Dimmer Switch

[Alan .204Participant @alan-204]

Hi guys the question for today is, I would like to fit a Grunfoss 1550 circulating pump on my milling machine to use as a suds pump, these pumps run at 50w I would like to know if I can run this through a dimmer switch so as to have a variable speed, has any one successfully done this if so how did you go about it.

Alan.

[Alan .204Participant @alan-204]

[keithmartParticipant @keithmart]

Hi

I have used a dimmer switch to run an ex sewing machine motor driving a small lathe. I have had no problems, although you wouldn't be able to claim under manufacturers guarantee if it went wrong.

A dimmer switch from screwfix is only about a fiver, so it is worth trying.

Regards

Keith

Leeds UK

[KWILParticipant @kwil]

Why would you want a variable speed? You can always put a "short circuit" across the pump complete with a valve, varying the amount of bypass valve setting will vary the output where you want it??

[Martin WParticipant @martinw]

Hi

The Grunfoss 1550 looks to be a central heating circulating pump an driven by an induction motor. Induction motors rely on the rotor rotating in sync with a field generated by the stator which is in part determined by the mains frequency. As such they are intended to run at a fixed speed and not as a variable speed unit, however the speed of this type of motor can be varied by the use of a variable frequency drive or VFD but these are usually quite expensive.

The standard dimmers as supplied by the local hardware shops are not VFD but switch the supply voltage at varying points in the cycle to effectively vary the power available to the load. Mains powered motors such as those used in sowing machines, hand drills etc are not synchronous (induction) motors and can be used with this type of dimmer, power regulation, unit. However I think you will find that using a standard dimmer with and induction motor wont give the results you want.

I stand to be corrected by the more knowledgeable.

Hope this helps.

Martin

PS  KWIL's suggestion is far more practical and will let you adjust the flow easily

Edited By Martin W on 11/11/2013 16:15:08

Edited By Martin W on 11/11/2013 16:15:36

[Alan .204Participant @alan-204]

If it will work through something a simple as a dimmer switch why wouldn't you do it, you don't always want the same amount of coolant running or at least I don't anyway, why would you want a variable speed on any thing if that's the case, some times its better to just answer the question posted if you don't know how to answer it why not just say so or don't reply to it, sorry KWIL if i seem a bit harsh, just trying not to complicate things.

Al.

[Alan .204Participant @alan-204]

Thanks Martin that's the kind of constructive reply i was looking for, not beat just yet though will see what the other guys have to say and then decide when every ones thoughts are on paper, i seem to remember someone else doing this before hope they chip in, would like to be able to control the speed a bit as i think on speed one it may throw it out a bit to fast.

Al.

[KWILParticipant @kwil]

I dont care if it is harsh, you wanted a variable flow,as Martin noted a simple plumbing answer will give it. A Grundfos pump is rather oversized I fear.

[JasonBModerator @jasonb]

If you must use a Grunfos why not get one of the three speed ones but even then as Kwil says 400-600-800gph may be a bit much. Easier to just put a UPVC ball valve on the return to alter flow.

J

[David JuppParticipant @davidjupp51506]

Or just put a valve on the outlet and throttle the pump that way – as long as you allow a minimal flow it won't harm a centrifugal pump. It's actually quite efficient way of doing things too, the power draw will roughly follow the flow through the pump.

Large industrial centrifugal pumps are often started against an almost closed outlet valve to limit the surge current at start up, then the valve is opened gradually.

[Alan .204Participant @alan-204]

Yes I understand all that Jason but that's not what I asked in the first place, I will say again so you all understand I would like to know if I can put a simple dimmer switch on the pump, that's it not a difficult question if you know the answer just tell me I'm not looking for other idea's at the moment, I don't need to know how to plumb it up with a return pipe tapped to balance the flow, I'm a plumber I do it every day.

Al.

[Alan .204Participant @alan-204]

Thanks David you learn something new everyday.

Al.

[Rick Kirkland 1Participant @rickkirkland1]

to back up Martin W, a central heating pump is an induction motor therefore speed variation is only possible via a frequency inverter. don't try putting it through a dimmer switch.

Rick K

[Ian PParticipant @ianp]

IMHO Kwil said nothing wrong, just common sense. Single phase induction motor are designed to run a one speed. It IS possible to change the speed over a smallish range (such as in a kitchen cooker hood) but for a centrifugal pump with a liquid medium, forget it.

Whilst a CH pump is massive overkill (depending on how much coolant you need, you might be machining full size locomotive cylinders for all we know!) Just fit a gate or needle valve and adjust the flow with that.

Bear in mind that the pump will not be self priming so it needs to be installed below the fluid reservoir level.

Ian

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi Alan,

The blunt truth is no the motor speed is not able to be slowed without modifications that are beyond most model engineers capabilities .

single phase induction motors have start and run windings and there are a few configurations depending on the motor used .

Yours may have a centrifugal switch to disconnect the start windings once the motor is up to speed and even if you do manage to to slow the speed down with a VFD the switch may drop back in and you would burn out the start winding very quickly . Some motors are configured with a capacitor only and can be slowed down and you really need to look to see if there is a centrifugal switch in the back of the motor before you try to connect a VFD .

A local electronics company here in Australia sell a kit to slow down pool pumps but it is as expensive as a 3Phase inverter and not worth the trouble .

If you really must slow the motor down use a 3phase unit and get VFD to suit then you still need to be aware that the fan will not cool the motor as well when running slow and you need to look at adding an external fan to keep the motor from cooking .

Ian

 

Edited By SLOTDRILLER on 11/11/2013 17:47:57

[JasonBModerator @jasonb]

Can I ask those in the know who say these motors cannot be speed controlled easily what is the method that the 3 speed versions of these pumps use to give the different speeds, must be quite small as there is not a lot insid ethe box on the side. Also The latest Grunfos pumps vary the speed automatically, again how are they doing this.

Hope you don't mind me asking this Alan.

J

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Alan .204 on 11/11/2013 15:09:41:

… I would like to fit a Grunfoss 1550 circulating pump on my milling machine to use as a suds pump, these pumps run at 50w I would like to know if I can run this through a dimmer switch so as to have a variable speed …

.

NO

[Ian PParticipant @ianp]

Posted by JasonB on 11/11/2013 18:01:15:

Can I ask those in the know who say these motors cannot be speed controlled easily what is the method that the 3 speed versions of these pumps use to give the different speeds, must be quite small as there is not a lot insid ethe box on the side. Also The latest Grunfos pumps vary the speed automatically, again how are they doing this.

Hope you don't mind me asking this Alan.

J

This is like bees not being able to fly but as they don't know that, they just carry on doing it.

Simple induction motors are basically a one speed device but somehow CH pumps, ventilation fans and lots of other (cost concious, usually) products have switched speed control. I don't actually know what techniques are used, windings with tapping are a possibilty but I would not be surprised if the latest offings were quite sophisticated and used brushless motors as the electronics are so cheap and having true variable speed is good for the environment.

Ian

[Michael GilliganParticipant @michaelgilligan61133]

This might be of interest to those looking for more than a simple YES or NO answer

Incidentally; the company is Grundfos, not Grundfoss.

MichaelG.

[Anonymous]

Posted by JasonB on 11/11/2013 18:01:15:

Can I ask those in the know who say these motors cannot be speed controlled easily what is the method that the 3 speed versions of these pumps use to give the different speeds, must be quite small as there is not a lot insid ethe box on the side. Also The latest Grunfos pumps vary the speed automatically, again how are they doing this.

Pole switching, in which case what's in the box is a simple mechanical switch.

Michael: Interesting datasheet, confirms that the bog standard versions are induction motors.

Regards,

Andrew

[KWILParticipant @kwil]

Thank you Micheal G for your support,

NO is the correct answer.

However if as our plumber knows his trade then an Alpha 2 might sort it out at several Cubic Metres / hour

[Martin WParticipant @martinw]

Hi

The speed of these motors is primarily determined by the applied frequency and the number of poles on the stator, this ignores the slip that is necessary to make them operate at their optimum/maximum torque.

Therefore speed control, without changing the percentage of slip of the rotor to the synchronous field, can be achieved in two ways. One is to change the frequency of the supply and the other is to change the number of poles being energised in the stator. It is quite easy to design an induction/synchronous motor that has a switch which changes the number of poles for different speeds. This gives a stepped change in speed, rather like changing gears, rather than the smooth change afforded by VFD supplies.

It is possible to vary the slip but the speed range is limited and it will affect the efficiency and torque of the motor and is probably not good practise.

Cheers

Martin

PS

Looks as if this posting has crossed previous entries on this thread.

 

Edited By Martin W on 11/11/2013 19:17:28

[Mike PooleParticipant @mikepoole82104]

I think dimmers are designed for a resistive load, driving a motor from one may not be ideal although a poster says it has been done. The only motor that a dimmer may work on is a universal brushed type motor like a sewing machine or power drill. Not being familiar with the grundfos pumps I would guess the speed changing model may use pole changing to effect 3 speeds ie a 2,4or 6 pole selection it adds complication to the motor wind but the control is just a switch.

Mike

I see Andrew and Martin proposed the pole switching solution while I was typing.

Edited By Michael Poole on 11/11/2013 19:21:22

Edited By Michael Poole on 11/11/2013 19:21:49

Edited By Michael Poole on 11/11/2013 19:46:35

[BazyleParticipant @bazyle]

This is a useful and informative thread. Pity it will not come up in searches because the title does not really indicate the subject matter.

Please think of a descriptive and search friendly title when starting threads.

Induction motors can be speed controlled by series resistors – my warm air central heating fan is doing that right now. However the motor is a version specifically designed fo rthis mode. Not all would work well and could overheat or something else bad.
A centrifugal pump can be throttled without bad effect and uses less power when that is done or they are delivering to a high head which is the same.
Some of the newest CH pumps with variable speed use a built in VFD – saves power in theory but cost more and will only have a fraction of the life of a traditional one thus earning the manufacturer more money and not saving the planet at all.

[davebParticipant @daveb17630]

CH pump bearings are lubricated by the fluid being pumped. They work fine with clean water but any contamination will soon reduce the speed to zero RPM.

Dave

[Author]

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