Monthly Archives: November 2016

Charge Doctor for INMOTION

INMOTION unicycles have 20S batteries (nominal voltage 72V, charger voltage 84V) instead of the 16S classic topology on most other electric unicycles. Models V3 and V5 use the “square Lenovo” connector and model V8 uses the GX12-3 pin connector (same connector and same wiring as hoverboards). Charge Doctors for IMMOTION wheels are now available, in single-input or double-input versions.

Warning, IMMOTION battery packs have less capacity than Gotways or King Song’s. So when using the CD-double-input, check that your setup does not charge at more than 1C (see article on “charge currents“). The CD’s usefullness is not only in allowing fast charging, it is mostly in the autocut function to automatically stop charging at 80% or 90% to preserve the the battery and considerably extend its mileage.

(72V nominal/ 84V charger)
Connector Wh
Charge* at 1.5A
(1 charger)
Charge* at 3A
(2 chargers in //)
V3 Lenovo 144 2 0.7C 1.5C to be avoided!!!
V5 Lenovo 288 4 0.4C 0.7C
V5+ Lenovo 460 6.4 0.2C 0.4C
V8 GX12-3 460 6.4 0.2C 0.4C
V10 GX12-3 650 9 0.17C 0.33C
V10F GX12-3 960 13.3 0.11C 0.22C

*For a 2Ah battery, 1C charge corresponds to charging at 2A. On LiIon batteries, a <0.5C charge is considered a soft charge, a >1C charge is not recommended.

Charge Doctor double input with Lenovo connectors, for INMOTION V3 & V5


Charge Doctor single input with GX12-3 connector, for INMOTION V8, V10, V10F, Solowheel Glide 3

Charge Doctor double input with GX12-3 connector, for INMOTION V8, V10, V10F, Solowheel Glide 3

Charger customization

Most e-wheels have settled for the GX16-3 connector. Some though use a different format and the corresponding charger may be difficult to find and are mostly more expensive. A customized charger with the right connector can be made from a generic 2A charger with the wiring instructions below.

Various e-wheel connectors, size and pin comparison

Most frequently found connectors

e-Wheel Socket Wiring Voltage Topo* Remark
Most e-wheels GX16-3 1: V+ ; 3: 0V 67.2V 16S connector for Solowheel, Airwheel, Gotway, Firewheel, King Song…
Gotway MSuper3 84V/1600Wh GX16-4 1: V+ ; 2: 0V 84V 20S other MSuper3 with battery <1600Wh have GX16-3 connectors
IPS (Holtz, Zero…) GX16-4 2: V+ ; 4: 0V 67.2V 16S warning, same connector as above but different wiring!
InMotion V8 ** GX12-3 1: V+ ; 2: 0V 84V 20S same connector & wiring as hoverboards
InMotion V3,V5 Lenovo Int:V+ ; Ext: 0V 84V 20S Lenovo square socket, originally for Lenovo laptop power supply
Ninebot One*** Lemo 63V 15S see photo for wiring***
Ninebot Minipro, Xiaomi ** GX12-4 1: V+ ; 4: 0V 63V 15S

*16S = 16 LiIon cells connected in series, total voltage calculated using battery full value = 4.2V/cell

** important, the numbering order on GX16-3 connectors is totally different from the GX12-3 : from left to right 3-2-1 for GX16-3 compared to 1-3-2 for GX12-3 !!! Likewise for GX12-4 and GX16-4

GX12 and GX16 plugs, note the difference in pin numbering

*** Wiring for Lemo on NinebotOne

Ninebot One’s Lemo female connector

Beware of the charger

For this mod, I recommand using the fanless 2A generic chargers. Even if they tend naturally to warm much more than a (noisy) charger with integrated fan, they have many great features: available for various voltages, noiseless, compact and transportable… They allow fast charging at 4A by a parallel connection with the original charger using a Duo Charge Doctor (or even at 6A with the Triplex CD).

Warning though, some 1.5A chargers are sold as 2A chargers. They have a smaller housing and are very hot when charging, thus unreliable in the long term. When buying it online, the vendor never details the housing dimensions and count on the buyers not checking the actual current to sell it. Any vendor with such dubious practices should be avoided anyway. Without stated dimensions, the difference can still be found looking at the distance between the rectangle and the grooves (see arrows on the picture). So don’t be misled, buy only the 2A charger with the bigger housing.
Chargers 2A and 1.5A, size comparison

Edit 4 dec/2016 : added image from Sylvain. Avoid the small housing charger!!
Small housing charger rated at 2A, too much heat melted the plastic housing.

Charge Doctor Triplex

Charge Doctor with 3 inputs to fast charge big batteries on Gotway wheels or scooters (eg Dualtron or Speedway). A multi-sockets but still very compact solution to connect in parallel multiple cheap generic chargers.

Datalogging on MAC

Some newer mac os x versions may be in conflict with USB dongle’s driver (chipset = CH340) leading to a computer crash when the dongle is inserted in any USB port. The problem is solved by removing the old driver and installing a new one (more details and help here or here).
A functional setup should see data coming from the Charge Doctor, check it using an ascii console set at 9600 bds.

ascii data from the Charge Doctor

Data can be plotted using a grapher, for example “Plot2”. Probably not the best one because of its un-intuitive and ugly user interface but still good enough for the purpose. A free version exists (with some nag screens) and is downloadable from the App Store.

graphic display of data by “Plot2”

attribution : images & data by Henrik M.

Autocut adjustment

How to adjust the autocut threshold on the Charge Doctor to stop charging at 80% or 90% of full capacity is a frequently asked question.

First, some essentials about LiIon batteries: charging to 100% leads to maximum voltage over the membrane separating + from – in the battery’s cell. The higher voltage, the more stress to the membrane and that has an impact on the cell’s health and lifespan. By stopping the charging at 90% or even 80% of full charge (the lower %, the better), the battery’s useful mileage can be doubled or even tripled, giving a substantial total cost reduction. Charging at 80% also means 20% less range, something not always possible or pratical on small batteries. But on bigger batteries (eg > 360Wh), it is mostly not a problem. So whenever possible, just do it with the Charge Doctor, since charging 10x at 80% is always better than charging 8x at 100%. It should be ok though to charge to 100% and riding just afterwards since it means the battery has not been submitted to Vmax over a long period. That’s the same reason why storing the LiIon battery should never ever be done at 100%.

The threshold default value is 1.00A, triggering, in most cases, the autocut at 90%. This threshold is an approximate value though since it depends on the charge current but also on the battery’s age. Fortunately, it doesn’t have to be accurate since the first goal is to avoid charging at 100%. Wether the autocut occurs at 80% or 85% doesn’t change the main picture.

However, if the threshold needs to be finetuned, here are the steps to follow, calculations has been made with Wh but can also be in Ah (consult the Charge Doctor’s user manual if needed) :

Step Screen
1. phase 1 : charge up until autocut => display voltage=67.7V, current = “OFF” (0A), charge = 183.2Wh (red). The Wh value of phase 1 depends of the emptiness of the battery at the beginning the of charge session. But it has no importance here since it is not used in calculations

2. reset the Wh counter (“0.0”, red)

3. disable the autocut : display = “—A” (or “0.00A” on firmware 2.02 or earlier) => charging resumes

4. phase 2 : charge up to 100% * (connect several hours or even one night for example)
End of phase 2 => voltage =67.7V, current = 0.05A (low enough to be considered as “end of charge”), charge = 30.4 Wh

5. divide phase 2’s charge (30.4Wh) by YOUR batteries nameplate capacity (Firewheel 260Wh in this example)
=> % residual capacity = 30.4/260=12%
=> the autocut occured at 88%
6. if the 88% doesn’t fit your desire, change the threshold (by repowering the CD with the button pressed) and restart at 1.
*Important : don’t forget to charge to 100% every 10 or 20 charges to enable cell-balancing, a vital requirement for LiIon batterie packs. To ensure proper cell-balancing, let the wheel rest one night or even 24h after charging, since riding would cause current outrush and a voltage drop that would cancel the ongoing balancing.

On big batteries (>680Wh), when charging at 2A, current drops very slowly towards the end of charge (after about 80%) so the threshold resolution may be insufficiant to autocut at 90%. To get more resolution and a more precise autocut, switch to autocut-by-voltage mode. The current and voltage thresholds are stored in separate non-volatile memories so their values don’t change when switching between modes. Voltage mode is less pratical since the threshold value depends on the battery type (12S on hoverboards, 14S on scooters, 15S on Ninebot wheels, 16S on most unicycles and even 20S on the Gotway MS3/1600Wh or on Inmotion…).

6A charger with the Charge Doctor

Electric scooters usually have high Ah batteries to make up for lower voltage compared to unicycles’ batteries. Dualtron scooters for example have 11Ah, 15Ah even 22Ah batteries! Charging at 2A with a single generic charger then becomes quite long.
Quick charging can be done using a multi-socket collector to connect up to 3x 2A-chargers, allowing more than 6A charge currents. For a 11Ah-battery, 6A corresponds to a 0.55C charge, so even such high current can still be considered a “soft” charge (recommanded charge current)).

Multi-socket collector Minimotors” for Dualtron, with 3 inputs

The Charge Doctor-duo can be used to connect up to 3 (even 4) chargers after a very simple, quick and free mod. While allowing fast charging, it also comes with the usual intelligent features: display of V, I, Wh, Ah, datalogging and most especially automatic charge-ending to prolong the battery life.

N.B. For Dualtron scooters, order the Charge Doctor on the Buy page, version reference = “Charge Doctor V2 DOUBLE INPUT for Airwheel, Solowheel, Firewheel”.


1) dismount the connectors of chargers 1 and 2
2) desolder charger 2 and solder its wires in parallel to charger 1
3) chargers 1 and 2 are now connected to one ouput connector to make a “double charger 1&2” delivering 2x2A= 4A

Charging at 6A with the Charge Doctor, connexion scheme

Charge current
2 A charge 3 alone
other option : double charger 1&2 with only charger #1 powered
4 A double charger 1&2
6 A charger 3 + double charger 1&2

*detailed steps

disassembled connector


chargers #1 and #2 soldered in // to the same connector


double charger 1&2 connector

Charge Doctor mixte for Ninebot

Ninebot uses two types of connectors for it wheels, Lemo and GX12.

Wheel = Ninebot One
Connector = LEMO
Wheel = Mini Pro, Mini Xiaomi…
Connector = GX12 – 4 pins

Batteries of Ninebot wheels are of type 15S (15 cells in series), odd value since the majority of unicycles use 16S batteries, except InMotion and some Gotway wheels with 20S batteries. Not so odd after all but more probably a marketing ploy from Ninebot to make its products in-compatible with others’ in order to charge eye-watering prices for spare parts (batteries & charger).

What’s nice however is that apart from the difference in connectors, the chargers are the same, meaning a Mini Pro charger can be used on a Ninebot One and vice-versa, with the good adapter. A version of Charge Doctor mixte for Ninebot has been made precisely for that, allowing lots of connection combinations :

  • Mini Pro charger -> Mini Pro
  • Mini Pro charger -> Ninebot One
  • Ninebot One charger -> Ninebot One
  • Mini Pro charger + Ninebot One charger -> Ninebot One (fast charging at 4A)
  • etc …

Charge Doctor mixte for Ninebot

Charge Doctor mixte for Ninebot, connector types

Charging NinebotOne with NinebotOne charger (white charger) : current = 2.00A


Fast charging NinebotOne with NinebotOne charger (white charger) + MiniPro charger (black charger) : current = 4.08A

images attribution: jvincent,

Charge Doctor V2, firmware V 2.03

Firmware V2.03 adds importants features to Charge Doctor’s V2.02. Please refer to this user manual for all CD shipped after June 2016, it replaces the now obsolete initial manual.

The CD is now available for a large range of electric wheels, from unicycles to hoverboards, bikes, scooters… It also exist in “mixte” versions for use on different models by the same CD (eg. Ninebot & Gotway). Here is a list of (non exhaustive) CD-compatible electric wheels :

  • Airwheels & clones, King Song, Gotway, Solowheel, Firewheel, Dolphin, Pinwheel…
  • Gotway 84V (GX16 4 pin connector)
  • IPS (GX16 4 pin connector)
  • Ninebot One (Lemo connector) an Minipro (GX12-4 pin connector)
  • InMotion V3 & V5 (Lenovo square socket) and V8 (GX12-3 pin connector)
  • Hoverboards
  • Scooter with XLR-3 pin connector or GX16-3 pin connector (GTX, Dualtron, Speedway,…)


Charge Doctor V2 features

  • Voltage: 20.0V – 100.0 V
  • Current : 0.00 – 10.00 A
  • Charge : 0.000-1000 Ah with automatic decimation
  • Energy : 0.0-10000 Wh with automatic decimation
  • End-of-charge by current threashold (0.1-8.0 A) or voltage threshold (30.0-85.0V)
  • Datalogging serial output 9600 bauds TTL
  • Dimensions : 85x50x20 mm
  • Weight : 65 g


At startup, displays “C-Dr” (blue) and firmware version “2.03” (red).


Top display shows alternatively voltage (“61.9U”) and current in amps (“1.99A”).

Image Image

Bottom display has 3 display screens:

Short click => screen change
1. Wh
2. Ah : “Ah” alternates with value to differentiate from Wh mode
3. Auto-shutdown threshold ( flashing display)
Long click
1. & 2. reset Ah and Wh counters
3. Enable/disable auto-shutdown (“—A” = disabled).
N.B. auto-shutdown threshold can
only be changed in “adjustment” mode
Image Image Image
screen 1: 148.2 Wh screen 2: 2.377 Ah screen 3: auto-cut threshold
short click =>change to screen 2
long click => Wh, Ah = 0
short click =>change to screen 3
long click => Wh, Ah = 0
short click =>change to screen 1
(automatically back to screen 1 if no click for more than 6s)

Screen 3 has 3 modes, press long click to change mode :

Image Image Image
screen 3 / mode 1 screen 3 / mode 2 screen 3 / mode 3
auto-cut when current is below threshold (1.20 A)

auto-cut disabled (use this mode to charge to 100%)

charge has been auto-cut (“off”). To resume charge, press long click or restart the CD by disconnect/connect charger

Easter egg: press 3 short clicks (interval < 0.3 between clicks) to turn off LED display
In display-off mode, the CD continues to work normally. Another click restores display


Enter adjustment mode by holding the button when powering on.
1) mode auto-shutdown, threshold adjustment : button hold < 5s
2) mode voltage & current calibration : button hold > 5s

1) Adjustement of auto-shutdown threshold

Top led displays current parameter. With no button click, the screen is cycled through 3 avaibles parameters every 2s. Any click holds up the actual parameter 6s for adjustment before the cycling restarts. Adjustment mode is terminated and the CD gets back to normal mode if no click for more than 10s.

Image 3 available parameters:

  • Auto : auto-cut
  • Pr1 : parameter 1, display off at auto-cut
  • Pr2 : parameter 2, auto-cut mode by current or voltage

“Auto” : auto-shutdown mode. Bottom led displays the shutdown threshold. When the threshold is reached, current is cut by the CD and the charge session is ended (I=0.00A). The threshold is incremented by 0.1A steps (auto-cut by current mode) or 0.1V steps (auto-cut by voltage mode). Hold the button for fast then ultra-fast increment. Voltage and current threshold are stored in separate non-volatile memories.
Important: disabling auto-cut can not be done in “parameter mode” only in normal mode (see above).

“Pr1” : parameter 1. Value = 1 => deep standby mode with Led display off at auto-cut. To power on, click button or disconnect/reconnect the CD.

“Pr2” : parameter 2. Available values, “dn A”, “up V”, “dn V”

Image Image Image
dn A : down A, auo-cut when charge current is below threshold. Default mode at first use.

UP V : auto-cut when charge voltage is above threshold. This mode generally allows more accurate auto-cut, to be used on big batteries (>560Wh) when auto-cut by current doesn’t have enough resolution.

dn V : down V, auto-cut when voltage drops below threshold. To be used only for discharge tests.




2) Calibration

Voltage and current are calibrated at +-10mV and +-1mA respectively before shipping. Avoid recalibration unless you have accurate instrumentation.

Top led displays actual parameter. With no button click, parameters changes every 2s in a round robin schedule for all available parameters. Any click keeps the actual parameter 6s before the round-robin restarts. To quit this calibration mode and revert back to normal mode, power-off then on Charge Doctor.

“down U” : decrease voltage gain
(about 10mV per click)
“UP U” : increase voltage gain
“down A” : decrease current gain
(about 1mA per click))
“UP A” : increase current gain
“00 A” : change current offset to calibrate 0.00A
ATTENTION : connect no charge (zero current) and hold button 2s to calibrate (short click is ignored to filter out manipulation error)

Data logging

Charge-Doctor transmits data every 10s by serial 9600 bds protocol, TTL level, 8 bit data, 1 bit stop, no parity. Data are in ASCII format with separator = coma. The format is identical to the first version Charge Doctor, see the blog’s article on Graphic Display for steps to download and process data in realtime.
N.B. Charge Doctor does not store data. For data logging, a PC must be connected during all the charge record.

Connection to dongle : the Charge Doctor’s output Tx must be connected to the serial-USB converter dongle’s input Rx :


IMPORTANT : at power-up, Charge Doctor sends a 2 line header containing various information such as the firmware version :

Charge Doctor V2.00-10A by HMC 01/2015
Time(s) Voltage(x0.1V) Current(x10mA) Charge(x0.1Wh)

These two lines will be recorded in file “log.txt” but they are not parsable by the grapher KST so the realtime display will stop : KST is quite pricky as to the data format and any error will stop the graph updates. Data and graph should change in realtime in KST when new data is logged into “log.txt” by datalogger.exe so if KST’s display freezes, then “log.txt” contains errors. To remove errors, quit KST and edit “log.txt” using a text editor.

The ininterpretable header lines can be removed from “log.txt” by two methods :

  • restart datalogger.exe 2 secondes AFTER restarting Charge Doctor so the header gets lost and not logged
  • Click “Stop logging”, UNcheck option “Append to file” then click “Start logging” in datalogger.exe => old file “log.txt” is deleted and replaced by a new blank file for logging, hence, without the uninterpretable header.

Pictures of Charge Doctor V2, versions with GX16 connector (most electric monocyles, bike, hoverboard, bikeboard) and Lemo connector (Ninebot monocycle).
(click picture for high resolution image)