# Dimmer stat



## Ben.M (Mar 2, 2008)

Can you use a heat mat on a dimmer thermostat or do i need a mat stat intead???


Ben.M :2thumb:


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## Crownan (Jan 6, 2007)

I think dimmers need at least 40W? So either a frickin huge mat or a few connected to the one stat.

Personally I prefer pulse proportional stats for mats, mat stats allow the temp to fluctuate too much IMO


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## Ben.M (Mar 2, 2008)

Well i was gonna need a dimmer then switched coz i needed to use a mat instead so i've just cancled the dimmer order and am about to order a mat stat(cant find a cheap pulse 1)

Thanx for your input,

Ben.M


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## fixitsan (Apr 15, 2008)

Ben.M said:


> Can you use a heat mat on a dimmer thermostat or do i need a mat stat intead???
> 
> 
> Ben.M :2thumb:


 
Yes you ought to be able to without any problem, as long as the heat mat maximum rated load is not larger than the stat is capable of controlling. 

In theory you could even use an ordinary household lighting dimmer switch to set the output of a heat mat to any temperature you want it to be at, from between off to fully on. The problem there is that there is no temperature control, so if the room the viv is in heats up, and in turn that heats up the viv, the mat will still run at the set output, and may warm up slightly more than before. Also if the temperature drops the mat won't increase output to accomodate, but if you don't expect more than a few degrees of room fluctauation it should work well enough and be able to give a fairly constant output.

The only time i wouldn't recommend this sort of system is when you rely on it for the only source of heating in the viv. If it just for a basking spot, or a daytime warm area it would be fine forever, but if you try to set the temperature of the whole viv with a large mat driven by a dimmer you will have difficulty getting a constant temperature.

You can also use a household dimmer to run an infra red ceramic lamp to fine tune it's heat output, again, just as long as the lighting dimmer is rated for enough watts of output from your heater there is no problem

Chris


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## peterf (Jul 27, 2007)

Dimmers have a maximum load of 600 watts but also the requirment of a minimum of 40 watts. 
Pulse has no minimum load requirment.
Household dimmers do not take into consifderation any temperature changes in the environment and will overheat. They do not contol the temperetaure- just the supply to the heater and remain at what you set them at.
If its a hot day and you have the household dimmer set at say 75% then it is very likely to overheat your cage and risk the wellbeing of your animals.


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## fixitsan (Apr 15, 2008)

peterf said:


> Dimmers have a maximum load of 600 watts but also the requirment of a minimum of 40 watts.
> Pulse has no minimum load requirment.
> Household dimmers do not take into consifderation any temperature changes in the environment and will overheat. They do not contol the temperetaure- just the supply to the heater and remain at what you set them at.
> If its a hot day and you have the household dimmer set at say 75% then it is very likely to overheat your cage and risk the wellbeing of your animals.



I was assuming that there would be seasonal adjustment made to all the equipment by an attentive keeper
To say they will overheat is to also say that the mat is capable of overheating if it receives 100% of power, but a dimmer can't ever provide more than 100%, so it won't necessarily cause any problem in itself. As I made clear, I would only use it for background heating devices of the sort which most people wouldn't normally run to the expense of a PP thermostat for.


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## peterf (Jul 27, 2007)

I do agree with you Fixitsan, but my point is that a thermostat will maintain the temperature it is set at which would be the preferred temperature for the animal. A rheostat will just reduce voltage to a heater or provide it with up to 100%.
Heat mats are not able to overheat if used properly (I am only referring to Habistats) but the will be proportionally higher than ambient when running at 100%. This could happen on a warm day when your at work if you are just using a rheostat type control. 
Thermostats take away that danger.
I do worry,as I have said in other posts, that people try to save money in the the wrong places. The most important bit of equipment for any reptile is the thermostat!


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## fixitsan (Apr 15, 2008)

peterf said:


> I do agree with you Fixitsan, but my point is that a thermostat will maintain the temperature it is set at which would be the preferred temperature for the animal. A rheostat will just reduce voltage to a heater or provide it with up to 100%.
> Heat mats are not able to overheat if used properly (I am only referring to Habistats) but the will be proportionally higher than ambient when running at 100%. This could happen on a warm day when your at work if you are just using a rheostat type control.
> Thermostats take away that danger.
> I do worry,as I have said in other posts, that people try to save money in the the wrong places. The most important bit of equipment for any reptile is the thermostat!


I agree, but a dimmer isn't a thermostat, and we're back to saying if a thermostat is even required. Keeping a constant environmental temperature has no known beneficial effect on animals. We're all designed with the ability to thermoregulate

If someone was really concerned about temperature control, then I would steer well clear of the overpriced Habistat branded equipment and buy the much cheaper more reliable, more accurate, and self teaching industrial type controllers, called PID controllers

Habistat 'proportional only' do a good job of keeping a standard temperature in an enclosed box which has no outside disturbances, but still they are more expensive than something which is more capable and more accurate. I've just priced up a self teaching PID controlled system at £40, using industrial strength certified components, with a digital readout display accuracy of 0.1C and an overall accuracy of 3%, which must be at least a whole magnitude better than using a Habistat.

We're talking about using the right thing for the right job obviosuly , but would be happy to use a UL listed lighting dimmer which has fault detection and cutoff built in, if I wanted to save the expense of buying a controller which has features I am never likley to need

When you're only talking about


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## peterf (Jul 27, 2007)

Well Chris,
As usual on this forum someone asks a valid question and it ends in unnecessary and ill informed slagging of people or products.
I am far too busy to be addressing self professed experts who post ridiculous statements on internet threads, but will take some time to address your points.

If you are looking for any qualification of my points I could send you my CV but as the largest breeder of colubrid snakes, possibly leopard geckos, reticulated pythons and numerous other species I guess I am fairly well versed in the captive requirements of reptiles.
I have the largest and most successful breeding facility in Indonesia.
I haven’t just kept a few garter snakes.

I am the largest reptile product manufacturer in the UK and possibly in Europe.

As the maker of Habistat thermostats I take exception to both your comments on costs and your criticism of my points.

“if a thermostat is even required. Keeping a constant environmental temperature has no known beneficial effect on animals. We're all designed with the ability to thermoregulate”

Reptiles cannot regulate their own body temperature. Most thermoregulate by using areas of warmth that, in captivity, are provided by managed heaters.
Even a heat mat, used uncontrolled on a hot day, will be out of their threshold of temperature requirement.

So in short, your recommendation of using a rheostat will achieve little effectively.

“If someone was really concerned about temperature control, then I would steer well clear of the overpriced Habistat branded equipment and buy the much cheaper more reliable, more accurate, and self teaching industrial type controllers, called PID controllers”

Habistats are made in the UK and have been for 20 Years.
They are older technology but are recognised as the best on the market for all the important issues. Reliability, accuracy and customer support. We have manufactured and designed systems for many Zoos and collections. 
We have distributors in the USA, all of Europe, Dubai and Australia.
They have a 5 Year guarantee and we offer a same day repair service. 50% of returns have no fault (it’s usually the heater or its associated wiring).

The ones with faults are usually caused by faulty heaters.

Accuracy has never been questioned by anyone in 20 Years! We use them on all our facilities and most Zoos and private collections use them on all their most precious snakes.

To claim that a PID controller is more accurate is nonsense. We have tried and tested many and, just because it has a digital readout does not mean that that is its level of accuracy. 

No PID controllers are dimmers.

Now to costs.
PID contollers are industrial controllers used to control everything from freezers to furnaces. We use them on the machine that we manufacture our heat mats on in Scotland.
They provide a signal to something else that turns your heater on and off. It will also need a component to sense the temperature.
Put these all together and you have a DIY thermostat. As a product this would be illegal for me to sell to you. As a finished item it would need to be put through low voltage safety testing and EMC testing. It would need to conform to all the safety and tamper regulations. It would need to be is a box that didn't allow the operator access to live parts, plugs fixed and sockets to plug your heater in to. 
PID controllers have to be hard wired to terminals which would not be allowed for domestic use.
To top it off, you are no longer permitted to modify or work on your household electrical equipment, other than put a plug on an appliace, so you would need to call in a qualified electrician to do this work.
So now this is made from bits at a cost of £40 (I doubt), without being able to pass the CE testing. 
Take the makers profit, sell that to a wholesaler who takes his cut, who sells it to a shop, who adds their margin and VAT and it ends up costing how much?
I would guess at £120.

As I sell over 1000 Habistats every week, I think your comments are inaccurate, incorrect and misleading.

We will have a new thermostat out around September which has been outlined on another forum.
This unit will encompass all the functions, we as reptile keepers see as necessary. It will be independently CE tested and approved and will be plug and play which is a part of the safety regulations. 
I will post some more data on it nearer the time.

On another thread I see your comments on cutting down heat cables. Well I would urge any buyers to buy the correct length as they are manufactured with the outside sheathing bonded to the plug. Cut it off and you will not be able to re-attach and it will not work.

Finally your thread on running heaters on low voltage.will be interesting.
You cannot run mains appliances on low voltage (12/ 24 volt) supplies. They will simply not work.


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## reptiles-ink (Nov 4, 2006)

Very well put peterf and I totally agree, I have used your thermostats and had no problems (think I have 3 running now).
I also make my own but have a very good understanding of electronics as it is my proffesion but for someone else to get various parts and put them together safely without knowlege of what they are doing is asking for trouble.
As for cutting down heat cable that is asking for trouble depending on the type of cable.
I would love to see how the mains required heaters would run on lower power without an inverter.


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## peterf (Jul 27, 2007)

Thanks for that support. 
I didn't want people to think I was having a rant, but some people just make sweeping statements without thinking of the implications.
I am afraid the internet has made everyone an authorative expert in all fields if they choose to claim they are.
All that Ben wanted was sensible advise and, in my opinion he received some very poor advise from some contributors.


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## fixitsan (Apr 15, 2008)

peterf said:


> Well Chris,
> As usual on this forum someone asks a valid question and it ends in unnecessary and ill informed slagging of people or products.
> I am far too busy to be addressing self professed experts who post ridiculous statements on internet threads, but will take some time to address your points.


I am sorry that you feel this way.

I wish I could see what was ridiculous about any of the sound advice I was giving, and I will address your responses accordingly.




> “if a thermostat is even required. Keeping a constant environmental temperature has no known beneficial effect on animals. We're all designed with the ability to thermoregulate”
> 
> Reptiles cannot regulate their own body temperature. Most thermoregulate by using areas of warmth that, in captivity, are provided by managed heaters.
> Even a heat mat, used uncontrolled on a hot day, will be out of their threshold of temperature requirement.


Reptiles can thermoregulate their temperature, and they do so by moving their whole body from an area at one temperature to another. As you then go on to say ' Most thermoregulate by using....." Yes, that is correct of you to say so.

I have a chameleon enclosure which will be at room temperature at night and have a higher temp during the day, the heat provided by small spotlights. I don't consider an additional heater to be necessary, and therefore I don't consider a thermostat to be essential equipment either. What I said, which you sseem to have responded badly to was when I mererly said 'if one is even necessary'. would you suggest people should by a thermostat and then set it to room temperature ?

I appreciate you have a lot of experience, which accounts for a great deal, but I know from testing my viv that a heater is not required, am I wrong therefore for saying 'If one is even required' ?




> So in short, your recommendation of using a rheostat will achieve little effectively.


As I haven't mentioned a rheostat I doubt that this comment was aimed at me, was it ?





> “If someone was really concerned about temperature control, then I would steer well clear of the overpriced Habistat branded equipment and buy the much cheaper more reliable, more accurate, and self teaching industrial type controllers, called PID controllers”
> 
> Habistats are made in the UK and have been for 20 Years.
> They are older technology but are recognised as the best on the market for all the important issues. Reliability, accuracy and customer support. We have manufactured and designed systems for many Zoos and collections.
> ...


It is itself nonsense to say that a device which has a silkscreen printed temperature scale and a knob with a fluted groove and variable width paint stripe can be as accurate as a digital scale in terms of resolution, and I wasn't suggesting that the digital display itself is any proof of accuracy, but PID controllers have the ability to drive a heater with more accuracy than a reactive controller. It well be overkill in some people's mind, and as far as I am concerned I mentioned enough about the caveats.






> Now to costs.
> PID contollers are industrial controllers used to control everything from freezers to furnaces. We use them on the machine that we manufacture our heat mats on in Scotland.


What is the reason they are fitted to furnaces, and to your machine here in Scotland, instead of just a basic controller with a knob pointer system ? A digital display isn't added just to give the manufacturer a reason to charge more is it ?






I do appreciate and respect your position. 

But I can't, for example, see the reason for the price differential between some products, other than they have features which can be charged for. Without beign too specific there is a large difference between the dimmer stats and the pulse proportional stats. I don't consider the price difference between the two to be representative of the relatively small circuit
changes which are required to go from dimmer to pulse proportional. You still have the cost of the triac/mains switch, and need to add either a comparater/op-amp (less than £1) or a microcontroller (less than £1) and a new pcb. Small fry in volumes of 1000 units per week.

I appreciate your right to defend your products and the desire to sell more, but I believe many people have the ability to make their own from other components. You are quite right that my DIY suggestion is just that, DIY, but there are many people with the desire to DIY their own equipemnt and many who already do.



You talked about a PID controller for £40 being unrealistic, but that was only when you spoke as a distributor.
A PID temperature controller with correct certification can cost as little as £19.99, comes with a thermocouple, and needs only a relay to be added. One model at £37 comes with a relay built in and needs nothing else at all.
For the hobbyist who is able to work on the South side of an ELCB they are certainly the cheaper off the shelf option to the the pulse proportional which retails at £49 in many shops. 

Many PID controllers come with the ability to program temperature cycles, such as individual day and night temperatures, and some have programs to create gentle fluctuations during each period if they were also required. In these cases no other timer or light sensors are required. Everything is in one controller. The controllers themselves already come certified. Any equipment which contains them only needs the lowest level of inspection and certification testing

PID control of temperature, which is the de facto with large time constant heating systems (and a vivarium has a very large time constant) could be included in many systems for very little extra charge




> On another thread I see your comments on cutting down heat cables. Well I would urge any buyers to buy the correct length as they are manufactured with the outside sheathing bonded to the plug. Cut it off and you will not be able to re-attach and it will not work.
> 
> Finally your thread on running heaters on low voltage.will be interesting.
> You cannot run mains appliances on low voltage (12/ 24 volt) supplies. They will simply not work.


[/quote]

The use of low voltage heating using mains heating cable is nothing new, it's tried and tested in many areas of engineering and industry, from the pipe defrosters on aircraft to life support systems in hospital. If people have access to low voltage equipment then the need for CE testing is negated by powering all the equipment from one single UL/CE listed power supply. The only difference between mains rated heating cable and the lower powered alternative is the length of the cable, and nothing else, the cable is merely a resistor in a power loss circuit.

A length of cable which has been cut for 240V ac mains, for example at 6m long, can run at 12V if it is shortened to .... 6/ (240/12), 6/20 = 0.3metres, in order to provide the same power output. I accept that terminations are not too easy when you have to meet the strict regulations for mains voltages, but the relatively harmless 12V/24V (Actually you could go as high as 36V and stay within the law) is much easier to cater for.

Finally, I am sorry if what was an off the cuff remark caused you any distress, not my intention at all. I have never bought one of your products, and the fact that you have been making them so long is nothing to be sniffed at. I am looking at things from the point of view of what it costs to make for yourself, and maybe this forum wasn't the correct one to use. Perhaps there is a DIY forum which could be created if there isn't one already, and that will be something the moderaters could comment on, and hopefully they will do.

Chris


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## fixitsan (Apr 15, 2008)

peterf said:


> Thanks for that support.
> I didn't want people to think I was having a rant, but some people just make sweeping statements without thinking of the implications.
> I am afraid the internet has made everyone an authorative expert in all fields if they choose to claim they are.
> All that Ben wanted was sensible advise and, in my opinion he received some very poor advise from some contributors.



I wish I could agree Peter, but your comment was also full of hypothesis and some slightly misleading affirmations and sweeping statments about all dimmer's, and all household thermostats.

On what type of tank construction, heater type and power levels did you base your conclusion on when you warned that on a warm day the heater would overheat and be dangerous ? I am struggling to appreciate those conditions at this point

I don't want this to be qualifactions war, but in order to differentiate myself from the self professed expert I have a BSc in Mechatronics, control and automation, (returnign to Uni to complete my Honours next year)and have worked as an engineer for most of my life. I have developed microcontroller products to perform many varied and interesting tasks.

I agree that the internet is far from perfect, and another bad side of the internet is the way in which people are sometimes prevented from taking a step towards helping themselves and building something they want to make for themselves, or understand the nuances of a situation for themselves, with complete and qualified guidance from others, just because of others who immediately throw out scare stories, and don't provide a useful framework for their warnings.

Chris

Chris


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## peterf (Jul 27, 2007)

fixitsan said:


> I am sorry that you feel this way.
> 
> I wish I could see what was ridiculous about any of the sound advice I was giving, and I will address your responses accordingly.
> I was referring to the sweeping statements about the overpriced, inaccurate and unreliable Habistat thermostats.
> ...


The use of low voltage heating using mains heating cable is nothing new, it's tried and tested in many areas of engineering and industry, from the pipe defrosters on aircraft to life support systems in hospital. If people have access to low voltage equipment then the need for CE testing is negated by powering all the equipment from one single UL/CE listed power supply. The only difference between mains rated heating cable and the lower powered alternative is the length of the cable, and nothing else, the cable is merely a resistor in a power loss circuit.

A length of cable which has been cut for 240V ac mains, for example at 6m long, can run at 12V if it is shortened to .... 6/ (240/12), 6/20 = 0.3metres, in order to provide the same power output. I accept that terminations are not too easy when you have to meet the strict regulations for mains voltages, but the relatively harmless 12V/24V (Actually you could go as high as 36V and stay within the law) is much easier to cater for.
Well, I cannot argue with your theory but would like to make a comment. All the heat cables we have manufactured have the live or neutral side bonded to the plug. This is very difficult to re attach and I would recommend against modifying it. The cables in our range are approximately 10 watts per metre. A 12 metre cable equates to around 100 watts and a 16 metre cable is 150 watts. Some of the cable is unheated.
Now if I cut a 12 metre cable down to 6 metres then it will still be 10 watts per metre and will be around 50 watts. There are low voltage cables marketed but I do not think (as a layman) that your theory holds ground here.
Finally, I am sorry if what was an off the cuff remark caused you any distress, not my intention at all. I have never bought one of your products, and the fact that you have been making them so long is nothing to be sniffed at. I am looking at things from the point of view of what it costs to make for yourself, and maybe this forum wasn't the correct one to use. Perhaps there is a DIY forum which could be created if there isn't one already, and that will be something the moderaters could comment on, and hopefully they will do.
I suspect the moderators may be wary of a DIY forum for many of the reasons previously discussed by us!

Chris[/quote]


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## peterf (Jul 27, 2007)

I wish I could agree Peter, but your comment was also full of hypothesis and some slightly misleading affirmations and sweeping statments about all dimmer's, and all household thermostats.

On what type of tank construction, heater type and power levels did you base your conclusion on when you warned that on a warm day the heater would overheat and be dangerous ? I am struggling to appreciate those conditions at this point
Uncontrolled heaters clearly _can_ have the capacity to possibly overheat a cage but as importantly, to make the warm area too warm for the reptile to utilise.. Factors like the volume of the cage, ventilation, capacity of the heater and ambient temperature are all factors. As I previously stated a heater running full power isn’t a danger but it would be to the animals in the enclosure and even a heat mat running at 40c on a hot day, would be too hot for most reptiles to use for basking. We are taking husbandry here, not the mechanics of the heater.

I don't want this to be qualifactions war, but in order to differentiate myself from the self professed expert I have a BSc in Mechatronics, control and automation, (returnign to Uni to complete my Honours next year)and have worked as an engineer for most of my life. I have developed microcontroller products to perform many varied and interesting tasks.
Chris clearly your qualifications speak for themselves and I would guess that you could have valuable technical and design knowledge that we could use when designing new products.
Having kept reptiles for 40 years and having been directly involved in the design and manufacture of products pertaining to their husbandry I feel I have something to offer and some principles to defend.
Concluding my points on your posts and the issues raised:
Go back 30 Years and many reptiles were kept in very poor conditions and the life expectancy of some could be measured in how quick they starve to death.
There was no live food producers, no appropriate heaters, no thermostats suitable for reptile keeping. No reptile equipment. Little knowledge of lighting, D3 and vitamin metabolism and dietary requirments.
Everything was DIY and some ideas worked and some didn’t.
I started Eurorep 20 years ago to try and put this right. 
It took a long time but eventually, along with the cheap mat stat, most everyone started to use thermostats to control their heaters. I agree that in some applications heaters can be used safely with no control, but those situations are rare and best not promoted. A thermostat on such a set up may never work- until that very hot day when everyone in the house is at work and the enclosure overheats causing distress, if not death to the cages inhabitants.
In your posts you completely dismiss a range of thermostats that, with another maker of the time, probably revolutionised reptile keeping World wide. Having dismissed them, you then admit to never having used one!
Accusing me of “throwing out scare stories” just because I recommended a thermostat as opposed to a manual dimmer switch is way off. If you take a look back on this site for posts pertaining to uncontrolled heaters you will find plenty of well experienced keepers condoning my point of view.
This is an information portal and lots of the people on here are young and inexperienced keepers.
I am sure you have a lot to offer with your qualifications and knowledge but I would exercise caution, before suggesting to new keepers that there are better alternatives to the sensible use of thermostats on heaters. This is a step backwards.
I would also avoid the suggestion of unqualified people make or modify their own equipment. You know the hoops all manufacturers have to jump through to get approvals in these days of health and safety.
You may well criticise the old technology in both the Habistat thermostats and Heat mats but I designed and manufactured them with quality, reliablilty and function in mind. 
We have several million pounds of liability insurance pertaining to these product lines. 
In 20 Years we have never had a claim levelled at us for any reason.
As I previously mentioned we do have a new thermostat in test and design at the moment. 
This will have all the PID functions and digital readouts, time and temperature zone switching, auto overtemp cutouts and will be dimming- and designed and manufactured in the UK.
Enough time spent now responding to a simple question. I think I have said all I need to in response to your questions Chris.

I wish you well with you reptile keeping and electronics!.

Pete



Chris


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## fixitsan (Apr 15, 2008)

peterf said:


> The use of low voltage heating using mains heating cable is nothing new, it's tried and tested in many areas of engineering and industry, from the pipe defrosters on aircraft to life support systems in hospital. If people have access to low voltage equipment then the need for CE testing is negated by powering all the equipment from one single UL/CE listed power supply. The only difference between mains rated heating cable and the lower powered alternative is the length of the cable, and nothing else, the cable is merely a resistor in a power loss circuit.
> 
> A length of cable which has been cut for 240V ac mains, for example at 6m long, can run at 12V if it is shortened to .... 6/ (240/12), 6/20 = 0.3metres, in order to provide the same power output. I accept that terminations are not too easy when you have to meet the strict regulations for mains voltages, but the relatively harmless 12V/24V (Actually you could go as high as 36V and stay within the law) is much easier to cater for.
> Well, I cannot argue with your theory but would like to make a comment. All the heat cables we have manufactured have the live or neutral side bonded to the plug. This is very difficult to re attach and I would recommend against modifying it. The cables in our range are approximately 10 watts per metre. A 12 metre cable equates to around 100 watts and a 16 metre cable is 150 watts. Some of the cable is unheated.
> Now if I cut a 12 metre cable down to 6 metres then it will still be 10 watts per metre and will be around 50 watts. There are low voltage cables marketed but I do not think (as a layman) that your theory holds ground here.



No this is incorrect. Would you believe me if I tell you how to check it, and you can check for yourself with a meter ?

If you cut down your 100W cable to 6m and reconnect it to the mains it will dissipate more power than 10W per metre, not less

The characteristic of the cable which dissipates power is it's resistance, measured as ohms per metre. Regardless of the length of the wire the resistance per metre is always the same and won't change even if a different voltage is applied.

You can test one of your cables with an ohmeter if you wish to confirm the following.

Your 12m cable has a total power of 100W at 240Vac.
The current through the cable (I = P/V) = 100/240 = 0.42A
The resistance of the cable (R = V/I) = 240/0.42 = 571 Ohms approx

( I think there could be +/- 50 ohms here due to power factor correction, but you can see that I am not just saying any old number)

The resistance of your cable is 571/12 = about 47 Ohms per metre 

If you now cut the cable down to 6m long it's resistance is 47 x 6 = 282 Ohms

To find the new power disipation we can find the new current from I= V/R
, when connecting 6m of cable across the mains, 240/282 = 0.85 Amps

And because P = I x V, P= 0.85 x 240 = 204W

(theory suggests it should be exactly double, but there is some maths rounding up applied here)

So when you cut your length of cable in half it changed from being a 100W heater to a 204W heater. but this is not unusual when you think about it, you are connecting a smaller resistance to the same voltage, therefore a larger current is bound to flow.

The reason you wouldn't want to do that is because disipating twice as much power per metre of the cable is dangerous, and so for that reason you must stay within the bounds of the manufacturer's recomended power disipation.

Now , because you have mentioned rheostats, it should be easy for you to see that your heater cable is a large resistor and you could if you wished, connect a wire through the insulation to the heater core and check that you get a different resistance as you move along the cable. You will also get a different voltage at different points along the length of the cable.

If you wanted to run this cable from 12V and you didn't want to use a meter probe to keep stabbing into the insulation to find where the 12V point is you can calculate it.

Luckily this maths is easy because we have a uniform resistance and therefore there is a uniform distribution of voltage too.

240V/12m = 20V per metre (for a 10W/metre power figure)

Therefore to run from 12Vac you use 12/20 = 0.6metres of cable.

You have respected the manufacturers limit of 10W/metre and you are dissipating 0.6 x 10 = 6 Watts of power,which would need a 12V power supply capable of supplying (I = P/V) 6/12 = 0.5Amps




Re your comments of calling a domestic lighting dimmer a rheostat, that may have been the case many moons ago, but for at least the last 20 years most domestic dimmers are thyristor/SSR solid state electronic devices, which will contain almost identical circuitry to the dimmer stat type of products sold on the market for vivariums. A rheostat is a length of resistance wire which uses the changing position of a metal slider to control voltage. They dissipate lots of heat, and are not safe as lighting controllers in the domestic environment, which is why all domestic dimmers are electronic.

Re the comments that most PID controllers are not proportional. The name PID is a shortening of the phrase _Proportional_ + Integral + Derivative. Not only are PID controllers proportional controllers, they are also designed to compensate for the inadequacies of basic proportional controllers by using maths functions relating to the intergal of time functions and the derivative, to produce a much more accurate heating function. The fact that we are now seeing self teaching PID controllers which eliminates the need for tuning them manually is a huge leap forward in simplicity. You are unable to tune most proportional controllers at all.

There is an excellent page on Wikipedia about PID controllers, including sample software which would take less than 150 bytes of memory in any microcontroller PID controller - Wikipedia, the free encyclopedia 

Re the comments about copper torroids, please will you elaborate some more on that. I am unaware of any dimmers which carry any copper torroids, most torroids are made from ferromagnetic material and I don't see why lighting or heating systems would require anything different. What does your dimmer stat use for mains noise filtering ? Presumably a torroid and a couple of capacitors ? 

Re your pulse proportional device, I may not have fully understood it's mode of operation, clearly there are at least two ways to proportionately control the length of power pulses, does yours use the zero-crossing method and control the duration of each ac half cycle, or the method where the on-time of the power switch is much greater than several cycles in length ?


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## the-tick (Nov 27, 2006)

on a side note peterf where can we see details of the new stat as I will be (along with a lot of rfuk) in Hamm and I will be looking at a dimmer stat with a day/night facility.

Now in my collection I use Habistat and Microclimate stats, both of which I am very happy with the reason I go with microclimate day/nights dimmers is the built in magic eye function. will the new stat have the said function and can you say what price range the new ones will be ??


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## fixitsan (Apr 15, 2008)

peterf said:


> I agree that in some applications heaters can be used safely with no control, but those situations are rare and best not promoted. _A thermostat on such a set up may never work- until that very hot day when everyone in the house is at work and the enclosure overheats causing distress, if not death to the cages inhabitants_.



With respect doesn't this paragraph suggest that the thermostat would be responsible for the death of an animal ?

A thermostat on such an enclosure would trip when it gets too hot. Why have such confusion over the purpose of a thermostat ?

I appreciate your comments, and note that you will be incroporating PID into your next design iteration. You have commented that PID is not proportional, but hopefully you will appreciate that Proportional/Derivative/Integral is actually a proportional controller in it's action, tempered by a derivative and integral function to improve the bullish response of a proportional controller.

Chris


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## Sprocket (Apr 21, 2008)

Yes, i want to know when the thermostats will be available !


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