Help with my new Johnson thermostat

[sophia]

I spent this weekend trying to get my snake's new tub set up for her. I can't seem to get the temps right. The instructions that came with the thermostat are really not helping me (actually, they make me feel really stupid), so I really don't understand all of the options like "dif" and "sp" and all that. Maybe I set one of those options incorrectly. The set-up:

Tub is raised slightly above the ground by 2 wood stakes. 12" Flexwatt covers 1/3 - 1/2 of the 41 qt. tub's belly. It is attached with aluminum tape. This is plugged in to a Johnson's thermostat set to 103 degrees. Acurite measuring temps and humidity. Warm side is 86, cool side is 75, humidity is 70% (I know that's high and will be soldering more holes tonight).

What's up with the nearly 20 degree difference between the thermostat setting and the temperature reading? I've checked with 2 thermometers, so I'm pretty sure the readings are accurate. The temperatures in my room can very quite a bit, so I'm not sure how much that's affecting it. Should I insulate the tub some? With what? I currently have a blanket over it.

Thanks in advance for your help.

[JLC]

I wish I could find my instruction sheet for my JohnsonC...then I could be of more help. I don't remember what "sp" is...but "dif" simply means how many degrees do you want to fluctuate before the t-stat kicks in. For our use, that is best set to "1". Then, the t-stat cuts on or off when the temperature gets 1 degree off of the setting you've given it. This means more "clicking"....but keeps the temps more stable over the long haul.


As for the temp differences you're reading....a number of things could be causing that. First thing to consider is the t-stat probe placement. If it's tucked between the flexwatt and the tub underneath, then it will be measuring the hottest point of the flexwatt.

If you have your thermometer probe placed on top of the substrate inside the tub, then it is measuring something entirely different.

The heat the flexwatt gives off is partly lost to the air beneath it and if you have too much of a gap beneath it, you could be losing a lot of heat there. A layer of "Reflectix" over the bottom of the tub can help fix that. (A sort of aluminum-covered bubblewrap found at any hardware store...easily cut and taped into place)

Also, if you have a thick layer of substrate, that will be absorbing much of the heat the flexwatt is giving off, so it must be set at a high temp in order to heat the top layer of substrate to proper temps. This is not ideal because there's always a chance of the snake snuggling down to the bare bottom of the tub and getting burned. This is best fixed by having a minimal layer of substrate...whether paper or aspen or bark....just enough to cover the surface of the floor to absorb waste is all you need. They don't need a "cushion" of aspen or anything.

I use two sheets of newsprint...my JohnsonC is set to 94 and the temps on top of the paper over the warm flexwatt stays at 91 inside the hide.

ALSO....I had trouble keeping the "cool" side of the tub warm enough with just one 12x11 piece of flexwatt. We just keep the house cool. You can try insulating with a blanket over the cool side, but that also holds in excess humidity. (My personal experience.) I used a small space heater to warm the area around the tub so the ambient temps there would stay around 80-82....until I was able to get a second t-stat and a second bit of flexwatt to set up two separate warming zones for the whole tub.

Hope all that rambling makes some sense!

[SatanicIntention]

Where do you have your thermostat probe attached? With the on/off type tstats like the Johnsons and the Rancos, I like to tape the probe over the hot spot in an empty tub in the rack. Then I set it to what temp it needs to be at. This way it gives a little bit of a buffer so the heat tape has time to heat up before the tstat shuts off.

If it's just taped to the flexwatt, then it won't give the flexwatt long enough to heat up, whereas if the probe is inside a tub or buffered/insulated somehow, then the flexwatt can heat up before being shut off. Or at least that's how I understand it, and how it works for me.

Hope that wasn't too confusing

[sophia]

Thanks for the thoughtful replies. The thermostat probe is currently taped on the underside of the Flexwatt (therefore surrounded on most sides by the variable temperature air). This is my only tub and I really don't have room for another one to put the probe in, although that sounds like a good idea. My substrate is two layers of the Sunday paper.

Would it be better if I put the probe in the tub and make sure it is secured very well with the aluminum tape? I guess that would mean covering it fully with the tape. Or between the Flexwatt and the tub?

I will get some Reflectix (I'm glad I know now what it is called!) for the bottom of the tub. Maybe I should cover the top as well, as long as I leave the holes for humidity clear.

Any more input?

Thanks - you guys are awesome.

[SatanicIntention]

I'd keep it on the outside of the tub since the snake will most likely be a nosy stinker and somehow move that tape.

If you can wrap the probe with a multiple-folded paper towel and tape it to the flexwatt, that should make a good buffer and the air temp won't be able to affect it. Set the tstat to about 95 or so when doing this and see what the temps in the tub are doing in 30 minutes to an hour after everything has settled.

[shag]

I'm using a JC in my glass enclosure and i have the probe between the flexwatt and the glass so that it gets an good reading. I loose about 1deg because of the small air gap but at least i know its not getting too hot. SP or S1 stands for the set point and would be the temp you want it to try and keep on the warm side, mines set to 93deg. DIF is differential temperature this is the tolerance for temperature fluctuation before the thermostat clicks on and off the smaller the number the more steady the temps will stay, mines set at 1. The C1 and H1 selects the mode (C1 for cooling H1 for heating).

Heres the exact instructions that came with mine

Step -1

To start programming, press the SET key once to access the Fahrenheit/Celsius mode. The Display will Show the current status, either F for degrees Fahrenheit or C for degrees Celsius. Then press either the Up or Down arrow key to toggle between the F or C designation.

Step -2

Press the SET key again to access the setpoint. The LCD will display the current setpoint and the S1 annunciator will be blinking on and off to indicate that the control is in the setpoint mode. Then press either the up key to increase or the down key to decrease the setpoint tot the desired temperature.

Step -3

Press the SET key again to access the differential. The LCD will display the current differential and the DIF1 annunciator will be blinking on and off to indicate that the control is in the differential mode. Then press either the up key to increase or the down key to decrease the differential to the desired setting.

Step -4

Press the SET key again to access the cooling or heating mode. The LCD will display the current mode, either C1 for cooling or H1 for heating. Then press either the up or down key to toggle between C1 or H1 designation. Press the SET key once more and programming is complete.

hope this helps

[lord jackel]

Thanks for the thoughtful replies. The thermostat probe is currently taped on the underside of the Flexwatt (therefore surrounded on most sides by the variable temperature air). This is my only tub and I really don't have room for another one to put the probe in, although that sounds like a good idea. My substrate is two layers of the Sunday paper.

Would it be better if I put the probe in the tub and make sure it is secured very well with the aluminum tape? I guess that would mean covering it fully with the tape. Or between the Flexwatt and the tub?

I will get some Reflectix (I'm glad I know now what it is called!) for the bottom of the tub. Maybe I should cover the top as well, as long as I leave the holes for humidity clear.

Any more input?

Thanks - you guys are awesome.

You need to move the probe...remember heat rises and you will also loose a lot since you have the tub elevated. I suggest you sandwich the probe between the flexwatt and the tub. Then use the Accurite inside the tub on the hot side. This way the Accurite will tell you the tub temp and the Thermostat probe will tell you the Flex temp...between these 2 readings you can dial in the temps.

Using Reflectix will help but so will just putting the tub onto a flat surface (like a dresser)...there is no reason to have it elevated as it just allows heat to escape.

[sophia]

I've heard in multiple places that you need to elevate it? But I'm still new, so I really don't know.

I put the probe between the Flexwatt and the tub and things are better. The thermostat is set to 99, hot side temp is 91, cool side is 78. So I'm approaching ideal temperatures.

So should I now put the tub on a flat surface? Should I insulate the cool side a bit? Does anyone else have an 8 degree difference between thermostat reading and actual temperature? Other suggestions?

Thanks!

[ctrlfreq]

What's up with the nearly 20 degree difference between the thermostat setting and the temperature reading? I've checked with 2 thermometers, so I'm pretty sure the readings are accurate.

Is your thermostat clicking on and off regularly, or does it stay on always? If your connection to the flexwatt isn't soldered or clipped well enough, it will never heat up properly, although it may put out some heat. I ran into this problem when I first built my rack because I had wired the flexwatt in 2-sheet series which were then wired in parallell. Ultimately I had to rewire the entire rack in parallell, and it started heating as expected.

[sophia]

Yes, it clicks on and off properly. That 20 degree difference is now a 9 degree difference, as I wrote in my most recent post.

It seems like all is OK with the Flexwatt. Reptile Basics did it for me.