Can you Mod a 3 pin Fan to still be able to read the rpm?

[mark]

What I am thinking is, getting 2 60mm Delta's the 38cfm ones, which come as 3 pin, then just connect the 12v to the 12v on my power supply, and the negative to the negative on my power supply, but leave the rpm sensor connected to the motherboard.
Will this work?
mark
http://www.mjstebbins.com/case.htm
f3ar

[cjtune]

Should be OK but the black (negative) wire must always be at 0 volts absolute, unless you want to screw up your rpm monitoring. You can even connect the red (positive) wire to the 4-pin connectors instead of to the mobo header if your fan wattage (voltage*current) rating exceeds that of the mobo header's max.

[The Doors]

It works fine, I did it on my Delta38 coz warried about my Mobo, I cutted the black and the red cable from 3Pin and reconnected to the 4Pin Molex, so the blu can report the Rpm to Mobo.
Now I'm thinking to use 7v for my Delta coz is annoying me! it's too much noisy, I'll connect the yellow/Ps (12v) to the red/Delta, and the red/Ps (5v) to the black/Delta.

I hope it helps you :-)

[cjtune]

Originally posted by The Doors
It works fine, I did it on my Delta38 coz warried about my Mobo, I cutted the black and the red cable from 3Pin and reconnected to the 4Pin Molex, so the blu can report the Rpm to Mobo.
Now I'm thinking to use 7v for my Delta coz is annoying me! it's too much noisy, I'll connect the yellow/Ps (12v) to the red/Delta, and the red/Ps (5v) to the black/Delta.

I hope it helps you :-)

I think the rpm (yellow) line uses the negative line as a reference voltage and it may screw up the readings or overload the rpm pin header. So try not to connect the black line to anything else other than another 0 V line.

[Rikimaru]

The Doors: RPM monitoring won't work if you run at 7Volts. Like cjtune said the negative lead needs to read 0Volts or it won't work. You could try useing a potentiometer or resistor to bring down the 12Volt line while still keeping negative on the negative line. I've tried running the Delta on 7Volts and it (RPM) didn't work. I havn't try using a potentiometer or resistor on the 12Volt line but it may work. If anyone has any insight please let me know.

[The Doors]

On my delta38 the red cable is the Positive, the black Negative and the blu Fan Rpm, so I don't understand what you wanna say, the only think I know is that it works really good like I did it and described.

[The Doors]

Ok guys, now I understand what you say's :-)
Excuse me, but I wanna mod my Delta for 7v, but still havn't tried ;-)
Thanx for your info.

[lennytiger]

Umm this is very silly, to be polite I know u have all done this to read the RPM but u have to make sure you do not overload the 12v output otherwise your mobo is going byebye!!

7v where the hells that??????????????

[Quaky]

7 volts is between the +12 volts line and the +5 volts line ;)

[cool_hand_joe13]

:D Only thing wrong with that is if the fans suck too muck voltage you will burn out your mobo headers.

[clocked1]

Of course you can!

Or, if you're lazy you can buy a pre-made cable to do it for $6 at http://www.sidewindercomputers.com/customrpmcable.html

[Rikimaru]

Add this http://www.sidewindercomputers.com/rheosformc.html to what Clocked1 said and that is your best bet. Time for me to start making some new leads. :D

[Fjeld]

Originally posted by Rikimaru
The Doors: RPM monitoring won't work if you run at 7Volts. Like cjtune said the negative lead needs to read 0Volts or it won't work. You could try useing a potentiometer or resistor to bring down the 12Volt line while still keeping negative on the negative line. I've tried running the Delta on 7Volts and it (RPM) didn't work. I havn't try using a potentiometer or resistor on the 12Volt line but it may work. If anyone has any insight please let me know.

A 100ohm 1/4watt resistor in the 12v (red) line works well! Got two 50mm fans running at 4000 rpm (6500 at 12v), almost complete silent.
The same trick for a 80mm fan, but used a 100ohm 1/2watt[/U] for that thing.
Just listen to the silence :)