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Need some assistance. I am not sure if this is the correct forum.

I have an OverDrive JLX RC vehicle. The original battery is 12V 800mAh and I am unable to find these batteries anywhere. I decided to make a 3S battery pack from 18650 cells with a 10A battery management system (BMS) board. The pack charges fine and when connected to the RC vehicle it runs fine, however the 18650 3S pack gets really warm and the wires get really hot.

I can't seem to find the specification for this toy so I am unable to tell what is the current draw of the motors. I assume it's getting hot because it is being discharged too quickly? Would adding a resistor suffice as current limiting, and if so, how would one calculate the value without knowing the current draw of the motors?

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  • \$\begingroup\$ Hi and welcome to SE. Let's add more info to help get your question get more attention. Do you know what chemistry (NiMh, Li-Pol, etc.) was your original battery? Any more info (photo, datasheet, or part number) available for your BMS system? It may help us see if it tries to protect the batteries from overcurrent which sounds like is the core of your issue. What is thickness of your wires? Are the original wires hot, or the ones installed by yourself? Can you estimate the temperature? (Too hot to touch?) In the meantime, be careful, hot batteries may be a fire/explosion hazard. \$\endgroup\$
    – akwky
    Jun 9 '20 at 10:52
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Current is a measure of motor torque load.

Power times thermal resistant causes temp rise is due to excessive current squared times resistance where Pd=I²R for R= ESR (equiv series R) that occurs in all batteries.

Current can be limited by controlling acceleration and thus force. Adding resistance might also but increases losses.

Better quality cells will have lower ESR higher mA and higher C charge ratings.

Your choice.

https://www.18650batterystore.com/18650-Batteries-s/106.htm

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