12v micro heater

Discussion in 'General Electronics Chat' started by Tifa, Dec 14, 2009.

  1. Tifa

    Thread Starter Member

    Nov 5, 2009
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    Hi Guys

    I'm in the process of trying to overcome a re occuring condensation problem within the dash on my motorcycle...

    Originally, condensate was collecting on the pcb causing all kinds of problems...

    Anyway, as suggested here, I coated the pcb with a recommended resin, and the electrical gremlins seem to have sorted themselves out...thanks for that! :)

    However, I think that a small heater within the guages might be a good idea..(same principle as used on external cctv camera enclosures, to prevent fogging on the inside of the glass) ?? :rolleyes:

    Providing you agree that the principle is sound, does anyone have any idea if a minature heating element is available? :rolleyes:

    I've thought of just using a resistor, but I'm a bit unsure of which value to go with...given that the casing is plastic ..and it'd be a £680 ( $1000 ?) disaster if it melted... :eek:

    Unfortunately, there's very little space inside the guages, so the smaller the element, the better

    Any input would be greatly appreciated... :)

    Thanks
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    How about light bulb(s)
     
  3. Tifa

    Thread Starter Member

    Nov 5, 2009
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    Yes, I've thought about a bulb, but given that space is really tight, and reliability could be an issue too I discounted that route. There's loads of vibration...so was thinking a wire wound resistor might be a little more compact & durable?

    Just a thought
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    What is your power cource? Wire wound resistors work fine as heaters. For inclosed swimming pool 120V AC outlets,' installel 15k, 5W wire wound resistors in each outlet, no more corrosion problems; drain only 8mA ,1 W. Can series several resistors to distribute heat.
     
  5. Tifa

    Thread Starter Member

    Nov 5, 2009
    10
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    thanks for that, sounds good

    power source is 12v DC

    3 or 4 small resistors wired in series would I think just about fit into the enclosure, but I'm struggling at where to start resistor value wise...
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    At 12V ,150 ohm[2W] on 10Ahr battery would last about 125 hours continuous; with a light controlled timer, turning on heater for maybe 6 hrs in the wee hours of the morning, you could forget to turn off heater for several days.
     
  7. Tifa

    Thread Starter Member

    Nov 5, 2009
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    thanks for that Bernard, power supply isn't really an issue as I plan to hard wire it into the motorcycles ignition circuit...with a small relay...so as not to upset things in that dept.

    the 150Ω 2W resistors....how hot are they likely to get please?

    I apppreciate that's a bit like asking 'how long is a peice of string'? ;)

    But I'm only after a rough idea of likely temps here...the reason I ask is, one of my main concerns would be the plastic casing melting....which financially would be a bit of a killer...
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I taped a thermometer to a 1 W 150 ohm resistor @ 12V- holding at 120 deg. F. Would break that 150 into something like 5-30 ohm 1/2 Ws.
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Just seal the casing with some silicone. It should be airtight but it is not, which is why you are getting the condensation problem. Normally they have a rubber seal or o-ring etc.
     
  10. Duane P Wetick

    Active Member

    Apr 23, 2009
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    I would think 1/8 Watt / cu in. of space in normal climes (sub-arctic) would be more than enough heating to keep condensation at bay. Trying to seal things against moisture is difficult and usually just serves to keep moisture in. That is probably what is happening to your gauge set. Estimate the volume and we will calculate the heating resistance for you.

    Cheers, DPW [ Always remember that you are not going to live forever.]
     
    Last edited: Dec 15, 2009
  11. Tifa

    Thread Starter Member

    Nov 5, 2009
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    I wish it were that easy...there is a design fault on the unit imho
    Which has been confirmed by the redesign on newer models
    It's impossible to get a perfect hermetic seal because of the way the multipin connectors exit the rear of the housing...
    Because of rapid air pressure changes (riding up & down hills etc..) air, sometimes moist, gets drawn in...causing the problem...
    To allow it to escape, I have already vented the enclosure with goretex membrane vents...these allow the moisture to escape, but keep out water, dust & creepie crawlies...
    It's a huge improvement over standard...but I guess a little heat in there can't hurt..?
     
  12. Tifa

    Thread Starter Member

    Nov 5, 2009
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    thanks for that Duane...I have a spare faulty set...when I get home later tonight, I'll get the exact internal volume...

    (I was thinking of filling them up with water, then pouring the contents into a calibrated measuring beaker... :rolleyes:)
     
  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Why bother with a relay- coil would give about as much heat as resistor string, maybe an auxillary switch for warm days.
     
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