12k ? ... i would like the amount of control to drop 3k rpm on each fan if i want .. im using a crap load of dc centuar III's 120mm by japan servo , they arent loud at all but because of the amount of air they push you hear a huge WOOOOOSH all the time .
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what ohm Kr for rheobus controls
- Thread starter Syndicate
- Start date
- Joined
- Sep 4, 2003
- Location
- Salmon Arm BC CANADA
BUMP (every one need some help and its not the tiep of thing that keeps getting asked over and over so i think ill bump it as its at the bottem and you still need help)
- Joined
- Sep 26, 2003
- Location
- Houston,TX-USA
Take a look at the links below..
CLICK HERE
AND HERE
THIS TOO
** Not sure if these will help but it's all I have at present..
CLICK HERE
AND HERE
THIS TOO
** Not sure if these will help but it's all I have at present..
- Joined
- Apr 1, 2004
- Location
- Vancouver Canada
Good links. Here is another explanation should you need it:
Time for a lesson in basic electronics
Ok, so lets start with 2 simple rules:
Current = Voltage/Resistance
Power = Curent * Voltage = (Voltage*Voltage)/Resistance
Current is in amps, Voltage in volts, resistance in ohms, power in watts.
So you have a 12V fan and you want it to run slower? what to do? simple, add more resistance to the circuit. How much though?
Start by finding the resistance of the fan. There are a few ways to go about it. One way is to take the voltage, square it, and divide by the power. (144/ watts = resistance)
Ok, so we know the resistance of the fan, but how big of a resistor do you add? time for more laws:
-The voltages in a circuit always add up to zero.
What this means is that if you are running something on a 12V line, the powersupply adds 12V to the circuit, and the things in the circuit take 12 volts out. If there is more than one thing in the circuit asside from the supply, then those things will remove 12V in total. (I know this is a terrable way of talkign about voltages and kirchoffs voltage law for all you who already know all this, but it get's the point across)
So when you have a fan and a resistor on the 12 volt line, some voltage is "lost" at the resistor and some is "lost" at the fan. how much voltage is lost at each depends on the ratio of the fan and resistors resistances. If they both have the same resistance, each will get 6V. If the resistance of the fan is twice that of the resistor, the fan will get twice the voltage of the resistor. This would mean the fan got 8V while the resistor got 4V.
Using this technique, you can rind approximatly what size of resistor you need. Most people use variable resistors, so if you buy one that will go to a slightly higher resistance than you need, it should work quite well.
There are some other effects that I am not considering here that will make this method not totally accurate. The resistance of a fan is not constant. As it slows down it's resistance drops. The amount it drops by is low enough howerver that if you do what I have described above it will work fine. It's just not academically perfect.
Congratulations to those that have managed to read all the way to here, sorry about the length of this post and it's ramblings. Good luck with your fans.
Time for a lesson in basic electronics
Ok, so lets start with 2 simple rules:
Current = Voltage/Resistance
Power = Curent * Voltage = (Voltage*Voltage)/Resistance
Current is in amps, Voltage in volts, resistance in ohms, power in watts.
So you have a 12V fan and you want it to run slower? what to do? simple, add more resistance to the circuit. How much though?
Start by finding the resistance of the fan. There are a few ways to go about it. One way is to take the voltage, square it, and divide by the power. (144/ watts = resistance)
Ok, so we know the resistance of the fan, but how big of a resistor do you add? time for more laws:
-The voltages in a circuit always add up to zero.
What this means is that if you are running something on a 12V line, the powersupply adds 12V to the circuit, and the things in the circuit take 12 volts out. If there is more than one thing in the circuit asside from the supply, then those things will remove 12V in total. (I know this is a terrable way of talkign about voltages and kirchoffs voltage law for all you who already know all this, but it get's the point across)
So when you have a fan and a resistor on the 12 volt line, some voltage is "lost" at the resistor and some is "lost" at the fan. how much voltage is lost at each depends on the ratio of the fan and resistors resistances. If they both have the same resistance, each will get 6V. If the resistance of the fan is twice that of the resistor, the fan will get twice the voltage of the resistor. This would mean the fan got 8V while the resistor got 4V.
Using this technique, you can rind approximatly what size of resistor you need. Most people use variable resistors, so if you buy one that will go to a slightly higher resistance than you need, it should work quite well.
There are some other effects that I am not considering here that will make this method not totally accurate. The resistance of a fan is not constant. As it slows down it's resistance drops. The amount it drops by is low enough howerver that if you do what I have described above it will work fine. It's just not academically perfect.
Congratulations to those that have managed to read all the way to here, sorry about the length of this post and it's ramblings. Good luck with your fans.
