive and three phase motor I would urge you to try one at your earliest opportunity, well worth the effort.

graham.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Ian Phillips on 10/08/2014 19:55:46:

but also to debunk the old wives tale that there is no torque at low speed and that motors overheat at low speed.

I too am very much converted to three phase motors and VFDs. However it isn't entirely an old wives tale that the torqu is low and that they overheat at low speed.

Let me explain:

The torque available from a three phase motor remains more or less constant with varying supply frequency so, yes the torque is maintained at low speeds. If you reduce the speed using gears or belts the torque is increased at low speeds in inverse proportion to the speed. Thus you do loose torque at low speeds. There are some tricks that can be done electronically to improve matters but not much. For that reason I have retained the belt change on my machines so that higher torque is available if needed.

As for temperature, the motor is cooled by a fan connected directly to the shaft. At low speeds the fan has little effect and the motor can overheat, depending of course on the load applied. Some motor manufacturers make motors with bigger fans for use with VFDs to help matters. It is a good idea when replacing a single phase motor with a VFD to use a motor about 50% higher rated.

Russell.

[Ian PParticipant @ianp]

Russell

I agree totally with your comments, my point about the overheating is that whilst it is a possibility, in practice, in a home workshop environment its probably highly unlikely to be a problem.

I am sure if a motor was run continuously at low speed with a full load it would only be a matter of time before the temperature increased. In my experience (with 3:1 reduction) I have never detected even the slightest warming of the motor. Some time ago I used my Boxford (in backgear) to machine 4 chunks of 6" diameter EN24, a process that took me several hours with the motor running on about 20Hz, again there was absolutely no overheating.

I'm not convinced of the need to use a bigger motor just because its driven by a VFD. I do not have a good technical knowledge of the inner workings of a VFD but if the motor torque remains roughly constant through the speed range then at higher shaft speeds surely motor is producing a greater amount of power?

When converting any machine to VFD drive, I would definitely recommend retaining any existing belt or gear speed changing to get the best of both worlds. Having said that I have not moved the belts on the lathe or the drilling machine in about 15 years!

Ian P

[OuBallieParticipant @ouballie]

Agree wholeheartedly with all positive comments on fitting them.

VFD drives have totally transformed using both the Warco BH600G and Mitco pedestal drill, and even made selecting a speed on the Boxford shaper a pleasure now.

All I do is select a speed that suits the cut or drill bit, and enjoy, as with being able to increase speed when parting off with manual feed. I really must get that battery drill connected to the Feed Rod.

The bench drill in the Carport is a PITA to use now, having to fiddle with changing belt position, so I seldom do so.

Wouldn't be without VFD drives.

The two milling machine still need converting, parts ready and waiting for me to pull finger out.

Geoff – Taking videos in the Workshop today

Edit:

IanP,

Very remiss of me not to say 'Thank you' for posting the videos. Just starting to do so myself, so starting to understand the obstacles.

G

Edited By OuBallie on 11/08/2014 12:00:50

[Bob Brown 1Participant @bobbrown1]

One consideration to take into account is swarf, when the connections are exposed then there is the chance swarf or particles of metal could get into the connections and cause a short or a risk of electric shock. With my VFD driving my mill I fitted it into an enclosure with just the buttons and display exposed.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Ian Phillips on 11/08/2014 09:59:56:

if the motor torque remains roughly constant through the speed range then at higher shaft speeds surely motor is producing a greater amount of power?

That's correct. In other words if you run the motor slower you get less power. It's a bit of a simplification but a 1 hp motor running at half speed will only give about 1/2 hp.

I have put 50% bigger motors on both my lathe and manual mill when fitting VFDs. The motor on the mill does get hot to the touch when cutting hard at low speed. If it gets too hot to keep my hand on I go more gently or have a cup of tea and let it cool down. Never notice a hot motor on the lathe.

Russell.

[jason udallParticipant @jasonudall57142]

Power = torque x rpm
( neglecting units for the moment)
So even with the torque the same (say) you can’t
help but have half power at half rpm

“Ye canna change the laws of physics”.. (apart from the whole ftl thing!)

I too like vfd even when 3phase is available as input.

[Oompa LumpaParticipant @oompalumpa34302]

Ian, if you don't mind, what size motor have you got there on the Fobco? and is it two pole or four. I would surmise four pole but thought I would ask anyway.

Sorry, one more question – are you happy with the power of the motor or do you think you should have put bigger on there?

Thanks,
graham.

Edited By Oompa Lumpa on 11/08/2014 22:28:45

[Gary WoodingParticipant @garywooding25363]

I converted the spindle and power traverse motors of my ancient Centec 2B to delta and fitted VFDs as shown in the photos. Neither motor was designed to be run in delta mode so I had to convert them by bursting the star-point and adding extension wires. The VFDs are fitted into the cavity previously occupied by the switch and control gear, and the VFD controllers are in a little box attached to the traverse motor.

The spindle motor is 1hp and the table motor is 1/2hp. Since they are the original motors they were never designed for VFDs, but I've had no problems with overheating. Both the spindle and table speeds are variable by means of gears, but I normally run with the mid gear ratios selected and vary the speed with the VFDs. Very occasionally I change the gearing when I need very high torque or speed.

Gary

[Ian PParticipant @ianp]

Posted by Oompa Lumpa on 11/08/2014 22:27:22:

Ian, if you don't mind, what size motor have you got there on the Fobco? and is it two pole or four. I would surmise four pole but thought I would ask anyway.

Sorry, one more question – are you happy with the power of the motor or do you think you should have put bigger on there?

Thanks,
graham.

Edited By Oompa Lumpa on 11/08/2014 22:28:45

The motors is an old 'squarish' Hoover motor, 1425rpm 1/2HP so that's two pole.

Its on the machine because its what I had spare and it has more then enough power for my purposes (14mm holes in steel no problem).

Ian P

[Gary WoodingParticipant @garywooding25363]

Posted by Ian Phillips on 12/08/2014 09:27:27:

The motors is an old 'squarish' Hoover motor, 1425rpm 1/2HP so that's two pole.

1425rpm would be a four pole.

[Ian PParticipant @ianp]

That's an 'Oops!' on my part. I need more coffee.

Ian P

[Russell EberhardtParticipant @russelleberhardt48058]

Great idea Garry, building an alcove in your workshop for the mill

Russell.

[Dave plus / minus 40 thouParticipant @daveplusminus40thou]

excellent thread, this one of my first replies to the forum so be gentle with me! , the torque loss is an important part the discussion – but thats the trade off – i run a colchester student 1800, a Van Norman 1-V mill ( circa 1941) and a Jones and Shipman 540p surface grinder all from a single chinese £150 single to 3 phase 5kW VFD (not the same time though!) – i have installed a ringmain in the w/shop with isolation sockets for each machine. All motor connnections have been changed.

I prefer to use the origional controls rather than the pendant type – to do this i run a seperate supply through the control circuits, my colchester runs on 110v powered from a yellow transformer (will change the contactor coils at some point to 240v) and others are on 240v. although i would not advocate this in an industrial situation i see no problem at home as it is only myself that uses the kit so isolation is not a problem if i need to work on the electricals.

The VFD is started and runs up, i can then turn the lathe on and off as needed, the VFD can handle the additional ampage at start up without any problems unless i want to run at 1800rpm, i then push the start handle down then turn on the VFD.

another benefit from using 3 phase is the smoothness of the cut / grind – a single phase motor can be problematic, i think this has been discussed elsewhere.

as long as i do not try to take 1/2" cuts it all works fine – if anyone wants any more detail on the above then give me a shout.

hope this helps

Dave

[Michael HornerParticipant @michaelhorner54327]

Posted by Russell Eberhardt on 11/08/2014 15:34:00:

Posted by Ian Phillips on 11/08/2014 09:59:56:

if the motor torque remains roughly constant through the speed range then at higher shaft speeds surely motor is producing a greater amount of power?

That's correct. In other words if you run the motor slower you get less power. It's a bit of a simplification but a 1 hp motor running at half speed will only give about 1/2 hp.

I have put 50% bigger motors on both my lathe and manual mill when fitting VFDs. The motor on the mill does get hot to the touch when cutting hard at low speed. If it gets too hot to keep my hand on I go more gently or have a cup of tea and let it cool down. Never notice a hot motor on the lathe.

Russell.

I have a Denford ORAC lathe which as far as I am aware has the original motor and VFD. When running it at 300 RPM for a while the motor got hot enough so that I couldn't hold my hand on it. I don't recall there being a smell of burning, I was concerned enough to put a fan to blow air over the casing.

Cheers Michael.

[Gary WoodingParticipant @garywooding25363]

Some motors are designed to run hot. I have a 150W 1ph motor in a small grinder/polisher which is often run for protracted periods. It gets too hot to comfortably touch but shows no signs of suffering despite being about 20 years old.

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