Lowest amperage heat source?
T Chap
Posts: 4,223
I am going to attempt to help out a few neighborhood stray cats this winter with a little insulated cat house. I can find a 100Ah car battery, and the goal is to swap out the battery the least amount of times, once a week would be nice. I am assuming if a heating pad is 1amp, then even if it ran non stop I could get 4 days between swaps. The place where I am doing this in at the edge of some woods where I feed the cats near my office, I don't own the land and there is no electricity, and it is wooded so I don't thing solar is an option. I am looking into what would be the most efficient heat source, and there are plenty of 12vdc pet pads. I am looking for other ideas for the least amount of effort keeping this up through the winter. I have a Prop board with a digital thermostat on it so it is rather easy to rig up a controller with a mosfet turning the heating device on and off.
Comments
BTW, I admire what you're doing! Down in the nearby boatyard, one of the shops has set up a little wooden shelter with a heat lamp. I've seen as many as three cats in there at once keeping warm in the colder months.
-Phil
Well not quite. A 25W heating pad is going to give you more heat than a 25W incandescent light bulb. And that is going to give off more heat than a 25W CFL bulb. So a watt consumed does not produce the same amount of heat. In this case, some of the energy is converted to light, which may or may not be felt as heat, especially the CFL example. You should look for a device that is made for heating, which minimizes wasted energy in light output. Unless you want to see the cats too.
Phil's comment is interesting. If they are truely feral cats, will they actually allow another cat in the enclosure? Cats are solitary best I know, so you may end up with a territorial issue?
Agree with the comments on a cheap insulated enclosure/s. I'd try to find some styrofoam coolers or get some of those plastic milk crates and insulate with that 2" foam flat stuff from Home Depot?
3-4 of those should be doable for $10 in foam, dollar store duct tape, and a midnight mission behind your local supermarket.
Extra karma-points for making entrances small enough to enter and exit only, to cut down on drafting. And, for using those cheapie silver mylar emergency blankets/sheet they have to re-radiate heat inside the enclosure.
Might be a good idea to put a couple of drain holes in the floor in the front near the exit and tip the back of the enclosure up, so the water from blowing snow and melting snowy cats can exit and not end up with a skating rink when there is no cat inside for several hours...
My understanding is that you will quickly kill a car battery if you go much below 50% DOD, so you should only expect a 100 AH rated battery to give ~50.
Personally, I think it would be nigh on impossible and a terrible waste of time in this situation to:
Run a Prop with a cheap load sensor or
PIR sensor (http://www.goldmine-elec-products.com/prodinfo.asp?number=G18937) to detect when there is actually a cat inside and turn on a small
12V 7.5W Polyimide Flexible Adhesive Thermo Foil Heater Heating Film (http://www.ebay.com/itm/like/231509156146?ul_noapp=true&chn=ps&lpid=82)
Or
http://www.ebay.com/itm/12V-Universal-Heated-Grips-Inserts-Handlebar-Heater-Warmer-for-ATV-Motorcycle-/252050029672?hash=item3aaf5a3c68&vxp=mtr
placed under a piece of sheet metal on the back/rear floor area of the enclosure. Not sure if it would work placed under a silver mylar sheet as mentioned above.
Heck, get a cheap 1-wire temp sensor, and you'd be able to only turn on heating when there is something in the enclosure, and cycle the heater on/off several times an hour maybe, depending upon whether the temp is below whatever setpoint you want.
Just moved back to NY, and while my dog is an inside dog, this would be a cool project for whenever I make him a dog house.
Course, dogs have lived in unheated, drafty knock-ups for centuries without them apparently freezing up stiff very often.. I expect cats would find an old styrofoam cooler with most of the entrance blocked off to be more than decent.
-Phil
But you do raise a valid point. We could say it's about "efficacy" rather than "efficiency".
One could use the same power to heat a large are by one degree or a smaller area by 10 degrees, for example. The former would be pretty pointless. And yes if all the power ends up as light radiated into space that is pretty useless.
My experience of feral cats living on dairy farms is that you rarely see them together. In fact you would rarely see them at all. But every morning you would see twenty odd cats with their heads in the same milk bowl at milking time. I guess being cold might make them very sociable as well.
AFAIK every form of energy produced by electricity eventually ends up as heat, so the conversion achieves 100% efficiency.
I think that is what I said isn't it?
That is why I brought up "efficacy". How effective is the thing?
You don't want all your energy going directly to heat the ground or radiating out into space or being taken away by the wind. No, you want it to go through the cat first !
Of course we could define "efficiency" here as the ratio of the amount of heat that goes through the cat to the amount that does not.
So we are going to need some insulation from the ground. And a little cat house with a small door. We might want a cat detector to wind up the heating a little when they are actually "home" so as not to waste so much when they are not.
Think Watts instead of Amps. .. Amps x Volts = Watts
Heat generated is measured in Watts, or a series of terms that are equivalent of Watts.
And why use a Lead acid battery in the winter? The battery itself will output significantly less Watts as the temperature drops.
In other words, you might as well use 110VAC or 220 VAC and 120 Watt light bulb to provide the equivalent of 10Amps at 12VDC. But you don't have the AC available, right?
And I haven't even addressed all the wasted power involved with charging the battery. IF you did want to be fancy, use a small hot water heater to heat water pumped through the floor of this cat shelter. I am not exactly sure where you would get the ideal small water heater, but the concept is sound. If the floor is warm, the cats will pretty much ward off the cold air with their fur.
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Have you just considered digging a cave and letting ambient ground temperature be enough? I have doubts that the battery idea is going to work out as well as a cosy hole in the ground.
If you desire to add heat, try a solar hot water heater and forget all that electrical stuff. Zero Amps might be a big win for the cats.
Watts are a unit of power. That is to say the rate at which work is done or energy consumed. 1 watt is 1 joule per second.
Certainly cold batteries are problematic. But I guess running a cable to where ever is even more problematic.
I'm guessing a hot water heater, solar powered or not, isn't going to work either.
Watts is indeed joules/sec. And if you really want to get into heat as work, there are more terms in thermodynamics.
The main thing is that when you get into sub-zero weather, the battery is going drastically under perform. Barring having a geo-thermal source of power on the propery, solar is your best bet -- even in sub-zero weather.
I know this thread is about cats, but there is a lot of knowledge out there about 'solar dog houses'... even in Arctic conditions.
But I can't find it anywhere on the Web. But there are Arctic dog house designs that might get you started. Just add a solar water heater panel and a floor that emits heat from the water. Apparently somebody is making solar air heater using recycled soda cans. Personally, I would go with heating water or even anti-freeze as you could store heat in the liquid in a reserve tank.
http://www.agcak.org/doghouseproject.html
Sorry about linking pinterest. I generally avoid them, but they do have an example.
You could perhaps use Solar energy (Electric or direct) to provide adequate energy levels to reset the Sodium Acetate reaction.
-Phil
My thought is that the Sodium Acetate could be inside of a heat exchange unit where it would remain stationary. Within this heat exchange unit, the Sodium Acetate reaction could also be reset as necessary. The fluid circulating within the heat exchange unit and the floor of the "cat box" could be water, saltwater, oil, etc. ... whatever was deemed "safe".
Reference:
https://en.wikipedia.org/wiki/Sodium_acetate
In other words, there are lots of liquids that could be used in a solar heat collector to both transfer and store heat to be use within the shelter. Water-based solutions are not a must, a light oil could be used in a closed loop with or without pumping (convection heat cycle can pump the fluid). Even recycled vegetable oil could be used if it would stay liquid.
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Having mentioned the 'Award-winning solar dog house', I dug out the book to see if I could copy the few pages to present to all of you. It ends up being a one-page plan for a passive solar heated dog house that is part of the USA's H.U.D. awards, not the A.I.A., circa 1979.
The passive design is even more environmentally safe. No liquids, no lead-acid battery, and such. It just has a brick floor for a thermal mass, a glazed window set to the specifics of local sun angle, and lots of rigid insullation... all within a dog house built from 2 sheets of 1/2" plywood.
The book itself is a classic as it rigourously demonstrates that snowy places get lots of sun and expensive, large homes can easily be heated throughout winter by passive solar.... if all the design features are exploited. Foggy places or places with lots of overcast rain are not optimal.
It is 2:50AM here, so I don't want to drag out the camera and get a photo to post of the page. Since it is H.U.D. publication, the copyright is public domain. Maybe tomorrow I will post it.
I simply don't think you need batteries, sophisticated chemistry, or expensive items to get this job done. The bricks can be swapped recycled concrete or flat rock. Rigid insultation and a bit of window glass (Are we going to provide thermo-pane?) would be most of the expense.
But considering how many ways I can think of building a cheap solar hot water panel, I still lean toward that and having tubes run through hollow concrete block packed with sand and gravel for thermal storage and floor. Getting the window right and the sun angle right is a bit tricky. And I still feel that the glass looses a lot of heat. A solar hot water panel can have much more surface area to capture solar heat that the size of the window.
Snow on the roof adds a lot to insulation.
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Here is old Taiwan, the cats winter over on top of the power transformers. Because we have so many typhoons, our power transformers are at ground level and not atop poles.
Personally, I doubt the cats need all that much help. It's Atlanta after all, not Alaska. Probably a cheap plastic storage container or two from Walmart with old blankets inside would be plenty good enough.
Any geo-thermal resources?
My best ideas seem to come to me after I turn off the computer and try to put my head in the pillows.
Why not set up a compost pile as a heat source?
Create a tunnel to the center of the pile where an upside-down tub or something provides the cats with shelter.
It seems like the kind of area that you will be able to get all the compost you need in the coming months. And the compost will provide both heat and insullation.
Also the idea of letting the cats generate the heat. Put the fuel into the cats.