Thread: Silicon Chip Magazine induction motor speed controller kit

Originally Posted by tea lady

So we need to befriend someone who works there.

Yea but the staff discount policy strictly stated that purchases were for employees only, maybe for a family member although I can't remember the exact details. It was about 23 years ago!

Having said that, a bottle of Bourbon can have influential properties!

Simon

But the gizmo still doesn't work with induction motors with centrifugal starting switches, so that rules out most of our single phase fixed machinery anyway. Looking at it, it is primarily usefull for synchronous motor electric clocks, or as a varispeed for pre 80's tape decks with induction capstan motors because heavy duty single phase motors use switched cap start systems to get them turning and up to speed.

Originally Posted by simonl

It does have the ability to vary the speed on a single phase motor, which is a major selling point but I'm not sure how well it actually works or how smooth it would be compared to an equivalent 3 phase motor and for $180 I have a 2.2KW VFD AND a brand new 3 phase motor!

Simon, any flavor of VFD's for single phase motors is only useful for applications like fans and pumps, where the power requirement reduces with the cube of the motor rpm. It may also be good enogh to drive a scroll saw or a mixer over a very small speed range. But for any serious machine tool application like a drill press or a mill or a lathe, I can assure you with 100% confidence that a VFD with single phase motor is useless.

Chris

There's an article in Silicon Chip Sept 12, Circuit Notebook pg 85. Title "induction motor centrifugal switch over-ride". It has a 555 timer, relay etc. The relay open circuits the centrifugal switch after 10 seconds.

JohnQ

Originally Posted by malb

But the gizmo still doesn't work with induction motors with centrifugal starting switches, so that rules out most of our single phase fixed machinery anyway. Looking at it, it is primarily usefull for synchronous motor electric clocks, or as a varispeed for pre 80's tape decks with induction capstan motors because heavy duty single phase motors use switched cap start systems to get them turning and up to speed.

It was a while ago that I read the SC article, but from memory it is primarily designed to reduce the speed of a single phase pool pump motor to around 70% of max after 30 seconds, in order to save electricity.

Originally Posted by cba_melbourne

Simon, any flavor of VFD's for single phase motors is only useful for applications like fans and pumps, where the power requirement reduces with the cube of the motor rpm. It may also be good enogh to drive a scroll saw or a mixer over a very small speed range. But for any serious machine tool application like a drill press or a mill or a lathe, I can assure you with 100% confidence that a VFD with single phase motor is useless.

Chris

Hi Chris,

I thought as much and now you have confirmed my thoughts. Hi JohnQ I wondered why no one had come up with such a mod years ago although 10 seconds sounds like a long time, I would have thought 1 - 2 seconds would be plenty.

Cheers,

Simon

simonl
Your guess is as good as mine. When the controller applies power to the motor, pin 10 from the micro-controller goes high to turn on the RUN led. This signal is connected to the 555/relay, this signal then goes low after 10 seconds. This inhibits the centrifugal switch until power is turn off then on again.

JohnQ

I'm also interested in getting a speed controller for an induction motor. Something smallish - to slow down the fan speed on my pedestal fan and hopefully reduce the noise..

I saw this VFD controller in eBay and I'm thinking it'll do the same sort of thing that the Silicon Chip circuit will do - whthout having to make it.

Now, I have a deft hand with electronics but no experience with induction motors but I think that a metal chassis case, a 15amp plug and socket, a little bit of wiring and I'd have a speed controller.

Am I right?

Norm

What sort of pedestal fan are we talking about Norm? Why do you need a 15A plug? Most fans have quite low wattage motors that can be controlled with a simple fan speed controller like these:

http://www.hpm.com.au/uploads/dimmers_datasheet.pdf

Can you give us more info on your fan?

Regards,
Chris

Hi Norm,
Is your pedestal fan 3 phase?

Stuart

Originally Posted by jack620

.... more info on your fan?

It's a Heller, 50CM deluxe pedestal fan, Model HPF55, 230-250V 50HZ, 100w. It's got four pushbutton switches for off, low, medium, and high.

My understanding is that "fans" and most other small motors are single phase, induction motors. Even in "low", it's blowing a whole bunch of wind, and making more noise than I like when watching TV.

I bought this one in particular because it was advertised as "very quiet" but, frankly, it makes more noise than my 40CM fan.

Back to the main thrust of question, you're right I definitely don't need a 15A plug! This particular VFD is advertised as "0.75kw, 1HP single to 3 phase VFD 0-400HzVariable Speed Drive VSD dual display". Click link here.

Yes, it's a case of rampant overkill just to quieten down a fan but I can see other uses for a speed control device - like in my workshop/shed.

So, thinking laterally here, am I right? Is it a reasonable replacement for the Silicon Chip / Jaycar unit. The cost would be in the same ballpark..

Originally Posted by Norm.Mareeba

So, thinking laterally here, am I right? Is it a reasonable replacement for the Silicon Chip / Jaycar unit. The cost would be in the same ballpark..

Short answer "No you arent and it wont work"
Longer answer, "It might just work but are you willing to blow $200 finding out?"

The Silicon Chip / Jaycar unit is for running single phase motors.
The VSD is for running 3 phase motors.

Now if you needed to control the speed of 3 single phase fans at once you might be onto something.

Stuart

Originally Posted by Norm.Mareeba

It's a Heller, 50CM deluxe pedestal fan, Model HPF55, ..

Norm,
that's a $45 fan. It would be a lot cheaper and easier to buy a smaller, quieter fan.

Originally Posted by Norm.Mareeba

Yes, it's a case of rampant overkill just to quieten down a fan but I can see other uses for a speed control device - like in my workshop/shed.

Which tools in your workshop do want to control Norm? The SC speed controller won't work on universal (brushed) motors like drills and routers.

You need this one for controlling those motors: Silicon Chip Online - 230VAC 10A Full-Wave Motor Speed Controller