Reptile & Amphibian Forums

I'm going to be converting two racks from cable belly heat to flexwatt or UTH pads.
My first option and the easiest is to use individual heat pads, 6x17, attached to the back panel on the inside of each shelf. Each shelf is 17 inches deep and 23.5 inches wide and 6 3/8 inches tall. I would then use two surge strips to connect the 10 pads and plug those into a Helix or Alife controller. I would also attach a 3/8 inch thick piece of rigid insulation on outside of the backpanel to help push the heat forward toward the boxes and not escape out the back panel. The boxes insert all the way into the shelf and will be about 1 inch away from the heat pads. I need the boxes to reach 88 degrees with one rack, ball pythons, and 80-85 degrees in the second rack which has colubrids.
The issue is that I am not a fan of back heat. In the past, with my first plastic racks, I lost too much heat out the back. I had to use 2 inch rigid insulation to stabilize the temps.

My second option is to use flexwatt on each shelf, wired in parallel. I need 10 pieces of flexwatt, 24 inches long, and would use the 3 or 4 inch flexwatt. Ten pairs of metal connectors and 10 pairs of plastic insulators per rack. I would place the flexwatt about 3 inches in from the back panel on each shelf. I would use foil tape attached to the clear plastic edge of the flexwatt to hold it in place. This would give me sufficient belly heat to get my two racks to the desired temps. Here's where I have a question and I'm not sure what to do. I do not want to use a router and make a groove for the flexwatt. I also do not want the boxes to come in direct contact with the flexwatt because it would eventually wear through. I have seen heat panels used on freedom breeder type racks and they appear to have flexwatt attached directly to galvanized sheet metal. Can I place a thin piece of galvanized metal over my flexwatt without creating an electrical hazard? The flexwatt would be sandwiched between the plastic shelf and the sheet metal. I have seen and experienced flexwatt shock when it was sandwiched between two layers of foil tape which obviously does conduct. It gave you a small shock depending on how the dimmer was set.
Any feedback from experience with this would be helpful.
Thanks
John Q

First lets talk about the "shock" you got with Flexwatt covered in foil tape. The alternating current in the Flexwatt produces an electric and magnetic field (as does any wire carrying current). When you lay Flexwatt over a plastic shelf and cover this with a flat foil, you essentially make a capacitor, which stores charge. When you touch it, the charge dissipates through you. Shock.

So, simply grounding the covering avoids shock. Freedom Breeder uses thicker sheet metal (not foil) and the heat strips are attached to the main frame. There is no way that the electric field is strong enough to carry through all that metal. No shock.

BTW, if you use small pieces of tape instead of one big strip, you won't get shocked.
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Mark

Idea #1:
As far as covering belly-heat Flexwatt, you can put thin felt pads on the bottom of the box, then cover the part on the Flexwatt with tape where those felt pads would come in contact with the Flexwatt.

Idea #2: (works if using the 3 or 4 inch wide Flexwatt):
You lay the Flexwatt on the shelf but way in the back, so the box only sits 1-2 inches of the heater. This is like a combination of back heat plus belly heat. Now you raise the box up with felt pads. On the rear of the box, you place the felt pads 3 or so inches from the back of the box. Now the box is raised over the Flexwatt but the felt never rubs on the heater.

Back heat stuff:
Years ago I had a small back-heated enclosed rack and kept a young Dumerils and carpet python in the rack. When the ambient room temp got into the 60s, the back of the boxes just couldn't maintain a high enough temperature. For colubrids it would have been fine, but for boids, not fine. I put insulation on the back of the rack - it helped a little, not enough for the boids.

Then came the novel idea - put a door on the front of the rack. My "door" was a piece of pegboard leaned up against the rack front. Temps went up a bit rather quickly. What I saw now was slightly higher ambient temps throughout the box, while the back of the box went up only a few degrees at most.

When I placed a solid covering over the rack front, of course the effect was greater, to a point. I was able to get 85-90 at the back of the box.

So, if you want to use back heat for ball pythons, and your room is very cool, you could cover the front. Just make sure you use a temperature controller with feedback, like a proportional controller or an ON/OFF with a probe.
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Mark