Reptile & Amphibian Forums

Hi everyone,

I recently bought a couple Animal Plastics cages with belly heat and I'm may get a new thermostat. I'm wondering most about safety. Is a proportional thermostat safer than the kind of thermostat that simply shuts on and off?

Thanks!

Proportional thermostats by design are solid state and no mechancal contacts to "stick" in the on position. All that I know of are programed to shut off power to the output on any type of fail situation.

Also, besides the obvious catastrophic stuck on fail mode mechanicals can have, They tend to have more intense temp swings because the heat element gets full power until the stat probe reaches shut off temp.
-----
Thanks,

Dave Colling

www.rainbows-r-us-reptiles.com

0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)

LOL, to many snakes to list, last count:
26.49 BRB
20.21 BCI
And those are only the breeders

lots.lots.lots feeder mice and rats

So your saying my Herpstat ND is safer than my Ranco ETC-111000?

Even though both are UL listed and kill power in the event of failure.

Remember the question was in regards to safety rather than which maybe better.

Cheers
-----
Jeremy Payne
JB Reptile
Specializing in Boa Morph's

1.0 Snow "Kahl"
0.2 Triple Het Moonglow "Kahl"
0.1 Orange Tail Hypo Het Leopard
1.1 Double Het "Sharp" Snow
1.0 Ghost
0.1 Possible Super Hypo
0.1 DH Ghost
1.1 "Kahl" Albino
1.0 Hypomelenistic
1.3 Pastel Hypo
0.1 Suriname/Columbian cross
0.1 Anerthrystic

I bet my setup using quad ranco etc 111000 is safer than a single herpstat or a single helix.
ARS rack, two 6" wide heaters, each on a different dual ranco thermostat. 33" deep tubs.
1 ranco goes hot, the second ranco kicks in and regulates it.
One ranco goes cold, they still have the other heat tape and pair or thermostats.
1 section of heat tape fails, I have the other.
Can it fail? Of course.
Is it safe. In my opinion, yes.
Do I have spares? Yes.

I use double Rancos and have never had a problem. I also have a Herpstat and like it alot. On the spider Robotics website, they detail how they are using more expensive parts than their competitors because of t-stat failure concerns and even suggest using an inexpensive enrty level t-stat plugged into the wall,set slightly higher and then having your regular T-stat plugged into that to give you extra peace of mind.

While I think solid state components are more reliable typically than their mechanical counterparts, please keep in mind a few things. (I did circuit board/surface mount repairs exclusively for almost 10 years.)
I haven't had any of those units apart, or checked their output, but there's only a few ways they can do what they have to do.
They don't simply reduce the voltage.
They switch the voltage on and off very fast, either via switching transistor, schottky diode, pwm controller, or some other means.
I have replaced all those parts before, lots of times. They have all failed, and while, I think they would have outlasted their mechanical counterparts if they had the same duties to perform, they simply don't. They are typically forced to do much more severe duty. It comes down to design, all parts can fail.
I use double and quad rancos because I just don't want a simple mechanical failure to cause the death of several of my pets.
I don't think they are more or less prone to failure, they just don't have any redundancy, so if they fail, they fail.
I personally also think that using a herpstat pro with no redundancy is also a bad idea. I wouldn't even use it to control all the devices in one tank, as I said, there HAS to be a component in there somewhere that can fail that will take all the outputs down, no matter how reliable it is. There's just no redundancy.

Thanks, It's nice to visit this Forum and get a chance to hear from folks who have a better idea about things.

Also, I have had the ranco 111000 apart, and the only moving part I see in there is the relay that switches power. The rest is solid state. Relays can fail, but mine only switches on/off every 10 minutes to 30 minutes (Depending on heatsinking and insulation of the tape, and temp of the room.), and has redundancy.
As previously mentioned, you can have the features of a proportional and some redundancy by just putting a ranco upstream of your proportional t-stat.
Just don't try putting 2 proportional t-stats in series, as one will kill the other. (They're territorial.)
I think some herpstats can be used in this fashion, but you'd give up some features.

I will note that I AM OCD (No lie.), but I just don't see the sense in having any temp controller watching a rack of snakes that could cost thousands of dollars, without some redundancy or failsafe.
Yes, I also have a UPS on my rack. A APC SU2200RMXL with the optional SU48RMXLBP battery pack. I was out of power for several days last winter, and that UPS saved my bacon.

Sorry not familiar. Also a question. I keep Temperate stuff in the cellar. Background temp only goes down to 60-65 so I'm not concerned about keeping heat up more concerned about accidental cooking. I'm looking at the ARS racks and as deep as they are (33" and generously ventilated do you think that if A T-stat failed open they are large enough that the animal could just go to the cool side and survive till you saw the problem? Cellar never much more than mid 80's in summer. Thanks.

UPS

Uninterrupted Power Supply
-----
Jeremy Payne
JB Reptile
Specializing in Boa Morph's

1.0 Snow "Kahl"
0.2 Triple Het Moonglow "Kahl"
0.1 Orange Tail Hypo Het Leopard
1.1 Double Het "Sharp" Snow
1.0 Ghost
0.1 Possible Super Hypo
0.1 DH Ghost
1.1 "Kahl" Albino
1.0 Hypomelenistic
1.3 Pastel Hypo
0.1 Suriname/Columbian cross
0.1 Anerthrystic

np

It depends on your heat.
If you use 4" heat tape, maybe.
The ARS racks aren't as open air as the freedom breeder racks.
Your snakes would be pretty pi$$ed at you, but I think they'd be fine as long as you checked on them at least once or twice a day.
I'd still think about putting a backup thermostat upstream of whatever you have if the snakes cost more than the thermostat.
With a freedom breeder rack and the small tape, your snakes would be fine, as long as they went to the cold spot, rather than trying to dig down to cooler substrate.
The freedom breeder uses screen as the top, ARS uses solid sheet metal with holes drilled toward the front of the rack.

I like your responses.

The probability of failure in the two units in series as you described is much lower than any single controller. So your description of a failsafe ON/OFF controller is right on the money as far as true safety is concerned.
-----
Mark

While I do not disagree with any of the replies, yeah they can all fail etc.

One point I do have in contention is the original post was about a proportional vs a simple on/off. Not a more elaborate setup with dual and quad rancos with UPS etc. I totally agree a dual Ranco is clearly safer than a single unit.

IMO THE SAFEST setup is one with redundancy AND monitoring by the owner. I don't care how many t-stats you use, if you don't periodically check and verify your temps, than any failure you do have could go un-noticed.

Lastly was my point about larger temp swings with on/off. Turned on at full power any heat element will put off more therms than at some percentage of full power. IMo that can easily lead to higher short term temps in the area of the heat element before the actual sensed temp rises to shut off level.

>>Proportional thermostats by design are solid state and no mechancal contacts to "stick" in the on position. All that I know of are programed to shut off power to the output on any type of fail situation.
>>
>>Also, besides the obvious catastrophic stuck on fail mode mechanicals can have, They tend to have more intense temp swings because the heat element gets full power until the stat probe reaches shut off temp.
-----
Thanks,

Dave Colling

www.rainbows-r-us-reptiles.com

0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)

LOL, to many snakes to list, last count:
26.49 BRB
20.21 BCI
And those are only the breeders

lots.lots.lots feeder mice and rats

As far as safety, two are better than one, but as Dave Colling pointed out, they are NOT a substitute for monitoring your temps.
I have personally seen heat tape discolor and suddenly get a hot spot. When I saw this I realized how unsafe bare tape was on a tub. It can crack glass, melt plastic, kill your babies, start a fire, what have you.
Now unless that hot spot forms right under one of your probes your therm just isn't going to catch it.
Of course, murphy's law states that any failure will occur when you aren't looking for one, and if a snake dies, it will be your most expensive one.
I like the freedom breeder/ARS way of putting heat tape in a channel made of aluminum, and having the tape insulated on the bottom. (Also, I think the foil tape goes to the ground lug on my strips!!!) That forms a big heatsink that really makes the temps stable (It's never off the setpoint, ever.). It also would help slow down and spread around any hotspots that may form to increase your chances of catching it in time, as well as minimizing the effect, as your probe is more likely to catch it.
It's really degrees of safety, as you're never 100% failsafe, no matter how good your system is.
Net effect: The temps are much more stable with on/off therms than one would think. Mine seriously click at 10-30 minute intervals. Of course, since I have 2 sections of tape next to each other (With different setpoints.), that may help stabilize as well.
I also didn't mean to imply that I thought that any single thermostat is safer than any other.

On the question of safety, there is no difference. Both proportional and ON/OFF can fail.

Rule of thumb for controller choice:
If you are using an ON/OFF controller on a setup, and the controller relay is clicking on and off more than once every 30 seconds, then a proportional controller is a better choice for your setup in terms of relay wear. Note that proportionals cannot be used for fans or heaters with moving parts, like space heaters.

When proportionals fail, they often fail ON. The most common cause - voltage spike or inherently defective output power device (triac, SCR). A surge protector is not a bad idea.

For safety, an ON/OFF in series with a proportional's output is the real way to have a safe system, as described by the other poster in this thread.
-----
Mark

If you have a tub sitting on bare tape, then yes, proportional therms are going to be more stable, but I really think that bare tape is a bad idea, as it just wasn't designed to be used like that. It's original use was heated floors, and it was meant to be used under tile.

You can also attenuate on/off controllers if your tape is too high output for the application, or you already have racks with tubs sitting on bare tape by simply putting a 600w dimmer DOWNSTREAM of your on/off controller.
Simply adjust it to 100%, and watch your thermostats click on and off.
I use a kill-a-watt meter set to watts/VA, start at 100% at say 120 watts for a section of tape, then put a mark on the faceplate of the dimmer switch every 10 watts, and label them.
You just calibrated your dimmer for wattage.
Now unhook your kill-a-watt, then turn it down 10 watts, and time how often it clicks. Plug a low wattage trouble light into your strip and check your watch. Turn it down 10 watts at a time until you get your thermostats cycling once every 10 minutes to a half hour, depending on the temp.

Also, I check the 'draw' of my tape every 6 months. If I have any tape that draws more than the rest, I swap it out for my bottom tape, then keep an eye on it.

The kill-a-watt meter is handy around the house, as well.
http://www.p3international.com/products/special/P4400/P4400-CE.html
I think there's another meter out there that does the same thing called the power angel, but I haven't tried it.

but they're actually PWM controllers.
Pulse Width Modulation.
They will control via 'duty cycle' and you can actually measure it with a kill-a-watt meter using the 'power factor' setting.
A lot of people imagine that they're set up like a volume control on an old style radio, or a potentiometer from radio shack, but that's simply not the case.
http://home.howstuffworks.com/dimmer-switch.htm
That's also very similar to how proportional thermostats work, I'd imagine. Yes, their output is rough on fans and light bulbs. Any motor plugged into a pwm will emit the distinctive 'buzz'. I would imagine that heat tape wouldn't know the difference, though. I'm not sure........

Yes, dimmers are PWM controllers. They are great for heat tape, heat pads and incandescent lights.

My current setup for under cage heating uses low wattage heat cable that at full power will not damage the cage or be too hot to kill the animal. Then I use a dimmer in series with an ON/FF controller. Like you said, I set the dimmer so the ON/OFF controller doesn't cycle very much. A watt meter would sure be handy here, thanks for the suggestion.

Certainly on warm days, the heater will be warmer because the dimmer setting doesn't change unless I manually change it. Snakes are very good at thermoregulating, so I do not care about exact temps. The snake can move around as needed, that is what they do so well in nature.

For incubator, I use a proportional, because eggs can't move around..
-----
Mark