27 March 2021

PROJECT: Turnigy Accucell-6 FW Update & Calibration

This project is part of the "why am I jumping to other projects before finishing off my old ones" series...

Many moons ago I tried using my Turnigy Accucell-6 battery charger to log charge/discharge data via DataExplorer, though sadly I could never get it working properly. Well it turns out that the Turnigy Accucell-6 (along with a bunch of other 4 button chargers according to my colleague) is basically a rebranded SkyRC iMax B6 mini, which is fully compatible with DataExplorer :D

So here I attempt to flash the iMax B6 mini FW and calibrate the charger

FW Update (v1.12 → v1.14)

The FW on my charger was changed from:

  • Turnigy Accucell-6 v1.12 (this would have been the original FW charger came with)
  • SkyRC iMax B6 mini v1.14

Interestingly the product page for SkyRC iMax B6 mini shows v1.13 as the latest FW, however only v1.14 has calibration functionality. Also updating the FW is super simple, you just need to connect your charger to the PC (via USB) and run the flash utility "B6mini_SK1.14.exe"


This step is a bit more tricky, luckily SkyRC have a video describing the whole process:

Things you will need to run through calibration:
  1. A charged 6S LiPo battery. Since I did not have one on hand I tried "simulating" one by pumping ~4.2mA into 6 1K resistors in series, but this did not work as the load/resistance (and thus "cell" voltage) changes as soon as you connected it to the charger; meaning you will need to have a voltage source at a minimum. So again my colleague was kind enough to let me borrow his 6S LiPo battery
  2. A calibrated multimeter. I used my trusty EEVblog 121GW which I verified against a calibrated multimeter (Keysight U1241B) at work

From then you basically record the voltage of each cell (remember cell 1 is the one closest to GND) with the multimeter, and then calibrate the charger by going into "BATT METER" and holding "Enter". At this point you enter the voltage (in mV not V) you read with the multimeter for each cell via +/- keys, and once you are happy hold "Enter" again to save & exit the calibration menu

Here is how my charger performed before/after calibration:

Cell # Volt. 121GW, [V] Volt. before CAL, [V] Err. before CAL, [%] Volt. after CAL, [V] Err. after CAL, [%]
Cell 1 4.1865 4.18 +0.16 4.18 +0.16
Cell 2 4.1910 4.19 +0.02 4.19 +0.02
Cell 3 4.1879 4.17 +0.43 4.18 +0.19
Cell 4 4.1909 4.18 +0.26 4.19 +0.02
Cell 5 4.1966 4.19 +0.16 4.19 +0.16
Cell 6 4.1958 4.17 +0.62 4.19 +0.14

So running the charger through calibration reduced the error range from 0.59% to 0.17%, and given this is a hobbyist-tier piece of equipment I am quite happy with the <1% accuracy

A couple of extra points about calibration results:

  1. It looks like the charger ADC/MCU likes to round the voltage down in a curious way. For example:
    • 4191mV will be rounded down (as expected) to 4190mV (4.19V on charger)
    • 4188mV will be rounded down to 4180mV (4.18V on charger, not 4.19V)
    • 4197mV will be rounded down to 4190mV (4.19V on charger, not 4.20V)
  2. If you perform calibration more than once you might notice that the mV reading is not quite the same as the multimeter value. Lot's of other people (see video comments) report the same "issue", which I suspect is totally normal for this hobbyist-tier piece of equipment
  3. I will be mainly using this charger for LiFePO4 batteries which are typically charged to 3.65V ± 0.05V per cell. Knowing that at worst the charger error is +0.19% this means when I charge to 3.65V the actual cell voltage will be more like 3.6569V, which is well within the ± 0.05V limit

Data Logging

As expected DataExplorer now talks without any issues. Here is me charging and discharging a 2S LiFePO4 battery:

NOTE: You can plot fancier looking graphs by exporting the data as .csv and plotting it in your favorite package 

07 March 2021

PROJECT: Woodworking & 3D Printing

Sometime in late 2018 my wife and I decided to upgrade her workspace. The initial plan was to tackle this in several sections:

  1. Build the left (self-contained) shelf
  2. Build the right (self-contained) shelf
  3. Bridge the two with a desk

Well we managed to complete left shelf within a couple of months, as for the last two... they basically took us till late 2020. Surprisingly we have COVID to thank for that, as being locked inside with nothing to do gave us a wee boost :D

An interesting aspect I wanted to try with this project is merging woodworking with 3D printing, as I felt the two could complement each other reasonably well especially with smaller fittings. So below I document such 3D printed items:

Small Drawers

Probably the only exception to the "smaller fittings" description. The larger drawer measures 320 x 300 x 70mm and both had to be split into several parts. The only things not 3D printed with these was the metal rods running through the body (for extra support), and the MDF base. Also the body is printed in PETG and fastened with Loctite Control Gel Super Glue

Drawer Handles

Wife wanted something flush yet accessible, so came up with this simplistic design

Drawer Supports

A while back we found a bamboo tray (on the street!) which we decided to convert into a drawer. Initially we were going to mount the drawer slides onto another piece of wood, but after realising how much work would be involved (and how uncool it would look) we decided to 3D print the supports instead

KVM Switch Bracket

Couple of brackets that hold a KVM switch (Unnlink 2 port). Side note, the switch makes it incredibly easy to jump between the laptop & desktop

HDMI Splitter Bracket

Couple of brackets that hold an HDMI splitter (CABLETIME C355). Again super useful for changing between the TV and monitor

Cable Holders

Super simple cable holder. Initially this was twice as tall (so you could cram more cables) but someone wanted a more flush design...

Outlet Bracket

Couple of brackets that hold an 8 way outlet (HPM D105PA8CC). The cylindrical cut-outs act as a cable runway (unfortunately the outlet mains cable was on wrong side...)

Wood Spacer

This one is probably the most "pure" merger of woodworking and 3D printing, a simple 7mm thick spacer that allows the desk and shelf surface to be level 


Fern Pot Brackets

Don't recall the exact plant pot & saucer combo, but suspect it's something like this & this

Laptop Stand (ゴ ゴ ゴ ゴ ゴ ゴ...)

Simple Metabox Alpha N850HJ stand, same one shown here

Desktop USB & HDMI Bracket

Makes USB (2.0 & 3.0) & HDMI ports more accessible, again same one shown here