When the Panasonic GA cells came out I got really excited, so excited in fact that I purchased 100 of them to build into a 7P14S pack in my spare time. Months went by and the batteries just stared at me from under the desk wishing that I would put them to good use. I ended up buying a spot welder off eBay, which ended up self-destructing before the pack was even finished. After a lot of procrastinating, I splurged for an even MORE expensive spot welder, which is the one that I should have bought from the get-go (review here). The entire process of building a very large pack like this from scratch was incredibly educational, frustrating and cathartic at the same time. I have a pretty strict rule that I won’t buy or use ANY product that I don’t completely understand how it works and that I can’t tear down and put back together. Building my own 18650 ebike pack seemed like a logical progression in support of that belief system.
For people who are looking to build your own ebike pack there are some great resources on Youtube under Damian Rene’s channel and Bruno ‘More Power’ Buccianti’s channel. Both these channels have tons of videos that show the entire pack building process from start to finish. For people who learn more easily by reading articles, Micah Toll did a great article on pack building right here on his ebikeschool website which is a must read before you build your first pack. I’ve tried very hard in this article to not repeat what Micah said in his article, so please read both. Everyone has their opinions, and I’m not a big fan of hot glued batteries and I would encourage people toward using plastic stencils instead. No matter what you decide to do, the first thing you need to do is buy some batteries.
How many batteries you need will depend on the configuration of the battery. This battery was a 14S7P which means I need 98 individual cells ( 14 x 7 = 98 ). The number of batteries in your series will depend on the voltage (13S for 48v & 14S for 52v). The number of batteries in each cell grouping (the number preceding the P) will depend on how many Ah you want your pack to have. If you are building a pack with 25R cells that have 2500mAh (2.5Ah) each and you want a pack that has 10 Ah then you will need to build a 4P pack ( 2.5 x 4 = 10 ). Before you settle on your P number make sure that the batteries can hit your discharge rate. My pack uses a 50Amp nom BMS and I have a 7P pack with GA cells which can put out 8Amps all day long. This means that my pack can safely put out 56 Amps with a 7P configuration so I am good ( 7 x 8 = 56 ). Under no circumstances should you build a pack that the BMS will be able to pull more power from the cell groupings than what they are going to be able to provide. When in doubt about the discharge rate, just use 25R cells which have an output current capacity which blows all other 18650’s out of the water. The 25R can do 20 Amps sustained PER CELL and can do 100 Amp bursts. I am not aware of any other 18650 2500Mah cell that can claim that capability. If there is one, please let me know.
With 18650 cells counterfeits abound, so be careful about who you are buying from. There are a lot of Alibaba and Aliexpress 18650 battery vendors that are selling counterfeit Chinese cells that are nearly impossible to differentiate from the real deal as the package wrapping and printing is exactly the same. These cells can dramatically underperform and also risk starting fires. If a deal seems too good to be true, it probably is. The safest place to buy 18650 cells is from a reputable US-based vaping or flashlight site that is known to sell genuine cells. If I need just a few cells I tend to buy from waveandvape.com which is owned by Eric of electricbike.com & Lunacycle fame. If you want to buy a lot of cells look for wholesale deals under the Bare cells section of the Lunacycle website. These GA cells came from the Lunacycle website right here and cost about $550 for 100 which as near as I can tell is a screaming deal. You can adjust the quantity by 10 using the drop down box as long as you buy at least 50 to get the best possible deal (ie, 50,60,70,80,90 etc). I can’t say enough good things about the GA cell which can put out 8 amps all day long. My 52v GA shark pack has been my go-to pack for the last 6 months and I’ve had no issues with it. I suspect that this large 25Ah GA pack will also give me many years of usage. Although 2016 brought out a lot of new exciting cells, none are as ideal as the GA cell which gives BOTH high power AND long-range in one cell. No matter what you decide, if you buy the cells 50 at a time they will be cheaper than buying a small quantity. The GA cells from the Lunacycle website are $5.50 each in quantities of 50 or more, whereas the cheapest you can get them for on WakeandVape are $6.50 each for 4 or $8 each if you want less than four. There are batteries that are much cheaper from Alibaba and Aliexpress, but I am extremely wary of Chinese 18650 battery dealers. When you can buy genuine, guaranteed cells from the US for a dollar or two more each, I believe it is worth the extra money for the piece of mind. Think of how much NOT having all your stuff burn up in a house fire is worth to you.
BMS is short for ‘Battery Murdering System’. If you have problems with your ebike packs and have not been physically abusing the pack then most often the problem is with the BMS. There are a whole lot of crappy Chinese BMSs on the market right now. The most important parts of your pack are
I really can’t emphasize this enough. If any of these components are sub-standard then so will your pack. If you’re going to waste countless hours of your life building your own ebike pack then DON’T cheap out on the BMS. The only BMSs I recommend are ones bought through Lunacycle. If you go to the BMS section on the Lunacycle website you’ll see that there are none listed there, but I told Eric to order a few thousand and Eric always does exactly what I say so soon they will be there and you can buy them again. If you know of another vendor that sells BMSs that actually work well, by all means, PLEASE tell me. No vendor is going to warranty their BMS for more than 30 days, and for non-reputable vendors in China they will probably not even do that. If you can get someone to vouch for a particular BMS on Endless-Sphere then it is probably decent, but there is a lot of crappy ones out there that will self-destruct if you look at them funny. Every problem with every ebike pack I have ever had has been caused by cheap, crappy, substandard BMSs. Just by looking at them there is no way to tell if a BMS is robust or flakey, the only way to know is if other people have used that BMS for extended periods of time and not had problems with them.
There is a lot of Chinese resellers selling nickel strips as 99.9% nickel when they are really just nickel plated steel. Nickel plated steel will weld better at lower power, but rest assured pure nickel strips are what you want. If you buy the strips, scratch them with a mat knife and soak them overnight in salty water and they look all rusted then you got duped. When in doubt you can buy from ebay which keeps vendors a little more honest as they will get crappy feedback otherwise. You can also ask people on endless-spheredrama.com who to buy from because lots of ebike builders have already gotten burned and want to make sure the same thing doesn’t happen to you. Make sure you get real nickel as steel has a MUCH lower current carrying capacity than nickel does as shown in this chart by master 18650 pack builder Damian Rene. The strips used in this pack were 8mm wide by .18 thick, I wouldn’t recommend anything smaller unless you are building a very low power pack. For my 50Amp pack I doubled up on these strips.
Clearly label the cell groupings so you don’t get confused. Notice 2 groups of 7 welds at the end and everything else is 14 cells. The other side is all groups of 14 cells.
Lay out the pack before you start in with the heat tape. Nice clean work bench kitchen table, right? Not.
Building your own ebike pack is something that every ebike enthusiast should take on at some point in their life. Although it is dangerous the danger can be easily mitigated by a little common sense. I am not a very technical person and although I have soldered quite a bit, I have a hard time reading electronic schematics and troubleshooting broken stuff. With a very modest skill set, I was able to sit down and in about 25 hours of work build a pack that looks like crap but actually works pretty well. Was it worth it in the end? No way. I didn’t do it to save money, I did it to say that I did it and so that I would understand what kind of labor went into every ebike battery I purchased. I have no regrets about the process, but I am skeptical that I would ever do it again knowing what I know now. When you can buy a complete battery with a warranty for just a few hundred dollars more, there is little financial incentive to build a pack from scratch. In the end, I have no regrets and there is no feeling like the satisfaction of beating the hell out of something that you created from scratch to fit into the frame of your full-suspension custom-built 3000W electric fat bike.
The battery heat-shrinked and wrapped in closed cell foam. The weight on the top keeps the pads down while the silicone dries.
Yeeeeeahhhh… I am happy for you that you finally got that homemade beauty finished =] The Sunko spot welder is an okay entry level welder and does a good job as long as you don’t push too hard with really thick nickel strip. Loved the “Bruno ‘more power’ Buccianti” hahahahaaa.. I am still laughing here…. *guess what.. I have a fatty surprise for you… I will make a video soon… you will love some hacking features hahaha =]
Haha I hope you make your packs from now on. Each one will get better and better although your first isn’t pretty after a couple builds they become super refined and things of beauty. Don’t stop you’ll get better I promise :-))
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Sorry, I’m a pessimist, I will be waiting for the “other” youtube video. Do you have a quick release from the bike?
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36v Electric Scooter
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