Reptile & Amphibian Forums

Hi,
I saw an ad for a proortional thermostat in the classifieds and was wondering what it was. I have seen porortional thermostats before, and they have also been reccommended to me. I just don't know the difference between a proportional thermostat and a thermostat such as Ranco. Or is Ranco a proportional thermostat? I would really like to get a thermostat soon, but want to find the best, in price and quality. I have seen ranco for $70 shipped and the proportional was something like $125 shipping. I just don't want to buy the proportional one and find out it is the same as the much less expensive ranco. I would greatly appreciate some help with this. Thanks in advance, Josh

I'm not sure but my guess is that a proportional would vary the voltage output thus making the source get more or less power while a non-proportional would simply shut the source on and off depending on the probe reading. Just a guess though....

A proportional thermostat increases or decreases the voltage output to the heat source while the Ranco thermostat is an on/off controller.

If you use a proportional thermostat like the Big Apple Herp model with a heat bulb you'll see the bulb dim once the desired temperature is achieved. If the temp drops the bulb will get brighter as needed to produce the right amount of heat.

Before I went to radiant heat panels I used to use red bulbs for heat because I needed heat at night as well as during the day. I had the thermostat set for a night drop in temperature and it was kinda neat to see the bulb go off as the night drop timer went on, and then the bulb would gradually brighten to keep the temperature where it should be. At night the bulb was always dim since less heat was required. When the night drop turned off in the morning the bulb would brighten.

Anyway, if I did this with an on/off Ranco, the bulb would go on at full brightness and then go off when the temp was reached. Then back on, off, on, off, etc. No dimming.

I have a bunch of proportional thermostats that I use to control my radiant heat panels and I am very happy with them.

Bill

bill s. you did an excellent job of explaining the proportional thermostat.i would just like to add that that the pro. therm. uses less electricity.it's like leaving a light bulb on or turning it off and on 1000's of times.it's something to consider if you are using mulitiple units.i have three and would not consider the on off types.

Technically, a proportional controller varies the POWER out to the heating device, not voltage level. For example, applying 120V AC to a light bulb for 1 second over a 1 second period is more power delivered than 120V AC to the light for only .25 sec over the 1 sec cycle. Voltage didn't change, but the ON time did, hence the power.

So, a proportional controller varies the ON time (and hence power) to maintain the setpoint temp.

Wow, THanks for all the great infomation everyone. I think I will get one of those as oppose to a ranco or any other thermostat. Thanks for the help, Josh

>>Technically, a proportional controller varies the POWER out to the heating device, not voltage level. For example, applying 120V AC to a light bulb for 1 second over a 1 second period is more power delivered than 120V AC to the light for only .25 sec over the 1 sec cycle. Voltage didn't change, but the ON time did, hence the power.

Ummmm... this kinda sounds like a conventional on/off thermostat! When I plug a light into my Helix proportional thermostat, it gets brighter and dimmer; it doesn't flicker on and off. Which sort of seems to contradict your explanation...

We humans think that if our eyes see something a certain way, then it must be that way. Your eyes just can't see the flickering, but it is there.

Tell me this - when you plug a cold heater into the Helix, isn't full power going to the heater? Yes it is, just like an ON/OFF controller. Also, if the heater is warm and you lower the setpoint on your Helix, doesn't the Helix stop all delivery of power? Yes, just like an ON/OFF controller.

What is different is the the proportional band - a range of temperature around the setpoint where the controller varies the power to the heater. Most proportional controllers are time-proportional and would flicker the light. Helix uses a cycle time that is very fast - probably around 60 Hz - so you don't see the flickering (your eyes can't discern anything faster than 50 Hz or so).

By the way, how do you think a lamp dimmer works? Same way - it turns ON and OFF the voltage and varies the time that the voltage is ON in a given cycle. It doesn't have feedback or setpoints like a controller. The ON time is governed by the dial setting.
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Mark