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Building battery pack with generic BMS

Jay Barnett

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Ive bought a generic BMS board from aliexpress and it arrived today in post. I have 32x 18650s to put together a kickass battery pack, but im looking for some diy instuctions or video of how to put it all together. Anyone know how its done. I have multimeter, solder and various parts needed.

I know its a little naughty to double up but im thinking of using 2x 18650s in parallel for each of the 16 connections on the BMS to give me 32x 18650s in total to give around 340wh in total. Im guessing this could mean the double pairs might get off balance over time and reduce the overall full charge capacity, but it will still be much greater than just 16s on their own and i only have one BMS board to use soooo, i recon it will be ok aye?!


provided that each double 18650 in parallel are totally evenly matched id say all good to go?!


all ive found so far


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This "battery doubling" mod should give you some useful information : http://hobby16.neowp.fr/2015/07/22/airwheel-q3-clones-how-to-double-battery/

Your setup is what's called 16S2P, very common (most 340Wh packs are 16S2P, on Gotway, Firewheel, Airwheel...) see the schematics and pictures for Gotway : http://hobby16.neowp.fr/2015/07/24/gotway-bms-shunt/

The Firewheel 680Wh is a 16S4P !!! No more problem of going off-balance than 16S2P or 16S1P. So go ahead, and post pictures if you have questions.


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  • 2 months later...

Right so two months later ive built and finished a 16s2p battery pack with the generic BMS from aliexpress. Heres some pics of the build.
It took about 2 full days to build from dismantling. So thats 32x 18650s paired with 16 in series.
I used old laptop batteries that I got for free from the local recycling centre. Im really lucky that I can get as many as I need only 5 mins drive from home. Ive learned quite a bit about the different types that come in the laptop packs. Ive settled with just two types. They are the metallic green and blue ones. They seem to be the newest, are all 2200mah and hold a good charge. Any battery with faded red, pink, or yellow I have returned as these are generally of lower capacity and from older laptops. I have decided to use an external plug and socket so I can fully remove it when needed. The socket is parallel with the internal battery wiring as per photo.
Im pretty happy with the results. It doesnt look too flash in the pics as it looks messy. It is messy. But I have a background in electronics and know how to solder and work out the wiring pretty easy. It was all self explanatory in the end. C- and C+ on the BMS board are the wires for the charger. V+ and V- are the main power wires to power the wheel. Bat + and Bat - are naturally the positive and negative connections for the 16 pairs in series on the board. I used the existing metal tabs on the cells and just bend and adjusted to get each set to fit. Some of the laptop battery packs already had 3 pairs of the 18650s in series (3S2P) so they were really easy to work with. Just keep them whole and add them to the series. 60V can give you quite a jolt, so its important to be really careful, and triple check every polarity and connection and make sure each cell is well insulated.
Any cells that had scratches from when I took apart the laptop packs I patched with insulation tape and then put a nice big plastic wall down the middle to stop any possible shorting from impacts or jolts. Its not until the last pair of batteries are hooked up that the whole 60v becomes live. Thats when you need to be extra careful.
I have heard of others using the existing charging socket to plug in an external battery pack but this seems dodgy to me as others have already discussed.
I means one pack has to charge through the other. Ive wired both packs in parallel to the controller with the external battery having a plug and socket so I can remove it fully for shorter commutes. Also the charging is totally separate and I can charge the external pack on its own without the EUC. Also I noticed that the internal charge wiring is very thin so id rather not use that to through out power to the other battery. It just seems better this way. I could easily install a switch so that I can turn off power to the internal battery so that each battery can run the EUC separately. This light be better than using 2 packs in parallel with different capacities. But I was concerned my large rocker switch could be accidentally knocked during riding and cause a shutdown so I will try it as is for now. 
Last job is to build a suitable mounting bracket for the external battery on the front of the EUC.. more pics when that jobs done tomorrow.
Right now im happy with the finish of the electrical side of this project! Battery is fully charged now and holding its charge according to the charger and now its balancing.
All the cells I used had at least 2.8V of charge when I took them out of the laptop packs. Any bad batteries were generally below 1v. They might be ok (as the balancing circuit of the laptop might have been faulty) and some cells can be recovered even if they are that low but its was much quicker to just open a lot of packs and use all the good cells.
I guess I opened about 10 laptop battery packs to get enough for this build. Each pack has about 6 batteries. So half the packs were good. Ok thats all for now.
Will post some reports of distance and how they perform in the coming week. My generic 132Wh pack gave about 10 kms per charge so id expect about 20 kms from the external pack, so a total of 30 kms, but more likely around 25kms id say.
Cost of my 32 cell pack. About $25 for the BMS board incl shipping. Batteries free from recycling depot. A couple of bucks for the heavy duty wiring from the recycle centre and some insulation tape and few odds and ends. Total cost about $35. Thats a very cheap 32 cell lithium pack!












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Nice project! Did you weld the cells together (where there were no strips already) or just solder them? If they're just soldered. do you think the solder-joints will hold despite all the vibration and shocks from bumps? Guess you're safe in the sense that the original 132Wh pack will keep giving power even if the new pack fails. ;)


Any bad batteries were generally below 1v. They might be ok (as the balancing circuit of the laptop might have been faulty) and some cells can be recovered even if they are that low but its was much quicker to just open a lot of packs and use all the good cells.

According to http://batteryuniversity.com/learn/article/low_voltage_cut_off  :

Do not boot lithium-based batteries back to life that have dwelled below 1.5V/cell for a week or longer. Copper shunts may have formed inside the cells that can lead to a partial or total electrical short. When recharging, such a cell might become unstable, causing excessive heat or showing other anomalies. 

 So probably best NOT try to use any cells that have clearly gone "too empty".

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ok great thanks for that.. good to know... all the batteries had strips on them so didnt need to solder directly onto any of them.. also the solder will handle bumps fine.. i used a LOT of solder and also I used thick wires to deliver the power from join to join so they have flex for jolts.

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