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Batteries

If you don’t think your battery life is all that it should be then;

  • Check the battery condition. The capacity of a battery reduces as it gets older. Also do a load test on it, we’ve seen batteries that gave 12.8V off load but that dropped to 11.1V as soon as a load was applied.
  • Check the condition of the power cabling. We’ve seen numerous cases where cable joints have degraded over time, overheated, and then caused a significant volt drop at the controller. Measure the voltage directly across the controller B+ & B- terminals whilst under load.
  • Is there mechanical drag in the system?
  • If all else fails, fit bigger batteries.  The controller can only do only one thing with the current it takes from the battery – pass it on to the motors. If the controller wasted any significant power – it would simply get hot and go up in smoke, so if the batteries don’t last – it’s a battery, a motor, a wiring, or a mechanical problem.

Yes….But….!

The great majority of lithium batteries now have a built-in battery management system [BMS] which protects the battery by sensing the voltage of each individual cell and the current flowing through it. If the cell voltage gets too low or too high, or if the discharge or charging current gets too high, the BMS will protect the battery by disconnecting it from the load. This disconnection can have serious consequences for a motor controller.

Our Pro-160 / 360 have settings that can prevent this damage, in short you need to do the following….

  • Set the under-voltage cut off point of the controller to be above that of the BMS, that way the controller will ensure a controlled stop before the BMS trips. The Pro-160 / 360 both have a low battery warning level that can be set higher than the BMS cut-off level that will allow a “limp home” mode under reduced power.
  • Set the over-voltage limit of the controller to be below the maximum charge voltage of the BMS. The controller will automatically adjust the deceleration ramp rate to keep the regeneration voltage below the BMS cut-off level.
  • Set the maximum current limit of the controller to be below that of the BMS, that way the controller will make sure that the BMS does not reach its threshold for tripping.
  • Set the regen current limit of the controller to be below that of the maximum charge current of the BMS, that way the controller will make sure that the BMS does not reach its threshold for tripping.

We’ve written a more in depth article on this subject here.

On our other, older controllers it is possible to have a low voltage cut-off, but full current and over-voltage limiting is not possible.

  • The DNO can have a simple modification done to set a low voltage cut-off.
  • Our BCM-5P1 battery meter has a low battery cut-off feature.
  • The 4QD-200 / 300 series have an adjustable current limit and low voltage cut-off.

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