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Re: DIY Substrate Heating Cables

I have built cables like you are contemplating.  I did not repeat your
calculations, but the wire length sounds similar to what I used.  My
advice is to add 5% to the length before cutting the wire, then measure
the resistance and trim the wire to match your desired output.

It has been awhile since I read the file, so I don't recall if this next
part is in there, but if it is, it bears repeating:  Be very careful to
make the connection between your feeder wire, and the heating cable
watertight.  I used 14 ga. wire between the transformer and the heating
cable.  I put heat shrink over the solder joint between the wire and the
cable, then sealed the ends of the heat shrink with silicone rubber,
then (after curing) put a larger heat shrink tube over that and sealed
its ends with silicone rubber.

I have had no troubles in long term (2 years+) usage.  My plants love
it.  The fish-room manager of my LFS was over the other day and could
not believe my aquarium.  He had never seen crypt wendtiis (that's what
the seller called them, I have not researched it) with leaves up to the
surface of a 55, or with such a deep maroon color on the underside.  But
then, his exposure is mainly to what comes in the door, not to the tanks
of the folks on this list.

Good luck,

Steve Garinger
In Lawrence, KS, where we are about to reclaim the town from the KU
students (for the summer).