Thermal Switch

Discussion in 'OnBoard Electronics & Controls' started by michael pierzga, Mar 4, 2013.

  1. Don H
    Joined: Apr 2012
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    Location: Queensland Australia

    Don H Junior Member

    Michael, it sounds like you need 2 fans. 1 inside the cabinet to move some air around the back of the plotter and a second at the top of the cabinet to remove the hot air.
    Forget thermostats and temp controls unless you really need to watch power usage. A simple on /off switch is enough. A heat sink will eventually get hot as well so there is no real advantage there.
    I have always avoided fans in our electronic equipment when possible as I consider them to have too short a lifespan. (Who hasn’t replaced the PC power supply because the fan seized and the supply failed?)
    Recently though I have found the newer types with magnetic bearings quite reliable and very quiet. I have some 90mm ones at the moment that only draw .13A at 2000rpm so current requirements are very low.
    The second fan mounted somewhere at the top of the cabinet will work best if it is extracting the air rather than try to blow air into the cabinet. You will need a vent somewhere towards the bottom of the cabinet to let fresh air in. It will need an opening at least the same size as the fan hole.
    If you don’t get enough airflow through the cabinet you may need to keep adding fans. Multiple fans are generally quieter than a single big fan howling away at high speed. We put up to 6 fans in our 19” rack gear and you can barely hear them.

    Thanks Don
     
  2. michael pierzga
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    michael pierzga Senior Member

    Thats the setup...one fan down low suppling the cabinet with air and one fan on top extracting hot air .

    The problem with an on off switch is esthetics....no place to locate the switch.

    The fans I picked up at the local electronics shop are ...EBMPAPST , Hungary... 25CFM ...they seem quite..dont know about bearing life. They were cheap.
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A fan can easily be wired in with the power supply switch. No separate switch, just turn on the plotter and up comes the fan too. I don't think two fans are necessary and I do think a heat sink is an effective option, but I do agree in the placement of one fan at the exit of the cabinet. A fan placed like this puts the cabinet in a negative pressure, which will remove heat quickly, but more importantly will not permit the smells of the heated electronics, to spill out into the cabin spaces. They are forced out the exit and I'll assume this is outside the cabin spaces. A fan placed like this will draw air across the heat sink (just what it needs) and suck heat out as well. I also disagree in that these types of fans die quickly. If you buy a cheap fan, you'll get the life span you might expect, but a good fan will out live the plotter.
     
  4. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    In all these years of usage of computers (and I have had many of them) not once has the fan died before the rest of the system. So lifespan is most probably not an issue - provided that the voltage is kept constant and in the correct range of values.

    I realize that my support to PAR's advices in this thread is becoming annoying, but I just can't help agreeing with them. So far they are imo the best and simplest to implement ones. The principle is always the same - keep it simple, if it can work that way. Things you don't have are those which will not break or burn.

    Cheers
     
  5. dzausta
    Joined: Feb 2013
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    dzausta Junior Member

    spot on.
    ps. he could have an enclosed char plotter that can't be tampered with, maybe thats why he's thinking of a switch

    if you dont than dont bother with the sensor
     
  6. Submarine Tom

    Submarine Tom Previous Member

    This thread is getting rediculous.

    Hard wire the fans into the power switch and forget it.

    Simple, cheap and idiot proof.

    End of story.
     
  7. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    They should not be cheap, so they are probably rejects. That doesn't make them bad, maybe a little unbalance in the rotor or a cosmetic issue.
    Papst has incredible quality control: I've traded over 10.000 rejects and never figured out what was wrong with them.
    MTBF for Papst ball bearing fans is 20.000 hours, 5.000-10.000 for sleeve bearings.

    Fans die because they collect dust and cobwebs. Finally they are completely clogged and stop turning; then the tiny motor overheats and dies.
    I'm in favor of using thermal switches, less noise and less dirt on the fan blades.
     
  8. Submarine Tom

    Submarine Tom Previous Member

    CDK,

    I would agree with you but he/she claims overheating issues.

    I think it best if they run when power on.
     
  9. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    The chart plotter is permanently power ON.... 300 days a year ? When not in use it is put in Standby mode.

    The other gear..Philips AP Navigator and Simrad AIS are also permanently on.

    With forced air circulation, will I need to filter the air supply ?
     
  10. hoytedow
    Joined: Sep 2009
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    hoytedow Wood Butcher

    It would not be a bad idea to put a lint screen at the intake fan position and check it from time to time.
     
  11. Submarine Tom

    Submarine Tom Previous Member


    Then hard wire them to be off in stand-by.

    Filters would be a great addition.

    Add their cleaning to your maintenance schedule.
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A couple of milliamps draw, even if continuous isn't a significant hit on an electrical system Michael.

    If I was doing this, I focus on two things, the first a effective evacuation setup, meaning it would likely have an enclosure, with a heat sink or two, funneling up to a fan at the exit. The second would be the switching, which means pulling the cover off the plotter and rigging an umbilical, but not a difficult thing, with some familiarity. You will need to determine if the switch is just momentary, that tells the board to power up, or if it's the supply side of the I/O, but this is fairly easy to figure out.
     
  13. Don H
    Joined: Apr 2012
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    Location: Queensland Australia

    Don H Junior Member

    Michael, I haven’t had a great record of reliability with fans but that being said mine have generally not been installed in very clean environments. I have a pc that runs a PCB milling machine that is on its 5th power supply in only 6 years. It does run continuously and each time the failure has been due to dirt clogging the fan. The shortest lifespan for a pc fan for me has been 3 weeks

    I would definitely agree that you should fit a filter. If the intake hole is positioned so that incoming air will flow past the plotter you might get by with only 1 fan. If you need to fit ducting to get air to the back, personally I would still fit a second fan inside to blow air around the plotter. Only experimenting and monitoring the temperature will tell if you fan is moving enough air. If you don’t want a switch to be seen you could wire it permanently on or perhaps give it longer wires and fit the switch in a remote, more aesthetically pleasing location.
    Be aware that if your plotter is new, any modifications like pulling it apart to take wires from standby/on, adding heatsinks etc will void its warranty. There may even be an installation section with requirements for enclosure size/ventilation requirements.

    Thanks Don
     
  14. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    We shall see...too cold outside to give the system an authentic trial run.

    I glued the heat sensor to the back of the chart plotter... then sank two teak grate exhaust vents into the top of the cabinet, plus one large intake vent on the bottom...a three fan setup. Two small fans screwed to the back of the teak exhaust grates and one bigger fan for intake.

    No filter yet...I need to investigate something.

    Runs quite, only a faint ...Hmmm...now I need to update the ships drawings..always the most tedious detail. As a non electrician I hate modifying professional work.

    What is the electrical symbol for the heat sensor relay ? a two amp inline fuse sufficient ? 5w at 24v total fan load.

    http://[​IMG] upload pics

    http://[​IMG] upload pics
     

  15. hoytedow
    Joined: Sep 2009
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    Location: North of Cuba

    hoytedow Wood Butcher

    Apples and oranges but a 5w 12 volt camera unit I just installed requires a 2 amp fuse. Does that help?
     
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