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I am working on an electric vehicle as a personal side project (a couch) and it is driven by 4 BLDC hoverboard motors and using aftermarket 3 Phase Motor Controllers. The couch is powered by a 2P6S 18650 battery pack with a 40 amp BMS works perfectly fine.

When the couch is pushed while unpowered, the motors generate about 36 volts on the power input lines. I currently have a diode to prevent reverse voltage into my BMS (35 volts on a 24 volt system seems like a bad idea.) I would love to know if I could use a buck converter to turn the about 36 volts into 24 volts that I could feed back into the BMS while the motors aren't being powered.

I could whip up some smart circuitry to detect when the couch is rolling and when it is powered and then open or close MOSFET gates to redirect the power as needed. However I wanted to see if this schematic holds any water.

schematic_for_regen_braking

It would use a buck converter with a diode on the output to only allow power into the battery. However I worry that the battery power would just freely enter the buck converter and then go back into itself, possibly creating a weird loop of wasted energy.

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  • \$\begingroup\$ Does the BMS allow the 2P6S battery pack to be safely recharged during regenerative braking? \$\endgroup\$ Commented Nov 16 at 8:10
  • \$\begingroup\$ I imagine that it does. It charges and discharges from the same two pads. amazon.com/dp/B0B7DT83CS?ref=ppx_yo2ov_dt_b_fed_asin_title . I would think that if no power is leaving it, it would be free to have power fed into it \$\endgroup\$ Commented Nov 16 at 8:24
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    \$\begingroup\$ Buying stuff from Amazon means you have no schematics, no assurance of quality or country of origin, no support or help route and very little provenance. Basically nothing that answers whether this can be done. On the other hand, if you bought stuff from a reputable supplier you would be able to get all these things. \$\endgroup\$ Commented Nov 16 at 10:40

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It looks like you do not know so much about electronic systems, but I want to give you an answer which could be useful for you.

No, regenerative braking/charging is not possible in a way you think it could work.

What you do first, to understand how things work is to build a simple regenerative braking system.

  1. You use diodes to make DC from the AC what you get from a BLDC motor.
  2. You charge a capacitor with this energy during you move your vehicle. Measure the voltage, the maximum what you can get.
  3. Apply a useful load, like a big resistor (use different values) or a 100W LED in line to this resistor to make the output power visible.

Here is a presentation with a nice circuit from microchip: https://ww1.microchip.com/downloads/en/devicedoc/regenerative%20braking%20of%20bldc%20motors.pdf

There is a reason why they are using a Boost-Converter, but to understand this, you have to do this little experiment.

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  • \$\begingroup\$ Wow thank you so much! I will set up a little bench test. The BLDCs do generate a DC current (leaving the motor controller, they obviously create a 3 phase sine wave directly from the hub motor but the board somehow powers the board and then the board regulates the output.) \$\endgroup\$ Commented Nov 17 at 8:57

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