simple power help.

[WeStSiDePLaYa]

ok this is a very noobish question, but i was wondering what the best way to connect a switch like this. here is my idea. anyone else have any better ideas? the plan is to be able to switch all of my fans from 12v to 5v via a pci bracket switch. the draw of all fans combined will be about 5amps.

[tiresias]

Re: simple power help.

ok this is a very noobish question, but i was wondering what the best way to connect a switch like this. here is my idea. anyone else have any better ideas? the plan is to be able to switch all of my fans from 12v to 5v via a pci bracket switch. the draw of all fans combined will be about 5amps.

Hang on a minute - why does the common ground wire go to the switch?

All you have to do is to connect the ground directly to the fan(s) in question, connect a line from the 12vdc and 5vdc to either pole of the SPDT switch and the center pin (assuming a standard config) wired to the positive terminal of your fans.

That way the switch will close either the circuit involving 12v input or that for 5v, depending on its position.

Or is the heat messing me up so I'm missing something?
...
Edit: cleared a silly typo.

[Rainbow]

Re: simple power help.

All you have to do is to connect the ground directly to the fan(s) in question, connect a line from the 12vdc and 5vdc to either pole of the SPDT switch and the center pin (assuming a standard config) wired to the positive terminal of your fans

This is the right way. And make sure that the switch can never ever connect both ends together!

[Per Hansson]

Re: simple power help.

Yea, as Rainbow said... I'd be very careful in selecting a switch that has a long "gap" or whatever you wanna call it between the two points..

Also there is no short circuit fuse between 5v and 12v so I would add a (in your case 5A) fuse for protection....

[Galvanized]

Re: simple power help.

tiresias is spot on with the ground wire comment. Just use the 5 & 12 to a SPDT switch.

Never thought of fusing inorder to protect the PSU, good point Per. That's something I'll remember.

PlaYa, go to silentpcreview.com, on the left you'll find fans&controlls. They show a 5 or 12 controll using a DPDT switch.(Note: All ATX PSU grounds are common). Radio Shack wants $5 for a switch. allelectronics.com or BGMicro they are $1.25 each or 10 for $10. BGMicro has a very good selection of ballasts,atm, if your interested. allelectronics carries some good cheap heat shrink.

[Per Hansson]

Re: simple power help.

Never thought of fusing inorder to protect the PSU, good point Per. That's something I'll remember.

It's generally completely unnecessary but a little added protection never hurts...

Plus that if you run fans on +7v (Red and Yellow on Molex connectors) you are without shortcircuit protection, therefore if you make a switch like this it is good to have a fuse, if you make an error in the assembly, the switch fails ot a wire just comes loose and shorts it out...

And also as I found out it would be good to have a fuse on the fans themselves, as I totally fried the fan voltage controller (according to CPU die temp) on a new Asus board; a strand of the +12v cable came loose and touched ground...

[tiresias]

Re: simple power help.

Plus that if you run fans on +7v (Red and Yellow on Molex connectors) you are without shortcircuit protection

I guess that could be the case with some nasty generic PSUs - but surely in a decent unit with overload protection, it would trip due to overcurrent (essentially a short) on the 12vdc out?

[Per Hansson]

Re: simple power help.

I guess that could be the case with some nasty generic PSUs - but surely in a decent unit with overload protection, it would trip due to overcurrent (essentially a short) on the 12vdc out?

Maybe, this is what I have read in every guide describing the +7v mod, so not from personal experience...

[willawake]

Re: simple power help.

why not just use a pot/rheostat on the 12v. imho the sweet spot is between 12v and 5v

[tiresias]

Re: simple power help.

why not just use a pot/rheostat on the 12v. imho the sweet spot is between 12v and 5v

Indeed - or even use the PWM-controlled motherboard fan headers together with some software such as Speedfan... of course, this only is an option if your motherboard is capable in that respect. And if you don't have more fans than headers, of course.

[Rainbow]

Re: simple power help.

Plus that if you run fans on +7v (Red and Yellow on Molex connectors) you are without shortcircuit protection, therefore if you make a switch like this it is good to have a fuse, if you make an error in the assembly, the switch fails ot a wire just comes loose and shorts it out...

Some PSUs don't like this - they will not turn on at all or the protection turns it off after a while. And I don't like it too.

[Galvanized]

Re: simple power help.

ok this is a very noobish question, but i was wondering what the best way to connect a switch like this. here is my idea. anyone else have any better ideas? the plan is to be able to switch all of my fans from 12v to 5v via a pci bracket switch. the draw of all fans combined will be about 5amps.

PLaYa, 12Vx5A=60W. That is alot of cfm and wattage.

If you have an open 5.25" bay, a Sunbeam Rheobus will handle 20W per each of it's four channels. I have two in use, they are linear (not PWM) and cause no fan clicking. They cost $10 here State side. Guys in the UK don't have'em. The only draw back is the uber-bright 5mm LEDs. These can be cured with several coats of dark nail polish. SPCR has a good review of it. The LEDs change from red to blue at about 7V. A buddy gave me one he burnt up. The Molex can be installed up-side-down if one is not careful. The Molex is opposite what most opticals are.

[kc8adu]

Re: simple power help.

dont rely on the ocp to save your stuff if you get a short.
the light gauge wire on fans wont pull enough to trip the psu.
short=smoke and fire!

[WeStSiDePLaYa]

Re: simple power help.

got the figured out a few minutes after i posted it.

and i didnt have the cash for fan controllers, so i used a pci bracket switch from a ccfl inverter.

and yes i know im using alot of power for my fans. i got some big fans, and lots of 80mm.

but this is running off a secondary psu.

and to the person who suggest running them off the mobo headers. are you f'ing nuts?! please dont ever recomemend that to others again. running the fans i am using off a header will fry them. i even stated i had high draw.