I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?
Switched caps in series seems to be a fairly common technique. There are
lots of cheap(ish) variable speed controllers but I doubt they're
inverter VFDs.
How do the cheap continuously-variable gizzmos like
https://www.ebay.co.uk/itm/Variispee...s/252403438896
work?

On Sun, 28 Jun 2020 19:36:10 +0100, wrote:

I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?

Inductive load maybe.



Switched caps in series seems to be a fairly common technique. There are
lots of cheap(ish) variable speed controllers but I doubt they're
inverter VFDs.
How do the cheap continuously-variable gizzmos like
https://www.ebay.co.uk/itm/Variispee...s/252403438896
work?

On Sun, 28 Jun 2020 19:36:10 +0100, nothanks wrote:

I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?
Switched caps in series seems to be a fairly common technique. There are
lots of cheap(ish) variable speed controllers but I doubt they're
inverter VFDs.
How do the cheap continuously-variable gizzmos like
https://www.ebay.co.uk/itm/Variispee...ble-Fan-Speed-
Controller-Hydroponics/252403438896
work?

I used S&P units - not cheap but they are fan manufacturers.


Cheers


Dave R


--
AMD FX-6300 in GA-990X-Gaming SLI-CF running Windows 7 Pro x64

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

On 28/06/2020 20:15, David wrote:
On Sun, 28 Jun 2020 19:36:10 +0100, nothanks wrote:

I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?
Switched caps in series seems to be a fairly common technique. There are
lots of cheap(ish) variable speed controllers but I doubt they're
inverter VFDs.
How do the cheap continuously-variable gizzmos like
https://www.ebay.co.uk/itm/Variispee...ble-Fan-Speed-
Controller-Hydroponics/252403438896
work?

I used S&P units - not cheap but they are fan manufacturers.


Cheers


Dave R


Are they VFDs, phase controllers or ???? (Google hasn't been helpful)

On Sunday, 28 June 2020 19:36:13 UTC+1, wrote:

I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?
Switched caps in series seems to be a fairly common technique. There are
lots of cheap(ish) variable speed controllers but I doubt they're
inverter VFDs.
How do the cheap continuously-variable gizzmos like
https://www.ebay.co.uk/itm/Variispee...s/252403438896
work?

Motor laminations avoid turning a bunch of 50Hz power into heat. When you greatly raise the frequency by chopping the waveform, that no longer holds true. Also motors depend on magnetic phase shift, which with some types is frequency dependant. When it is, messing with the frequency messes with the phase shift thus efficiency plummets, or it doesn't work at all.


NT

wrote:
I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?
Switched caps in series seems to be a fairly common technique. There are
lots of cheap(ish) variable speed controllers but I doubt they're
inverter VFDs.
How do the cheap continuously-variable gizzmos like
https://www.ebay.co.uk/itm/Variispee...s/252403438896
work?

https://www.electroschematics.com/mo...or-with-triac/

That one is phase angle (switch-on time) control.

The circuit uses a snubber, when an (inductive) motor is connected.

One of the commenters asks a question about the motor noise.

*******

They address VFD here a bit.

https://www.wolfautomation.com/blog/...-phase-motors/

"As our tech support will readily tell you, incorrectly fitting
a motor can cause repeated motor failure and equipment downtime
costing you in the long run.

Compatible Incompatible

Permanent Split Capacitor (PSC) Split Case
Shaded Pole Induction Motor Capacitor Start
AC Synchronous Repulsion Induction
Series Universal (AC/DC)
Any motor with starting switch (centrifugal or relay)
Any motor with separate starting winding
"

They talk of derating, which means the temperature increases
as you abuse the motor.

*******

There are permanent split capacitor motors with taps
for speeds. They're used as blower motors for air handlers.
You select the tap for the speed you want and apply power there.

There are smaller versions of those, but probably not
small enough for your application (1/10th to 1/20th HP).

*******

There are some motors that run insanely hot. Exactly
how the wire insulation holds up (enamel) is really
hard to guess. You cannot use an alternate insulation
(say asbestos) without adversely affecting turns count.
The motors run hot enough, to burn up the lubricating oil.

*******

Another kind of solution would be a DC motor. And with
a governor, depending on motor type and how load
sensitive it is. Preferably brushless, for a long life.

Paul

On 28/06/2020 20:06, Cursitor Doom wrote:
On Sun, 28 Jun 2020 19:36:10 +0100, wrote:

I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?

Inductive load maybe.




If its synchronous you need a variable frequency drive.



--
"Women actually are capable of being far more than the feminists will
let them."

On Tue, 30 Jun 2020 09:07:32 +0100, The Natural Philosopher
wrote:

On 28/06/2020 20:06, Cursitor Doom wrote:
On Sun, 28 Jun 2020 19:36:10 +0100, wrote:

I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?

Inductive load maybe.




If its synchronous you need a variable frequency drive.

People talk about "electric motors" like as if they're all essentially
the same basic design. They're NOT. There are so many variations and
unless you know exactly what type your dealing with, it's impossible
to say which type of speed controller - if any - will work with that
specific motor.

On 30/06/2020 18:27, Cursitor Doom wrote:
On Tue, 30 Jun 2020 09:07:32 +0100, The Natural Philosopher
wrote:

On 28/06/2020 20:06, Cursitor Doom wrote:
On Sun, 28 Jun 2020 19:36:10 +0100, wrote:

I need to control the speed of a kitchen extractor fan so have been
investigating how best to do it.
Using a phase-control light dimmer seems to be a no-no but I can't see
why except, perhaps, for starting torque - can anyone here explain?

Inductive load maybe.




If its synchronous you need a variable frequency drive.

People talk about "electric motors" like as if they're all essentially
the same basic design. They're NOT. There are so many variations and
unless you know exactly what type your dealing with, it's impossible
to say which type of speed controller - if any - will work with that
specific motor.

well in a sense they are all; the same in basis. They are a;l
synchronous, but those with commutators use the commutator to generate
the synchronicity..

And all follow the basic rule that they cant go faster than the applied
voltage will let them, unless they have variable magnetic fields.Series
would field coils being an interesting example.


--
"A point of view can be a dangerous luxury when substituted for insight
and understanding".

Marshall McLuhan