Electric Bikes – a quick battery check

When I got home on Friday, Lynn’s bike was on charge, whirring away (noisy charger!). As she only left an hour or so before me, this was OK. However, when I did the rounds at bedtime (4 hours later), checking doors etc, it was whirring away. The first thought is that it is “still whirring away” rather than just “whirring away”. I checked the voltage of the battery ,and it was at about 42v so I was a bit puzzled. I turned it off and made a mental note to take a look at it. As we had a bit of a busy physical weekend doing some landscaping, it got left until today (Monday). Lynn arrived at the shop with just 12km since the last charge, so I put it on the shop based charger, connected up the individual cell voltmeters, and checked the voltages. They were all roughly 3.3 volts (3.28 to 3.35v) which is acceptable, so we went out to lunch. When we got back, the battery voltage was approaching fully charged, so I sat and watched the individual cell voltages ticking upwards. After 10 minutes of watching all the cells creeping up at around 3.57 to 3.65 volts, at 43.3 volts the charger switched off. So while not perfectly balanced, no cell was getting more than 3.65 volts, so everything is good with the cells (and the shop charger). Good news, especially after nearly 6000kms with daily charging every 20kms or so!

Bad news, I still don’t know what happened on Friday! Two thoughts occur, firstly, the battery charger is faulty (I have already replaced one of this brand, which came with the Headway cells when I bought them from China). I can check that tonight by repeating the charging test with the home based charger. Secondly, it could be that the charger had shut down properly some hours before, but had just reached the point where the batteries had self balanced and discharged slightly through the charger, so the charger kicked back in again to top up the cells. If this is the case, it’s even better news. I will know that the cells and the charger are fine! Tonight’s test should confirm either way.

Given that the mileage is clocking up on my bike too (7220kms), I will probably repeat the tests on that bike too. I did 36kms on my bike since the last charge and it felt as good as new pedaling into the wind on the last 2kms to work, so I am confident there won’t be too many problems. Since fixing up the battery connections, swapping the Anderson power poles for some XT90s and MT60s, I have not really had much call to look at the batteries, so it is probably well overdue.

18/10/2016 – checked out the charge last night, and everything charged as it should and switched off, so all is good, and I know the battery is still OK! Checked mine this morning, and it is still withing acceptable limits, one cell is a bit low (0.04 volts down) but that is probably less than the errors in the voltmeters!

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