# General Husbandry and Supplies > DIY Forum >  DIY Rheostat (dimmer) for temp control

## JD Constriction

While a proportional thermostat (helix, herpstat, etc.) with a backup on/off thermostat (ranco, johnson controls, etc.) is usually best for any herp setup not everyone wants to go down that path or has the money to do so.

Alot of times I see new keepers with entry level on/off thermostats that alone in my opinion just aren't enough piece of mind for your animal(s) and vary temps too much as the heating source is either fully ON or fully OFF, no happy medium.  Also on/off thermostats or proportional thermostats can fail in the on position, hence the need for redundancy by having a backup.  If you ONLY have a proportional thermostat or one on/off thermostat you run the risk of the unit failing and potentially harming your collection no matter what brand they are.  They all run the risk of failing.  So always have a backup.

For an affordable and reliable alternative to two on/off thermostats or a proportional thermostat and on/off thermostat backup, you can use a rheostat with an on/off thermostat as a backup.

The most affordable and what I would consider bare minimum for anyone keeping herps is a rheostat/dimmer in combination with a lower end on/off thermostat (500r, bah-1000, etc.).  This setup to me is safer than a proportional (helix, etc) or on/off (ranco,etc.) alone.

With this setup the easiest rheostat to use is at your local Walmart or almost any superstore for around $10.  A in-line dimmer switch:


Entry level on/off thermostats can be found at a number of herp stores such as Big Apple Herp, Bean Farm, or even at reptile shows for around $30. (I apologize that I don't have a pic as I use Rancos or Johnson Controls on/off thermostats only)

Setup is fairly simple.  Using just the dimmer set the temp to a couple degrees warmer than your desired temp.  Think of this as the MAX temp you ever want your heat tape/rope to get for your herps.  Then connect the dimmer to your on/off thermostat and then set the on/off thermostat to your desired temp.  If either one should fail in the ON position the other is the backup and in most situations due to how they are structured the rheostat doesn't fail in the ON position.  

Keep in mind the rheostat is setting the maximum amount of heat provided on the tape or heat rope.  So if for instance you set it in the summer when the room is warm when winter comes and the room cools down you might need to adjust the dimmer to hit your desired temp.

Now something a bit more complicated.  What if you have a rack system and ALOT of flexwatt or heat rope connected to an on/off thermostat and you want to use a dimmer with your on/off thermostat? 

I personally like using an on/off in combination with a rheostat for all my hatchlings and subadults.  The rheostat makes for a smoother temperature curve and also helps to keep my electircal bills down as the heat tape isn't going fully ON when the on/off kicks in, thus using less electricity.

The problem with the dimmer model above is that most models are limited to 300w.  While this really corresponds to quite a bit of heat rope/flexwatt sometimes more is needed for a full rack system.

For situations like this I personally like to spend a few dollars more and make my own dimmer/rheostat.

Most items can be picked up at your local Lowes or Home Depot and putting it together is easier than you might think.

Here is what you'll need.

Supplies:
single gang work box <$1
work box cover <$1
single pole dimmer switch(600w is common but 1000w is also available) <$10
6ft extension cord <$2 (grounded versions cost ~$8)
Total = $14 ($20 grounded)

Tools:
wire cutter/stripper
philips screwdriver
3 electrical caps (usually come with the dimmer)
utility knife (or a razor blade)
electrical tape



First cut the extension cord in 1/2.
Then pop two inlets into the work box using the screwdriver and thread in the wire.
Using the utility knife separate the wires.


Find the "hot" wires connected to the wider plug (polarized) end of both the female and male ends and strip the wires. (note: the wires usually have some indicator to denote one from the other, usually markings or ridges)
Using the wire caps and the dimmer connect one lead on the dimmer to one wire and the other lead to the other on the dimmer.  Essentially causing the "hot" wire to pass through the dimmer.
Next strip the other two "neutral" wires.


Connect the "neutral" wires to each other with the 3rd wire cap.  Essentially connecting them back together.
It should now look like this:


If you are using an extension cord with a ground wire you would connect the two grounds to the ground on the dimmer with a wire cap.  After all caps are in place secure the caps and the ground wire (if left bare) with electrical tape.


Next pull some of the wire back through the work box and put the dimmer in the box.
Screw it in place with the included screws with the dimmer.


Lastly put the face plate over the dimmer to give it a nice clean look.


After getting everything together plug a light into the dimmer to be sure that it can turn the light off and on as well as dim the light using the dimmer.  If it works you are all set.  :Smile: 

Here is a pic of a grounded version I made.  The extension cord is slightly more expensive but well worth it for working with grounded on/off thermostats.


I hope all of this information helps.  If anything to get people to use backups because no matter how much you spend on a thermostat without redundancy there is a chance it could fail and harm your animals.

Thanks for reading!

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_cmack91_ (11-26-2011)

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## Clear

This setup works perfect, I use a similar version for my heating setup for feeders!

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## AaronP

Fantastic guide! I'll have to build one this weekend!

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## RichardA

Thanks for the guide......these are very useful if you cant get a thermostat in quickly before the cold front....lol

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## cane

Made my dimmer switch but it does not work, first time i pluged it in it blew the breaker to the house.  Fixed the mixed up wires then pluged it in and nothing with regular lamps but will turn my baby monitor on and off.  Does nothing when hooked to the flex watt.

What did i do wrong?

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## cane

Could I have ruined the dimmer switch.

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## Clear

> Could I have ruined the dimmer switch.


It sounds like the dimmer switch is bad and you wired it wrong.

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## JD Constriction

> It sounds like the dimmer switch is bad and you wired it wrong.


Seconded.  I think the dimmer is toast.

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## ride_gnu

I've been trying to understand this for a while now and still now 100% on this.  At the moment I have my heating sources on a dimmer, if i see a low temp, i turn it up, if I see a high temp in the tank, i turn them down.  So essentially this is all he that is being accomplished in this thread is the construction of a dimmer for more then one light.  

Now is their a way I could have my heat sources to heat the tank to a certain temperature and then stop?  Just like on my fish tank, heater turns on if temp drops below 24 and turns off if tank is above 25, is this acheivable for a BP tank?

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## JD Constriction

The prebuilt dimmers (e.g. walmart $10 mentioned above) can goto one or more devices if you plug in an extension cord.  

The real limitation with the walmart model is that you can only have so many devices hooked up to it before you overload the dimmer (up to 300w worth).

For about the same money as the pre-built model you can build your own that will handle twice as much wattage (600w).

Really the walmart model is best for most small applications but I like to build things rather than buy sometimes.  That and I wanted a dimmer with a ground plug for my 1500w ranco on/off thermostat.

For what you want you would need a thermostat (on/off or proportional) to shut the heat off at a certain temp and turn it back on again when it cools off.  The dimmer basically just keeps the same temp difference.....not the same temp.   

So if you have an 80 degree room and set the dimmer so that the hot spot is 90 degrees the dimmer essentially is set to +10 degrees.

So if the room heats up to 85 degrees then the hot spot will change to approximately 95 degrees if you don't change anything on the dimmer....same +10 degrees

Hope that makes sense  :Smile: 




> I've been trying to understand this for a while now and still now 100% on this.  At the moment I have my heating sources on a dimmer, if i see a low temp, i turn it up, if I see a high temp in the tank, i turn them down.  So essentially this is all he that is being accomplished in this thread is the construction of a dimmer for more then one light.  
> 
> Now is their a way I could have my heat sources to heat the tank to a certain temperature and then stop?  Just like on my fish tank, heater turns on if temp drops below 24 and turns off if tank is above 25, is this acheivable for a BP tank?

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## ride_gnu

> The prebuilt dimmers (e.g. walmart $10 mentioned above) can goto one or more devices if you plug in an extension cord.  
> 
> The real limitation with the walmart model is that you can only have so many devices hooked up to it before you overload the dimmer (up to 300w worth).
> 
> For about the same money as the pre-built model you can build your own that will handle twice as much wattage (600w).
> 
> Really the walmart model is best for most small applications but I like to build things rather than buy sometimes.  That and I wanted a dimmer with a ground plug for my 1500w ranco on/off thermostat.
> 
> For what you want you would need a thermostat (on/off or proportional) to shut the heat off at a certain temp and turn it back on again when it cools off.  The dimmer basically just keeps the same temp difference.....not the same temp.   
> ...


Makes perfect sense, dimmers change the heat but need to be contorlled by you.  What I am looking for is a "Set it and forget it thing"  I currently have 2 dimmers from home depot, one for hot side and one for cold side.  They work fine, but for instance when I go to sleep at night, by body heat can change the temperature in the room to at least 4 degrees higher, thus increasing the tempertaure in the tank 4 degrees high, just as you said.  What I was looking for is something that will keep a constant temperture in the tank no mattter the temperture in the room so if I set it at 82 and my room increase 10 degrees i wont get a 92 degree, I hope this is understandable.   :Smile:

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## TurboSE

Will this type of dimmer control an under tank heater? If so, what is the safe temp for a UTH?

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## llovelace

Yes it will control you uth, safe temp to bp 92-94*, they work best if your room temps are stable, if your room temps are not stable, you will have to monitor your thermostat carefully.

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## TurboSE

This is my plan for a dual rheostat with two constant 110v plugs.

It doesn't seem to be very good at controlling the temp of my UTH. Any ideas?

I have it set at about 10 o'clock, (8 o'clock being full "off",  4 o'clock being full "on"). and the surface temp of the glass above my UTH is still reading about 100*F. 



edit: ignore the orange dots, I was out of wire nuts and was planning to raid my dad's garage...I was counting how many "at most" I'd need.

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## kitedemon

Dimmers work great it an area of constant temperature (dedicated room that is heated/cooled to 80 degrees for example) if you are in an area of variable temps the dimmers will allow that amount of variable as well (if you set a dimmer system to be correct at a room temp of 68 and the room goes up to 73 the uth will also rise by the same 5 degrees. They are great in a controlled area but in a regular room that changes (day and night season to season) a thermostat is they only way to adjust to that variables. Proportional ones will not allow the surfac temp of the uth to go much higher than the set temp non proportional will click on and off 100% and 0% That is likely what your problem is turbose

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Ally. (08-24-2012)

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## TurboSE

I check my temps around the same time everyday..after work..4-5pm EST.

Should I hook the whole setup into a thermostat?

Current temps:

UTH glass: 98*
In viv: 88*
Cold-side glass: 72*
Hot-side glass: 74*

She hasn't left the cold-side since I put her in the tank....

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