Difference between revisions of "Power Reduction"

Latest revision as of 02:24, 31 March 2020

This describes any riding situation where the relationship between throttle input and power is diminished.

Effects

• The rate of power onset with throttle input is reduced.
• The limit of power at full throttle twist is reduced.

Potential Causes

• The direct cause is typically current limiting by the MBB and/or controller.
• Low battery voltages at low SoC can trigger current limiting.

  Power (kW) = Current (A) × Voltage (V)

  So, a given power demand will require more current at low voltage than at higher voltages.

  The MBB and/or controller typically impose current limits on the main power bus for performance models (SR, DSR, FX, and FXS) at SoC below roughly 40%.

  Very low voltages (below 96V?) will trigger significant power reductions.

• Cold battery temperatures can trigger current limiting, since internal resistance rises at low internal temperatures.
• High battery temperatures can trigger current limiting directly.

  The MBB will limit current to reduce internal heating of the battery.

  Often, very hot ambient temperatures can reduce the battery's ability to cool itself while riding, which makes this condition easier to trigger.

Potential Solutions

• For low battery voltages, charge the bike to get more/full power.
• For low battery temperatures, riding at slow speed while monitoring battery temperature can raise its temperature until the condition clears.
• For high battery temperatures, successive year builds of the battery typically offer lower lower internal resistance.

  Basically, a newer bike will be more robust against current limiting conditions by not heating up as readily.

References

• From EMF:

... higher internal resistance of the battery at colder temperatures causing current limiting, ... It can be a little disconcerting when this happens right as I am trying to overtake slower vehicles.

You can even see that in the logs.

You'll see entries discharge current limited (XX%).

That tells you the percentage the power (=battery current) has been limited to, because of the high voltage sag due to higher internal resistance because of the cold.

Right behind that you will read a MinCell entry

this one tells you which cell was the weakest and caused the limitation and with what voltage.

The limitation of power is directly related to topspeed, as you need more power the faster you ride.