# 7 Volt mod



## Necrofire (Nov 30, 2007)

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.


----------



## Namslas90 (Nov 30, 2007)

Then ask your brother to design you a simple voltage devider circuit off the 12 volt rail.


----------



## Necrofire (Nov 30, 2007)

I don't get it.


----------



## Namslas90 (Nov 30, 2007)

Necrofire said:


> I don't get it.



Ok, then impress him by doing it yourself...

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html

It's very simple.

If your PSU is of any quality I dought that too much harm would occure from the 7-volt trick.  The worst would be a little niose (acting as ripple)on that rail. as long as that rail is spare it shouldn't cause too much harm.


----------



## Necrofire (Nov 30, 2007)

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?


----------



## Namslas90 (Nov 30, 2007)

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?



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.


----------



## Necrofire (Nov 30, 2007)

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.


----------



## Namslas90 (Nov 30, 2007)

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.


----------



## Necrofire (Nov 30, 2007)

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


----------



## Namslas90 (Nov 30, 2007)

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



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.


----------



## Necrofire (Nov 30, 2007)

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)?


----------



## Namslas90 (Nov 30, 2007)

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)?



Whats the make/model of the fan??


----------



## Necrofire (Nov 30, 2007)

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.


----------



## Namslas90 (Nov 30, 2007)

Well here's the spec sheet, for all the help is it....

http://www.cbs.it/acrobat/jamicon/jf0825_00.pdf

Yeah, it's gonna be low so try it with 80 Ohms, see what you get, should be ok,


----------



## Necrofire (Nov 30, 2007)

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.


----------



## Mussels (Nov 30, 2007)

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.



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.


----------



## Necrofire (Nov 30, 2007)

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?


----------



## lemonadesoda (Nov 30, 2007)

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.


----------



## strick94u (Dec 1, 2007)

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.



Agree just get a tri cool antec fan set it on low and forget it.


----------



## lemonadesoda (Dec 1, 2007)

Oh, second tip... put 2 fans in series across the 12v. Each gets 6v. (Assuming they are the same make/model).


----------



## Bluefox1115 (Dec 2, 2007)

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!


----------



## Necrofire (Dec 2, 2007)

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!



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.


----------



## strick94u (Dec 2, 2007)

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?


----------



## Bluefox1115 (Dec 2, 2007)

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%..


----------



## Necrofire (Dec 3, 2007)

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.


----------



## Bluefox1115 (Dec 3, 2007)

LOUD is not the answer! Then again.. neither is electrical fire...


----------



## Mussels (Dec 4, 2007)

Necrofire said:


> 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.
> 
> ...



loud is bad  all my systems rate as either quiet or silent (the air conditioner here drowns them out from two rooms away)


----------



## t_ski (Dec 4, 2007)

I was going to suggest trying to make a simple fan controller out of parts that cost less than $5, but cliff Anderson's www.fanbus.com is no longer working.  BUt since it isn't, the best I can come up with ATM is a link to one already made:

http://www.sidewindercomputers.com/rheosformc.html

$10.


----------



## Namslas90 (Dec 4, 2007)

t_ski said:


> I was going to suggest trying to make a simple fan controller out of parts that cost less than $5, but cliff Anderson's www.fanbus.com is no longer working.  BUt since it isn't, the best I can come up with ATM is a link to one already made:
> 
> http://www.sidewindercomputers.com/rheosformc.html
> 
> $10.



Here's a guide;LINK


----------



## t_ski (Dec 4, 2007)

Yeah, that's a link for a basic switch-type.  The one I had in mind was based on a rheostat and (depending on the load of the fan or fans), can run anywhere between 4V and 12V.

In fact, I think I may still have a couple of the rheostats I used in the garage.  All you have to do is cut the 12V wire and solder the rheostat in place.  Pretty easy stuff.

EDIT:  Found this:

http://www.virtual-hideout.net/guides/rheostats/index.shtml


----------



## strick94u (Dec 4, 2007)

I guess I don't understand what he is trying to do here. He wants to reduce the voltage to the 12 volt fans but he wants to do it cheap. So I don't see where building a 30 or 40 dollar fan controller would do when you can buy one just as cheap. Fact is his first link shows a strange way of doing it, his brother has a degree in electrical engineering yet won't help him figure this problem out. So far there are half a dozen different ways to do it here but all cost more than 3 dollars. My point is this if you want a whisper quite PC its going to cost more than 3 dollars. 
Sorry truth hurts


----------



## keakar (Dec 4, 2007)

go to radio shack and buy some (large diodes #1N4003), they will drop the voltage down 0.75v for each one you use so if you use 8 of them soldered end to end you will drop your voltage from 12v to 8v, you can add as many as needed to reach the desired fan speed but you might not get enough cooling if you go too slow.

NOTE: diodes only allow voltage to go in one direction just like leds so pay attention to how you connect them, the stripe always goes on the fan side for the red wire and if used on the negative wire the stripe goes to the plug side away from the fan.


----------



## t_ski (Dec 4, 2007)

strick94u said:


> I guess I don't understand what he is trying to do here. He wants to reduce the voltage to the 12 volt fans but he wants to do it cheap. So I don't see where building a 30 or 40 dollar fan controller would do when you can buy one just as cheap. Fact is his first link shows a strange way of doing it, his brother has a degree in electrical engineering yet won't help him figure this problem out. So far there are half a dozen different ways to do it here but all cost more than 3 dollars. My point is this if you want a whisper quite PC its going to cost more than 3 dollars.
> Sorry truth hurts



Nah, mine only costs about $3 per fan or two.


----------



## Mussels (Dec 4, 2007)

t_ski said:


> Nah, mine only costs about $3 per fan or two.



i pay upto $30 per fan... thn again, i'm willing to pay for quality here.


----------



## t_ski (Dec 4, 2007)

Part of the fun in those days was being able to make something like these fan controllers.  I must have made half a dozen of them.  Today, I have a Zalman MFC1 that I use instead, and I love Yate Loon fans: they're inexpensive, not too loud at full speed even though they're pushing a good amount of air, and at 5v they're quieter than any other fan in the system.


----------



## Mussels (Dec 5, 2007)

t_ski said:


> Part of the fun in those days was being able to make something like these fan controllers.  I must have made half a dozen of them.  Today, I have a Zalman MFC1 that I use instead, and I love Yate Loon fans: they're inexpensive, not too loud at full speed even though they're pushing a good amount of air, and at 5v they're quieter than any other fan in the system.



cant get yates in aus  i get teh nexus orange and run them at 7v  pretty much the same as you. (i've heard that nexus orange are rebadged yate loons)


----------



## strick94u (Dec 5, 2007)

keakar said:


> go to radio shack and buy some diodes, they will drop the voltage down 1.5v for each one you use so if you use 4 of them soldered end to end you will drop your voltage from 12v to 8v, you can even add a 5th diode to get it down to 6.5v if you really need to but you might not get enough airflow if you go too slow.
> 
> NOTE: diodes only allow voltage to go in one direction just like leds so pay attention to how you connect them, the stripe always goes on the fan side for the red wire and if used on the negative wire the stripe goes to the plug side away from the fan.



Diodes drop approximately .5 volts per diode


----------



## Necrofire (Dec 6, 2007)

Well, doesn't the power get converted to heat?
Heat = bad in my book.
Rheostats are nice, but a little pricey. I'm just gonna leave my setup as it is:
Quiet adjustable fan I already own in front, 80mm quiet fan on GPU, and tornado fan on desk somewhere.

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.


----------



## t_ski (Dec 6, 2007)

Usually with a rheostat, if the ground wires are connected to the third terminal on the rheostat, then it will generate a lot of heat.  When I made ones for my rigs I did not do that, and never noticed any issues or excess heat.

Many fans can start at 5v, but there are some that won't start until 7v.  In that case, you just need to crank it up for the fan to start, then turn it back down to where you want to run it at.


----------



## keakar (Dec 10, 2007)

strick94u said:


> Diodes drop approximately .5 volts per diode



the ones im using (1N4003) have a 0.75v voltage drop so it depends on the size you use. with the ones i use it takes 2 to get a 1.5v drop measured with a multimeter.

the main advantage of the diode over the resister is the resistor gets way way hotter than the diode will so while the diode will be very warm, the resistor will be HOT


----------



## t_ski (Dec 10, 2007)

I suppose that may depend on the resistor you are using.  None of the resistors I've used got hot, however I didn't use them for fans.

BTW, a diode is basicly a one-way resistor.  Another advantage is the voltage can't go back through the wrong way.


----------



## keakar (Dec 10, 2007)

Necrofire said:


> Well, doesn't the power get converted to heat?
> Heat = bad in my book.
> Rheostats are nice, but a little pricey. I'm just gonna leave my setup as it is:
> Quiet adjustable fan I already own in front, 80mm quiet fan on GPU, and tornado fan on desk somewhere.
> ...



most times its just the 120mm + fans that have trouble starting on only 5v


----------



## keakar (Dec 10, 2007)

t_ski said:


> I suppose that may depend on the resistor you are using.  None of the resistors I've used got hot, however I didn't use them for fans.
> 
> BTW, a diode is basicly a one-way resistor.  Another advantage is the voltage can't go back through the wrong way.



when you start putting some juice through em resistors will get hot enough to burn your fingers.


----------



## Necrofire (Dec 10, 2007)

keakar said:


> most times its just the 120mm + fans that have trouble starting on only 5v



That's waht I thought also. Seeing as how this fan is a 120mm fan, I had just assumed it didn't start at 5 volts. It makes sense, the smaller the fan, the smaller the motor (generally) and the less resistance to "turning over."
Anyway, the fan turns over at 5 volts, so I'm happy that I don't have to mess with 7 volt crap or anything. What I might do though is put a switch that'll go between 5 volts and 12 volts.

Molex___12V___              
.....................|__...........____Neg____molex
Molex___5V____...|.........|
......................|..|........|
....................Switch____Fan

Yay for ascii diagrams


----------



## keakar (Dec 10, 2007)

Necrofire said:


> That's waht I thought also. Seeing as how this fan is a 120mm fan, I had just assumed it didn't start at 5 volts. It makes sense, the smaller the fan, the smaller the motor (generally) and the less resistance to "turning over."
> Anyway, the fan turns over at 5 volts, so I'm happy that I don't have to mess with 7 volt crap or anything. What I might do though is put a switch that'll go between 5 volts and 12 volts.
> 
> Molex___12V___
> ...



noooo  dont do the switch, its rare to happen but it can "bridge" the two if the switch fails and while the psu protection should kick in and trip, you always have that chance something can be hurt by a short. just not worth risking for a minor convienience

http://www.kpsec.freeuk.com/components/switch.htm#standard


----------



## Necrofire (Dec 10, 2007)

keakar said:


> noooo  dont do the switch, its rare to happen but it can "bridge" the two if the switch fails and while the psu protection should kick in and trip, you always have that chance something can be hurt by a short. just not worth risking for a minor convienience
> 
> http://www.kpsec.freeuk.com/components/switch.htm#standard



I had already pondered that happening, and the switch I tested can't do that. I tested it, and as soon as it's about middle way, it's off for both sides, so I'm in the clear unless somehow the switch magically expands to contact both at once momentarily while switching. The switch I have is a SPDT, and it's nearly impossible to contact the opposite ends.


----------



## t_ski (Dec 11, 2007)

Most of the fan controller I built for myself were made that same way.  Only recently did I find the rheostat version.  Never had any problems.


----------



## Necrofire (Dec 11, 2007)

No need for a rheostat, I'm building a custom case and I won't need that much fine tuning for the fans, just a "low" setting and a "tornado" setting.


----------

