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  1. #1
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    Heating your crib (hammock) with DC

    Hello all,

    first time poster here. I have recently discovered the joys of stringing up my hammock while out camping. At first all my friends thought I was nuts, but the tide changed once they say how comfortable I was all night

    A few weeks ago I took my cordless down to a favorite spot we had been going to for years, but had always slept on the ground. With a few anchor points installed into the rock face (dynabolts) we had room for up to four hammocks. All of us stayed dry inside this little riverside cave, despite a decent down pour in the night. I did however get a slight chill on my back, partly due to insufficient windbreaking. Ive learnt alot just trawling through these forums on how I can remedy this, but seeing just how COLD some of the temperatures are that users battle I was inspired to come up with something that could help.

    I did a quick search and couldnt seem to see anyone that had posted this idea before, though Im sure it has been thought of countless times. What I propose is a portable, efficient heated blanket (or item of clothing?) powered by a small DC rechargeable source. Given the power consumption for electrical heating is generally very high the challenge will be:

    Efficient and quick heating of the area safely.

    Portability, repeated cycles (IE, not damaging the battery) and run time.

    User functions, like the ability to regulate heat/amperage draw.

    Some of you may laugh at this idea, and I will admit I did at first, but after a quick stroll through the web I discovered that this might actually be possible.

    I already have a reasonable knowledge of the electronics involved, being a hobbyist in my spare time as seen on my channel http://www.youtube.com/user/shannrenn. All of my electrical hobbies involve DC power, batteries are my life here I recently built a custom high power torch from a gutted dorcy, I call her the "pocket sun" powered by a single lithium battery, but thats for another thread perhaps.

    So first up I stumbled across this page. http://www.hastie.org.uk/heatedjacket.html

    Being a motorcyclist in my past I can sure appreciate the need for a heated jacket/pants/golves on a cold night. But a search of commercial products saw me forking out over $150 for a basic model. Come on people, its a bit of nichrome wire sewn into the lining of a jacket......

    Some other possibilities included DC heated blankets (for use in the car usually) and even heated pet mats! The heated pet mats are specialty items and are thus almost as expensive as the heated clothing, but the DC blankets are more on par, some as cheap as $20. All of them vary from 12v @ 1 amp (12 watts) to 12v @ 5 amps plus (60 watts). Not too sure how warm the 12 watt matt gets, but if its useable, I could build a lithium power pack with three/four D cells that would last for approx 7 hours (3.7v 7amp/h D cells, about the size of a large maglite). The other thing is this doesnt have to run all night. You could warm it up to start with and then not even need it for the rest of the night. It could be helpful in an emergency too I guess.

    I would probably look at installing a PWM (pulse width modulation) controller or variac that would allow the duty cycle or resistance to be varied, thus controlling the input current. Ive learnt some very clever unconventional techniques that may also allow for energy recovery/recycle power back to the source which could boost efficiency even higher. Of course there would be a fuse installed as well for safety.

    My wife is a master seamstress, which will surely make things easier, as I dont have a clue about sewing! I have already prepped her on the basics, and she says it will be easy to sew, especially if it just a flat mat to heat your back and bum. This could even end up being incorporated into a hammock if it worked well. Imagine being wrapped in that warm cocoon!

    It might just give the edge to those looking to battle the freezing temperatures in the snow, or it could just end up being a dud But I will have alot of fun on the way, I have plenty of spare wire so why not.

    One things for sure, my missus will only come hammocking with me in winter if it works, cant get her outside other wise, might need to make a fully heated yeti suit for her.....

    Thoughts and comments appreciated. Sorry about the lengthy post...

    Regards

    Ren

    (PS second picture is the view from my hammock, hanging from the rock face )
    Attached Images Attached Images

  2. #2
    Senior Member mitch's Avatar
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    Welcome REN, and thank you for sharing the great idea. I also had heated clothing for my cycle and it was great. I think you should give it a valiant try anyway. Could be the heat wave of the future for hammocks. Great pics!

  3. #3
    Senior Member hiker_DC's Avatar
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    Quote Originally Posted by Ren View Post
    Some other possibilities included DC heated blankets
    I hope my wife doesn't see this. She will think I am heating up some hammock other than my own.

    Doc
    I have two doctors, my left leg and my right. ~G.M. Trevelyan

    Everywhere is walking distance if you have the time. ~Steven Wright

  4. #4
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    Thanks guys

    @ hiker DC. You could have two hammocks then, one for lone wolfs and the other for special cuddles

    Regards

  5. #5
    Senior Member TiredFeet's Avatar
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    You will still need some pretty good insulation under the heating pad to insure that the heat goes in the desired direction, up into you.

    Also, a reflective surface like a space blanket would help a lot.

    If you need to much insulation in addition to the heating pad, ....?

    Won;t really know until you give it a try and see what develops. Be very interesting to see how it works.

  6. #6
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    Spot on TiredFeet.

    Already have a mate who is a paramedic donating a couple of space blankets for me to chop up. Need to figure out what the best sort of material is going to be to sandwitch the wires between, normal electric blankets use what looks like a common fleece? Of course they have the mattress against their back for insulation, so perhaps I could use the reflective surface on the bottom of the pad?

    The fun part will be the testing, with fire extinguisher in hand. Wanna make sure there is no possible way it can catch fire and/or melt!

    I use my sleeping bag like a tube, unzipp the bottom and thread it over the hammock. This way you are not flattening the bottom layer of your bag, Id imagine this would also help insulate the bottom surface somewhat.

    As you say, we wont really know until we give it a go. I can make the blanket for peanuts, and test it on a DC power supply first. No use spending $50-$100 on the lithium batteries if its no good.

    Regards

  7. #7
    Senior Member Strapped-4-Cache's Avatar
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    I've got to admit that when I saw the title I was wondering how Dutch Clips could be used to heat a hammock.

    Since I'm stuck being a car camper for a while I'm interested in where the research might lead. A little extra weight to provide some extra warmth on a cold night would be worth it to me.

  8. #8
    Senior Member trouthunter's Avatar
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    Welcome REN,

    So you are an innovator, nothing wrong with that, we need innovation.

    I read about a project a while back using nanotechnology to produce paper thin flexible batteries that could be used in multiple applications including sleeping bags, jackets, (quilts too?), that would keep you warm.

    Try Googling it.

    For now I think the best approach is good ole' simple insulation under the hammock, ie. a quilt made just for this purpose. Once we start making things unnecessarily complicated we invite problems. Insulation does not "break".

    But thanks for the mental stimulation.
    I like to go solo - off trail - immerse myself in the area - explore - eat really well - and make it back home.

  9. #9
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    Yeah I thought that might be a little interesting for those not common with the electrical terms AC/DC (alternating current/direct current).

    Funny enough, it seems DC is used also here, Dutch Clips I am assuming are a product name? Or a method of clipping (like Dutch oven) lol.

    This would be a piece of piss for car camping, Since you dont have to lug your battery around, assuming you are camping near your car? You could have a big deep cycle battery in the back (dual bank so your main doesnt go flat) and run your DC blanket straight off that, or use an inverter to run a 120/240v mains blanket (AC).

    The end goal for me however is one that is portable, Im leaning to installing it in a jumper, you get double function out of it then. But perhaps I am getting too far ahead of myself now. First the pad/blanket, then if that works I'll start unstitching a perfectly good jumper.

    @ Trout hunter. You could be right at the end of the day. But my thought is this. If you are going to have an insulated pad in your pack anyway, why not thread some wire through it? The blanket/pad itself will weigh pretty much the same as your insulation pad will, maybe less cause it doesnt have to be as big? There will be less than 20 grams of wire in there, and a small electronic connection/cord.

    That nano tech sounds cool, but no doubt is 5 years off being affordable (or 50 years who knows?). Still, Im going to check them out.

    If your batteries double as your source for torch or other electrical appliance then you are carrying them already. I can handle 3-4 D cells of extra weight anyways.

    Looking at your name, Id imagine you have seen similar products before, for Fisherman The heated seat cushion, keeps your bum warm when you're sitting on the rocks.

    Im sure we can all have a good laugh at this effort at least, if all else fails maybe I can use the wire to rig up a toaster lol.

    Regards
    Last edited by Ren; 05-28-2010 at 22:06.

  10. #10
    Senior Member TiredFeet's Avatar
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    Well if you can make it run off 3 or 4 D cells for say 1, 2 or 3 hours for the night, then go for it.

    As you say, the wire itself isn't that much (well not for a non-SULer anyway ) and could buy you a lot in terms of needed insulation on cold nights. If it can stretch a 2 or 3 season set-up into a 3 or 4 season set-up, it could be worth it.

    Of course, as you get along the development curve and add in the temp sensors so that the heat is only used when the temp inside the insulation drops sufficiently and is then shut off again, the battery life goes up which helps a lot. Might need zones, say 3, one for the upper torso, one for the lower abdomen/butt and one for the legs, with corresponding priority.

    The complexity goes up, but not excessively.

    As for insulation not "breaking" - probably not, but if down, it can (and sometimes does at the most inconvenient time ) get wet. There is potential complexity in everything.

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