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.

*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

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

*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 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.

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) :

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…).

Gotway

New models of Gotway BMS don’t have the infamous power cut mosfets, Gotway has finally been aware of the danger of powercut and has made the right BMS for monocycles. Good ! Continuer la lecture →