Recently, we have seen several kits for assembling a battery pack out of 18650 cells. Here are some examples, so you can see if that is something that might interest you. And remember, these aren’t just for ebikes, you can assemble any voltage or size you want, for any job you need a battery to power.
The Headway company makes cylindrical cells that use the Lithium-Iron-Phosphate chemistry (LiFePO4), which provides 3.2V per cell nominal. The other thing they are famous for is that their cells come from the factory with threaded studs on both ends of the cell. Also, their website provides all the parts to assemble a pack…including pre-cut metal bus-plates, and square plastic end-caps. I don’t know when they started this, but I wrote an article about a build that used these back in 2013, so this example of assembling a pack has been around since then, at the very least.
Since this is clearly awesome (because you don’t have to solder or buy a spot-welder), then…why aren’t they more common?
Headway cells don’t come in a variety of sizes (there are only two), and the smallest one is the 38140. This means that they are 38mm in diameter and 120mm long…and that, my friend?…that is BIG. The 38120 cell is 10-Ah for one cell, so a 2P pack would be 20-Ah. Although 20-Ah is a good size of pack (that I very much approve of), the only shapes you can configure them in is usually a big fat rectangle.
我们的朋友teklektik建立一个浴霸世界报长尾cargobike早在2012年，这些细胞，再加上“Juicer” board tracker ebikes have used the 38120，and also, here isa pic of a pack that was assembled to replace a 24V lead-acid pack on an electric wheelchair。
Micah Toll’s pack-building kickstarter
We were excited to write about Micah’s kickstarter campaign. He realized that there were a lot of battery pack builders who didn’t want to buy a spot welder (commonly $300 or more for a very basic unit), but many of the home-builders were comfortable making the series connections with a fat wire and a soldering iron.
Damien Rene pack-building spot-weld article
达米恩刘若英是在西班牙的电动自行车发烧友。我们的一个最一贯流行的文章是关于如何在一个he builds spot-welded battery packs for ebikes, found here。话虽这么说，最基本的点焊单元则可以从中国直接购买是SUNKKO 709A，它可以为大约$ 300在2017年被发现，即使为“合格”为模式，你可以在google搜索“SUNKKO失败”，并找到如何修复讨论线程和升级设备上的胆量。
有18650细胞点焊模型比SUNKKO 709A更强大和可靠的，但是......他们的成本也超过$ 300。
For a very long time, there has existed a plastic end-cap design that helps the pack-builder to assemble a pack. The “slot” on top of the cells is an 8mm wide alley, which is often filled with a 7mm wide ribbon of pure nickel (nickel bus-ribbon that is o.15mm or 0.20mm thick are the most common).
因为我发现，当我正在研究的18650格式的单元结构的文章，认为双方每18650细胞的底部是一个连续的导体（即：侧面和电池的底是带负电荷的）。这意味着…these plastic end-caps are very important。Vibration over the years can break through the PVC insulation-sleeve that comes over the sides of the cells, and a break right there will allow a short-circuit near the positive end.
积极的肩膀阴极附近的区域of the cell is the “danger zone”, and a compromise there is something that I call a “shoulder short” (the end with the white ring, in the pic below). It is VERY beneficial to add a self-adhesive fiber insulation washer to the positive end, and to use some type of plastic end-cap.
一旦你决定塑料端盖的可用模型，你怎么连接串联和并联每个单元？下面的PIC是一个共同的2S / 4P总线板。在该PIC，在镍母板上的四个垂直通路携带高系列电流。如果这些是10A细胞，然后四个垂直运行中的每一个进行，每10A，总共40A的整个包。
To be clear, if you are charging your pack with a 5A charger, that 5-Amps is charging “in series” too, so…the parallel connections will only carry a tiny amount of balancing current, under all charging and discharging conditions.
事实上，镍是不是一个伟大的指挥家。它仅用于两个主要原因。I ‘would’ state that it has very strong anti-corrosion characteristics, but…nickel-plating over copper bus-plates [or aluminum] has the same corrosion protection, and that composition would conduct better and costs less (nickel is expensive, and getting pricier each year). The first reason is that…pure nickel is stiff, and provides some structural strength, while copper or aluminum is malleable (soft and easily bendable).
The second reason is that pure nickel [as a bus material] will spot-weld quite easily and very fast, which helps the assembly-line move along rapidly. Although many packs are still spot-welded in China one cell at a time by a person, the trend is to have robots spot-weld a pack together very rapidly.
Personally, I am a fan of the “honeycomb” configuration, over the now common rectangular “rank and file” shape (shown above). For roughly the same volume of battery pack, the honeycomb layout provides more air-flow between each cell. Whether you are trusting in passive heat-shedding, or a pro-active fan-cooling system…if you have a more consistent air-flow envelope around each cell? It will help each cell to shed any of the heat that develops.
The endless-sphere forum member “Agniusm” is a very smart enthusiast from Lithuania. I am posting his “NESE” modules first because…the 6P modules have been tested at 80A (13A per cell), and the bus-strips only warmed to 30C / 86F.
This business model recognizes that any new clever design can be copied and produced very cheaply in China, so…rather than create the modules himself and ship them around the world…he provides the design code for free, so each builder can have them produced locally from a 3D printer service. The difficult part that he does provide for the customers is…the metal 6P bus-plates, which can be trimmed-down to fit in any of the other sizes of case, along with the Poron foam backing (6P, 5P, 4P, 3P, 2P, etc).
Beneath the orange 3D-printed protective insulating caps, these modules shown below are connected positive-to-negative in order to “series” them into the desired voltage. Do your home work, and exercise caution!
The Vruzend kit adds plastic cell-end caps to each end of a cell, and each cap has a metal contact inside, along with a tiny bolt that extends out to create a threaded stud for attaching bus strips.
The pic below shows one Vruzend cap cut open, and the metal contact has been removed to show its exact shape. It is a “corrosion-resistant” stainless steel, and it acts as a “leaf spring” that has a “C” shape. It also performs the duty of being the conductor, so these are limited to 3.5A each. A future version may have a copper foil overlay to provide a higher-amp version, but those are not available yet.
The original kit was based out of India, and now…there is now a US-based dealer in Florida…which is managed by Micah Toll.
If you wish to experiment with a copper foil overlay to increase the safe amp-carrying capabilities of these contactors, I recommend that your initial experiments use 0.25mm thick copper foil (also called, 10-mil, or 30-ga)
I bought one box of these to test, and I am impressed. They are similar to other kits, but there are two differences that interested me. First, the electrical contact and the spring that holds the contact against the cell-end are two separate elements. This means the spring can be made from a material that is perfect for a long term application of tension.
Second, since the spring and contact are two different materials, the contact can be made from copper (and pure copper is a great conductor, but a horrible material for a spring). The Nishi contacts are zinc-plated for corrosion protection, and I have sanded the plating off of several samples to verify that the contacts are indeed copper. The width and thickness of the strip has the same cross-section as 13-ga copper wire, so it can handle temporary occasional current peaks of 15A, which means it will work for my favorite ebike cell, the Samsung 30Q.
The materials shown off to the left in the pic above are 1/4-inch plywood, and 1/4-inch HDPE kitchen cutting board. Either one would make good side-panels to hold and protect a pack made from the Nishi pack-building system. These caps also connect side-by-side using splines on their sides that interlock.
The most noteworthy feature of this kit is that…they use asmall-but-strongneodymium “button” magnet as the connector to each cell-end. These magnets are mostly composed of steel, so…they are not good for high amps. This is not any issue for a very large “low-amps-per-cell” Power Walls. However, if you want to use these for the battery of a a longtail cargobike, upgrading the amp-capacity of the connections may involve adding a copper foil ribbon in-between the magnet and cell-tips (for initial experiments, you might consider using 0.25mm thick, 10-mil / 30-ga copper sheet).
Battery Bloc kits are available in a variety of configurations (4P, 6P, 8P, etc), so take your time shopping to see if these would work for you.You can find their website by clicking on the link, here。
The Energus company makes modules very similar to the NESE modules at the top of this article. However, they prefer to produce complete modules, which already have the cells inserted. As such, you must specify which cell you want inside the module (max amps, max range…or something in-between). and they also have a “plug and play” wiring harness available for the BMS, if you want.
如果你喜欢这些，their website can be found, here。
A reader sent me this link to “Ann Power” in China. The Chinese “ebay” is called Aliexpress. Sometimes you can get a good deal on there, and sometimes you get ripped off, but…it exists.
The brass threaded insert seen below only holds the nickel bus-plate onto all the cells in that group while you are spot-welding them, and then the bolts hold a copper sheet over the nickel to help increase the conductivity and lower current resistance.