[VAC] Re: 12V water heaters and power calculations

[Jon Fitz <jon.fitz@xxxxxxxxxx>]

Here's another perspective on 12V power.  As someone else already pointed
out, Electrical power(watts)=voltsxamps.  So, if current (amperage) is
unchanged, when you go from 120 to 12V, you have decreased the power by a
factor of 10!

Now consider AC water heaters.  All but the smallest ones use 220 or 240V. 
That's because you need more current at 110V.  You just can't get enough
current through the wires without going to larger, non-standard wiring.  It
is cheaper to simply up the voltage.

So, if this is true at 110V, imagine how much more dramatic it is at 12V. 
This is why the comments about wire gage must be considered very seriously. 
An electrical heating element is really just a wire that is designed to
withstand the rigors of carrying "too much current".  The wires that supply
the heater are not designed to handle that kind of current, and a fire will
eventually result if they are forced to do so.  Basically, 12V systems are
ill-suited to any truly high-powered applications.

Most boxed coils of wire will have a current rating printed on them.  If you
need to figure out your current at 12V, just divide the wattage by 12.  I
always go conservative, since the incremental cost of the wire is
insignificant compared to the consequences.

Jon
'68 Overlander