# Sensor scraped from a pc battery pack

I scraped some battery cells off two old pc battery packs. In both packs there were a sensor but I can't figure out what kind of sensor it is. Can someone explain what kind of sensor these are? I have of course tried googling the number on the sensors, but nothing shows up. If possible do you know what the number indicates? Is it a serial number or does it indicate an operating voltage or other info on the sensor?

Usually it's a 10K ohm thermistor.

$\beta_{25/85}$ perhaps 4100. The Steinhart-Hart equation can be used to find the temperature from the resistance.

Where $T_0$ is 298.15 K (25°C) and T is in Kelvin.

• I can be even more precise: it's a JEITA compliant NTC, which means it's 10kohm at 25 degrees and $\beta_{25/85}$ is 3500K. See for instance this datasheet: farnell.com/datasheets/1752258.pdf, page 29 bottom for how this is designed into battery packs. – user36129 Jul 2 '14 at 14:52
• @user36129 The JEITA specification does not appear to call out any particular beta, only the temperatures. There are battery monitor thermistor with beta 3380, 3577, 3940, 4100 and the number varies a bit depending on the two temperatures its specified at. – Spehro Pefhany Jul 2 '14 at 15:38
• @user36129 Do you know that the beta is 3500 from the datasheet? I can't find a way to calculate that from the datasheet – Attaque Jul 2 '14 at 20:31
• @SpehroPefhany Is there a way i can calculate beta then? Maybe with a voltage measurement in arduino and calculating backwards to find beta? Or will this be too unpredictable? – Attaque Jul 2 '14 at 20:34
• Since we couldn't really agree on what the beta value was, I decided to make some measurements and calculate the temperature using a,b and c parameters. My regular temperature meter shows 28 degrees and with Arduino and the temperature sensor I'm measuring 28.23, so it works pretty well :) – Attaque Jul 3 '14 at 0:23

Those look like temperature probe/ Thermistor.

They need to keep track of the temperature of the cells to optimize charging, and shutoff the battery if it is over a certain temperature.

• Thank you! Actually did google for thermistor, but didn't find any pictures that resembled those. – Attaque Jul 2 '14 at 14:40
• Mostly because thermistors vary widely in application, with battery monitoring being on the small end of the spectrum. It is mostly done to reduce space/weight. – Jeff Wurz Jul 2 '14 at 15:57