Help with electrical stuff

[nickmv]

I'm about to wire up three 140mm case fans in my fermentation freezer, and need some help.

Each fan's spec is:
Voltage 12VDC
Current (Ampere) 0.08A
Input (Watt) 0.96W


I'm looking to wire them in parallel, basically as they'd be inside a computer case. Basically, all three hooked together through the molex connecters and splitters that are standard on all case fans. Then I'd strip off the wires from the first fan's connecter, and wire it into a rheostat, and finally into a PSU unit.


I have absolutely no idea what spec rheostat or PSU unit I'll need for this. Can anyone help spec that out for me?

I've done some basic research here and found that I'd want about a 150 Ohm rheostat for ONE fan, (12v/.08A = 150 Ohms), but I have no idea about doing 3 parallel. I know that I'd need 3 watts output on my PSU, but I don't know about PSU amps, and I don't know how many Ohms my rheostat would need (again 3 watts obviously for the rheostat).

 

[Wynne-R]

Good job on the 150 ohms. With three of ’em, the equivalent resistance is 50 ohms. Rt = 1/ (1/R1+1/R2+1/R3) is the formula for parallel resistors. Since they’re all the same, you could just look at it and say ‘huh, must be 50ohms'.

Not sure what your goal is, but I’m guessing once you get the fan speed you like you won’t be adjusting it further. You’re going to have a rough time finding your pot.

You could get a couple of 2W 47ohm resistors easier. If you use one that’ll give you roughly half. Use two in series and you get one third. In parallel you get three fourths. This is resistor combinations in series with the load. That’ll give you three speeds, not counting full speed.

 

[raysmithtx]

Just a thought...instead of a rheostat use 12V adjustable power supplies. Switchable from 4 volts to 12 volts and with a higher amperage rating. I use 3 in parallel on one circuit and 2 in parallel on the other. Using 2 power supplies because I couldn't find one small enough with enough amperage to use just one.