What resistor do i need to get 5V from 12V ?

[BuBu Shofronea]

What resistor do i need to get 5V from 12V ? ( Leds for case fan )

 

[sizzling]

Not that simple, would need to know total current draw. Why dont you just pick up the 5v rail from a molex connector, that's what I did

 

[mbarnes86]

Hi


In PC molex connector gives 5 v & 12 v
5 v red to black
12v yellow to black

Often resistor used to slowdown 12 v fan to about 7 v

You need to know resistance of device you need to reduce voltage on
Eg

If device 1 amp at 12 volt v= I x R
R. 12 ohm
Add 12 ohm resistor in series and 6 volts through device and 6 volts heats up resistor.

Best to use 5 volts supply if 5 volts needed

Regards
Mike Barnes

 

[Rookie_MIB]

Why do that? From your PSU, a molex cable/connector has 4 wires. Two Ground, one 12V+, one 5V+. Just tap into a 5v wire coming off a molex (and FYI, SATA supplies the same. Another option is to find a USB header that's being unused. That provides 5V+, Data,Data, Ground. So - take a USB header cable, from something like a rear output piece that goes into one of the case slots, cut the header cable off, find the red wire, and black wire, and use that to connect into motherboard.

 

[BuBu Shofronea]

Not that simple, would need to know total current draw. Why dont you just pick up the 5v rail from a molex connector, that's what I did

Well, i'd like to attach them to the wires of my fan - 4-pin fan, but i can't tell which one is 5v cuz the wires are colored in this order : Black, Yellow, Green, Blue.

And what do i attach the negative then ? to teh same 5v wire ?

 

[Rookie_MIB]

Not that simple, would need to know total current draw. Why dont you just pick up the 5v rail from a molex connector, that's what I did

Well, i'd like to attach them to the wires of my fan - 4-pin fan, but i can't tell which one is 5v cuz the wires are colored in this order : Black, Yellow, Green, Blue.

And what do i attach the negative then ? to teh same 5v wire ?

None of those are 5v for the fan. The fan wires outputs are (in no particular order)

3pin: 12v, Ground, Tach Read (fan rotation speed)
4pin: 12v, Ground, PWM control, Tach read.

ALL fan outputs are 12v, which is why I suggested the 5v from either the molex or the USB header.

 

[BuBu Shofronea]

Not that simple, would need to know total current draw. Why dont you just pick up the 5v rail from a molex connector, that's what I did

Well, i'd like to attach them to the wires of my fan - 4-pin fan, but i can't tell which one is 5v cuz the wires are colored in this order : Black, Yellow, Green, Blue.

And what do i attach the negative then ? to teh same 5v wire ?

None of those are 5v for the fan. The fan wires outputs are (in no particular order)

3pin: 12v, Ground, Tach Read (fan rotation speed)
4pin: 12v, Ground, PWM control, Tach read.

ALL fan outputs are 12v, which is why I suggested the 5v from either the molex or the USB header.

Thanks, but i finished up by getting 12V LEDs and it works like a charm now.
But will it work if i attach 12V LEDs to a 5v source ? will they light ? ( source being a usb cable )