Tamiya TBLE-02S mod for LiPo cut-off

In 2014 Tamiya changed their kit ESC to the TBLE-02S model. The speed controller features a low-voltage cut-off function, but it is set to 4.9V -- much too low for LiPo batteries that most RC enthusiasts use nowadays.

However, by adding a single resistor we can modify the cut-off voltage to a LiPo-safe 6.0V or 6.3V.

(Click on image to enlarge)

WARNING: This and other DIY projects are purely "at your own risk". If you are at all uncomfortable or inexperienced working with electronics, please reconsider doing the job yourself.

In the picture above you can see the modified TBLE-02S. Below the micro-controller in the left-top corner is a string of three resistors. The two right-most resistors form the voltage divider that reduces the battery voltage to a range that the micro-controller can measure.

The right-most resistor measures 33 kOhm; its right terminal connects directly to the battery terminal of the ESC. The left resistor measures 10 kOhm and its left terminal connects to ground. The resistors are connected together, so they form a voltage divider. The center tap of the voltage divider connects to an ADC (Analog to Digital Converter) input of the micro-controller, and the software performs the actual cut-off.

By default the cut-off voltage is 4.9V. In order to raise this voltage, we have to either increase the 33 kOhm resistor, or reduce the 10 kOhm resistor. It is generally speaking easier to reduce the resistor value of the bottom resistor (the 10 kOhm in our case) in the voltage divider, as we can simply put another resistor in parallel.

To get a cut-off voltage of 6V, we can add a 33 kOhm resistor in parallel to the 10 kOhm resistor. Some people don't like to discharge their batteries all the way down to 6V; by using a 27 kOhm resistor in parallel to the existing 10 kOhm resistor they can achieve a cut-off voltage of 6.3V.

Since the original 10 kOhm resistor in the ESC goes towards ground, we can mount our new 33 kOhm parallel resistor anywhere where ground is easily accessible. On the top of the PCB, just right of the micro-controller, is a ground test pin marked "G" (not visible in the photo as the resistor we added covers the label) that we can use.

Note that the circuit board has been conformally coated; you need to scrape off the coating before you can apply solder. A lot of care has to be taken when soldering to one of the existing resistors.

Once the new 33 kOhm resistor has been soldered onto the ground point, we can run a very thin wire between the voltage divider center tap and our newly added resistor.

That's it; all done! It is actually easier than it was to modify the TEU-104BK.

Depending on your soldering skills it does not take more than 10 minutes to modify the ESC. With the modification the ESC shuts off at just the right time when your LiPo batteries deplete.

One word of warning when disassembling the TBLE-02S: the case holds a tiny pin that pressed onto the push-button. This pin can easily fall out when the circuit board is removed from the housing. Don't lose it...

Update 2016-10-15:The highlighted position in the photo below (click on the image to enlarge) is easier to solder the wire to. The highlighted pad connects to the resistors above.