Re: heat tape

["S. Hieber" <shieber at yahoo_com>]

Ed Dumas asked about heat tape:


> This is a very interesting idea, Roxanne, and seems reasonably
> affordable. Where do you get the rheostat from?
A good source whenever you need quick reasonably  priced electronics
parts is

 http://www.parts-express.com/

If you're looking for something more specific, or Part-Express doesn't
carry it, then you really ought to try

http://www.mouser.com/

You can view PDF versions of the printed catalogue if you choose, which
helps you pick out the right parts.

Instead of a rheostat, you can use a household dimmer switch, the
rotary kind that they make to dim (incandescent) lights.  These often
have more circuitry than just a rheostat, so they can be more energy
efficient.  They can be found in any hardware store and many grocery
and drugstores, too.

> Do you put the heat
> tape
> under the bottom glass? Assuming that, do you need then to cover the
> heat tape with insulation or anything else? 

Manufacturer says don't enclose the tape or too much heat could build
up in some situations -- not too likely if the tape is securely against
the glass of a water filled tank.

> Also, is there a specific
> length that one must have for these,

Absolutely not other than you will want to have enough length to get as
many watts as you want.

> and can one connect two or more
> pieces together for aquariums which have a reinforcing brace down the
> middle of the bottom?

Sure.  Although the tape doesn't get hotter than about 95 degrees, why
heat polystyrene plastic, which is sensitive to heat over the long
term, if you don't have to, especially if it is a critical sturctural
element of the tank?  Wire the pieces of tape in parallel, the end of
one to end of the other and electrically, it's as if the tapes were one
long piece.

The tape is like a long chain of resistors wired in parallel across two
lengths of wire so that they look sort of like a ladder.  Since the
"resistors" are all connected, you can cut the tape at any length and
all the resistive elements within the length are still attached to the
"sides of the ladder."  The longer the "ladder" the more resistors you
have in parallel, which means more "ways" for the current to flow
between the two sides of the ladder.  More resitors in parallel means
less total resitance and higher current flow.  Thus, the longer the
ladder, the higher the current flow => the higher the total power level
(watts) => higher heat (BTUs or Cal.s).  Hey, wouldn't more resistors
mean more resistance and, therefore, less current flow?  That is so
*only if* the resistors (or lengths of heat tape) are wired in series.

Hope that helps,
Scott H.

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