Extractor motor rpm

[OXFORDBEE]

I have this picture in my head of a disaster area.

Apparenty, wooden wired frames and conventional wired foundation will effectively turn your extractor into one when frames are extracted at high speed!

What's the situation with electric drills and their rated usage? My mortar mixer is rate for 1/2 hours continuous usage. I'm assuming that with stop start extracting this won't be a problem....

 

[JCBrum]

Don't worry about it oxfordbee.

In your case you should continue to use your 3-phase motorised extractor with your GEC inverter.

I don't know whether you've ever noticed, but the problem is that when mixing plaster it begins to set and goes very stiff after 20 mins or so. That is what will kill your drill, not turning a free-spinning honey extractor.

 

[roche]

That is what will kill your drill, not turning a free-spinning honey extractor...

Although lots of extractor motors have died due to the honey rising above the rotating frame. Big argument for a motorspeed controller with current limitng...

 

[JCBrum]

Most plaster mixers now have current limiting, That's what Plumber meant by 'soft-start'.

There is always a case for advice regarding sophisticated motorised extractors. It when you personally have to pay to follow the advice that attitudes alter somewhat.

I rather suspect Veg was looking for an economy solution.

 

[VEG]

You are correct JC

 

[roche]

Most plaster mixers now have current limiting, That's what Plumber meant by 'soft-start'.

I rather thought soft start only applied during start, not during run.

 

[JCBrum]

which make and model of extractor do you have roche ?

 

[roche]

A hand wound one of Italian origin - I cannot remember the details. But I do design motor speed controllers...

 

[DulwichGnome]

One bit of advice I was given this year was to replace the slit pin at the top of the spindle with a nail or similar soft metal. This gives it a point of failure if the frames get jammed. Not had any jam on me yet but sounds right.

Mike.

 

[JCBrum]

A hand wound one of Italian origin - I cannot remember the details. But I do design motor speed controllers...

Is that as your job, or in an amateur enthusiast capacity ? Are your motor speed controller designs for A.C. mains, or low voltage / battery situations. ?

Do they control synchronous induction motors, or commutator type motors ?

perhaps you could design one for Veg ?




p.s. 'soft-start' was Plumbers terminology, I suspect they have an overall current limiter, do you have any actual information on this point ?

 

[roche]

Its a bit of a subset of my job...

AC mains, synchronous, single phase and low voltage DC brushed.

As far as I have seen, soft start is aimed particularly at the first few cycles of motor start, to limit surge currents due to coming up to speed or starting under load. That can be important if you are running off an invertor or generator.

Depending on what motor Veg settles with, yes - I would be interested...

 

[JCBrum]

Ha Ha, information from Makita reveals that their mixer drills do have current limiting, but I am told the soft start feature is most appreciated because it helps avoid splashes on the operator's hair and clothing caused by rapid commencement of action

 

[JCBrum]

Its a bit of a subset of my job...

AC mains, synchronous, single phase and low voltage DC brushed.

Depending on what motor Veg settles with, yes - I would be interested...

Say for example a single phase 230v 4-pole induction motor of about 150 watts, and fitted with a 40:1 worm drive gear box.

The speed variation required would be from approx zero to + 200%.

Could you design a controller to do that ?

 

[roche]

I haven't tried overdrive, and although it would be interesting I suspect Vegs cost targets could be significantly over-run. 0-100% would be much cheaper...

 

[JCBrum]

Ok, although they are rarer a 2 pole motor could be employed.

How then, would you achieve say a -50% speed reduction ?

 

[roche]

I would tend to be using phase angle switching in either case, but using a 4 pole motor for higher torque, although with the gearing involved thats a bit moot.

I think Hedgerow Petes ideas on truck wiper motors or similar have got some mileage - must be lots of those floating around...

 

[m100]

Ok, although they are rarer a 2 pole motor could be employed.

With regards to small frame size motors there are probably just as many 2 pole as 4 pole motors out there. Above 4 pole they start to reduce in number, in (much) larger frame motors, greater than 4 pole motors tend to predominate.

It blows most budgets if bought new, but with a 3 phase induction motor and a single phase (13A socket) variable frequency drive you can run most 4 pole nominally 1500rpm on 50Hz motors from around 200 to 4000rpm although at continuous low speeds you will probably run into cooling problems. Such installations are commonplace on many machine tools.

Assuming they are from a reputable manufacturer and not from Won Hung Lo cheapy electrical based just outside Shanghai, then mechanically they are constructed on the same production lines in an identical manner to nominally 3600rpm 60Hz 2 pole ones in terms of bearings, heat dissipation, windage etc. OK they might be slightly less efficient but at the end of the day all you are essentially doing is making the 50Hz AC just a bit faster

 

[GingerNut]

perhaps you could design one for Veg ?

Veg is not the only one who would like a cheaper option that the £269 conversion kit from Thornes

Yours Roy

 

[JCBrum]

m100,

I do agree with your post. It shows a good understanding of the problem.

This is the relevant bit -

It blows most budgets if bought new, but with a 3 phase induction motor and a single phase (13A socket) variable frequency drive you can run most 4 pole nominally 1500rpm on 50Hz motors from around 200 to 4000rpm although at continuous low speeds you will probably run into cooling problems. Such installations are commonplace on many machine tools.

The budget available is the problem. Variable speed inverter drives are not cheap, and can be very complex to construct on a one off prototype basis.

The problem is easy to solve for £300 - £400, but not so easy for £30 - £40.

 

[JCBrum]

roche, deeper investigation might be required.

I would tend to be using phase angle switching in either case,

It's my opinion, that phase angle switching is only appropriate for use with a commutator brushed motor, and will not work at all with a synchronous induction motor such as is commonly and cheaply available on the surplus / low cost market. Such motors must be driven by a variable frequency inverter if speed control is required.

I think Hedgerow Petes ideas on truck wiper motors or similar have got some mileage - must be lots of those floating around...

This observation is entirely consistent with your speed controller utilising phase angle switching, and is an avenue that you could usefully explore and advise us all upon. It does however probably depend on a suitable low voltage supply to drive the speed controller, and that in itself could be expensive or cumbersome.

A mixer drill does already incorporate those ideas and is available from £40 upwards, already made.

My experience with trying to obtain 'truck wiper motors' and such things, is that the search is very time consuming, and the prices asked are often high even as second hand components.

Have a look at the requirements for speed control of synchronous induction motors, and tell me whether your view changes with the research.

JC.