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resistive heating

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dukebound85

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Hey all, I am making a resistance heater and am trying to figure out the best way to have the heat generated. I came across a thermoelectric chip that can generate 19.7W of power with a max T of 60 deg C. Is there any other possibly better way to do this such as the use of large resistors?, for this chip costs like 20 dollars. Also, one of my goals is to be able to have a variable heat setting. I would like to do this by the use of a dimmer switch for a potentiometer would generate alot of heat in this application. Any ideas on how to configure this? Thanks alot for any replies

Jonathan
 
dukebound85 said:
Hey all, I am making a resistance heater and am trying to figure out the best way to have the heat generated. I came across a thermoelectric chip that can generate 19.7W of power with a max T of 60 deg C. Is there any other possibly better way to do this such as the use of large resistors?, for this chip costs like 20 dollars. Also, one of my goals is to be able to have a variable heat setting. I would like to do this by the use of a dimmer switch for a potentiometer would generate alot of heat in this application. Any ideas on how to configure this? Thanks alot for any replies

Jonathan
You need to indicate what you're going to heat, what your power source is, and any other details you can think of. The more info you give, the better answers you will get.
 
Thanks for the fast reply. As far as heating goes, I would like a space heater that pretty much heats up a small confined space. I plan to power this off the regular AC wall socket at 120Vrms and 60Hz. However, For some components I will be using a 12V dc power supply and then using a voltage regulator to reduce the voltage to 5V for some components. I plan to use the 12V to run a stepper motor (controlled by a PIC16F88 and a L293D stepper driver) that can oscillate the unit and possibly drive another motor to run a fan. The 5V is mainly for led's, maybe a fan motor, and possibly a buzzer. If I could get the resistance heating to run off of 12 volts, that would be ideal for I would only need one power source. As far as the dimmer, would this be possible with DC? I would like to be able to make the heater be hot, mild, cold etc. And if this dimmer worked, could I hook it up to a thermoelectric chip? If anyone knows of a more efficient way for space heating resistors (ie big power resistor or something) it would be greatly appreciated. Thanks for any input on this matter and your time in assisting me.

Jonathan
 
There is a lot of work here just to heat up a "small confined space".

You need to consider the size of this space and how well it is insulated.
My first thought is that a 19.7w device would be just right to heat up something the size of a biscuit tin.

How big is your space?

JimB
 
You've provided lots of information however I am still left to wonder what it is that you are trying to heat (air, water, metal) and how much heat you need. How fast you need to heat matters and is radiation a more helpful mode of heat transfer?

It sounds like you've settled on electricity as a source of heat. Efficiency of a heating system can be a tough one. If you limit your heating methods to resistive types (things that loose all power applied as heat and do not move heat from one souce to another - heat pump for example) then virtually all of the electricity supplied to the element(s) will be converted to heat. The challenge might be to get all of that heat where you need it and let none go where it's not needed. Consider that voltage drops in conductors supplying electricity to the heating element(s) as well as the control are sources of inefficiency.

How will you transfer the heat from the element to substance that is to be heated. Are you heating the air within a space to heat something in the space? Could you put a heating element on the thing that is to be heated so the heat conducts directly?

Heating elements that get warm are different in some ways than those that get red hot. A warm or hot pipe containing hot water transfers heat to the air by conduction/convection - the air touches the hot surface. A red hot heating element transfers much of it's heat via IR radiation. The radiation passes thru the air with little loss - warming objects rather than the air.

You can purchase all kinds of heating elements but I'd guess you want to make your own. All resistors produce heat as a result of current flow. The right length and size of copper wire can be as effective as a resistor - a shorter length of nichrome wire is pretty good too. The amount of heat you need will help define what might work. Light bulbs can be excellent sources of heat - much of their heat being given up as radiation. A spot light or other bulbs with reflectors can direct the heat.

I've seen projects where temperature drift was an issue. The solution was to warm an enclosure with the sensitive electronics using a number of 1/2 watt resistors and a PWM control.

Hope this helps.
 
First of all, thanks for all of the help. As for the size of space, it isn't that big. My goal is to have the device produce enough heat for if it is cold, someone could sit in front of it and warm up. Therefore, I was thinking that the means to transfer this heat would be done by convection(by use of a fan to drive the heated air towards the object). So this leaves me with what option would be best used to do this heating. I was thinking resistors but I do know know what size would be adequate for this purpose. Your posts now have me thinking that maybe the usage of a heating lamp would work(as in the kind that farmers use to keep chickens warm per say). This would be relatively easy to hook up to a dimmer switch, however then light becomes a problem, for I do not want a lot of light to make it too bright to be near by. A one sentence summary of my project would probably be that I want to make a portable space resistance heater that lets a person who's near it warm up to a degree for comfort-much like the usage of a fire when camping. I hope this helps more clearly define my project statement. Once again, thank you all for your help.

Jonathan
 
Is this an educational project, or do you just need to heat a small space? It must be the former. If it is the latter, you could just buy a small space heater.
 
Keep in mind that a campfire heats or warms those who enjoy it by radiating a considerable amount of heat. Convection certainly is a part of it but the hot gases usually rise so what you feel to the side is the result of radiation. That might cause you to consider heating elements that glow - you can make them or buy them.

Take a look at various portable heaters and you'll see that some take advantage of radiation in order to direct the heat where you want it.

I think others would agree with me - safety is all important here. I'd hope you wouldn't even consider doing anything more than demonstrating what you've constructed and keeping it disconnected from power otherwise.
 
dukebound85 said:
. As for the size of space, it isn't that big. My goal is to have the device produce enough heat for if it is cold, someone could sit in front of it and warm up.

Jonathan

This would indicate that you need a heating source from a few hundered watts to a kilowatt or more, if its very cold.
Which just about rules out any 12V heating as the currents involved are too large for enconomical wiring. You can't use ordinary dimmers on 12V either, they only work on AC.
So, the suggestion of using a space heater ( fan, bar, oil filled, whatever) is a good one. These usually just have a switch type control where you can select full or half power. The fan heaters and the oil filled ones often have a temperature control as well.
While you could make such a heater it seems a silly exercise to me, even for a project, since ready made space heaters are widely available. They could be dangerous for home construction since you are dealing with mains voltages and there are rules you have to conform to as well.

From what you write it seems to me that you want to complicate what is basically a readily available, cheap and simple item, why?

Klaus
 
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