Low volt DC heater

Discussion in 'The Projects Forum' started by magtech, Dec 3, 2010.

  1. magtech

    Thread Starter New Member

    Dec 3, 2010
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    I am looking at making a low volt DC heater, 12V or less. My heater will be used to keep water from freezing using a tip-up, ice fishing. i am looking at resistive heating currrently. I have to make 4 such items so they design will have to be cheap. I am hoping to use rechargeable batteries to power the element , the less the better. i will have a 1.5 inch piece of high-density foam over top of my ice hole. I am thinking of incorporating the heating element on the bottom of the foam. It doesnt have to contact the water, but it can if needed. The exterior temps here can get -15F but with the foam insulating the hole water from the exterior winds i cant see this being terribly bad. I have never made a resistive element before and i am knowledgeable in ac/dc, but i want to build my heating element as cheap as i can.

    I have attached a basic picture of my thoughts.
    Any ideas or help would be greatly appreciated.
     
  2. iONic

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    Nov 16, 2007
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    Water, if it isn't ice, is ~31 deg F. Placing a 1.5inch piece of foam over the hole would remove much of the windchill and ambient temperature. I wouldn't think that you would need too much heat to maintain 30 - 31 deg F. But with batteries connected directly to the resistive element alone would produce heat continuously, which is OK if the resistance is set perfect for maintaining that temp on that day. A temp sensor that controls the surface temp under the foam would be a more efficient method, otherwise you would be heating more water than necessary. As far as the battery, I would suggest a 12V 10AH (?), something you can carry and not drain down too far during the course of your fishing day. Aluminum grounding wire would not corrode, I might be concerned about it's thickness.

    I've experimented a bit with 12V 1A wall warts and computer IDE cable wire to make a leg warmer. PWM was the way to go for maintaining the desired heat. The length/resistance of the wire is the tough part.
     
  3. wayneh

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    Sep 9, 2010
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    Well, one thing that comes to mind is a light bulb, although this might have negative effects on fish? Light bulbs are cheap, fairly reliable, easy to buy, and you can easily tell it they are working. And they do an excellent job of converting electricity to heat. They also shatter when a hot bulb hits ice water, so you'd need to design around preventing that. Constant submergence might be OK.

    Since I don't think you want any solution that contacts electricity with the water directly (probably illegal?), you can't use a lab immersion heater wand. Those are kind of like a stove element and normally are plugged in, but I think it'd make heat with 12v. I'm thinking a heat sink off an old CPU cooler might be useful to you as a way to transfer heat into the water itself. You could use resistors or even a TEC to make heat, and then let the heat sink deliver it to the water.

    Do you have any idea how much wattage you need, and for how long? I'm thinking it's enough that rechargeable batteries are going to be severely taxed. Maybe maintaining ice-free doesn't need as much heat as I think. But even, say, 12W at 12 volts would require a 1A current. That means batteries will be, by far, your highest cost. Things look brighter if you only need 1-5 watts.

    Hey, what about one of those dipstick engine block heaters?
     
  4. magtech

    Thread Starter New Member

    Dec 3, 2010
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    i want to melt the ice just to keep the water from freezing. With the wind out of the way i dont want to melt the ice on the sides of the holes itself... Just a small amount of heat to keep the water from icing over. i am comtemplating a fan to circulate the air/water under the foam. Although this would not heat it would create a current on the surface of the water to help it from freezing. I remember growing up we cold buy fans that sit in your hand for $1 and they ran on batteries. I havent looked for them in a long time. how long do u think i could run 2 D cells with just a nominal value of heat. All i want to do is keep the air in like a .5 cu ft of air space a couple of degrees above the water temp.

    How many watts do u think i would need for that. I am thinking 5 watts which shouldnt be to much of a problem. Or would circulating the air be a better idea?
     
    Last edited: Dec 3, 2010
  5. wayneh

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    Fan circulation is maybe a good idea. You really can't lose, since any power delivered to the chamber can only end up as heat. The little fans I'm familiar with are 12v CPU coolers. They're more than $1 to buy new, but you can get a whole computer with one inside for free, if you don't mind taking time to pull it out. This would also get you a heat sink that might be handy.

    But I'm still partial to the lightbulb approach. You could enclose it in a chamber (cat food can?) if you don't want the fish to see it. BTW, using a lightbulb solves the temp regulation problem mentioned by iONic. It doesn't address efficiency, though. You could cycle it off to save power.
     
  6. John P

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    Oct 14, 2008
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    Would just putting a foam block over a hole be sufficient? You might find that if you keep ambient air away, the temperature of the water will be sufficiently high that it won't freeze over the course of a day's fishing.
     
  7. iONic

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    Nov 16, 2007
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    I'd start off with a 5W light bulb,apply 12V to it and see how warm it gets, if it get to hot to hold in your hand I'd think you would have enough. A small .1A CPU cooling fan might help distribute the heat, but you don want to draw any outside air into and under the foam cover. A simple PWM circuit could give you some temperature control. There needs to be a way to efficiently transfer the light bulb heat to the water. Direct heat sinking is the best, but difficult with an bulb. If the light bulb produces enough heat, then us some heat tolerant flat black grill paint on it so as not to scare the fish.
     
  8. iONic

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    Nov 16, 2007
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    Another idea.

    Make yourself an Octagon(6 side) with 1.5 inch PVC. Create two openings with 2 T's
    In one T secure a 5W - 7.5W 12V bulb. Leave some space for airflow. In the other T opening secure a 2 inch 12V muffin(CPU) fan with a currernt rating of .2A or less. The fan will either blow out or draw air in and warm the air under the Polystyrene cover.
    The T's may not have to be positioned perpendicular to the water's surface. You could point them in towards the center of the Octagon. The addition of a thermistor and comparator circuit could be used to regulate the temperature.

    Sounds so neat I want to build it myself, but I don't ice fish! Maybe I could use it around my neck and blow warm air down my shirt!

    iONic
     
  9. Kermit2

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    Feb 5, 2010
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    Remember water has a higher specific heat than almost any other substance known to man. Meaning it takes more heat to raise 1 gram of water 1 degree Celsius, than 1 gram of most other substances. You will need more power than you think to keep the water ice free. There is also the hydrogen bonds that must be broken between each atom of water when it changes from solid to liquid, so there is additional energy required just to melt it, besides raising its temp.
     
  10. SgtWookie

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    Jul 17, 2007
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    Sorry, but I think you're going to be pretty frustrated trying to use battery-powered heaters to keep your fishing hole(s) open.

    Water is one of the best conductors of heat there is; it's about 1.4 times as efficient as copper. Under the ice, the water will be in constant circulation. Trying to maintain even a small body of water at a fixed temperature would take quite a bit of energy.

    Pleasure boaters sometimes use air bubblers to keep the water from freezing around their hulls. You might have better luck with a bubbler than a heater, but it'll take energy to force air under the surface of the water.

    You might consider using something like 5-gallon paint bucket with some sand or rocks in it to weight it down, and fill the remainder of the bucket with insulating foam. Stick the bucket in the hole when you're done for the day. Of course, as time goes by, the ice will close in around the bucket and eventually crush it.

    It takes a LOT of energy to melt ice.
    [eta]
    I cross-posted with Kermit2; what he wrote is in agreement with what I wrote.

    I just did a Google search for air bubblers, and found this article interesting:
    http://www.wes.army.mil/REMR/bulls/vol12/no2/text/bubbler.html
    Heat panels, air bubblers, and high-density polyethylene sheets are mentioned.
    My 5-gallon paint bucket idea relates to the high-density polyethylene sheet usage; similar albeit a slightly different twist.
     
    Last edited: Dec 5, 2010
  11. iONic

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    Nov 16, 2007
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    Is it not really the water we are concerned with? We would need to keep the air at the same temperature as the water, one small degree above the freezing point.

    I also was not aware that the purpose was to keep the hole open overnight and assumed it was to keep the hole open while fishing only. Overnight would take 3-4 times the energy.
     
  12. wayneh

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    Sep 9, 2010
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    The water in the hole loses heat to both the air above and the icy walls, which are some temperature below freezing (otherwise the OP has a bigger problem!)

    It's not necessary to melt any ice or even heat any water (no net temp increase), you just need to reduce that heat transfer out the top and sides, and make up for whatever heat does escape.

    It's important to remember that the water below the hole is ... water, and a potential heat source. If you could recirculate lake water up into the hole, it would stay open. So the bubbler makes sense except that the ambient air (the bubbles) could be quite cold. Maybe you could warm it. A small prop might be better.
     
  13. retched

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    Dec 5, 2009
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    How about a "stir-er".

    Using the FOAM cap idea, and mounting a small low rpm motor in the foam with an offset stirrer would keep the warmer water moving in the hole and the foam would keep the freezing air away from it.

    Black foam would be a smart idea, getting some solar heating out of the mix.
     
  14. t06afre

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    May 11, 2009
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    What is this "invention" meant to do, and which problem do you want to solve? I have done some fishing on the ice in my time ;). And as some has mentioned. You will need a lot energy to keep the water free from ice
     
  15. retched

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    So how do you keep clear your ice-hole, t06?
     
  16. t06afre

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    After the hole is drilled. I first have to clean the hole by scooping out icedust. I also use the same scoop to keep the hole free from new ice forming.
     
    Last edited: Dec 6, 2010
  17. magtech

    Thread Starter New Member

    Dec 3, 2010
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    You guys have some great ideas. The light bulb would be a legitmate idea as i already have the foam to seal the hole. Being that the water is already above freezing if i seal the hole with foam i am told that this is suffecient. My first step will be to try this if/when this fails i hope to have my standby powered one to alleviate these issues. I do have extra computers laying around and i might try a computer fan to some batteries. Thats cheap, free, and can be of low power consumption. After the fan i am thinking i will make one with a light bulb setup... Kinda one the size of the old christmas tree lights... this way i can achieve different color variations spread into the water to attract fish. I cant see me fishing to much out here at night, but it is a possibility. I might have to frankenstein something together tonight and see what i can achieve. One thing i didnt take into consideration is battery output at low temperatures. Ever start a car at -20... Sometimes the battery wont hold a charge that low. Anyone know how to mathmatically determine a batteries output at X temperature?
     
  18. wayneh

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    The guys around here use the scooper mentioned above. ;)

    The only problem with a static plug is that the sides will get wet and freeze to the surrounding ice, becoming permanent.
     
  19. magtech

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    Dec 3, 2010
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    i scoop the holes clean when i am jigging but ive seen a tip-up hole ice over pretty bad in the winter. If i just have a rod i can probably bust the ice...But why work harder when i can make something work for me. I'm all about making things and enjoying them working. I bought the ice-house flasher and auger this weekend. The guy i fish with is buying the rest, poles, tip-ups and etc. Maybe i'll just make him buy some insulated tip-ups... but then again that takes all the fun out of building one.
     
  20. SgtWookie

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    Jul 17, 2007
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    The idea with the 5 gallon plastic paint bucket is that the sides are tapered, very smooth and slippery - new ones, at any rate. They're cheap, too - abut $3 at Big Orange and Big Blue hardware stores. A bit of Maguire's car wax would make the sides even more slippery, and would be ecologically friendly.

    If the top of the bucket were well-insulated, and even a small amount of heat was generated internally, ice would have a hard time forming around the outside of the bucket; even if it did, it would likely be easy to break free.

    If a lead-acid battery were in the bottom of the bucket, it could be used to power a small lamp to generate some heat. The insulation on top and water contact on the bottom would keep the battery temp right around freezing.

    Insulating the battery would help it to retain heat. A lead-acid battery has about 76% of it's rated power available at 32°F/0°C. I don't think you'd get very good performance from NiMH or NiCD batteries at such low temps, but I have no data available at the moment.
     
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