Will a single molex chain of 5 connectors handle 32x 3.3W fans?

[TheNaitsyrk]

I'm using Splitty9 Actives and I want to hook up 32 fans to them, but want to power them via molex for convenience. How much power can a chain take?

 

I know a single connector is about 54W but wanted to see how about the entire cable.

[Skiiwee29]

<-- Moved to Power Supplies -->

[Tegneren]

The 54W are for the each seperate cable, not for each conector. That doesnt mean you cant go over that, but the cable might get hot or in worst case melt or catch fire if pushed hard enough. 

So for 32 3.3W fans i would use at least two seperate cables

[TheNaitsyrk]

2 minutes ago, Tegneren said:

The 54W are for the each seperate cable, not for each conector. That doesnt mean you cant go over that, but the cable might get hot or in worst case melt or catch fire if pushed hard enough. 

So for 32 3.3W fans i would use at least two seperate cables

Thank you. I was thinking the same.

 

I hope I have 3x separate molex connectors.

[Somerandomtechyboi]

Why are you even hooking up that many fans in the first place?

 

A meme worthy case made entirely of fans?

 

 

Yea i do think that you should atleast have 2 seperate cables powering the fans as the cables can catch on fire if theres too much wattage, only reason you may get away with 1 cable is if you have some really thicc psu cables, but thats not even mentioning the fan hubs and whatnot

[TheNaitsyrk]

3 minutes ago, Somerandomtechyboi said:

Why are you even hooking up that many fans in the first place?

 

A meme worthy case made entirely of fans?

 

 

Yea i do think that you should atleast have 2 seperate cables powering the fans as the cables can catch on fire if theres too much wattage, only reason you may get away with 1 cable is if you have some really thicc psu cables, but thats not even mentioning the fan hubs and whatnot

 

[TheNaitsyrk]

15 minutes ago, James Evens said:

That's 100W for fans? 

If you run it with 12V it is fine as long as the PSU use thick cables (1.5mm^2 should be fine).  Molex connectors are roughly capable of 10A which would be approx. 120W@12V.

 

Btw. Does your active fan hubs support soft start? Otherwise you might run into a issue if all 32 fan spinn up at the same time.

Sometimes 3 don't spin it's odd but after restart all of them start spinning.

[TheNaitsyrk]

4 minutes ago, James Evens said:

That's odd.

Motor aka. fans consume additional current when they start. If you have a lot of those e.g. 32 that might be enough to blow a fuse. A soft starter is there to control the initial inrush current. another strategy would be spinning them up staggered (one group at the time).

 

 

But that would mean either all or a entire fan hub wouldn't work not just 3 fans.

 

They been working fine 16x fans per one SATA string, but I got molex to make it prettier and was wondering if it's fine 

[TheNaitsyrk]

5 minutes ago, James Evens said:

That's odd.

Motor aka. fans consume additional current when they start. If you have a lot of those e.g. 32 that might be enough to blow a fuse. A soft starter is there to control the initial inrush current. another strategy would be spinning them up staggered (one group at the time).

 

 

But that would mean either all or a entire fan hub wouldn't work not just 3 fans.

 

It's normal with Splittys if 3 don't start because there is so many and all the Splittys are connected to Octo.

[seon123]

42 minutes ago, James Evens said:

If you run it with 12V it is fine as long as the PSU use thick cables (1.5mm^2 should be fine). 

There is no PSU with that thick Molex cables. 1.5mm^2 is apparently 16 AWG, which is what you get for the main PCIe cables (not the pigtail part) in high end PSUs. Typically, they are 18-20 AWG for Molex, which is 0.75-0.50mm^2

[Somerandomtechyboi]

1 hour ago, TheNaitsyrk said:

 

Multi gpu watercooling build???

 

Idk but that seems abit excessive to me

[mariushm]

The wire is good for around 10-13 A of current.

The pin and connector that goes into the power supply is rated for around 9A of current (~100w).

Each individual molex connector is rated for maximum 5A of current ( 60w with 12v) but I'd suggest not going over around 30-35w.

 

When a fan starts, it will pull more current than the average current used during operation.  So, if your fan is advertised as 12v  0.275A ( 3.3w) estimate that it could take around 5w for 1-3 seconds when it starts spinning up then drop down to that 3.3w. 

 

So basically, as you say you have 32 fans, I'd suggest connecting at most  up to 8 fans on a single molex connector, but I'd be more comfortable with just 6 fans connected to a single molex connector.

I'd also use TWO "chains" of molex connectors, so you have TWO 12v wires from the power supply to the fans... OR, use a 6 pin / 6+2 pci-e cable and you then have 3 x 12v wires to play with.

 

You could make your own delay switch with a capacitor, a resistor and a mosfet, to start some of the fans after some fans are already started, and reduce peak currents.

The resistor and capacitor are for a RC delay, which means the voltage on the output will slowly ramp up towards 12v, and you can choose a mosfet that only turns on at some minimum voltage threshold, like let's say 3v.

You can then pick the resistor and capacitor values in such a way so that the voltage is gonna be 3v on the gate of the mosfet in around 3-5 seconds.

 

For example, this cheap DMN6140 mosfet has a minimum threshold voltage of 1v, and maximum of 3v : https://www.digikey.com/en/products/detail/diodes-incorporated/DMN6140L-13/4794893

You can use an online calculator to play with values, for example the one on this website : http://www.ladyada.net/library/rccalc.html

For example, a generic 100uF electrolytic capacitor and a 100 kOhm resistor will cause the output voltage to reach 1v in around 870ms, and 3v at around 2.9seconds :

 

 

 

So your circuit would basically be: 

--12v ------------------------------------------------------------[ drain of mosfet ]
--12v ------ [ resistor ] ----[.]-------- [ gate of mosfet ] 	                                
                               |       
                  capacitor   ___ +                 
                              ---  		
                               | 
--gnd ------------------------[ ]----------[ fan negative ]       [ source of mosfet ]--------------- [ fan positive ]   


fan can also be wired like this :  12v ---> fan positive voltage  , fan ground wire ---> drain of mosfet  , source of mosfet -> gnd

 

but you can pick mosfets with higher minimum threshold voltage, for example this one has minimum 2.5v , max 4v : https://www.digikey.com/en/products/detail/vishay-siliconix/SQ2398ES-T1-GE3/7566741

 

or this one with minimum 3v ... max 5v : https://www.digikey.com/en/products/detail/onsemi/FDD5N60NZTM/2804169

 

If you use a molex you have 5v available, so you could use 5v instead of 12v for the time delay circuit, if the mosfet you choose is guaranteed to have a threshold voltage below 5v.  With smaller input voltage, you could also use smaller capacitors, so you may be able to use a 10-22uF ceramic capacitor instead of a big electrolytic (for example, use a 470kOhm resistor and a 10uF ceramic capacitor, to get 3v in around 4s)

[TheNaitsyrk]

8 minutes ago, Somerandomtechyboi said:

Multi gpu watercooling build???

 

Idk but that seems abit excessive to me

You are not cooling 1000W Kingpin BIOS 3090 and 10980XE OCed to brim. Had 5950x connected to it too. 4.9Ghz on all cores no problem.

[Somerandomtechyboi]

1 minute ago, TheNaitsyrk said:

You are not cooling 1000W Kingpin BIOS 3090 and 10980XE OCed to brim. Had 5950x connected to it too. 4.9Ghz on all cores no problem.

At that point dont bother with water and just swap to phase change entirely

 

Or just ditch all the rads and put a water chiller in their place

[TheNaitsyrk]

4 minutes ago, Somerandomtechyboi said:

At that point dont bother with water and just swap to phase change entirely

 

Or just ditch all the rads and put a water chiller in their place

Nope this works perfectly 

[Somerandomtechyboi]

1 minute ago, TheNaitsyrk said:

Nope this works perfectly 

Hmm

 

Is there any benifit to running that many rads?

 

I mean theres prob got to be a diminishing returns zone eventually, so im guessing that the extra rads help with temps over prolonged periods of time?

[TheNaitsyrk]

2 minutes ago, Somerandomtechyboi said:

Hmm

 

Is there any benifit to running that many rads?

 

I mean theres prob got to be a diminishing returns zone eventually, so im guessing that the extra rads help with temps over prolonged periods of time?

Yes.

Friend uses same setup. 3x 360mm XE rads. 1.2V = 100c.

 

My setup same settings 60c instead.

 

Also lower fan speed 

 

[Somerandomtechyboi]

2 minutes ago, TheNaitsyrk said:

Yes.

Friend uses same setup. 3x 360mm XE rads. 1.2V = 100c.

 

My setup same settings 60c instead.

 

Also lower fan speed 

 

I am looking to build a custom loop for my testbench & pc in the near future, so i guess this is the effect of more rads, thx for the info

 

 

Btw what fans are you running? Since 3.3w translates to around 0.25a, i plan on just using some cheap 48v server fans since most of them seem to be focused on static pressure and boost converters are pretty cheap aswell + they give me control over the fan speed

[TheNaitsyrk]

3 hours ago, Somerandomtechyboi said:

I am looking to build a custom loop for my testbench & pc in the near future, so i guess this is the effect of more rads, thx for the info

 

 

Btw what fans are you running? Since 3.3w translates to around 0.25a, i plan on just using some cheap 48v server fans since most of them seem to be focused on static pressure and boost converters are pretty cheap aswell + they give me control over the fan speed

Just get what I got. 3000RPM Noctua fans.

[Somerandomtechyboi]

49 minutes ago, TheNaitsyrk said:

Just get what I got. 3000RPM Noctua fans.

Damn, ~0.25a/3.3w for a 3000rpm fan? I guess some fans are really efficient

 

But those prob gonna cost a fortune compared to 2$ for a 48v fan, though the inconveniences with a 48v fan is having to hook it up to a boost converter, also a strong point since you can adjust fan speed, then theres also noise and vibrations, but for 2$ a peice you get what you pay for, then again i dont need 69$ fans for a custom loop that will cost around 35$ (yes ik aircoolers might be a better option but all i can get at this price is an ereboss and se 224 xt)

 

Though maybe in the future if i build a higher quality more expensive loop ill consider more expensive fans, though ill prob get arctic p12 fans over them noctuas cause p12 seem to be on par with the noctuas in terms of performance, even a single p12 will buy 5 48v server fans so thats why i chose server fans

 

 

Also what flow rate do your pumps have? And does a fast flow rate give better temps?

or do i have to find a good flow rate that isnt too fast nor too slow?

[TheNaitsyrk]

1 hour ago, Somerandomtechyboi said:

Damn, ~0.25a/3.3w for a 3000rpm fan? I guess some fans are really efficient

 

But those prob gonna cost a fortune compared to 2$ for a 48v fan, though the inconveniences with a 48v fan is having to hook it up to a boost converter, also a strong point since you can adjust fan speed, then theres also noise and vibrations, but for 2$ a peice you get what you pay for, then again i dont need 69$ fans for a custom loop that will cost around 35$ (yes ik aircoolers might be a better option but all i can get at this price is an ereboss and se 224 xt)

 

Though maybe in the future if i build a higher quality more expensive loop ill consider more expensive fans, though ill prob get arctic p12 fans over them noctuas cause p12 seem to be on par with the noctuas in terms of performance, even a single p12 will buy 5 48v server fans so thats why i chose server fans

 

 

Also what flow rate do your pumps have? And does a fast flow rate give better temps?

or do i have to find a good flow rate that isnt too fast nor too slow?

I don't know about the flow rate. It works I'm happy. 

 

The Noctuas I have are £25 each. I have 42x.