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I've been doing a lot of reading on different motion control approaches both for hardwire industrial motion, as well as EV applications.

While I've skimmed a few IEEE papers that sought to study the effects of regen braking on lithium-ion batteries as it impact battery capacity retention (cycles) they seemed somewhat inconclusive. This also only examines the common LiIon chemistry but doesn't even address other popular lithium-containing chemistries like LiFePo4 or NMC. I'm no chemist.

At a much smaller scale, we see use of NiCad and SLA batteries that are robust to being charged in a "don't care" fashion. However, lithium cells tend to be a bit more picky when it comes to being charged. Negating the aspect about total cell cycle degradation for a moment--what about safety when it comes to regen braking lithium-based cells?

Assuming the cell is sitting behind some basic controller--what happens to back-EMF from a large (200W+) motor if the cell is "fully" charged and the BMS shuts off the back-EMF transient? We know it will generate heat..but does that heat stay in the motor? Or are we talking about dissipation into the motor's bus/wiring? Should high-power (EV) motors powered by lithium chemistry employ shunt regulators if extending battery life by regen braking is not necessary? (Thinking more about industrial robots rather than EVs).

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  • \$\begingroup\$ You are right - you need to be very careful - the energy from the motor (in the form of current) can feed into the lithium battery if you are not careful about the circuit design. \$\endgroup\$
    – Andy aka
    Commented Jan 20, 2021 at 18:41
  • \$\begingroup\$ Tip: chemical elements have their symbols capitalised but are lowercase when spelled out. See aje.com/arc/editing-tip-capitalization-chemical-compounds/…). for more. \$\endgroup\$
    – Transistor
    Commented Jan 20, 2021 at 18:43
  • \$\begingroup\$ You can always have a mix of battery technologies with different capacitances, e.g. a large lithium based battery for range, and something more tolerant with charge/discharge cycles for short bursts when accelerating and braking. The battery management system would first charge the buffer during regenerative braking, and only start charging the lithium cells as the buffer fills up (e.g. because you're going downhill for an extended time). \$\endgroup\$ Commented Jan 20, 2021 at 18:44
  • \$\begingroup\$ Yes, thank you. I do see that as a concern. The information I am missing is: what is the commonplace standard for safe operation of high powered motors and lithium based chemistries? A charge-controller--yes. But does this then imply, all motion-based applications also must have a means of shunting/braking in the event the pack is at max-potential? \$\endgroup\$
    – Matt001
    Commented Jan 20, 2021 at 18:45
  • \$\begingroup\$ Braking is mechanical only if the pack is full. You get less braking force, but still more than you have traction on the road (so there is no difference in handling), and the energy is dumped into the brake pads. \$\endgroup\$ Commented Jan 20, 2021 at 18:47

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Assuming the cell is sitting behind some basic controller--what happens to back-EMF from a large (200W+) motor if the cell is "fully" charged and the BMS shuts off the back-EMF transient?

200W for an electric vehicle is rather small, if not to say microscopic. A Nissan Leaf from 2010, if I'm not mistaken a relatively small commercial EV, has around 80 kW, i.e. the 400-fold in power.

You're right, there's a controller, and a bidirectional AC/DC converter between motor(s) and battery(ies).

That converter's job on recuperation is to rectify the voltage from the batteries; since its bidirectional nature requires this rectification to be synchronous, the controller will also control the duty cycle with which that happens, and hence the voltage on the DC and thus the charging current

In case you brake with a full battery, only little energy will be allowed to flow through that converter; most will either simply left in the AC circuitry (i.e. like disconnecting the motor) or sunk into a resistor.

If you need the decelleration, then the converter will instead of charging discharge the battery to cause a current opposing to that which the turning of the motor causes.

For street-legal western EVs (i.e. not golf carts or similar), you underestimate the amount of cost that flows into the control and build of the converters. These things don't "blindly" let power flow between motor and battery.

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  • \$\begingroup\$ Indeed--I am mainly thinking of the small-medium scale (or "gray area") at the moment such as personal "vehicles" (scooters/bicycles etc.). I am trying to think-through edge cases. E.g. What would happen to an electric bicycle, with a fully charged pack, if you began your trip at the top of a big hill and coasted all the way down? Where is that energy going? If the motor is "disconnected" you would expect some resistance from the axial-inline motor as it opposes your travel, correct? \$\endgroup\$
    – Matt001
    Commented Jan 20, 2021 at 18:52
  • \$\begingroup\$ yes, but much less than if these motors would be used to charge anything. \$\endgroup\$ Commented Jan 20, 2021 at 18:58

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