"No, Ohms law is not applicable in this case as the resistance is not fixed but varies substantially. Suppose that a given installation requires say 1,000 watts to maintain the required temperature. At 250 volts that will be 4 amps, and at 200 volts it will be 5 amps.
This is a considerable advantage and simplifies the design, and may save energy."
Hi Broadgage. I'm still trying to get my head round this. The implication from above is that varying the line voltage to a fixed length of PTC tape varies the resistance of the tape to allow the current to adjust to provide a specified power. This requires the PTC ceramic to change resistance with applied voltage. I thought the resistance was temperature dependent but your saying it's also voltage dependant. Ohm's law will of course still apply, i.e. V=IxR irrespective of the material characteristics surely? Am I still missing something?
"No, Ohms law is not applicable in this case as the resistance is not fixed but varies substantially. Suppose that a given installation requires say 1,000 watts to maintain the required temperature. At 250 volts that will be 4 amps, and at 200 volts it will be 5 amps.
This is a considerable advantage and simplifies the design, and may save energy."
Hi Broadgage. I'm still trying to get my head round this. The implication from above is that varying the line voltage to a fixed length of PTC tape varies the resistance of the tape to allow the current to adjust to provide a specified power. This requires the PTC ceramic to change resistance with applied voltage. I thought the resistance was temperature dependent but your saying it's also voltage dependant. Ohm's law will of course still apply, i.e. V=IxR irrespective of the material characteristics surely? Am I still missing something?
