Author Topic: Thermistor value in Schlage/Trane thermostat?  (Read 5285 times)

Offline robinnes

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Thermistor value in Schlage/Trane thermostat?
« on: April 15, 2011, 11:11:32 am »
Have the common TZEMT043AB32MAA Schlage/Trane Z-Wave thermostat that many people use here.

Pulled the thermistor from the thermostat's PCB and attached it to 20' UTP remote leads to suite my needs. Works fine, calibration is still good according to two independent digital thermometers at the now "remote probe" location. So all is good, the T-stat and remote probe work fine- that part's done!

Thinking ahead, I want to order a spare thermistor in case/when I want to return this t-stat to normal service with thermistor soldered back onto the main PCB.
The OEM thermistor is extremely delicate with frail leads and I don't think it will survive another solder session so I'm looking to source a replacement thermistor.
When I removed it from the PCB I attached it to my DVM and it returned a value of around 8.7K Ohms, IIRC the room was in the mid 70's F but I was handling the thermistor at the time so that may have some effect on the reading. Found a chart online for a 10K Ohm thermistor  (http://www.alliedelec.com/Images/Products/Datasheets/BM/GE_INFRASTRUCTURE_SENSING/239-0005.PDF) that would seem to put the 10K thermistor in the right ballpark for this resistance versus a mid 70's F temperature. Here's the replacement thermistor that seems to be a good candidate for an OEM replacement: http://www.alliedelec.com/search/productdetail.aspx?SKU=2390005

Any comments or suggestions as to if this would be the correct thermistor to use for a replacement?

Thanks!!

Offline oTi@

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Re: Thermistor value in Schlage/Trane thermostat?
« Reply #1 on: April 15, 2011, 11:38:38 am »
I believe I've seen the spec for the outdoor sensors for the RCS TZ43 somewhere. You could try looking for that. Might be the same. Perhaps you can even use one of those sensors as is, for your application?
Dezwaved at the moment...

Offline JOD

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Re: Thermistor value in Schlage/Trane thermostat?
« Reply #2 on: April 15, 2011, 11:59:09 am »
I have one of the RCS TZ43 with the dual remote sensors. It's identical to the Trane (except the firmware sub-base and 4 extra pins on the T-stat)
I'll ohm out one of the remote sensors tonight and post back.

JOD.
I'm sorry, my responses are limited. You must ask the right questions.

Offline robinnes

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Re: Thermistor value in Schlage/Trane thermostat?
« Reply #3 on: April 15, 2011, 12:12:46 pm »
I have one of the RCS TZ43 with the dual remote sensors. It's identical to the Trane (except the firmware sub-base and 4 extra pins on the T-stat)
I'll ohm out one of the remote sensors tonight and post back.

JOD.
Thanks very much, if you don't mind- note the room temp when you take the reading too.
Cheers!

EDIT- no need to check your sensor JOD.
oTi@ suggested I search for the RCS TZ43 manual which did indeed list the spec for the sensor... thanks again for the offer of assistance!
« Last Edit: April 15, 2011, 12:52:50 pm by robinnes »

Offline robinnes

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Re: Thermistor value in Schlage/Trane thermostat?
« Reply #4 on: April 15, 2011, 12:49:28 pm »
I believe I've seen the spec for the outdoor sensors for the RCS TZ43 somewhere. You could try looking for that. Might be the same. Perhaps you can even use one of those sensors as is, for your application?
Thanks for the cross-reference info!
Found the PDF for the RCS TZ43 (http://oldsite.rcstechnology.com/docs/thermostats/zwave/TZ43%20INSTALLATION%20MANUAL%20141-01652-04.pdf) and it states:
Remote sensors compatible with the TZ43 need to have the following characteristics:
10K NTC Thermistor.
Wire specification: 2 conductors, 22Ga twisted pair or Cat 3/5 wire, 100ft maximum length.

That's exactly the info I needed! A common 10K NTC thermistor $4.36 via alliedelec.com.

Thanks so much oTi@

Offline oTi@

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Re: Thermistor value in Schlage/Trane thermostat?
« Reply #5 on: April 15, 2011, 04:15:12 pm »
There you have it. That's indeed what I had seen before, and was impressed that this was specified.

Of course we're assuming the outdoor sensors are the same type as the internal one; but your empirical data seems to back that up.

Please do post back your result at some point; assuming you went ahead and ordered the part.
Dezwaved at the moment...

Offline robinnes

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Re: Thermistor value in Schlage/Trane thermostat?
« Reply #6 on: April 16, 2011, 09:07:29 am »
Please do post back your result at some point; assuming you went ahead and ordered the part.
Ordered two since the thermistor was as much as the shipping.
It should be here in a week, so I'll report back once it arrives and I test it.

Offline robinnes

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Re: Thermistor value in Schlage/Trane thermostat?
« Reply #7 on: July 27, 2011, 02:40:39 pm »
Was just reminded in another thread that I forgot to update this thread....oops.

The thermistor I ordered worked perfectly- I've been using it on the end of a 50'+ run of cat5 for over three months now.