A recent quote from ES member SamTexas on claimed max C-rates: “…I have in front of me Samsung’s own Nickel (Manganese) 18650 cells….I have tested these cells at 3C continuous and they do deliver full capacity at that rate. Push it to 5C and they become hot and capacity is greatly reduced…“
Yes, that’d work, but I’d get an additional 7s battery so you have 20s total. Also, you should know that the older your original 48V battery is, the more time it will take your new 72V combined battery to balance, as the first 13 cells will likely have less capacity in comparison to the newer cells. I made a video recently showing how to do this upgrade that you’re talking about: https://www.youtube.com/watch?v=9KHo-T74IWA
That might of sounded confusing, so let’s talk in real numbers. My pack is about 70 mm high and about 65 mm wide. That means that half of the perimeter of my pack is 70+ 65 = 135 mm. So I need some heat shrink tubing that has a flat width (or half circumference) of between 135 to 270 mm, or to be safer, more like between 150-250mm. And if possible, I want to be on the smaller end of that range so the heat shrink will be tighter and hold more firmly. Luckily, I have some 170mm heat shrink tube which will work great.
But what if you didn’t have to compromise? What if you could build your own ebike battery to your exact specifications? What if you could build a battery the perfect size for your bike, with all of the features you want, and do it for cheaper than retail? It’s easier than you think, and I’ll show you how below.
Hailong makes some of the more refined of the generic battery enclosures from china. You’ll see them online everywhere, stuffed with whatever cells and BMS circuit appropriate to the market being addressed. They secure to the water bottle eyelets on the down tube of your bike frame, and the narrow height of this pack design allows it to fit even on smaller or hybrid frame geometries that wouldn’t normally fit a pack. We have the smaller Hailong-01 enclosure in 36V (10s 5p) and 52V (14s 4p) layouts suitable for 20-25A current setups, and the larger Hailong-03 enclsoure in 36V 23.5Ah (10s 7p) and 52V 16.5Ah(14s 5p) sizes for higher current and capacity.
After writing my question, I did more research on these cells regarding overcharging and over-discharging and I see where you’re coming from regarding not having connections between the parallel cell blocks to smooth out differences between individual cells. So as a permanent installation, it’s not going to work. However, I’ve had another thought, which I’ve put at the final paragraph.
Lastly, regarding the spot welder. I actually prefer to use the kind like you said, with the two arms that lift up and provide equal pressure at each weld. The kind with two long welding cables like this welder has both options which is nice, especially for if you need to reach to the middle of a pack to make a repair or if you missed a weld. I mostly use the short rigid arms though and just weld one row at a time before adding more cells – that way I can reach all the cells with the short arms.
When you buy your battery, make sure you know what its maximum amp output is. Remember, by multiplying amps and voltage you get the actual current capacity of the battery. For example a 48-volt 25 amp pack can put out 1200 watts.
In the rush to upgrade from lead acid to the latest NiMH and lithium packs, it seems that most companies forgot about the old venerable Nickel Cadmium battery as a suitable option for ebikes. Although they are somewhat heavier than the NiMH and lithium options, they are still a substantial weight savings over lead. NiCd packs have had a solid and proven track record in demanding rechargeable battery applications.
This page is embarrassingly old, referencing chemistries that are completely obsolete, and is due for a rewrite. In the meantime, we recommend checking out our Battery Kits Product Info page for a more current explanation on lithium specific battery packs.
eBay determines trending price through a machine learned model of the product’s sale prices within the last 90 days. “New” refers to a brand-new, unused, unopened, undamaged item, and “Used” refers to an item that has been used previously.
12V increments are easier to do with LiFePO4 due to the 3.2V per cell. So for 12V, 24V, 36V and 48V they go 4 cells, 8 cells, 12 cells and 16 cells. Li-ion is more annoying because the 3.7V per cell doesn’t play as nicely. The general convention for the same 12V increments is 3 cells, 7 cells, 10 cells, and 13 or 14 cells. 3 cells is just a bit low for a 12V system (about 11V nominal) but will work for most applications until the voltage drops to about 9.5 or 10V depending on your device’s cutoffs. Regarding the balancing issue, if you’re using those packs that claim to remain in balance then I’d imagine you can just trust them. If their packs had problems with balance then they’d probably be having tons of returns. Worst come to worst you can occasionally open the case and measure the cells to make sure they are all staying balanced. One word of advice: be very careful with the series/parallel switch setup. If you make a mistake or the switch melts you could end up shorting your batteries and ruin the whole lot…
If you are thinking about building your own LiPo pack, a 48V / 10-Ah battery pack can be made for around $300. However to undertake this project you should research extensively on www.endless-sphere.com on how to build and take care of your pack. batteries for electric scooters replacement hours of reading before you are ready to build a pack of your own.
Rang: 18-25km(36v 6ah). Motor: 36V 250W brushless. Battery: 36V4/6AH lithium battery. The eco-friendly bicycle is 100% electric and emissions free, saving both your wallet and the environment. New Out…
I’m not familiar with this copper serial connection you’re talking about. I guess you mean to reinforce the series connections to handle more current? As long as you are using enough strips of nickel (and ensuring that it’s pure nickel and not nickel coated steel) then you shouldn’t need copper reinforcements. I try to use at least 1 strip of nickel for every 5A my battery will carry. So if I’m looking for a 20A max load, I’d use 4 strips of nickel in each series connection. That’s easy to do if each cell in a parallel group of 4 cells is connected to the next group by one strip each.
Actually, the protected cells aren’t a great option for ebike packs. The protection circuit on every cell can overcomplicate things, not to mention that it usually isn’t rated to handle the same current the cell could without a protection circuit.
Thank you so much for taking the time to write the battery chemistry article. I am looking at buying my first electric bike, and needed to understand the differences in LiOn batteries. There are still retailers selling SLA battery pack bikes and wasn’t sure if that was what I wanted, or LiOn. Your article helped me greatly.
Used PL-350 electric bike kit, The battery does not charge. Charger is fine but only shows a red light. It sat dead for about a year. Then the controller showed about 80% after charging. Everything wo…
If I regroup my 12 paralled cells in 10 modules, can I then join these in series using single wires (one for neg, one for pos) between modules, instead of wiring each terminals of each cells like you are doing. Could this affect BMS and/or have any negative impact on cells balance?
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.
The only two ebike companies that sell LiPo to the public are Optibike and Pi-cycles, and both contain the battery in a strong metal box which makes up of the frame. The companies fire tested these enclosures and are confident that their frame are effective and safe vessels for LiPo storage.
However, when you factor in the shorter life cycle of lead acid batteries, they become comparable to lithium batteries over the entire life of the electric bicycle. For example, a lithium battery may cost five times the price of a lead acid battery, but it could easily last five times as long as well, making the price about the same over the life of the lithium battery. You’d have to buy at least four replacement lead acid batteries (maybe even more) by the time your lithium battery finally kicks the can.
If you are excited about this improvement in battery chemistry, (NCM being 25% smaller/lighter that the fussy LiFePO4, and 300% better C-rate than the reliable and non-fussy LiMnO2) you may also be asking the question…What chemistry is next?
You’ll also notice in the following pictures that my charge and discharge wires are taped off at the ends with electrical tape. This is to keep them from accidentally coming in contact with each other and short circuiting the pack. A friend of mine recently tipped me off to another (and probably better) option to prevent shorts: add your connectors to the wires first, then solder them onto the pack and BMS. Doh!
36v 10Ah Bottle Type Battery. Rated capacity: 10Ah. 36v 14Ah Rear Rack Type Battery. Rated capacity: 14Ah. 48V 14Ah Rear Rack Type Battery. Recommended to be used with 36V 250W electric bicycle motor.
So after buying a 48v 20 Amp battery from Ebay (and knowing very little at that point), I realized it didn’t have a BMS and heard rumors that if i attached it direct to the controller, it would see it as a short (controller would be closed) and blow the controller.
I then took my second sense wire (or your third sense wire if you have one more sense wires than parallel groups) and soldered it to the positive terminal of the second parallel group. Again, note that I’m soldering this wire to the nickel in between cells to avoid heating any cell directly.
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My thinking is that because each of the batteries is only 50% stressed, that the probability of problems due to overcurrent, etc. would be negated and I wouldn’t use a BMS for the supplementary battery.
I am new to the ofrum and to the ebike world so I would like to seek some advice please. I have recently bought a sondors fat bike to the UK and want to make some tweaks, I would like to upgrade the battery on a budget, I was thinking of 4 x 12v 5ah lead acid batteries in series, would this give me 48v 20ah or have I got this totally wrong? I want to replace the stock contoller for a 48v 25amp one, would this suffice? lastly it comes with a stock 350w bafang motor, if I make the battery and controller upgrades will the motor handle the increase in wattage? could I drill venting holes in the case cover to expell some heat? Your thoughts and advice would be most welcome,
For discharge wires you’ll want something bigger, like 14 awg silicone wire. 12 awg would be better but might be overkill for your use. For charge wires, 16 awg silicone wire would be fine and you could probably get away with 18 awg silicone wire.
I finally made it happen on BMS #3 (the unfortunate thing about AliExpress is that every dumb mistake that kills a part is another month added to the project) and the battery seems to work great, though it only has a couple miles so far.
First of all, NCR18650B cells cannot be discharged at 2C. Those are 5A MAX cells, and really you should keep them closer to 1C to keep them cool and happy. They are economical cells. They do better when in large parallel groups so you can take advantage of their high capacity without the downside of their low discharge rate. They are great cells, but not for low AH packs.
Many people are tempted to use cheaper 18650’s sold under names like Ultrafire, Surefire and Trustfire. Don’t be one of those people. These cells are often marketed as up to 5,000 mAh but struggle to get more than 2,000 mAh. In actuality, these cells are just factory rejects, purchased by companies like Ultrafire and repackaged in their own branded shrink wrap. These B-quality cells are then resold for use in low power devices like flashlights where their weaker performance is less of an issue. If a cell costs less than $2, it simply isn’t worth it. Stick to the name brand cells, like my favorite Samsung cells, if you want to build a safe, quality ebike battery.