Using a dimmer WITH a thermostat

[Nroc]

I added a thermostat to my existing UTH with dimmer. With just one day's worth of data, I am VERY happy with the results.

It is a Leviton $10 dimmer from Home Depot, and a Zoo Med 500R thermostat which I got for $29 shipped through Amazon.

When using the dimmer with thermostat, I am able to maintain 2 degrees of temperature variance. Without the dimmer, it's about 5-6 degrees of variance. I am dimming the UTH, not the thermostat. The thermostat I have has a cover that hides the cables. However, with the dimmer attached, the cover does not go on. Do they make 1ft extension cords? This would solve this aesthetic issue for me.

My findings:

When running the UTH at full throttle, the thermostat turns off at about 86-86.5 degrees. However, the temperature continues to rise another 3.5 degrees as it was running full throttle when the thermostat turned it off. It shot up to 89.9 degrees and then fell to 84 degrees before being switched on again.

So without a dimmer, it turns on at 84 degrees, and turns off at 86 degrees, but reaches a high of 90 degrees. This is about 6 degrees of variance.

However, with my dimmer, it is not on full throttle, and warms up more gradually. I have found that it turns off at 86 degrees, and goes up about a half degree max before falling to 84 degrees when it turns back on again. Some vairance may be from the thermometer, so there is a margin of error on all my figures.

There are a few things to keep in mind. When using a dimmer, you are limiting the output of your UTH. If something tragic were to happen to your heating, the dimmer may prevent the UTH from ever reaching the cutoff temperature. For example, if the heat stops working, and the dimmer has the UTH at 1/3 power, when the room temp dips to 50 degrees, the UTH may not be capable of getting the tank up to the right temperature. You may only get up to 80 degrees. This is the main consideration to keep in mind. When you limit the UTH with a dimmer, you may not have enough juice to heat up the tank given an extreme situation. Running the UTH at full juice will overcome this issue.

The dimmer and thermostat sort of back each other up. I don't have a single point of failure (except the electricity) anymore. The dimmer is set to provide at least 86 degrees in a 70 degree room. My room temps could drop to 67 under normal conditions, so I need to test and see if it can keep the tank at 85 degrees when the room temp is 67 degrees. I noticed that in the mornings, it would be about 82 degrees in the tank using just the dimmer at it's original setting before getting the thermostat. I raised the dimmer a tad to overcome this, but have not tested anything as of yet. When I left for work this morning, it was 85.5 degrees in the tank. PERFECT!

To summarize, running a dimmer with a static-switch thermostat can provide a 2 degree variance. Running a UTH on a thermostat without dimmer can provide a 5-6 degree variance. This setup provides some redundancy as well. If either the thermostat or dimmer fail, temperatures will not sky rocket. Keep in mind that the dimmer will limit power to the UTH and if room temps fall unexpectedly far below normal, your dimmer setting may not be able to provide ample heating. This setup provides redundency only with regards to keeping temps from getting too high. It will not prevent them from dropping too low in the event of a failure of either device.

I will probably upgrade to a Herpestat near the end of this year, and use the Zoo Med thermostat as the failsafe. The dimmer will be retired then.

 

[Aislin]

Thank Nroc..that was really useful information and I have to say I am impressed with research you are putting into this.

 

[ComoxCorn]

Personally, I opt just to use rotary dimmers, although I will be upgrading to Herpstats this summer. I haven't really seen anyone give the ZooMed thermostats a good review. The thing with dimmers, is that you always need to check the heat, although, my heat seems to stay pretty constant. The temp is more affected by the ambient room temperature when fluctuations occur, but I remedied that by providing a tower heater in my snake room and keep the room temperature at a constant also.
Although you are getting good results with the way you have set things up, it appears that the ZooMed wasn't doing the job in the first place. I'd opt to remove it entirely from the system.

 

[Nroc]

Personally, I opt just to use rotary dimmers, although I will be upgrading to Herpstats this summer. I haven't really seen anyone give the ZooMed thermostats a good review. The thing with dimmers, is that you always need to check the heat, although, my heat seems to stay pretty constant. The temp is more affected by the ambient room temperature when fluctuations occur, but I remedied that by providing a tower heater in my snake room and keep the room temperature at a constant also.
Although you are getting good results with the way you have set things up, it appears that the ZooMed wasn't doing the job in the first place. I'd opt to remove it entirely from the system.

I don't think you understand. The rheostat wasn't cutting it. I added the thermostat yesterday, not the rheostat. The Zoo Med has been in use for 22 hours as of this post.

The Zoo Med does its job just fine. When the cutoff temp is reached, it shuts off power. The Zoo Med can't help that shutting off power does not mean temps go down immediately.

Think of it this way, using just the ZooMed, you are accelerating your car at full throttle. The gas pedal is floored...and when you reach the desired speed limit, you take your foot off the gas. When the car slows down by 5mph, you floor it again until the right speed. Repeat this process of FLOORING it each time you want to increase temps. this is how the Zoo Med, and most all $30 thermostats work. they floor it, and then shut off completely over and over again to maintain the right temps.

With the rheostat, I am now gently pressing the gas pedal in order to accelerate. When i hit the desired speed, I take my foot off the gas, but when its time to accelerate again, I gently place my foot on the gas again instead of flooring it.

Does this analogy make sense?

 

[wstphal]

Analogy makes PERFECT sense! You seem to have achieved what a fancy (expensive) proportional thermostat does with a rheostat + the ZooMed t-stat. Neat.

 

[elipsis1]

Good post. I guess the real question is, how does a 6 degree temperature swing that lasts a few minutes affect snake happiness? I guess we may never know.

I observed the same thing you did Nroc, with my bigappleherp.com $35 thermostat, full on, then off, and about a 5 or six degree temp swing.

I do still have my leviton dimmer, which is in use on our little juvi corn's viv right now, but $10 is nice and affordable, so I may buy another

Thanks again for this post, very helpful info.

 

[elipsis1]

Nroc, if that dimmer fails, the thermostat is your failsafe right?

I guess my question is, when dimmers fail, do they basically give full current to the UTH?

 

[wstphal]

I think when a dimmer fails it quits conducting at all. That would mean the UTH is ~off~. Possibly someone with experience can tell if me I'm right?

 

[Nroc]

I think when a dimmer fails it quits conducting at all. That would mean the UTH is ~off~. Possibly someone with experience can tell if me I'm right?

I agree with that in theory. It does not make sense that a failure at the rheostat would create a wide open circuit, but I think I read about someone's experience here where that actually happened.

The thermostat is not as much a failsafe for the rheostat...rather, the rheostat is a failsafe for the thermostat. It also keeps the UTH from having to wokr at full capacity. I like this as it keeps my temps more in check, and gives me some degree of redundancy.

This is a temporary situation for me anyway. I'll get the snake a Herpestat for Christmas this year, and the Zoo Med thermostat can be a redundant failsafe for the Herpestat.

 

[Ripsaw642]

Dimmer WITH On/Off T-stat

Firstly, I know this thread is really old, it is also the only relevant thread I can find anywhere on the subject, so I thought I'd resurrect it
I've built myself an on/off t-stat using an stc-1000 temperature controller from amazon. I would like to put a dimmer into it as well, as a failsafe, and to stop the on/off cycling so much. If it's on 3/4 power, it should turn on/off way less. Currently it's set to a 2c differential, this is adjustable on this unit as well. I already have a second electrical box installed, the dimmer just needs to be wired in, I just thought I'd ask for thoughts on this.... Thoughts?

 

[smigon]

I don't think you understand. The rheostat wasn't cutting it. I added the thermostat yesterday, not the rheostat. The Zoo Med has been in use for 22 hours as of this post.

The Zoo Med does its job just fine. When the cutoff temp is reached, it shuts off power. The Zoo Med can't help that shutting off power does not mean temps go down immediately.

Think of it this way, using just the ZooMed, you are accelerating your car at full throttle. The gas pedal is floored...and when you reach the desired speed limit, you take your foot off the gas. When the car slows down by 5mph, you floor it again until the right speed. Repeat this process of FLOORING it each time you want to increase temps. this is how the Zoo Med, and most all $30 thermostats work. they floor it, and then shut off completely over and over again to maintain the right temps.

With the rheostat, I am now gently pressing the gas pedal in order to accelerate. When i hit the desired speed, I take my foot off the gas, but when its time to accelerate again, I gently place my foot on the gas again instead of flooring it.

Does this analogy make sense?

Yep, you are now on cruise control!!!