fans in series

[jla...@highlandsniptechnology.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




--

I yam what I yam - Popeye

[John Robertson]

On 2022/01/12 7:48 p.m., 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

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
jla...@highlandsniptechnology.com wrote in
<hm5vtg599rmbp88m0...@4ax.com>:

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, 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.

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.

[jla...@highlandsniptechnology.com]

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!

[Chris Jones]

On 13/01/2022 22:41, 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?

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]

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>

[jla...@highlandsniptechnology.com]

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.

[Lasse Langwadt Christensen]

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]

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]

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]

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.

[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 .....

[Cydrome Leader]

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.

[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

[jla...@highlandsniptechnology.com]

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.

[jla...@highlandsniptechnology.com]

On Sun, 16 Jan 2022 20:50:15 -0000 (UTC), Cydrome Leader

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.

[jla...@highlandsniptechnology.com]

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.

[Lasse Langwadt Christensen]

https://www.amazon.com/Cooler-Cooling-LGA1156-LGA1155-Utral-Thin/dp/B07PFH5B69

[legg]

On Sun, 16 Jan 2022 07:30:08 -0800, jla...@highlandsniptechnology.com
wrote:

Use a centrifugal impeller rather than a consumer-grade fan.
Guaranteed to come in standard system voltages and tango under
35mm thickness.

If 24V, you could check for spare fans used on 3D printers,
though these are usually 30-40mm, not 35mm and are toy quality.

ebay 182623902047, 182623900436, 223792320319, 274774441334

RL

[Rick C]

There are fans mounted on GPU boards and inside laptops that would fit in the space. Probably 5 V though. Why not 48V > 5V and make life easy picking the fan?

--

Rick C.

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

[Phil Allison]

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
>

** Tested a handful of different 35/40 mm 12VDC 0.6W to 1.3W fans.

1. Load current ( average value ) goes up by 70 to 100% when stalled.

2. Current is drawn in steady pulses of about 90% duty cycle, frequency related to RPM and number of poles.

3. During the "off" time current draw swings briefly negative.

4. All fans are quiet, some damn quiet.

IMO all are nice, easy to use items.

Go with the 4 x 12V zener idea - using at least 3W types.




...... Phil

[Cydrome Leader]

These beasts are deep (possible design constraint), redundant and last
forever. Pretty loud at full blast too.

https://www.nidec.com/en/product/search/category/B101/M111/S100/NCJ-R40W-F9/

That's the 40mm version, the make 38 and 35 commie units sized one too, in
case you're looking to harmonize with cuba, north korea and russia.

1.6" doesn't quite give enough space for a centrifugal blower, unless your
heatsink shrinks into something like an Al square tube. If this is your
current sink project, you probably want as much thermal mass as possible
though.

Not sure what reliability you want, but small thin fans suck, I think some
sort of hokey laptop cooler fan in mentioned in the thread. It might help
dissipate low tens of watts on a good day. Everone has seen how laptops
die. They overheat more and more often and then the thermal stresses
finally break connections on system board. That's no accident.

[jla...@highlandsniptechnology.com]

On Mon, 17 Jan 2022 20:25:57 -0000 (UTC), Cydrome Leader

I'd like to dump at least 100 watts on the dummy load board. The
little 35 mm fans are good for maybe 7 cfm each unrestricted. Three
might manage 15 cfm in real life, maybe less. 100 watts into 15 cfm
heats the air roughly 10c, not bad. The heat sink and mosfet temps
will of course be higher.

So, how hot might we allow the heat sink to get? 100c? With a sticker

WARNING HOT SURFACE

The giant fets wouldn't get a lot hotter than the sink.

[three_jeeps]

On Wednesday, January 12, 2022 at 10:49:34 PM UTC-5, 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
>
>
>
>

> --
>
> I yam what I yam - Popeye

From a reliability standpoint, I wouldn't do it. One fan opens up and the others quit functioning.

[three_jeeps]

On Wednesday, January 12, 2022 at 10:49:34 PM UTC-5, 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
>
>
>
>
> --
>
> I yam what I yam - Popeye

Are you pushing air over the exchanger fins or pulling air through them? the diagram suggest pushing.
I remember reading a paper some time ago that one needs to consider the spacing of the fins...it is a tradeoff: amount fin spacing/surface area, air flow, and channel cross sectional area.
Heat transfer optimally occurs with turbulent flow, R =>3500. Also shrouding of the fan and heat exchanger assembly can usually increase the heat transfer rate.
If you want to model this, COMSOL Multiphysics with the heat transfer module is a nice tool and would probably give you some useful results. You can get rather detailed and account for all 3 forms of heat transfer (conductive, convective, and radiative ).

Then again, you could experiment with some RTDs, fan orientation, channels/shrouds, etc. Would five you some sight as to necessary fan flows, and not make the device sound like a jet engine when running.
J

[whit3rd]

On Tuesday, January 18, 2022 at 11:50:56 AM UTC-8, three_jeeps wrote:
> On Wednesday, January 12, 2022 at 10:49:34 PM UTC-5, 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.

It might be simpler to use a 120V fan in a big box, with a thermostat fan control.
Regulated voltages are unnecessary, dependence on the 48V source is unnecessary,
fitting into the thin box is unnecessary, and a thermostat allows complete independence
of any logic signals. When the fan needs lube, the guy in the field doesn't need to open
a computer at a static-safe station and recalibrate a precision instrument.

[jla...@highlandsniptechnology.com]

https://www.dropbox.com/s/o1ikkiolefx9csv/3_fans.jpg?raw=1

The idea is to stuff air into the heat sink. Some sort of channeling
might help. If the heat sink has high fin density, there will be a lot
of flow restriction - we *want* a lot of flow restriction - so the air
will want to sneak around the heat sink and not go through the length
of the fins.

Think we can dump 100 watts? Maybe we should dump the little fans...
they would be a nuisance to install and wire up. With a really big
heat sink, the overall box air flow might work as well.

We need to try it.

"One experiment is worth a thousand expert opinions."

I think Werner Von Braun said that.

[Phil Hobbs]

Well, he was a very flexible fellow. ;)

https://www.youtube.com/watch?v=TjDEsGZLbio

Cheers

Phil Hobbs

[Cydrome Leader]

The supreme leader would like a word with you.

[Reinhardt Behm]

On 1/13/22 06:47, John Robertson wrote:

> On 2022/01/12 7:48 p.m., 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
>

> Uneven airflow loading could burn out a fan...

So make sure that at least one fan is running to git rid of the smoke.


--
Reinhardt

[jla...@highlandsniptechnology.com]

I ordered one just for fun. I'd have to stick my four giant mosfets on
the bottom somehow.

[Lasse Langwadt Christensen]

flip the whole pcb uupside down and place them around a square cutout in the middle of the pcb?

mount them tap up and squeeze them between the pcb and heatsink with the X bracket

[jla...@highlandsniptechnology.com]

On Sat, 29 Jan 2022 14:38:15 -0800 (PST), Lasse Langwadt Christensen

Spehro has been helping us with the thermals of our dummy load module.
He found this heat sink

https://www.dropbox.com/s/0kszc4nltr1q8d3/P944_HS_2.jpg?raw=1

which I think we can push 250 LFPM or so of air flow through without a
local fan. That might get us down to maybe 0.2 to 0.25 K/W... on a
PCB!

Well, the pcb is mounted on the heat sink more than vice versa.

If we put two giant fans on the front of the rack box, and make their
speed adaptive on heat sink temps, they will deafen only a minority of
our customers.

We can bolt that bottom heat sink fin to the bottom of the rackmount
enclosure. That will improve cooling some, and keep things from
ripping apart when some UPS guy throws it off the back of a truck.