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Re: Yet another DIY substrate heating cable question

At 3:48 -0400 6/9/98, bickford at black-hole_com (Jay Bickford) wrote:

>According to my calculations (using the formulas set forth in the Resler /
>article in the March 1995 issue of Aquarium Fish Magazine) I need a 12
>Volt, 4.5 AMP
>transformer rated to handle at least 65 watts.  So far, so good.  After
>that I ordered a catalog from All Electronics Corp.,
>(http://www.allcorp.com/), a
>source for transformers also mentioned in the same article. I found what
>looked like
>a suitable transformer within its pages, (a 12 V.C.T. @ 5 AMP job)  but no
>ratings were given, just the voltage and the amperage.  I E-mailed All
>Corp. to ask them what the wattage rating of the transformer in question
>is.  Their
>answer to me is that they don't have that information, but that a formula for
>determining the wattage rating of a transformer is available, but they
>don't have
>that either.  So my question (for someone who isn't as electrically
>challenged as I)
>is what is that formula?  I don't want to build a system that is unsafe or
>will have
>the potential to "melt down", but I also don't relish the thought of
>paying for a
>commercial system either.

P = I * E, P = 12 * 5, P = 60 watts.

Something is wrong with your calculations as a 12 volt, 4.5  amp
transformer is only good for 12 * 4.5 = 54 watts.