running fans at 7v

[Sokratz]

ok, while i had my old psu in my comp i could run the put the pos wire to the 12v and the neg wire to 5v creating a 7v fan. worked peachy. now i'm jumpering it outside of the case adn i can't run any of my fans 7v. when i do so, the psu sounds like it's getting a power drain and nothing happens. bad ground or something? I did use tape to wrap up the cables. What's my funk?

 

[Sokratz]

well i have another antec 430 (The previous was a antec 300w). Both are jumpered to run outside the computer, 7v trick works on the 430, but not the 300...?

 

[Mark R]

You need to have a heavy load on the 5V line for this to work - like several HDDs or a Mobo.

If the load is too light, the 7V trick won't work - you risk injecting to much 12V power into the 5V line and tripping out, or even damaging, the PSU.

 

[Sokratz]

is there a way that you can fake this heavy load?

 

[Mark R]

Put something that uses lots of power on the 5V line.

I use a set of car fog-lights for testing PSUs. Connect a foggy to the 5V line, and that should keep the PSU happy.

Massive waste of electricity though.

 

[arcas]

I'd recommend that you go with a pulse-wave modulation circuit anyway. That way your fan is fed a full 12V (so no worries about stalling your fan with too little voltage) and you won't have to worry about properly loading the 5V line. If you're handy with a soldering iron, you can even buy PWM kits for under $15 at various electronics surplus shops. Check http://www.allelectronics.com or http://www.mpja.com.

 

[Sokratz]

I think i may do that or just get a fan bus, I do'n think it has anyhtin to do with the amount of load. My 430 works just fine w/o any extra load, but the 300 won' work at all. thanks for the pwm idea.