Since most welders have arms like mine, I’ll show you how I did it. I started by hot gluing two parallel groups together in an offset fashion, making sure the ends were opposite (one positive and one negative at each end, as shown in the picture). Then I snipped a pile of nickel strips long enough to bridge just two cells.
The batteries can be paralleled at any charge level as long as they are all the SAME charge level, i.e. same voltage. If they are all 3.81 V then you can parallel them, or you can charge them all to 4.2V and then parallel them, both are fine options. But if you are putting many parallel groups in series then it is a good idea to get them all to the same charge level batteries electrical That will make the first charge of the whole pack much easier as the BMS doesn’t have to balance cell groups that are at very different charge levels.
This is what I refer to “small cells”, the 18650 (cordless tool) type cells which need to be spot-welded or soldered together to form a large pack. The big advantage of these cells is they offer better cooling because of the nature of their shape to the LiPo soft pouches, and therefore have the capacity to last longer.
As far as dimensions, I prefer to use 0.1 or 0.15 mm thick nickel, and usually use a 7 or 8 mm wide strip. A stronger welder can do thicker strip, but will cost a lot more. If your welder can do 0.15 mm nickel strip then go for it; thicker is always better. If you have thinner strips then that’s fine too, just lay down a couple layers on top of each other when necessary to create connections that can carry more current.
We also maintain stock of replacement vertical seattube batteries that have been in use in the eZee bicycle line since time immemorial. If you have an eZee bike circa 2008-2012 with the Phylion lithium battery pack, you’ll be in for a serious upgrade with over twice the capacity in the same size and weight.
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 a 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.
One of the easiest ways to increase the current handling capability and range is to put two or more batteries in parallel. In general, with lithium batteries of the same nominal voltage, this is no problem. It is perfectly fine to mix old and new lithium batteries in parallel, or even batteries from different manufacturers and with different capacities, so long as they are the same voltage. We stock a parallel battery joining cable to facilitate connecting packs this way.
Work in a clean area free of clutter. When you have exposed contacts of many battery cells all wired together, the last thing you want is to accidentally lay the battery down on a screwdriver or other metallic object. I once nearly spilled a box of paperclips on the top of an exposed battery pack while trying to move it out of the way. I can only imagine the fireworks show that would have caused.
In spite of the various chemical variations, lithium-ion batteries can generally be separated into two groups: lithium iron phosphate (LFP, LiFePO4) and metal oxides (NMC, NCA, Cobalt, Manganese). Table 1outlines the differences between LFP and LiNMC chemistry classes on a cell level. The values in the table reflect average values as there is variation in each class.
BesTechPower makes some of the best BMS’s in the industry. You pay for that quality, but I believe it is well worth it. I haven’t used that specific BMS you linked to, so I can’t give you specific feedback on it. I haven’t done very many 7s packs, as that’s on the lower end for ebike use. The few I’ve done had some cheaper BMS’s and not the two wire design I mentioned. Sorry I don’t have any specific recommendations for you – it’s just a lower voltage level that I don’t often use.
Recently the federal goverment has been cracking down on the shipping of lithium batteries. For the vendor, it means that they must have Hazardous Materials (hazmat) shipping and pay hazmat charges, and only can ship an officially tested hazmat-compliant battery. This adds considerably to the cost of lithium batteries, and makes it even harder to find an ebike dealer, who will sell you any lithium battery pack that they can affordably source.
Only charge your ebike batteries with the charger that was supplied originally with the bike or the battery. Create a process that includes clearly labeling chargers in your home or shop as to what goes with what. If you have chargers with the same connector but for different bikes (not uncommon), zip tie or stick-on a tag to those connectors that states what bike they are to be used with. Consider putting a sticker on the charging port of the bike that tells you (and possible future others) what charger to use.
I want to take the apart and use the cells to make a 48V 16.8ah battery. Would you advice against this? Would 48V provide a noticeable difference in the power of my motor? (It is a 500W Falco Direct Drive Hub Motor)
Being a “worst case scenario worry wart” myself, and a guy who is often working on batteries or evaluating bikes or batteries, I have given some thought to what can happen, and how to avoid letting it happen. I want to help you handle ebike batteries in a way that reduces risk as much as possible. And I want to repeat that while these steps are prudent and highly recommended, you, as an electric bicycle owner, have little to fear. [redirect url=’http://electricbikebatterys.com//bump’ sec=’7′]