12v to 7v fan mod

[crushing_grief]

I an attempt to quiet my Vantec Tornado 80mm cpu fan, I have decided to try the 12v to 7v mod. My question is how will this effect the specifications/outputs of the fan?

At 12volts, the Tornado is rated as follows: 5700rpm, 84.1cfm and 55.2dBA.

If my simple math calculations are correct, these should be the new output specifications:
3323.1 rpm
49cfm
32.4dBA

Do these numbers sound right? Has anyone tried this mod before? How will it effect performance and noise?

[dimmreaper]

The difference between RPMs will be pretty close to linear, but the same will not be true of volume pressure and noise ratings.

[Allan]

The noise level will drop quite a lot - or at least thats my experience. Since its an easy mod you can always make it back, if you think its no good.

[Aedan]

From experience so far, dropping the RPM a small amount at the top end brings a far larger reduction in noise level. It would appear to be a log function rather than linear.

AidanII

[dimmreaper]

Like Aidan says, a small reduction in RPM seriously cuts the noise level, 10V really seems to be the sweet spot for 12V fans from my expirience.

[cloasters]

And how much amperage is available with the standard 12v-to-7v mod? That's easy, for the conservatively minded(as far as PC mods go) none. Might as well be none. Personally, I won't do this mod.

[dimmreaper]

The amperage is identicle to that which is available on the 12V rail so long as sufficient power is being consumed by devices attached to the 5V rail. This is not really an issue of amperage, it is an issue of electromotive force.

[Aedan]

Originally posted by cloasters
And how much amperage is available with the standard 12v-to-7v mod? That's easy, for the conservatively minded(as far as PC mods go) none. Might as well be none. Personally, I won't do this mod.

As Dimm's already pointed out...

The bridge between 12v and 5v to provide 7v volts works because...

The PSU will deliver only 5v to the 5v line. Connecting your fan between the 12V and 5V causes the following to happen.

The current drawn by the fan is passed onto the load (as it's at 5V, it's a usable 5V). The PSU then delivers a fan sized less current to the 5V line, as it's coming from the 12V line.

Technically, if you had plenty of power on the 12V line, you could use this sort of technique to bolster up a sagging 5V line. I'd not recommend it for too much load though, as the fan doesn't pass enough current.

The only problem you have to watch out for is that the load across the 12v and 5V lines isn't larger than the load across the 5V line. Given the current consumption on the 5V line, that's unlikely, unless you unplug motherboards from the PSU.

AidanII

[cloasters]

Looks like I didn't have all of the facts straight, again. I like 12v better. Ossification has set in. Aaahh!

[slack]

Rig the PSU fan to the five volt out on one of hard drive connectors. This makes the PSU close to silent :-D But it will run warm though.

John

[Renod]

You can make a 12V to 7V or 5V molex . It took me all of 5 minutes the first time and they work great. Easy way to test the results without making a permanent change.

[SteveI]

I've noticed on a few fans, 7v may not be enough to overcome inertia and spin up initially.

I personally love this mod.. I've got about 7-8 fans atm running on 7v, including a 6cm delta 7000rpm screamer. Since 2 of my pcs on in kid's bedrooms, and the weather is getting cooler, I've managed to silence 1 machine, and seriously quiet 2 more.

Whenever voltmodding is done, extra care must be taken. When done properly, the results can be joyous silence.