Actually I have ran into a problem – a few days ago I was riding it up a hill on a hot day when the power cut off and it wouldn’t start again. When I tried to charge it, the light on the charger just flickered from green to orange. I took out the battery and found that one of the cells had corroded from what looks like overheating. I think that the battery pack failure was most likely caused by too much of a load applied to the battery pack.
The Panasonic NCR18650PD cells can be purchased at Fast Tech dot Com, who reliably processed and shipped my transaction. Good prices, too, from this Chinese-based vendor. I “tested the waters” by buying just 4 cells first and will certainly be buying more from them. I’d like to make my own e-bike pack with these cells and further inquired to AllCell to see if I could obtain one of their PCM blocks. Unfortunately, they will only sell these on bulk wholesale basis to established pack-building businesses. The DIY pack builder will have to explore other options.
I then put one set of welds on each cell end of the first parallel group, effectively tacking the three nickel strips in place. Then I added another set of welds on each of the negative terminals of the second parallel group. This gave me 6 weld sets, or one weld set for each cell. Lastly, I followed up those single weld sets with another couple welds per cell to ensure good contact and connection.
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Offset packing results in a shorter pack because the parallel groups are offset by half a cell, taking up part of the space between the cells of the previous parallel group. However, this results in a somewhat wider pack as the offset parallel groups extend to each side by https://en.wikipedia.org/wiki/Electric_bikes quarter of a cell more than they would have in linear packing. Offset packing is handy for times where you need to fit the pack into a shorter area (such as the frame triangle) and don’t care about the width penalty.
In the event of a fire, evacuating the building is more important than fighting the fire. Calling the fire department (911) is essential. Keeping yourself safe and not breathing the fumes is more important than saving property. Even if the fire is safely moved outside, call 911, for these fires are tough to extinguish.
Now this step is very important: I’m going to turn the pack upside-down and perform this set of welds between the positive caps on the second parallel group and negative terminals on the third parallel group. Essentially, I’m welding on the opposite side of the pack as I did when I connected the first two parallel groups. Skip down a few pictures to see the completely welded pack to understand how the alternating side system works.
If not possible, try charging them individually. Some of them might come back but others might be dead. The tricky thing is that they will likely not be able to deliver their full capacity anymore and the actual capacity will likely vary from cell to cell. Two year old cells at a very low voltage are quite a gamble.
To calculate the max amps the battery can deliver, you have to know the max amps of the cells you used. For example, Panasonic 18650pf cells can deliver 10A continuous, and I used 3 cells in series in this battery, so the battery can deliver 3 x 10A = 30A. However, you also need to know how much current the BMS can deliver. If I put a 15A continous BMS on this pack then that would be the “weakest link” so to speak, meaning the pack with the BMS could only deliver 15A continuous.
In many situations, especially if you are replacing a battery pack on an existing setup, the voltage is defined by the controller electronics and cannot be readily changed. Otherwise, the voltage determines the maximum speed at which your vehicle will travel, and you have a degree of freedom in selecting the voltage to meet your performance expectations. If you know the volts/rpm for the motor, then it is straightforward to calculate how fast it will go for a given voltage. Select a value that gives an unloaded speed of about 20% greater than your desired cruising speed for best performance. [redirect url=’http://electricbikebatterys.com//bump’ sec=’7′]