Voltage threshold on Charge Doctor

The Charge Doctor autocut default settings are current mode & 1.0A threshold (charging is cut when current drops below 1.0A). This corresponds to a 90% charge, in general. Autocut by current is a handy mode and is ok for most users because when using the CD on wheels with different battery voltages, there is no need to readjust the threshold.

But there are cases when autocut by voltage is preferable:

  • on big batteries, eg > 560Wh, a 1A threshold corresponds to 95% even 99%! A threshold of at least 3A would be needed to cut at 90%, which is of course impossible using a single 2A charger (no problem using a CD-double-input and two chargers though)
  • on even bigger batteries (eg >1000Wh, Dualtron, MSuper3…), the wheeler would like to cut charge only to 70%, even 50% to best preserve the battery. Such charge levels are in the constant current phase so autocut by current is not possible

To set the threshold in autocut-by-voltage mode, use the following approximation (for LiIon cells only) : 3.3V/cell for 0%, 4.2V/cell for 100%. Some calculations based on those values are in table 1. Those are just calculations, to adjust accurately the threshold, follow the steps described previously.

Cells 0% 30% 60% 70% 80% 90% 100%
Total discharge cycles* 1800-3600 1200-2400 950-1900 700-1400 500-1000 300-600
Hoverboard 10 33.0 35.7 38.4 39.3 40.2 41.1 42.0
Duatron 14 46.2 50.0 53.8 55.0 56.3 57.5 58.8
Ninebot 15 49.5 53.6 57.6 59.0 60.3 61.7 63.0
Generic 16 52.8 57.1 61.4 62.9 64.3 65.8 67.2
Inmotion/ GW1600Wh 20 66.0 71.4 76.8 78.6 80.4 82.2 84.0
Table 1: voltage threshold to set into the Charge Doctor as a function of % charge, values in Volts
* calculated from Battery University‘s thumb rule : number of cyles doubles with  14% less charge

Examples :    

  • 30% charge is used for battery storage
  • Charging to 80% instead of 100% more than doubles the number of cycles, to 700-1400 instead of 300-600
  • On the Dualtron, set threshold to 55.0V for a 70% charge
  • On the Inmotion, set threshold to 80.4V for a 80% charge.

2 thoughts on “Voltage threshold on Charge Doctor

  1. Javier

    I think that voltage cutout can not be calculated based on this table.
    In example, voltage cutout for ninebot at 90% would be 61.7v based on that table.
    But, it is not the same to charge at 61.7V (CV), that to cutout as soon as 61.7V is reached.
    To charge at 61.7V means mantaining voltage at this value and let the battery take the current it wants. The current will go down slowly and the battery eventually will charge to 90%.
    To cutout at 61.7V means disconnect the charger as soon as 61.7V will be reached. This will happens at the CC stage (maximum constant current) and the battery is not at 90% in that point.
    I think that voltage cutout is a very useful funtion, but the table needs to be updated to have this into account.

    Reply
  2. hobby16 Post author

    It’s not 90% but quite close since the constant voltage phase you mentionned probably charges less than 5%. The thresholds depend a lot on battery’s internal resistance and charge current (a same threshold will trigger the auto cut-off sooner when charging at 4A a 840Wh battery than when charging at 2A a 360Wh battery). That’s why I called them “approximation” and showed how to finetune for the correct threshold.

    Reply

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