Ok i have slightly modified this circuit from cpemmas site. I want to have 4 fans running so i have repeated my modified circuit 4 times. I want a switch to change from 12V to vairiable and OFF . I also want a Blue LED to show when the fan has current and change brightness with the fan speed and a Green LED (these are 12V LED's - i have a few lying around) to show when i have switched the fan to 12V. I think i need a 470ohm resistor between the LED and the switch, is this the correct place for the LED and the resistor ? Also for the switch do i need a 3 position locking at both sides SPDT? (maplin code FH00A). The resistor that is connected to the pot is 1k (as per cpemmas site) what value would i need if i want to be able to adjust the voltage from say 3.5V upwards (not sure if this is nesessary really)? Will this do what i want and will it work? TIA cheebs
Yes, you do need a resistor for the green LEDs. They can go before or after the switch, just as long it resists only the LED and not the rest of the circuit. You don't need to be able to go down to 3.5v as almost no fan will keep spinning at that voltage. You can hit 5v with some fans, but you should be able to get 6/7v consistently.
Thanks for the reply Ok i take it you mean Blue LEDs as the green ones are 12V LEDs and only come on when i switch the fan to full power. If i put the resistor between the switch and the LED then the switch, LED and Fan will be in series yea? will the resistor then limit the voltage to the Fan as well as to the LED? If so, and i suspect this could be the case, where do i need to put the LEDs and their resistors? Would it be from the 12V lead to the switch to after the fan (in paralell?) for the Green ones and just from above to below the FAN for the Blue ones? You have to excuse my noobness, its been about 12 years since i did any electronics but it is starting to come back to me. I will be running one cheap 120mm fan from, maplin (Bi-sonic 12V 0.38A) and 3 80mm (Pabst 12V 110mA 1.3W) They all start with 5V and run with no problems as far as i can tell. i think they woiuld actually go slower too but the 120mm one which is blooming loud at 12v is near silent at 5V so im wondering if there is any point in trying to get it to go slower. Will the componants that cpemma recomends be man enough for these fans? (ie a BC107B for T5,6,7&8, a TIP42A for T1,2,3&4 and a 1K pot maplin VP93B for each fan) [edit] Blooming heck, just realised that the 120mm one is 4.5 W . That seems alot more than the pabst ones!!
You're right, the led in series with fan is wrong. To show the fan is powered up put the led and its resistor in parallel with the fan. For your 2-led system I think you'll need a more complicated switch to do what you want, possibly a double-throw centre-off. That controller will run the fan up to 11.3v so unlike a 317T controller a full-speed switch won't do much. No problem. Even the cheaper TIP32A would do fine. The 32A's 3A rating = a 36W fan.
Thanks mate thats what i guessed after taking another look at the diagram. Ill ammend it and post a new version. Just want to make sure i am thinking about it in the right way. BTW thanks for your site. Its been a great help. Its even helped me to remember some of the stuff i have forgotten
OK here is the new diagram. I have moved the blue LEDs down the bottom of each of the 4 fans but i think something is still wrong with the Green LEDs (12V jobbies) that are sposed to come on when i switch the fan to 12V. Its still in series so i presume the inbuilt resistor on the 12V JED will be limiting the fan. How to i switch it on and have it paralell to the motor. I'm guessing i need a DPDT switch so i'll have a play and post again the next evolution so someone could tell me if that one is correct.
Thanks. I have replaced the SPDT for DPDT so if DPDT work the way i think i remember them working i think this is correct now. Can anyone confirm? Sorry the diagram is a bit messy now but i hope you can see what i tried to do. I have the Motor connected to both terminals on one side then on the other side im assuming that it connects to 2 contacts on each throw. One of these contact has the variable part of the circuit on it and its pair is empty. The other pair has one connected to the LED and one connected to 12V. Please say this is correct cos its been making my brain hurt TIA cheebs
