I finally got around to the job of adding a remote temperature sensor to the Tracer 4210rn 40 amp MPPT charge controller. It didn't all work out as planned, but in the end it'll be worth it.
^ Here we have a picture of the Tracer 4210rn. As you can, it has a front mounted temperature sensor. This would work acceptably if the charge controller were located next to the batteries. This is not the case for mine.
To open the cover on the charge controller, 8 little screws need to be removed; 4 on one end and 4 on the other. The cover easily pulls off.
Now the thermistor is exposed (temperature sensor). It looks like a small, dark LED to the right of the actual LEDs. Hhere is where I had a problem. The thermistor sits on top of a little black pedestal. The leads for the thermistor are about 1/2" long, but they go through the pedestal. I tried to crush and break the black pedestal off, but ended up damaging the thermistor as well. Oops! Whatever.. moving on.
With the thermistor damaged I had no problem cutting the leads near the top and removing both the thermistor and the pedestal. After doing so there were two nice little leads to solder a length of wire to. This was trivial. Don't forget the heat shrink!
After that was all done up I grabbed the hot glue gun and secured the leads and wires to the circuit board so I don't accidentally break the leads. After that I made a knot in the wires (with some hot glue to hold it together); drilled a hole in the side of the cover; pulled the wires through; tested the continuity of the wires; and screwed the cover back on. Now it looks like this:
Ok, so I now have reasonably long leads. What should I put on the end? To determine this took some probing.
My brother and I grabbed a multimeter and a high-accuracy potentiometer. We set resistance values and watched the temperature value on the charge controller's display. We then used a really nice Steinhart-Hart thermistor calculator at SRS Thermistor Calculator
to determine the R(25°C) value. Here's what we found out:
So I ordered a couple thermistors. Some with an R(25°C) rating of 47KΩ and some at 50KΩ. I was hoping for one at 40KΩ or 43KΩ, but could only find them in bulk packaging (500 minimum order). I'm sure one of the ones I ordered will be acceptable.
Once they arrive I will adhere the most accurate one to a plate of aluminium with thermal glue and secure it to the side of the battery for a good temperature reading. What fun!