How do you 5/7v a fan with only 2 wires (PSU)

-ANDY- · Post by **-ANDY-** » Fri Jun 27, 2003 10:41 am

Maybe a silly question but been looking on the forums and all the guides seem to assume you have 3 wires? My PSU has only 2 wires soldered to the board so how do you 5/7v them?

sclawson · Post by **sclawson** » Fri Jun 27, 2003 1:26 pm

The third wire is only for monitoring the speed of the fan; it isn't needed to make the fan actually work. Therefore, connect the two wires to the positive and negative terminals on the fan (or the positive and negative wires coming out of the fan, if it's already wired). Hope this helps!

DonP · Post by **DonP** » Fri Jun 27, 2003 3:49 pm

-ANDY- wrote:Maybe a silly question but been looking on the forums and all the guides seem to assume you have 3 wires? My PSU has only 2 wires soldered to the board so how do you 5/7v them?

The 5/7V fiddle only works when connecting to the four wire molex connectors which plug into your hard disk/CD/DVD. That connector supplies 12V on the yellow wire and 5V on the red wire (I think).. and these are both relative to ground (the balck wire). Therefore if you want 5V to the fan you connect the fan to red and black, for 12v connect to yellow and black. For 7V you could connect the fan between yellow and red, the relative voltage between them is therefore 7V.

In the PSU however, and I do mean inside the PSU, not the wires coming out of it, there may only be two wires which would be 12V and ground. It may not necessarily be 12V because it could be thermistor controlled (and therefore a variable voltage which is a function of temperature somewhere). Anyway.. in this case there is no 5V against which you can get your 7V. The best way to undervolt your fan then is to run a resistor in series with it.. that's been dealt with in other threads.

One last thing.. about the RPM sensor on fans in the PSU (and on CPUs).. some BIOSes will complain if they don;t receive this signal, assume fan failure and won't boot - I've never tried this myself but I'm told you can usually disable it somewhere in the BIOS.

DonP.

sclawson · Post by **sclawson** » Fri Jun 27, 2003 7:11 pm

Sorry!

Just realized I misread your question. I thought you were just confused about how to hookup the fan, and the 5/7V thing didn't register. My bad!

Anyway, this is admittedly a quick-and-dirty (read LAZY) idea for you, but you could use one of the Zalman Fanmate regulators to control the voltage' just ignore the RPM sensing terminal on both input and output sides (or if you have access to the RPM sensing terminal, use it!).

Hope this helps a little more...

cliche · Post by **cliche** » Sun Jun 29, 2003 4:47 pm

sclawson wrote:Sorry! Just realized I misread your question. I thought you were just confused about how to hookup the fan, and the 5/7V thing didn't register. My bad!

Anyway, this is admittedly a quick-and-dirty (read LAZY) idea for you, but you could use one of the Zalman Fanmate regulators to control the voltage' just ignore the RPM sensing terminal on both input and output sides (or if you have access to the RPM sensing terminal, use it!).

Hope this helps a little more...

Yup, done this on mine running a panaflo L 80mm with fanmate.
Bloody quiet, but PSU whine from el-cheapo Q-Tech (not Q-technology) PSU has forced me to order a Seasinic 400 watt PSU (as per Mike C's recommonded list)

grnarrow · Post by **grnarrow** » Sun Jun 29, 2003 5:02 pm

I just happened to be looking at a page that might help you.
http://www.subzeropc.com/article/fantail.htm

DonP · Post by **DonP** » Sun Jun 29, 2003 5:30 pm

sclawson wrote:... but you could use one of the Zalman Fanmate regulators to control the voltage...

This is an idea but, at least in the UK, these things are damn expensive (about 10 to 18 gbp, ~15 to ~27 USD, excl delivery).. If you have a PSU with two fans it could add 50% to the cost of the PSU.

Non-variable alternatives are the use of (fixed) resisitors as I mentioned before or the use of diodes in series. Some speed reduction cables like the 10V one made by Akasa use three diodes in series.. a P-N junction in a diode drops about 0.6V.. three in parallel would be 1.8V, ergo ~10V.

Dropping the voltage like this can however make the diodes quite warm. Get some big ones ( diodes I mean

). But I don't really like this method because you need a lot to drop down to something like 7V (about nine of them).

Personally I think you can try a variable resistor (potentiometer) and drill a hole in the back of the PSU and stick it out the back. Some Enermaxes have something like this. Not sure what kind of wattage you'd need on it but I think it should work (I've seen some noiseblocker fans come with a pot rather than a transistor controlled voltage regulator [which can sink a bigger load]).

Oh, and one last idea.. it's a major hack and I'm not sure about it's reliability, but if you have two identical fans in the PSU which are connected in parallel then you could always connect them in series - they'd both get 6V across them in that case. Problems with this are that they must be identical otherwise they won;t drop the same voltage (and one may not start), and if one burns out then it'll stop the other one from working.

DonP.

sclawson · Post by **sclawson** » Mon Jun 30, 2003 1:06 am

DonP, as I am happily residing in the States I had no idea the Zalman Fanmates are so expensive in the UK! I had bought a batch of them for something like $6 each about a year ago. Seems ridiculous that there's so much of a markup in the UK! Maybe ordering several at once from a store in the States, perhaps combining orders with others, would result in some good savings?

Regarding the variable resistor, I'm admittedly not perfect with my electrical calculations, but it seems like a typical low-noise 80mm fan runs on 0.1A-0.2A current, so let's use 0.2A for calculations. Then a 7V drop (from 12V to 5V) would result in the pot handling 1.4W or power. Are commonly-available pots rated to absorb this much?

Kostik · Post by **Kostik** » Mon Jun 30, 2003 1:32 am

sclawson wrote:Regarding the variable resistor, I'm admittedly not perfect with my electrical calculations, but it seems like a typical low-noise 80mm fan runs on 0.1A-0.2A current, so let's use 0.2A for calculations. Then a 7V drop (from 12V to 5V) would result in the pot handling 1.4W or power. Are commonly-available pots rated to absorb this much?

Using 0.2A as the fan current (even though an L1A draws 0.07A) :
Fan resistance : 12*12/2.4 = 60 (ohms)
Resistor value for 7v drop : 7/5 * 60 = 84 (ohms)
power rating for resistor : 7*7 / 84 = 0.583 (watts)

Commonly-available indeed

Reference :
- http://www.cpemma.co.uk/diodes.html
- http://forums.silentpcreview.com/viewtopic.php?t=4707

cliche · Post by **cliche** » Mon Jun 30, 2003 2:42 pm

DonP wrote:
sclawson wrote:... but you could use one of the Zalman Fanmate regulators to control the voltage...
This is an idea but, at least in the UK, these things are damn expensive (about 10 to 18 gbp, ~15 to ~27 USD, excl delivery).. If you have a PSU with two fans it could add 50% to the cost of the PSU.

DonP.

http://www.aria.co.uk/DisplayProducts.a ... 3&orderby=

Do them here for 4 quid -enjoy, I have bought 6 (in my home town) so out of stock. Will be in soon tho

DonP · Post by **DonP** » Mon Jun 30, 2003 3:20 pm

cliche wrote: http://www.aria.co.uk/DisplayProducts.a ... 3&orderby=

Do them here for 4 quid -enjoy, I have bought 6 (in my home town) so out of stock. Will be in soon tho

Wow - 4.70 gbp is pretty cheap.
I've been looking at loads of places and even though prices have come down a bit in recent months the cheapest I found was 8 gbp.

Although Aria do want something like 7 gbp for delivery.

Thanks for that - I think I'll be putting a bulk order in

DonP.

cliche · Post by **cliche** » Mon Jun 30, 2003 3:41 pm

DonP wrote:
cliche wrote: http://www.aria.co.uk/DisplayProducts.a ... 3&orderby=

Do them here for 4 quid -enjoy, I have bought 6 (in my home town) so out of stock. Will be in soon tho
Wow - 4.70 gbp is pretty cheap.
I've been looking at loads of places and even though prices have come down a bit in recent months the cheapest I found was 8 gbp.

Although Aria do want something like 7 gbp for delivery.

Thanks for that - I think I'll be putting a bulk order in

DonP.

No worries

If I get some time, I'll pop in and buy u some. Just give me the price of a jiffy and postage (and goods !) . Bulk order might be best though

wrathbringer · Post by **wrathbringer** » Tue Jul 01, 2003 3:20 pm

I wonder if you can extend the fan cables in psu through soldering and connect the PSU fans to fan bus. What type of wires does these fan use? I might just try it out and report my results since 5v or 7v modding a fan would of course be better than having to pay 20bucks to buy 2 new fans.

Dave2986 · Post by **Dave2986** » Wed Jul 02, 2003 12:01 am

could you use one of theses 3 pin reduction cables?

Jan Kivar · Post by **Jan Kivar** » Wed Jul 02, 2003 12:38 am

Have You considered soldering fan wires to the pins where the wires start in the PSU (ATX and the rest)? There You will find 5V wire and ground wire easily.

Try the PSU without the fan attached. Some PSUs won't start if there is no fan connected to the fan connector.

Cheers,

Jan

sclawson · Post by **sclawson** » Wed Jul 02, 2003 4:55 am

wrathbringer wrote:I wonder if you can extend the fan cables in psu through soldering and connect the PSU fans to fan bus. What type of wires does these fan use? I might just try it out and report my results since 5v or 7v modding a fan would of course be better than having to pay 20bucks to buy 2 new fans.

I did exactly that with one of my Enermax Whisper PSU's. I replaced the stock fan with a Panaflo and brought the fan leads out of the PSU through the same hole that all the other wires use, then connected the leads to a Zalman Fanmate and finally to one of the fan headers. That way I was able to control the speed of the fan without opening the PSU, although I still had to open the side of the case. It's been working fine for at least a year now...

al bundy · Post by **al bundy** » Wed Jul 02, 2003 5:12 am

sclawson wrote:I did exactly that with one of my Enermax Whisper PSU's. I replaced the stock fan with a Panaflo and brought the fan leads out of the PSU through the same hole that all the other wires use, then connected the leads to a Zalman Fanmate and finally to one of the fan headers. That way I was able to control the speed of the fan without opening the PSU, although I still had to open the side of the case. It's been working fine for at least a year now...

I've done this as well with several different PSU's now. I've also been using a 3-to-4 pin adapter so that the Fanmate can be run from one of the standard 4-pin PSU connectors.

Do you run the fan at the slowest speed that the Fanmate allows? If you are doing this successfully, then I might try turning the fan speed down all the way too...

wrathbringer · Post by **wrathbringer** » Wed Jul 02, 2003 5:23 am

another idea I have is that since the 4pin connector wires are everywhere in the PSU, find 1 set and cut the head part out. Then you have a red, yellow and 2 blacks to use inside the PSU. If you have 2 fans in the PSU both in series taking power from one 12v(yellow line) wouldn't it roughly be 6v on each fan presumming that both fans are the same? you can also make a 7v mod and run both fans in parellel, which i'm sure the power supply rail can take the amperage.

DonP · Post by **DonP** » Wed Jul 02, 2003 7:12 am

Dave2986 wrote:could you use one of theses 3 pin reduction cables?

If you are talking about the 10V cable I've found them to be pretty useless - hardly no difference at all. It's the cable I mention (three diodes in series) in my earlier post.

The 7V cable on that page needs to plug into the 4pin molex - which you don;t have inside the case (without cutting other cables).. hence this whole problem.

DonP.

DonP · Post by **DonP** » Wed Jul 02, 2003 7:18 am

cliche wrote: http://www.aria.co.uk/DisplayProducts.a ... 3&orderby=

Do them here for 4 quid -enjoy, I have bought 6 (in my home town) so out of stock. Will be in soon tho

You wouldn't happen to know of a cheap source of Thermalright SLK-900U CPU heatsinks? overclockers.co.uk want 53 GBP.. about as much as I paid for my PSU

DonP.

wrathbringer · Post by **wrathbringer** » Wed Jul 02, 2003 7:52 am

DonP, take a look at the zalman 7000AlCu they're more silent than the thermaltake and perform similar.

sclawson · Post by **sclawson** » Wed Jul 02, 2003 9:40 am

al bundy wrote:Do you run the fan at the slowest speed that the Fanmate allows? If you are doing this successfully, then I might try turning the fan speed down all the way too...

I *have* run on the lowest speed in the past, though currently that PSU is in a higher-powered PC for which I increased the speed.

I'd feel the air coming out the back of the PSU and check temperature readings inside the case. Start at a higher speed, let things stabilize, then turn the fan's speed down and stabilize again. If the temps increase beyond what you're comfortable with, bring the speed up a bit. Of course, if the temps never stabilize, there's no question that you'll need to run it faster!

It also helps to have an exhaust fan mounted just below the PSU to help remove some of the heat -- in other words, the PSU fan is mainly responsible for PSU heat, while the other fan is responsible for most of the heat generated by CPU, graphics card, etc. That fan can be turned all the way down, too, and the combination of both fans can allow you to run each on the lowest setting. I know from experience that definitely works well. Even if one of those fans has to run full speed (assuming the fans are Panaflos), the noise won't be too bad, and will sound like a whisper-volume gentle blowing of air, with absolutely no high-pitched whine.

(I just got up from a nap, so hopefully this post isn't incoherent!

)

sclawson · Post by **sclawson** » Wed Jul 02, 2003 9:42 am

It's worth noting that plugging the PSU fan into one of the motherboard fan headers, you can have the motherboard itself control fan speed, which can be a big win if you have the good fortune of your motherboard's BIOS supporting variable fan speed based on temps...

cliche · Post by **cliche** » Wed Jul 02, 2003 10:42 am

DonP wrote:
cliche wrote: http://www.aria.co.uk/DisplayProducts.a ... 3&orderby=

Do them here for 4 quid -enjoy, I have bought 6 (in my home town) so out of stock. Will be in soon tho
You wouldn't happen to know of a cheap source of Thermalright SLK-900U CPU heatsinks? overclockers.co.uk want 53 GBP.. about as much as I paid for my PSU

DonP.

sorry no, but wrathbringer is correct- I have a Zalman 7000 cu (heavy bugger), and is soo quiet

DonP · Post by **DonP** » Wed Jul 02, 2003 10:44 am

wrathbringer wrote:DonP, take a look at the zalman 7000AlCu they're more silent than the thermaltake and perform similar.

Thanks, but I really like the idea of putting my own fan on the HS.. a SLK-900U with a 92mm papst would be good.. but due to it's price I'm investigating the Alpha PAL8942t.. with a panaflo or a papst.. depending on which one I can find with a speed sensor.

The Zalman 7000CU is pretty good.. but it costs the same as the SLK.. I'll investigate the 700ALCU some more but it'll probably be just as good as the 8942t and the price is the same.

Thanks, DonP.

wrathbringer · Post by **wrathbringer** » Wed Jul 02, 2003 3:47 pm

well, here's a mini review from some guy at the [H] about the zalman and the 900 slk, seems like zalman is a good choice esbcially the AlCu version which is about 10 bucks cheaper than the copper and light so you save on shipping.

http://hardforum.com/showthread.php?s=&threadid=624949

wrathbringer · Post by **wrathbringer** » Thu Jul 03, 2003 5:04 am

well I finished my PSU mod now and it wasn't very hard. I took the wires of both fans and made them go out the PSU, then solderd the positives in paralell and negitive in paralell and after that I soldered the positive to the 12v line on a molex connector and the negitive to a 5v line. Worked perfectly, both fans are now at 7v.

-ANDY- · Post by **-ANDY-** » Thu Jul 03, 2003 11:07 am

DonP wrote:
cliche wrote: http://www.aria.co.uk/DisplayProducts.a ... 3&orderby=

Do them here for 4 quid -enjoy, I have bought 6 (in my home town) so out of stock. Will be in soon tho
Wow - 4.70 gbp is pretty cheap.
I've been looking at loads of places and even though prices have come down a bit in recent months the cheapest I found was 8 gbp.

Although Aria do want something like 7 gbp for delivery.

Thanks for that - I think I'll be putting a bulk order in

DonP.

I only want 2 but its going to cost me £17.57 the postage doubles the price thats crazy!

Anyone want to do a joint/bulk order, I figure it'll only cost £1 to send one of these through the post if a couple of us order together we can get them for say £6 each or less if people want more than one.

Anyone interested or wouldn't mind adding my order to theirs

send me an email [email protected]

How do you 5/7v a fan with only 2 wires (PSU)

How do you 5/7v a fan with only 2 wires (PSU)

Re: How do you 5/7v a fan with only 2 wires (PSU)