Identify thermistor 1.7A / 20% / 82E

[gkmaia]

I need help to confirm a thermistor. It does not have markings and as per service manual is should a 1.7A / 20% / 82E

the thing I need help with is the last bit. Is it 82ohms @25ºC?

[fzabkar]

It would appear that you are correct:

http://electronicsunlimited.in/EU/images/EUD%205%20-%20Reistance%20to%20Temperature%20charts.pdf

[gkmaia]

Awesome!! thanks!!

[gkmaia]

Sorry got another question. How do i convert it's power rating?

DUT needs 1.7A and the datasheet for the replacement talks about 2.1W

As it sits after the mains rectifiers it will take 220AC*1.41 = 310VDC.

But 310VDC at 82OHM will take 1KWatt or 3.7Amps... confusing as it is quite a lot.

https://docs.rs-online.com/8e5f/0900766b816e727e.pdf

[fzabkar]

I'm embarrassed to say that I have never thought too much about NTC resistor ratings. However, it would appear that the I2R rating of 2.1W is derived from Imax and Rmin at an ambient temperature of 25C. You can work through the numbers on page 3.

For example, for Imax = 6A and Rmin = 0.057 ohm …

P = I x I x R = 6 x 6 x 0.057 = 2.05W

Simply speaking, because you have an NTC thermistor, its resistance falls substantially due to ohmic self heating. In other words, the rated resistance of 82 ohms only applies when I = 0, ie no self heating.

[gkmaia]

Cool, thanks mate. I also found the original datasheet!

https://www.casa.co.nz/resistors/nonlinear/Philips-NLR-Data-1977_29x~yp.pdf