Pro/Forums - View Single Post

Since87 · 12-02-2002, 02:10 PM

punish3r,

I looked over that schematic. Depending on the fan load, the 10 Ohm resistor (R6) is going to limit the voltage to the fan(s) substantially. For example if the fan load is 0.5 Amps at 12 Volts, the max voltage the fans will get with that circuit is 8.5 Volts.

It appears the only purpose for R6 is to protect the transistor from excessive current draw through the capacitor at power-up. I'd be inclined to replace R6 with a 2 Ohm 10 Watt resistor and use the TIP120 transistor available at Radio Shack. (It has an 8 Amp peak rating.) This would get the maximum voltage to around 11V.

You might be able to get away with throwing out R6 and C1 altogether. Many brushless "DC" fans draw current in pulses though, so the cap is probably a good idea.

12-02-2002, 02:10 PM	#13
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	punish3r, I looked over that schematic. Depending on the fan load, the 10 Ohm resistor (R6) is going to limit the voltage to the fan(s) substantially. For example if the fan load is 0.5 Amps at 12 Volts, the max voltage the fans will get with that circuit is 8.5 Volts. It appears the only purpose for R6 is to protect the transistor from excessive current draw through the capacitor at power-up. I'd be inclined to replace R6 with a 2 Ohm 10 Watt resistor and use the TIP120 transistor available at Radio Shack. (It has an 8 Amp peak rating.) This would get the maximum voltage to around 11V. You might be able to get away with throwing out R6 and C1 altogether. Many brushless "DC" fans draw current in pulses though, so the cap is probably a good idea.