Sunday, 23 August 2015

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 2016-01-30: The video below shows how to perform the modification.

Update 2016-10-15: As shown in the video, 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.

17 comments:

  1. Hello there

    I added a 22K resistor to the ESC so the cutoff is around 6.6v.

    Thanks for the info! It really helps!

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    1. Thanks for reporting back! Glad to hear that this little info helped. It makes those Tamiya kit ESC so much more useful for sure.

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  2. Hi, do you have a step by step picture of soldering the resistor to the board? Can you show me how the resistor look like? Fyi I am new to rc world and electronic. My email is hadribakri@gmail.com

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    1. Hi! I made a video showing how to perform the modification: https://youtu.be/jgr4BSvf-uc
      It is also embedded above. Happy modding!

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  3. Hi Thanks for this mod but it didnt seem to work for me and I followed the video, but on the blog the wire is soldered to the measure but in the video its soldered just above C9 where you scraped the conformal coating off. My soldering and work seems ok and it all still works it just doesnt cut off. So am now using a lipo alarm. Should I have soldered the wire to the measure like in your pic ?

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    1. Hi Galvo, it does not matter weather you solder onto the resistor, or onto the area above C9. Originally I soldered on the resistor, but then I found out that the pad above C9 carries the same signal, but is easier to scrape and solder to.
      If your's doesn't work, could it be that you disabled low voltage cut-off in your ESC settings? Please refer to the ESC manual on how to check and re-enable it.

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  4. Hello, can I use a standard resistor? Like a cylindrical brown one. I soldered it but the esc now detects the batery as discharged and it is fully charged

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    1. Hi Aly,
      yes you can use a standard resistor, given you have enough space.

      If after the mod the battery is detected as empty then you may have a wrong resistor value. It should be 33 KOhms (color bands on the resistor: orange-orange-orange) or 27 KOhms (red-purple-orange).

      You could have also accidentally created a short circuit to ground somewhere, or the resistor between "Vbatt" and "measure" (refer to picture in my blog post) may be dislodged or damaged. Use a multimeter to measure what voltage you see on the "measure" point. It should be 1.3V if the battery is 6.9V.

      Good luck with troubleshooting, Werner

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  5. Hi, Thanks for sharing this great tip. but I just want to make sure what size of smd resistor you used? This would help me to get right one. Cheers.

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    1. I used a 0805 size.
      0603 is fiddly to handle but would work too. There may be enough room to fit a 1206 but I haven't tried that.

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  6. Hi, Thanks for the great tip! Before I get this started, I just want to make sure the size of smd resister that you used. Thanks, Jangho.

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  7. Hi! great tutorial!
    I have one question: 4.9V are not enough? Other esc have the cutoff at 3.8V. I would use it with a 2S 5000mha battery.

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    1. Hi! A LiPo battery cell must not be discharged below 3.0V. So for a 2S pack, the pack must not go below 6.0V or you risk permanently damaging the battery. The damage can be perceived in form of bloat, rise of internal resistance, and loss in capacity.

      There is anyway no gain discharging below 3V per cell, as the energy remaining below 3V is extremely small.

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    2. Okay, thank you very much! Now I understand, I thought that the 3.0V was for the whole battery and not for each cell.

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  8. Do you know what resistor to use for 3.6v per cell? Thanks for taking the time to do all this for us! Thanks

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    1. Sure! For 3.6V per cell (7.2V cut-off) the resistor needs to be 16KOhm (not a standard value, you could put a 15KOhm and 1KOhm in series).
      Note that the restart voltage in that case would be 8.3V (i.e. once the voltage drops below 7.2V, it needs to go back above 8.3V to get the ESC to restart; power off/on restarts it as well of course)

      Closest standard resistor values: 18KOhm gives 6.96V, 15KOhm gives 7.38V.


      Technical info to make your own calculation: The voltage is measured with a simple voltage divider. There is a 33KOhm resistor R1 on the "top" (towards the battery voltage, and a 10KOhm resistor R2 at the "bottom" to Ground (where the MCU measures).

      The MCU cuts off when the voltage across R2 goes below 1.135V. The ESC restarts when the voltage goes back up above 1.305V.

      To increase the cut-off voltage, we need to decrease the R2 resistor value. We do that by adding another resistor in parallel.

      cut_off_voltage = 1.135V * (R1 + R2) / R2

      We can calculate the needed R2 for the desired cut-off voltage (R1 remains 33KOhm), and then find a suitable value resistor to parallel the existing 10KOhm to obtain the desired R2 value.

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    2. Have a 16k SMD resistor coming from ebay item 331913215194. Looking forward to either ruining the ESC or saving me from buying a Castle SV3 :-). Thanks again.

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