I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.

Can I replace this with a computer cooling fan? What size do I
need? How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

Advice please.

Thanks,
Phil

"Phil Anderson" wrote in message
news:WMgZa.74397$Oz4.17285@rwcrnsc54...
I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.

**Er, use a smaller value resistor. Alternatively, you could replace the fan
with a new one, which has better bearings and can cope with lower Voltages.
You could also kick the fan into high speed, at switch on, then allow the
resistor to come in, to drop the speed down.


Can I replace this with a computer cooling fan?

**Not usually. Computer fans are generally 12 Volt DC and pretty crappy.
They're also difficult to add speed control to.

What size do I
need?

**Same size as the oringal.

How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

**Papst make some excellent termperature-sensitive fans, which would be
appropriate for your needs.

--
Trevor Wilson
www.rageaudio.com.au

Thanks for the reply. More below.


"Trevor Wilson" wrote in message
...

"Phil Anderson" wrote in message
news:WMgZa.74397$Oz4.17285@rwcrnsc54...
I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with
an
inline resistor. I got the voltage so low that the fan will
not
even spin unless I reach inside and give the blade a spin.
That
is both easy to forget and annoying to do.

**Er, use a smaller value resistor. Alternatively, you could
replace the fan
with a new one, which has better bearings and can cope with
lower Voltages.
You could also kick the fan into high speed, at switch on, then
allow the
resistor to come in, to drop the speed down.

As it stands, the fan has only one speed with the resistor in
place. I do not know how to "allow the resistor to come in"
later. The resistor I used was recommended at the time by the
amps designer, though he sounded very much like he was guessing.
With my luck, if I guess at another value, I will get one that
makes it loud again. I would just as soon start out by completely
replacing the puppy with something quieter, i.e., better
bearinged, as you advise.



Can I replace this with a computer cooling fan?

**Not usually. Computer fans are generally 12 Volt DC and pretty
crappy.
They're also difficult to add speed control to.

The Antec and Zalman fans in my computer are speed controlled, and
mighty quiet, too. More important, I am pretty sure the fan in my
'zilla is 12V DC.

What size do I
need?

**Same size as the oringal.

I guess I deserved that answer. My hope was that someone knew the
size offhand so I would not have to take the puppy apart once to
measure, and another time to put a fan in later when the order
arrives.


How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat
after
a few hours.

**Papst make some excellent termperature-sensitive fans, which
would be
appropriate for your needs.

I've heard all sorts of good things about Papst computer fans, but
it seems like going the temp sensitive route is just a more
complex guessing game than is playing with resistor values. I
have no idea what temps I want. I do know the amp sounds better
when it is quite warm, and that a very slow turning fan seems to
move enough air over the heat sinks that it will never overheat
under the conditions I expose it to.

Which takes me back to wanting some sort of speed control. I can
turn it up just high enough to be sure the fan will spin at turn
on, but remain inaudible. And, on the off chance I decide to
drive it a lot harder than I do now, I can just turn it up further
still. A Papst that is not temp-sensitive might well fit the
bill, if I can just figure out what size to get.

Again, thanks for the reply.

Phil


--
Trevor Wilson
www.rageaudio.com.au

"Phil Anderson" wrote in
news:WMgZa.74397$Oz4.17285@rwcrnsc54:

I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.

Can I replace this with a computer cooling fan? What size do I
need? How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

Advice please.

Thanks,
Phil




Do like McIntosh does and put a thermoswitch on the output heatsinks and wire
it to the fans. The fans will then only come on when needed.

r

--
"Any sufficiently advanced technology is indistinguishable from
magic."

Arthur C. Clarke (1917 - ), "Technology and the Future"

"Phil Anderson" wrote in message
news:uoiZa.74573$Oz4.17482@rwcrnsc54...
I would just as soon start out by completely
replacing the puppy with something quieter, i.e., better
bearinged, as you advise.

Be aware that the bearings are not the only thing that make a noise. The air
flow itself is a major factor. Papst and others make fans with different
CFM ratings (cubic feet per minute) and corresponding SPL levels, for the
common sizes.

Temperature sensitive electronic fan speed control, is usually the best
option though.

TonyP.

"Phil Anderson" wrote in message
news:WMgZa.74397$Oz4.17285@rwcrnsc54

I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.


Can I replace this with a computer cooling fan?

Yes.

What size do I need?

Start out with a fan the same size as the existing fan.

How about a speed control?

Computer cooling fans typically are rated for use with 12 volt DC power at
something like 0.1 amp.

Therefore you need to arrange for an appropriate voltage source in your
ampzilla. There's plenty of power DC there, but you'll need to drop the
voltage. An ideal way to accomplish this would be to build a variable
voltage DC regulator whose output voltage is controlled by a simple
potentiometer. Then adjust this potentiometer for the desired fan speed.
Most PC-style fans operate pretty stably down to 7 or 8 volts. Much below
that, stalling at power up can be a problem.

My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

If a fan the size of the existing fan is too noisy and pushes too much air,
replace it with a smaller fan mounted in a baffle plate. Your goal is to use
a larger fan spinning at the slowest speed that moves enough air and avoids
stalling at power up.

One way to avoid stalling at start-up is to drive the fan through a resistor
with a fairly large electrolytic cap in parallel. The cap will provide a
kick to get the fan rolling, and the resistor will run it at a slow steady
speed.

Thanks to everyone for the replies. You've helped me to get
further down the road toward figuring out what to do. Here is
what I know now:

The current fan is a Toran A450, rated at 115V and 0.25amps, if I
am reading it right. The size, in mm, is 119x119x38.

Papst fans seem to be almost impossible to find in the US. They
are marketed in the US under the name EBM Industries, but even
knowing that does not seem to help a lot.

My Ampzilla barely needs a fan at all. I do not use it all that
often nor all that long. With the current fan barely spinning, it
will run forever without becoming too hot to touch.

So, I guess my first question is whether I should even replace the
fan at all. With the current resistor, I have to 'finger-start'
the fan, but once it is going, it is completely inaudible to me.
Even if I find a Papst, it cannot get quieter in any meaningful
sense. Yes, I can understand that a better fan will move more
air, resulting in a cooler amp, and still remain inaudible, but I
do not feel I need anything cooler than what I have right now.

Still, if I could find a high-quality, slow turning fan that will
run inaudibly without the need for resistors, thermisors,
rheostats or wombats, I would be happy to go that route instead of
trying to find a way to reduce the voltage to the current fan. I
very much like the idea of simply screwing something in, attaching
two wires, and declaring victory.

So, my first question: Is there a good source for such fans? No
bells, no whistles, just the right size and slow, quiet turning.
To emphasize what I said above, airflow is not really an issue. A
little is enough.

Sub-question: What is a good brand name, assuming I cannot find
Papst/EBM in the US.

Second question: Does size matter? I am guessing that whether
the replacement is 25mm thick or 38mm think won't matter in this
amp. But what about that 119 x 119 part? I have seen listings
for 118 x 118, 119 x 119, and 120 x 120 (all without prices, BTW).
Are all these fans interchangeable, or does a single millimeter
matter?

Third question: If I do not replace the current fan, what is the
SIMPLEST way to confidently regulate the speed of the current fan?
While most of you have figured this out already, let me make it
plain in case anyone has missed it. I am not an electrician. Not
only do I not play one on TV, I have never met anyone who plays
one on TV. I have replaced plenty of outlets and light fixtures,
and even a ceiling fan or two, but my mind simply does not seem to
grasp concepts much more complex than that.

If I keep the current fan, I would like an alternative method of
speed control that meets the following criteria:
First, it should involve little more than splicing a device into a
wire.
Second, it should not involve a great deal of trial and error. I
really do not like the idea of picking up a half-dozen resistors
and swapping them in and out until one works just right.
Third, it should be SIMPLE. I understand why temperature
sensitive devices may be the BEST solution, but I do not see how
to make them the simplest. What temperature do I want? How do I
find a device with that temperature setting? Where do I put the
sensor? What other questions am I missing? Given that I do not
understand this whole process all that well, going this route just
seems to me to be an invitation to error; a way for me to screw up
without even knowing it.

That is why the idea of a rheostat, or something with a knob I can
turn or a switch I can flip between positions, appeals to me. If
I find the right device, I should be able to splice it in place
and then adjust the speed until I am sure it will spin up when
power is applied, but won't spin loudly enough for me to hear more
than a foot or two away.

In summation, and having gone on much too long already, I want
either or both of two things:
1. A source for a quality, slow turning, quiet fan, and/or
2. Advice on speed-controlling the current fan in the simplest
possible manner.

Thanks again,
Phil

PS. It is really a shame this is not a 12V fan, as there are all
kinds of solutions in the computer world, including, possibly, the
120mm Antec Smart Fan I added to my Sonata case.

"Trevor Wilson" wrote in message
...

"Phil Anderson" wrote in message
news:uoiZa.74573$Oz4.17482@rwcrnsc54...
Thanks for the reply. More below.


"Trevor Wilson" wrote in message
...

"Phil Anderson" wrote in
message
news:WMgZa.74397$Oz4.17285@rwcrnsc54...
I need advice on replacing the cooling fan on my GAS
Ampzilla.
[snip]

"SAIL LOCO" wrote in message
...
Why not use a Whisper fan? They are made for this purpose. My
Dynaco Stereo
400 uses one.
S/V Express 30 "Ringmaster"
Trains are a winter sport

OK, I can find teh specs, but googling has not unearthed a source
yet. One 'click to order' link led to a page not found, but that
is as close as I've gotten so far.

"Phil Anderson" wrote in message
news:9ztZa.78172$cF.24225@rwcrnsc53...
The current fan is a Toran A450, rated at 115V and 0.25amps, if I
am reading it right. The size, in mm, is 119x119x38.

Here's a couple computer fans that are the correct dimensions:
http://www.newegg.com/app/viewProduc...180-009&depa=1
http://www.newegg.com/app/viewProduc...999-007&depa=1

Like most all computer fans these are rated to run on 12VDC, and will run
slower with reduced voltage. But going too low might make startup
unreliable, as you've already found. Both of these are quite robust with
airflow ratings over 100CFM, so you'll probably want to slow them down. The
Panasonic fans have a pretty good reputation.

Other possible sources (perhaps you could even find a 120VAC fan) are
www.digikey.com and www.mouser.com . Good luck.

"Phil Anderson" wrote in message
news:9ztZa.78172$cF.24225@rwcrnsc53...
Thanks to everyone for the replies. You've helped me to get
further down the road toward figuring out what to do. Here is
what I know now:

The current fan is a Toran A450, rated at 115V and 0.25amps, if I
am reading it right. The size, in mm, is 119x119x38.

Papst fans seem to be almost impossible to find in the US. They
are marketed in the US under the name EBM Industries, but even
knowing that does not seem to help a lot.

My Ampzilla barely needs a fan at all. I do not use it all that
often nor all that long. With the current fan barely spinning, it
will run forever without becoming too hot to touch.

So, I guess my first question is whether I should even replace the
fan at all. With the current resistor, I have to 'finger-start'
the fan, but once it is going, it is completely inaudible to me.
Even if I find a Papst, it cannot get quieter in any meaningful
sense. Yes, I can understand that a better fan will move more
air, resulting in a cooler amp, and still remain inaudible, but I
do not feel I need anything cooler than what I have right now.

Still, if I could find a high-quality, slow turning fan that will
run inaudibly without the need for resistors, thermisors,
rheostats or wombats, I would be happy to go that route instead of
trying to find a way to reduce the voltage to the current fan. I
very much like the idea of simply screwing something in, attaching
two wires, and declaring victory.

**You really don't have much choice.Besides, it is not that difficult.
You've tried one resistor and the fan does not quite start. Reduce the value
of the resistor by (say) 20% and try again.


So, my first question: Is there a good source for such fans? No
bells, no whistles, just the right size and slow, quiet turning.
To emphasize what I said above, airflow is not really an issue. A
little is enough.

Sub-question: What is a good brand name, assuming I cannot find
Papst/EBM in the US.

**Most are decent enough. Look for a nice cast alloy chassis and ball
bearing races.


Second question: Does size matter? I am guessing that whether
the replacement is 25mm thick or 38mm think won't matter in this
amp. But what about that 119 x 119 part? I have seen listings
for 118 x 118, 119 x 119, and 120 x 120 (all without prices, BTW).
Are all these fans interchangeable, or does a single millimeter
matter?

**Nope. I said 120mm, but the actual size is 119mm. 119mm is a standard.
Looking at the airflow, you'll note that 120mm fans move around double the
amount of air as the next size down. Stick with 120mm and run it slower.


Third question: If I do not replace the current fan, what is the
SIMPLEST way to confidently regulate the speed of the current fan?
While most of you have figured this out already, let me make it
plain in case anyone has missed it. I am not an electrician. Not
only do I not play one on TV, I have never met anyone who plays
one on TV. I have replaced plenty of outlets and light fixtures,
and even a ceiling fan or two, but my mind simply does not seem to
grasp concepts much more complex than that.

**I suggest you play around with different resistor values. You have tried
value X. Now try 80% of X. Or thereabouts.


If I keep the current fan, I would like an alternative method of
speed control that meets the following criteria:
First, it should involve little more than splicing a device into a
wire.
Second, it should not involve a great deal of trial and error. I
really do not like the idea of picking up a half-dozen resistors
and swapping them in and out until one works just right.

**Why? It's easy, cheap and it'll work. Other methods are going to require
that you do a lot more work.

Third, it should be SIMPLE. I understand why temperature
sensitive devices may be the BEST solution, but I do not see how
to make them the simplest. What temperature do I want?

**You want the fan to kick off, at around 40oC. You want the fan to be
running reasonably hard at 50oC. You want it to be REALLY running at 80oC.

How do I
find a device with that temperature setting? Where do I put the
sensor?

**On the heat sink, close to the output devices.

What other questions am I missing? Given that I do not
understand this whole process all that well, going this route just
seems to me to be an invitation to error; a way for me to screw up
without even knowing it.

**Just drop your present resistor size by 20%. That should work fine.


That is why the idea of a rheostat, or something with a knob I can
turn or a switch I can flip between positions, appeals to me. If
I find the right device, I should be able to splice it in place
and then adjust the speed until I am sure it will spin up when
power is applied, but won't spin loudly enough for me to hear more
than a foot or two away.

**Not practical, since you are dealing with mains Voltages. Keep it simple.
Either use a different resistor, or buy a temperature sensing fan.


In summation, and having gone on much too long already, I want
either or both of two things:
1. A source for a quality, slow turning, quiet fan, and/or
2. Advice on speed-controlling the current fan in the simplest
possible manner.

Thanks again,
Phil

PS. It is really a shame this is not a 12V fan, as there are all
kinds of solutions in the computer world, including, possibly, the
120mm Antec Smart Fan I added to my Sonata case.


**12 Volt DC fans are difficult to control. They have internal circuitry
which regulates the speed. Varying the input Voltage, is not very
successful.


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote in message


**12 Volt DC fans are difficult to control.

Simply not true.

They have internal circuitry which regulates the speed.

Nope. Some have tachometers, but any speed regulating circuitry involved is
not in the fan.

Varying the input Voltage, is not very successful.

It's very successful. There are even inexpensive products that make
controlling them literally plug-and-play. This is an example:

http://www.computergate.com/products...?prodcd=BCFZFM

It's just a variable voltage regulator with support circuitry and heat sink
in an insulating case, with plug-and-play wires attached. Often available
for as little as $4.95 $US. One of many products that are available for the
purpose. IME very effective.

The rule of thumb is to keep the applied voltage above 7 volts. This allows
almost a 2:1 adjustment range which is more than enough for a vast number of
purposes. Take a fan that spins at 5,000 rpm and knock it down to less than
3,000, and the noise decrease is impressive. Another rule of thumb is to
avoid using series resistors.

I covered most of these points (except the Fanmate) in a post yesterday
morning. Did it get lost in the bowels of Usenet?

Trevor Wilson said to ****-for-Brains:

I covered most of these points (except the Fanmate) in a post yesterday
morning. Did it get lost in the bowels of Usenet?

**Probly. My current newserver is brutal. 24 hours retention, if I am lucky.
Often it is less than that.

Regardless, you were right to post your own info. Even if you had
seen Mr. ****'s post, and even if you had agreed 100% with
everything it said, you'd still have been right to post it. That's
because anybody who doesn't know the subject would naturally assume
Turdborg was lying again.

I wish I'd known how difficult controlling a 12VDC fan was;
I wouldn't have done it. I have two fans, fed by a self
designed and built controller. An IC sensor (output volatge
linearly related to temperature) feeds a servo circuit
(separate one for each fan) that keeps it running at the
lowest speed that will produce 50 degrees C at the power
amplifier heat sinks (I have two Aragon Pwier amps, 2 and 3
channels respectively, that sit in an enclosed cabinet).
Cogging is prevented by starting each fan only when its
drive voltage is greater then 6V. The circuit is simp.icity
itself, (3 ICs).

This have been working reliably for a few years now and
shows no signs of difficulty. The amps never overheated. The
fans are standard 12VDC fans, chosen for lowest noise. They
don't know how difficult what they are doing is, either.

-- Ron




On Mon, 11 Aug 2003 19:34:02 GMT, "Trevor Wilson"
wrote:


"Arny Krueger" wrote in message
...
"Trevor Wilson" wrote in message


**12 Volt DC fans are difficult to control.

Simply not true.

**I'll amend that to: MOST 12 VDC fans are difficult to control.


They have internal circuitry which regulates the speed.

Nope. Some have tachometers, but any speed regulating circuitry involved
is
not in the fan.

**Oh, yes it is. Modern 12VDC fans use an internal oscillator, driving a 3
phase, brushless motor. The only proper way to control the speed is to vary
the frequency of the internal oscillator. That is a difficult thing to do,
given that the circuitry is embedded.


Varying the input Voltage, is not very successful.

It's very successful. There are even inexpensive products that make
controlling them literally plug-and-play. This is an example:

**I did say: "Not very successful." It is possible to vary the speed within
certain limits. Cogging is common with primitive Voltage controls on such
fans.


http://www.computergate.com/products...?prodcd=BCFZFM

It's just a variable voltage regulator with support circuitry and heat
sink
in an insulating case, with plug-and-play wires attached. Often available
for as little as $4.95 $US. One of many products that are available for
the
purpose. IME very effective.

**I call "effective" a speed control which can vary the speed from (say) 10%
of max RPM to 100% in smooth controllability. You can't do it with a Voltage
regulator.


The rule of thumb is to keep the applied voltage above 7 volts. This
allows
almost a 2:1 adjustment range which is more than enough for a vast number
of
purposes. Take a fan that spins at 5,000 rpm and knock it down to less
than
3,000, and the noise decrease is impressive. Another rule of thumb is to
avoid using series resistors.

**That ain't decent speed control. I use 240VAC fans, which I can control
down to around 120RPM, all the way up to several thousand. You can't do that
with simple Voltage regulators and 12VDC fans.


I covered most of these points (except the Fanmate) in a post yesterday
morning. Did it get lost in the bowels of Usenet?

**Probly. My current newserver is brutal. 24 hours retention, if I am lucky.
Often it is less than that.

"Ron" wrote in message
...

I wish I'd known how difficult controlling a 12VDC fan was;
I wouldn't have done it. I have two fans, fed by a self
designed and built controller. An IC sensor (output volatge
linearly related to temperature) feeds a servo circuit
(separate one for each fan) that keeps it running at the
lowest speed that will produce 50 degrees C at the power
amplifier heat sinks (I have two Aragon Pwier amps, 2 and 3
channels respectively, that sit in an enclosed cabinet).
Cogging is prevented by starting each fan only when its
drive voltage is greater then 6V. The circuit is simp.icity
itself, (3 ICs).

This have been working reliably for a few years now and
shows no signs of difficulty. The amps never overheated. The
fans are standard 12VDC fans, chosen for lowest noise. They
don't know how difficult what they are doing is, either.

**You still can't lower the speed much below 40% of maximum PRM. That ain't
speed control. A resistor in series with an AC fan is just as precise.


--
Trevor Wilson
www.rageaudio.com.au

Ron wrote:

I wish I'd known how difficult controlling a 12VDC fan was;
I wouldn't have done it. I have two fans, fed by a self
designed and built controller.

Go here http://xoxide.com/fancontrollers.html and make your
choice of fan controllers...

Trevor Wilson wrote:


**You still can't lower the speed much below 40% of maximum PRM. That ain't
speed control. A resistor in series with an AC fan is just as precise.



The fan on my CPU cooler goes from 1632 to 3887 by cranking the
knob up or down.

"WindsorFox[SS]" wrote in message
news:%bYZa.9210$qf.2506@lakeread06...
Trevor Wilson wrote:

**Oh, yes it is. Modern 12VDC fans use an internal oscillator,
driving a 3
phase, brushless motor. The only proper way to control the
speed is to vary
the frequency of the internal oscillator. That is a difficult
thing to do,
given that the circuitry is embedded.



Obviously you refer to somethin other than 12 Volt computer
fans.

FWIW, guys, and I don't want to get in the way of a good fight,
but we were talking about cooling fans for my Ampzilla, and it
turns out that Trevor was completely right that the fan in
question was 120VAC and not 12VDC. All the talk about regulating
computer fans is interesting, but not helpful with my problem. I
have a Zalman fan mate on my Zalman CNPS-7000-Cu, and it works,
but not over nearly the sort of range of speeds that Trevor is
talking about. Oh jeez, now you have me following off topic as
well.

Anyway, to paraphrase what I wrote earlier:
Digikey carries fans from Papst/ebm Industries. I found the
115VAC
model 4800Z for just under $30, plus about $4 for shipping. It
moves 56CFM at 28dBA. Mouser carries some ebm stuff as well, but
seems to have higher prices and a slightly smaller selection.

Is this a good place for me to stop looking and start acting? The
price seems a bit much but if it is quiet without the need of a
resistor, it should at least solve all of my problems. I've found
a few other 115VAC fans, but all seem to have quite a bit higher
CFMs and dBAs.

This is a power amp we are cooling here, not a computer. I am
leaning more and more to the opinion that a quality quiet fan
should be my first step, and that it just might turn out to be my
last step as well.

"WindsorFox[SS]" wrote in message
news:%bYZa.9210$qf.2506@lakeread06...
Trevor Wilson wrote:

**Oh, yes it is. Modern 12VDC fans use an internal oscillator, driving a
3
phase, brushless motor. The only proper way to control the speed is to
vary
the frequency of the internal oscillator. That is a difficult thing to
do,
given that the circuitry is embedded.



Obviously you refer to somethin other than 12 Volt computer fans.

**Nope. For such a cheap, ubiquitous item, they are surprisingly
sophisticated. It was not always so. 12 Volt fans did use brush type motors,
but their MTBF was significantly lower than modern fan motors. I know of no
modern fan motor which is not a brushless type. Some may still exist, in
VERY cost sensitive computer equipment. No sane engineer would specify them,
IMO.


--
Trevor Wilson
www.rageaudio.com.au

"WindsorFox[SS]" wrote in message
news:ynYZa.9276$qf.8586@lakeread06...
Trevor Wilson wrote:


**You still can't lower the speed much below 40% of maximum PRM. That
ain't
speed control. A resistor in series with an AC fan is just as precise.



The fan on my CPU cooler goes from 1632 to 3887 by cranking the
knob up or down.

**(SIGH) And 40% of 3887 is........


--
Trevor Wilson
www.rageaudio.com.au

"WindsorFox[SS]" wrote in message
news:zfYZa.9231$qf.1890@lakeread06

Ron wrote:

I wish I'd known how difficult controlling a 12VDC fan was;
I wouldn't have done it. I have two fans, fed by a self
designed and built controller.

Go here http://xoxide.com/fancontrollers.html and make your
choice of fan controllers...

Not to mention all the motherboards with fan controllers built in.

IMO anybody who says that applying speed controls to 12v fans are
ineffective because the range of speed adjustment is limited, is showing
their lack of practical experience. For one thing, the noise and air
movement coming off a fan is a very nonlinear function of speed, Turning fan
speed down to 40% may not seem like much on paper, but in the real world
it's very significant.

The difference between the same fan running at 5000 rpm and 2000 rpm is like
night and day. Furthermore, if you look at fans that have low noise
characteristics, the major difference is that they spin slower. Indeed, in
my investigations of quiet CPU coolers I found one product line that
provided a full range of cooling ratings (Molex), using heat sinks and fans
that were identical, other than fan speed.

On Mon, 11 Aug 2003 21:00:40 GMT, "Trevor Wilson"
wrote:

**You still can't lower the speed much below 40% of maximum PRM. That ain't
speed control. A resistor in series with an AC fan is just as precise.

Or he could use a simple PWM circuit to control the speed of the fan.
That should get it down as slow as he wants and would give the most
consistent results. I think a series resistor would yield variable
results, especially for low RPMs. OTOH, he could bypass the resistor
with a large capacitor to give full voltage for a brief moment when
the fan is turned on, hopefully avoiding a turn-on stall. Or maybe
make a variable voltage regulator that applies full voltage at turn-on
and then relaxes to the required minimum voltage over a period of a
second or two.

--
Thine

Which version of this GAS unit do you have? I owned the original (model with
crazy lettering logo). The fan was very noisy, and I reduced it by elevating
it up from the shelf. I put 4 of my kid's building blocks beneath the feet
and most of the noise was gone, as if it were in large part caused by the
rush of air upon the shelf surface. My Ampzilla IIi, never remained in
repair long enough for me to be bothered the fan noise (which was far less).
I think you are extremely fortunate in having a working unit. (None of the
GAS amps generated the current required to drive speakers of 4 ohm
impedance, so mine ended up driving a pair of Stax headphones.) My GAS unit
is really idling since is too big to use as a doorstop and not owning a
boat, I'm not in any need of an anchor.

"Phil Anderson" wrote in message
news:WMgZa.74397$Oz4.17285@rwcrnsc54...
I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.

Can I replace this with a computer cooling fan? What size do I
need? How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

Advice please.

Thanks,
Phil

"Trevor Wilson" wrote in message

"Arny Krueger" wrote in message
...
"WindsorFox[SS]" wrote in message
news:jW_Za.10115$qf.4685@lakeread06

Right, I wondered what a 12 Volt fan had to do with your
question, it's so cross posted now I thought I'd missed something
and was just replying to the 12V comments.

I plead guilty to bringing up 12 volt fans. I did so because 12 volt
fans are plentiful and readily adjustable. They can be adapted for
use where
the
original fan was 12 volt when DC power is readily available, such as
in a power amp.

I've experimented with fan speed controls on 120 VAC fans, and had
disappointing results. 120 VAC fans are based on synchronous motors
and IME
they get pretty ugly at low speeds if you turn their speed way down.

**Then you're not doing it right.

Letsee fan, resistor...

With simple series resistors and a
decent fan, speed reductions of at least 40% may be obtained very
easily, cheaply and reliably.

Just a second. Wasn't 60% reduction somehow inadequate when the fan in
question ran off of 12 volts?

With more sophisticated methods, an AC
fan may be controlled almost down to 0RPM.

I suspect the same can be said of 12 volt fans.

This cannot be achieved with DC fans.

Nor is there any need to do such a thing.

About 40% of max RPM is the best that can be attained.
Even within that range, 'cogging' is a real possibility. Ultimately,
lowering the speed of an AC fan will most likely provide worthwhile
noise reductions, whilst the cogging which occurs with DC fans, when
lowering their speeds, may create more problems than it solves.

There is no reason why a 12 volt fan would "cog" any more than a 60 Hz AC
fan. I've definately seen 60 Hz fans cog when trying to slow them down.
There's a tendency for AC fan motors to run synchronously.

I come back to the requirements of the original poster. He has already
stated that his preference is for extreme simplicity.

I have Phil Anderson's initial post here right here before me. I see no
requirement for extreme simplicity.

A series resistor on the original AC fan, is overwhelmingly the
appropriate
choice, for this guy.

In his inital post Phil said he tried that, and he had stalling problems.

That may not be the case for others.

What's simpler than an off-the-shelf fan speed regulator?

"Arny Krueger" wrote in message
...
"Trevor Wilson" wrote in message


**No, difficult as in reducing the speed to a reasonably low level
(say: 10% of max RPM).

Straw man argument. Knocking fan speed down to 40% of rating makes a very
dramatic change in noise and air flow.

**Not if cogging occurs. A real possibility with DC fans.


If a really weak 120 mm fan is required, a couple of days ago I
recommended
fabricating a baffle plate (15 minutes) and using a smaller fan. If a
wider
range of air flows is required, using a switched array of fans would be a
solution.

**Points:

* Fabrication times of 15 mins, assumes the OP ahs the appropriate
facilities.
* It would take far longer than 15 mins to remove the original fan from the
Ampzilla.
* It would take considerably less time to choose an appropriately sized
resistor, for the existing fan.


And further, the original poster expressed
some trepidation about placing a series resistor in circuit with a
110VAC fan.

IME, a basically ugly process that works even worse with 120 volt fans
than
changing the speed of 12v DC fans. Series resistors have been largely
superceded by variable regulators (often PWM in the case of motherboard
fan
regulators) in 12 volt fan applications because of the problems with
stalling.

**I'm sure they're very effective on mother boards. They may not be
appropriate for the OP, given his preference for a simple solution.


A regulator is a fair bit more complex than that.

Except that I provided a reference to an off-the-shelf pre-packaged
regulator unit.

**Which is still far more complex to implement than a series resistor.


The statement that 12 volt fans are difficult to control is truly the
voice
of inexperience. The claim that modern DC fans incorporate their own AC
power supplies is true as far as it goes, but it's not a fixed AC
frequency.

**It may not be. They're still not as controllable as a fan whose motor is
directly accessible. And for the record: I have quite a bit of experience in
controlling all sorts of fans, including DC motor ones.


--
Trevor Wilson
www.rageaudio.com.au

On Tue, 12 Aug 2003 12:38:40 +0100, Lived EHT
wrote:

On Mon, 11 Aug 2003 21:00:40 GMT, "Trevor Wilson"
wrote:

**You still can't lower the speed much below 40% of maximum PRM. That ain't
speed control. A resistor in series with an AC fan is just as precise.

Or he could use a simple PWM circuit to control the speed of the fan.
That should get it down as slow as he wants and would give the most
consistent results.

Wow... I am all aghast. Someone that actually knows how to
control a fan... My hat off to you, sir...

Actually, you can't go 'as low as you want', but 10% - 15%
is a piece of cake. Below that, the efficiency of the blades
is down to zilch.

I think a series resistor would yield variable
results, especially for low RPMs.

In addition, it will consume power and *add* to the heat.

-- Ron


OTOH, he could bypass the resistor
with a large capacitor to give full voltage for a brief moment when
the fan is turned on, hopefully avoiding a turn-on stall. Or maybe
make a variable voltage regulator that applies full voltage at turn-on
and then relaxes to the required minimum voltage over a period of a
second or two.

On Tue, 12 Aug 2003 18:53:57 GMT, "Trevor Wilson"
wrote:


"Arny Krueger" wrote in message
...
"WindsorFox[SS]" wrote in message
news:jW_Za.10115$qf.4685@lakeread06

Right, I wondered what a 12 Volt fan had to do with your question,
it's so cross posted now I thought I'd missed something and was just
replying to the 12V comments.

I plead guilty to bringing up 12 volt fans. I did so because 12 volt fans
are plentiful and readily adjustable. They can be adapted for use where
the
original fan was 12 volt when DC power is readily available, such as in a
power amp.

I've experimented with fan speed controls on 120 VAC fans, and had
disappointing results. 120 VAC fans are based on synchronous motors and
IME
they get pretty ugly at low speeds if you turn their speed way down.

**Then you're not doing it right. With simple series resistors and a decent
fan, speed reductions of at least 40% may be obtained very easily, cheaply
and reliably.

Further proof that little knowledge is worse than no
knowledge at all. He was taking about SYNCHRONOUS MOTORS.
Putting resistors in series with a synchronous motor is
folly.



With more sophisticated methods, an AC fan may be controlled
almost down to 0RPM. This cannot be achieved with DC fans. About 40% of max
RPM is the best that can be attained. Even within that range, 'cogging' is a
real possibility. Ultimately, lowering the speed of an AC fan will most
likely provide worthwhile noise reductions, whilst the cogging which occurs
with DC fans, when lowering their speeds, may create more problems than it
solves.

I come back to the requirements of the original poster. He has already
stated that his preference is for extreme simplicity. A series resistor on
the original AC fan, is overwhelmingly the appropriate choice, for this guy.
That may not be the case for others.

"Norman M. Schwartz" wrote in message
...
Which version of this GAS unit do you have? I owned the original
(model with
crazy lettering logo). The fan was very noisy, and I reduced it
by elevating
it up from the shelf. I put 4 of my kid's building blocks
beneath the feet
and most of the noise was gone, as if it were in large part
caused by the
rush of air upon the shelf surface. My Ampzilla IIi, never
remained in
repair long enough for me to be bothered the fan noise (which
was far less).
I think you are extremely fortunate in having a working unit.
(None of the
GAS amps generated the current required to drive speakers of 4
ohm
impedance, so mine ended up driving a pair of Stax headphones.)
My GAS unit
is really idling since is too big to use as a doorstop and not
owning a
boat, I'm not in any need of an anchor.

This one started out really original. I bought it from the
original owner, who built it from one of the original kits offered
before GAS got together enough money. The only thing that was not
original in mine was the fan.

Shortly after I received the amp, one channel died. I contacted
the designer, James Bongiorno, and sent him the 'chimney' and he
replaced and updated the circuitry, as well as added a bass servo
unit of his design. I sought his advice on the fan, but since it
was not the original, he was not sure about the proper resistor to
slow it down. He noted that the amp only needed a very small
amount of cooling from the fan, so how slow it was was not an
issue.

I installed the resistor he thought of as his best guess but the
hystersis effect (is that the right term) means it often does not
spin when I turn it on. I finally got tired of having to pull out
the amp and reach up inside it every time I turned it on, and
posted my question here. I am currently leaning toward a German
made Papst fan, since they seem to have the reputation of spec'ing
their noise figures much more accurately than most.

BTW, I am using the amp to drive Dahlquist DQ-10s, and have a
Thaedra for my pre-amp. I got the Zilla and the Thaedra from
different owners over the net. Both are the 'original' model 1,
but I do not know the Thaedra's pedigree.

It is interesting to see how subjects can morph. Let me try to
clear up a little, and say where I am leaning now.

First, in both my original post, and my first reply to Trevor, I
was insistent that I had a 12V fan in there. I asked if I could
use a computer fan its place. That is where the whole 12V issue
got started.

But Trevor was right and I was wrong. I have a 115VAC fan. It is
the Torin A450, and my quick Google search got me the Torin
website, but it did not find anything resembling this fan. I do
know that at full voltage it is very fast and very loud.

James Bongiorno updated and replaced the circuitry in my Ampzilla.
When I asked about quieting the fan, he was unsure, as it was not
original and he did not know the model. He did state that the amp
required very little cooling, and that an extremely slow turning
fan would be just fine. He suggested a couple of different values
of resistors to try. I found it very awkward trying to attach a
resistor to very stiff solid core wiring, so stopped with the
first resistor I tried. It makes the fan very slow and quiet, and
keeps the amp cool enough, but it often does not start at all at
turn-on. Is this called a "hystersis effect?"

I have simply lived with this problem for a long time, until
recently deciding to seek advice on what to do about it. I recall
that in the past I had trouble finding the resistors that
Bongiorno recommended, and did not really feel comfortable
interpreting the packaging. That is why I originally expressed
interest in either some sort of potentiometer (which I now
understand to be a bad idea in this application) or else a
replacement fan that is naturally slow and quiet.

As an aside, some months ago I set off on another quest to quiet
down my computer. In my reading on that subject, I gained the
strong impression that German made Papst fans are the Holy Grail
of quiet computers. I also learned they are almost impossible to
find in the US and wound up with some different solutions, mostly
from Zalman, a Korean company.

Anyway, an email from 'tater' gave me a large number of fan links,
and I learned that Papst is marketed in the US under the ebs
Industries label. My current fau is 119 x 119 x 38mm. Papst
makes a number of fans in that same size, and I chose one rated at
28dBA that turns slowly and moves only a little air. Digikey
wants about $30 plus $4 shipping for the best one I could find for
my purposes. Papst seems to make some still slower and more quiet
fans, but I have not found a US source for those models.

My current thinking is to put in a Papst/ebs fan and remove the
resistor. I hope that will be quiet enough. If it is not, I
suspect a much lower value resistor will do the trick. Before
taking that step, I will return to these groups for advice.

Thanks everyone for all the help, and a great deal of
entertainment as well!

Phil Anderson

"Ron" wrote in message
...
On Tue, 12 Aug 2003 18:53:57 GMT, "Trevor Wilson"
wrote:


"Arny Krueger" wrote in message
...
"WindsorFox[SS]" wrote in message
news:jW_Za.10115$qf.4685@lakeread06

Right, I wondered what a 12 Volt fan had to do with your question,
it's so cross posted now I thought I'd missed something and was just
replying to the 12V comments.

I plead guilty to bringing up 12 volt fans. I did so because 12 volt
fans
are plentiful and readily adjustable. They can be adapted for use where
the
original fan was 12 volt when DC power is readily available, such as in
a
power amp.

I've experimented with fan speed controls on 120 VAC fans, and had
disappointing results. 120 VAC fans are based on synchronous motors and
IME
they get pretty ugly at low speeds if you turn their speed way down.

**Then you're not doing it right. With simple series resistors and a
decent
fan, speed reductions of at least 40% may be obtained very easily,
cheaply
and reliably.

Further proof that little knowledge is worse than no
knowledge at all. He was taking about SYNCHRONOUS MOTORS.
Putting resistors in series with a synchronous motor is
folly.

**No, it is not. It is a popular and effective method of reducing the speed
of such fans. It is very important to realise that a synchonous motor, as
used in a fan, is under constant, heavy loading. It can never reach it's
theoretical maximum speed, which is determined by the frequency and number
poles used. If the motor was under light, or no load conditions, then a
resistor WOULD be a dumb idea. Fortunately, on this planet, we have air to
load the fan blades.

Actually, there is another way to lower the speed of the fan, with no hot
resistors. That would be to choose an appropriately sized capacitor.
Unfortunately, the results can be rather hit and miss, depending on the
inductance of the fan motor. Start up problems, however, are largely gone.

And, for the record: I have used all manner of fans and speed controls, over
the years. A resistor in series with an AC fan works just fine. What is
more, they run for a very long time, with high levels of reliability.


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote in message

"Ron" wrote in message
...

Further proof that little knowledge is worse than no
knowledge at all. He was taking about SYNCHRONOUS MOTORS.
Putting resistors in series with a synchronous motor is
folly.

**No, it is not. It is a popular and effective method of reducing the
speed of such fans. It is very important to realise that a synchronous
motor, as used in a fan, is under constant, heavy loading. It can
never reach it's theoretical maximum speed, which is determined by
the frequency and number poles used. If the motor was under light, or
no load conditions, then a resistor WOULD be a dumb idea.
Fortunately, on this planet, we have air to load the fan blades.

The irony is killing!

First, Trevor makes up the fiction that 12 VDC motors are fixed-speed and
"cog" if you try to reduce their speed, and then he denies that synchronous
motors are unhappy when run way below synchronous speeds. Next thing you
know he'll tell us they don't "cog".

Actually, there is another way to lower the speed of the fan, with no
hot resistors. That would be to choose an appropriately sized
capacitor.

And still another way, run synchronous motors from a variable-frequency
power supply.

Unfortunately, the results can be rather hit and miss,
depending on the inductance of the fan motor. Start up problems,
however, are largely gone.

It's like people don't pick the resistors they put in series with AX fans by
heuristic methods. Double irony!

And, for the record: I have used all manner of fans and speed
controls, over the years. A resistor in series with an AC fan works
just fine.

Not nearly as well as DC fans running from regulated power supplies...

What is more, they run for a very long time, with high levels of
reliability.

In the history of cooling technology, first there were AC fans and when the
limitations of those became fully apparent, they developed DC brushless
fans...

Truth be known I've been trying to run AC fans at variable speeds for years,
pushing air though my fireplace insert. When I try to turn them way down
they make the most horrible noises... ...always did!

I guess I should take my own advice and pop in some 12 volt 120 mm fans with
a regulated variable power supply.

In article ,
"Arny Krueger" wrote:

Series resistors have been largely
superceded by variable regulators (often PWM in the case of motherboard fan
regulators) in 12 volt fan applications because of the problems with
stalling.

Yep. But it's not even necessary to use a real regulator. I've used a
zener diode or a chain of ordinary diodes to provide a fixed voltage
drop. This offers much better regulation than a resistor, preventing
startup and stall problems so long as you keep to the fan's rated
voltage range, and is much cheaper than a real regulator.

PWM, I've heard of it causing problems (rough operation or
chattering) with some brushless fans. Seems plausible to me since
brushless motors must use some kind of timed circuit to energize and
deenergize coils in a sequence, and a chopped power supply could easily
interfere with the proper operation of such a circuit. Wouldn't
surprise me if it's used a lot in motherboards anyways, since PWM is
cheaper than a programmable regulator, might still work on many fans,
and most PC motherboards are all about cheap.

--
Tim

"Arny Krueger" wrote in message
...
"Trevor Wilson" wrote in message

"Ron" wrote in message
...

Further proof that little knowledge is worse than no
knowledge at all. He was taking about SYNCHRONOUS MOTORS.
Putting resistors in series with a synchronous motor is
folly.

**No, it is not. It is a popular and effective method of reducing the
speed of such fans. It is very important to realise that a synchronous
motor, as used in a fan, is under constant, heavy loading. It can
never reach it's theoretical maximum speed, which is determined by
the frequency and number poles used. If the motor was under light, or
no load conditions, then a resistor WOULD be a dumb idea.
Fortunately, on this planet, we have air to load the fan blades.

The irony is killing!

First, Trevor makes up the fiction that 12 VDC motors are fixed-speed and
"cog" if you try to reduce their speed, and then he denies that
synchronous
motors are unhappy when run way below synchronous speeds. Next thing you
know he'll tell us they don't "cog".

**OK. Fans 101:

AC motor fans use a 'shaded pole' motor system. They are synchronous and
THEORETICALLY their rotational speed is dependent upon the number of poles
and the frequency applied. They are under constant, heavy load (from the
air). As such, they can never reach their synchronous rotational speed.
Reducing the input frequency will reduce their speed (obviously). Reducing
the input Voltage will also decrease their speed. Since the fan is usually
under a constant, heavy load, the variation in speed will be reasonably
predictable. If the air load varies, then the result will be unpredictable
and simple Voltage reduction systems are not recommended. Variable frequency
schemes would be a better idea, in this case. PLEASE NOTE: A series resistor
not a perfect solution. It is, however, simple, cheap and effective, if the
air load is reasonably constant.

DC motor fans come is a very wide variety of flavours. Too many to address
individually here. Broadly speaking, they fall into several groups.

DC brush motors: I have not seen one of these for quite awhile. They can be
easily and effectively changed in speed, by the simple matter of altering
the input Voltage. This could be by using a resistor, zener diode, linear
regulator or a switch mode regulator. Such motors don't last very long,
under continuous duty, however. Brushes wear out.

DC brushless motors: These come in a bewildering array of types. Some are as
simple as a couple of transistors, which set up an AC signal to drive an AC
motor. Others have sophisticated motor control systems, with hall effect
devices, and constant speed regulation circuits. Some have external access
to speed regulation circuitry, allowing thermal sensors to vary speed. It is
these last types, which have the best success in speed altering. Other types
are very much hit-n-miss affairs. Some respond to varying input Voltages,
reasonably well. Some do not.They don't because the internal circuitry
'expects' to 'see' an input Voltage of a reasonable range (say; 10 ~ 12
Volts). Voltages outside this range may cause the internal oscillator to
malfunction. Gogging usually results.


Actually, there is another way to lower the speed of the fan, with no
hot resistors. That would be to choose an appropriately sized
capacitor.

And still another way, run synchronous motors from a variable-frequency
power supply.

**An excellent idea, but well beyond the requirements of the original
poster. A series resistor of the appropriate value, is STILL the best option
for him. That may not be the best option for someone else.


Unfortunately, the results can be rather hit and miss,
depending on the inductance of the fan motor. Start up problems,
however, are largely gone.

It's like people don't pick the resistors they put in series with AX fans
by
heuristic methods. Double irony!

And, for the record: I have used all manner of fans and speed
controls, over the years. A resistor in series with an AC fan works
just fine.

Not nearly as well as DC fans running from regulated power supplies...

**It depends on the fan. I just grabbed two, different 12 Volt DC fans. One
operated fine (albeit with cogging noise) down to 3 Volts. The other ceased
operation at 7.5 Volts. I also grabbed two, different 240VAC fans. One
stopped operation at 60 Volts and would not start up until 70 Volts. The
other stopped at 65 Volts and started up at 70 volts.


What is more, they run for a very long time, with high levels of
reliability.

In the history of cooling technology, first there were AC fans and when
the
limitations of those became fully apparent, they developed DC brushless
fans...

**The only limitations of AC fans, are their higher costs (more materials,
etc). Their reliability is somewhat higher than any DC fan.


Truth be known I've been trying to run AC fans at variable speeds for
years,
pushing air though my fireplace insert. When I try to turn them way down
they make the most horrible noises... ...always did!

**Then you're doing it wrong. My power amp uses a (continuously) variable
speed AC fan. When the fan is just ticking over (about 200 RPM), the noise
from the fan is lower than the (potted, shrouded) toroidal power
transformer. And the transformer is VERY quiet. I measured the noise spectra
using my LMS system. Even with the amplifier and measurement mic fully
enlcosed with several blankets and a doona, the ambient noise at 4:00 AM was
higher than the fan noise.


I guess I should take my own advice and pop in some 12 volt 120 mm fans
with
a regulated variable power supply.

**I guess you should.


--
Trevor Wilson
www.rageaudio.com.au

"Ron" wrote in message
...
On Tue, 12 Aug 2003 18:53:57 GMT, "Trevor Wilson"
wrote:


"Arny Krueger" wrote in message
...
"WindsorFox[SS]" wrote in message
news:jW_Za.10115$qf.4685@lakeread06

Right, I wondered what a 12 Volt fan had to do with your question,
it's so cross posted now I thought I'd missed something and was just
replying to the 12V comments.

I plead guilty to bringing up 12 volt fans. I did so because 12 volt
fans
are plentiful and readily adjustable. They can be adapted for use where
the
original fan was 12 volt when DC power is readily available, such as in
a
power amp.

I've experimented with fan speed controls on 120 VAC fans, and had
disappointing results. 120 VAC fans are based on synchronous motors and
IME
they get pretty ugly at low speeds if you turn their speed way down.

**Then you're not doing it right. With simple series resistors and a
decent
fan, speed reductions of at least 40% may be obtained very easily,
cheaply
and reliably.

Further proof that little knowledge is worse than no
knowledge at all. He was taking about SYNCHRONOUS MOTORS.
Putting resistors in series with a synchronous motor is
folly.

**You would, of course, be wrong. It is a widely used practice, for slowing
FANS using shaded pole motors down to lower speeds. You seem to be
forgetting that although fans use sychronous motors, they are under
constant, heavy load. As such, they can never reach the theoretical
synchronous speed, which is determined by the number of poles and the
frequency of operation. As such, use of a resistor (or even a cap) is a most
effective form of speed control.

And again, I refer you to the original poster's requirement that the speed
control be SIMPLE.


--
Trevor Wilson
www.rageaudio.com.au

**You would, of course, be wrong. It is a widely used practice, for slowing
FANS using shaded pole motors down to lower speeds. You seem to be
forgetting that although fans use sychronous motors, they are under
constant, heavy load. As such, they can never reach the theoretical
synchronous speed, which is determined by the number of poles and the
frequency of operation. As such, use of a resistor (or even a cap) is a most
effective form of speed control.

And again, I refer you to the original poster's requirement that the speed
control be SIMPLE.


Oh, people always ask "What's the easiest way of....". :-)
Sometimes you have to give them the right answer, not the quick fix.

"Laurence Payne" wrote in message
...

**You would, of course, be wrong. It is a widely used practice, for
slowing
FANS using shaded pole motors down to lower speeds. You seem to be
forgetting that although fans use sychronous motors, they are under
constant, heavy load. As such, they can never reach the theoretical
synchronous speed, which is determined by the number of poles and the
frequency of operation. As such, use of a resistor (or even a cap) is a
most
effective form of speed control.

And again, I refer you to the original poster's requirement that the
speed
control be SIMPLE.


Oh, people always ask "What's the easiest way of....". :-)
Sometimes you have to give them the right answer, not the quick fix.

**I agree. Now, you tell me: PRECISELY what is wrong with putting a resistor
in series with an AC fan, to slow it down?

In your answer, you may care to refer to the many thousands of amplifiers,
from dozens of manufacturers, which are so equipped (with series resistors).


--
Trevor Wilson
www.rageaudio.com.au

Oh, people always ask "What's the easiest way of....". :-)
Sometimes you have to give them the right answer, not the quick fix.

**I agree. Now, you tell me: PRECISELY what is wrong with putting a resistor
in series with an AC fan, to slow it down?

In your answer, you may care to refer to the many thousands of amplifiers,
from dozens of manufacturers, which are so equipped (with series resistors).


Nothing at all.
It was a general comment :-)

(snip)


Further proof that little knowledge is worse than no
knowledge at all. He was taking about SYNCHRONOUS MOTORS.
Putting resistors in series with a synchronous motor is
folly.

**You would, of course, be wrong. It is a widely used practice, for slowing
FANS using shaded pole motors down to lower speeds. You seem to be
forgetting that although fans use sychronous motors,

No so, see below.

they are under
constant, heavy load. As such, they can never reach the theoretical
synchronous speed,

Which is why they are not synchronous motors.

which is determined by the number of poles and the
frequency of operation.

Correct as a definition of synchronous speed, viz.:
At 50 Hz:
2 pole machine, synchr. speed - 3,000 rpm.
4 pole machine, synchr. speed - 1,500 rpm.

At 60 Hz:
2 pole machine, synchr. speed - 3,600 rpm.
4 pole machine, synchr. speed - 1,800 rpm.

As such, use of a resistor (or even a cap) is a most
effective form of speed control.

Two points of information:
1. Shaded pole motors are not synchronous motors, they are
induction machines that run below synchronous speed by an
amount related to the torque load. This difference is
called "slip" and it's the means by which current is induced
into the rotor so that it can be pulled round by rotating
the stator magnetic field. No slip = no torque, so it can't
happen!

A synchronous machine must run at synchronous speed. If it
"pulls out" due to too much torque load, it stalls. In this
case the rotor field is provided by a DC current source.
Some synchronous machines are "induction start" - they
accelerate as induction motors under no load, then "pull
in".

2. A resistance in series with the motor stator field, in
this case the shaded pole field coil, will slow it down but
will reduce motor efficiency. A capacitance is more
efficient (no I2R loss) but the motor loss due to high slip
remains. This is never done in an industrial drive motor but
will work on a small fan where efficiency is not the prime
concern. I'll be the first to admit it's not elegant, but
you can do it.

(snip)

Trevor Wilson
www.rageaudio.com.au

Cheers,

Roger
--
Roger Jones, P.Eng.
Thornhill, Ontario,
Canada.

"Friends don't let friends vote Liberal"

"Engineer" wrote in message
...
(snip)
Two points of information:
1. Shaded pole motors are not synchronous motors, they are
induction machines that run below synchronous speed by an
amount related to the torque load. This difference is
called "slip" and it's the means by which current is induced
into the rotor so that it can be pulled round by rotating
the stator magnetic field. No slip = no torque, so it can't
happen!

A synchronous machine must run at synchronous speed. If it
"pulls out" due to too much torque load, it stalls. In this
case the rotor field is provided by a DC current source.
Some synchronous machines are "induction start" - they
accelerate as induction motors under no load, then "pull
in".

**Thanks for clarifying the differences.


2. A resistance in series with the motor stator field, in
this case the shaded pole field coil, will slow it down but
will reduce motor efficiency. A capacitance is more
efficient (no I2R loss) but the motor loss due to high slip
remains. This is never done in an industrial drive motor but
will work on a small fan where efficiency is not the prime
concern. I'll be the first to admit it's not elegant, but
you can do it.

**You sure can. Some of the results can be unpredictable, due to the
inductance of the motor and the capacitance, when they form a resonant
circuit. It does, indeed, work, however.


--
Trevor Wilson
www.rageaudio.com.au