Hi everyone.
I plan to use a 11.1V 3s Li-poly RC battery to power a robotics project. The battery is 30C and 2800 mah. Such batteries are commonly used in drones with ESC (electronic speed controllers) which provide protection for overdischarging and limit current as well.
In my robotics project, I am using servo motors. So, I cannot use ESC. I am using a buck convertor to provide me with constant 6V. The buck convertor has a rating of 10A. I am facing two challenges;

1. How to avoid going below minimun voltage of the battery as buck concvertor cannot handle it. I can use micro-controller as well but it will keep the whole system on all the time.
2. How to provide protection in case of short circuit.

The battery is similar to the one provided in the link below. It has a connector for power supply and a four pin connector for battery charging and cell balancing. I am using a IMAX B3 charger for charging it which provides cell balancing.

To hangle the above issues, I want to use a 3s BMS with a current rating of 20A. This will provide me with over dischaging protecting and current protection while I can remove battery and charge it with IMAX charger out of the device for safety. However, 3s BMS has B1 and B2 connections in except for B+ and B- and it will make it complicated and difficult to provide B1 and B2 connections to the BMS.

My questions are:

1. Will my approach work?
2. Is it okay to use 3s BMS without connecting B1 and B2 for above purposes?
3. Can you suggest better approaches to the problem like using fuses etc.

Regards
Muhammad Hamza Shafique


Battery:
https://www.auselectronicsdirect.com.au/11.1v-5000mah-lipo-3s-battery-pack-with-traxxas-co
Charger:
https://electrobes.com/product/imax-b3-lipo-battery-balance-compact-charger-for-rc-quadcopter/
BMS:
https://www.aliexpress.com/i/32809110553.html

 

Please supply the "Locked-Rotor", or "Stalled", Motor-Current for your Servos,
and the Maximum-Voltage that your Servos are designed to operate with,
for a more comprehensive response to your question.
( I'm guessing that it's 5-Volts, and around 1-Amp, but there are thousands of different kinds of Servos ).

My approach would be to install a separate 2S Battery, just for the Servo(s),
followed by a LDO, ( low-drop-out-V ), Linear-Voltage-Regulator for EACH Servo.

This "Servo-Battery" should be sized such that the Main-Traction-Motor-Battery
will run dead way before the Servo-Battery runs-dead,
this way You don't have to be concerned about "Low-Voltage-Damage" to the Battery.

Recharge the Servo-Battery EVERY TIME the Traction-Motor-Battery is charged.

The LDO-Linear-Regulator(s) will act as individual Current-Limiter(s).
This function is built-in to the Regulator(s) by the manufacturer.

Buy the Regulators from a reputable supplier
like DigiKey, or Mouser, or RS, etc, NOT Ebay or Amazon, or Alibaba .
This will eliminate aggravations with the very real problem of counterfeit Components.

If You are worried about direct Short-Circuiting,
improve your Wiring practices in such a way that Shorts are extremely unlikely to occur.

You will need a Linear-Regulator for each Servo,
( Bonus #1, they're dirt-cheap and very simple to implement ).
They will require mounting to an Aluminum-Panel or an Aluminum-Box,
or maybe even a "real" Aluminum-Fined-Heat-Sink, for Heat-Dissipation.
( the exact requirements will be determined when the Specs of the Servo(s) are known )

Additional Bonus #2 ........
You won't have any problems with RF-Noise from the Buck-Converter causing
Remote-Control-RF-Signal interference.

Additional Bonus #3 ........
The Servos will provide very consistent performance
regardless of the Loads placed on the Traction-Motor(s), or any other individual Servo-Motor.
.
.
.