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Slowing down a box fan

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April 2, 2005 8:46:16 PM

Archived from groups: rec.audio.tech (More info?)

NMB min boxer
Model 3610NL-04W-B10
12 VDC 0.13 AMPERES

I have a wall wart
Output
12VDC 200mA

The fan makes too much noise and pushes much more air than I need. If I
can slow the fan down to make it quieter it will still push enough air
for me. How can I accomplish this? Power resistors?

More about : slowing box fan

Anonymous
April 2, 2005 8:46:17 PM

Archived from groups: rec.audio.tech (More info?)

In article <UoE3e.14444$g47.2846@fe12.lga>, ren <ren@ren.ren> wrote:

> NMB min boxer
> Model 3610NL-04W-B10
> 12 VDC 0.13 AMPERES
>
> I have a wall wart
> Output
> 12VDC 200mA
>
> The fan makes too much noise and pushes much more air than I need. If I
> can slow the fan down to make it quieter it will still push enough air
> for me. How can I accomplish this? Power resistors?

You can use a three pin 5V regulator that comes in a TO-220 case.
They're a dime a dozen and easy to find. Connect +12V to pin IN. Run a
220 Ohm resistor from pin OUT to pin GND. Put a 330 Ohm potentiometer
between pin GND and the negative power. Put the fan on pin OUT and the
negative power. That will let you adjust from 5V to full voltage. (A
12V brushless fan usually stalls around 4V)

3-pin
5v Regulator
+12V ----- IN OUT ---+------ + Fan
GND |
| 220 Ohm
| |
+--------+
|
Pot
|
0V --------------------+------ - Fan


Another option is to use a 12V thermal sensing exhaust fan. Pick a fan
with the temperature you desire and it only spins as fast as it needs
to. They're common at computer parts stores.
April 3, 2005 6:43:03 PM

Archived from groups: rec.audio.tech (More info?)

Kevin McMurtrie <mcmurtri@dslextreme.com> wrote in
news:mcmurtri-08EDE7.15402302042005@corp-radius.supernews.com:

> In article <UoE3e.14444$g47.2846@fe12.lga>, ren <ren@ren.ren> wrote:
>
>> NMB min boxer
>> Model 3610NL-04W-B10
>> 12 VDC 0.13 AMPERES
>>
>> I have a wall wart
>> Output
>> 12VDC 200mA
>>
>> The fan makes too much noise and pushes much more air than I need.
>> If I can slow the fan down to make it quieter it will still push
>> enough air for me. How can I accomplish this? Power resistors?
>
> You can use a three pin 5V regulator that comes in a TO-220 case.
> They're a dime a dozen and easy to find. Connect +12V to pin IN. Run
> a 220 Ohm resistor from pin OUT to pin GND. Put a 330 Ohm
> potentiometer between pin GND and the negative power. Put the fan on
> pin OUT and the negative power. That will let you adjust from 5V to
> full voltage. (A 12V brushless fan usually stalls around 4V)
>
> 3-pin
> 5v Regulator
> +12V ----- IN OUT ---+------ + Fan
> GND |
> | 220 Ohm
> | |
> +--------+
> |
> Pot
> |
> 0V --------------------+------ - Fan
>
>
> Another option is to use a 12V thermal sensing exhaust fan. Pick a
> fan with the temperature you desire and it only spins as fast as it
> needs to. They're common at computer parts stores.
>

Overkill. A 33 ohm 2W resistor will do the job nicely.
Related resources
Anonymous
April 3, 2005 11:24:52 PM

Archived from groups: rec.audio.tech (More info?)

"ren" <ren@ren.ren> wrote in message
news:UoE3e.14444$g47.2846@fe12.lga
> NMB min boxer
> Model 3610NL-04W-B10
> 12 VDC 0.13 AMPERES
>
> I have a wall wart
> Output
> 12VDC 200mA
>
> The fan makes too much noise and pushes much more air than I need.
> If I can slow the fan down to make it quieter it will still push
> enough air for me. How can I accomplish this? Power resistors?

An off-the-shelf device:

http://www.jab-tech.com/customer/product.php?productid=...
Anonymous
April 3, 2005 11:47:14 PM

Archived from groups: rec.audio.tech (More info?)

In article <nJ-dnWYwedra2s3fRVn-iA@comcast.com>,
Jimbo <jimbo@not-for-sale.com> wrote:

> Kevin McMurtrie <mcmurtri@dslextreme.com> wrote in
> news:mcmurtri-08EDE7.15402302042005@corp-radius.supernews.com:
>
> > In article <UoE3e.14444$g47.2846@fe12.lga>, ren <ren@ren.ren> wrote:
> >
> >> NMB min boxer
> >> Model 3610NL-04W-B10
> >> 12 VDC 0.13 AMPERES
> >>
> >> I have a wall wart
> >> Output
> >> 12VDC 200mA
> >>
> >> The fan makes too much noise and pushes much more air than I need.
> >> If I can slow the fan down to make it quieter it will still push
> >> enough air for me. How can I accomplish this? Power resistors?
> >
> > You can use a three pin 5V regulator that comes in a TO-220 case.
> > They're a dime a dozen and easy to find. Connect +12V to pin IN. Run
> > a 220 Ohm resistor from pin OUT to pin GND. Put a 330 Ohm
> > potentiometer between pin GND and the negative power. Put the fan on
> > pin OUT and the negative power. That will let you adjust from 5V to
> > full voltage. (A 12V brushless fan usually stalls around 4V)
> >
> > 3-pin
> > 5v Regulator
> > +12V ----- IN OUT ---+------ + Fan
> > GND |
> > | 220 Ohm
> > | |
> > +--------+
> > |
> > Pot
> > |
> > 0V --------------------+------ - Fan
> >
> >
> > Another option is to use a 12V thermal sensing exhaust fan. Pick a
> > fan with the temperature you desire and it only spins as fast as it
> > needs to. They're common at computer parts stores.
> >
>
> Overkill. A 33 ohm 2W resistor will do the job nicely.

Some brushless fans will not reliably start with a series resistor of
high enough value to slow them down. A series 47 Ohm wirewound pot and
a series 1000 microfarad capacitor would more reliably start up.

1000µF 16V
+----|(----+
| |
----+--- 47 ---+----
Ohm pot

I think a 3-pin regulator and a 330 Ohm pot is cheaper. Electronics
surplus stores have them for 20 to 80 cents each.
April 4, 2005 1:02:02 AM

Archived from groups: rec.audio.tech (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in
news:jfudnRc9pOfY5s3fRVn-gw@comcast.com:

> "ren" <ren@ren.ren> wrote in message
> news:UoE3e.14444$g47.2846@fe12.lga
>> NMB min boxer
>> Model 3610NL-04W-B10
>> 12 VDC 0.13 AMPERES
>>
>> I have a wall wart
>> Output
>> 12VDC 200mA
>>
>> The fan makes too much noise and pushes much more air than I need.
>> If I can slow the fan down to make it quieter it will still push
>> enough air for me. How can I accomplish this? Power resistors?
>
> An off-the-shelf device:
>
> http://www.jab-tech.com/customer/product.php?productid=...
> ogle
>
>

Costs 10 times as much as a resistor.
April 4, 2005 3:01:02 AM

Archived from groups: rec.audio.tech (More info?)

On Sun, 03 Apr 2005 14:43:03 -0500, Jimbo <jimbo@not-for-sale.com>
wrote:

>> Another option is to use a 12V thermal sensing exhaust fan. Pick a
>> fan with the temperature you desire and it only spins as fast as it
>> needs to. They're common at computer parts stores.
>>
>
>Overkill. A 33 ohm 2W resistor will do the job nicely.

Better yet, a zener diode. You could buy a couple different voltages
to experiment with.
Anonymous
April 4, 2005 8:22:49 AM

Archived from groups: rec.audio.tech (More info?)

"Jimbo" <jimbo@not-for-sale.com> wrote in message
news:jt-dnX4Bt4uHPc3fRVn-sg@comcast.com
> "Arny Krueger" <arnyk@hotpop.com> wrote in
> news:jfudnRc9pOfY5s3fRVn-gw@comcast.com:
>
>> "ren" <ren@ren.ren> wrote in message
>> news:UoE3e.14444$g47.2846@fe12.lga
>>> NMB min boxer
>>> Model 3610NL-04W-B10
>>> 12 VDC 0.13 AMPERES
>>>
>>> I have a wall wart
>>> Output
>>> 12VDC 200mA
>>>
>>> The fan makes too much noise and pushes much more air than I need.
>>> If I can slow the fan down to make it quieter it will still push
>>> enough air for me. How can I accomplish this? Power resistors?
>>
>> An off-the-shelf device:
>>
>>
http://www.jab-tech.com/customer/product.php?productid=...
>> ogle

> Costs 10 times as much as a resistor.

Depends on the resistor. For opener's the product I mentioned above is
variable.

The product also provides a low source impedance to the fan motor,
which tends to reduce stalling and cogging.
April 4, 2005 7:15:21 PM

Archived from groups: rec.audio.tech (More info?)

ren wrote:
> NMB min boxer
> Model 3610NL-04W-B10
> 12 VDC 0.13 AMPERES
>
> I have a wall wart
> Output
> 12VDC 200mA
>
> The fan makes too much noise and pushes much more air than I need. If I
> can slow the fan down to make it quieter it will still push enough air
> for me. How can I accomplish this? Power resistors?

Anyone have any pointers on where I can tap 5 or 12 volts DC without
introducing hum into the output signal:

http://www.freeinfosociety.com/electronics/schematics/a...

Or explain why the footswitch power supply upgrade is listed on page three.
Anonymous
April 4, 2005 9:52:34 PM

Archived from groups: rec.audio.tech (More info?)

On Mon, 4 Apr 2005 04:22:49 -0400, "Arny Krueger" <arnyk@hotpop.com>
wrote:

>"Jimbo" <jimbo@not-for-sale.com> wrote in message
>news:jt-dnX4Bt4uHPc3fRVn-sg@comcast.com
>> "Arny Krueger" <arnyk@hotpop.com> wrote in
>> news:jfudnRc9pOfY5s3fRVn-gw@comcast.com:
>>
>>> "ren" <ren@ren.ren> wrote in message
>>> news:UoE3e.14444$g47.2846@fe12.lga
>>>> NMB min boxer
>>>> Model 3610NL-04W-B10
>>>> 12 VDC 0.13 AMPERES
>>>>
>>>> I have a wall wart
>>>> Output
>>>> 12VDC 200mA
>>>>
>>>> The fan makes too much noise and pushes much more air than I need.
>>>> If I can slow the fan down to make it quieter it will still push
>>>> enough air for me. How can I accomplish this? Power resistors?
>>>
>>> An off-the-shelf device:
>>>
>>>
>http://www.jab-tech.com/customer/product.php?productid=...
>>> ogle
>
>> Costs 10 times as much as a resistor.

Which is still insignificant compared to what the fan is likely
cooling.

>Depends on the resistor. For opener's the product I mentioned above is
>variable.
>
>The product also provides a low source impedance to the fan motor,
>which tends to reduce stalling and cogging.

I'd want such a device to be able to detect the varying current of
a running fan (I've not tested this but I presume these small fan
motors pull varying pulses of current as different coils are
switched), and if it's NOT varying then it's NOT running, and it
should put more voltage/current into it until it DOES start running.
This could be done with a little circuitry, perhaps even using a
cheap 8-bit microcontroller, which could detect the rotational speed
from the current pulses pulled, and run the fan at any desired RPM up
to it's max.
Even a series diode or pot and emitter-follower transistor circuit
(providing a voltage that does not significantly drop with increased
load) would be better than a resistor which may not put enough voltage
to start up the fan if it gets loaded with dust.

-----
http://mindspring.com/~benbradley
Anonymous
April 4, 2005 9:52:35 PM

Archived from groups: rec.audio.tech (More info?)

Ben Bradley wrote:
>
> I'd want such a device to be able to detect the varying current
of
> a running fan (I've not tested this but I presume these small fan
> motors pull varying pulses of current as different coils are
> switched), and if it's NOT varying then it's NOT running, and it
> should put more voltage/current into it until it DOES start running.

Many PC cooling fans have built-in tachometer. Circuitry on the system
board that monitors rpms, detects stalled fans, etc; provides
interface to software running on the PC.
April 4, 2005 10:57:51 PM

Archived from groups: rec.audio.tech (More info?)

On Sat, 02 Apr 2005 16:46:16 -0500, ren wrote:

> NMB min boxer
> Model 3610NL-04W-B10
> 12 VDC 0.13 AMPERES
>
> I have a wall wart
> Output
> 12VDC 200mA
>
> The fan makes too much noise and pushes much more air than I need. If I
> can slow the fan down to make it quieter it will still push enough air
> for me. How can I accomplish this? Power resistors?

Another way is to connect the black lead to +5 instead of 0v. That puts 7v
across the fan (leave the red lead on +12v!), which is usually enough to
let it start reliably yet still run quietly. I ran the PSU fan like this
on a 486 operating as a router for a couple of years without problems. I
wouldn't recommend delving inside the psu though... ;-)

--
Mick
(no M$ software on here... :-) )
Web: http://www.nascom.info
Web: http://projectedsound.tk
Anonymous
April 5, 2005 4:42:27 PM

Archived from groups: rec.audio.tech (More info?)

ren wrote:
> NMB min boxer
> Model 3610NL-04W-B10
> 12 VDC 0.13 AMPERES
>
> I have a wall wart
> Output
> 12VDC 200mA
>
> The fan makes too much noise and pushes much more air than I need. If I
> can slow the fan down to make it quieter it will still push enough air
> for me. How can I accomplish this? Power resistors?

Try a 12-16 volt light bulb in series with the fan. I've done this
quite a few times with the desired results. The problem with just
regulating the 12 volts down to 5 or so is the fan may not start every
time. A light bulb has a low resistance when cold (off) and will allow
almost a full 12 volt drop across the fan motor when it starts. As the
fan speeds up the bulb is also warming up and increasing resistance,
dropping the voltage across the fan and slowing the fan. You may have
to try a couple different bulbs until you find one that goes well with
the fan, but always use a bulb with a higher voltage rating than your
supply voltage so it doesn't burn out.

I have a few of these in use, some have been going almost twenty years
without having to change the bulb.

-W8LNA


--
Galen Watts
RF Engineer
National Radio Astronomy Observatory
PO Box 2 (or) Route 28/92
Green Bank, West Virginia 24944-0002
http://www.gb.nrao.edu/
304-456-2134
304-456-2200 fax
Anonymous
April 5, 2005 5:20:02 PM

Archived from groups: rec.audio.tech (More info?)

On Mon, 04 Apr 2005 17:52:34 GMT, Ben Bradley
<ben_nospam_bradley@frontiernet.net> wrote:


>>
>>The product also provides a low source impedance to the fan motor,
>>which tends to reduce stalling and cogging.
>
> I'd want such a device to be able to detect the varying current of
>a running fan (I've not tested this but I presume these small fan
>motors pull varying pulses of current as different coils are
>switched), and if it's NOT varying then it's NOT running, and it
>should put more voltage/current into it until it DOES start running.
> This could be done with a little circuitry, perhaps even using a
>cheap 8-bit microcontroller, which could detect the rotational speed
>from the current pulses pulled, and run the fan at any desired RPM up
>to it's max.
> Even a series diode or pot and emitter-follower transistor circuit
>(providing a voltage that does not significantly drop with increased
>load) would be better than a resistor which may not put enough voltage
>to start up the fan if it gets loaded with dust.

That can be solved by putting a fairly large bypass capacitor in
parallel with the resistor. the fan will receive a large starting slug
of current and when the capacitor charge equallizes, the resistor will
take over.

Regards,

Bruce
Hitting reply is futile, use the following:
..(wb4yuc@juno.com).
Anonymous
April 5, 2005 8:27:14 PM

Archived from groups: rec.audio.tech (More info?)

On Tue, 05 Apr 2005 13:20:02 GMT, I@dont.know (Bruce Burke) wrote:

>On Mon, 04 Apr 2005 17:52:34 GMT, Ben Bradley
><ben_nospam_bradley@frontiernet.net> wrote:
>
>
>>>
>>>The product also provides a low source impedance to the fan motor,
>>>which tends to reduce stalling and cogging.
>>
>> I'd want such a device to be able to detect the varying current of
>>a running fan (I've not tested this but I presume these small fan
>>motors pull varying pulses of current as different coils are
>>switched), and if it's NOT varying then it's NOT running, and it
>>should put more voltage/current into it until it DOES start running.
>> This could be done with a little circuitry, perhaps even using a
>>cheap 8-bit microcontroller, which could detect the rotational speed
>>from the current pulses pulled, and run the fan at any desired RPM up
>>to it's max.
>> Even a series diode or pot and emitter-follower transistor circuit
>>(providing a voltage that does not significantly drop with increased
>>load) would be better than a resistor which may not put enough voltage
>>to start up the fan if it gets loaded with dust.
>
>That can be solved by putting a fairly large bypass capacitor in
>parallel with the resistor. the fan will receive a large starting slug
>of current and when the capacitor charge equallizes, the resistor will
>take over.

True, and someone already suggested that, but even with that I can
imagine a temporary power drop where the fan would stop but the
capacitor not be discharged. Perhaps that would never be a problem,
but still, I was thinking of the product Arny linked to. I'd only want
to sell a commercial product like that if I have a very high
confidence of it turning on the fan every time (by, ironically, adding
a microcontroller, the thing every embedded designer fears is in a
product).

>Regards,
>
>Bruce
>Hitting reply is futile, use the following:
>.(wb4yuc@juno.com).

-----
http://mindspring.com/~benbradley
Anonymous
April 6, 2005 8:18:50 AM

Archived from groups: rec.audio.tech (More info?)

Jimbo <jimbo@not-for-sale.com> wrote:

> Kevin McMurtrie <mcmurtri@dslextreme.com> wrote in
> news:mcmurtri-08EDE7.15402302042005@corp-radius.supernews.com:
>
>> In article <UoE3e.14444$g47.2846@fe12.lga>, ren <ren@ren.ren> wrote:
>>
>>> NMB min boxer
>>> Model 3610NL-04W-B10
>>> 12 VDC 0.13 AMPERES
>>>
>>> I have a wall wart
>>> Output
>>> 12VDC 200mA
>>>
>>> The fan makes too much noise and pushes much more air than I need.
>>> If I can slow the fan down to make it quieter it will still push
>>> enough air for me. How can I accomplish this? Power resistors?
>>
>> You can use a three pin 5V regulator that comes in a TO-220 case.
>> They're a dime a dozen and easy to find. Connect +12V to pin IN.
Run
>> a 220 Ohm resistor from pin OUT to pin GND. Put a 330 Ohm
>> potentiometer between pin GND and the negative power. Put the fan on
>> pin OUT and the negative power. That will let you adjust from 5V to
>> full voltage. (A 12V brushless fan usually stalls around 4V)
>>
>> 3-pin
>> 5v Regulator
>> +12V ----- IN OUT ---+------ + Fan
>> GND |
>> | 220 Ohm
>> | |
>> +--------+
>> |
>> Pot
>> |
>> 0V --------------------+------ - Fan
>>
>>
>> Another option is to use a 12V thermal sensing exhaust fan. Pick a
>> fan with the temperature you desire and it only spins as fast as it
>> needs to. They're common at computer parts stores.
>>
>
> Overkill. A 33 ohm 2W resistor will do the job nicely.

I think you will find that the fan desires about 66% of it's rated
voltage to start and about 33% to continue to run once started. You
would do better to put a thermal sensor in series with it so it only
runs when needed.
Anonymous
April 6, 2005 11:16:18 PM

Archived from groups: rec.audio.tech (More info?)

ren wrote:
> NMB min boxer
> Model 3610NL-04W-B10
> 12 VDC 0.13 AMPERES
>
> I have a wall wart
> Output
> 12VDC 200mA
>
> The fan makes too much noise and pushes much more air than I need. If I
> can slow the fan down to make it quieter it will still push enough air
> for me. How can I accomplish this? Power resistors?

Since your already mousing it with a wall wart, why not just try a
9 volt and 6 volt wall wart and see what happens?

At one time, rat shack sold one that had a variable output voltage
switch on it.

Bob

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
Anonymous
April 6, 2005 11:26:51 PM

Archived from groups: rec.audio.tech (More info?)

On Wed, 06 Apr 2005 19:16:18 -0500, Bob Urz <sound@inetnebr.com> wrote:


>ren wrote:
>> NMB min boxer
>> Model 3610NL-04W-B10
>> 12 VDC 0.13 AMPERES
>>
>> I have a wall wart
>> Output
>> 12VDC 200mA
>>
>> The fan makes too much noise and pushes much more air than I need. If I
>> can slow the fan down to make it quieter it will still push enough air
>> for me. How can I accomplish this? Power resistors?

>Since your already mousing it with a wall wart, why not just try a
>9 volt and 6 volt wall wart and see what happens?

>At one time, rat shack sold one that had a variable output voltage
>switch on it.

Or just stick a 70ohm resistor in series.
A lot cheaper than another wallwart.
April 7, 2005 6:21:34 AM

Archived from groups: rec.audio.tech (More info?)

On Wed, 06 Apr 2005 04:18:50 GMT, "wß" <wb@nomail.com> wrote:

>I think you will find that the fan desires about 66% of it's rated
>voltage to start and about 33% to continue to run once started. You
>would do better to put a thermal sensor in series with it so it only
>runs when needed.

It needs current to run, actually, which is why the zener diode method
works better than a resistor - the zener will not restrict current to
the motor, like a resistor will.
Anonymous
April 7, 2005 6:21:35 AM

Archived from groups: rec.audio.tech (More info?)

On Thu, 07 Apr 2005 02:21:34 GMT, dizzy <dizzy@nospam.invalid> wrote:
>On Wed, 06 Apr 2005 04:18:50 GMT, "wß" <wb@nomail.com> wrote:

>>I think you will find that the fan desires about 66% of it's rated
>>voltage to start and about 33% to continue to run once started. You
>>would do better to put a thermal sensor in series with it so it only
>>runs when needed.

>It needs current to run, actually, which is why the zener diode method
>works better than a resistor - the zener will not restrict current to
>the motor, like a resistor will.

Yes it will. It'll reduce the voltage at the motor, reducing the current.
Anonymous
April 9, 2005 1:53:58 PM

Archived from groups: rec.audio.tech (More info?)

Grab a bunch of 1N4001 (or '02 or '04 etc) diodes from Radio Shack.
They're dirt cheap. Put them in series to reduce the voltage and slow
the fan. Each diode will drop around 600mV. Unlike a resistor they
won't interfere with starting current OR the commutation transients.
Like someone posted zeners can work as well and can use fewer parts if
you're dropping a larger voltage (say 5V). However, putting all the
power dissipation in one zener may be too much power for the zener.

As for sensing failure either get a fan with a tachometer output or one
with a stall indicator. Both use the third wire. Connect a resistor
(10k or so) from the third wire to +5V or +12V. You'll get two pulses
per revolution for the tach output or a steady voltage for the stall
indicator.
April 11, 2005 4:46:24 AM

Archived from groups: rec.audio.tech (More info?)

On Wed, 06 Apr 2005 23:09:53 -0500, TCS
<The-Central-Scrutinizer@p.o.b.o.x.com> wrote:

>On Thu, 07 Apr 2005 02:21:34 GMT, dizzy <dizzy@nospam.invalid> wrote:
>>On Wed, 06 Apr 2005 04:18:50 GMT, "wß" <wb@nomail.com> wrote:
>
>>>I think you will find that the fan desires about 66% of it's rated
>>>voltage to start and about 33% to continue to run once started. You
>>>would do better to put a thermal sensor in series with it so it only
>>>runs when needed.
>
>>It needs current to run, actually, which is why the zener diode method
>>works better than a resistor - the zener will not restrict current to
>>the motor, like a resistor will.
>
>Yes it will.

No, it will not, "like a resistor will".

> It'll reduce the voltage at the motor, reducing the current.

Yes, it reduces voltage at the motor, that's what it would be there
for. But, compared to a resistor, a diode adds very little source
impedance, so it will NOT limit the available startup current like a
resistor will.
Anonymous
April 11, 2005 10:38:01 PM

Archived from groups: rec.audio.tech (More info?)

dizzy is correct.

A resistor can work but a zener (or the series string of diodes I
suggested) is a better solution. One of the fans I have draws a
nominal 230mA at 12V. Peak starting current varies but I have measured
over 2A. Each commutation spike is over 1A. With this fan a 24.9 ohm
resistor drops the running voltage to about 6V. However, the fan will
only start about 25% of the time. You can kick start the fan by
spinning it with you finger and it will start running. It also has the
problem of once running if the load increases (back pressure or a
finger to slow the blades down) the fan will stall and may or may not
restart. It can be bad enough that if you put your hand over the
intake (not actually touching the fan) it will stall and not restart.
A 100uF capacitor across the fan can help prevent stalling during
running. However, it decreases the chances of starting since the
capacitor charging current robs the fan of badly needed startup
current.

In the absence of a stiff regulated voltage source a diode (zener or
series string) is the more reliable solution.
Anonymous
April 12, 2005 5:25:38 PM

Archived from groups: rec.audio.tech (More info?)

On 11 Apr 2005 18:38:01 -0700, "Rusty B." <rustybx@knology.net> wrote:

>dizzy is correct.
>
>A resistor can work but a zener (or the series string of diodes I
>suggested) is a better solution. One of the fans I have draws a
>nominal 230mA at 12V. Peak starting current varies but I have measured
>over 2A. Each commutation spike is over 1A. With this fan a 24.9 ohm
>resistor drops the running voltage to about 6V. However, the fan will
>only start about 25% of the time. You can kick start the fan by
>spinning it with you finger and it will start running. It also has the
>problem of once running if the load increases (back pressure or a
>finger to slow the blades down) the fan will stall and may or may not
>restart. It can be bad enough that if you put your hand over the
>intake (not actually touching the fan) it will stall and not restart.
>A 100uF capacitor across the fan can help prevent stalling during
>running. However, it decreases the chances of starting since the
>capacitor charging current robs the fan of badly needed startup
>current.

That's why the capacitor is in shunt with the resistor, not across the
fan.


Regards,

Bruce
Hitting reply is futile, use the following:
..(wb4yuc@juno.com).
April 13, 2005 3:21:43 AM

Archived from groups: rec.audio.tech (More info?)

On Tue, 12 Apr 2005 13:25:38 GMT, I@dont.know (Bruce Burke) wrote:

>On 11 Apr 2005 18:38:01 -0700, "Rusty B." <rustybx@knology.net> wrote:
>
>>dizzy is correct.
>>
>>A resistor can work but a zener (or the series string of diodes I
>>suggested) is a better solution. One of the fans I have draws a
>>nominal 230mA at 12V. Peak starting current varies but I have measured
>>over 2A. Each commutation spike is over 1A. With this fan a 24.9 ohm
>>resistor drops the running voltage to about 6V. However, the fan will
>>only start about 25% of the time. You can kick start the fan by
>>spinning it with you finger and it will start running. It also has the
>>problem of once running if the load increases (back pressure or a
>>finger to slow the blades down) the fan will stall and may or may not
>>restart. It can be bad enough that if you put your hand over the
>>intake (not actually touching the fan) it will stall and not restart.
>>A 100uF capacitor across the fan can help prevent stalling during
>>running. However, it decreases the chances of starting since the
>>capacitor charging current robs the fan of badly needed startup
>>current.
>
>That's why the capacitor is in shunt with the resistor, not across the
>fan.

No.
April 15, 2005 10:36:18 PM

Archived from groups: rec.audio.tech (More info?)

"Rusty B." <rustybx@knology.net> wrote in message
news:1113269881.363101.316410@g14g2000cwa.googlegroups.com...
> dizzy is correct.
>
(snip)

> ... It also has the
> problem of once running if the load increases (back pressure or a
> finger to slow the blades down) the fan will stall and may or may
> not
> restart. It can be bad enough that if you put your hand over the
> intake (not actually touching the fan) it will stall and not
> restart.

If you block the air flow to a fan it does less work and so pulls less
power, not more, so it speeds up. Try it with a canister vacuum
cleaner - block the tube and listen.

Cheers,
Roger
Anonymous
April 15, 2005 10:36:19 PM

Archived from groups: rec.audio.tech (More info?)

On Fri, 15 Apr 2005 18:36:18 -0400, Engineer <nobody@nowhere.net> wrote:
>"Rusty B." <rustybx@knology.net> wrote in message
>news:1113269881.363101.316410@g14g2000cwa.googlegroups.com...
>> dizzy is correct.
>>
>(snip)

>> ... It also has the
>> problem of once running if the load increases (back pressure or a
>> finger to slow the blades down) the fan will stall and may or may
>> not
>> restart. It can be bad enough that if you put your hand over the
>> intake (not actually touching the fan) it will stall and not
>> restart.

>If you block the air flow to a fan it does less work and so pulls less
>power, not more, so it speeds up. Try it with a canister vacuum
>cleaner - block the tube and listen.

I'll keep that in mind next time I have a canister vacuum cleaner that
runs off a DC box fan.
Anonymous
April 17, 2005 2:42:54 AM

Archived from groups: rec.audio.tech (More info?)

Note I did not say "work". I said load.

Technically, you are correct. Work by definition requires
displacement. Pick up a heavy monoblock amplifier and hold it above
your head. Work is done hefting it above your head but no work is done
just holding there.

So blocking the air flow does reduce the work being done in the
technical sense. However, the force exerted by the motor changes
depending upon impeller design. The blades in your vacuum obviously
stall which reduces the load. For the DC brushless fans we're talking
about the load increases.

Try two things:
1. Measure the current drawn by the fan in free air and with the
intake blocked. Which one draws more current and thus power?
2. Put a resistor in series with the fan. Size the resistor so the
fan almost stalls. Block the intake and watch the fan stop.
!