Help Identifying a Thermistor? (I have temps and Ohms)

[stevepeck1]

I have a heat pump water heater and the manufacturer has gone out of business. One of the thermistors in the system has failed. Fortunately there are TWO of these in the system and I have been able to test them with an ohmmeter at different temperatures. I'm trying to find a replacement.

Resistance was tested on a multimeter in the k Ohms setting as
32.1 @ 3 degrees Fahrenheit
14.0 @ 32 degrees Fahrenheit
5.14 @ 75 degrees Fahrenheit (ambient air)
3.62 @ 93 degrees Fahrenheit

It looks like this for what it's worth:
http://www.ebay.com/itm/252004457599

Can anyone help me identify what the actual thermistor I need to buy is based on these measurements?

 

[73's de Edd]

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Sir Steve . . . . .



Fully realizing that you are not Radio Shack . . .but you got answers ? . . . . . 'cause we gots questions.


Did the same units have any identifiable numbers on them ?, and I might assume that the SS housed units are like the BAY picture , but without that 'lebenteen foot cable.
Seems like from a design aspect, that they might just be using one for a variable ambient air reference temp IN the control electronics AREA, while the other is taking
heated water temp. Then two comparators in the control electronics feed heater switching action to the heating Calrods.

If the unit in the heat area has failed * , seems logical to use the other identical unit to swap with it and then use a generic 5K unit to be the "reference" unit in the housing.
The one in the heated water proximity is the one that has to experience the greatest heat swing, while the one in the control areas only has long time correction between
Summer and Winter temps . . . .OR ! . . . .not even that, if its being located within temperature controlled environs.

* Is it reading open circuit ?

Looking back to the Bay example if it mechanically will fit your specs, looks like its 5 K version would be the one.
Can't confirm the temp range of the cabling , nor do I know how its being mechanically mounted.

DEFINITELY can't grasp their pricing, unless they are NOS failure prone units ?

Standing by . . .


73's de Edd


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[stevepeck1]

There are no identifiable numbers on these. I have talked with an EE I am acquainted with and he believes that this may be a 5K J-Curve Thermistor of Standard Precision. (I laughed when he said that, too) These are for the compressor output and the coils. The other ones are for other purposes. one is for ambient. These are all over eBay in CHINA for under $1 shipped but the specs I find suggest that they are not exactly the right thermistor because my numbers (measured on the good one) aren't quite to these... more than several % off. Is there a "generic 5K" in a US source that has that plug on it?

 

[Alec_t]

Thermistors are generally specified by their resistance at 25C (= 77F), so your readings tie in with it being a 5k one.

 

[73's de Edd]

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Sir Steve . . . . .



But . . .but . .but . . .(stuttt tttt ttter) . . . . BUT . . .BUT . . . .BUT . . .. the manner of the your failed sensor's MOUNTING was not given and is it being in dry or wet (immersed) environs ?

Plus the failure mode of the sensor ( open circuited ? )

Tech Refrencing:

http://www.energy.ca.gov/reports/500-04-018/2004-05-21_500-04-018_A3.PDF
Sensor failure mode Adobe page 10.

Plus how long has this HPHW unit served you so far ?

Comparing the ambient temperature to the high end 145/155 temp of hot water, the Fenwall Curve 16 ( J ) seems to comes close enough, after all this is hot water heating, not photographic film developing, with any miss tracking deviation showing up at the VERY COLD end of the temp spectrum.

On the Fenwall brand . . . .Honeywell has enveloped them now, as their Sugar Daddy . . . . the only 5 K SS sheathed immersible thermistor pobe I found was this one :

http://nz.mouser.com/ProductDetail/...9lHW8MhPY70VUk75U/3NwkzmgOmwhyrPf4025mzrkMg==

You put on any extra wire length needed, plus your old connector.

As per the pricing of Amerikanski units compared to the original Further Eastern model.
If its easy access to change out, and considering that the original lasted you say 4-5 years, I would just buy a "cigar box" full of the E-bay offerings, they must have already sold their earlier 169 of them to SOMEONE ? (Flies by Night, Heated and Airless Conditioning . . . . . . Consortium. )


What say ye ?

73's de Edd



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