I like to cut most of my nickel strip in advance so I can just weld straight through without breaking my flow to stop and cut more nickel. I measured out the width of three cells and cut enough nickel strip to weld the top and bottoms of 10 sets of 3 cells, meaning 20 strips of nickel that were each 3 cells wide, plus a couple spares in case I messed anything up.
If you don’t have an actual heat gun, you can use a strong hair dryer. Not all hair dryers will work, but my wife’s 2000 watt model is great. I own a real heat gun but actually prefer to use her hair dryer because it has finer controls and a wider output. Just don’t go mess up your wife’s hair dryer!
Regarding the cell question, its a mixture of both. Cheap ebikes use cheap cells. You can bet the Sonders ebike had the cheapest cells available. Name brand ebikes usually use Samsung cells, but sometimes LG and occasionally Panasonic cells can be found in name brand ebikes (the Panasonics are some of the most expensive and so they are rarer). That being said, I’ve seen some shadier internet sites selling high quality (and genuine) Samsung/Panasonic packs, and I’ve seen some nice ebikes with some no-name cells. You should always check with the vendor/manufacturer if you want to ensure you’re getting good cells. Unfortunately, it can be hard to verify the cells yourself though without voiding the warranty, as they are usually sealed under shrink wrap. A good vendor will be happy to confirm the cells for you ahead of time and may even be able to show you some pictures of opened packs to verify.
2. Lithium-Ion Shrink Wrapped Shrink Wrapped Lithium-Ion Batteries are housed in a soft PVC heatshrink material. It protects the battery from moisture and short-circuits, but not from being dropped or punctured. View Shrink Wrapped Lithium E-Bike Batteries
HERE ARE 100 GENIUNE LG LGDAS31865 18650 2200MAH CELLS. YOU CAN’T FIND A BETTER DEAL THAN THIS. Capacity: 2200mAh. THE PHOTOS SHOW HOW WE GET THESE IN AND BREAK THEM DOWN. STOP GETTING RIPPED OFF AND …
I figured this would be a critical step I wouldn’t want to mess up. Thanks for the advice on using the multimeter. That’s good to know as I thought I might need to open up the controller and see which wires went where on that male xlr connection which I guess would be an option too. Thanks again!
192 watt-hours is about the smallest battery size you would want for an ebike. Many of the store-bought ebikes have about this much capacity since it keeps the battery cost down. For people who want to actually commute reasonable distances of 40-50km, then I would recommend on the order of 400 watt-hours. While it can vary a lot with usage habits, an energy consumption of 9-10 watt-hrs / km is typical on normal direct-drive setups.
I’m not sure what cells exactly you’ve got there, but a good replacement cell (assuming it has similar specs to your cells, which you’ll have to confirm) could be the Samsung 26F cell. It’s a good quality economical battery cell. I’ve gotten them from here and had great experiences with the vendor: Samsung 26F 18650 lithium battery cells
36V10Ah Li-Ion NiCoMn “Little Frog” ABS shell ebike battery pack. Included 2p10s 5Ah polymer cells, 1pcs 15A continuous discharge current BMS, 1pcs 36V2.5Amps EMC-120 Lithium Ion battery Alloy shell charger.
These cells are distinctive due to their cylindrical shape and are about the size of a finger. Depending on the size of the battery you plan to build, you’ll need anywhere from a few dozen to a few hundred of them.
Assuming the original battery is a li-ion battery and has the same number of cells in series (same voltage), then yes it should charge it. However, looking at the picture of the battery in that listing, I can tell you that is not a picture a 24V 25AH battery. That picture has 6 cells, and a 24V 25AH battery will have something more like 56 cells. That picture looks like a 22V 3AH battery. It could be that they simply used the wrong picture in the listing, though I doubt it as that would be an insanely good price for that size of a battery. but I’d be wary of that offer either way.
I want to build some custom batteries, but I am hesitant to do the spot welding myself. Aren’t there modular and affordable pieces of hardware one can use to connect the batteries? Something like this?
Now you have the required specs on the pack, namely its voltage and capacity, so it’s a matter of finding one that meets your budget and weight restrictions. To a first order, for a given voltage and capacity, NiCad will cost twice as much as lead acid but come in at half the weight, NiMH will be 30% lighter and more expensive than NiCad, and lithium will be twice the cost of NiMH and a further half the weight again.
Lead acid batteries are much larger and heavier than lithium batteries, limiting their placement on ebikes. They almost never come packaged with ebike specific mounting hardware which means that they generally have to go in a bag on the rear rack or in panniers on either side if the rear wheel. Mounting them up high on the rack isn’t a good idea either because it will negatively affect handling. Generally speaking, you want to mount your batteries as low as possible to keep the center of gravity of the ebike lower towards the ground. This will significantly improve your ebike’s handling.
It’s not impossible, but I don’t have high hopes. When a few cells die like that, they tend to kill the other cells in the same parallel group and often can kill cells in the series groups adjacent to them. You could be looking at replacing a large number of cells outside of the ones with obvious damage, and it will be hard to confirm that you’ve found all the dead cells without pulling apart most of the pack. If you’d like to try, there’s a chance you can end up saving the pack for less than the cost of replacing it, but it’s going to be an uphill battle.
When it comes to choosing a BMS, the number of cells you have in parallel aren’t important. Only the number of series cells matters. The same BMS will work with 1 or 100 cells in parallel, as the voltage stays the same regardless of the number of parallel cells.
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.
Another excellent answer, thanks so much! Now it has arisen a few related questions, if you don’t mind answering them. I’m using authentic Samsung ICR18650-26FM cells. I had already purchased a 24V 15A BMS before I slightly understood all of this. I was also able to obtain more cells since my original idea, so I was planning a 7S10P pack (around 30Ah), 70 cells total. I see each cell can do around 5A, making a 10P pack put out 50A total. If I stick with my 24V 15A BMS, that will give me 15A * 24V watts, or 360 watts total for my 500 watt motor. I’m going to number these to make it easier:
Battery: 36V 8AH lithium battery. Power: 250W. The frame folds via a 2 part locking mechanism which ensures the catch safely remains locked when the bike is in use and can be operated with one hand fo…
Most commercially available 36V packs are around 10Ah, meaning our pack will be just a bit smaller. We could have also gone with a 4p configuration giving us 11.6 Ah, which would have been a slightly bigger and more expensive pack. The final capacity is totally defined by your own needs. Bigger isn’t always better, especially if you’re fitting a battery into tight spaces.
I am working on a similar project, and was wondering if the BMS’s that you recommended would handle any back EMF from the motor (from regenerative braking, for example.) I see that there are separate leads for charging and discharging, so I’m guessing if current flowed back through the discharge circuit that would be bad. Do you have any recommendations on a BMS (or something different) that would handle this condition?
thanks for detail explanation batteries for e bikes I was enjoj reading it. Well, I am interesting why did you pick this tipe of battery, I was thinking to use LiFePO4, I know there are usualy 3.2V it is less than 3.6V like here? Also, can you explain me how to calculate max current of battery, it says that you get 8.7Ah, but how much Ampers and what is the power of battery, how many Watts (P = U * I)? Furthermore, without welding, can I do on contact connection, like for example are battery in remote control?
As a side-note, the Boeing 777 Dreamliner battery fire was using LiCo. They wanted a battery that was as light as possible, and as compact as possible. I am not an engineer, but I agree with the statement made by “Tesla” electric car maker Elon Musk, when he said that there was NOT adequate heat insulation between each cell. Better individual cell insulation would prevent a bad cell that was getting hot from heating up the surrounding cells. That is what led to a domino effect. The Tesla cars have a cell cooling system, and the on-board computer can detect and cut-off any cell-group that is getting hot.
Also changing the fuse to a higher one could cause the wires to start a fire and the whole house would burn down if the wires are not thick enough. Also in sweden a fuse gets bigger as they are rated higher so you can fit a 20A fuse in a 10A slot, for safety.