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Enclosure Heater — Parallax Forums

Enclosure Heater

xanaduxanadu Posts: 3,347
in General Discussion
I have an enclosure that is 2.5' cubic volume. It sits indoors, which is around 70f. I need a heater to keep the inside at 130f. I'd like to use a fan to blow around the air to prevent hot spots. I would like to buy a heater and fan as one unit, then use a Prop to build the thermostat. I'm not ruling out built in thermostats, but they aren't required so either way is fine.

I found this - http://www.omega.com/pptst/FCH-FGC1.html It looks perfect. After a phone call they said it's not deigned to produce temps that high. It doesn't have a built in thermostat so I'm guessing there is some internal limiter. It seems to me a 12v 60 watt heater should be able to reach 130f in a confined space.

Does anyone have a suggestion on something that would be able to maintain 130f in a small space?

Input 12-24v DC, 20 amp max
=< 60mm fan to keep size down
Usage is 2000 hours /yr

Thanks.

Comments

  • RDL2004RDL2004 Posts: 2,554
    edited 2015-11-27 20:51
    If this is for a personal, diy type project, you might look around at your local pet supply store for reptile cage and fish tank heaters and such... don't know if 130F is feasible with that type of stuff though, maybe if well insulated. A suitable PC type fan should be easy to find, I have a box full, all sizes from 25mm to 120mm.

    edit: ah, 12-24 volt, probably won't find that at a pet store. How about a bunch of big ceramic type resistors?
  • abecedarianabecedarian Posts: 312
    edited 2015-11-27 20:54
    Maybe I'm going off tangent-like here, but a heat gun with the heat element controlled thermostatically sounds like a fairly decent solution.

    *edit- Smile. Just read you want 12-24VDC
  • RDL2004RDL2004 Posts: 2,554
    edited 2015-11-27 21:42
    12 volt spaceheaters made for cars and RVs

    http://www.ebay.com/sch/i.html?&_nkw=12+volt+spaceheater

    also try 12 volt space heater and 12 volt defroster

    Another possibility, but would require a bit of hacking, is to modify a cheap hot air soldering/desoldering station.
  • xanaduxanadu Posts: 3,347
    RDL2004 wrote: »
    If this is for a personal, diy type project, you might look around at your local pet supply store for reptile cage and fish tank heaters and such... don't know if 130F is feasible with that type of stuff though, maybe if well insulated. A suitable PC type fan should be easy to find, I have a box full, all sizes from 25mm to 120mm.

    edit: ah, 12-24 volt, probably won't find that at a pet store. How about a bunch of big ceramic type resistors?

    There are a lot of DC heating elements on ebay That gets plenty hot and has the option to control each element individually.
    abecedarian wrote: »
    Maybe I'm going off tangent-like here, but a heat gun with the heat element controlled thermostatically sounds like a fairly decent solution.

    *edit- Smile. Just read you want 12-24VDC

    I've been using a 120vac heat gun for testing, it works very well. Plastic PC fans can take a lot of heat, but not the high setting for very long. The other thing is a heat gun has cool air coming into it. This setup is supposed to recirculate air so it doesn't heat up the room it's in.

    I can shed my worries because these guys list very high operating temps. So I have a heating element, and now a fan.

    Now I need a thermostat, or make one. This looks nice http://www.omega.com/pptst/CN7800.html

    Begin wait for parts.
  • kwinnkwinn Posts: 8,697
    For durability your best bet is to mount the fan motor on the outside of the enclosure and have the shaft protrude into the enclosure. With a bit of insulation it shouldn't require much wattage to produce 130F. I used a 6x6x6 inch metal box, a 12V fan, and 4 car turn signal bulbs to test and determine calibration factors for some thermostats. Got all the parts in the surplus section of Princess Auto.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    One could simply purchase nichrome wire, but this usually is supported by ceramic insulators that are hard to come by. The nichrome wire is easy to purchase.

    One or more incadescent light bulbs might do the trick and be the easiest to deploy in a small space. I wonder how 150watt 120volt light bulb might perform on 24vdc. I think it is worth looking into. Also try automotive or motorcycle headlamps. Some actually are a bulb that is inserted into a reflector and produce quite a bit of heat.
  • msrobotsmsrobots Posts: 3,704
    Enclosure @Heater.?

    - well -

    Even his ranting against Windows is annoying, putting him into a enclosure goes honestly to far.

    Enjoy!

    Mike
  • xanaduxanadu Posts: 3,347
    kwinn wrote: »
    For durability your best bet is to mount the fan motor on the outside of the enclosure and have the shaft protrude into the enclosure. With a bit of insulation it shouldn't require much wattage to produce 130F. I used a 6x6x6 inch metal box, a 12V fan, and 4 car turn signal bulbs to test and determine calibration factors for some thermostats. Got all the parts in the surplus section of Princess Auto.

    Great idea, I hadn't given putting the motor on the outside much thought. I hope it doesn't take much heat/watts, it doesn't seem to me like it would.
    Loopy Byteloose wrote: »
    One could simply purchase nichrome wire, but this usually is supported by ceramic insulators that are hard to come by. The nichrome wire is easy to purchase.

    One or more incadescent light bulbs might do the trick and be the easiest to deploy in a small space. I wonder how 150watt 120volt light bulb might perform on 24vdc. I think it is worth looking into. Also try automotive or motorcycle headlamps. Some actually are a bulb that is inserted into a reflector and produce quite a bit of heat.

    A lot of the food safe heaters were light bulbs. I've noticed them in restaurants but never gave it much thought. I'm going to try some of the eBay heaters because I got a little order happy.

    Also I used Rick's suggestion with the resistor, for testing my ability to code a decent thermostat. I taped a thermal sensor to the resistor and pointed a fan at them both in a smaller insulated box. It's a fun experience for someone that doesn't often dabble in that kind of thing.

    This box should be a lot of fun. I'm going to shoot some time-lapse involving the effect of heat over time on an object(s).
  • abecedarianabecedarian Posts: 312
    Just a side thought- maybe look at some of the automotive heater blower assemblies. Some of them are metal scroll housings with "squirrel cage" type fans so can take a fair amount of heat.

    The heating element from a hair drier can probably be shortened to make up for the voltage change from 120 to 12V, and most all of them have a bi-metal safety switch for over-temp protection.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2015-11-29 15:36
    A nice 100-watt resistor of the correct value may do the trick. There are also 500-watt resistors (try Mouser or Digikey).
    http://www.ebay.com/sch/i.html?_nkw=100+watt+resistor

    Actually, I came up with the light bulbs because that is a common solution of hatching chicken eggs.... they need to stay warm.
  • xanaduxanadu Posts: 3,347
    It's nice to have a datasheet. It looks like a phone call to TE Connectivity is in order. Digikey has a lot of these chassis mount resistors. Thanks! I'm guessing two 8 ohm 100 watt should do the trick.

    This would be fun to have :)

    2-1879450-5.JPG
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    Happy to hear two 8 ohm 100 watt resistors might work. If you ever desire to repurpose your project, those can serve as audiophile dummy loads to stand in for 8 ohm speakers on a 100 watt stereo amp.

    Speakers actually are not a flat 8 ohm across their entire response range. So in bench testing performance of a stereo amp, dummy loads sometimes are used to see what the amps linear response is over the whole audio range.
  • xanaduxanadu Posts: 3,347
    edited 2015-12-16 03:46
    I'm slowly learning how to calculate what I need. I built a heating element to test results. Keep in mind we're maintaining 130f in a 2.2' cube with a 70f ambient temp and light insulation.

    I picked up ten 10 ohm 25 watt flame-proof resistors from Fry's. 5% tolerance but close enough, in parallel I should have 1 ohm, it ended up being 0.91 ohm. The good news is that I'm well under 25 watts per resistor, and 40 degrees c below max rated temp. We're well within my target 12 V and 20 A max too. The peak current was 14 A at 100% duty.

    Next I have to choose a FET (300w?) and a temp sensor. I'm looking forward to writing the controller code on the Propeller.

    Once all of that is done and working I will buy an equivalent PTC heating element and see how much more efficient it is, and have something a lot nicer looking.

    Here are some pics of my test heater. I need a bigger heat sink for the top.

    This will take 1 cu ft of air 70f to 130f in 9 minutes :) There's an 80mm fan blowing on it to circulate the air. The temp sensor was positioned 3" from the top of enclosure. So far so good :)
    r1.JPG
    816 x 612 - 206K
    r2.JPG
    816 x 612 - 149K
    r1.JPG 206.3K
  • ercoerco Posts: 20,254
    edited 2015-12-16 05:14
    How about a Cantenna and a pirate coax splitter off a nearby 2kW ham shack?

    Gallon paint can + gallon oil + resistor + coax connector = DIY dummy load!

    Now are there trans fats in transformer oil? :)

    http://www.kb6nu.com/be-careful-with-old-dummy-loads/
  • xanaduxanadu Posts: 3,347
    Interesting because all of this has made me wonder if there's an easy way to make a giant dummy load. Good stuff thanks!
  • JonathanJonathan Posts: 1,023
    If you are talking about a dummy load for ham use, remember that it must be non-inductive. So no wire filaments. Use carbon resistors. You can buy thick film carbon power resistors or even gang up regular carbon resistors. Lots of how-to's out there.

    Jonathan
  • Heater.Heater. Posts: 21,230
    Oh no, they want to put me in an enclosure!
  • msrobotsmsrobots Posts: 3,704
    Heater. wrote: »
    Oh no, they want to put me in an enclosure!

    I told them already but they will do it anyway - http://forums.parallax.com/discussion/comment/1356343/#Comment_1356343

    Back to the topic, there are also infrared incandescent light bulbs, build to produce heat not light.

    Mike

  • xanaduxanadu Posts: 3,347
    Heater. wrote: »
    Oh no, they want to put me in an enclosure!

    I've been trying to work in a pun about you.
    Jonathan wrote: »
    If you are talking about a dummy load for ham use, remember that it must be non-inductive. So no wire filaments. Use carbon resistors. You can buy thick film carbon power resistors or even gang up regular carbon resistors. Lots of how-to's out there.

    Jonathan

    Thanks. I ordered an LC meter for $30 on eBay so I could figure out the inductance of the dummy loads. It should be here soon. I would like to make some more dummy loads because it's actually kind of fun, and rarely do I work with more than a couple amps.
    msrobots wrote: »
    Heater. wrote: »
    Oh no, they want to put me in an enclosure!

    I told them already but they will do it anyway - http://forums.parallax.com/discussion/comment/1356343/#Comment_1356343

    Back to the topic, there are also infrared incandescent light bulbs, build to produce heat not light.

    Mike

    I had thought about that. I'd rather have the hot air radiate from the heater. With the IR you have to heat a surface which then heats the air right?

    Still waiting for my giant 300w MOSFET to arrive. I need to figure out the rest of that circuit too. I'd like a nice smooth power draw while using PWM.
  • JonathanJonathan Posts: 1,023
    Just put a reflective surface in the enclosure and the IR bulb should work fine, just use a small fan to even it all out.

    Jonathan
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