Cooling fan question

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?

If I have the female plug that accepts the adapter's male part, it's a
straight connection is that right?

If let's say I don't have the female plug, I can cut off the male part
of the adapter and solder the adapter wires directly to the fan?

Lastly, if I want to hook up two fans together, can I use a 12V adapter
and hook up the fans in parallel as described above?

 

[John Fields]

On 24 Jul 2006 12:39:58 -0700, sharonesgurvits@gmail.com wrote:

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?

---
Depends. Most unregulated 12V wall-warts will have an output
voltage higher than 12V if their load draws less than the specified
current.

For a fan load it may not matter, but it wouldn't hurt to make some
measurements in order to find out.
---

If I have the female plug that accepts the adapter's male part, it's a
straight connection is that right?

---
Not necessarily, since the polarities may be reversed between the
two.
---

If let's say I don't have the female plug, I can cut off the male part
of the adapter and solder the adapter wires directly to the fan?

---
Yes, but watch the polarity.
---

Lastly, if I want to hook up two fans together, can I use a 12V adapter
and hook up the fans in parallel as described above?

---
Yes, but watch the polarity.


--
John Fields
Professional Circuit Designer

 

Excellent, this is just what I thought. As for the polarity you
mentioned, that is something that i will keep in mind of course. I know
that on most adapters I've seen, they label which part is positive and
which is negative.

Thanks again!


John Fields wrote:

On 24 Jul 2006 12:39:58 -0700, sharonesgurvits@gmail.com wrote:

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?

---
Depends. Most unregulated 12V wall-warts will have an output
voltage higher than 12V if their load draws less than the specified
current.

For a fan load it may not matter, but it wouldn't hurt to make some
measurements in order to find out.
---

If I have the female plug that accepts the adapter's male part, it's a
straight connection is that right?

---
Not necessarily, since the polarities may be reversed between the
two.
---

If let's say I don't have the female plug, I can cut off the male part
of the adapter and solder the adapter wires directly to the fan?

---
Yes, but watch the polarity.
---

Lastly, if I want to hook up two fans together, can I use a 12V adapter
and hook up the fans in parallel as described above?

---
Yes, but watch the polarity.


--
John Fields
Professional Circuit Designer

 

[default]

On 24 Jul 2006 12:39:58 -0700, sharonesgurvits@gmail.com wrote:

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?

If it is rated for 12 volts DC (not AC) it should work.

The wall wart - supplies pulsating DC with an average RMS value of 12
volts when under load - your fan may not like the pulsating DC or may
try to synchronize to it - speed will fluctuate - in that case you'd
need to put a capacitor in there to smooth it out. Wall warts, as a
rule, don't contain filter caps. A few do.

If I have the female plug that accepts the adapter's male part, it's a
straight connection is that right?

DC fans are polarity sensitive and have to have the correct polarity
to work.

If let's say I don't have the female plug, I can cut off the male part
of the adapter and solder the adapter wires directly to the fan?

Lastly, if I want to hook up two fans together, can I use a 12V adapter
and hook up the fans in parallel as described above?

Should work. You may notice speed fluctuations as result of one fan
trying to sync to the other - usually only with two identical fans -
and if the slight noise doesn't bother you it won't hurt anything.

Fan speed and noise can be controlled, over some range, by lowering
the voltage too.

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[John Fields]

On Tue, 25 Jul 2006 07:57:13 -0400, default <none@nobody.net> wrote:

On 24 Jul 2006 12:39:58 -0700, sharonesgurvits@gmail.com wrote:

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?

If it is rated for 12 volts DC (not AC) it should work.

The wall wart - supplies pulsating DC with an average RMS value of 12
volts when under load

---
That's not true. If it were, the DC peaks would be at around 17V.
---

- your fan may not like the pulsating DC or may
try to synchronize to it - speed will fluctuate - in that case you'd
need to put a capacitor in there to smooth it out. Wall warts, as a
rule, don't contain filter caps. A few do.

---
That's also not true. Unregulated AC to DC wall-warts, almost
without exception, contain the filter cap and put out their rated DC
voltage (plus ripple) when properly loaded.


--
John Fields
Professional Circuit Designer

 

[default]

On Tue, 25 Jul 2006 11:38:03 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Tue, 25 Jul 2006 07:57:13 -0400, default <none@nobody.net> wrote:

On 24 Jul 2006 12:39:58 -0700, sharonesgurvits@gmail.com wrote:

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?

If it is rated for 12 volts DC (not AC) it should work.

The wall wart - supplies pulsating DC with an average RMS value of 12
volts when under load

---
That's not true. If it were, the DC peaks would be at around 17V.

Well got one here and measured DC out with a scope and has 18.6 VDC
zero to peak - unloaded - rated 12VDC 200 ma.

---

- your fan may not like the pulsating DC or may
try to synchronize to it - speed will fluctuate - in that case you'd
need to put a capacitor in there to smooth it out. Wall warts, as a
rule, don't contain filter caps. A few do.

---
That's also not true. Unregulated AC to DC wall-warts, almost
without exception, contain the filter cap and put out their rated DC
voltage (plus ripple) when properly loaded.

Damn I must be the exception then - three out of three had 100% ripple
- but I have seen caps in some of the ones I took apart.

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[John Fields]

On Tue, 25 Jul 2006 13:18:57 -0400, default <none@nobody.net> wrote:

On Tue, 25 Jul 2006 11:38:03 -0500, John Fields
jfields@austininstruments.com> wrote:

On Tue, 25 Jul 2006 07:57:13 -0400, default <none@nobody.net> wrote:

On 24 Jul 2006 12:39:58 -0700, sharonesgurvits@gmail.com wrote:

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?

If it is rated for 12 volts DC (not AC) it should work.

The wall wart - supplies pulsating DC with an average RMS value of 12
volts when under load

---
That's not true. If it were, the DC peaks would be at around 17V.

Well got one here and measured DC out with a scope and has 18.6 VDC
zero to peak - unloaded - rated 12VDC 200 ma.

---
What does it measure loaded to 200mA average DC out?
---

- your fan may not like the pulsating DC or may
try to synchronize to it - speed will fluctuate - in that case you'd
need to put a capacitor in there to smooth it out. Wall warts, as a
rule, don't contain filter caps. A few do.

---
That's also not true. Unregulated AC to DC wall-warts, almost
without exception, contain the filter cap and put out their rated DC
voltage (plus ripple) when properly loaded.

Damn I must be the exception then - three out of three had 100% ripple
- but I have seen caps in some of the ones I took apart.

---
Maybe they were purpose built to be used with a specific piece of
equipment which had the filter external to the wall wart?


--
John Fields
Professional Circuit Designer

 

[default]

On Tue, 25 Jul 2006 15:11:14 -0500, John Fields
<jfields@austininstruments.com> wrote:

What does it measure loaded to 200mA average DC out?

Fuse on my ammeter is dead but with a 75 ohm 5 watt resistor I see
16.4 zero to peak. May be a poor choice, I think this particular wall
wart was to float charge a battery.

---
Maybe they were purpose built to be used with a specific piece of
equipment which had the filter external to the wall wart?

No telling where some these came from, just acquired them in my junk

box (room). Nothing on the label suggests a product manufacturer.

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[John Fields]

On Tue, 25 Jul 2006 16:23:04 -0400, default <none@nobody.net> wrote:

On Tue, 25 Jul 2006 15:11:14 -0500, John Fields
jfields@austininstruments.com> wrote:


What does it measure loaded to 200mA average DC out?

Fuse on my ammeter is dead but with a 75 ohm 5 watt resistor I see
16.4 zero to peak. May be a poor choice, I think this particular wall
wart was to float charge a battery.

---
That makes sense, since what's required to charge a battery is to
pump current into it until its voltage rises to where it's supposed
to be to be charged. No filter is required because it wouldn't do
anything helpful.

Good call. I hadn't thought about that application, so I guess
there _are_ quite a few wall-warts out there without filters.

Thanks.
---

---
Maybe they were purpose built to be used with a specific piece of
equipment which had the filter external to the wall wart?

No telling where some these came from, just acquired them in my junk
box (room). Nothing on the label suggests a product manufacturer.

---
OK...


--
John Fields
Professional Circuit Designer

 

[Jamie]

In <s8kcc2tj0jc6pbs1d8jnhldo1gvmsshurp@4ax.com>,
default <none@nobody.net> mentions:

On Tue, 25 Jul 2006 11:38:03 -0500, John Fields
jfields@austininstruments.com> wrote:

On Tue, 25 Jul 2006 07:57:13 -0400, default <none@nobody.net> wrote:

On 24 Jul 2006 12:39:58 -0700, sharonesgurvits@gmail.com wrote:

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?

If it is rated for 12 volts DC (not AC) it should work.

The wall wart - supplies pulsating DC with an average RMS value of 12
volts when under load

---
That's not true. If it were, the DC peaks would be at around 17V.

Well got one here and measured DC out with a scope and has 18.6 VDC
zero to peak - unloaded - rated 12VDC 200 ma.

My own experiments with walwarts concur with yours, they seem to have very
strange voltages. (particularly new ones w/out a load) I've suspected it
was the newer switched minimal-transformer transformers. (I hate those..)

For whatever reasons, (suspect each one is different) it's always a good idea
to make sure there is a small load on them if you want the voltage right.

---
That's also not true. Unregulated AC to DC wall-warts, almost
without exception, contain the filter cap and put out their rated DC
voltage (plus ripple) when properly loaded.

Damn I must be the exception then - three out of three had 100% ripple
- but I have seen caps in some of the ones I took apart.

I've seen it too, (the ripple) I usually put a capacitor on them when I power
something sensitive with them, though, I doubt it matters much with a motor.
(I have a walwart that makes a mess of a radio if I don't)

Jamie
--
http://www.geniegate.com Custom web programming
guhzo_42@lnubb.pbz (rot13) User Management Solutions

 

[Ernie Werbel]

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?

AC != DC. If the fan runs on 12 volts DC then you can't connect AC to it or
you will destroy it. You will have to feed it through a rectifier first.
If the 12VAC is actually an RMS value, the real value (RMS * SQRT(2)) is
about 17V peak. So you will need to drop the extra 5V somewhere (a 5.1
Zener could do the job). But I would say if you can find an adapter that
outputs 12 volts DC, that would be the best way to go.

If I have the female plug that accepts the adapter's male part, it's a
straight connection is that right?

It doesn't matter how you connect it physically, as long as the voltage is
correct.

If let's say I don't have the female plug, I can cut off the male part
of the adapter and solder the adapter wires directly to the fan?

Please see above.

Lastly, if I want to hook up two fans together, can I use a 12V adapter
and hook up the fans in parallel as described above?

Parallel can work so long as the voltage is the same. Remember DC != AC
(not equal). Just make sure that the adapter can put out enough current
(amperage) to drive all of the fans. You add up the currents of all the
fans in parallel. Your power adapter has to be able to put out at least
this much current.

 

[John Fields]

On Thu, 27 Jul 2006 23:20:00 GMT, "Ernie Werbel"
<no_spam_please@fake_email_address.xyz> wrote:

I've got a plain 12V DC cooling fan that I took out of an old computer
that I'd like to reuse in another place. If i got an ordinary AC
adapter that's rated at 12V, I can wire the adapter to the fan without
any problems correct?


AC != DC. If the fan runs on 12 volts DC then you can't connect AC to it or
you will destroy it. You will have to feed it through a rectifier first.
If the 12VAC is actually an RMS value, the real value (RMS * SQRT(2)) is
about 17V peak. So you will need to drop the extra 5V somewhere (a 5.1
Zener could do the job).

---
No. If the adapter puts out 12V RMS, and the motor runs on 12VDC,
then as long as the output of the rectifer isn't filtered everything
will be just as it should be, neglecting the timing/syncing effects
that rectified AC may have on the fan.
---

But I would say if you can find an adapter that
outputs 12 volts DC, that would be the best way to go.

---
Unless it's regulated, it needs to put out 12V at the fan's rated
current, since the lightly loaded output voltage may be more than
the fan was designed to handle.
---

If I have the female plug that accepts the adapter's male part, it's a
straight connection is that right?


It doesn't matter how you connect it physically, as long as the voltage is
correct.

---
If you go back and read the thread, particularly:

news:1153772588.328262.44900@p79g2000cwp.googlegroups.com

You'll find that she's using an AC ->DC adapter, so the polarity of
the connection becomes important.
---

If let's say I don't have the female plug, I can cut off the male part
of the adapter and solder the adapter wires directly to the fan?


Please see above.

---
Please see above.

--
John Fields
Professional Circuit Designer