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Cell Tester For Chevrolet Volt Battery

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Wanting a means of quickly comparing the cell voltages of my 48 V (12-cell) Chevrolet Volt Li-Ion Battery, I noticed a device called a "Cell Meter 7" - which appears to be popular among RC Modelers. Seeing that it is advertised as compatible with a number of battery types - and can be had very inexpensively
(about $5 direct order from China), I decided to give them a try. The tester is rated for up to seven cells in series.Since the Volt battery has 12 cell groups, I figured that two Cell Meters, daisy-chained, should do the job. Good guess.

The next problem is connecting the Cell Meters to the cells to be measured. None of the folks selling them provided any information regarding cables and connectors. Continuing to look around, I came upon a 6-circuit (7-wire) "Extender" with male and female ends. These are known as a "JST-XH-6S".
Hoping that the female end, at least, would fit the Cell Meter, I ordered two of the Extenders. They fit just fine (leaving the 8th pin (Circuit 7) unconnected.

Then there was the matter of marrying up the cables with the original BMS cable that came with the battery. I noted that each circuit in the intermediate connector had two terminals - one of which is female, and about the size of the male pins of the Extender. Having nothing to lose, I decided to remove said male pins from the plastic connector housing and find out if they fit. They do! I cut away the plastic with narrow-jaw side cutters. You may be able to pull the wires with pins out the back (didn't try - but noted that the pins are spot welded to the wire).

Other than connecting things up, the only other task is to join the two halves of the assembly together (circuit 6 of the lower group to the Low Reference of the upper). these are the red and black wires in the photo. This I did by soldering, followed by replacing the shrink tubing on the pair of wires going to a single pin. Hookups to the intermediate connector are as follows:

Cell Meter 1 - pin (Battery Lo Ref) Black Violet wire
Cell Meter 1 1 pin (Cell 1 Voltage) Violet wire
Cell Meter 1 2 pin (Cell 2 Voltage) Yellow Brown wire
Cell Meter 1 3 pin (Cell 3 Voltage) White wire
Cell Meter 1 4 pin (Cell 4 Voltage) Grey Yellow wire
Cell Meter 1 5 pin (Cell 5 Voltage) Yellow Green wire
Cell Meter 1 6 pin (Cell 6 Voltage) Green wire
Cell Meter 1 7 pin - - - - - - - - - - No connection
Cell Meter 2 - pin (Cell 6 Voltage) Green wire
Cell Meter 2 1 pin (Cell 7 Voltage) Yellow Brown wire
Cell Meter 2 2 pin (Cell 8 Voltage) Blue wire
Cell Meter 2 3 pin (Cell 9 Voltage) Green Black wire
Cell Meter 2 4 pin (Cell 10 Voltage) Blue Grey wire
Cell Meter 2 5 pin (Cell 11 Voltage) Green Grey wire
Cell Meter 2 6 pin (Cell 12 Voltage) Brown wire
Cell Meter 2 7 pin - - - - - - - - - - - No Connection

I mounted the Cell Meters on a small clipboard, using Velcro. The spring clip holds the intermediate connector in position, serving as a strain relief (since
there is nothing else to prevent the male pins from being pulled out). However, done this way the wiring is reasonably secure. No doubt someone will figure out a way to improve on this aspect of the tester.

In use one plugs the BMS connector into the battery then sets the battery type (Li-Ion) on both Cell Meters. Then step through and note the Cell Voltages for Cells 1-6 using Cell Meter 1. The last step will show Total Volage for Cells 1-7. Next Step through and note the Cell Voltages for Cells 7-12, using Cell Meter 2. Once again note the Total Voltage, and add this figure to the Cell 1-6 Total for Total Battery Voltage.

IMHO this device is cheap and easy to make - and works like a charm.