Fan Motor

Guest
Sorry for such a simple question, but I've got a few 120mm
240V .125A (?30W) axial fans like a bigger version of the case
cooling fans in a computer.

I've set one up in a box with a large truck air filter so I can run it
24/7 to remove dust from my house atmosphere. At the moment, the
aircons and computers do it :)

Unfortunately these fans are a little too energy hungry and noisy.

What are my options for slowing them down a tad?

I thought of adding a resistance in line, but this would only
dissipate heat -- not lost in Winter, but a waste of money in Summer.

Then I thought about running two of these in series.

Is there any cheap and cheerful way to cut down on these over
enthusiastic, but otherwise great little ball bearing fans?

Thanks, jack
 
On Mon, 21 Apr 2008 23:47:42 +0800, spamfree@spam.heaven wrote:

Sorry for such a simple question, but I've got a few 120mm
240V .125A (?30W) axial fans like a bigger version of the case
cooling fans in a computer.

I've set one up in a box with a large truck air filter so I can run it
24/7 to remove dust from my house atmosphere. At the moment, the
aircons and computers do it :)

Unfortunately these fans are a little too energy hungry and noisy.

What are my options for slowing them down a tad?

I thought of adding a resistance in line, but this would only
dissipate heat -- not lost in Winter, but a waste of money in Summer.

Then I thought about running two of these in series.

Is there any cheap and cheerful way to cut down on these over
enthusiastic, but otherwise great little ball bearing fans?
Click to expand...
PWM is the usual way. Some good discussion at
<http://www.cpemma.co.uk/pwm.html>

--
Rich Webb Norfolk, VA
 
john jardine wrote:
Just wire it to a lamp dimmer.
Click to expand...

Not a good idea. There are speed controls made for ceiling fans that
will work, though.


--
http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm
 
On Tue, 22 Apr 2008 14:25:24 +0800, spamfree@spam.heaven wrote:

On Mon, 21 Apr 2008 23:47:42 +0800, spamfree@spam.heaven wrote:

I've read that a transformer would be OK.
I see a cheapie 36V that would suit.
What speed would the fan likely do (fraction of full speed) at 36V?
Perhaps around half speed, if the curve I/rpm is logarithmic?
Click to expand...
Could someone check my calculation, please?

The motor draws 125mA at 240V.
So at 36V, it should draw roughly 36/240 x 125 = 18.75 mA
The VA (~Watts) here will be 18.75 x 36/1000 = 0.675 W
Which will cost me ~ $1 per annum to run.

What would be the approximate efficiency of the transformer?

Cheers, jack
 
spamfree@spam.heaven wrote:
On Tue, 22 Apr 2008 14:25:24 +0800, spamfree@spam.heaven wrote:

On Mon, 21 Apr 2008 23:47:42 +0800, spamfree@spam.heaven wrote:

I've read that a transformer would be OK.
I see a cheapie 36V that would suit.
What speed would the fan likely do (fraction of full speed) at 36V?
Perhaps around half speed, if the curve I/rpm is logarithmic?

Could someone check my calculation, please?

The motor draws 125mA at 240V.
So at 36V, it should draw roughly 36/240 x 125 = 18.75 mA
The VA (~Watts) here will be 18.75 x 36/1000 = 0.675 W
Which will cost me ~ $1 per annum to run.

What would be the approximate efficiency of the transformer?

Cheers, jack
Click to expand...

You're assuming that the current draw is linear over a wide range of
source voltage.

This is a mistake.
 
spamfree@spam.heaven wrote:
Thanks guys. I'll look for a fan speed controller, but I guess they
usually only come cheap with fans?
Click to expand...

Home improvement stores sell them as an accessory for ceiling fans in
the US. You should have something similar in Oz.

--
http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm
 
On Mon, 21 Apr 2008 23:47:42 +0800, spamfree wrote:

Sorry for such a simple question, but I've got a few 120mm
240V .125A (?30W) axial fans like a bigger version of the case
cooling fans in a computer.

I've set one up in a box with a large truck air filter so I can run it
24/7 to remove dust from my house atmosphere. At the moment, the
aircons and computers do it :)

Unfortunately these fans are a little too energy hungry and noisy.

What are my options for slowing them down a tad?

I thought of adding a resistance in line, but this would only
dissipate heat -- not lost in Winter, but a waste of money in Summer.

Then I thought about running two of these in series.

Is there any cheap and cheerful way to cut down on these over
enthusiastic, but otherwise great little ball bearing fans?
Click to expand...
It depends on what kind of motor. Different types use different
methods of controlling the speed. Most of them don't like just
reducing the voltage to them. Do you have any more information
about the motor, like a brand name, part number, maybe a nameplate
with some information?

Thanks,
Rich
 
On Tue, 22 Apr 2008 23:37:04 GMT, Rich Grise <rich@example.net> wrote:


It depends on what kind of motor. Different types use different
methods of controlling the speed. Most of them don't like just
reducing the voltage to them. Do you have any more information
about the motor, like a brand name, part number, maybe a nameplate
with some information?
Click to expand...
Thanks for your help Rich.

The fan is a Sirocco brand.
Model YX2517
Ball bearing
AC230/240V 50Hz
125 mA
Impedance Protected
Made in Taiwan

That was from the label on the fan.

The cattledog says:
Air volume 3 m^3/min
rpm 3000
Input Watts 17
Current 125 mA
Noise 47 dBA

Maybe a diagnostic feature is that it freewheels without any cogging
for a long time after you switch it off. I guess that means there are
no permanent magnets in it.

I realise that it would be the ideal to buy another fan with less
current draw, but these are what I've got, and I can't see anything
more suitable. These were spot on, on paper, just that the acid test
shows them to be noisy little buggers -- I should have investigated
that 47 dB :)

Cheers, jack
 
On Wed, 23 Apr 2008 12:32:32 +0800, spamfree wrote:
On Tue, 22 Apr 2008 23:37:04 GMT, Rich Grise <rich@example.net> wrote:

It depends on what kind of motor. Different types use different
methods of controlling the speed. Most of them don't like just
reducing the voltage to them. Do you have any more information
about the motor, like a brand name, part number, maybe a nameplate
with some information?

Thanks for your help Rich.

The fan is a Sirocco brand.
Model YX2517
Ball bearing
AC230/240V 50Hz
125 mA
Impedance Protected
Made in Taiwan

That was from the label on the fan.

The cattledog says:
Air volume 3 m^3/min
rpm 3000
Input Watts 17
Current 125 mA
Noise 47 dBA

Maybe a diagnostic feature is that it freewheels without any cogging
for a long time after you switch it off. I guess that means there are
no permanent magnets in it.

I realise that it would be the ideal to buy another fan with less
current draw, but these are what I've got, and I can't see anything
more suitable. These were spot on, on paper, just that the acid test
shows them to be noisy little buggers -- I should have investigated
that 47 dB :)
Click to expand...
Well, it sounds like it's definitely probably maybe an induction motor.

Controlling the speed of an induction motor, short of a VFD, is kind of
out of my league - maybe try a google (or any handy search engine) search
on "control induction motor speed" or the like.

Good Luck!
Rich
 
On Thu, 24 Apr 2008 22:53:14 GMT, Rich Grise <rich@example.net> wrote:


Well, it sounds like it's definitely probably maybe an induction motor.

Controlling the speed of an induction motor, short of a VFD, is kind of
out of my league - maybe try a google (or any handy search engine) search
on "control induction motor speed" or the like.
Click to expand...

Thanks, Rich, I've done some reading and it seems that small fans on
mains power are generally large-slip motors which are amenable to
speed control with voltage, as opposed to most induction motors that
approach synchronous speeds and not much away from that.

Now, I calculated that this fan has an "effective resistance" of
around 3.3 kOhms. I happen to have a 3.3 kOhm 10W resistor handy and
so I connected it in series with this fan.

The fan ran magnificently. Just about right, maybe a little faster
would be better, but perfectly quiet and acceptable.

Unfortunately, after about 3 minutes, the resistor was so hot it could
have burned me. I know that wirewound cement resistors can run really
hot, but this appeared to be absorbing more Watts than my calculation
would have led me to believe.

The motor says it draws 0.125 A but the catalogue says "input Watts
17" So I assume that that current is startup current. And the running
current is actually 17/240 = 0.071 A.

I suppose the effective resistance (reactance, impedance and all that)
of the motor can only be found by measurement, so it's possible that
the resistor was absorbing anything up to about 15W in the circuit
that I tried it.

Anyways, that is going to be too expensive to run 24/7.
I can't seem to find a transformer that would drop 240VAC to around
150VAC or so. I have a book of calculations for making your own
transformers, is this an efficient possibility?

Perhaps stripping out the secondary of an existing tranny and rewiring
to suit? Are big transformers less efficient than one just above
specs? Do you know of an easier way to efficiently drop the mains
voltage to two thirds?

Disclaimer : All advice taken without any implied responsibility of
the adviser. Rest assured that I treat electricity with all the
paranoia it deserves. No touchy when plugged in!

Cheers, and thanks, jack
 
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