I have finally got all the parts together and the design roughed out.
This will be a fan controller to go behind fridges in motorhomes. I want one or more fans to keep my fridge working at it's optimal however I hate the noise of fans unless they are absolutely essential.
I have looked around at various controllers and they all have various problems. Here is the requirements I have.
1. Must be totally silent/off when not needed.
2. Must take into account ambient air temperature.
3. The controller must be able to accept multiple fans.
4. Must be extremely energy efficient.
Anyway the design I have come up with uses 2 temperature sensors. One which will be located near the bottom vent to sense ambient temperature. And one in the air flow area at it's warmest point.
I will then use an Arduino ATTiny85 programmed to use PID to operate the fans at the lowest possible speed using PWM to bring the difference between the two sensors as close as possible.
The reason I am doing it this way is a single sensor that just detects the temperature would need to be pre-programmed with a set speed based on the detected temp. So for instance I could set the fan speed to be 25% at 25C, 50% at 30C, 75% at 35C for example. This would work fine in this country but if I went to the South of Spain and the ambient temp was 40C the fan would be blowing at full speed all the time and actually achieving nothing. Running the fan when there is no difference in temperature between the top of the fridge and the bottom would be pointless and just create noise and use 12v power for no purpose.
The design.
The ATTiny85 is an 8 pin microcontroller. I will configure 2 of the pins as inputs and use 2 x 18B20 one wire accurate temperature sensors. Another 1 of the pins will be programmed as a PWM output which will drive an IRL540N Mosfet which can control a number of Computer fans. The total component count so far is 1 Microcontroller, 2 resistors, 1 diode, 1 mosfet and 2 temperature sensors. I will also need to make a 12v to 5v dc-dc converter. During development I will be using one I have bought.
In the final design I will be using 140mm fans as these can shift a lot more air than 80mm fans at a much lower speed and power. For testing I will just use an 80mm fan I already have.
Once the temperature on the lower sensor has fallen below a certain level for a fixed period of time. The microcontroller will go to sleep for 15 minutes and wake up to check if the temp has started rising again. This is to keep power usage/noise very low overnight or during cooler parts of the year.
Because I am using PWM and PID the power efficiency should be extremely high.
I am picking up the first batch of parts tomorrow (Hopefully they are all there) and will start building the first prototype early next week. I will post pictures as I make progress
I have ordered enough components to do all the electronic projects for the motorhome and will post more information as I make progress
If you have any questions please don't hesitate.
This will be a fan controller to go behind fridges in motorhomes. I want one or more fans to keep my fridge working at it's optimal however I hate the noise of fans unless they are absolutely essential.
I have looked around at various controllers and they all have various problems. Here is the requirements I have.
1. Must be totally silent/off when not needed.
2. Must take into account ambient air temperature.
3. The controller must be able to accept multiple fans.
4. Must be extremely energy efficient.
Anyway the design I have come up with uses 2 temperature sensors. One which will be located near the bottom vent to sense ambient temperature. And one in the air flow area at it's warmest point.
I will then use an Arduino ATTiny85 programmed to use PID to operate the fans at the lowest possible speed using PWM to bring the difference between the two sensors as close as possible.
The reason I am doing it this way is a single sensor that just detects the temperature would need to be pre-programmed with a set speed based on the detected temp. So for instance I could set the fan speed to be 25% at 25C, 50% at 30C, 75% at 35C for example. This would work fine in this country but if I went to the South of Spain and the ambient temp was 40C the fan would be blowing at full speed all the time and actually achieving nothing. Running the fan when there is no difference in temperature between the top of the fridge and the bottom would be pointless and just create noise and use 12v power for no purpose.
The design.
The ATTiny85 is an 8 pin microcontroller. I will configure 2 of the pins as inputs and use 2 x 18B20 one wire accurate temperature sensors. Another 1 of the pins will be programmed as a PWM output which will drive an IRL540N Mosfet which can control a number of Computer fans. The total component count so far is 1 Microcontroller, 2 resistors, 1 diode, 1 mosfet and 2 temperature sensors. I will also need to make a 12v to 5v dc-dc converter. During development I will be using one I have bought.
In the final design I will be using 140mm fans as these can shift a lot more air than 80mm fans at a much lower speed and power. For testing I will just use an 80mm fan I already have.
Once the temperature on the lower sensor has fallen below a certain level for a fixed period of time. The microcontroller will go to sleep for 15 minutes and wake up to check if the temp has started rising again. This is to keep power usage/noise very low overnight or during cooler parts of the year.
Because I am using PWM and PID the power efficiency should be extremely high.
I am picking up the first batch of parts tomorrow (Hopefully they are all there) and will start building the first prototype early next week. I will post pictures as I make progress
I have ordered enough components to do all the electronic projects for the motorhome and will post more information as I make progress
If you have any questions please don't hesitate.
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