Category Archives: Divers

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

*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

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…).