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Discussion Starter · #21 ·
Re: Tesla 3 Battery Thermistor Spec

I know the output of my heating system will be warmer. What I still need to know is:

a) which is the better battery fluid line to use for inlet - or does it even make a difference? It certainly does for automotive radiators, but that is because they are mounted vertically. My batteries are horizontal.

b) which thermistor is closest to which inlet? I need this info because I want to use the exit temperature. The thermistor with the yellow wires is closest to the negative battery terminal, but this does not necessarily means it is closest within internal fluid flow to the opposite fluid inlet tube. I don't know the battery plumbing.

In my RV coach application, there will be negligible battery heating. I am more concerned about very low ambient temperature. No mechanism is provided for battery cooling.
 

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Discussion Starter · #24 ·
Re: Tesla 3 Battery Thermistor Spec

THANK YOU KennyBobby! This picture makes perfect sense. I now know the "lower" thermistor will be nearest the "lower" fluid inlet tube. I will feed the heated fluid into the lower tube, and measure the exiting fluid temperature from the upper.
 

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TLDR: The B value is about 4300, A better value is likely a 4365.

This thread is long dead, but considering this is the first google search result for "Tesla Battery Thermistor Parameters", I figured this would be the ideal place for this.

I have the 'Tesla Smart Battery' used in the Mercedes Benz B Class.
They're different from what most people here are using, but I don't see why Tesla would have used different thermistors, especially considering the design of the batteries are nearly identical.

While not super robust, I used a calibrated temperature probe, and measured the thermistor temperature over a range of temperatures. I weighted the values based on the difference between both thermistors on the module (2 values close together indicates that the system is at a temperature equilibrium and my probe is probably measuring very accurately).
There were some temperature values, such as while heating up quickly, or cooling down quickly, that are consistently moving with the same slope of the line, but are off because of that 'temperature equilibrium' I referred to.



After exploring various thermistors online, I found this standard NTC thermistor that appears to match all the characteristics the best:
Thermistor 4365K on Mouser
Meaning the value would be 4365.

I wrote a Matlab script to do the curve-fitting, if you want it feel free to PM me, but if you want to do a real basic version of this, this SRS Thermistor Calculator is very good:
SRS Thermistor Calculator

 
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