rheostat splitting?

Quote:

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Originally Posted by Kaorte

If your room temperature is not constant you will see temperature fluctuations with a rheostat. They can't measure the temperature of the heating element so it can't adjust when it gets too hot or too cold, you have to manually adjust it.

Skiploder, would you recommend a rheostat over a thermostat?

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No question - a t-stat.

Again, if you keep your room ambient temp in a reasonable range, a rheostat works fine.

I watch my proportional t-stats all the time. In most cases (with the exception of power failures, instances where the animal lays on top of the probe, or in situations where you are opening a cage door for extended periods of time), once up to temp, they run at almost a constant percentage 24/7.

Quote:

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Originally Posted by kitedemon

I agree, they do not change the ambient but a proportional thermostat will compensate for ambient variations that a rheostat cannot it just set a specific output percentage nothing more. If you have the constant ambient temps the rheostat works perfectly that is ideal.

Also there is two ambient temps that we have to be concerned with the ambient room and ambient enclosure. A enclosure heat source will effect the ambient enclosure temps mine does as the enclosures ambient temp (taken from about 2 inches off the bottom on the centre line middle and front not an IR but a probe style for ambient temps) is higher than the ambient room temps. This is from the thermal gain of the primary enclosure heating.

"None of my thermostats, be it on an RHP, flexwatt, bulb or UTH could make up for the 14 degree ambient variance you listed."

Mine does! The cool side is currently at 81.1 the room ambient is 77.3 and my hot side is at 91.1 running at 10% power (13.8º) I had to run tests and have a higher than normal wattage for my enclosures to compensate and over come the variations. I can handle a drop of another 7-10 degrees in a pinch. I had to increase the efficiency of the enclosure to handle that however.


I have no experience with rack systems but quite a lot with temperature regulated control systems. I am sure a rack could be designed that would work perfectly in a 68º room. It just requires lots more money. Now I think about it I am kinda surprised that they are not available, too small a market to mass produce enough to make it cost effective I guess.

OP Skiploader is correct a rheostat hooked to a heat pad is not going to affect the ambient temp if properly set. If you are using heat pads you must limit the voltage with a rheostat, for this to work correctly you must also have a room temp set to the cool side temperature of 80º. The alternative to this is more complex and expensive.

Skiploader I think we are actually saying the same thing in a differing way. I am sorry for a bit of a side track everybody it is a personal project of mine, I love technical problems.
Alex

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Alex:

I think we are too. But consider this:

In most flewatt applications, the t-stat probe is put between the flex and the bottom of the tub or tank. In that application, ambient temps barely, if at all, come into play.

As for racks, if you could design a rack wherein the ambient temp can be raise at the cool end of the tub, I'm sure there are many people who would be interested in such a set-up.

Skiploder,
I don't have much experience with rack systems, mine are display enclosures and are basically one off loops. I have not used flexwatt myself but have seen it, with what you describe I am sure ambient temps are not figured in. I think you are describing a inefficiant system as well? If you turn off the power how fast does it take to cool off. It takes about 20 hours to have the hot side temps dip to below 80 degrees with no power and no external help.

I absolutely can design a rack that has a control unit that you set the hot end and cool end it will settle in and maintain the temps accurately. I have a unit at work that does that and is accurate to .3ºC that could be adapted to a rack with a lot of work. It would likely hold 80 degrees for quite a while depending on outside temps but it is very expensive.