A cooling fan for an air compressor

Discussion in 'The Projects Forum' started by Kermit2, Sep 24, 2010.

  1. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    I'm starting a project. I have an air compressor that seems to get very hot while running. I realize they do this as part of the process of compressing the air, but the heat developed also contributes to the inevitable future failure of the compressor. To help prevent a short lifespan, and keep my investment in top shape for a longer period of time, I have decided to to place a fan near the piston of the compressor to aid in cooling it. I don't want the fan to run all the time the it plugged in, and I don't want it to turn on and off at the same time as the compressor, so I need a circuit to keep the fan running till it has cooled off, then switch it off.

    I've decided on using a thermistor. http://www.alliedelec.com/search/productdetail.aspx?SKU=2540072#tab=Specs

    which will feed into an op amp.

    http://www.alliedelec.com/search/productdetail.aspx?SKU=3830229

    this will power a solid state relay connected in the emitter circuit of a 2222 transistor.
    http://www.alliedelec.com/search/productdetail.aspx?SKU=6824068

    This is the compressor I have is a nice little ingersol rand branded one and will feed two seperate tanks besides it's own. Both of them will be in my workshop in the house and will have isolation valves on them to remove them from the air compressor air distribution piping.

    Purchased here(It was on sale for less than it is selling for now)

    For a power supply I used an a 5 volt adapter from one of my wifes old, no longer used, cell phones.
    http://www.everypowercable.com/lg22gt2.html

    And it will power a muffin fan, almost identical to this [​IMG]

    I have cut and bent and drilled out some mounting holes on a piece of aluminum. The fan will be mounted on it and aimed at the piston. It looks like this.
    [​IMG]
    The relay coil is actually not one. Since I went with a solid state relay device instead of a mechanical one. The compressor vibrates A LOT and I got to thinking that might not be compatiable with a mechanical contact type relay.

    The circuit I have come up with is this one.
    [​IMG]


    Hopefully I'll get the parts I ordered tomorrow, if not then next week on Monday or Tuesday(At the mercy of FedEx) and will get to work mounting the circuit components this weekend (or next)

    If it all works out like I hope I'll post it in the completed projects forum.


    Kermit
     
  2. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    My thermistor and op amp and solid state relay have arrived.

    HURRAY! You don't have to be happy for me. I'm happy enough for ALL of us

    :D

    One step closer to home shop Nirvana,
    Kermit
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    Interesting that your post shows up right next to my cooler circuit, which would accomplish a similar task. (My needs are more complex and the circuit is more elaborate, but similar concepts.) Just curious, why did you choose the transistor instead of a MOSFET? I guess the fan doesn't draw a lot of power so anything will work.

    Your circuit doesn't address what happens when the temperature is right at the switching point. It might oscillate and cause the transistor to not switch cleanly. It might get hot if/when it's not fully on or off. Make sure you feel it for heat when you first try your circuit, and be sure you don't cheat by changing the thermistor temp too quickly past the switching point, making things appear to work nicely. In real use it may hover at the switch point for enough time to be a problem.

    [update] Oops, just read that you're fan is AC (mine is DC). So you're transistor switches the relay, not the fan directly. Makes sense now.
     
    Last edited: Sep 24, 2010
  4. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Looking at the picture of your compressor, what is the black shroud thing jut to the right of the cylinder? It looks like a deflector to direct air flow directly to the cylinder. Is there already a fan on the motor blowing air?
     
  5. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    The "shroud" is just a thermoplastic formed cover that keeps all the mechanical appearing components from view and causing confusion in Mr and Mrs. Average Joe. It serves no purpose that I can fathom other than appearance. The one edge that isn't fastened down vibrates noisily when the motor kicks in. :) Might take it off if it gets in the way, or it appears that I can keep the system cooler without it in place.
     
  6. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    R8 is supposed to give the switch over point a small bit of hysterisis. When the negative(ref) input voltage goes higher than the Thermistor input voltage, the op amp goes to "off", or switches to a low output voltage. This not only turns off the relay, but through r8 feeds back that negative voltage to the Thermistor divider network, sending its voltage further in the low direction, insuring that the thermistor input point falls a few millivolts lower than the point required to switch the op amp. Meaning there will be a few degrees of temp difference between the switch on and off points of the fan.
     
  7. eblc1388

    Senior Member

    Nov 28, 2008
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    @Kermit2,

    Both the following two methods of output are possible but there are subtle difference.

    Why have you chosen the type A circuit over type B?

    [​IMG]
     
  8. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    So I looked around for an outlet that I could FIT into the area provided under the cover of the compressors AC switch mechanism.

    A plug with a ground pin was not needed in this instance and besides, one that size wouldn't fit in the small space available. Remembering some old amps I have had two prong aux. outlets on the back and finding one that seemed to have a damaged slot on one side, I decided to utilize that in the project. This called for application of the dreaded "HACK SAW". Not usually a good thing when you have to bring out that tool to complete a small electronics project, but in this case, it was surely not to be done without.

    [​IMG]

    [​IMG]

    Now I'll also have to cut a matching "HOLE" into the ac shroud on the compressor, but that can wait till I get some other things built first.

    [​IMG]

    The little "chingaletties" I purchased from www.alliedelec.com

    I'm not an employee or a paid promoter of that web site/company, but I will recommend them highly. Especially if you live in Oklahoma, Texas or Louisiana. With a warehouse/office in Dallas, TX, I get my orders the very next day, for the UPS 3day ground rate!

    Next to chop up a small piece of circuit perf board, that will fit inside the AC shroud, and do some arranging and re-arranging till the puzzle pieces seem to fit together. Then I'll be back and continue to put this project together in pictures for those of you who are following along.

    GOOD SAT MORN everyone,
    Kermit
     
  9. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    Honestly, I don't have a reason for choosing A over B. It could just be one or the other and I choose one. If you have a reason why the other might be better in this application, I'd be interested in hearing. Always ready to learn from others, of better ways or safer methods.

    Thanks for looking and posting,
    Kermit
     
  10. eblc1388

    Senior Member

    Nov 28, 2008
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    The configuration in A is in the form of emitter-follower. As such the transistor is never fully turned ON and the relay will never see a full 5V across it. e.g. if the Opamp outputs 4.5V, then there is a further 0.65V drop from the transistor's base to emitter and it means only 3.85V for the relay.

    No such problem with circuit configuration B, which is why 99% of circuits are using it. The NPN will operate in the saturated region and drops about 0.2V leaving 4.8V for the relay.
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    That's funny, my compressor's uses a fan mounted on to the shaft and cools it self.
    Wonder what u have.
     
  12. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    Okay, some changes and revisions have been made and details added.

    [​IMG]

    And the physical / mechanical portion of the project is progressing.

    [​IMG]
     
  13. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    [​IMG]
    [​IMG]

    The icky, hacked up, intestinal components of "the device". Kinda scary isn't it? :)

    [​IMG]

    and a little tiny piece of real estate to build on.

    [​IMG]

    Still contemplating the details of an epoxy sealed cable termination for embedding the thermistor in, and making thermal contact at the compressor piston

    Boo! :)
     
  14. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    Stubbornness, and a can of condensed impertinence. Served with humble pie most days, but occasionally I get some red meat and prefer that med. rare. with a nice sharaz and fresh bread sticks.

    And You?
     
    Last edited: Oct 31, 2010
  15. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I know it is a fun project to make, but why not just run the fan continually when the compressor motor is on? With the heat generated, I don't think a single fan will cool it enough for it to ever shut off when the compressor is running.

    Tap into (or hall effect sensor) the lines to the motor to determine if compressor is running, if so, run AC fan(s) to blow air across cooling fins.

    Just a thought.
     
  16. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    Mostly because I want the fan to continue running after the compressor stops. If it cycles a few times while I'm using it then the fan will only blow for a few seconds at a time and stop. The compressor head will just be starting to reach a peak temp by then. Letting it keep blowing until the temp has dropped back to 120 or 110 is what I thought I would aim for. getting it back down to ambient between it's recharging cycles would have it running continuously. This just struck me as a simple project to get my feet wet again after so many years.

    Thanks for your interest in this project.
     
  17. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Try just plugging the fan in to see what the cooling ability is.

    Nothing fancy, just an extension cord to the compressor, and time how long it takes to get to the temperature desired.

    I thing maybe even two fans would be a bit better. I have a DeWalt englo, and it does get quite hot when I use it for painting with an HVLP gun. It has a fan built in as well, but doesn't seem to get down to "warm" until a while after it isn't running.

    In a nutshell, test the concept before designing the circuit. Maybe even a 5 minute delay would be better than the temp sensing, as the temp sensor is bound to vibrate loose sooner or later unless it is screwed to a fin on the compressor head. If it ends up hanging in free air, there would be no cooling.
     
  18. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    I really appreciate the suggestions. I could do something simpler I'm sure, and any cooling at all where there was none before is a good thing. Mostly it was just to get back into 'tinkering', and since I had never used a thermistor in anything I've built before, that's what I decided to do. Just a ProjecT is all. Nothing fancy, nothing critical.


    A hack a day, keeps my boredom at bay. :) The power into the compressor will be tapped and fused at 1 amp, and be switched through a two blade AC socket. The Fan will have a male two prong plug(coiled AC power cord from an old electric razor) that will plug into the socket. It was done like that so I could move the fan to another "thing" some future day.
     
  19. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    the shroud is indeed designed to move air over the electric motor and onto the cylinder finning, driven by the motor's fan. Removing it would not be a good idea. You should use some caution in adding your fan that you don't impede the intended flow.

    You might be farther ahead to improve the efficiency of the exsisting motor fan by tightening the clearances on the intake.
     
  20. Kermit2

    Thread Starter AAC Fanatic!

    Feb 5, 2010
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    There is indeed an impeller fan on the shaft of the electric motor, but it is housed in a ventilated cover and serves its purpose cooling the electric motor very effectively. It however, has no effect on the cooling situation around the fins of the compressor piston. The fan I'm adding will be to cool that area only. If the shroud is serving any purpose other than cosmetic, it would be to add an irritating rattle to the working of the device, and maybe to keep water and dirt off of the motor and mechanical workings beneath it.

    Should have another update by next weekend.

    Kermit
     
    Last edited: Nov 1, 2010
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