Affordable Lipo for Everyman

[tongxinpete]

Some while ago I built a battery from BMS 7070260 Lipo cells, at the time they were on a really good offer & pretty much the best bet for a low power motor. Have been looking into making another but with these cells
https://bmsbattery.com/ebike-battery/625-high-c-rate-10ah-lifepo4-cells-battery.html
The air shipping is a bugbear with all cells so I came up with this idea ; if a group of us got together to get a larger number sea shipped for our mutual use would the costs be much less? I picked this cell as it could be built 12S 1P as I did, giving 10Ah, or say maybe 2P 12S thus building a 20Ah batt. Also other combinations could give 48v nominal. I am just using this as an example of a standardized building brick bought directly in bulk from say alibaba. The shipping on other bms products seems more reasonable.
The tabs on the 7070260 cells happily soldered using Laco plumbers flux, I annealed some 15mm copper pipe scrap & cut strips for linking busbars / strengthening tabs to facilitate drilling for self tappers. I put two cells side by side, alternating the layers 'top & tail' like many kids in a double bed. Happy to put a photo with link somewhere if any interest. I ended up with a BMS after other 'self balance' methods did not work (I was mis informed over this but once the BMS installed then all well). A different cell or chemistry may be picked (but the lower cycle life of Lico mn seems to outweigh the lower number of cells needed per batt & also safety issues)
Just wondered if any mileage in this idea. I am looking to upgrade to a Q128H or BPM code 12, hence the higher C rate (only do 5 miles between ability to recharge & a second charger is not costly)

 

[cwah]

I'd advise not to buy NMC cell and get ncr18650be or similar type of cells.

Nkon is selling ncr18650bl cells:
http://eu.nkon.nl/sony-ncr18650bl.html

It can be good price if you do bulk purchase.

shelf life is much better, you can easily shape it the way you want, its higher capacity and i have access to a spot welder.

It does feel for me its a much better deal

 

[tongxinpete]

I had not considered using 18650 cells but having studied this
nkon.nl/sk/k/NCR18650BL-specification.pdf it says use lead plate spot welded on (presumably lead strip to make a parallel group of 3 or 4 cells?)

I have also seen a holder with sprung mechanical caps designed to be rebuild able. Also I heard of individual fuse caps per cell being used in one build.
Would the parallel group of 3 cells be treated as a single cell by the BMS?

I did calculate that a 10 Ah 36v batt would cost £109.66 as my understanding is the price includes Vat in the Netherlands (neither shipping costs nor BMS included). What is the expected calender life & cycle life of these cells?
Great tip, thanks, but feel I must do much research into this type of build first
Could I ask if you have any photos of a build with these cells ?. Very interesting, Thanks again. Pete

 

[cwah]

Here is my DIY battery pack:

Protected by computer sleeve:

Then inside a waterproof bag:

Working quite well

Tesla is providing 7 years warranty on their NCR battery pack, so it can't go wrong with proper care

 

[tongxinpete]

Thanks for the pics, looks a great build. I see nickel strips rather than the lead mentioned in the Nkon pdf (I did wonder if it was a miss translation as I have not seen it before) One thing that worries me a little is having one rogue cell in the build (is this a likely event?) I did think of using if possible a cell holder that would hold a 3P group & having a spot welded strip across these 3 cells. The cell holder then clipping to an identical one, (a bit like the Headway ones) with mechanical series links. Thus if I had a bad cell the problem could be isolated to a group of three. I also found this
http://ntsworks.com/battery/battery-technology/ it is a system that uses mech connections throughout Cells can easily be replaced down the line. I think there has been a home build like this but not sure how it worked long term.
I would like to find a shunting BMS with LED's showing when each cell group was full & current being shunted, like the ones ping used. This would aid fault finding if ever needed. I did also think of individual tags spot welded on to each cell allowing a mechanical connections, perhaps i am being too pessimistic?

 

[cwah]

Thanks for the pics, looks a great build. I see nickel strips rather than the lead mentioned in the Nkon pdf (I did wonder if it was a miss translation as I have not seen it before) One thing that worries me a little is having one rogue cell in the build (is this a likely event?) I did think of using if possible a cell holder that would hold a 3P group & having a spot welded strip across these 3 cells. The cell holder then clipping to an identical one, (a bit like the Headway ones) with mechanical series links. Thus if I had a bad cell the problem could be isolated to a group of three. I also found this
http://ntsworks.com/battery/battery-technology/ it is a system that uses mech connections throughout Cells can easily be replaced down the line. I think there has been a home build like this but not sure how it worked long term.
I would like to find a shunting BMS with LED's showing when each cell group was full & current being shunted, like the ones ping used. This would aid fault finding if ever needed. I did also think of individual tags spot welded on to each cell allowing a mechanical connections, perhaps i am being too pessimistic?

Links looks good but I can't see a single picture of the pack construction, so it may just be some BS.

There is always a trade of between price and quality. I usually get Bestek power BMS because of decent price for what I got. But if you want the best, just get an adaptto board with integrated BMS

 

[mfj197]

Nice find on the cells cwah. Tongxinpete, for a cheaper pack you can use Panasonic NCR2900PF cells again from Nkon. The PFs are good for high current usage and there is only about 200mah difference between them and the NCR3400B at high current drain. You can also get them with tags already welded on, although they are more expensive (and currently out of stock).

Michael

 

[tongxinpete]

Pity the sony ncr 18650bl do not come with a tag option as this fits the bill, also the panasonic could be made in 4P groups. Finding a cell holder that is either slot together modular or can allow a single cell to be removed without dismantling the whole pack is another wish. I had come across BesTech & am interested in this shunting BMS http://www.bestechpower.com/37v10spcmbmspcbforli-ionli-polymerbatterypack/PCM-D178.html
I have somewhere a couple of little monitoring pcb modules that read out the voltage of each cell in turn, & are on xlr plugs. This may be a better option than the LED's that show shunting in progress. D8veh says not to rely on a BMS without actually checking if it is working. Do BesTech send the little plug & per cell wires & also diagram for all wiring? bmsbatts used to stock this model but no longer do so. They had pdf drawings for all BMS on the old site.
I'm really sold on mechanical connections as a bad cell could be removed & also the pack rebuilt at the end of it's life. Thanks to both for the good info. I guess 18650 cells are driven by the laptop market, hence they are more widely available. Pouch cells seemed simpler but if there is no stock in uk/europe, well not good