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Proportional T-stat Question
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by Venomjunkie on March 8, 2007
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i have one T-10 AP cage and im planning on getting a rack for when i breed my boas. i want to get a proportional t-stat (either helix or herpstat, not sure which yet) and i was wondering if it is ok to hook up more than one heat source (in this case the cage and the rack) to one of these t-stats as long as the total output isnt more than 500 watts (which is what both of these models can support) and the heat sources are similar. ive read that its not a good idea if the heat sources are completely different (such as a heat lamp and heat tape) but would it be ok if they are similar (the cage has a heat cable and the rack would either have a heat cable or heat tape most likely)? thanks in advance for any help!
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RE: Proportional T-stat Question
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by LarryDFishel on March 8, 2007
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You might get away with it, but it sort of defeats the purpose of using a thermostat, since it can only monitor the temp in one place.
Make SURE that whatever heat source is used where you DON'T have the thermostat, is not powerful enough to cause a fire (or roast your snakes) if it runs at full power (in case a bowl of water gets dumped on the probe in the other cage for instance.)
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RE: Proportional T-stat Question
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by Venomjunkie on March 9, 2007
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thanks for the reply Larry! im not sure i understand what you mean by "defeats the purpose" though. if i were to hook up the AP T-10 cage and a rack to one outlet on a proportional T-stat and put the probe on the heat source on the rack and set it for 90 degrees (just a random figure), wouldnt the T-stat keep both the heat source on the cage and the rack at the same temp? this is what i was thinking the case would be. can someone confirm this or explain why im thinking wrong here?
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RE: Proportional T-stat Question
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by kacz on March 11, 2007
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Dylan, one thermostat will probably not be enough to satisfactorily control the temperatures in a rack system. It would be virtually impossible to control such a system if a temperature gradient is desired in each cage. With only one sensor, located in a single area, you cannot monitor the rest of the system. Due to convection the heat will rise and create a temperature differential between the top and bottom of the rack. With only one thermostat and controller there is nothing you can do about it. Also you may get some dangerous hot spots. Under the right conditions heat tape with a power density as little as one watt per inch can cause fires. You would be better off using a less sophisticated and expensive t-stat (thermostat) controller and using more of them. The proportional feature is a luxury that you can do without if your rack system is placed in an area that is not subject to rapid fluctuations in temperature.
Paul M. Kaczmarczik
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RE: Proportional T-stat Question
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by Venomjunkie on March 12, 2007
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Paul, thanks for the input. however, i thought that by putting the t-stat probe directly on the heat source of the rack and setting it for a certain temp, the t-stat wouldnt allow the heat source to exceed that desired temp ANYWHERE on the rack and not just where the probe was, therefore making one t-stat sufficient to control the heat source throughout the entire rack. im sorry if im being a pain here but i dont quite understand why one proportional t-stat couldnt control an entire rack.
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RE: Proportional T-stat Question
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by kacz on March 12, 2007
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An honest question always deserves an answer, so you are certainly not being a pain. First of all it’s a bad idea to regulate the temperature by direct contact with the heat tape. The sensor, whether it has an internal thermostat, thermocouple, or thermistor, is not designed to respond to conductive heat transfer. You will notice that the sensor is encased in a relatively large housing. As such it is meant to respond to the overall ambient temperature, that is, the air around it, not to a high temperature point source. Trying to use it the way that you intend will result in fluctuations and errors in your ability to control the system. This would be similar to putting the thermostat in your living room directly in front of a heat vent, or in the heater itself.
Now let’s look at the proportional feature of the units you mentioned. What that means is that when the temperature is much lower than the desired temperature the controller will allow a lot of current through the heat tape to heat it quickly. As the temperature rises closer to the desired setting, the controller will cut back on the current and the temperature will increase more slowly. This seems like a good idea, but it doesn’t do much in a system where the heat source (the tape) is outside the individual cage, but inside the rack. It’s a large expense that you just won’t use. You would be just as well off with a controller that allowed the tape to be either “on” or “off” with no proportionality. Remember that due to convection, heat rises. As a result, expect to have the higher cages slightly warmer than the lower cages. This can be compensated for by putting more tape near the bottom of the rack than at the top.
Your best bet would be to place the sensor in the rack somewhere nearer the top, near (but not in contact, or directly over) the heat tape. You can then place the tape near the back of the rack so that the front end of each cage will be cooler. A few thermometers placed in the warmest areas of each cage will let you know at what temperature to set the single controller. It doesn’t have to be done all at one time. A little patience in moving the thermometers around to each cage before you start putting in the herps will avoid disaster.
Remember, with only one sensor it will be impossible to create zones and regulate each one individually. The best way to do it is to set things up with the heat tape secured but not permanently affixed to the rack. Turn it on low (so nothing gets fried right off the bat) and raise the temperature as you move the tape and the sensor around. With a couple of days of experimenting you should be able to approximate the results that you desire.
Paul M. Kaczmarczik
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RE: Proportional T-stat Question
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by Venomjunkie on March 13, 2007
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ok i think i understand what your saying now. thanks a lot for taking the time to answer my question thoroughly. the info is much appreciated!
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