heater project

[freckle101]

hi guys

one of my main hobbys is shooting

problem: when guns get cold they shoot really really bad

Solution: i want to build a case that has a built in heater to keep the bad at around 10-20 degrees all the time!

it needs to run off a battery so i can use the case while out on a shoot

how the hell do i do it and where do i start

i really do not have a bleeding clue on this one - where would you start and how would you tackle it?

thanks

steve

 

[MikeMl]

I did some testing where I put a small lamp in a styrofoam cooler. When placed outside at about 20degF, even a 5W lamp would keep the contents of the cooler warm (at 50 to 80degF).

Another data point. I have a refrigerator that I keep in an unheated aircraft hangar. For a few weeks of the year, the mean 24hour temperature in the hangar gets below freezing, and the drinks in the fridge would freeze. Putting a 3W lamp in the refrigerator from October to March will prevent the drinks from freezing. Once the temperature in the fridge gets below ~35degF, the compressor never turns on. The 3W lamp is enough to keep the fridge where the compressor runs occasionally, allowing the fridge to regulate the temperature normally, even when the temperature outside the fridge is colder than the temperature inside it...

 

[ke5frf]

For a portable application such as this, you have several options.
I might think of using a film heater of some kind, like you see on this site:

**broken link removed**

Another approach might be a thermoelectric peltier cooler...which also generates heat. The hot side could be heat-sinked to a metal box that the gun is stored in, which should also be insulated some way on the outside. The other side of the cooler gets very cold. It is simply a matter of sinking both sides to accomodate the heat and cold. A simple thermostat in series between battery terminals should be enough to control the temperature.

The same use of a thermostat would apply to any other heat method you might use. It doesn't sound like precise control is what you are after.

 

[MikeMl]

What could be simpler than a 5W lamp as a heater?

 

[freckle101]

the peltier is a sound idea! could also work in summer when i need to cool it...

the light also is but the case i have is a soft one

the rifles are stable between about 8 degree C too about 20 degree C

anything between that is super!

our climate gets anything from -4C to about 33C if we are lucky

if i could keep it nice and light that would be good - the case i have now is very thin and not very insulated can sort that though i think

will look into the options - if anyone thinks of any more solutions please speak up

 

[MikeMl]

The insulation is everything! You need a styrofoam beer cooler long enough for rifles.

 

[ke5frf]

What could be simpler than a 5W lamp as a heater?

I certainly agree with that, I was just thinking about ruggedness and easy of mounting inside a small, portable case.

 

[Menticol]

What about a non electrical option? Ammo, weapon, sights, sodas, that's heavy!

Mixing some chemicals in a bag would be lighter than the battery required to drive the bulb/peltier

 

[Andrew Leigh]

Hi,

adapt the idea I used on my fish tank. I found some insulated resistance wire and laid it under the sand, in your case the padding. This allowed for even heating, was at 12V so was safe and worked a treat. Is this one of those hard carry cases?

How about 15.2m of 38#SWG Enamelled Copper Wire spiralled at the bottom of the case will amount to 14.4 Ohms at 12V and will produce 10W with a current draw of 0.83A.

Mike will this work as a suggestion?

Cheers
Andrew

 

[freckle101]

What about a non electrical option? Ammo, weapon, sights, sodas, that's heavy!

Mixing some chemicals in a bag would be lighter than the battery required to drive the bulb/peltier

the sport i shoot is field target - it uses air rifles (with compressed air hence they are temperature sensitive)

the chemical thing would work - could just use the hand warmer things but if it leaked it goes all over my pride and joy

i have a hard case and a soft case btw - i want to heat the soft one as its easier to carry around the shoot

the enamelled copper sounds good! the peltier looking into it is a little bulky but i would add this as well i think when summer kicks off again

the copped would be the easiest to add as well i think

 

[MikeMl]

The trick is to quantize the heat flow from inside the case to the outside, i.e. the quality of the insulation. This analogous to designing a heatsink, where the power dissipated is known, and you calculate the temperature rise based on the thermal resistance between the heat source and the ambient. Here, you turn the calculation around to figure how many watts you have to dump into the case to maintain a desired Δt based on how good the insulation is.

If you have a near-perfect heat insulator (styrofoam), then it takes only a small amount of power to maintain the temperature. If you have a crummy insulator, it could take many watts to hold the temperature inside...

 

[Andrew Leigh]

Hi

The problem with a soft case is that the wire is extremely fine. YHuo will need to find something robust at low resistance.

Andrew

 

[freckle101]

the soft case has about 10mm of soft foam then a 2mm polyester outside shell

if we said it was similar to about 5mm of styrofoam i don't think we would be too far off the mark

how do i work out how much W i need?

i am a complete noob to this as you can probably tell lol - i haven't done much past 555 timers ect really so thanks for all the help so far- hope i aren't driving you up the wall lol

and how do i go about temperature control with the wire? - would it be as simple as adding a pot?

EDIT - @ the thin wire comment i was thinking i could mount the wire on a 2"x44" acrylic length and place it at the bottom of the case so the rifle sits on top - should be ok there i would think

 

[colin55]

Just use some nichrome wire from an old heater.

 

[MikeMl]

I'm guessing that your soft case will not be a very good insulator compared to the styrofoam beer cooler I tested. To find out, put a small heater (5W 12V automotive lamp) inside the case, hook it up, and let it run for an hour. Use an accurate thermometer to measure the temp inside the case, and then the air immediately outside the case (ambient).

The temperature difference (in to out) will be the same you would achieve in the field with a colder ambient. If the difference is not as much as you would like on the coldest day, you need more watts in the heater.

On the coldest days, you can size the wattage of the heater such that you wouldn't need a thermostat. If the ambient is not as cold, then a thermostat would cycle on/off to reduce the average power in the heater.

I suspect that your case will have a substantial rate of heat loss, so you will likely need a 10 to 20W heater, which is within the capacity of a 12V 10Ah Sealed Lead Acid battery. 20W is 1.66A at 12V, so a 10Ah battery would keep your case warm for 6 hours.

 

[Mr RB]

You can glue more foam on the inside of the case, maybe weave the heater wire through a layer of the foam. Even some on the outside. Bubblewrap too is a good insulator. Where i used to live the ummm "Europeans" used to wrap their outside hot water systems in bubblewrap to save electricity.

The best option would be to use the hard case with better insulation, and you can put the battery in the hard case. Then make a good shoulder strap etc for it to fix the ease of carrying issue.

 

[Andrew Leigh]

Hi,

a couple of years ago we tried to enter the underfloor heating market. We produced a product which is stranded resistance wire covered in ETFE which is a tough polymer rated at about 155°C if I remember correctly. The resistance is 11.93 Ohms per m. I happen to have some left over.

You should be able to get a workable solution with this. 3 pieces of 3m each wired in parallel will give you 12 Ohms drawing 1 Amp and producing 12W.

Play around with some configurations, when you know how much you need PM me with a postal address and I will post the wire to you.

Cheers
Andrew