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Motor driver planning
Selecting a motor driver to work with the Lithiumate Lite.

You can get a DC motor driver ("controller") or an AC one ("inverter").
The Lithiumate Lite will work with either one.

For pack voltages above 40 V, you need a motor driver that is isolated, meaning that the B- input (the negative of the battery pack) is not connected to the ground of the 12 V system.

Otherwise, there is a shock hazard.

Maybe, more than getting shocked, you may mind having a damaged controller.
Non isolated motor controllers are far more likely to be damaged if you accidentally short any cell terminal to chassis.
That can happen quite easily: the handle of a socket wrench that you use to tighten a bolt, may barely touch the EV's chassis, and you get a spark; then, when you try to drive off, you discover that the motor controller is fried.

So, regardless of the pack voltage, get an isolated motor controller.

Ideally, the motor driver must have an enable input, so that the BMS can shut it down it it needs to (to protect the battery).

However, even if there is no such input, there are other, indirect ways that you can wire the BMS to shut down the motor driver (such as by removing 12 V power from it).

Some motor drivers include the ability to regenerate electric energy when braking (inverters for AC motors always do that).

The Lithiumate Lite is compatible with regen.

Ideally, the motor driver must include a control input to disable just regen. That way, if the battery is already full, the BMS can disable the just the regen function, without having to disable the entire motor driver.

Newer, more powerful motor drivers have a CAN bus to enable them to be controller "by wire" instead of dedicated lines.

Most can be used either way. The Azure DMOC is the only one we are aware of that can only be controller by CAN bus.

The Lithiumate Lite does not have a CAN bus (the Lithiumate Pro does).

That doesn't mean that you cannot use a motor driver that has a CAN bus.
It just means that you need a motor driver that can be used without its CAN bus, or you need a VCU (Vehicle Control Unit) that can talk to the motor driver so the Lithiumate Lite doesn't have to.

The idea here is that the best way to help the driver from getting stranded is to reduce the available drive when any cell voltage starts getting too low.

That will help in the following ways:

  • The resulting sluggishness warns the driver that the battery is low, so that the driver can take precautions
  • Operating at low current reduces sag in the cell voltages, therefore allowing more charge to be extracted from them before the low voltage cutoff is reached
  • Operating at low current makes the EV run in a more efficient range

You can implement this function in one of 2 ways:

  • By suddenly putting the motor driver in a "Valet" or "Limp home" mode
  • By gradually reducing the available drive

While this function is not required to protect the battery, it is a great convenience to the driver, and we strongly recommend that you implement it.

To implement this function, look for a motor driver that either uses a throttle pot, or has a "valet" control input.

Here is a list of available motor drivers.

 

 
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Page published on: Jul 19 2013.      Installation manual