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
fans in series
Started by ●January 12, 2022
Reply by ●January 16, 20222022-01-16
Reply by ●January 16, 20222022-01-16
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
Reply by ●January 16, 20222022-01-16
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
Reply by ●January 16, 20222022-01-16
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.
Reply by ●January 16, 20222022-01-16
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 .....
Reply by ●January 16, 20222022-01-16
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.
Reply by ●January 16, 20222022-01-16
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
Reply by ●January 16, 20222022-01-16
On Sun, 16 Jan 2022 09:38:36 -0800 (PST), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>s�ndag 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 toWe 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
Reply by ●January 16, 20222022-01-16
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
Reply by ●January 16, 20222022-01-16
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
