fans in series...

[server]

Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

Here\'s the idea:

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1




--

I yam what I yam - Popeye

 

[John Robertson]

On 2022/01/12 7:48 p.m., jlarkin@highlandsniptechnology.com wrote:

Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

Uneven airflow loading could burn out a fan...

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

This sounds like it would work. Should probably add a fuse to it.

Worst case, I can make a 48 to 12 switcher.

Zeners and pass transistors would also work.

John :-#)#

Here\'s the idea:

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1

--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"

 

[Jan Panteltje]

On a sunny day (Wed, 12 Jan 2022 19:48:59 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
<hm5vtg599rmbp88m0smfr7bsd05e4nh18t@4ax.com>:

Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

Here\'s the idea:

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1

My system using Meanwell 7.5 V supplies in series allows any
voltage output in steps of about 6 to 8 V.

In your case and if customer has only 48 V,
bolt an ebay 48 V to 12 V switcher in the housing,
maybe something like this:
https://www.ebay.com/itm/383691634312
add a fuse in primary..

 

[Chris Jones]

On 13/01/2022 14:48, jlarkin@highlandsniptechnology.com wrote:

Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

You should use the switcher or buy 48V fans.

More fancy fans have things in them to intermittently attempt to restart
after they stall without running the windings continuously, and other
fancy things. There is no reason to believe that the fans would each
want to draw the same current at all times. If you put zeners across
each fan, it might work, but in the event that one fan doesn\'t draw
current (e.g. stalls and goes into intermittent restart attempts) the
corresponding zener might get very hot.

 

[server]

On Thu, 13 Jan 2022 22:16:20 +1100, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

On 13/01/2022 14:48, jlarkin@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

You should use the switcher or buy 48V fans.

Why?

For some reason, 35mm fans only seem to come in 5 or 12 volts. They
only need 50-90 mA. High voltage switchers are a nuisance.

This might be OK:

https://www.mouser.com/ProductDetail/XP-Power/SRH05S12?qs=w%2Fv1CP2dgqoB4ok%252BZU%252BVXg%3D%3D

$7, if we can get them.

More fancy fans have things in them to intermittently attempt to restart
after they stall without running the windings continuously, and other
fancy things. There is no reason to believe that the fans would each
want to draw the same current at all times. If you put zeners across
each fan, it might work, but in the event that one fan doesn\'t draw
current (e.g. stalls and goes into intermittent restart attempts) the
corresponding zener might get very hot.

But we have forced air cooling!



--

I yam what I yam - Popeye

 

[Chris Jones]

On 13/01/2022 22:41, jlarkin@highlandsniptechnology.com wrote:

On Thu, 13 Jan 2022 22:16:20 +1100, Chris Jones
lugnut808@spam.yahoo.com> wrote:

On 13/01/2022 14:48, jlarkin@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

You should use the switcher or buy 48V fans.

Why?

Well, if you are sure that your fans don\'t have anything smart in them
and always draw current, monotonically increasing with voltage, or if
the power of the fans is small enough that you can dissipate the same
amount of power in a parallel zener if you need to, then fine you could
put them in series.

I have seen some fans that when you stall them, they go into some
low-power mode and then every second or two, briefly have a go at
restarting, so they are high-impedance most of the time then draw a big
spike of current when they try to restart. I don\'t think these would
work well in series without the zeners.

 

[Cydrome Leader]

jlarkin@highlandsniptechnology.com wrote:

Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

Here\'s the idea:

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1

Don\'t do it. They will not share voltage and the losers will burn out on
the first start. Been there, done that. Find 48 volt telecom fans or 24
volts ones and use individual series resistors. Fans are mechanical so
don\'t increase your failure rate by using any sort of chain.

 

[whit3rd]

On Thursday, January 13, 2022 at 5:34:42 PM UTC-8, Cydrome Leader wrote:

jla...@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

Don\'t do it. They will not share voltage and the losers will burn out on
the first start.

Yeah, it\'s the equivalent of a house with a floating neutral; well known for wild
voltage fluctuations. If the fans are identical, after the first fails, will the others
fail the same way, and make a short? Or will one or more fail open and leave
everything unventilated pending combustion?

I want to see that video.
Meanwhile, enjoy this one
<https://youtu.be/YSOpl4gG95w>

 

[server]

On Fri, 14 Jan 2022 01:34:35 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

Here\'s the idea:

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1

Don\'t do it. They will not share voltage and the losers will burn out on
the first start. Been there, done that. Find 48 volt telecom fans or 24
volts ones and use individual series resistors. Fans are mechanical so
don\'t increase your failure rate by using any sort of chain.

The 35mm fans I want to use seem to only come in 5v and 12v. And the
supply is 48.

I suppose I can make a 48-to-12 switcher on this board. Still, a
series string with shunt zeners ought to work.



--

I yam what I yam - Popeye

 

[Lasse Langwadt Christensen]

søndag den 16. januar 2022 kl. 16.30.17 UTC+1 skrev jla...@highlandsniptechnology.com:

On Fri, 14 Jan 2022 01:34:35 -0000 (UTC), Cydrome Leader
pres...@MUNGEpanix.com> wrote:

jla...@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

Here\'s the idea:

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1

Don\'t do it. They will not share voltage and the losers will burn out on
the first start. Been there, done that. Find 48 volt telecom fans or 24
volts ones and use individual series resistors. Fans are mechanical so
don\'t increase your failure rate by using any sort of chain.
The 35mm fans I want to use seem to only come in 5v and 12v. And the
supply is 48.

I suppose I can make a 48-to-12 switcher on this board. Still, a
series string with shunt zeners ought to work.

once you add a switcher you can also stop it sounding like jet engine when it doesn\'t need to

 

[Phil Allison]

lang...@fonz.dk wrote:
===================

jla...@highlandsniptechnology.com wrote:


I suppose I can make a 48-to-12 switcher on this board. Still, a
series string with shunt zeners ought to work.

once you add a switcher you can also stop it sounding like jet engine when it doesn\'t need to

** Ever heard the *roar* of a 35mm, 1W fan ?




...... Phil

 

[Rick C]

On Thursday, January 13, 2022 at 6:41:32 AM UTC-5, jla...@highlandsniptechnology.com wrote:

On Thu, 13 Jan 2022 22:16:20 +1100, Chris Jones
lugn...@spam.yahoo.com> wrote:

On 13/01/2022 14:48, jla...@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

You should use the switcher or buy 48V fans.
Why?

For some reason, 35mm fans only seem to come in 5 or 12 volts. They
only need 50-90 mA. High voltage switchers are a nuisance.

This might be OK:

https://www.mouser.com/ProductDetail/XP-Power/SRH05S12?qs=w%2Fv1CP2dgqoB4ok%252BZU%252BVXg%3D%3D

$7, if we can get them.

More fancy fans have things in them to intermittently attempt to restart
after they stall without running the windings continuously, and other
fancy things. There is no reason to believe that the fans would each
want to draw the same current at all times. If you put zeners across
each fan, it might work, but in the event that one fan doesn\'t draw
current (e.g. stalls and goes into intermittent restart attempts) the
corresponding zener might get very hot.

But we have forced air cooling!

I expect you will have some size issue that prevents you from using a single fan, but you get a lot more CFM with less noise from a single larger fan than three or four small ones.

https://www.mouser.com/c/thermal-management/fans-blowers/fans/dc-fans/?operating%20supply%20voltage=48%20VDC&width=40%20mm~~70%20mm&rp=thermal-management%2Ffans-blowers%2Ffans%2Fdc-fans%7C~Width&qty=1&sort=width

https://www.digikey.com/en/products/filter/dc-brushless-fans-bldc/217?s=N4IgjCBcpgLFoDGUBmBDANgZwKYBoQB7KAbRACZyA2MKgVhAF0CAHAFyhAGU2AnASwB2AcxABfArCoIQySOmz4ipELAAMVAJx0AHCEkbNOiAa2aIzEO048BI8RIor0gpgWnQQ-ACacp%2Bqw5Ibj4hUQI2AE8WHE40LGQxMSA

Looks like many are unobtanium, but sizes down to 40 mm with 60 mm being in stock.

Why the need for 35 mm exactly? Cooling different parts of the design?

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Sunday, January 16, 2022 at 2:24:50 PM UTC-5, palli...@gmail.com wrote:

lang...@fonz.dk wrote:
===================

jla...@highlandsniptechnology.com wrote:


I suppose I can make a 48-to-12 switcher on this board. Still, a
series string with shunt zeners ought to work.

once you add a switcher you can also stop it sounding like jet engine when it doesn\'t need to

** Ever heard the *roar* of a 35mm, 1W fan ?

Yes, one that moves any air is like a very large mosquito. Very annoying! Put three in the same box with slightly different speeds and it\'s quite annoying.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Cydrome Leader]

whit3rd <whit3rd@gmail.com> wrote:

On Thursday, January 13, 2022 at 5:34:42 PM UTC-8, Cydrome Leader wrote:
jla...@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

Don\'t do it. They will not share voltage and the losers will burn out on
the first start.

Yeah, it\'s the equivalent of a house with a floating neutral; well known for wild
voltage fluctuations. If the fans are identical, after the first fails, will the others
fail the same way, and make a short? Or will one or more fail open and leave
everything unventilated pending combustion?

I want to see that video.
Meanwhile, enjoy this one
https://youtu.be/YSOpl4gG95w

That guy is pretty bold with the stuff he does indoors.

For brushless fans, they just give up smoke and go open, and there\'s
likely a fusible resistor in the larger ones. Never seen on fail short and
consume more current than expected.

 

[Cydrome Leader]

jlarkin@highlandsniptechnology.com wrote:

On Fri, 14 Jan 2022 01:34:35 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

Here\'s the idea:

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1

Don\'t do it. They will not share voltage and the losers will burn out on
the first start. Been there, done that. Find 48 volt telecom fans or 24
volts ones and use individual series resistors. Fans are mechanical so
don\'t increase your failure rate by using any sort of chain.

The 35mm fans I want to use seem to only come in 5v and 12v. And the
supply is 48.

I suppose I can make a 48-to-12 switcher on this board. Still, a
series string with shunt zeners ought to work.

If you can go for a larger diameter fan, even mounted at an angle. They
run slower, make less noise and can last longer. This also opens up the
ability to get telecom fans. Fancy options allow for analog or PWM speed
control as well.

If reliability is key, run two fans in series (air flow wise). There is no
major performance difference otherwise. You can even get counterrotating
double thick fan modules as used in servers. The major brand ones like
Nidec are actually extremely reliable at high temps and speed, even with
ball bearings. They really figured figured these things out.

 

[Phil Allison]

gnuarm.del...@gmail.com wrote:

==============================

jla...@highlandsniptechnology.com wrote:


I suppose I can make a 48-to-12 switcher on this board. Still, a
series string with shunt zeners ought to work.

once you add a switcher you can also stop it sounding like jet engine when it doesn\'t need to

** Ever heard the *roar* of a 35mm, 1W fan ?

Yes,

** Liar.

> one that moves any air is like a very large mosquito.

** Bullshit.

Why do you fucking LIE so much??

Rhetorical question .....

 

[Lasse Langwadt Christensen]

søndag den 16. januar 2022 kl. 21.42.26 UTC+1 skrev Cydrome Leader:

whit3rd <whi...@gmail.com> wrote:
On Thursday, January 13, 2022 at 5:34:42 PM UTC-8, Cydrome Leader wrote:
jla...@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

Don\'t do it. They will not share voltage and the losers will burn out on
the first start.

Yeah, it\'s the equivalent of a house with a floating neutral; well known for wild
voltage fluctuations. If the fans are identical, after the first fails, will the others
fail the same way, and make a short? Or will one or more fail open and leave
everything unventilated pending combustion?

I want to see that video.
Meanwhile, enjoy this one
https://youtu.be/YSOpl4gG95w
That guy is pretty bold with the stuff he does indoors.

he\'s done all the proper safety assessments https://youtu.be/EZBhiJq4TL4?t=128

 

[server]

On Sun, 16 Jan 2022 09:38:36 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

søndag den 16. januar 2022 kl. 16.30.17 UTC+1 skrev jla...@highlandsniptechnology.com:
On Fri, 14 Jan 2022 01:34:35 -0000 (UTC), Cydrome Leader
pres...@MUNGEpanix.com> wrote:

jla...@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

Here\'s the idea:

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1

Don\'t do it. They will not share voltage and the losers will burn out on
the first start. Been there, done that. Find 48 volt telecom fans or 24
volts ones and use individual series resistors. Fans are mechanical so
don\'t increase your failure rate by using any sort of chain.
The 35mm fans I want to use seem to only come in 5v and 12v. And the
supply is 48.

I suppose I can make a 48-to-12 switcher on this board. Still, a
series string with shunt zeners ought to work.

once you add a switcher you can also stop it sounding like jet engine when it doesn\'t need to

We plan to control the speed of the two giant fans on the front panel
of the 3U rackmount box. But the three little fans will be on a
plug-in board, specifically a programmable ac/dc dummy load board.
Those boards will be deep inside so not very audible.

We will know the heatsink temperature, and we have an fpga on each
board, so we could get fans with a pwm control input and throttle.
That would probably improve fan life.

Of course to pwm all three it would be rational to have all the fans
grounded.

I guess we\'ll switch from 48 to 12.





--

I yam what I yam - Popeye

 

[server]

On Sun, 16 Jan 2022 20:50:15 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Fri, 14 Jan 2022 01:34:35 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

I guess I could be cautious and put a cap and a 12v TVS across each
fan. Hmmm, 3 fans and 4 TVSs might work.

Worst case, I can make a 48 to 12 switcher.

Here\'s the idea:

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1

Don\'t do it. They will not share voltage and the losers will burn out on
the first start. Been there, done that. Find 48 volt telecom fans or 24
volts ones and use individual series resistors. Fans are mechanical so
don\'t increase your failure rate by using any sort of chain.

The 35mm fans I want to use seem to only come in 5v and 12v. And the
supply is 48.

I suppose I can make a 48-to-12 switcher on this board. Still, a
series string with shunt zeners ought to work.

If you can go for a larger diameter fan, even mounted at an angle. They
run slower, make less noise and can last longer. This also opens up the
ability to get telecom fans. Fancy options allow for analog or PWM speed
control as well.

If reliability is key, run two fans in series (air flow wise). There is no
major performance difference otherwise. You can even get counterrotating
double thick fan modules as used in servers. The major brand ones like
Nidec are actually extremely reliable at high temps and speed, even with
ball bearings. They really figured figured these things out.

https://www.dropbox.com/s/5hx2hzrq4edd3ye/P944_Load_Module_1.jpg?raw=1

I considered all sorts of ways to use one big fan, horizontal or
angled, and couldn\'t make it work. It would need some sort of ducting,
and the next board is 1.6\" away so there\'s no way to get the air into
and out of a big fan. We do want to shoot the hot air out the rear of
the box, not stir it around inside, another constraint.

We\'re building a mockup for thermal testing. I have no analytical or
simulation tools for a thing like this, and my instincts for air flow
are all mediocre guesses.





--

I yam what I yam - Popeye

 

[server]

On Sun, 16 Jan 2022 20:42:19 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

whit3rd <whit3rd@gmail.com> wrote:
On Thursday, January 13, 2022 at 5:34:42 PM UTC-8, Cydrome Leader wrote:
jla...@highlandsniptechnology.com wrote:
Has anyone run bldc fans in series? I want to run three 12v fans from
a 48v supply, with a resistor or something in series

Don\'t do it. They will not share voltage and the losers will burn out on
the first start.

Yeah, it\'s the equivalent of a house with a floating neutral; well known for wild
voltage fluctuations. If the fans are identical, after the first fails, will the others
fail the same way, and make a short? Or will one or more fail open and leave
everything unventilated pending combustion?

I want to see that video.
Meanwhile, enjoy this one
https://youtu.be/YSOpl4gG95w

That guy is pretty bold with the stuff he does indoors.

For brushless fans, they just give up smoke and go open, and there\'s
likely a fusible resistor in the larger ones. Never seen on fail short and
consume more current than expected.

It wouldn\'t be hard to make a rotating magnetic field that would spin
a metal disk or sphere to, say, a million RPM, enough to tear anything
apart.



--

I yam what I yam - Popeye