New Gadget project started. Fridge fan controller.

Discussion in 'Tech/Mech General' started by Gromett, Oct 8, 2016.

  1. Gromett

    Gromett Funster

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    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.
     
    Last edited: Oct 8, 2016
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  2. FJmike

    FJmike Funster

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    Not wishing to pee on your parade Gromett but having used fans on my fridge when visiting south France if you wait for the high temperature before switching the fan on it takes nearly all day to make a difference. Would it be a better approach to fit quite fans?
     
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  3. Gromett

    Gromett Funster

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    That is what my system avoids. It doesn't wait till a high temperature. It automatically adjusts the speed based on the differential. The PID part reacts to the speed of the change in temperature to help anticipate the rate of change as well (y)

    I am sensitive to man made noise, and even the quietest fans bug me.
     
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  4. Snowbird

    Snowbird Funster Life Member

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    I have fitted 2 brushless computer fans in the past controlled by a temp sensor bought from Maplin. It worked fine in southern Spain in August. No noticeable noise from fans which take little or any power from the batteries. Another system I have tried that worked well even in Morocco was a small solar panel connected directly to a computer fan, the advantage of this is that it only works when in full sun, which is generally when the fridge needs it most. Does not work during the night when slight noises can be an issue.
     
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  5. matamoros

    matamoros Funster

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    Mine is a really simple sensing system.......me!.......when it is getting hot I switch the fans on and when it gets cooler I switch them off. My switching system is even simpler, I have them connected to a cigarette lighter plug which I push into the multi socket located in a cupboard next to the fridge which houses the TV and a previously wired in 12v socket......and I can't hear the fans.

    I am only a simple soul so like simple solutions:)
     
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  6. Gromett

    Gromett Funster

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    Solar panel method is a nice idea. However I work in the van during the day and don't want the fans running at all if they are not needed.

    The components for this project are costing me less than £5 and once I get the PID parameters configured the fan(s) will be rotating at the lowest possible speed necessary to achieve the best efficiency.
     
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  7. Gromett

    Gromett Funster

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    No good for me, I would be up and down like a yoyo, and fans running at full speed drive me up the wall.

    You may be simple but I am lazy, all that getting up and down and pressing switches is too much for me. For less than £5 I will have something that turns it on and off for me and adjusts the speed on the speed controller for me :p
     
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  8. matamoros

    matamoros Funster

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    I did buy a temperature sensor/controller when I bought the fans but fitting it started to get complicated, needed more wires, holes etc and began to confuse me so reverted to quick and easy fix.

    I don't switch them on and off much, just leave them on if it's hot as I can't hear them it is not a problem and I work on the theory that if they are on when not really needed it won't do any harm ( I hope:) ). I f the fans wear out prematurely they are not expensive so will just replace.
     
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  9. Nirvanauk

    Nirvanauk Funster

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    Well, this makes my toilet extractor fan purchased from Weldom that I hang with a rubber sucker above my top vent on the outside of the van seem a bit Mickey Mouse doesn't it?
     
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  10. Gromett

    Gromett Funster

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    For those interested here is a list of the parts, link and price.
    ATTiny85 Microcontroller. £0.98 each.
    IRL540N Mosfets. £0.99 each
    DS18B20 temp sensors. £0.79 each (£1.58)

    The rest of the components cost less than 1p each.
    Diode, I bought a pack of 100 for £2.08
    Resistors I bought a pack of 1460 for £7.08

    So all told it will be less than £4 in parts.
     
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  11. Gromett

    Gromett Funster

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    I am keeping my system very very simple. It will need a 12v supply only. You then plug the fans into it. That is all. No need for wires coming out to a control panel or anything else. It will be fully automatic (y)

    On the circuit board there will be 2+ sockets to plug the fans into. A terminal block to attach the power to.
    then I will just velcro the box to the inside of the fridge ventilation area and forget about it.
     
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  12. John Laidler

    John Laidler Funster

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    What temperature are you thinking of setting the upper sensor to? That was the thing I was unsure of when I did mine. It's set quite low at the moment (30) but I think it could be a lot higher.
     
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  13. Gromett

    Gromett Funster

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    Thanks for pointing this out to me. Just went to look for the fan sockets. didn't want to have to wire them directly to the board.

    http://www.ebay.co.uk/itm/301830511722
     
  14. Gromett

    Gromett Funster

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    The top sensor doesn't need to be set in my configuration. It works on the differential between the 2 sensors. So at say 2C difference it will barely turn the fan. At say 10C difference the fan will go full blast. The speed will not only vary on the difference but the speed at which the temperature differential changes. The PID process is pretty impressive.

    Because I am working using the differential between 2 sensors the absolute temperature is irrelevant.
     
  15. Madcaravanner

    Madcaravanner Funster

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    I have a system on my caravan fridge it is a large turbo fan from a computer not the flat type it is wired via a simple fused switch feed and is usually on once we are on site I switch it off when we are travelling
    In Benidorm the outside ambient temperature was 36-38 but the freezer remained at -18 without going hi tech just simple wed fan
     
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  16. Gromett

    Gromett Funster

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    The problem with that for me as previously mentioned is
    a) the fan is going full blast.
    b) the fan is running all the time.

    I am sensitive to fan noises and that would drive me up the wall.
     
  17. hilldweller

    hilldweller Funster Life Member

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    What an elegant idea.
     
  18. Viennese

    Viennese Funster

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    Will you be offering your design and skills to others Karl?
     
  19. Gromett

    Gromett Funster

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    Don't know what you mean sorry?

    I will be fully documenting the project(s) and will publish all the software for free.
     
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  20. jockaneezer

    jockaneezer Funster

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    Sounds like another project for my "to do" list. Bought a pid controller, fan and temp sensor to make an air supply controller for doing low and slow on the barbecue, but my new Webber is almost set and forget. I'll be watching this with interest. (y)
     
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