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Installation of the coulometer LCD display

April 29, 2020 — BarryK

The previous post in the powerbox project:

The finishing touch is to install and calibrate the Amptron coulometer. As already discussed, the shunt is already mounted on the wiring-board. This is what I have:

If you search on eBay and elsewhere, for "battery coulometer", you will find this available from many vendors, and there are also setup videos on YouTube.

Installing the coulometer

There is a shielded cable to connect the shunt to the LCD display, and this is a problem, as it is very long. This is for the situation where you want the display somewhere else, maybe on the dashboard of the vehicle, or whatever.

I want to cut it right down, as the LCD display is close to the shunt. So, I cut the plugs off each end, and joined the cable. I am familiar with delicate electrical work, as I was an electronic engineer in my working days. I have a small soldering iron and fine solder for the purpose. The wires inside this cable are so tiny, this photo blows it up, but in actuality they are so tiny. The photo shows after I have stripped each wire and twisted them together:


...I then very carefully soldered each join, then put heatshrink tubing over each join, then bound it all together with electrical tape.

I know that such delicate work will be a challenge for many -- well, you could just go and buy a ready-made powerbox! But it is not insurmountable. The wires are so tiny, I stripped them with my thumbnail, pressing onto the table -- my cable stripper does not handle such tiny wire.

Calibrating the coulometer

I watched one of the YouTube videos on how to calibrate the coulometer, but it is misleading. They set "full" and "empty" corresponding to certain battery voltages, but this could be very inaccurate.

Here are the instructions:



What I did was first charge the battery to 100%, using the Amptron mains-input lithium 15A battery charger:

...this has eyelet lugs, that I replaced with a black Anderson plug -- very convenient, just plug it into the powerbox, and it will charge until 100%.

Following the above instructions, I then pressed the "up" key for three seconds to set the display at 100%.

Following the "User Settings", I then chose battery capacity as 50AH -- note, the buttons have to be very firmly pressed, and getting out of "engineering mode" proved to be difficult.

That's it, I did not set "FULL" and "ZERO" voltages, as that is not a reliable indicator of 100% and 0%.

Using the coulometer

I plugged my Powertech 150W inverter (purchased many years ago from Jaycar, and used on many camping trips) into a cigarette lighter socket, and plugged in a desktop lamp:


Fantastic, working! Here is the LCD display:


Very nice! That snapshot is after running the lamp for a short time, the capacity has dropped a bit below 50AH.

EDIT 2020-05-04:
After further reflection, I decided it is a good idea to minimize "error creep" of the State-Of-Charge, by setting a lowest voltage for 0%. See this later post:   

Tags: nomad