120mm 12v fan to a 7v 3pin fan adapter

Gyustarr

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Sep 11, 2014
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Greetings. I have an old desktop in desperate need of good airflow, and I want to add 2 3pin 120mm 12v led fans that I was given.
However the mobo headers are occupied by the cpu fan and a front led fan. So, I'm thinking of buying a 4pin molex to 3x3 pin fan adapter either of 5v or 7v directly plugged to the psu.
My question is this: are the fans going to work with a lower voltage adapter? Or should I find a Y splitter that connects to the mobo?
In case it's relevant, here are the fans I was given: https://www.aliexpress.com/store/product/Aigo-Z6-120mm-Computer-PC-Case-Cooling-Fan-LED-Quiet-High-Airflow-CPU-Radiator/1751463_32820194400.html

Thank you for your time.
 
Solution
You can buy the 7v one , if it works & the fans spin up on boot & you're happy with led brightness then all good
If not its a 2 minute job to rewire it back to 12v anyway (it's simply pulling a pin from the molex plug & swapping it to a different socket)
Back in the day a lot of motherboards didn't even have fan headers. All fans came with a molex connector. An adapter should be fine.

A Y splitter is fine as well and will give you some feedback or control (I forget which pins gets axed in this situation) but not as much as if each fan was plugged into the motherboard directly.

another option would be to get a fan controller. In your case it's probably not worth it.
 


when you plug a fan into a molex connector on a 4 wire fan you lose the sense and control wire leaving just the voltage and common, on a 3 wire fan you loose the sense (RPM) wire. The PSU has no way of telling the motherboard how fast the fan is spinning.
 


I'm fine with no control, I just want to make sure they would work even with the voltage difference between the fans and the adapter.
 
Its hard to say if the fans will work or not. I have a fan controller in one of my computers, when you boot the computer up it will start the fans with 12v and then drop them down to the set voltage which is around 7.4v If i turn the voltage off with the knob and then slowly turn it up you have to get in he 8-9v range before the fans will spin, then you can turn them back down to 7v
 
Why not just run them at 12v ??
They're only 1100rpm anyway & look to be pretty quiet full speed.

Also dropping voltage on led fans dims the LED's drastically too.
At 7v I'd imagine they'll be very very dim.

They're not affected by pwm control because the off time between pulses is too short for the LED's to actually switch off.
 


I can't find molex to 3pin adapters with 12v, best I've found in my country is this but only in 7v.
 
You can buy the 7v one , if it works & the fans spin up on boot & you're happy with led brightness then all good
If not its a 2 minute job to rewire it back to 12v anyway (it's simply pulling a pin from the molex plug & swapping it to a different socket)
 
Solution


I'm not familiar with such process. I didn't need worry about voltages until now :/ . Do you happen to have a video that demonstrates this?

You can buy molex to 4 pin you know ??
.Can't find a 12v either.
Would a fan controller solve my issue?
 
https://youtu.be/SyrvdDkS_SA

On that video he's down rating from 12 to 7v.

The fan cable you linked only has 2 cables as it is.

A 7v cable will come with a molex that has a pin on each outside edge of the connector, this shorts the 12v & 5v lives creating resistance which brings it down to around 7v .

Four_Pin_Molex_Connector01.png


You simply pull the 5v pin out & put it back into one of the 2 centre ground sockets



That puts it back at 12v , it's a simple 2 minute process & just requires a small jewellers screwdriver.


 


I see. Thanks for the informative post!

There was a debate in the comment section about this method and how it affects the psu. I think it would be better if waited a bit and I bought a decent fan controller instead.
 
If you're running a $10 PSU on a system pre 2009 then it could possibly , but unlikely, create issues .on a decent PSU & a fairly modern system its 100% safe.

& anyway what I'm suggesting ia buying the 7v cable if that's all that's available (which is theoretically out of spec at 7v) & swapping it back to 12v (which would put it back in spec)

 


Well, the psu is a relatively new evga 600W 80+, as for the mobo it's about 7 years old.
But you gave me some good advice to consider. Thank you for it!
 
As I said nothing dangerous about it .
It is considered 'crossloading' which sounds bad but the fact is to cause any damage to the PSU you would have to have more current draw ampage wise on the fans than there is in the rest of the system.

Which is impossible because fans generally drop .25a each at the max.

A system at idle is still going to pull 70-80w.

To crossload that dangerously with fans would require you to wire up around 150 fans minimum .

The guy who said it blew his PSU did not have the rest of the system connected & his PSU will have been a bag o crap generic model anyway.

For you its perfectly safe IMO