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Wattage = Wattage

> From: David Webb <dwebb at ti_com>
>
> I may be wrong about this but I was under the impression that the reason low
> volgates are used for heating cables is that wires tend to waste more
> electricity to heat a wattage W when voltage V is lower than at the same
> wattage W when another voltage V1 is higher.

I don't really understand what the above e-mail was trying to say, David.
(been racking my brain for a bit trying to decipher it).

Watts is watts.  Power, heat, same stuff.  Where in many circuits, you
have some concept of efficiency (which is how much of the electrical
energy is converted into heat instead of light, sound, whatever),
heaters are guaranteed to be 100% INefficient.  They convert all the
electricity into heat!

The only place energy can "leak out" is by heating the parts of the
circuit that are not in direct contact with the tank.  This is actually
going to be MORE likely for lower voltage than high voltage.  First, that
120 volt Ebo Jager plugs right into the wall, but your cable heater goes
through a 120-24 volt transformer (touch it, it gets hot!  It isn't
heating your tank!).  Then the wires leading to the tank are going to not
easily have different resistance than the wires in the tank
(consider the same 1 ohm out-of-tank cable being used with either a 10 ohm
heating cable for 24 volts, or a 10 * (120/24)^2 = 250 ohm cable for 120
volts... more relative heat is dissipated in the out-of-tank cable).  OK,
this last part is probably not a big contributor, so I should probably not
have even mentioned it.

---
Erik Olson
eriko at wrq_com