Modding down 2 casefans from 12V to 7 V

[marinlicina]

I'm building a P4 system in a Chieftec Dragon Miditower. I'm planning on putting in 2 case fans in the back and one in the front. But I would also want to volt-mod the two fans from +12 to + 7.

- Can I do this safely with both fans attached to same power feed. (I know one casefan on 7V is safe, but two means loss of 10V)

- Do you think the 2 7V fans are good enough to create low pressure (the front fan will stay 12V)?

Thanks to all who reply.

 

[Gaunt]

Although I have seen some people say that using the 7v mod can cause problems with the PSU, I haven't had any issues.

I built a simple baybus (4 switches, 12v, 7v, and off positions) that had a single connection to the PSU and powered 4 case fans. This should be along the same lines as what you're attempting to do. In the year that that case was used, and running almost 24/7, I didn't have any power issues at all. So unless I just got really lucky, you shouldn't have any problems either.

 

[zsa]

Couple of questions about this:

To get the 7V you wire across the 12V and 5V lines on the Molex?

I assume that the drop in voltage results in a proportional drop in RPMs, and a proportional drop in CFM, but an exponential drop in decibels. Is that correct?

Is there a way to get 7V from a 3-pin fan connector on the MB? I'd be interested in seeing the RPMs.

 

[Gaunt]

Yes, using the 5v and 12v lines from the molex will give you a 7v supply for your fan. As for the drops in RPM, CFM, and decibels... what you said sounds about right, but I would imagine it depends largely on the fans you're using. I'm just not sure that the sound level drops enough decibels to be considered exponential, but since a small drop in dB is an exponential drop in "volume"...

I don't know what the pinout is on a 3-pin fan connector, but I'd imagine it's just ground, 12v, and RPM, so you couldn't get 7v out of it. What you CAN do, is use the 7v from a molex connector, and plug the 3rd lead from the fan into a 3-pin fan header on the motherboard, just to monitor RPM. (sometimes fans come ready for this, with a molex connector for power, and a single lead for RPM with a 3-pin connector)

Edit: Corrections, and an appology for taking so long to reply.