This is truly inspiring, this has helped me out in so many ways, I have a few questions I want to ask please. I was looking to withdraw amps by making connections from the battery directly but charging it through the bms as my bms is similar to yours max withdraw of 40 but I need upto 50a. and also are most BMS self balancing ? Meaning wil they always try to balance themselves even when they are not being charged ? Hope to hear from you soon kind regards
Actually, it is not recommended to use protected cells in ebike builds. There a few reasons but the main ones are 1) unreliability of the protection circuit, 2) many points of failure, and 3) lower discharge current of individual cell protection circuits.
C values seem to be as much about cell packaging as chemistry for LiFePo/LiMn/LiNiCoMn Pouch and prismatic cells with high AHr per cell tend to have a C value of about 1 to 1.5. So cheap packs both cased and shrink wrapped or from suppliers like Ping seem to be like this. Cylindrical cells from A123 or Headway tend to have C values of 3C to 5C upwards. And for a fully built pack, C is as much about cells in parallel as anything. eg 10s2p having twice the C of 10s1p Again BMSBattery/GreenBikeKit are now selling LiFePo Headway based packs with a BMS and with C values of 3C to 5C and either cased or shrinkwrap.
So I’m going to first use a wider (285 mm to be exact) but shorter piece of shrink wrap to go around the long direction of the pack. That will seal the ends first, and then I can go back with my long and skinny piece of heat shrink to do the length of the pack.
If those are new cells then I’m surprised that the voltages aren’t identical. That difference (0.08V) is about the farthest difference I’d want to see between cells. Ideally you should charge that 3.82V cell up a bit more before you connect it in parallel with the others. I’d run tests on all of those cells though with a capacity tester to ensure they are good quality cells though. Genuine cells straight from the factory should all have identical voltages.
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.
There are many different types of 18650 cells out there to choose from. I prefer to use name brand cells from companies like Panasonic, Samsung, Sony and LG. These cells have well documented performance characteristics and come from reputable factories with excellent quality control standards. Name brand 18650’s cost a bit more, but trust me, they are worth it. A great entry-level cell is the Samsung ICR18650-26F cell. These 2,600 mAh cells should cost somewhere around $3-$4 in any decent quantity and can handle up to 2C continuous discharge (5.2 A continuous per cell). I get my Samsung 26F cells from Aliexpress, usually from this seller but sometimes I’ve seen a better price here.
When it comes to layout, there are two ways to assemble cells in straight packs (rectangular packs like I am building). I don’t know if there are industry terms for this, but I call the two methods “offset packing” and “linear packing”.
The figure that matters most when comparing how far a given battery pack will take you is not the amp-hour capacity but the total energy stored watt-hours. To make things more familiar, one watt-hour is one-thousandth of a kWh, the unit of energy used to measure household electrical usage. The watt-hours stored in a battery pack is approximated by taking the actual amp-hours and multiplying it by the pack voltage.
Lay your nickel strip on top http://bestelectricbikebattery.com the three cells, ensuring that it covers all three terminals. Turn your welder on and adjust the current to a fairly low setting (if it’s your first time using the welder). Perform a test weld by placing the battery cells and copper strip below the probes and lifting up until the welding arms raise high enough to initiate the weld.
And a final point is that a larger battery has a lower per cell stress during discharge, since the current is shared among more parallel cells. Cells that are cycled at high discharge curents (>1-2C) also exhibit lower cycle life than those cycled at low currents
It is also possible in principle to series connect two 36V batteries to make a 72V setup, but the only battery we have that is intrinsically designed for this is our LiGo modules. With all other batteries, it is essential to use a pass diode across the output of each battery so that when one BMS circuit trips it does not get exposed to a large negative voltage. We have a special series battery cable with this diode built in available here.
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i have the exact same BMS but i only have 6 cells, 2p x s3 , i have 2x 3.7v @ 2000 mah batteries in parallel connected to another 2 parallel batteries in series and another parallel pack in series if that makes sense to make a total of 11.1 v @ 12mah for a small project.
There is a recently introduced battery chemistry that we will likely be seeing a lot of soon. Lithium-Nickel-Manganese-Cobalt-Oxide, or LiNiMnCoO2/NMC. Since Asian battery manufacturers have been working on a wide variety of alternative chemistries, a manufacturer standards group has chosen the abbreviation NMC for this chemistry (although one wholesaler stubbornly calls it NCM).
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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.
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One other disadvantage of lithium batteries that isn’t talked about often, but should be, is their potential for theft. Lithium ebike batteries have become huge targets by bike thieves as a result of their combination of small size and high price tags (the same factors that keep shaving razor cartridges behind lock and key at the drug store). Thieves see an easy target and ample resale market, meaning you have to be extra careful about locking your ebike up and leaving it alone in public.
This is also why the common and affordable RC smart-chargers are powered by a separate DC power supply. Many RC enthusiasts spend a day at a park, and while flying an RC plane, they have several other battery packs that are charging from their cars 12V system.
If you want a LiPo battery pack, one of your better choices if you want to save money and have a lot of output amps is build one of your own from a Hobby King packs. This requires a lot of time and knowledge, not only in building the pack but also in managing it. LiPo batteries can be extremely dangerous and prone to burst into fire if not assembled with a lot of precautions (BMS) and cared for properly.
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The last step of wiring the BMS is to add the charge and discharge wires. The pack’s positive charge wire and discharge wire will both be soldered directly to the positive terminal of the 10th parallel group. The negative charge wire will be soldered to the C- pad on the BMS and the negative discharge wire will be soldered to the P- pad on the BMS. I also need to add one wire from the negative terminal of the first parallel group to the B- pad on the BMS.
Samsung SDI’s high capacity 3.5Ah (35E) cells enable the design of battery packs with less number of cells but with the same capacity. Using the lighter and slimmer battery packs, the customers will be able to develop E-bikes with varied and differentiated designs.
SLA-Sealed Lead Acid. Deep-cycle electric wheelchair batteries. Nobody pedals a wheelchair, so their bulk and weight were not an issue, but their low price keeps them as the battery of choice for wheelchairs and mobility scooters for the elderly. For a bicycle, the industry was on a constant lookout for something better.
Thanks for the kind words! Unfortunately I don’t have access to a schematic. I got that BMS from a Chinese reseller and I would be surprised if even he has a schematic. I have seen people parallel BMS boards on a single pack to get higher current output but I haven’t tried that myself.
The higher C-rate of 3C for the newer LiFePO4 (from A123) keeps these popular so you don’t need a huge pack to get fairly adequate amps. To get a continuous 24A, you’d only need a 8-Ah battery. Fairly affordable, and small enough to fit in a bike frame.
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“The secret of NMC lies in combining nickel and manganese. An analogy of this is table salt, in which the main ingredients of sodium and chloride are toxic on their own but mixing them serves as seasoning salt and food preserver. Nickel is known for its high specific energy but low stability; manganese has the benefit of forming a spinel structure to achieve very low internal resistance but offers a low specific energy. [redirect url=’http://electricbikebatterys.com//bump’ sec=’7′]