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 Post subject: Quick/Easy 7V mod for fans w/3pin tails - Now with pics :)
PostPosted: Mon Dec 08, 2003 5:24 pm 
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*Disclaimer* I am not responsible for any damage to your system as a result of this mod.

I just wanted to write up this quick mod that I came up with for all the Panaflo users out there using 3-pin to 4-pin converters. It's real simple to do, it only took 10 minutes from beginning to end :).

I've been using my Panaflo's at 12V for awhile but I kept hearing that they were much better at 7V so I decided to try it out today. Here's what you'll need:

- 1 toothpick
- "branch" of 12V wiring coming from your PSU with no other components connected to it.
- As many case fans as you like, as long as they as they connect through 3-pin to 4-pin converters.
- As many Y-connectors as needed. These are the 3-pin to 4-pin connectors I am talking about, they have two molex connectors one male one female and one male 3-pin connector

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How it's done:
Make sure there is nothing connected to the PSU "branch" you will be using because once you do this mod, everything on that branch will effectively operate at 7V
Image

First use the toothpick to gently press the sides of the male molex of the Y-connector's red and black wire. That is your molex connector should have the wires as follow (from left to right): Yellow, black, black, red. If you do it properly the crimped wires should slide out effortlessly from the connector.
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Next, Place the black connector into the red connector's old spot. Note that this black connector should have both the molex's black wire and the 3-pin connector's black wire crimped. Now slide it gently and make sure it is in solidly by tugging lightly on it, the connector should not slide out.
Image

I strongly suggest at this point that you label the pass-through cable "7V fan IN" using a plain label for future reference.

Now you have a red wire that is dangling, I covered mine up with electrical tape so that I can undo the mod if I ever have to go back to 12V on these fans. This is very important as you don't want a loose ground pin flopping around in your case.. For a more permanent solution, simply cut the cable flush with the other molex connector.

Your modifies molex connector should now have cables in this order: "Yellow-Empty-Black-Black"
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Image

I suggest you label this end "7V FAN ONLY" as anything that gets connected to this branch will only be receiving +7V

Now simply connect all other Y-connector (3-pin to 4-pin) in series as needed and connect to the branch of the PSU you had previously cleared. Now connect all the fans as usual and you're ready to go. All the fans will be receiving +7V.
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Check with a multimeter if you like:
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Be aware that this may not be the best idea if you have a PSU that doesn't support too much current on the +5V rail and you have some large power hungry fans.


Last edited by RaynorWolfcastle on Tue Dec 09, 2003 7:56 pm, edited 5 times in total.

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 Post subject:
PostPosted: Mon Dec 08, 2003 5:38 pm 
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Are you sure, RaynorWolfcastle? I'm pretty sure that the standard way to get 7V from a mod like that is to use the red wire (+5V) instead of the black (ground=0V), to achieve a potential difference of 12-5=7 volts. Perhaps I misunderstood what you were saying...

It might be a good idea for you to use a multimeter to ensure you're getting the correct results this time (and always) before you connect components.

Here's how I would suggest getting 7V & 5V from a Molex connector:
12V (normal) -> yellow-black-black-red
7V -> yellow-red-black-black
5V -> red-black-black-yellow

Does this sound right to you SPCR-ers?


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 Post subject:
PostPosted: Mon Dec 08, 2003 5:44 pm 
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Oh, sorry! I just understood what you meant -- you are modifying the 3-4 adaptor, not the PSU Molex connector. My apologies. It should be noted that this will not affect other things on the main PSU "branch" as you called it, but it certainly would have an adverse effect on any non-fan components you might connect to the pass-through adaptor.

Somebody confirm/challenge this, please, before people take my advice and I cause some innocent newbie's house to burn down.


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 Post subject:
PostPosted: Mon Dec 08, 2003 5:51 pm 
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Putz wrote:
Oh, sorry! I just understood what you meant -- you are modifying the 3-4 adaptor, not the PSU Molex connector. My apologies. It should be noted that this will not affect other things on the main PSU "branch" as you called it, but it certainly would have an adverse effect on any non-fan components you might connect to the pass-through adaptor.

Somebody confirm/challenge this, please, before people take my advice and I cause some innocent newbie's house to burn down.


That's correct, the mod leaves the PSU untouched. And you are right, it doesn't affect other things on the other PSU connectors on that branch. Nonetheless, I suggested clearing a branch for this to avoid any confusion regarding where you would be getting 7V instead of 12V.

If you're really picky about your fan voltages, you can set-up that PSU branch to have +7V, +5V and +12V connectors using the Molex configuration you describe.

Again, the reason I suggested putting this on a separate branch is to try to avoid confusion or a newbie burning their house down.


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 Post subject:
PostPosted: Tue Dec 09, 2003 6:56 am 
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It has been argued before that the 7V mod is not that great for the PSU. You will be using the PSU in a way it was not designed to, so depending on how your PSU is designed this might not be a great thing to do.

I would much prefere putting diods on the hot wire that goes to the fan.
A quick check on a local electronics store say you get 25 diods for $1.50.
Depending on how many you put in series you can pick what voltage you want, and you can have different voltage on each fan if you like to.
Downside is slightly more work.


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 Post subject: diodes
PostPosted: Tue Dec 09, 2003 7:45 am 
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i have modified my setup for 7v by switching the 5V and 12V ground lines as described above. All fans are run off of 1 branch of the wires. I have wrapped these wires with yellow electrical tape so as not to plug in an HD into one of these accidentally.

In any case, the reason you reccomend using diodes is if the fan circuitry shorts is that correct? Wont the PSU simply shut down as it should?

What is the type of diode used in such a circuit? Doesnt a diode just allow current to flow through in one direction, but not the other? How would this be used in a 7V mod?

Thanks in advance

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 Post subject:
PostPosted: Tue Dec 09, 2003 7:50 am 
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silvervarg wrote:
It has been argued before that the 7V mod is not that great for the PSU. You will be using the PSU in a way it was not designed to, so depending on how your PSU is designed this might not be a great thing to do.

I would much prefere putting diods on the hot wire that goes to the fan.
A quick check on a local electronics store say you get 25 diods for $1.50.
Depending on how many you put in series you can pick what voltage you want, and you can have different voltage on each fan if you like to.
Downside is slightly more work.


I mentionned in my it has been argued before that the 7V mod is not good for your PSU. In all honesty, I'm not sure why people worry about this since the +5V line on most PSU's is rated to some ridiculously high figure like 35A.

Now consider that most fans used by silence enthusiasts draw less than 0.1A at 12V and you'll see that you really have to put a lot of fans (or high powered fans) to start causing a problem.

Putting the fans in this manner also adds an inductive load to your circuit but I doubt that changes much.

Maybe someone with a more intimate knowledge of power supplies can shed some light on why it is considered bad to do this 7V mod?

Of course the diode mod is more granular in that you can pick whatever voltage you like for your fans but it also requires some soldering and causes heat losses.

Until I see my PSU blow up, I'm happy with my current mod. :)


Last edited by RaynorWolfcastle on Tue Dec 09, 2003 8:58 am, edited 1 time in total.

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 Post subject:
PostPosted: Tue Dec 09, 2003 8:50 am 
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Quote:
Tay:
What is the type of diode used in such a circuit? Doesnt a diode just allow current to flow through in one direction, but not the other? How would this be used in a 7V mod?


The diods will not be for protection of short circuit. Each diod you pass will give you a drop in voltage (normally 0.7volts). By passing through a couple of diods you can more or less pick what voltage you want.
As pointed out you probably want to solder diods in and use shrink material to isolate bare metal so you don't risk any short circuit.

I am not sure about the heat generation when passing diods. Can someone tell what the heat generation would be?


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 Post subject:
PostPosted: Tue Dec 09, 2003 10:37 am 
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i'm probably misunderstanding but is the above poster saying that all 7V mods are bad? like the ones many of us do on our fans? is 5V equally as bad?


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 Post subject: 7V vs 5v
PostPosted: Tue Dec 09, 2003 11:07 am 
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5v mods are fine as they use the +5V line with the -5V ground. You just switch the wires around as Putz suggested earlier on.

The 7V mods use the +12V line and the +5V line as ground. (12-5=7). If you have a short in your fan, your 12V and 5V supply lines are connected. This could cause bad things in your PS (I havent come across anything definitive), but at the very least will cause a circuit to trip and your PSU to shut down and not turn on until you take care of the fan. Diagnosing that the fan caused this would be a PITA of course.

So 5V mods are completely fine to use, I think 7V mods are safe with modern PSUs as well until I see some evidence to the contrary.

WRT the diodes silverarg, why not just use a couple of resistors? Is it because the resistor will have different voltage drop depending on the fan connected to while the diode will always give you 0.7V? Youd need 9 diodes to get to 6.6V on the 12V which sucks. Although u could mount a little heatsink or w/e to a little series diode circuit.

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 Post subject:
PostPosted: Tue Dec 09, 2003 1:26 pm 
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Modern high quality PSU's should have protection againt most stupid things on all outputs. That means it is hard to damage the PSU by doing stupid things or if comonents like a fan short circuits.
On the other hand many of us do use rather cheap PSU's, that might lack these good features.

Even a good PSU might work a bit strange or shutdown if there is a short circuit or something strangely wired (like a 7V mod). It could also possibly interfere with the voltage regulation on the 5V line.

Putting resistors or diods or something else to regulate your fans should be perfectly fine.
The benefit with diods are that they will give same voltage drop for any fan. I believe they will also have a low resistance, so the heat generated will be lower than if a resistor was used (and spread on several components).
The drawback is that you have to use quite a lot of them. However I think Tay calculated a bit wrong. 9 diods with 0.7V drop each will give 12 - 0.7*
9 = 5.7 volt.
going for 7V you would put 7 diods 12 - 0.7*7 = 7.1volt.
You would normally connect the diods instead of the red fan wire, so your wire will be slightly bulky.
Another alternative is the fanmate, or similar linear voltage regulators.
Going even further down the road we get to PWM (puls width modulation), and that is in my opinion the most elegant way to control fan speed.


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 Post subject:
PostPosted: Tue Dec 09, 2003 2:13 pm 
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Can I have some piccies please?
You know what they say, a piccie paints a thousand words!


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 Post subject:
PostPosted: Tue Dec 09, 2003 3:28 pm 
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I'm completely guessing here, but I imagine silverarg is referring to the potential reverse amperage through the +5V line in the PSU when he says it could be harmful.

The standard 7V mod is sort of equivalent to getting 6V potential by having a 9V battery, and putting two 1.5V AA's in series with the opposite polarity. (It would be like the AA's and the 9V fighting to get current to go in the direction they want it to, but since the 9V is stronger, it would win... by about 6V.) This would create a reverse current flow through the poor little AA's, and, in this case, would be dangerous.

But, considering how little current fans tend to draw (especially low-voltage quiet fans), in most cases (pun intended), the net current on the 5V line should still be way into positive amperages, so I wouldn't be too afraid.

Are there also any other important issues we should be discussing, silverarg?


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 Post subject:
PostPosted: Tue Dec 09, 2003 7:36 pm 
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adder wrote:
Can I have some piccies please?
You know what they say, a piccie paints a thousand words!


Ask and ye shall receive ;)

putz I hadn't considered the possibility of a reverse current, but as you said, I'd be surprised if you draw any more than an amp or two even if you put many fans in, as long as they are low power fans. Either way, I am not responsible for any damage to your system resulting from this mod.


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 Post subject:
PostPosted: Thu Dec 11, 2003 3:11 am 
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By chance I just noticed that this UK site sells pre made 7V mods without hesitations.
You get the 7V on both 3-pin and 4-pin output.
Actually you can choose between 5 and 7V when ordering.
Price is £1.20 (excluding VAT and shipment).


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 Post subject:
PostPosted: Sat Dec 13, 2003 8:47 pm 
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When you were doing this mod, did the metal connector that holds the pin ever get loose (due to "picking" at it to get the red cable out)? If so, what did you use to tighten it?


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