Thoughts on a fan controller I have been tinkering with
Posted: Wed Aug 26, 2009 6:09 pm
People,
I have been tinkering with some electronic circuits for a few months now and I have a first cut at a circuit for a good PWM fan controller. This is my first post but I have been lurking these forums for a while now. I haven't seen anything like this, but I haven't seen everything.
The purpose of this controller is to allow a user to set the desired temperature and the controller will speed/slow the fan to maintain this desired temperature. You set it and forget it.
My apologies if the following sounds too commercial and violates some kind of terms. I don't know any other way to get hard information on this.
Here is what I currently have:
1) Fan speed is controlled by a temperature probe. Fan speed increases if above the user set point, it decreases if temperature is below the set point.
2) The fan is controlled by a PWM circuit for efficient power usage. I have adjusted the circuit to avoid 'chirping' from the PWM pulses.
3) The current version has two knobs. One knob sets the desired temperature, the other knob sets the minimum speed.
4) This controller will start up with full power to the fan for about 3 seconds to ensure the fan starts every time. This is "hard start" feature to avoid stalled fans when powering on. After startup, fan speed will drop to the level required to maintain the temperature setting. The minimum speed can be set so low that you can easily watch the fan blades turn slowly.
5) The controller should handle about 2 amps of fans with no problem, probably more. I haven't tested the upper limit yet.
6) The circuit is one generic 14-pin DIP IC plus a bunch of resistors (about 30) and a few other parts. I use a FET for the PWM control and a thermistor for temperature sensing. The control circuit is completely analog (not digital) so there are an infinite number of settings to get just the right amount of cooling for any set of load conditions.
7) Temperture range for the controller is currently about 75F to about 95F. I can change this range by adjusting part values. The user can dial in any desired value. The controller will spin the fan fast enough to keep it there or until max/min speed limits are reached.
8) Power is +12VDC. You plug one side of the controller into the power supply and the fan plugs into the other side. The circuit robs a wee bit of power from the supply to run things and pulses the fan to control temperature.
9) There are no indicator lights or readouts. I monitor temperatures with a separate digital thermometer from WalMart. It's much cheaper that way.
10) The circuit is technically a proportional-Integral control loop. (No Differential term is used). The circuit will control the fan(s) to maintain the desired temperature, no matter what the heat load is.
11) The idea was that you could mount the thermistor probe at a desired spot in your case (like close to the CPU) and the fans would then find the correct speed for any power burn. Less noise when you are idle, more air when you are making heat.
12) There is no purpose for the tachometer, if your fan has one. I'm not sure if some BIOSes will complain if the tachometer is disconnected.
13) The response time of the circuit is fairly quick. Any change is a smooth adjustment, no sudden steps in noise. The circuit will take about 10 seconds to adjust, depending on system parameters. I can slow this down or speed it up by changing component values.
Questions/Observations:
--------------------------------
1) Have you seen something like this? If so, where?
2) I could add more circuitry to allow the use to set maximum speed but that seemed like overkill and would raise the price of parts. You would be limiting the fan to a max speed that may be insufficient to keep the CPU cool.
3) I could add more circuitry to allow you to set the response rate of increasing/decreasing the fan speed. Again, I am not sure this is required and it would require more knobs. Knobs are expensive, require space, and add complexity.
4) The FET I use is rated for 4 amps but I can get just about any size required. How much cooling does one computer need? Is 4 amps of fan power enough?
5) I suppose you could have two controllers that monitor different points in the case but they would tend to fight each other because you can never set them for exactly the same temperature. I would think it makes most sense to have just one probe sensor.
6) I was thinking about maybe offering this as a product. If so, what do you think is a fair price?
7) The circuit is complicated due to the number of resistors. I don't think it is something you would build from scratch because there are too many unique resistor values to be economical for building one copy. I don't think you could buy the correct resistor values at some place like Radio Shack, so that means mail order. What about a kit?
8) The current circuit will easily fit inside an Altoids can. If I make a PCB, I can put it just about anywhere. What kind of form factor would you like to see? Something that plugs into the ISA bus connector and has knobs sticking out the back? Something that mounts like a fake disk drive so you can have knobs on the front?
9) I can set the temperature range for any value. What seems reasonable?
10) I don't see a need to completely stop the fan from turning, do you? If a CPU fan actually stops, it will stall and be difficult to start when you need to cool. A stalled fan also adds lag between a CPU that suddenly warms up and when the thermistor can sense this to react. I think it is best to leave fans turning slowly. The airflow difference between slowest and fastest is about 6 to 1 or more.
Let me know your thoughts and questions on this concept. I don't know what I want to do with the circuit yet. Ideally, I would like to sell some of these but I don't know if that is practical or profitable. Your input is appreciated.
Sincerely,
-M
I have been tinkering with some electronic circuits for a few months now and I have a first cut at a circuit for a good PWM fan controller. This is my first post but I have been lurking these forums for a while now. I haven't seen anything like this, but I haven't seen everything.
The purpose of this controller is to allow a user to set the desired temperature and the controller will speed/slow the fan to maintain this desired temperature. You set it and forget it.
My apologies if the following sounds too commercial and violates some kind of terms. I don't know any other way to get hard information on this.
Here is what I currently have:
1) Fan speed is controlled by a temperature probe. Fan speed increases if above the user set point, it decreases if temperature is below the set point.
2) The fan is controlled by a PWM circuit for efficient power usage. I have adjusted the circuit to avoid 'chirping' from the PWM pulses.
3) The current version has two knobs. One knob sets the desired temperature, the other knob sets the minimum speed.
4) This controller will start up with full power to the fan for about 3 seconds to ensure the fan starts every time. This is "hard start" feature to avoid stalled fans when powering on. After startup, fan speed will drop to the level required to maintain the temperature setting. The minimum speed can be set so low that you can easily watch the fan blades turn slowly.
5) The controller should handle about 2 amps of fans with no problem, probably more. I haven't tested the upper limit yet.
6) The circuit is one generic 14-pin DIP IC plus a bunch of resistors (about 30) and a few other parts. I use a FET for the PWM control and a thermistor for temperature sensing. The control circuit is completely analog (not digital) so there are an infinite number of settings to get just the right amount of cooling for any set of load conditions.
7) Temperture range for the controller is currently about 75F to about 95F. I can change this range by adjusting part values. The user can dial in any desired value. The controller will spin the fan fast enough to keep it there or until max/min speed limits are reached.
8) Power is +12VDC. You plug one side of the controller into the power supply and the fan plugs into the other side. The circuit robs a wee bit of power from the supply to run things and pulses the fan to control temperature.
9) There are no indicator lights or readouts. I monitor temperatures with a separate digital thermometer from WalMart. It's much cheaper that way.
10) The circuit is technically a proportional-Integral control loop. (No Differential term is used). The circuit will control the fan(s) to maintain the desired temperature, no matter what the heat load is.
11) The idea was that you could mount the thermistor probe at a desired spot in your case (like close to the CPU) and the fans would then find the correct speed for any power burn. Less noise when you are idle, more air when you are making heat.
12) There is no purpose for the tachometer, if your fan has one. I'm not sure if some BIOSes will complain if the tachometer is disconnected.
13) The response time of the circuit is fairly quick. Any change is a smooth adjustment, no sudden steps in noise. The circuit will take about 10 seconds to adjust, depending on system parameters. I can slow this down or speed it up by changing component values.
Questions/Observations:
--------------------------------
1) Have you seen something like this? If so, where?
2) I could add more circuitry to allow the use to set maximum speed but that seemed like overkill and would raise the price of parts. You would be limiting the fan to a max speed that may be insufficient to keep the CPU cool.
3) I could add more circuitry to allow you to set the response rate of increasing/decreasing the fan speed. Again, I am not sure this is required and it would require more knobs. Knobs are expensive, require space, and add complexity.
4) The FET I use is rated for 4 amps but I can get just about any size required. How much cooling does one computer need? Is 4 amps of fan power enough?
5) I suppose you could have two controllers that monitor different points in the case but they would tend to fight each other because you can never set them for exactly the same temperature. I would think it makes most sense to have just one probe sensor.
6) I was thinking about maybe offering this as a product. If so, what do you think is a fair price?
7) The circuit is complicated due to the number of resistors. I don't think it is something you would build from scratch because there are too many unique resistor values to be economical for building one copy. I don't think you could buy the correct resistor values at some place like Radio Shack, so that means mail order. What about a kit?
8) The current circuit will easily fit inside an Altoids can. If I make a PCB, I can put it just about anywhere. What kind of form factor would you like to see? Something that plugs into the ISA bus connector and has knobs sticking out the back? Something that mounts like a fake disk drive so you can have knobs on the front?
9) I can set the temperature range for any value. What seems reasonable?
10) I don't see a need to completely stop the fan from turning, do you? If a CPU fan actually stops, it will stall and be difficult to start when you need to cool. A stalled fan also adds lag between a CPU that suddenly warms up and when the thermistor can sense this to react. I think it is best to leave fans turning slowly. The airflow difference between slowest and fastest is about 6 to 1 or more.
Let me know your thoughts and questions on this concept. I don't know what I want to do with the circuit yet. Ideally, I would like to sell some of these but I don't know if that is practical or profitable. Your input is appreciated.
Sincerely,
-M