Charge Doctor Features

Hobby Wheel Gadget Factory is proud to present the « Charge Doctor », specifically designed to monitor the unicycles’ batteries.
It’s in fact an off-the-shelf USB charge monitor I have hacked and reprogrammed for our use.
BEWARE : Max current is 3 A. Plugging a 4A fast charger would toast the Charge Doctor !



  • Voltage 40.0V – 80.0V
  • Current 0.00 – 3.00A
  • mAh-meter 0-19999 mAh
  • Energy meter 0-999.9 Wh
  • Connector 3-pin GX16 compatible with Airwheel & clones, TG, iezWay, Gotway, Firewheel… (not on Ninebot One with a different charge plug)
  • Comm serial ascii output for logging, 9600 bauds, TTL levels
  • Plug & play

User instructions

First line: voltage and current.
Second line: total charge in mAh or Wh, click pushbutton (PB) to alternate between mAh and Wh.
Hold PB for 2 s to reset the total charge.
Hold PB for 6 s to enter calibration mode (see below).

Data logger

Charge Doctor sends out data every 10s in ascii line format with ‘,’ separator, at 9600 bauds, TTL level
Line format: Seconds, Voltage (x10mV) , Current (x10mA) , Wh (x100mWh)
example 110,582,194,31 <=> 110s, 58,2V, 1.94A, 3.1Wh

Data are sent to a PC, MAC or Linux using TTL serial-USB converter dongle (cost < 2 $) and a terminal emulator for disk storage or graphic display. See this article for a setup example. Data can also be formatted using this Excel model. Look up « CP2102 USB converter » or « CH340G USB converter » on eBay (avoid PL2303HX chip based dongles which work fine but rather pricky when installing driver).

N.B. Charge Doctor does not store data. A PC must be connected during the charge to log data in real time.


Voltage is factory (ie by me) calibrated at +-20mV and current at +-2mA.
Recalibrate when necessary only if you have an accurate multimeter.
Press & hold the pushbutton (PB) for more than 6 s when the second counter is at the corresponding number :
1: decrease voltage gain (about 0,02V per PB click, so you must click 5x to see the number change)
2: increase voltage gain
3: decrease current gain (about 2mA per click)
4: increase current gain
5: reset current offset = 0 (no load)

The variable to be calibrated flashes and the change direction is indicated by the display’s up or down arrows.
The calibration mode ends after 10s of no PB click.

Some pictures

Lastest batch of Charge Doctors. Thank you Ironfox for being the first international buyer and for ordering 4 (four !) of them.

Charge Doctor display, charging a 260Wh empty battery.
1) beginning: V=60.2V, I=2.11A, Charge=29.1Wh
2) near end: V=67.1V, I=0.4A, Charge=230.8Wh
3) end of charge: V=67.1V, I=0.0A, Charge=243.4Wh
Notice that it’s a generic wheel (TG) battery with Chinese cells, so total charge is only only 243.4Wh, the nameplate « 260 Wh capacity » cannot be reached. On the Firewheel 260Wh, with Panasonic cells, I can charge up to 285 Wh.

Charge Doctor – PC link using a Serial-USB converter dongle, data logging by terminal emulator puTTY. Only two connexions of the dongle are used: 0V and RxD

Serial link : blue=0V, orange=Transmit (connect to dongle’s RxD)

This page has been published in Reference on 16 juillet 2015 .

3 réflexions sur « Charge Doctor Features »

  1. sbouju

    I have « toasted » my Charge Doctor with a 2A too, just connecting it to my wheel… I am not specialist at all, but when CD will be used between the charger and the unicycle, I hardly recommand to connect and aliment the charger to the AC wallet first, and to connect the GX16 connector of Charge Doctor to the unicyle last.


Laisser un commentaire

Votre adresse e-mail ne sera pas publiée. Les champs obligatoires sont indiqués avec *