"The PTC tape will therefore be APPROXIMATLY a constant wattage load at any reasonable voltage. An ALMOST constant wattage requires more current at a lower line voltage.
Experiment and observation beats argument, buy a small PTC heating element and take measurements at different voltages and at different temperatures."
I completely agree with you regarding experiment and I wasn't actually arguing but was puzzled by the statement regarding the increase in current with reduction in voltage and following on the idea that Ohm's Law didn't apply.
I think Roger has explained more clearly that the power generated as heat reaches a balance (almost constant wattage) as a result of the composite material changing resistance in a negative feedback loop. Ohm's Law will therefore always apply and the measured current is a product of line voltage applied and the resistance of the cable and hence power is produced (V²/R). There is I expect a drop in power production at some temperature point when reducing voltage as the cable resistance no longer reduces dramatically with lowering temperature depending on the composition/mixture as determined during manufacture.
I may take up your suggestion and get some tape as it could very very useful to stop the pipes freezing.?
"The PTC tape will therefore be APPROXIMATLY a constant wattage load at any reasonable voltage. An ALMOST constant wattage requires more current at a lower line voltage.
Experiment and observation beats argument, buy a small PTC heating element and take measurements at different voltages and at different temperatures."
I completely agree with you regarding experiment and I wasn't actually arguing but was puzzled by the statement regarding the increase in current with reduction in voltage and following on the idea that Ohm's Law didn't apply.
I think Roger has explained more clearly that the power generated as heat reaches a balance (almost constant wattage) as a result of the composite material changing resistance in a negative feedback loop. Ohm's Law will therefore always apply and the measured current is a product of line voltage applied and the resistance of the cable and hence power is produced (V²/R). There is I expect a drop in power production at some temperature point when reducing voltage as the cable resistance no longer reduces dramatically with lowering temperature depending on the composition/mixture as determined during manufacture.
I may take up your suggestion and get some tape as it could very very useful to stop the pipes freezing.?
