UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Other Vintage Household Electrical or Electromechanical Items

Notices

Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details.

Reply
 
Thread Tools
Old 12th May 2020, 10:07 pm   #1
Tractorfan
Nonode
 
Tractorfan's Avatar
 
Join Date: Mar 2008
Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.)
Posts: 2,930
Smile Motor soft starting

Hi,
I have a water pump that uses a single phase induction motor with a capacitor permanently in circuit of about a quarter hp at 230 volts. (Is that called a split phase motor?)
I would like it to start at a reduced torque to avoid pressure shocks to the pipework.
I've been kicking ideas around such as a resistor, diode or even a transformer with a bucking winding that is shorted out after a short period when the motor is at speed.
I've looked on eBay, but most soft start units there seem to be for star/delta starting of polyphase motors.
Ideally it would ramp up to full revs (which, of course, it won't with my simple ideas), but I'd happy if it started in two steps.
Another thought is, maybe, a gadget that reduces resistance as it heats up (I can't think what they're called), then is shorted by the aforementioned timer.
Any thoughts appreciated.
Cheers, Pete.
__________________
"Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."
Tractorfan is offline   Reply With Quote
Old 12th May 2020, 10:23 pm   #2
Lucien Nunes
Octode
 
Lucien Nunes's Avatar
 
Join Date: Apr 2008
Location: London, UK.
Posts: 1,842
Default Re: Motor soft starting

It's a 'permanent split capacitor' motor. It can be started at reduced torque using reduced voltage or by adding series resistance or reactance as you suggest (although not with a diode, as the resulting DC current in the winding will screw things up royally). You can also buy purpose made single-phase soft starters that ramp up the conduction angle when powered on, then cut themselves out of circuit. E.g. RS 2.2kW single-phase soft start

Note that only the torque can be readily controlled in this way; induction motor full running speed cannot practically be reduced below around 80-90% by voltage control. Therefore, to be sure the soft-start would work correctly, it is important to have an idea of the torque/speed curve of the load. What type of pump is it? Centrifugal / positive displacement?

But, taking a step back, if the pump startup is causing a hydraulic shock, how about fitting an accumulator or pulsation damper that will absorb the shock? Obviously this will depend on the application (which we don't know yet), e.g. 5 litre accumulator
__________________
Three anodes good, six anodes better!
Lucien Nunes is offline   Reply With Quote
Old 12th May 2020, 10:38 pm   #3
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 9,397
Default Re: Motor soft starting

I have been using a "collapsible hose" in the garden (the type that shrinks and expands with pressure, quite amazing), a length of that would act as a shock damper. Available at all good stores.

I don't do a lot of gardening, I was just watering plants under instruction!
__________________
Cats have staff, it's dogs that have owners.
merlinmaxwell is offline   Reply With Quote
Old 13th May 2020, 3:24 pm   #4
Richard
Heptode
 
Richard's Avatar
 
Join Date: Feb 2003
Location: Garnant, near Ammanford, South Wales, UK.
Posts: 566
Default Re: Motor soft starting

Hi

Agree, accumulator after the pump should solve the problem.
You can easily make a small one with an upside down T fitting, the upright has a length of pipe on it with a blank end.

Richard
__________________
BVWS member.
Richard is offline   Reply With Quote
Old 13th May 2020, 4:36 pm   #5
TrevorG3VLF
Octode
 
TrevorG3VLF's Avatar
 
Join Date: Apr 2011
Location: Matlock, Derbyshire, UK.
Posts: 1,378
Default Re: Motor soft starting

Accumulators have flexible bags inside which are filled with air which is compressed by the water. Such devices are used in central heating systems to keep the radiators pressurised and need to be pumped up if there is a leak.
__________________
If I can help somebody as I travel along
Then my living shall not be in vain.
TrevorG3VLF is online now   Reply With Quote
Old 13th May 2020, 5:46 pm   #6
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 9,397
Default Re: Motor soft starting

They can also be a simple closed vertical pipe (closed at the top!), the problem there is eventually all the gasses get dissolved in the water. This kind are used a lot in the USA and when "hammering" becomes a problem the solution is to drain the system and let the air back in. Saw that in an episode of "This Old House".
__________________
Cats have staff, it's dogs that have owners.
merlinmaxwell is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 3:31 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.