Re: Substrate heaters

>From: glen at harlie_pps.com (Glen Osterhout)
>You can simplify your project by using a 12 volt transformer instead of
>a 24 volt one if you are using 30 guage wire.  You only need about 10
>meters of wire at 12 volts.

Yup. You are quite right.

I wanted to come up with a design where everything you needed could be
bought at a single store like Radio Shack, i.e., something that could
be put together by other people without too much trouble.  But I was
having trouble locating a 12V transformer that delivered 4 amps.


>From: William.Keith.Brummett at att_com
>    From: "shaji (s.) bhaskar" <bhaskar at bnr_ca>
>    > I finally broke down and decided to try DIY substrate heating. ...
>    > I'm going to do this using 4 reels of 50-foot wire, wound in
>    > parallel on a frame built of solid steel-core, vinyl-insulated
>    > clothesline from my local hardware store. ...
>    > The frame will be glued to a 46" x 16" piece of plastic carpet
>    > backing and placed at the bottom of my tank. ...
>    Is this "carpet backing" the white plastic mesh sold in craft stores?

No. The wire will be wound on the clothesline grid.  The carpet
backing is just a flat piece of plastic to which I will glue the grid.
I want to use the plastic because this will remove the need to glue
the grid to the bottom of the tank.  Installation and removal will be
very simple.  And the backing only costs 3 or 4 dollars.

>    I've been thinking of a rectangular frame of 1/2" PVC pipe,
>    with some number of small cross pieces (rigid air-line tubing?).  The
>    wire would be spiralled around the cross pieces much as with your
>    clothesline.

Replace the pipe and airline tubing with clothesline, and you have my
planned setup minus the plastic backing.

>    As an alternative, where might we find some high-resistance, thickly-
>    insulated cable like that used by Dupla and Dennerle, but without the
>    price associated with the (100% pure unobtainium, hand-crafted by
>    Bavarian elves) german products?

A couple of possibilities I played around with: Could we use the
cables used to keep gutters from freezing over in the colder climates?
The Home Depot people look strangely at me when I ask them about these
cables.  Maybe someone living where it actually snows can help.
Another possibility is the heating cable used for keeping seedlings
warm in early spring.  I have never seen this beast, either.


>From: Erik Olson <olson at phys_washington.edu>
>> From: "shaji (s.) bhaskar" <bhaskar at bnr_ca>
>> I've decided on a 24V, 2A transformer, and 30 gauge wire-wrapping
>> wire, both from Radio Shack.  The only major problem is that I need
>> 200 feet of wire to get 30 watts of power.  I'm going to do this using
>> 4 reels of 50-foot wire, wound in parallel on a frame built of solid
>> steel-core, vinyl-insulated clothesline from my local hardware store.
>Won't the steel core rust?  That vinyl insulation ain't too waterproof 
>once you get a little cut.  And it cuts easily.

I went home and tested this out.  It is possible to cut the vinyl
insulation fairly easily with a knife, but it is extremely unlikely
that gravel will cause trouble.  I boiled a piece of the clothesline,
and the insulation did not soften too much at high temperature either.

>Hmm.  I still think the wire-wrap wire is too fragile and brittle for 
>such a task, and the amount of work it's going to take you to wrap 200 
>feet of wire around the core (I assume this is some sort of rack?)
>is probably worth more than it'll cost to buy the Dupla cable.

Well, I am planning to do four 50-foot reels in parallel, so it will
only be 50 feet that I'll have to wrap, not 200.  I'll then solder the
reels in series to get a 200-foot length of wire.

I don't plan to assemble the whole grid before doing the wrapping.
I'll cut 15 or 20 sixteen-inch lengths of the clothesline, and wrap
the wire on these pieces.  These pieces will be the part of the grid
that runs front-to-back inside the tank.  Once the winding is done,
I'll complete the grid by glueing the longitudinal strips into place.


>From: Stephen.Pushak at hcsd_hac.com (Stephen Pushak)
>The only problem there might be (not sure) would be corrosion and
>the lead in the solder.

I'll probably use aquarium sealant to make the soldered joints
waterproof.  As you say, epoxy could work as well.

>It would be nice  to have a water tight jacket over everything

I'm a bit concerned about heat buildup if I do this.  But I'll do some
experimenting with this idea.

>How long a piece of clothesline would you need? You can get cheaper,
>thinner PVC tube from the hardware store than from the aquarium store.

A 50-foot long clothesline costs under $3.00.  I am planning on 18
front-to-back strips of 16 inches, and 5 longitudinal strips of 46 inches.