• Welcome to TechPowerUp Forums, Guest! Please check out our forum guidelines for info related to our community.
  • The forums have been upgraded with support for dark mode. By default it will follow the setting on your system/browser. You may override it by scrolling to the end of the page and clicking the gears icon.

7 Volt mod

Necrofire

Necrofire

New Member
Joined
Nov 1, 2007
Messages
585 (0.09/day)
System Specs
System Name Chuck
Processor Core i5-2500k @ 4.5Ghz
Motherboard msi P67A-C43
Cooling hyper 212, 2 120mm fans
Memory 8GB DDR3 1600MHz
Video Card(s) XFX 6870
Storage 60GB sata3 sandforce ssd, 1TB samsung hdd
Display(s) Yamakazi Catleap
Case Possibly Antec, not sure
Audio Device(s) Onboard
Power Supply Rosewill 600W
I want to do the 7-volt trick for a noisy fan in my case. The problem I have is that my brother said that anything that would use the same 5 or 12 volt line, there would be feedback of some sort and it might damage either the power supply or whatever was on those lines. Is this true? Is there something bad about getting 7 volts from the 12 and 5?

He does have a bachelors in electrical engineering, btw, so if don't have any background using electricity or have done this mod yourself for more than a couple of months, I don't want to hear it.

EDIT: I'm so stupid, I had just assumed that my 12 volt fan could not start at 5 volts. Well, I'm thinking of reusing my 12 volt tornado at 5 volts, since I just tried it and it's really quiet.
I can't believe I never thought of just trying it.
 
Last edited:
Then ask your brother to design you a simple voltage devider circuit off the 12 volt rail.

:toast:
 
I don't get it.
 
Well, since most power supplies, or at least everyone I have ever seen, only have 1 5V rail, I guess it wouldn't be the spare.

How do I check the resistance of a fan?
 
Necrofire said:
Well, since most power supplies, or at least everyone I have ever seen, only have 1 5V rail, I guess it wouldn't be the spare.

How do I check the resistance of a fan?
Click to expand...

Use Google to search for the specs on your fan by searching the model Number.

You know the easiest thing to do is just get a variable speed fan with controller.:toast:
 
I have one fan like that, but I don't have another $16 to go get another.

EDIT: The one fan I have that has variable speed is in use by my graphics card, I burnt out the stock fan and slapped a 120mm on it.
 
IF you have an old and unused PSU laying around just use it for the mod (temperaily), just use a piece of wire(or paperclip) to connect the green wire on the 20(4) pin atx connector to the black wire on the same atx connector. This "shunt" will bypass the safety default (motherboard detect) so the PSU will run.

:toast:
 
I know all about turning power supplies on. It's how I'm testing the 7 volts right now.
I thought that power supplies needed a certain load on all the rails to function properly, which is why I didn't do this in the end and just bought a new power supply
 
Necrofire said:
I know all about turning power supplies on. It's how I'm testing the 7 volts right now.
I thought that power supplies needed a certain load on all the rails to function properly, which is why I didn't do this in the end and just bought a new power supply
Click to expand...

we're only talking about running one fan here, and not forever; just untill you can get another fan....I'm not talking about replacing the PSU running the computer. Just use the other PSU to run that one fan on 7 volts, (or several if you want). Sure it will look like heck, but only till you get the new fan.

Or- just make the voltage devider, "safe" it up with some heatshrink or use insulation pulled off spare wire.

:toast:
 
I really appreciate the answers. I assumed it was ok, but I needed another opinion.

BTW, google didn't turn up anything for ohms on the fan. Is it safe to assume that it's 80 ohms (12v/0.15a)?
 
Necrofire said:
I really appreciate the answers. I assumed it was ok, but I needed another opinion.

BTW, google didn't turn up anything for ohms on the fan. Is it safe to assume that it's 80 ohms (12v/0.15a)?
Click to expand...

Whats the make/model of the fan??
 
Jamicon
Kaimei electronic corp
JF0825S1M
But this is for the fan that I was testing, the fan I want to run 7 volts on is in an inaccessible place right now (in front of 3 hard drives).

EDIT: your specs are funny btw. I used to have a bunch of junk computers laying around. I also had a bunch of junk laying around, various resistors, capacitors and the like from numerous dead mobos and power suppplies.
 
Last edited:
I'm confused as to how to work my multimeter.
When I put the multimeter on 2000k, I get 400 on the screen. I've only measured volts and amps with this thing.

EDIT: and continuity.

EDIT2: Whoops, forgot to mention that I measured the fan.
 
Last edited:
Necrofire said:
I want to do the 7-volt trick for a noisy fan in my case. The problem I have is that my brother said that anything that would use the same 5 or 12 volt line, there would be feedback of some sort and it might damage either the power supply or whatever was on those lines. Is this true? Is there something bad about getting 7 volts from the 12 and 5?

He does have a bachelors in electrical engineering, btw, so if don't have any background using electricity or have done this mod yourself for more than a couple of months, I don't want to hear it.
Click to expand...

i know this trick and use it all teh time.

The ONLY time its dangerous, is if you draw more 7V wattage than you do between the 5V and 12V lines. a 1-2W fan isnt going to do anything remotely close to the rest of your system, so it is perfectly safe - i do this trick all the time and have NEVER had a problem.
 
Umm, wouldn't the fan still be pulling the same amount of amps?
Let's see.. 7V x 0.25A = 1.75W. I guess it can't hurt.
I have 2 12 volt rails, and (obviously) one 5 volt rail. And you guys are sure that it won't hurt the hard drives or anything?

I had another question, how about tapping the 5V and the -3.3V?

Also, what does pulling high or low mean?
 
Last edited:
STOP RIGHT THERE.

As Mussels said, you'd be ok.

But you are wasting more time, and buying those fan resistor kits, is going to cost you more money thatn buying a new 12v fan with a lower speed rating. Just look at the spec sheet you were given. There are MULTIPLE fans, with different speeds, volume flows, and noise, ALL RUNNING AT 12 V.
 
lemonadesoda said:
STOP RIGHT THERE.

As Mussels said, you'd be ok.

But you are wasting more time, and buying those fan resistor kits, is going to cost you more money thatn buying a new 12v fan with a lower speed rating. Just look at the spec sheet you were given. There are MULTIPLE fans, with different speeds, volume flows, and noise, ALL RUNNING AT 12 V.
Click to expand...

Agree just get a tri cool antec fan set it on low and forget it.
 
Oh, second tip... put 2 fans in series across the 12v. Each gets 6v. (Assuming they are the same make/model).
 
how hard is it to just go buy a freaking $3 fan at a local computer store? if you're lucky they may give you one free! :p
 
Bluefox1115 said:
how hard is it to just go buy a freaking $3 fan at a local computer store? if you're lucky they may give you one free! :p
Click to expand...

Very, I have fans that work fine, why would I go out and buy a new one?

Anyway, my tests with an 80mm fan worked fine for about 2 hours, until I got bored and turned my power supply off. When I went to try my 120mm, the power supply shut off instantly.

I decided in the end to just take the VERY quiet 120mm fan I already have and put it in front, and put a smaller 80mm fan that I have that also happens to be very quiet.
 
Big problem with most of us are were over clockers and that means our pc's sound like central air conditioning units. All the adjustable fans use are simple adjustable resistors,you want to cut the current in half take a resistor that has the same amount of resistance as your fan and place it in the power wire the 2 loads in series 6 volts each no big deal. Lower volts may make the fan not want to start as it gets older though this is one of the reasons its better to just get a fan thats setup for it all ready whats 14 bucks for something that has what you need built in?
 
thats my point. I have all Antec tri cools, all set on high, and I dont think they are loud at all. in fact I think they are fairly quiet being at 100%..
 
That fan blows a crap load of air. It's some cheap fan with 7 fins. It's just loud.

I traded it for the quiet one I have, and put a quiet 80mm on my graphics card in place of that. Now my system purrs along.

For $3 more than the Antec Tricool fans, I got a variable fan that is ~5dB quieter on its lowest setting, and is louder on highest setting than all these items combined...
1. 3 hard drives
2. stock 8600GTS fan
3. cpu fan on highest setting
4. 2 80mm fans in power supply

It's like a miniature tornado when I turn it up.
 
You must log in or register to reply here.
Back
Top