26′ rear wheel 48v 1000w hub motor (powerful Motor with hall sensor ) Electric Bike Kit With or Without Battery. 26′ size REAR WHEEL 48V 1000W ELECTRIC BIKE KIT WITH or WITHOUT BATTERY. 48v 1000w brus…
I don’t think there is any danger to parallel more than 4 cells. Tesla cars have literally hundreds of 18650 cells just like these paralleled. The issue is that if you ever did have a problem with one cell, like a factory defect that caused it to short circuit, it could die and drag all the other cells down with it, killing the entire parallel group. That’s why Tesla uses individual cell fusing, but that’s not really employed on the small scale like for ebikes.
It’s best to try and match the cells as closely as possible based on capacity by using a lithium cell tester like this one. If you plan on using the battery you build for a high drain application, different current ratings will be more of an issue. If you have many cells in parallel and will only pull low current from each one, then different current ratings are less of an issue. It’s always best to use perfectly matched cells, though I know that’s not the cheapest option and is outside of the budget for many.
My daily driver ebike has 8 cells paralled (14s8p) and it’s been working great for a long time. You can certainly make two 13s4p packs and parallel them after the fact, but don’t be afraid of making a single pack. As long as you use good quality cells, the risk of a parallel group dying is incredibly small.
Many retailers suggest charging the battery at least once a month if the bike is not ridden much, and say that the more the bike is ridden, the stronger the battery will be. All batteries, though, will deteriorate in time and they will need to be replaced and disposed. When that time comes, it’s best to ask your local retailer how to dispose of the battery, but bear in mind that local authorities should provide recycling and disposal facilities.
One of the first advantages of lithium batteries is their small size. You can fit a lot of lithium on a bicycle frame. This alone can give your ebike some seriously impressive range. Two or three mid to large batteries for electric scooter lithium batteries could easily fit on one ebike, giving potential ranges of 100 miles (160 km) or more. I guess this would be great for people that don’t mind sitting on their bike for three to five hours at a time, or that for some reason don’t want to charge up for weeks (hey, when riding your ebike through a zombie apocalypse, the last thing you want to be doing is searching for an outlet).
Hello Micah: Thanks for this most interesting and useful article! I want to build a battery in a 39mm x 520mm seatpost for fueling a 250W motor that normally uses a 7.2 Ah – 25 V bottle-shaped battery. The new seatpost battery should only have an autonomy of 7 miles of steep hills (40%) between each daily charge. What are your recommendations? Happy day! Fred
If any one battery cell varies significantly from the others, do NOT connect it to the other cells. Paralleling two or more cells of different voltages will cause an instantaneous and massive current flow in the direction of the lower voltage cell(s). This can damage the cells and even result in fire on rare occasions. Either individually charge or discharge the cell to match the others, or more likely, just don’t use it in your pack at all. The reason for the voltage difference could have something to do with an issue in the cell, and you don’t want a bad cell in your pack.
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.
Either way works, but my orange jig saves me one hot glue step which just makes for a cleaner looking pack. Of course it’s all the same after the pack gets covered with shrink wrap, so you can use any method you’d like. I’ve even found that some of those cylindrical ice cube trays are perfectly sized to hold 18650 cells. Cutting off the top would leave it clear for welding. I’d add some strong neodymium magnets to the backside to hold the cells in place like my orange jig has, but other than that it’s a perfect jig almost as-is.