Temperature Sensor for Trace & Xantrex Solar Charge Controllers
The Xantex/Trace C-series charge controllers are some of the finest controllers on the market. Charge controllers are essential in solar and wind energy systems that charge lead acid batteries. The controller's role is to charge the batteries at their optimum rate and to keep them from over charging.
The C-series controllers (C-12, C-35, C-40, and C-60) can compensate for temperature variations if you add the optional BTS Battery Temperature Sensor. With temperature compensation, the controller can optimize the charge voltage, boosting it slightly if the batteries are cold and lowering it if the batteries are warm.
The Xantrex BTS sells for about $35.
There is a less expensive alternative. The Homebrew Temperature Sensor shown in the photo below is made by me using a 100Kohm thermistor that matches the characteristics of the Xantrex BTS. My temperature sensor costs $12.
The temperature sensor is encased with silicone in a polyethylene sleeve and then coated with thick vinyl plastic to ensure rugged resistance to the elements. The cable is about 3 feet long and the RJ11 connector is pin-compatible with the Xantrex BTS so all you have to do is plug it in to the socket on the charge controller and it works. If you need a longer cable, you can extend it with a regular 4-conductor telephone extension cable.
People have asked if this temperature probe will work with other charge controllers. The answer is generally no because each manufacturer designs to different specifications. According to the Xantrex web site, the Xantrex BTS will work with the DR and UX inverters as well as the C-Series charge controllers, so it is safe to say my temperature sensor will also work with these models. I have only actually tested it with my C-40 charge controller. With that unit, my batteries charge exactly as they should given their temperature.
If you own one of the Xantrex or Trace products that uses the BTS, or if you need a temperature sensor for your own electronics project, here is your chance to get one at a reasonable price.
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Homebrew Temperature Sensor with detailed electrical and product description U.S. $12
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How is this unit applied, does it lay on the side of the battery?? HOW
Thanks, John for your question. In my battery array, I just pushed the red
sensor down between two of my batteries. You could also affix it to the
side of a battery using duct tape or electrical tape. What you want to do
is just get the sensor in the vicinity of the batteries so it will register
the ambient temperature of the compartment that holds the batteries. Hope
this helps.
Hi:
I was wondering how you attach the sensor to the battery. Most of the ones
I have seen, bolt to the lug of the battery. How about this one?
Please advise.
Thanks.
Hi: Additional comments;;;;;;
I was wondering how you attach the sensor to the battery. Most of the ones
I have seen, bolt to the lug of the battery. How about this one?
Please advise.
I was under the impression that the purpose of the sensor was to monitor
the heat caused by charging and to allow the controller to reduce the
amount of charge when needed. If it has to wait for the ambient
temperature to be recorded, doesn't that harm the batteries? Just
wondering
Thanks.
Jon, you raise some very interesting questions. The short answer is ambient
temperature is a bigger concern than internal heat caused by charging, and
therefore, it is not absolutely necessary to thermally clamp the sensor
onto the battery. Ambient temperature is good enough for solar charging
applications. You are correct that the chemical reaction inside the battery
during charging is exothermic (i.e. it gives off heat). This process,
however, is spread out over a relatively long period of time so the heat
generated is easily radiated out. Of greater concern is the ambient
temperature, particularly if the battery is located in a place that
experiences large fluctuations. Most battery specifications are determined
at a temperature of about 85 degrees F. If it is colder than that, battery
capacity is reduced and a greater rate of charge and float voltage may be
applied to compensate. The reverse is true in warmer temperatures. The
probe senses temperature and the Xantrex controller responds accordingly. I
will refer you to the article titled, Basic Chemistry of Gas Recombination
in Lead Acid Batteries, for more information on this topic. You will find a
link to it in the "Go to link blog" bookmark found in the left gutter.
Finally, if internally generated heat is still a concern for you based upon
your specific application, the homebrew sensor may be affixed to the side
of a battery using duct tape or some other type of adhesive. In comparison,
the Xantrex BTS may optionally be affixed to a battery using pressure
sensitive material. The end result will be about the same for both units.
Thanks for your questions.
Dear Tom,