Who wanted the induction motor soft start?

Thread Starter

ian field

Joined Oct 27, 2012
6,543
Everyday Practical Electronics Jan 2019 published an induction motor controller project.

It explains a fair bit about how IMs work and might help the TS.
 

MaxHeadRoom

Joined Jul 18, 2013
19,028
Everyday Practical Electronics Jan 2019 published an induction motor controller project.

It explains a fair bit about how IMs work and might help the TS.
There are a few forms of (1ph) induction motors, some do not control well.
What versions do they propose?
Max.
 

Thread Starter

ian field

Joined Oct 27, 2012
6,543
There are a few forms of (1ph) induction motors, some do not control well.
What versions do they propose?
Max.
CBA reading all of it - they explain that you can't control them well buy just varying the voltage, its better to vary frequency - but there's a gotcha.

They have the same problem as early VGA Multisync monitors. On slow scan rates; the current is on longer and causes the flyback transformer to saturate - they have to reduce B+ for the lower scan rates. The early ones had tapped PSU transformers with multiple rectifiers switched in by power managemenr transistors. Then they did DAC controlled Buck regulators that blew everything when the pass chopper faild. Not long before the demise of CRTs; they went boost converters that stop the PSU when it all goes tits up.
 

MaxHeadRoom

Joined Jul 18, 2013
19,028
Sounds like the article is a little misleading if they don't state the motor technology type.
Anything over 0.5hp has a problem with both phase angle and frequency control. Usually relegated to fans etc.
This is why most DIY'ers use a 1ph/3ph VFD and a 3phase motor for reliability in power applications.
Max.
 

Thread Starter

ian field

Joined Oct 27, 2012
6,543
Sounds like the article is a little misleading if they don't state the motor technology type.
Anything over 0.5hp has a problem with both phase angle and frequency control. Usually relegated to fans etc.
This is why most DIY'ers use a 1ph/3ph VFD and a 3phase motor for reliability in power applications.
Max.
Its probably escaped into the wild by now - the PDF might be floating around the web somewhere.
 

MaxHeadRoom

Joined Jul 18, 2013
19,028
I see that it does only apply to PSC (permanent start cap) motors, they mention up to 1.5hp such as pool pump motors, switched start cap motors are exempt.
It is rare to see a PSC motor over 0.5 HP.
I don't really see much value if most other motor application are not covered.
Max.
 
Sorry to revive, but is there any relatively simple method of soft starting this type of motor?

I'm looking to try and soft start a shower pump (initial noise)

It says it is a 'Capacitor start and run induction type motor'. Controlling by frequency sounds pretty complicated
 

MaxHeadRoom

Joined Jul 18, 2013
19,028
Generally neither simple or involved ways work, VFD's (frequency) have been attempted but are not very successful for 1ph, especially a motor that starts on load.
As I mention in #4, the preference is to use a 1ph-in VFD and a 3 ph motor.
Max.
 
Generally neither simple or involved ways work, VFD's (frequency) have been attempted but are not very successful for 1ph, especially a motor that starts on load.
As I mention in #4, the preference is to use a 1ph-in VFD and a 3 ph motor.
Max.
Going to have think of something else then.

What effect would changing out the capacitor have? Sorry, I'm more of an avid DIYer than a circuit expert
 

MaxHeadRoom

Joined Jul 18, 2013
19,028
The capacitors are selected for optimum starting, if changing them you may run into motor issues.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
19,028
If it starts under load, is there a way you could unload it with a by-pass valve and timer?
Max.
 

Thread Starter

ian field

Joined Oct 27, 2012
6,543
If it starts under load, is there a way you could unload it with a by-pass valve and timer?
Max.
Just thinking out loud: - you can get comtinuously variable ratio gearboxes (probably seriously expensive). Have something like a clock spring type arrangement pulling the adjuster shaft round to the highest reduction. Use a ball weight governer like they had on stationary stem engines to operate the adjustment shaft - the motor starts on minimum torque - it should also stop cranking up the adjuster if the torque gets too high as it runs up to speed.
 
Just thinking out loud: - you can get comtinuously variable ratio gearboxes (probably seriously expensive). Have something like a clock spring type arrangement pulling the adjuster shaft round to the highest reduction. Use a ball weight governer like they had on stationary stem engines to operate the adjustment shaft - the motor starts on minimum torque - it should also stop cranking up the adjuster if the torque gets too high as it runs up to speed.
To be honest, I'm sick of the bloody thing. Have probably spent enough time/money on it; had to replace hall sensors (genuinely irritated by the cost of these for the pump, surely they pretty cheap to produce), fix a leak, redo my piping. Just thought there may be an easy solution, my dad mentioned they had soft starters on loads of his machines at work.

Saw someone mention one of these NTC Inrush current limiters and hoped there was something similarly easy that I could just splice on for my case

Pump is actually tame noise wise when running; just makes a right kick when starting up
 
If these are industrial motors, most likely 3ph, For which there are 3ph soft start, electronic contactors.
What was the function of the hall sensors?
Max.
Yeah probably, I did see some wildly expensive solutions when searching. At least wildly by my domestic needs; I guess if it saves you an industrial motor they are cheap

A little magnet inside the pipework moves when water flows; i.e. a tap or shower is on

It triggers the pump to start. Otherwise I'd have gravity hot water pressure
 
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