AC Fan Motor Controller; Much Help Needed

Discussion in 'The Projects Forum' started by wescat, Apr 11, 2010.

  1. wescat

    Thread Starter New Member

    Apr 8, 2010
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    Great site, seems to be a bunch of good people on allaboutcircuits. I've been reading here for a while now, and I recently joined. I am a newby, this is my first post.

    I need to build a controller to control the fan motor inside an upright, frost free freezer. The OEM design energizes the fan whenever the compressor is energized: compressor on, fan on; compressor off, fan off. I need additional functionality.

    The fan controller shall have 2 modes of operation, manual and automatic, switched by a 2 position toggle. In manual mode, the fan shall run continuously. In automatic mode, the controller must perform 2 types of fan control: a timer, and a delay timer. The timer shall control the fan on and off time intervals whenever the compressor is not energized. On will range from 1 to 10 minutes, off will range from 10 to 60 minutes. I currently expect to converge on a 1-5 minutes on, 20-30 minutes off type cycle, following trials and data analysis. The delay timer shall delay the de-energizing of the fan after the compressor de-energizes: the compressor kicks out, the fan continues to run for (time value) minutes. The time window will range from 1 to 10 minutes. I expect to converge on a ~ 5 minute time window, following trials and data analysis. If any of these time windows add large complexity or cost to the circuit, I can specify narrower windows.

    Both the fan and compressor operate on standard 120V AC. Anytime the compressor is running, the fan must run. The signal that the compressor is/is not running shall be the 120V that energizes the compressor. I will have to access the fan motor to determine the wattage it pulls. I Google’d a replacement fan motor, the picture had 7.7W printed on the motor winding wrap.

    So, with the toggle switch in manual mode, the fan runs continuously, no matter what the thermostat, compressor, timer, or delay timer say or do. The only way the fan de-energizes is by unplugging the freezer. With the toggle switch in Automatic mode, the timer runs the fan for XX minutes, turns it off for YY minutes, cycles this way infinitely. No matter where the timer is in its cycle, if the compressor kicks in, the fan runs the entire time that the compressor is energized, and then continues to run for ZZ minutes after the thermostat drops the compressor, as per the delay timer.

    Example of Automatic mode operation: (and this is what I currently think the final time values will be close to).

    Example time values:
    Fan on time value: "XX" = 2 min
    Fan off time value: "YY" = 20 min
    Fan delay-on-drop time value: "ZZ" = 5 min

    The example starts when the freezer thermostat engages the compressor; the controller simultaneously turns the fan on. The compressor runs until it reaches thermostat set point and then cuts out. The delay timer in the controller keeps the fan running for 5 more minutes, at which time the controller cuts power to the fan and the timer in the controller starts counting off 20 min. At the end of 20 min, the controller turns on the fan and it runs for 2 minutes, this 2 on 20 off cycle continues till the thermostat engages the compressor again. (Note: I would prefer the fan timer to start its fan off (YY) timer count when the compressor kicks out (de-energizes). If that complicates the circuit, start the YY count at the end of the ZZ count. Either works.)

    I have been researching how to build this controller for a few weeks, and I have some ideas, but I am not an electronics guy, my skills are in the mechanical realm. I can solder, read a wiring diagram (12V and 120/240V), etc. I built a digital clock for a digital devices class many years ago. I am very good at automotive wiring diagnosis and repair. I repair most things around my home.

    I do not have a circuit diagram for this controller. If practical, I would like to build the controller with devices that allow for adjusting the 3 time values.

    Any and all help is greatly appreciated.
     
    Last edited: Apr 16, 2010
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    I would want to separate the circuit from the unit, electronically, using the compressor as a signal to activate the fan.

    You can use a current sensing device to determine when the compressor is running, and allow for an interrupt in the timing cycle to force the fan on while the compressor is on. I would go for this rather than tapping the thermostat line. But either will work.

    When the compressor cuts off, you will receive a LOW on the sensor. Now depending on the switch position, auto or manual, the circuit will determine where to go from here.

    Using a uC, you could easily adapt changes to the delays and runtimes via code, or you could use a couple of 555 with POTs to adjust the delays. The uC way will be more accurate and if you select one that uses interrupts, could have this together pretty quickly.
     
  3. wescat

    Thread Starter New Member

    Apr 8, 2010
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    retched, thanks for the reply. Can you point me to a circuit diagram that would be similar to what I am trying to build?
     
  4. Bychon

    Member

    Mar 12, 2010
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    Which method do you choose to use? A microprocessor or some timer chips?
     
  5. wescat

    Thread Starter New Member

    Apr 8, 2010
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    I do not know enough about either option to make an informed decision. What equipment do you have to have to program the microprocessor? Is there a significant reliability difference between the 2? Cost difference between the 2? Thanks.
     
  6. Bychon

    Member

    Mar 12, 2010
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    Reliability is not a big factor. Either circuit, designed well, is reliable.

    As for the equipment needed, timer chips require less equipment because you don't need a computer to write programs and tell the microprocessor its instructions.

    The pricing, I don't know. Retched will soon reply with more information. Meanwhile, I have helped a little bit...I hope.
     
  7. retched

    AAC Fanatic!

    Dec 5, 2009
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    Sorry, I skipped over the thread earlier.

    If you are not interested in further microprocessor projects, it may not be worth the investment in time and money to go that route. You may find someone ___ that will program a uC (microcontroller) for you and ship it to you for a small fee. That would reduce your part count pretty well. Either way you can use POTs to dial in your delays and times.

    You just have to decide which way to go. We will help either way.

    [ed]

    Also, are you considering using this as a one-off? Or are you working on a design you want to reproduce?
    [/ed]
     
    Last edited: Apr 13, 2010
  8. wescat

    Thread Starter New Member

    Apr 8, 2010
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    Thanks for the replys, and the willingness to help. Lets go with the 555's and pots.

    It will be a one-off for now, with the possibility of reproducing it in the future.
     
  9. wescat

    Thread Starter New Member

    Apr 8, 2010
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    I am bumping my own thread.
     
  10. retched

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    Ok, bumper. I haven't forgot about you. I wont have any real time to work this out until the weekend. I have subscribed to the thread so I wont forget about you.

    In the mean time, It would really serve you well to get to know the basics of the parts we are going to be working with to help cut down on confusion during the building process.

    Give Bill_Marsdens blog a read, especially the 555 pages.

    http://forum.allaboutcircuits.com/blog.php?b=378

    In an hour or so, you will have a good idea on how the timing and triggering works.

    Once we have that, the rest is pretty straight forward.

    Also, Im am guessing we will be using the 24v that is standard in HVAC transformers for the power supply? If so, we can use a voltage divider to get into the "happy" range for the 555 chips. Also, it will simplify finding relays with coils to match the voltages we are going to be working with.

    Do you have any delay-on-make timers that are typically used for compressor delays and the such?

    Also, since we will be using a relay to switch the fan on and off, we are going to need a full time 120vAC source that can supply the fan motor in modes when the compressor is not feeding power to it. i.e. The times you want the fan on while the compressor is off. During these times, there will be no power to the original leads that feed the fan motor, so we will have to supply it from somewhere else. Coming to think of it, we can use these original leads as the signal for compressor on times.

    Anyway. Get a educatin' of the 555.
     
    Last edited: Apr 16, 2010
  11. wescat

    Thread Starter New Member

    Apr 8, 2010
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    Retched, thanks for the reply. I have read Bill Marsden's blog a few times. We can use any power supply we choose, all the componetry currently on the freezer is 120V. I do not have any delay-on-drop timers in mind. I assumed we would build our own in the circuit. I have the full time 120V for the fan issue covered. You are correct about the compressor on signal. I look forward to your input.
     
  12. retched

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    Ok. I was wondering if you had any delay-on-make timers for informational purposes, not for use in the design. We will be making our own with the 555s and such.

    If you could, figure the time band that we WILL require. Is it going to be 1 to 10 minutes or are you wanting more like 3 to 9? Having these set for design purposes will be helpful. As we are going to change values for time changes, so it will be helpful.
     
  13. wescat

    Thread Starter New Member

    Apr 8, 2010
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    retched, I do not have any delay timers to use for informational purposes.

    OK, time bands. I will use the nomenclature from my original post for clarity:

    Fan on time value; "XX" time band; 2-10 minutes
    Fan off time value; "YY" time band: 6-20 minutes
    Fan delay-on-drop time value; "ZZ" time band: 3-15 minutes

    Let me know if any of these time band values overly complicate the circuit, I'll re-evaluate.
     
  14. retched

    AAC Fanatic!

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    Ok. In auto mode, the delay-on-drop would have to be interrupted if the compressor engaged.
    .. Ill have to put some stuff together. I'll get it together over the weekend
     
  15. Roy Von Rogers

    New Member

    Oct 13, 2009
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    I've read the original post several times and I may have missed something. My question is why do you want to do this, and what is your goal doing it.

    Btw I'm an aplliance tech and I'm just curious.

    Roy
     
  16. retched

    AAC Fanatic!

    Dec 5, 2009
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    Ok. I have started to put together a little breadboarded circuit for you design.

    A few things Id like to know. Do you have the power supply? Or can I have design privilege? I will most likely use a wall wart, but if you had a source in mind, let me know now so I can avoid having to reconfigure stuff.


    Lemme know. Also, can we mount this in the cavity that the compressor and coil is located in? or do you want to have it external so you can easily adjust the timing knobs?
     
  17. wescat

    Thread Starter New Member

    Apr 8, 2010
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    On the power supply, please select as you see fit. I have many wall wart's that I've saved over the years, I can dig through them if that'll help. I do plan on mounting this unit in the cavity where the compressor, etc are located.
     
  18. retched

    AAC Fanatic!

    Dec 5, 2009
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    Ok. I am going to have to get my hands on a 12v relay for the switching, as I do not have any in my piles. Ill check around my boxes at work. If not, im going to stop and pick a few up.

    I would appreciate it if you would PM, as I have a few questions for you outside of public forum.

    Click on my name in the post and under the menu, click Send a private message.
     
  19. wescat

    Thread Starter New Member

    Apr 8, 2010
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    Retched, the system will not let me send you a PM, so I sent you an email.
     
  20. retched

    AAC Fanatic!

    Dec 5, 2009
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    ok. Ill check.
     
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