Seeing as the big trip in my last post did not flatten the battery I thought I would have another go to see how it was performing in terms of capacity. Unfortunately after not doing any top up charges last week it cut out after about 6.4 amp-hours which is where it has cut out on my previously. I should at least be getting 8 or 9 amp-hours so I sent an email query to Justin at ebikes.ca. As usual I got a reply very quickly! Justin informed me that yes I should be getting more out of the pack and that it was likely a cell balance issue. He offered me a replacement pack straight away or a chance to pull it apart and have a go at fixing it. I went for the chance to fix it as sending mine back to Justin overseas may have been problematic with our laws regarding postage of battery packs. And I was also keen to see the inside of the pack!
I was instructed to do a full recharge and then pull the pack apart and check the voltage of each battery cell. Getting it apart was fairly easy and I must say it is very well put together. As you can see from the photo it has 2 separate groups of 5 battery cells that are securely attached and wired together with some circuitry to manage the charging, balancing and low voltage cutoff (LVC) to protect the cells.
When fully charged each cell should be 4.15 volts or higher however one of mine was only 4.02 and Justin thought this cell might be prematurely tripping the LVC. To fix it I found an old charger that put out about 5 volts and soldered some alligator clips to the output wires. I attached the clips to the weaker battery cell (making sure they were the right polarity!) turned it on and waited.... and waited .... and waited for the voltage to increase. Eventually it got up to 4.04 and we were on our way. It took about 7 hours to reach 4.17 volts! I asked Justin why it was taking so long and he figured that given my charger was only 500 mili-amps, and that the cell was cutting out about 3amps short of where it should (ie at 6 instead of 9 amp-hours), that it would likely take about 6 or 7 hours to put another 3amps of capacity in to it.
So I got it all charged, put it back together and have been riding around this week to see how far it would go. Today I hit 8.5 amp-hours before it cut out! The lowest voltage was 28.9 and for the last little bit of riding (around 8.3 to 8.5 amps) it got a bit sluggish as I hit the 30 volts limit I had on the Cycle Analyst. At 8 amps the lowest voltage was 33.3 so the last bit of use really drops the volts off quickly. The range was 42 km which I am very happy with!
So the battery is back on the normal charger and hopefully I will get a similar range next time without having to pull the pack apart again. I am confident that will be the case. As an added bonus Justin offered me 25% off any future battery pack I purchase off them in recognition of my receiving an unbalanced pack and the work I put in to hopefully fix it up! Outstanding!