It's project day at Weber's house, and he's finding lower range than usual (80 km compared with 130 km when new). One of the cells has been playing up, and was replaced a few weeks ago. He replaced it with one that seemed to have the lowest internal resistance of his spares. But that one seems to have low capacity. So today's project was to find the best of the spare 8 cells, 4 of which are being used as his auxiliary battery.
We spent half the day getting the 8 cells top balanced. Well, 7 of them; one of them ruled itself out of contention by its behaviour when charged at a paltry 6 A. While that was happening, Weber constructed the load resistor: about 2.5 metres of 0.7 mm dia steel wire, aiming for about 1 Ω. This was wound around a piece of wood (ceramic would have been better, but wasn't to hand). The ends were soldered to some copper wire and battery clips from some other project. The resistor and board went into a 10 litre bucket of water. The wood tended to float (who'd have thought), so a dead drill battery was used as a weight to hold it down.
This is near the end of the test:
- Making bubbles sm4.jpg (129.81 KiB) Viewed 475 times
You can see hydrogen and oxygen bubbles streaming from it, due to electrolysis of the water. The blue thing is an ice-brick.
After about 70 minutes, the first cell went low voltage, with its Cell Monitoring Unit beeping. The others had a good enough spread of voltage that we could pick the winner, and in fact rank the rest of the cells in case more are needed later.
Learning how to patch and repair PIP-4048 inverter-chargers and Elcon chargers.
