Potential cheap temperature controller?

[jhmn]

Hi,

Apologies if this has been discussed before - I did a couple of searches and didn't find anything.

I came across these while looking for temperature controller stuff on eBay. It's a digital, touch screen wall thermostat designed to control underfloor heating. It comes with a 3m NTC probe and can be set to 'manual' and 'external' control, which according to the manual means you can set a temperature and it will heat until the probe temperature (the big reading in the middle of the screen) reaches the set temperature (smaller reading below), ignoring any programming and the internal ambient temperature sensor.

According to the manual -

Power Supply: 85-250VAC 50/60 Hz
The maximum switch power: 2A/16A
External sensor measurement range: 0 - 95°C.
Setting range: 0 - 90°C (factory settings: 50°C)

(This model has a 16A relay)

It seems it just fits into a pattress box and can therefore wired up vaguely safely.

Any thoughts on using this as a temperature controller? I've got a 3000w HLT - do you think it will cope?
I'm slightly worried by the fact you can't earth the thermostat itself - if anybody with more than my basic grasp of household electricity has an opinion on this, I would be interested to hear it.

http://www.ebay.co.uk/itm/261335456888

LCD Digital Touch Screen Programmable Room Thermostat

[lord groan]

Looks like it ought to work, temperature probe getting toward its limits though in an HLT (0-95c) perhaps you can be the JBK guinea-pig on this?
I've just finished my own HLT build and the controller I used was this one;
http://www.ebay.co.uk/itm/Digital-40-to ... 27d549dc5e
It has a higher switching power @30A, although I'm only running a single 2.5kw or thereabouts element off it. Seems to be working well enough on the test runs I've done.
Must admit I like the look of the display on your one better than the one I used.

[jhmn]

Yes, I'm thinking of trying it out, but I'm going to wait a bit to see if anybody spots a (literally) fatal flaw beforehand.

The temperature range could be an issue. I've got a feeling it's to do with the firmware, rather than the probe itself, which is annoying.

Your controller is my plan #B, so I'm glad to hear it's working alright. I've meant to order one for a while, but keep forgetting to buy one when they are in UK stock.

[ryanshelton]

Looks like it ought to work, temperature probe getting toward its limits though in an HLT (0-95c) perhaps you can be the JBK guinea-pig on this?
I've just finished my own HLT build and the controller I used was this one;
http://www.ebay.co.uk/itm/Digital-40-to ... 27d549dc5e
It has a higher switching power @30A, although I'm only running a single 2.5kw or thereabouts element off it. Seems to be working well enough on the test runs I've done.
Must admit I like the look of the display on your one better than the one I used.

Does this work on a burco boiler which is now my hlt and if so how?!

[themadhippy]

I'm slightly worried by the fact you can't earth the thermostat itself - if anybody with more than my basic grasp of household electricity has an opinion on this,

no need for an earth on the stat,they'd normally be connected in the pattres/metal back box.The technical reason why is theres no touchable conductive parts that may become live under fault conditions.

[Dr. Dextrin]

The usual issue with cheap thermostat solutions is that the dead-band is too large, so the temperature hunts up and down by too large a range. However, heating thermostats have improved a lot in recent years and some are now pretty sophisticated, so maybe it'll be OK. Only one way to find out I guess...

[aamcle]

It looks fine but it costs more than a STC1000 and the STCs have a proven track record.

Atb. Aamcle

[lord groan]

Looks like it ought to work, temperature probe getting toward its limits though in an HLT (0-95c) perhaps you can be the JBK guinea-pig on this?
I've just finished my own HLT build and the controller I used was this one;
http://www.ebay.co.uk/itm/Digital-40-to ... 27d549dc5e
It has a higher switching power @30A, although I'm only running a single 2.5kw or thereabouts element off it. Seems to be working well enough on the test runs I've done.
Must admit I like the look of the display on your one better than the one I used.

Does this work on a burco boiler which is now my hlt and if so how?!

@Ryan - yes I've fitted mine in a hole cut in the skirt at the bottom of my burco, I fitted an additional illuminated mains power switch as well. I'll fully document the build with pictures under my "new hlt" posting soon (tonight hopefully!)

[jhmn]

It looks fine but it costs more than a STC1000 and the STCs have a proven track record.

Atb. Aamcle

Yes - in the end, I picked up one of the 30A temperature controllers that look like an STC-1000. I'm impressed with it given the price.

If I do end up trying out one of these wall thermostats I'll update this thread. Thanks for all the ideas.

[rorymullan]

I have an STC-1000 for the brew fridge and a lookalike 30A for my twin element HLT.

Both great. A warning though that the temperature probe on my look alike died after 1 month and I now have to use the STC-1000 probe with it aswell. Not much of a problem, but the build quality difference of the probe is fairly evident.

Still the STC-1000 itself can't be use with the HLT.

[darkonnis]

It looks fine but it costs more than a STC1000 and the STCs have a proven track record.

Atb. Aamcle

True, but by the time you've bought all the bits I'll bet there isn't much in the price, this also does significantly more than the STC does with its built in timer, and clock UPS in case of power failure.

[Jeltz]

FWIW I've found it (the one from the OP) a few quid cheaper and ordered one. Will see how it works, to control my HLT, if at all.

[Jeltz]

Well it appears to work, in a fashion.

The initially I thought it would fit a patress box but it won't, instead I fitted it into a 95mm X 95mm junction box by drilling a circle out of the lid and securing in place with screws.

in the end it looks like this



Testing has been a little tricky as my element died (nothing to do with this kit) so I have been using an old one which doesn't get beyond 96°C. I've ordered a new one and will re test it but it seems OK to control an HLT, it won't do a boiler though as its limited to 95°C. The timer is a little awkward to get to grips with IMO but OK once you have played about with it and the battery backed up clock seems to keep reasonable time.


The biggest issue is that its slower than I would like to register temperature changes, as such it over shoots the target temperature as it doesn't switch off the element soon enough and once it has the sensor is still catching up. By default the hysteresis (i.e. the level above target that it switches off) is set to 3°C, when tested it in a kettle it shot up to over 10L°C over the target temperature. However the small volume of water exacerbates this and the hysteresis can be set to 0.5°C. When tested with 13L of water, which is about what I usually mash with, it was much better at keeping the temperature to within 1.5°C of the target, as it reads it and my unit reads about 0.5°C higher than my thermapen which is apparently certified.

I think that the way to use this is to set it to 1°C below the target temperature and check the water with another thermometer before using it.

[darkonnis]

Where abouts is the probe in the HLT? I'm calibrating a PID now (manually, yes, such fun.) and I find that too close to the element and it undershoots and takes a while longer to get on track (convection is so slow) at the top it overshoots by about 5c, somewhere in the middle seems to be the best bet thus far.

[Jeltz]

I tied it to a spoon as the curly wire was trying to lift itself out of the water. It was not awfully close to the element but its at the bottom of the HLT, it is the lag in registering which allows the over shooting as while its still registering the change its still heating, its not too bad though.