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Technical help on building a low wattage heater.


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Low wattage and heater are opposite words.
Low wattage makes no heat or very low heat. An electric heater uses a very high amount of power.

My electricity is produced at Niagara Falls and by nuclear stations so it is fairly inexpensive. But most people near me heat their homes by burning natural gas because it costs less than using electricity.

Motorcycle drivers heat their gloves in winter with a battery heater. Its amount of heat is low and the battery does not last long.

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The reason you were probaly not having as much heat as you wanted would probably depend on the power supply. At a voltage that low, I believe you'd need to increase the current as with a constant resistant, current is inversely proportional to voltage, as in: less current is required as more voltage is applied.

If you were trying to power this small amount of wire with a battery, it would give a resistance (at 4 inches) of 0.556Ohm, which at 1.5v would require 2.7A - 1.5v/0.556Ohm

Even if you were using a D cell, the internal resistance of the battery would limit the current massively.

For an Energizer Alkaline D cell (a standard D cell battery), the internal resistance is between 150m and 300mOhm, already limiting the maximum current draw to 5A.

Unfortunately, with a battery, when the current is that high, the cell voltage decreases proportionally to the current drawn.

I think I might be thinking the wrong way round but if you get a thinner gauge wire, the resistance should increase but due to a decreased volume of nichrome, it should get hotter?

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It would be more useful for you to tell us what you are trying to heat.  It is straightforward to calculate the POWER dissipated in a given length of a given type of wire at a given voltage.  Except for very standardized conditions and media, calculating the TEMPERATURE attained (In the wire?  In the fluid medium?  In the surrounding insulator?) is a very complex calculation involving surface areas and shapes, fluid flow, Reynold's numbers, thermal conductivities, etc.

Consider a small space heater.  The thermal POWER put into the room is fixed by the electrical characteristics of the heating element and the voltage but the TEMPERATURE of the element or of the air could vary over an  extremely wide range depending upon the airflow.  Or consider an immersion type tea water heater.  The temperature will stay below 212 degrees F until the water boils away, at which time the temparature will shoot up by several hundred degrees and the heater will melt.

So, what are you trying to do?

Oh, yeah.  Wire.  Almost any wire material CAN be used as a heater but only a few are practical.  In general, copper makes a lousy heater because it is too conductive.  10, or 100 amps through (approximately) zero ohms produces (approximately) zero power.  Nichrome alloys are most often used for electrical heating elements because they have relatively low electrical conductivity so you can generate a useful amount of power using a practical length and size of wire.  It is also resistant to oxidation.

For special, short-term applications you can use iron wire but it will rust and has much higher conductivity than Nichrome.  I have used a couple of inches of iron wire on a small very low voltage transformer as a quick and dirty nylon rope cutter for years.

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