I'm going to build a coffee heater for a school project.
I know I have to take advantage of the Joule effect (Joule heating). I am restricted to using a resistance between 330 Ω and 1 MΩ. The voltage supply is 5 V, via USB connection.
If I use resistors, then the circuit won't get hot. If I use diodes, their temperature will increase but not enough.
How do I generate enough heat in the circuit to heat coffee?
Answer
What you are doing is not going to work. Sorry, but there it is.
A USB power supply will put out a maximum (typically) of 1.5 amps. Total power is volts times amps, so this is a maximum of 7.5 watts.
However, with a 330 ohm resistor, current is 5 volts divided by 330, or .015 amps. Power is then 5 volts time .015 amps, or .075 watts, and this is just not enough to warm anything.
If you were to connect a bunch of resistor is parallel, and all were 330 ohms, each would produce .075 watts separately, so 100 of them would produce the maximum power.
So your demand that 330 ohm to 1 megohm resistors must be used condemns you to failure.
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