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Ok. I tried a pipe stat on the 22mm hot water supply to the current bathroom job. Idea being it was a quick and basic means of detecting heat ( eg someone running the bath / shower / basin ) so that would bring on the large mirror demister pad. Crap hysteresis and pretty unreliable.

Question....

How much additional electronics are involved to just make the cable off to a thermistor instead and have that operate a solid state relay / similar to control the demister ? Can I get a 230v thermistor to save going low voltage DC control and the associated electronics etc as this needs to be left behind for the customer and not rocket science to repair / maintain ?

Thanks in advance. :S

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A thermistor is basically a resistor who's resistance varies with temperature. However the change in resistance is modest so you need a circuit that turns it into an on/off signal. This is usually done by a comparator that compares the resistance of the thermistor with that of an adjustable resistor. When one is greater/lower than the other it switches the output on/off.

 

There are probably circuits on the web or modules on eBay/napkin that will do this.

 

Some Heatmiser room stats have an optional external sensor mode but they only cover a narrow temperature range as you don't usually want to set a room to say >30C.

 

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Cheap simple and accurate try something like Ebay item 1688573745, I use one to control a circ fan on top of a rad and it's been seamless for a couple of years. Pay a few quid more for a UK vendor if you're in a rush 112079287480.

 

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Thanks all. :)

 

5 hours ago, dpmiller said:

Cheap simple and accurate try something like Ebay item 1688573745, I use one to control a circ fan on top of a rad and it's been seamless for a couple of years. Pay a few quid more for a UK vendor if you're in a rush 112079287480.

 

For the price, you can't go wrong. 

Its a bit over complicated for what I need but if it's only set it up once and forget then happy days. 

Questions...

@Onoff. The one you linked is the most simple and 'fit for purpose', just 3 times the price of the one @dpmiller linked. Does anyone know how these two items will respond to a power cut? My fear is the cheaper eBay one may need buttons pressing for it to go back into temp sensing 'mode' which will be a right pita. 

Anyone able to confirm / deny with either unit please? This will be in an enclosure in kick space in the walk in wardrobe, so not something I want the customer to have to do anything with ( ideally ). 

Cheers.  

 

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Ive emailed Cebek's tech department to ask what happens in a power cut with the I-108 module. I'd suspect it carries on as before as the potentiometer sets the threshhold.

 

The I-108 comes c/w probe:

 

i-108.pdf

Edited by Onoff
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the wee one from Ebay doesn't care- temperature is hard set using dip switches.

 

edit- crap! just realised I'd posted the wrong item, I'd composed a post offfering the digital one as well and deleted the wrong list sorry.

 

try this:

http://www.ebay.co.uk/itm/DC-12V-Heat-Cool-Temp-Thermostat-Temperature-Control-Switch-Thermometer-20-90-C-/282297684188?epid=1131968094&hash=item41ba40d0dc:g:RkcAAOSwDN1UPOpM

 

Edited by dpmiller
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Had a look at the I-108 data and is says it needs a 10KOhm NTC thermistor. Think that's same as Heatmiser stats. Annoyingly Maplin don't seem to stock them (strange).

 

Rapid have

 

Probes..

https://www.rapidonline.com/atc-semitec-103at-11-ip67-10k-precision-ntc-thermistor-probe-with-600mm-lead-61-2040

https://www.rapidonline.com/atc-semitec-103at-11-50081-ip67-10k-ntc-thermistor-probe-with-1500mm-lead-61-2041

 

Bare thermistors..

https://www.rapidonline.com/tks-dht0a103f34d3sy-10k-3435k-1-axial-glass-ntc-thermistor-55-1229

https://www.rapidonline.com/tks-ttc05103jsy-10k-5-radial-straight-lead-ntc-thermistor-55-1259

 

Film..

https://www.rapidonline.com/tks-ttf3a103f34d3ay-10k-1-insulation-film-type-ntc-thermistor-55-1265

 

Think any would probably work just a case of ease of mounting and response time.

Edited by Temp
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48 minutes ago, Onoff said:

There's an RS Components in Pontypridd. Should have a selection of 10K thermistors:

 

https://uk.rs-online.com/mobile/search.html?searchTerm=Thermistor+10k

 

Stick your multimeter probes across the thermistor to measure it's resistance.

 

Where are you working/easy to get to? Swansea is it?

Yes, Swansea. 

image.jpg

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41 minutes ago, Onoff said:

Would decent pvc tape last to attach it? As in would it go brittle?

Maybe, yes. Just a thought. Maybe better to bond it for heatvteansfer, and use the pvc tape to hold it until the bond has cured ?  

How's that 12 ohms ( taken @18oC ambient ). I'd really like to just whack that in right now as it's stopping me plasterboarding. ?

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21 minutes ago, Nickfromwales said:

Yes, Swansea. 

image.jpg

 

I that ohms or k.ohms?

 

If a 10K one there, in a room slightly below ambient you'd get a higher value. A cleverer person will be along shortly!

 

EDIT: Ohms I think from zooming in?

 

EDIT 2: I'm an IDIOT, just read you said it's ohms! :ph34r:

 

So that's pretty low, does it make it a PTC thermistor? If so, no good as you want NTC,

Edited by Onoff
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Just back from searching a wheat field in 27 degree heat for the Samsung one of my kids dropped on a sponsored walk so just a bit knackered but...

 

3 hours ago, Nickfromwales said:

What about the thermistor that's in with my multimeter for the temp range? Can I nick that and use it just to save any delays? If I can that would be the jam in my jelly roll :)  . 

 

Not sure what that is. Perhaps a thermocouple rather than a thermistor? Differently beasts.

 

If you are going to use the I-108 it needs to be 10k not 15k or the temperature settings will be around 20C out. It might be possible to change a resistor or two on the I-108 to correct for this but the data sheet doesn't have a circuit diagram.   

Edited by Temp
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