*&$@! Johnson Control.....

I am using a Johnson Thermostat A419 to control a 40 foot run of 11 inch Flexwatt. I have it set at 93 but am getting a huge flux in temps. Rarely, if ever is the tape 93 even just a few feet from the control. I have the probe taped directly to the tape about 1 foot from the control. I moved the probe to the far end of the Flexwatt only to see the temp skyrocket to 112 degrees! I moved the probe back up top and it reads 84. The control is at a set point of 93, diff of 1, with the rest of the options being set to zero. Why is this happening?

Griz

Sounds more like a problem with the heat tape than the thermostat.

I did double check my connections and they are solid.

Griz

Give the company a holler tomorrow, I bet if they can't pinpoint the problem, they might just send you a new one.

I just started using a lamp dimmer switch. I have a difference of 3 degrees throughout my 15 foot heat tape line. I have seven 11 inch heat tape wired on one line. It is not as long as yours, but this is what I am using. If I were to set my hottest tape to 93 degrees, the lowest will be 90 degrees. To check the temps on a regular basis I use a temp gun to check each tape individually.

Originally Posted by Junkyard

I have a difference of 3 degrees throughout my 15 foot heat tape line.

Thats why I think he is having the problem, if you are losing 3 degrees in 15 feet than it would be even worse in 40 feet. I think you would be better off breaking that into smaller increments to have a better control of temps. Try breaking into 8 ft sections and see if your temps average out better.

Griz,
Just need to clarify one point before moving on...the temperature readings that you quoted - were they from the T'stat display, or were you spot checking with a temp gun. If they were from the T'stat, something may be wrong with the unit (possibly a setting, but unlikely IMO), because it should not continue heating once the set temp is exceeded by 1 degree. Part of the problem may be that the probe is taped directly to the tape. Flexwatt, when run without a rheostat or proportional t'stat, will hit temps of up to 130. What ends up happening is that the power goes on and off almost constantly (the tape will heat up, and hit 93 in less than 1 minute, turn off, cool, and right back on again). you may want to either move the probe off the tape or run it through a rheostat controlled by the T'stat for more precise control.

Originally Posted by dutchoven

I did double check my connections and they are solid.

Griz

Hey Griz,

I just checked the recommended lengths for 11" heat tape and it says "max length 25 feet". So I'm sure the reason is dramtic heat loss over high lengths. I would break your heat tape run down to individual shelves, It will be alot more wiring but should even out your heat loss issues. Good Luck!!

Well, there is good and bad news. My temps are checked with a PE1 gun so I know I am right on the money temp wise. I played with it a bit more today and still have a wide variance. I am also having an issue with humidity control now that the weather has turned cold. The good and bad news is that I have decided, after a whole lot of sweat and work, to scrap my current rack system and just bought a 10 stack of boaphiles. This will force me to run small 2 foot lengths of heat tape vs one long 40 foot length. I already have a 5 stack and 2 neo's that I was not using so between all of these I will have 17 cages running.

This of course means that I now have to hire someone to come in this weekend and frame/drywall an extension to my room but I reckon it's money well spent in the scheme of things. Now if only I can figure out the humidity issue. I have a whole house humidifier running 24/7 in the room and cannot get it to break 40% right now. I am misting the cages constantly which is a bit frustrating.

Griz

I remember seeing something about new setup (sorry it didn't work as planned), but I don't recall the details. If you could refresh my memory (and that of others), we may be able to offer some ideas that interest you.