running case fans at low voltage

[divxdude]

so the cheapo fan in ATX supply is about shot ...looking at 120mm fans
on Ebay trying to find a bargain.
found some nice ballbearing fans rated at 48vdc. had a note about
24vdc starting volts and i was wondring if they would turn slow and
quiet at 12vdc.
the seller said he never tried so i dug out some 12v 40mm ballbearing
fans i have..good ones Sanyo denki or something like that. i put 3.5
on them and they semd to like it , turning slow and quiet.
can i expect the same from the larger 120s anyone know?
i tried the same with a 120mm i have but did not work at 3v tho the
fan was rated for 12vdc.

my question is does anyone have a 48vdc fan they run at 12vdc? or
just wont work?

 

[Baron]

divxdude Inscribed thus:

so the cheapo fan in ATX supply is about shot ...looking at 120mm fans
on Ebay trying to find a bargain.
found some nice ballbearing fans rated at 48vdc. had a note about
24vdc starting volts and i was wondring if they would turn slow and
quiet at 12vdc.
the seller said he never tried so i dug out some 12v 40mm ballbearing
fans i have..good ones Sanyo denki or something like that. i put 3.5
on them and they semd to like it , turning slow and quiet.
can i expect the same from the larger 120s anyone know?
i tried the same with a 120mm i have but did not work at 3v tho the
fan was rated for 12vdc.

my question is does anyone have a 48vdc fan they run at 12vdc? or
just wont work?

Most of the fans I've seen and used have been electronically commutated
and will run at voltages much lower and higher than the voltage they
are rated at. The problem is that they don't move as much air at lower
speeds and the drag may not allow them to start up at all if you reduce
the voltage too much. I would not want to vary the voltage by more
than, say +/- 25% ie 36v for a 48v fan. You can pick up 12v ex
equipment fans for ÂŁ1 or so, that are all but new.

--
Best Regards:
Baron.

 

[Lostgallifreyan]

divxdude <divx.dude@gmail.com> wrote in news:edb4a4fa-f298-4617-b4e1-
23962450901a@o4g2000vbo.googlegroups.com:

so the cheapo fan in ATX supply is about shot ...looking at 120mm fans
on Ebay trying to find a bargain.
found some nice ballbearing fans rated at 48vdc. had a note about
24vdc starting volts and i was wondring if they would turn slow and
quiet at 12vdc.
the seller said he never tried so i dug out some 12v 40mm ballbearing
fans i have..good ones Sanyo denki or something like that. i put 3.5
on them and they semd to like it , turning slow and quiet.
can i expect the same from the larger 120s anyone know?
i tried the same with a 120mm i have but did not work at 3v tho the
fan was rated for 12vdc.

my question is does anyone have a 48vdc fan they run at 12vdc? or
just wont work?

I've run 12V fans at 7 volts, from the 5V and 12V lines on an ATX supply).
That works ok. The speed drops off sharply as voltage falls from intended
values though, so you won't get a lot out of a 48V fan on a 12V supply, you'd
be lucky it it got enough torque to start, or even maintain running if you
nudged it first. And a stalled fan will overheat fatally even if you're
feeding it from a lower voltage. (Has more to do with the electrics than the
lack of airflow).

 

[ian field]

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns9D89E6978CB5Czoodlewurdle@216.196.109.145...

divxdude <divx.dude@gmail.com> wrote in news:edb4a4fa-f298-4617-b4e1-
23962450901a@o4g2000vbo.googlegroups.com:

so the cheapo fan in ATX supply is about shot ...looking at 120mm fans
on Ebay trying to find a bargain.
found some nice ballbearing fans rated at 48vdc. had a note about
24vdc starting volts and i was wondring if they would turn slow and
quiet at 12vdc.
the seller said he never tried so i dug out some 12v 40mm ballbearing
fans i have..good ones Sanyo denki or something like that. i put 3.5
on them and they semd to like it , turning slow and quiet.
can i expect the same from the larger 120s anyone know?
i tried the same with a 120mm i have but did not work at 3v tho the
fan was rated for 12vdc.

my question is does anyone have a 48vdc fan they run at 12vdc? or
just wont work?




I've run 12V fans at 7 volts, from the 5V and 12V lines on an ATX supply).
That works ok. The speed drops off sharply as voltage falls from intended
values though, so you won't get a lot out of a 48V fan on a 12V supply,
you'd
be lucky it it got enough torque to start, or even maintain running if you
nudged it first. And a stalled fan will overheat fatally even if you're
feeding it from a lower voltage. (Has more to do with the electrics than
the
lack of airflow).

Running from the +12V & -12V outputs might be a partial solution, but
personally I wouldn't want to risk such a reduction in airflow.

 

[GregS]

In article <8bbNn.26024$jh6.9642@hurricane>, "ian field" <gangprobing.alien@ntlworld.com> wrote:

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns9D89E6978CB5Czoodlewurdle@216.196.109.145...
divxdude <divx.dude@gmail.com> wrote in news:edb4a4fa-f298-4617-b4e1-
23962450901a@o4g2000vbo.googlegroups.com:

so the cheapo fan in ATX supply is about shot ...looking at 120mm fans
on Ebay trying to find a bargain.
found some nice ballbearing fans rated at 48vdc. had a note about
24vdc starting volts and i was wondring if they would turn slow and
quiet at 12vdc.
the seller said he never tried so i dug out some 12v 40mm ballbearing
fans i have..good ones Sanyo denki or something like that. i put 3.5
on them and they semd to like it , turning slow and quiet.
can i expect the same from the larger 120s anyone know?
i tried the same with a 120mm i have but did not work at 3v tho the
fan was rated for 12vdc.

my question is does anyone have a 48vdc fan they run at 12vdc? or
just wont work?




I've run 12V fans at 7 volts, from the 5V and 12V lines on an ATX supply).
That works ok. The speed drops off sharply as voltage falls from intended
values though, so you won't get a lot out of a 48V fan on a 12V supply,
you'd
be lucky it it got enough torque to start, or even maintain running if you
nudged it first. And a stalled fan will overheat fatally even if you're
feeding it from a lower voltage. (Has more to do with the electrics than
the
lack of airflow).


Running from the +12V & -12V outputs might be a partial solution, but
personally I wouldn't want to risk such a reduction in airflow.

If i want to change voltage or test the fan, i hook it up
to a variable supply and test it out. Whats so hard ?

greg

 

[Lostgallifreyan]

zekfrivo@zekfrivolous.com (GregS) wrote in
news:hu5nt6$rj2$7@usenet01.srv.cis.pitt.edu:

In article <8bbNn.26024$jh6.9642@hurricane>, "ian field"
gangprobing.alien@ntlworld.com> wrote:

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns9D89E6978CB5Czoodlewurdle@216.196.109.145...
divxdude <divx.dude@gmail.com> wrote in news:edb4a4fa-f298-4617-b4e1-
23962450901a@o4g2000vbo.googlegroups.com:

so the cheapo fan in ATX supply is about shot ...looking at 120mm
fans on Ebay trying to find a bargain.
found some nice ballbearing fans rated at 48vdc. had a note about
24vdc starting volts and i was wondring if they would turn slow and
quiet at 12vdc.
the seller said he never tried so i dug out some 12v 40mm ballbearing
fans i have..good ones Sanyo denki or something like that. i put 3.5
on them and they semd to like it , turning slow and quiet.
can i expect the same from the larger 120s anyone know?
i tried the same with a 120mm i have but did not work at 3v tho the
fan was rated for 12vdc.

my question is does anyone have a 48vdc fan they run at 12vdc? or
just wont work?




I've run 12V fans at 7 volts, from the 5V and 12V lines on an ATX
supply). That works ok. The speed drops off sharply as voltage falls
from intended values though, so you won't get a lot out of a 48V fan
on a 12V supply, you'd
be lucky it it got enough torque to start, or even maintain running if
you nudged it first. And a stalled fan will overheat fatally even if
you're feeding it from a lower voltage. (Has more to do with the
electrics than the
lack of airflow).


Running from the +12V & -12V outputs might be a partial solution, but
personally I wouldn't want to risk such a reduction in airflow.



If i want to change voltage or test the fan, i hook it up
to a variable supply and test it out. Whats so hard ?

greg

Using one when you haven't got one? Lot of people haven't. If any of them
are reading now, Google LM317, then try to find one, the datasheet tells you
a few useful circuits. Very few parts. A car battery charger or similar 12V
supply makes a useful raw supply for it. Even standard fixed regulators can
be made to regulate arbitrary voltages at useful currents.

Re testing fans for low speeds, I just stick resistors in the supply wires
and read volts and amps for the fan when I find a resistor that gets it
turning how I want it. That's the easiest way I know. IF you have a meter...

 

[Lostgallifreyan]

Lostgallifreyan <no-one@nowhere.net> wrote in
news:Xns9D8BB43B6B0A4zoodlewurdle@216.196.109.145:

Re testing fans for low speeds, I just stick resistors in the supply
wires and read volts and amps for the fan when I find a resistor that
gets it turning how I want it. That's the easiest way I know. IF you
have a meter...

And if you haven't, just leave the resistor there and tape it up after
twisting wire connections firmly together and removing stray strands. This is
something I could do when I was too young to have my own money never mind be
trusted alone with a soldering iron. Just use your wits and try to think of
what can go wrong, like dust, grime, blocked airways, slowing the fan till
it stalls. Don't leave too weak a margin of low speed or it won't work for
long.

 

[GregS]

In article <Xns9D8BB43B6B0A4zoodlewurdle@216.196.109.145>, Lostgallifreyan <no-one@nowhere.net> wrote:

zekfrivo@zekfrivolous.com (GregS) wrote in
news:hu5nt6$rj2$7@usenet01.srv.cis.pitt.edu:

In article <8bbNn.26024$jh6.9642@hurricane>, "ian field"
gangprobing.alien@ntlworld.com> wrote:

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns9D89E6978CB5Czoodlewurdle@216.196.109.145...
divxdude <divx.dude@gmail.com> wrote in news:edb4a4fa-f298-4617-b4e1-
23962450901a@o4g2000vbo.googlegroups.com:

so the cheapo fan in ATX supply is about shot ...looking at 120mm
fans on Ebay trying to find a bargain.
found some nice ballbearing fans rated at 48vdc. had a note about
24vdc starting volts and i was wondring if they would turn slow and
quiet at 12vdc.
the seller said he never tried so i dug out some 12v 40mm ballbearing
fans i have..good ones Sanyo denki or something like that. i put 3.5
on them and they semd to like it , turning slow and quiet.
can i expect the same from the larger 120s anyone know?
i tried the same with a 120mm i have but did not work at 3v tho the
fan was rated for 12vdc.

my question is does anyone have a 48vdc fan they run at 12vdc? or
just wont work?




I've run 12V fans at 7 volts, from the 5V and 12V lines on an ATX
supply). That works ok. The speed drops off sharply as voltage falls
from intended values though, so you won't get a lot out of a 48V fan
on a 12V supply, you'd
be lucky it it got enough torque to start, or even maintain running if
you nudged it first. And a stalled fan will overheat fatally even if
you're feeding it from a lower voltage. (Has more to do with the
electrics than the
lack of airflow).


Running from the +12V & -12V outputs might be a partial solution, but
personally I wouldn't want to risk such a reduction in airflow.



If i want to change voltage or test the fan, i hook it up
to a variable supply and test it out. Whats so hard ?

greg


Using one when you haven't got one? Lot of people haven't. If any of them
are reading now, Google LM317, then try to find one, the datasheet tells you
a few useful circuits. Very few parts. A car battery charger or similar 12V
supply makes a useful raw supply for it. Even standard fixed regulators can
be made to regulate arbitrary voltages at useful currents.

Re testing fans for low speeds, I just stick resistors in the supply wires
and read volts and amps for the fan when I find a resistor that gets it
turning how I want it. That's the easiest way I know. IF you have a meter...

I guess you could also wire up a dozen AA cells and select what voltage you
want. The resistor idea is good.

I have wired fans for temperature control by varying speed with thermisters, etc.,, both DC and AC.

greg

 

[Lostgallifreyan]

zekfrivo@zekfrivolous.com (GregS) wrote in
news:hu6ca0$30b$1@usenet01.srv.cis.pitt.edu:

I have wired fans for temperature control by varying speed with
thermisters, etc.,, both DC and AC.

Interesting. I've wired thermistors to an entirely passive network as part of
a laser diode constant current drive, to match temperature coefficient
inversely for constant(ish) output. I think the variation might be too small
for fan speed control though, unless some fairly large and expensive
thermistors are used. Cheaper to use a small cheap one and an active gain
stage to control the fan.

 

[ian field]

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns9D8BDFCFB4604zoodlewurdle@216.196.109.145...

zekfrivo@zekfrivolous.com (GregS) wrote in
news:hu6ca0$30b$1@usenet01.srv.cis.pitt.edu:

I have wired fans for temperature control by varying speed with
thermisters, etc.,, both DC and AC.



Interesting. I've wired thermistors to an entirely passive network as part
of
a laser diode constant current drive, to match temperature coefficient
inversely for constant(ish) output. I think the variation might be too
small
for fan speed control though, unless some fairly large and expensive
thermistors are used. Cheaper to use a small cheap one and an active gain
stage to control the fan.

Older PC PSUs often had a small sub panel clipped to a convenient heatsink
with a few transistors between the thermistor and fan, they were easier to
salvage and use for other things.

Later PSUs have the fan control circuit integrated onto the main PCB, but
the circuit is pretty simple - usually no more than 3 transistors and a few
resistors, so its easy to trace the circuit by hand and copy it on a bit of
stripboard.

 

[Baron]

GregS Inscribed thus:

In article <Xns9D8BB43B6B0A4zoodlewurdle@216.196.109.145>,
Lostgallifreyan <no-one@nowhere.net> wrote:
zekfrivo@zekfrivolous.com (GregS) wrote in
news:hu5nt6$rj2$7@usenet01.srv.cis.pitt.edu:

In article <8bbNn.26024$jh6.9642@hurricane>, "ian field"
gangprobing.alien@ntlworld.com> wrote:

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns9D89E6978CB5Czoodlewurdle@216.196.109.145...
divxdude <divx.dude@gmail.com> wrote in
news:edb4a4fa-f298-4617-b4e1-
23962450901a@o4g2000vbo.googlegroups.com:

so the cheapo fan in ATX supply is about shot ...looking at 120mm
fans on Ebay trying to find a bargain.
found some nice ballbearing fans rated at 48vdc. had a note about
24vdc starting volts and i was wondring if they would turn slow
and quiet at 12vdc.
the seller said he never tried so i dug out some 12v 40mm
ballbearing fans i have..good ones Sanyo denki or something like
that. i put 3.5 on them and they semd to like it , turning slow
and quiet. can i expect the same from the larger 120s anyone
know? i tried the same with a 120mm i have but did not work at 3v
tho the fan was rated for 12vdc.

my question is does anyone have a 48vdc fan they run at 12vdc?
or just wont work?




I've run 12V fans at 7 volts, from the 5V and 12V lines on an ATX
supply). That works ok. The speed drops off sharply as voltage
falls from intended values though, so you won't get a lot out of a
48V fan on a 12V supply, you'd
be lucky it it got enough torque to start, or even maintain
running if you nudged it first. And a stalled fan will overheat
fatally even if you're feeding it from a lower voltage. (Has more
to do with the electrics than the
lack of airflow).


Running from the +12V & -12V outputs might be a partial solution,
but personally I wouldn't want to risk such a reduction in airflow.



If i want to change voltage or test the fan, i hook it up
to a variable supply and test it out. Whats so hard ?

greg


Using one when you haven't got one? Lot of people haven't. If any
of them are reading now, Google LM317, then try to find one, the
datasheet tells you a few useful circuits. Very few parts. A car
battery charger or similar 12V supply makes a useful raw supply for
it. Even standard fixed regulators can be made to regulate arbitrary
voltages at useful currents.

Re testing fans for low speeds, I just stick resistors in the supply
wires and read volts and amps for the fan when I find a resistor that
gets it turning how I want it. That's the easiest way I know. IF you
have a meter...



I guess you could also wire up a dozen AA cells and select what
voltage you want. The resistor idea is good.

I have wired fans for temperature control by varying speed with
thermisters, etc.,, both DC and AC.

greg

Some variable speed fans have a thermistor built in. Its usually in the
air flow path so as the air gets hotter the fan spins faster. You can
often find them in computer PSU's.

--
Best Regards:
Baron.

 

[Lostgallifreyan]

"ian field" <gangprobing.alien@ntlworld.com> wrote in
news:E0ANn.58284$bb1.41145@hurricane:

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns9D8BDFCFB4604zoodlewurdle@216.196.109.145...
zekfrivo@zekfrivolous.com (GregS) wrote in
news:hu6ca0$30b$1@usenet01.srv.cis.pitt.edu:

I have wired fans for temperature control by varying speed with
thermisters, etc.,, both DC and AC.



Interesting. I've wired thermistors to an entirely passive network as
part of
a laser diode constant current drive, to match temperature coefficient
inversely for constant(ish) output. I think the variation might be too
small
for fan speed control though, unless some fairly large and expensive
thermistors are used. Cheaper to use a small cheap one and an active
gain stage to control the fan.


Older PC PSUs often had a small sub panel clipped to a convenient
heatsink with a few transistors between the thermistor and fan, they
were easier to salvage and use for other things.

Later PSUs have the fan control circuit integrated onto the main PCB,
but the circuit is pretty simple - usually no more than 3 transistors
and a few resistors, so its easy to trace the circuit by hand and copy
it on a bit of stripboard.

Worth doing for sure, few parts to deal with. I like passive though, and I
suspect that some systems overcompensate wildly, starting strong after an
initial almost idle state, then backing off sharply. These weren't on/off,
they had various states they'd settle at, it was just a bit extreme, not
very proportional. Judging by how much change in speed a smallish change
in series resistance makes, a passive network might do it, though
calculating it might be more trouble than using a simple active control.

Mine wasn't entirely passive, it was an NTC thermistance wired into the
sense resistance of an LM317 in constant current config, so the whole
thing is a 2-terminal system that can be added like a series resistor. It
varied laser diode current to over 25% at 50°C above what it would be at
0°C. As far as I remember, wiring for more extreme swings was possible. It
did depend on the three parallel SMT thermistors being somehow mounted on
a heatsink though, dissipation was great enough that waving them in the
air stream of a fan wouldn't be good enough. They could be mounted on the
first heatsink the air hit though.

I wrote it all up neatly one time thinking of posting it somewhere but
didn't, for long. At the risk of overdoing it, here it is. Word wrap might
make it look ugly but I'm trying to post with no wrap to prevent that...


------------------------------------------------------------------------------------------------

Opnext/Hitachi Laser Diode HL6526FM; current for 80 mW output at specified temperature.

Sample 0°C=107 mA Sample 0°C=108 mA Sample 0°C=109 mA Sample 0°C=109 mA
1: 25°C=116 mA 2: 25°C=118 mA 3: 25°C=118 mA 4: 25°C=118 mA
50°C=133 mA 50°C=136 mA 50°C=136 mA 50°C=136 mA

------------------------------------------------------------------------------------------------

RS order code 247-7244, 150 ohm, SMT NTC thermistor, b constant 2750, 5% tolerance and low cost.

Power rating at 25°C 125mW
Optimum working dissipation 1mW
Resistance tolerance 5%
b constant 2750 to 4100
Thermal dissipation constant 1.5mW/°C
Thermal time constant 4 seconds
Operating temperature range -55°C to +125°C
Dimensions L=2, W=1.25, TO5


Equations for deriving values from the technical data, 1K scale, 2.326K at 0°C and 0.49K at 50°C:


T = K(R/1000) T is the value of the compound thermistor at given temperature,
K is the known value of a 1K thermistor at given temperature,
and R is the known value of the compound thermistor at 25°C.

1/F + 1/T I is the resulting current in amps, supplied by the regulator.
I = --------- F is the value of the known fixed resistance,
0.8 and T is carried over from before.

P = T(1.25/T)^2 P is the resulting power dissipation at given temperature.


If T is 75 ohms, made from two 150 ohm NTC thermistors in parallel, and F is a network of metal
film resistors equal to 12.4 ohms at 1% tolerance, the regulator tracks the current/temperature
curve of the laser diode extremely well, and the total regulator parts cost is less than Ł2.00.


|ŻŻŻŻŻŻŻŻŻ| Ą--/\/\/\--Ą
I for 0°C-50°C | | Ś F Ś
-----------| LM317 T |---Ś Ś---Ą-----------
0°C=107.97 mA | | Ś T /Ż Ś Ś
25°C=117.47 mA |_________| !--/\/\/\--! Ś
50°C=134.82 mA Ś / Ś
Ś Ś
!-----------------------!

Dissipation.

0°C=8.96 mW They will be dissipating a lot more power than the optimum 1 mW,
25°C=20.8 mW but well within specs for the operating temperature range. They
50°C=21.3 mW will be thermally clamped, bonded to the laser diode heatsink.

------------------------------------------------------------------------------------------------

Note: While scaling is excellent, the offset isn't, given only 5% tolerance in the thermistors,
so a 1% metal film resistor network must be built with a variable resistance to finely tune it.
The statement (1/75+1/(1/(1/(4*3.3)+1/(100+470))))/0.8 allows a 470 ohm multiturn preset to set
the current between about 4 mA and 6 mA off-range, just enough to accommodate a 5% error. While
it looks safe, the calculation predicts a very non-linear response, so this one must be tested.
The main resistance will be four 3.3 ohm resistors in series, parallel with a network of series
values, 100 ohms and the 470 ohm preset. Which is wired so the current falls, not rises, if it
goes open circuit.

------------------------------------------------------------------------------------------------

 

[Lostgallifreyan]

Baron <baron.nospam@linuxmaniac.nospam.net> wrote in
news:hu6kjt$q3t$2@news.eternal-september.org:

Some variable speed fans have a thermistor built in. Its usually in the
air flow path so as the air gets hotter the fan spins faster. You can
often find them in computer PSU's.

Nasty things. Well, there's the poor thermal coupling between sink and
air, and a horrible lag in response, plus a tendency to wildly overshoot in a
crude compromise for that lag. I like the ones with a probe on wires that you
can place onto a heatsink though. They can usefully protect something very
specific then.