Problem after connecting case fan to 5V from PSU

Derek12 · Aug 20, 2011

I have installed a old case fan to 5V because it doesn't have a mobo header and with 12V it's very noisy, I had connected to 5V from the power supply and it works fine and quieter but..

After shutting down the computer, it immediately turns on again. This only happens with the fan connected.

Anyone knows why this strange behavior with the fan??

Many thanks

BraveSoul · Aug 22, 2011

strange,, have u tried a diff fan,,, or connecting to motherboard's 5v

de.das.dude · Aug 22, 2011

i think the 5V line is on even when standby. or power is off.
this means that the fan is still "running".

i guess there must be something in the PSUs circuitry that when the current draw during standby gets over a certain limit (for your case this is due to the fan) the PSU automatically starts. this is probably as a safety measure to make sure the transistors and stuff are cooled.

its better to use a 1/2watt resistor in series with the fan in connection to a 12V supply.

if your fans current rating is 'i' in amperes

then

solve this equation.
R=16.8/i

to get the resistance required in ohms.

if youre interested who that came out:

Jetster · Aug 22, 2011

Change the power options in the BIOS?

Mussels · Aug 22, 2011

Derek12 said:
I have installed a old case fan to 5V because it doesn't have a mobo header and with 12V it's very noisy, I had connected to 5V from the power supply and it works fine and quieter but..

After shutting down the computer, it immediately turns on again. This only happens with the fan connected.

Anyone knows why this strange behavior with the fan??

Many thanks

thats a weird one, i've changed the wiring on heaps of fans and never seen that happen before. can you show us some pics of how you have it wired in?

de.das.dude · Aug 22, 2011

check my post. its updated!

Mussels · Aug 22, 2011

de.das.dude said:
i think the 5V line is on even when standby. or power is off.
this means that the fan is still "running".

his problem is that the PC turns back on, not the fan still spinning.

also, the 5V doesnt stay on. there is a 5VSB rail, but he'd hafta do some weird shit to connect that to a fan, as its not on a molex or 3 pin connector.

de.das.dude · Aug 22, 2011

Mussels said:
his problem is that the PC turns back on, not the fan still spinning.

also, the 5V doesnt stay on. there is a 5VSB rail, but he'd hafta do some weird shit to connect that to a fan, as its not on a molex or 3 pin connector.

cheap PSU = all are same check the guide in my siggy.

all rails are interconnected for me.

Mussels · Aug 22, 2011

de.das.dude said:
cheap PSU = all are same check the guide in my siggy.

all rails are interconnected for me.

true but how can his 5V rail trigger a power on through the sense wires there?

your electrical... crap is beyond me. not my field.

de.das.dude · Aug 22, 2011

5V is in use.

the fan takes some power. that means a rise in the current in the circuit and hence transistors and the like.

more current = more heat
so if there is a overheating protection, that would trigger the PSU to self start which inturn switches on the cooling.

this is just my logic. i am not sure. this just seems to justify what is going on in the easiest way. i dont know PSU circuits in detail

i hated electronics the way it was taught.

anyhoo he should use my formula to find out the resistance and use that for fan controlling.

Derek12 · Aug 22, 2011

Many thanks to all

@BraveSoul, yeah, if I connect to 12V no problem happens! I don't have another fan to try

@de.das.dude I will try your circuit, I will get a resistor and connect to 12V so it will reduce its speed

@Jetster I checked bios and all seems fine, though the problem only happens with the fan without it it shuts down correctly and stays there.

@Mussels Sorry I don't have a camera on my own

I connected it to a red and black terminals on the floppy connector and insulated with electric tape (yes very fudge

) though I didn't shorted anything by now LOL

Yeah the problem is veeeery strange doesn't matter if I shutdown via Windows or via the button or from BIOS, the computer shuts down for .5 second, then it gets up and boot again normally and if I stop the fan with the hand before shutting it down, the computer doesn't come up again, so seems that the fan spinning inertia introduce some noise and trigger the PSU or mobo to turn on

newtekie1 · Aug 22, 2011

The fan spinning is likely creating a charge that is somehow signalling the computer to turn back on. That is odd.

scaminatrix · Aug 22, 2011

newtekie1 said:
The fan spinning is likely creating a charge that is somehow signalling the computer to turn back on. That is odd.

Could it be something to do with the rig waiting for a 5v wake-up when turned off (like it's waiting to be turned on with the keyboard)? And it's getting it with the residual power from the fan?

Try going into BIOS and turning off an option that says something like "wake up on 5v" or "5vSB"

de.das.dude · Aug 23, 2011

scaminatrix said:
Could it be something to do with the rig waiting for a 5v wake-up when turned off (like it's waiting to be turned on with the keyboard)? And it's getting it with the residual power from the fan?

Try going into BIOS and turning off an option that says something like "wake up on 5v" or "5vSB"

yes that could be the reason too.
fans do have caps that can store the charge and release it

Derek12 · Aug 24, 2011

Many thanks to all

Yeah that's what I'm thinking that the fan inertia would cause some voltage spikes and make the motherboard to turn on :?:

Meanwhile I solved it, I used a series resistor like de das dude show and connected to 12V and now the computer is fine while the fan spins at low speed.

The resistor is 45ohm taken from a broken PSU and the fan voltage is now 8,5 V. the resistor, being very huge (I think it's 2W LOL), warms considerably.

BTW @scaminatrix, I can't find "wake up on 5v", though there are: "Power On By Keyboard" "PME Event Wake Up" "Power-On by Alarm" and "USB Wake Up from S3" I believe (I will check first) that they are disabled but the latest one.

Derek12 · Aug 24, 2011

%&·$·$$%!!

I ear a pop and the fan stopped but the computer still run OK
The resistor has blown literally, poured smoke, burned the molex luckily the components haven't suffered damage despite the resistor was NEAR the video card LOOOL and it blackened a bit because of the smoke!

I will choose a better resistor.

EDIT: well the computer is artifacting now, I will clean the video card soot, if it still fails I will swear a lot!!!

Cleaned and new resistor, now the computer is fine and the fan is running and the resistor isn't overheating

de.das.dude · Aug 25, 2011

dude you need at LEAST a 1/2 watt. it better if you first try with higher wattage.

anyhoo so my formula and ckt is working?

Derek12 · Aug 25, 2011

de.das.dude said:
dude you need at LEAST a 1/2 watt. it better if you first try with higher wattage.

anyhoo so my formula and ckt is working?

Well the resistor used was very big and thick (approx 4cm long and 2.5cm thick) I though that it was 1/2W or greater I think that it failed shorted. The resistor, BTW it was pink with 4 color lines that I can't remember currently.

The fan sticker doesn't indicate the current and I haven't got a amperimeter (I have a multimeter but no current measure)

I will suppose that this fan is 0.45A (it's a 80mm one) so I will search a 36 Ohm resistor (or approximately one) and big and I will report the result.

Many thanks

scaminatrix · Aug 25, 2011

I would just buy a new fan.

Derek12 · Aug 25, 2011

scaminatrix said:
I would just buy a new fan.

Maybe, though those I saw on stores are also 3 pin and would run full speed I can't find 4 pin ones with PWM. I can't find fan controllers neither

Lazzer408 · Aug 25, 2011

http://www.ebay.com/itm/4Pin-3Pin-P...601?pt=LH_DefaultDomain_0&hash=item2312ef4f19

You can also use diodes to drop voltage. About .6v per diode. If the fan is generating a current thats keeping the supply on, you can try using just one diode in series with your resistor to block the generated current from flowing back into the psu.

scaminatrix · Aug 25, 2011

I've got one of these with a 3-pin to molex adapter I can chuck you for price of postage. If you're interested, PM me.

Derek12 · Aug 26, 2011

Lazzer408 said:
http://www.ebay.com/itm/4Pin-3Pin-P...601?pt=LH_DefaultDomain_0&hash=item2312ef4f19

You can also use diodes to drop voltage. About .6v per diode. If the fan is generating a current thats keeping the supply on, you can try using just one diode in series with your resistor to block the generated current from flowing back into the psu.

Good idea, I will pull out a diode from the trash PSU and I will insert it in the circuit

that's the product I want!

scaminatrix said:
I've got one of these with a 3-pin to molex adapter I can chuck you for price of postage. If you're interested, PM me.

That's what I would like to have, I will try to convince my parents to buy online (they are very reticent to do so :mad:

) if I am successful, I will PM you

de.das.dude · Aug 26, 2011

diodes are messy and even they go bork! bork!

Derek12 · Aug 26, 2011

de.das.dude said:
diodes are messy and even they go bork! bork!

I tried a diode from my trash PSU and the fan doesn't spin up, the diode is correctly polarized (I tried reversing the diode just in case) so maybe the diode is bad

System Name	Custom Built
Processor	AMD Ryzen 5 3600
Motherboard	Asus PRIME A520M-A
Cooling	Stock heatsink/fan
Memory	16GB 2x8GB Corsair Vengeance LPX 2400MHz
Video Card(s)	MSI 1050Ti 4GB
Storage	KINGSTON SNVS250G 256GB M.2 + 2 data disks
Display(s)	Dell S2421NX
Case	Aerocool CS103
Audio Device(s)	Realtek
Power Supply	Seasonic M12II-520 EVO
Mouse	Logitech MX Master 2S
Keyboard	Logitech
Software	Windows 11 Pro 64-bit

System Name	Filtration tower
Processor	i9 7900@4.4ghz
Motherboard	ASRock X299 Taichi
Cooling	Air
Memory	64g 3200 quad channel
Video Card(s)	ASUS GTX 1080Ti
Storage	500gb Nvme, 200gb SSD, 1700gb HDD
Display(s)	34" Acer Predator 3440x1440
Case	Thermaltake v71
Power Supply	EVGA supernova 850 T2

System Name	Monke \| Work Thinkpad \| Old Monke
Processor	Ryzen 5600X \| Ryzen 5500U \| FX8320
Motherboard	ASRock B550 Extreme4 \| ? \| Asrock 990FX Extreme 4
Cooling	240mm Rad \| Not needed \| hyper 212 EVO
Memory	2x16GB DDR4 3600 Corsair RGB \| 16 GB DDR4 3600 \| 16GB DDR3 1600
Video Card(s)	Sapphire Pulse RX6700XT 12GB \| Vega 8 \| Sapphire Pulse RX580 8GB
Storage	Samsung 980 nvme (Primary) \| some samsung SSD
Display(s)	Dell 2723DS \| Some 14" 1080p 98%sRGB IPS \| Dell 2240L
Case	Ant Esports Tempered case \| Thinkpad \| NZXT Guardian 921RB
Audio Device(s)	Logitech Z333 \| Jabra corpo stuff \| Some USB speakers
Power Supply	Corsair RM750e \| not needed \| Corsair GS 600
Mouse	Logitech G400 \| nipple \| Dell
Keyboard	Logitech G213 \| stock kb is awesome \| Logitech K230
VR HMD	;_;
Software	Windows 10 Professional x3
Benchmark Scores	There are no marks on my bench

System Name	Juliette // My HTPC
Processor	Intel i7 9700K // AMD Ryzen 5 5600G
Motherboard	ASUS Prime Z390X-A // ASRock B550 ITX-AC
Cooling	Noctua NH-U12 Black // Stock
Memory	Corsair DDR4 3600 32gb //G.SKILL Trident Z Royal Series 16GB (2 x 8GB) 3600
Video Card(s)	ASUS RTX4070 OC// ASUS RTX 4060 OC
Storage	Samsung 970 EVO NVMe 1Tb, Intel 665p Series M.2 2280 1TB // Samsung 1Tb SSD
Display(s)	ASUS VP348QGL 34" Quad HD 3440 x 1440 // 55" LG 4K SK8000 Series
Case	Seasonic SYNCRO Q7// Silverstone Granada GD05
Audio Device(s)	Focusrite Scarlett 4i4 // HDMI to Samsung HW-R650 sound bar
Power Supply	Seasonic SYNCRO 750 W // CORSAIR Vengeance 650M
Mouse	G903 and a Master Mouse MM710/No mouse, MS game copntroller
Keyboard	EVGA / Logitech K400
Software	Windows 11 Pro // Windows 10 Pro

System Name	Rainbow Sparkles (Power efficient, <350W gaming load)
Processor	Ryzen R7 5800x3D (Undervolted, 4.45GHz all core)
Motherboard	Asus x570-F (BIOS Modded)
Cooling	Alphacool Apex UV - Alphacool Eisblock XPX Aurora + EK Quantum ARGB 3090 w/ active backplate
Memory	2x32GB DDR4 3600 Corsair Vengeance RGB @3866 C18-22-22-22-42 TRFC704 (1.4V Hynix MJR - SoC 1.15V)
Video Card(s)	Galax RTX 3090 SG 24GB: Underclocked to 1700Mhz 0.750v (375W down to 250W))
Storage	2TB WD SN850 NVME + 1TB Sasmsung 970 Pro NVME + 1TB Intel 6000P NVME USB 3.2
Display(s)	Phillips 32 32M1N5800A (4k144), LG 32" (4K60) \| Gigabyte G32QC (2k165) \| Phillips 328m6fjrmb (2K144)
Case	Fractal Design R6
Audio Device(s)	Logitech G560 \| Corsair Void pro RGB \|Blue Yeti mic
Power Supply	Fractal Ion+ 2 860W (Platinum) (This thing is God-tier. Silent and TINY)
Mouse	Logitech G Pro wireless + Steelseries Prisma XL
Keyboard	Razer Huntsman TE ( Sexy white keycaps)
VR HMD	Oculus Rift S + Quest 2
Software	Windows 11 pro x64 (Yes, it's genuinely a good OS) OpenRGB - ditch the branded bloatware!
Benchmark Scores	Nyooom.

Problem after connecting case fan to 5V from PSU

Derek12

BraveSoul

de.das.dude

Pro Indian Modder

Jetster

Mussels

Freshwater Moderator

de.das.dude

Pro Indian Modder

Mussels

Freshwater Moderator

de.das.dude

Pro Indian Modder

Mussels

Freshwater Moderator

de.das.dude

Pro Indian Modder

Derek12

newtekie1

Semi-Retired Folder

scaminatrix

de.das.dude

Pro Indian Modder

Derek12

Derek12

de.das.dude

Pro Indian Modder

Derek12

scaminatrix

Derek12

Lazzer408

scaminatrix

Derek12

de.das.dude

Pro Indian Modder

Derek12

Processor	Intel Core i7 10850K@5.2GHz
Motherboard	AsRock Z470 Taichi
Cooling	Corsair H115i Pro w/ Noctua NF-A14 Fans
Memory	32GB DDR4-3600
Video Card(s)	RTX 2070 Super
Storage	500GB SX8200 Pro + 8TB with 1TB SSD Cache
Display(s)	Acer Nitro VG280K 4K 28"
Case	Fractal Design Define S
Audio Device(s)	Onboard is good enough for me
Power Supply	eVGA SuperNOVA 1000w G3
Software	Windows 10 Pro x64

System Name	Benny
Processor	Phenom II 1055t @ 3.3GHz; 300x11; 1.380v; NB 2700; HT 2400
Motherboard	ASUS Crosshair IV Formula (2002 BIOS)
Cooling	Thermalright TRUE 120 Black + 2 Xilence Red Wing PWM 120mm (push/pull) + polycarbonate fan holders
Memory	8GB GeIL Ultra 2133MHZ C9 running at 1600MHz @ 7-7-7-21 1T 1.5v
Video Card(s)	MSI Twin Frozr II GTX470 @ Stock w/CPU fan cable-tied on, as one of the GPU fans broke.
Storage	60GB OCZ Agility3 (OS);500GB WDC Grn; 1x1TB WDC Blk (Backup)
Display(s)	ASUS PA823Q
Case	Silverstone Raven 2 (all cables custom sleeved with velcro mod on side panel...)
Audio Device(s)	X-Fi (Onboard) + Harmon Kardon HK6100 amp powering JVC HA-RX700's with Zalman mic
Power Supply	Corsair HX650W
Software	Win7 Pro x64
Benchmark Scores	No benchies so making this space useful! Corsair M90, Logitech G19. Phobya FlexLight LED's (gawjus)

Processor	i7 2600k@4.6ghz
Motherboard	MSI z68ma-ed55
Cooling	Silentx Extreem 120mm
Memory	2x4gb XMS 7-8-7-20 1600
Video Card(s)	HD6870
Storage	2x128gb Kingston Hyper-X (Raid0), 2x750gb RE3 (RAID1), 2x750gb RE3 (RAID1)
Display(s)	Soyo 24", Gateway 22"
Case	Fractal Design Arc Mini 6x120mm fans.
Audio Device(s)	Onboard
Power Supply	Zalman 750w
Software	Windows 7