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flexwatt is intended to be used with a dimmer or a rheostat, but should not be run at > 95F according to the manufacturer, so an "on/off" thermostat is not recommended.

However, proportional thermostats are really expensive.

What I'm thinking of doing is using a rheostat to figure initially adjust it to 90F and then measure the resistance of the rheostat, and using a much cheaper "on/off" thermostat with the flexwatt tape.

Is there any technical reason why this would not work? essentially a rheostat is just a variable resistor, is it not?

It seems a lot cheaper to me than buying a bunch of expensive thermostats in order to achive different night/day temperatures.

For one cage, I might just buy the proportional thermostat, but I'm planning on building about a dozen independent cages (IE not in a rack).

Thoughts/comments?

I'm sorry - I should have previewed my post first.
It's a little hard to read.

What I'm looking to do is figure out the resistance needed for the flexwatt so it does not exceed 90F - and then use an inline resistor of that resistance with all my cages in combination with the cheaper on/off thermostats, so I can set them to 85Fday/80F night - yet have the resistance to prevent the flexwatt itself from ever exceeding 95F.

Obviously the resistance needs will be different for different lengths/widths of flexwatt, but all the cages I'm going to be building will be identical.

Esentially a on/off thermostat is a rheostat set at a particular temperature rather than a particular voltage.

People used to avoid rheostats because back in the day when the rheostat was reset IE power outage it came back on at max setting. Wth the triac and the modern rheostat this doesn't happen anymore, to my knowledge.

I use dimmers or rheostats on all my flexwatt applications, ihave yet to have a problem. I also find that the temps are usually perfect with a dimmer once set up correctly. I used to use ranco's but now I use dimmers.

There are particular cases where I would recommend a ranco or other thermostat. In my temp regulated room, all my cages need supplemental heat and the dimmer powers it nicely.

Just use the dimmer I mean how much will you be saving over buying the resistor and the on/off thermostat?
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Jeremy

"I am become death, the destroyer of worlds" July 16, 1945 Robert Oppenheimer

1.1 Double Het "Sharp" Snow RTB's
1.1 Hypomelenistic RTB's
0.2 Pastel Hypo RTB's
2.0 Double Het Stripe Albino RTB's
0.1 Suriname RTB
0.1 Anerthrystic RTB
0.0.11 Red Bearded Dragons
1.1 Rhinoceros Iguana's
1.0 Green Iguana
1.0 Ball Python
1.1 Cream Golden Retrieviers
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0.3 Catus Terribilis
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The point is to set a different temperature for day/night.

Also, I do not want to use a dimmer because I have little brothers that have mental disabilities. One of them is deaf and autistic, and has a thing for light switches and doors as part of his autism - a dimmer is just too inviting to be played with when they come and visit.

I suppose once set I could remove the knob from the dimmer. But I'd really prefer a night/day setting on the cages, run them a little bit cooler at night.

It also should be noted that the ambient air temperature of my house is not constant. I live in Redding, CA - which gets very hot in summer, and I do not have air conditioning, I have a swamp cooler. Today it hit 106F outside and 82F inside. With that much variance in ambient temperature, a thermostat really is necessary to prevent the caging from overheating when set to warm enough for the cooler days.

That's why I'm looking for a solution to restrict the current to the flexwatt so that it can be used with a cheaper on/off thermostats. Adding air conditioning to my home would be expensive, and that's before the power bills ... (window sitting air conditioners for a single room are strictly forbidden by my HOA)

Actually I think you just agreed with me if your temp in your room fluctuates. A resistor will not be the correct answer because it may take x voltage one day and y voltage the next to make the same temp.

Dimmers will allow for this flexability I check mine on nearly a daily basis.

Controlling the room temps is my key to succsesful keeping of my particular species. It gives me a control point from which I can work.

It is possible to run bot a bank of dimmers during the daytime hours and a on/off thermostat during the nighttime hours off of a single timer. That way you can achieve both day temps hot and ambient and night time drops by simply specifing how cold you want it to get on the thermostat.

The wiring may be complex but if you are willing to wire in resistors than you certainly have the ability.

As for children and anyone that may tamper with your controls, put them in a lock box of sorts or higher on the cage so they can't mess with them. I keep mine behind a false front, this could be locked if needed I don't.

Good Luck
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Jeremy

"I am become death, the destroyer of worlds" July 16, 1945 Robert Oppenheimer

1.1 Double Het "Sharp" Snow RTB's
1.1 Hypomelenistic RTB's
0.2 Pastel Hypo RTB's
2.0 Double Het Stripe Albino RTB's
0.1 Suriname RTB
0.1 Anerthrystic RTB
0.0.11 Red Bearded Dragons
1.1 Rhinoceros Iguana's
1.0 Green Iguana
1.0 Ball Python
1.1 Cream Golden Retrieviers
1.0 Pomeriaian
0.3 Catus Terribilis
0.1 Spouse
0.0.1 Youth -coming soon-

> Actually I think you just agreed with me if your temp in your
> room fluctuates. A resistor will not be the correct answer
> because it may take x voltage one day and y voltage the next to
> make the same temp.

That's what the on/off thermostat is for.

The same amount of current will always flow through the flexwatt when the on/off thermostat is "on" - and no current will flow through the flexwatt when the on/off thermostat is "off".

The problem with using a cheaper on/off thermostat with no resistor is that when "on" - more current will be running through the flexwatt than is good for it. So a resistor to limit that current should, in theory anyway, make it possible to use it with an on/off thermostat. Unless there is something about it that I'm not understanding.

Of course, I can't use a regular ceramic resistor intended for low power DC applications, but I'm sure something out there exists to limit the current on 120V A/C

So your going to use a variable resistor IE the thermostat inconjunction with a regular resistor.

A dimmer is just another variety of variable resistor and they are easier to use and most likly cheaper than a resistor for 120v applications, probally easier to find.

Sounds like you know what you want it is just not clicking in my head why. Let me know via forum or personal contact when you get it up and running. I am curious what you figure out, and how it all works.

I know from experiance that somethings while genious in ones own head don't actually pan out to be the best idea. Not that yours is one but it happens.

If you know electronics map it out on a wiring diagram if it makes sense then it will work if it doesn't than well back to square one.

You could always skip the work use a proportional with night drop and call the whole thing good for under a $150.

Good Luck
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Jeremy

"I am become death, the destroyer of worlds" July 16, 1945 Robert Oppenheimer

1.1 Double Het "Sharp" Snow RTB's
1.1 Hypomelenistic RTB's
0.2 Pastel Hypo RTB's
2.0 Double Het Stripe Albino RTB's
0.1 Suriname RTB
0.1 Anerthrystic RTB
0.0.11 Red Bearded Dragons
1.1 Rhinoceros Iguana's
1.0 Green Iguana
1.0 Ball Python
1.1 Cream Golden Retrieviers
1.0 Pomeriaian
0.3 Catus Terribilis
0.1 Spouse
0.0.1 Youth -coming soon-

First off, the lamp dimmer is really a manual power control device that is more than a variable resistor. It uses a low-power variable resistor along with a capacitor to set the ON time to a triac trigger that delivers power to the heater.

For low dimmer settings (dimmer set to very low power output), if the ON/OFF thermostat breaks the circuit, when it returns (thermostat contacts back on) the dimmer will remain OFF. Why? Because the dimmer needs an initial trigger voltage of some value higher than the low dimmer setting allows. To get the dimmer back on, you need to turn the knob up.

So, an ON/OFF thermostat used in series with a dimmer is fine for an overtemp safety, but it has its drawbacks when you dim way down and expect tight control.

So, what you should do is either get a proportional controller (they aren't that expensive in the long run really considering the cost of cages and animals and food) or just use the dimmer alone. If you want to put an ON/OFF in series as a safety, fine, but just know that you'll need to reset the dimmer if the thermostat trips (if the dimmer setting is low.)

BTW, don't mess with resistors and such in series with Flexwatt. There are better ways. For example, 2 pieces of Flexwatt in series will result in each piece having 1/4 the power of one piece alone. That is one way to have it have less power (but it may be too little power for your application.)

OK - I'm convinced.
I'll just go with a proportional thermostat.

i recently purchased two herpstat II's from the bean farm and they are IMNSHO the best value available.700 watts per probe,built in night drop and tons of other features.sounds like they would be a good fit for your project.have fun!