Wires to produce heat. Need to adjust power to maintain Temp

Hello, this is my first post here, and hopefully somebody is smarter than I am on this subject. I'm an Industrial Designer, not an Electrical Engineer, but I'm trying to build a fairly simple circuit, and need some help. I apologize in advance for using the wrong terms in describing this, please correct me.

Here's the scenario: My main hobby is Airsoft, which is played like Paintball. People have guns and shoot each other, all in fun. The guns I use are powered by Propane. Propane only has the correct PSI (Pounds per Square Inch) to propel the BB at above 70 degrees, so I can't play any games when it's cold outside, and in new Jersey, that's 4 months out of the year I can't engage in my favorite hobby.

So my idea is to make a warmer for the Magazine (which holds the Propane and BB's), which is battery powered, and maintains a specific, adjustable temperature. When I apply current to any wire (in this case 22 ga.), the wire produces heat, exactly like a pair of battery-operated heated socks or gloves, this will be used as the heating element for the magazine.

So the only chip, and diagram, I have so far (on advice of a ham radio guru at Radio Shack) is an Adjustable Voltage Regulator. The guy told me that in conjunction with that chip I can get another chip that regulates the current of the battery based on temperature; on and off (or lower/higher current), to maintain a specific temperature (which has to be adjustable).

So in the end, I need something that will heat up the wire to a temperature I can adjust, and tell the battery to give more or less current to the heated wire to maintain that temperature. If at all possible (and this is probably asking too much) I would like a simple 2-3 digit digital readout of the temperature (like the red numeric displays Radio Shack sells for a couple of bucks).

If anybody needs more info, please respond to this post or email me at jessedougherty(at)hotmail(dot)com.

The only thing I have to offer in return for helping me is a credit for this project (who knows, I may enter it into a contest at some point, or try to get it manufactured, I did win the 2004 I.D. magazine Annual Design Review last year, well 2nd place...). I'm also a Graphic/Web designer, if that would be of use to anybody.

Any help, or pointing me in the right direction, would be greatly appreciated. -Thanks, -J

The first idea that sprang to mind , along with a solution
of what to do with those odd socks that lurk everywhere...
**broken link removed**
As did the non electric solution of reusable gel packs,
though this idea I disregarded as the thermal output
is not constant and perhaps to high when first activated.

Do you need a fully portable solution or a can an insulated magazine that plugs into an automotive power socket suffice ?
As for the temperature display.. plenty of ready built modules with LCD digital displays can be found, some even with a user setable temp alarm wich could be used to turn on or off the heating system.

Minco sells flexible resistive heaters with adhesive and built in temperature sensor. The larger sizes are something like $50 in quantity 1 - a bit pricy but perfect for what you want.

As for power: if you can get some surplus lithium Ion cell phone batteries they have great power output for their weight.

A simple on/off type controller is probably your best bet- just a temperature sensor and comparator that drives a power transistor. If you want to go for the slickest solution a small microcontroller could run your control algorithm and drive your display.

I wonder if they make catalytic heaters that run on propane - like the Weller butane portable soldering iron but with propane. It seems a shame to carry around batteries when you are already carrying a great heat source.

tansis said:

The first idea that sprang to mind , along with a solution
of what to do with those odd socks that lurk everywhere...
**broken link removed**
As did the non electric solution of reusable gel packs,
though this idea I disregarded as the thermal output
is not constant and perhaps to high when first activated.

Do you need a fully portable solution or a can an insulated magazine that plugs into an automotive power socket suffice ?
As for the temperature display.. plenty of ready built modules with LCD digital displays can be found, some even with a user setable temp alarm wich could be used to turn on or off the heating system.

Click to expand...

Thanks for the reply. That's the first thing that I bought to test this out, but there is only 3" of wire that is heated with those socks, and I need much more, and I also need a way to regulate the temperature so the magazine doesn't get too hot.

I need a portable, battery powered solution, because I play these games outside, so the magazine has to be at a certain temperature constantly to work outside the way it should.

bmcculla said:

Minco sells flexible resistive heaters with adhesive and built in temperature sensor. The larger sizes are something like $50 in quantity 1 - a bit pricy but perfect for what you want.

Click to expand...

Thanks, I'll do a search for those. Does the temperature sensor regulate the temperature? (meaning will it turn the heat on and off to maintain a specific temp?)

bmcculla said:

A simple on/off type controller is probably your best bet- just a temperature sensor and comparator that drives a power transistor. If you want to go for the slickest solution a small microcontroller could run your control algorithm and drive your display.

Click to expand...

Do you know of any diagrams of how to wire that configuration? If I see it, I can usually buy the parts, and put it together on my breadboard to test it. But the real problem is that I'm just following the diagram blindly, not really knowing the why behind how the circuit works. I was schooled in design, not engineering.

On the Minco flexible heaters the temp sensor doesn't regulate the temperature it just lets your controller know the temperature of the object being heated. Minco also sells controllers but they are way overpriced for what they do.

The circuit you're looking for is basicly a thermostat. Try doing a search for thermostat circuits on this site and google - you should get tons of possible circuits.

bmcculla said:

The circuit you're looking for is basicly a thermostat. Try doing a search for thermostat circuits on this site and google - you should get tons of possible circuits.

Click to expand...

I did a search, but unfortunately I don't even know enough to pick the proper diagram for my needs. I'm really just a designer, If I have a diagram, and know what all the symbols mean, I can buy the parts and build it, but I never know the 'why' behind making the circuit, I just follow directions. So when I'm taking 2 circuits and combining them, I'm totally lost without direction/supervision.

If this will help anybody......

Here's the chip that I purchased from RadioShack on advice of the Radio/Electronics Guru I met there. I circled the part he said to replace with a temperature guage, and he said that would regulate the voltage to maintain the temperature.....but that seems too easy for me, since I can actually make this circuit.

It's a RadioShack LM317T Positive Adjustable Voltage Regulator

**broken link removed**

What do you people think? Could it work, or no way.....

bmcculla said:

Minco sells flexible resistive heaters with adhesive and built in temperature sensor. The larger sizes are something like $50 in quantity 1 - a bit pricy but perfect for what you want.

As for power: if you can get some surplus lithium Ion cell phone batteries they have great power output for their weight.

A simple on/off type controller is probably your best bet- just a temperature sensor and comparator that drives a power transistor. If you want to go for the slickest solution a small microcontroller could run your control algorithm and drive your display.

I wonder if they make catalytic heaters that run on propane - like the Weller butane portable soldering iron but with propane. It seems a shame to carry around batteries when you are already carrying a great heat source.

Click to expand...

I personally think this solution is most suitable. If it were me, I would work out roughly the temp I want to keep it at. There is no sense in trying to maintain +/- a few degrees if its ok for temp to vary more. You know, if it is maintained at 70 deg F, its prolly ok at 60 also.. - knowing this can make a difference to your approach.

Also I think more importantly, consider how long you need to maintain temp. Obviously the longer the better. With that said, if you use that LM317, it has horrible efficiency so you would be wise to also make it part of the heating element. Of the options so far, I think bmculla's idea is best.

just my .02

Optikon said:

I personally think this solution is most suitable. If it were me, I would work out roughly the temp I want to keep it at. There is no sense in trying to maintain +/- a few degrees if its ok for temp to vary more. You know, if it is maintained at 70 deg F, its prolly ok at 60 also.. - knowing this can make a difference to your approach.

Also I think more importantly, consider how long you need to maintain temp. Obviously the longer the better. With that said, if you use that LM317, it has horrible efficiency so you would be wise to also make it part of the heating element. Of the options so far, I think bmculla's idea is best.

just my .02

Click to expand...

Thanks for the input, but I don't know enough about electronics to make that idea work. If I can get a diagram, I can build it, if not, my concept will never spring to life. That's why I posted the chip I do have, along with what somebody else told me I have to change on the layout to make it work

And about Temperature, I need to be able to change it, as I will need to fine tune the temperature accordingly to the outside temp (for example, if it's 20 out, I need the mag heated to 100 degrees. If it's 40 out, I should be fine heating it to 85-90 degrees, but I don't know for sure yet, since I haven't tested it.)

Wire heaters are almost all "nichrome" wire. This alloy has a very high resistance for a metal but still has good physical properties. It is not insulated in its raw form however, and must be isolated from shorting out if in contact with metal, using insulation capable of potentially high temps depending on your app.

To be realistic, in this application with a metal tank, you could likely use resistors or transistors to make heat directly. It is simply a matter of whether it can transfer heat efficiently enough. Several resistors could be used to distribute the heat effectively over a larger area.

Insulated nichrome wire CAN be swiped out of a number of products. You need not stick with the intended voltage or even ac vs dc if you're going to cut it up, but it is essential to get the right resistance for the voltage you will be using. This is a matter of knowing the hot resistance of the wire you found, and cutting it to the right length.

Nichrome wire resistance increases substantially as it heats up. In a constant-voltage system, this does help self-limit the temp somewhat, but it will not be enough in the system you want.
You want to insulate around the tank and heater element.
The tank is best heated from the bottom, where the propane will always be right on the other side of the wall.
The tank will cool down further as propane is vented, it is evaporative and this is a strongly endothermic process. Substantial heat may be required.
Of course you need to be careful that the heater cannot overheat the tank, nor will it overheat if the tank is removed- for example, if the thermistor was located with the expectation that the tank will conduct the heat over to it, so it would not sense the high temp if accidentally turned on without the tank in place.

Oznog said:

The tank will cool down further as propane is vented, it is evaporative and this is a strongly endothermic process. Substantial heat may be required.
Of course you need to be careful that the heater cannot overheat the tank, nor will it overheat if the tank is removed- for example, if the thermistor was located with the expectation that the tank will conduct the heat over to it, so it would not sense the high temp if accidentally turned on without the tank in place.

Click to expand...

I have a very old heat pad (for sprains and such), that's what I used to test this idea. On the lowest setting the magazine gets up to 105 degrees. At this temperature the gas in the magazine exerts so much pressure that the hammer on my gun can't open the valve. If I let it sit for 3-4 minutes, it works perfectly, even when it's 30 degrees outside. That's why I'm saying that around 90 degrees would be the perfect temperature.

It will also be impossible to maintain the 90 degrees when I'm shooting, the cool-down effect is too much. But when I use the heat pad, I heat up the mag to the correct temp, then go outside, with nothing still heating the pad; then I can shoot fine.

I'm planning on having the temperature (probe, or whatever it is) be directly touching the magazine, probably with the heated wire over top of it. Even if the temperature gauge reads wrong, because the wire is in contact with it, I can still adjust the temperature (whatever it will be), so that it works fine; even if the actual mag temperature is 90 degrees, and the thermometer is reading 130 degrees, that will still work.


****** I just want to thank everybody that has given input into this design so far, And I'm positive that if I can find somebody in my area to read this post, that they will be able to help me construct this device. But since I don't know anybody in my area why is willing to help me, what I'm really looking for from this forum is a Diagram of a similar circuit (that somebody has used in the past), that does the same thing (regulate temperature through adjusting the current of the heated wire) that I can hopefully make for myself. Although I sincerely appreciate it, most of these replies are way over my head, and I'm looking for something more concrete. -Thank You once again.

Get a snap-action thermostat that opens when it gets to your desired temperature, some suitable resistance wire, and put them in series. Mount the thermostat where it will be indirectly heated (not directly on the wire). Remember that each turn of wire needs to be insulated from all the others. Here are some links, which may or may not be suitable:

resistance wire:
http://www.surplussales.com/Wire-Cable/Resistance.html
See the round wire at the bottom of the page. 10 feet will give you about 10 watts maximum power with 28 volts across it. You may need more or less wire. Power=V^2/R.

75C thermostat:
http://www.electronicsurplus.com/commerce/catalog/product.jsp?product_id=75138&czuid=1106177915575
Do a Google search for this part. It is available elsewhere.
Here is the **broken link removed**.
This particular part switches off at 75C, and on at 50C. If you need better regulation, the solution gets more complex and expensive.
You obviously won't be able to read the temperature. Get a cheap digital thermometer for that purpose.
Edit:
After reading your posts more carefully, I guess I was being overly simplistic. You can't adjust the temperature with this scheme. Why do you need to?

Ron H said:

Edit:
After reading your posts more carefully, I guess I was being overly simplistic. You can't adjust the temperature with this scheme. Why do you need to?

Click to expand...

I need to be able to change the temperature because at 30 degrees outside I need the magazine heated up to 90 degrees, whereas at 50 degrees, it only needs to be heated up to 80 degrees (approximately). I also need to be able to change the temperature because depending on where I mount the thermometer, I may have to heat it up to 110, when the real temperature of the magazine would be 90 degrees.

So if that thermostat has many different variations of this chip, as in if it turns on at 75, off at 90, OR on at 80, off at 100, that may be a very easy way to test this idea at various outside temperatures. And since I actually understood when you said to put the circuit in series, I could actually make that as a first run trial.

Is that wire you listed Nichrome? And, can I get it wrapped in heat-resistant rubber or something like that, since it's not going to be easy to wrap it around the magazine without the wires touching each other? (it would be impossible actually, if this was to be manufactured, that would be no problem, but for this prototype, I couldn't do it)


******NOTE: I have this same post being answered on another website, if that would help anybody:

**broken link removed**

there's a diagram of the circuit that will/should work for this application. What do you think?