18650 battery pack build Kepler style

Batteries, Chargers, and Battery Management Systems.
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Kepler
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18650 battery pack build Kepler style

Post by Kepler » Dec 29, 2014 6:19 pm

The following build was documented in pieces through my latest bike build thread and as such I thought i would consolidate the battery side of this build as one thread and in the most appropriate section.

The aim for this build was was to build and 18650 pack that looked like it belonged on the bike and could be built without the need for specialist tools.

The battery was for use with a Bafang BBSO2 750W mid drive and as such needed to be able to deliver 20A continuous. Normally the Bafang uses a 13S Lithium Ion pack for 48V nominal however I wanted to up the voltage slightly so I could reduced my max amps the 18A. Subsequently a 14S4P configuration was decided upon.

Another design criteria was that the battery needed to be quick release as I always charge the battery off the bike in my office when commuting to work. It also needed to be very secure as the bike is used for some serious single track work on weekends and gets a real pounding.


The finished product on the bike
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finished.jpg
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HV.jpg
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Last edited by Kepler on Dec 30, 2014 2:48 am, edited 3 times in total.
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Re: 18650 battery pack build Kepler style

Post by Kepler » Dec 29, 2014 6:20 pm

First item on the list was to come up with an aesthetically pleasing shape that could hold 54 cells and associated BMS. I tried quite a few combinations and shapes but settled on this one.
check fit.jpg
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An 80mm wide, 2mm thick aluminium plate was cut to length by my local aluminium supplier for $5 and was then bent to shape in my workshop by wrapping it around various size pipes acting as mandrels. Once I was happy with the shape the aluminium plate was joined using a machined aluminium spacer. The spacer is also used to attach the side plates too.
bent ali plate.jpg
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joined ali plate.jpg
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Another 3 posts were machined up to act as spacers and attachment points for the side covers.
attachment posts.jpg
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Last edited by Kepler on Dec 30, 2014 2:46 am, edited 4 times in total.
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Re: 18650 battery pack build Kepler style

Post by Kepler » Dec 29, 2014 6:21 pm

Next item on the agenda was the mounting system. As mentioned previously, it needed to be quick release and secure.

Firstly hardened counter sunk screw were attached to the bottle cage blind nuts.
mounting system bike.jpg
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A slide plate was then fabricated out of 1.2mm Cromo Steel with elongated holes for mating with the bottle cage screws. Made for a very secure attachment however I still need to come up with second attachment point at the back of the case to secure it the seat tube. Also a plastic plate shaped the down tube profile was added underneath the batter case to support the majority of the weight.
mounting system case.jpg
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A rear attachment point was also required and needed to provide strong lateral support to the case but also stick with the quick release requirement. To solve this, 2 posts were machined up to capture the bike seat tube and then secured to bike using a heavy duty O ring.
rear attachment.jpg
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rear att on bike.jpg
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Next job was the side covers. Rough cut them out of 5mm Acetal sheet then finished them off in the mill. Added some simulated vent holes to break up the large surface area and sanded it with wet and dry to give it a nice mat finish to match bike colour scheme.
side plate machining.jpg
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side plate.jpg
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The completed battery case ready for cells and BMS to be installed
sideplate fitted.jpg
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Last edited by Kepler on Dec 30, 2014 2:49 am, edited 2 times in total.
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Re: 18650 battery pack build Kepler style

Post by Kepler » Dec 29, 2014 6:21 pm

Just to recap, the cells are LG 2850 mah from this thread https://endless-sphere.com/forums/viewto ... 31&t=61608

My configuration is 14S 4P which means 56 cells are required. Ended up buying 60 cells which came packaged up as per the picture below (10S 3P) x 2
Batt.jpg
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First job was to break the packs down to individual cells. This required breaking off all the spot welded tabs so the plastic cell spacers could be removed. Was a bit disappointing having to break off all the spot welded tabs but unfortunately there was no other option if i was to squeeze 54 cells and a BMS into this battery box.
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Next step was to make sure 54 cells actually fitted including the BMS.
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Cells were then arranged as individual 4P 1S packs and parallel soldered using 3mm wide solder wick to bridge each cell
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Of course soldering is not the ideal method of joining the cell however this was my only option if I wanted to build an 18650 battery pack. Each cell had the spotweld remnants ground off with a Dremel tool which also gave a roughened nice clean surface for the solder to stick too. Using an 80 Watt soldering iron, each cell was tinned with only a few seconds of heat being applied. Compressed air was then immediately blown on to soldered area to ensure all heat was quickly removed. After a quick blast with compressed air, the soldered area was immediately cool to the touch. The solder wick by nature solders with very little effort so it only took a quick touch of the soldering iron to attach the solder wick link to the battery. Again the soldered area was immediately cooled with compressed air.

Cells were hot glued and linked together in manageable sections with the 3 main sections joined and linked afterwards.
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20141229_153726.jpg
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Before installing the BMS, I wanted to test out the pack and make sure it performed as expected. Also wanted to make sure the solder wick links were handling the current OK. Female 5mm bullet connectors were soldered directly to the positive and negative tabs of the pack and a 12 gauge power cable attached.
20141229_154042.jpg
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A quick 10km ride was completed with a good mix of moderate to high power used. Pack was then removed straight off the bike and all connections checked. Also used an infrared heat gun to see if there were any hot spots. Pack was an even 25 degC across every terminal and cell voltage had stayed nicely in balance.
Last edited by Kepler on Dec 29, 2014 7:23 pm, edited 1 time in total.
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Re: 18650 battery pack build Kepler style

Post by Kepler » Dec 29, 2014 6:21 pm

Final stage of the build was to install the BMS and to make sure the cells are well supported within the battery case.

Installed the balance leads followed by the main power cable and charge lead.
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20141230_173055.jpg
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After double checked all wiring and voltages the BMS was fully connected and left to hopefully fully balance the cells overnight. At the moment the highest ceill is 4.07V and the lowest cell 4.04V. Will be interested to see how close the BMS brings the cells together.
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20141230_173944.jpg
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Completed pack with BMS installed
20141231_102037.jpg
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Last edited by Kepler on Dec 30, 2014 11:52 pm, edited 3 times in total.
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Re: 18650 battery pack build Kepler style

Post by spinningmagnets » Dec 29, 2014 6:31 pm

I remember the first brief posting of this pack in the bikes build thread. I was hoping you'd post more details. Excellent work!

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Re: 18650 battery pack build Kepler style

Post by ridethelightning » Dec 30, 2014 4:52 am

nice work!
i know the feeling of pulling apart those bosch packs. i just popped 5 of em open in similar fashion. seems a shame to destroy a beatifully made thing.

i ended up cutting the the tabbs and bending em up to pull off the spacers on the one side(and the small black plastic stubs pulled off the other)to get them apart.

was a pain in the arse and there was cutts and lightning several times :shock: but that gave me most cells with the tabs still on both sides for soldering. then i got the guys at batteryworld to tabweld the remaining cells,whinging and maoning all the way...."we dont weld liion....very dangerous...dead shorts....flames....will dammage the cells...the world will explode"....blah blah blah...
definately need to get my own spotwelder.....
i hate soldering for days too.


i now have 20s10p,72v28.5ah pack that seems extraordinarily small and light, and very good price.

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Re: 18650 battery pack build Kepler style

Post by Allex » Dec 30, 2014 6:01 pm

Thx for the documentation. I want to build a similar battery holder for a lightweight bike.
Hope your cells work good after that heating treatment.

BTW does anybody know how old those Bosch cells are? It would be a shame if those batches was made like 3-4 years ago.

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Re: 18650 battery pack build Kepler style

Post by ridethelightning » Dec 30, 2014 7:32 pm

good point allex. id love to know too. the packs look very clean/new, no corrosion/tarnish on raw copper etc.
so id guess they were not that old, but still, getting a date from the batch number would be the only real way to tell i guesse.

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Re: 18650 battery pack build Kepler style

Post by Kepler » Dec 30, 2014 11:48 pm

Hopefully heat was kept to minimum using compressed to air cool each solder joint. As ridethelightening said, the packs look very clean/new. Time will tell how they perform over the long run. I do a heap of km's on this bike so hopefully will have some useful data on their performance fairly quickly.
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Re: 18650 battery pack build Kepler style

Post by Rodney64 » Dec 31, 2014 10:32 pm

Kepler, thanks' for taking the time to post up. I was wondering how you build the pack.

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Re: 18650 battery pack build Kepler style

Post by TheBeastie » Dec 31, 2014 11:05 pm

Kepler wrote:
An 80mm wide, 2mm thick aluminium plate was cut to length by my local aluminium supplier for $5 and was then bent to shape in my workshop by wrapping it around various size pipes acting as mandrels. Once I was happy with the shape the aluminium plate was joined using a machined aluminium spacer. The spacer is also used to attach the side plates too.
Love it, have you ever considered selling the case build minus cells and BMS or maybe with depending on what people might want?
I bought one of these ( http://www.aliexpress.com/store/product ... 64183.html ) and it was a PITA to get cells into, very tight space, would of been much easier with the space of of your case design.
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Re: 18650 battery pack build Kepler style

Post by cruzin » Dec 31, 2014 11:09 pm

That is a very nice setup Kepler. You did a great job with efficiency and appearance, it is just great overall.

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Re: 18650 battery pack build Kepler style

Post by tomjasz » Dec 31, 2014 11:34 pm

Great details, perfect primer for my first build. Thanks. Sweet case!
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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Re: 18650 battery pack build Kepler style

Post by tomjasz » Dec 31, 2014 11:39 pm

Question. Goot Wick is sold as a "solder remover" on eBay. You used it as the connecting wire? Looks like a really clean connection. Ordered.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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Re: 18650 battery pack build Kepler style

Post by Kepler » Jan 01, 2015 2:56 am

Thanks for the positive responses. Much appreciated.
TheBeastie wrote: Love it, have you ever considered selling the case build minus cells and BMS or maybe with depending on what people might want?
I bought one of these ( http://www.aliexpress.com/store/product ... 64183.html ) and it was a PITA to get cells into, very tight space, would of been much easier with the space of of your case design.
No thoughts on selling cases. As with most hand made projects, there is just too much time involved. I think most people would have little trouble building their own case in similar fashion though. You don't need any special tools. The side plates can be hand cut and finished a file and sandpaper. The mounting posts can be cut from 14mm aluminium bar stock and filed flat on one side.

Those cases are a nice shape and I have used them on other bikes I have build for other people. They are designed for upto 52 cells (13S4P). I have 56 cells in my case could probably squeeze in 60 cells for 15S4P or 10S6P setup. That would be a capacity of 600Wh which is some serious range on a lightweight low powered bike.
tomjasz wrote: Question. Goot Wick is sold as a "solder remover" on eBay. You used it as the connecting wire? Looks like a really clean connection. Ordered.
It is solder remover. I believe it has a flux impregnated into it. Solder flows to it with very little effort so you spend far less time putting heat into the cell.

Soldering cells is not ideal however I was willing to take a risk and give this method a go. I use to use this method to solder Nicads packs together in the days before LiPo was available. I understand the chemistry and cell construction is quite different however the packs worked perfectly and had great longevity.
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Re: 18650 battery pack build Kepler style

Post by friendly1uk » Jan 01, 2015 8:47 am

Nice job. Particularly the appearance of the side covers.
bmsbattery sent me broken and incorrect stuff, and won't even talk to me about it.

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Re: 18650 battery pack build Kepler style

Post by quamau » Jan 01, 2015 9:56 am

Awesome job, Kepler! I had to do something similar but my results are waaay less high-quality than yours. My cells are in the 32113 format though, so I had to make as wide a box as possible (ended up with sthg like 10cm) and still the cells need to be installed slightly oblique..

The reason I'm writing is to ask how you dealt with the interface to the box. How do the power cables exit the box? Ditto for the charge leads. An additional question is how you managed to have your pack sitting on the box with an even distribution of load on every cell. Thanks for the details: your build is going to be an inspiring reference for my next improved box.

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Re: 18650 battery pack build Kepler style

Post by 999zip999 » Jan 01, 2015 5:23 pm

Are you using any protection on the pos. end to keep that solder wick from shorting on the neg. Case ? Like a gasket ?

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Re: 18650 battery pack build Kepler style

Post by Kepler » Jan 01, 2015 11:29 pm

No I am just relying on the gasket built into the battery. The built in gasket and heat shrink give a double layer of insulation which providing it isn't heat damaged through the soldering, should be fine. I think an extra gasket would have been a good precaution though and would certainly consider using them next time. I have rechecked all solder bridges this afternoon just incase. All good :)
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Re: 18650 battery pack build Kepler style

Post by Kepler » Jan 01, 2015 11:38 pm

quamau wrote:Awesome job, Kepler! I had to do something similar but my results are waaay less high-quality than yours. My cells are in the 32113 format though, so I had to make as wide a box as possible (ended up with sthg like 10cm) and still the cells need to be installed slightly oblique..

The reason I'm writing is to ask how you dealt with the interface to the box. How do the power cables exit the box? Ditto for the charge leads. An additional question is how you managed to have your pack sitting on the box with an even distribution of load on every cell. Thanks for the details: your build is going to be an inspiring reference for my next improved box.
Here is shot of the main power cable and charge lead. Main power plug is an EC5 which is the standard plug I use across all my builds.
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Cells have some support from the bottom by sitting on rubber blocks however the cells are mainly supported by being sandwiched between the two side plates
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20150102_130631.jpg
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Re: 18650 battery pack build Kepler style

Post by tomjasz » Jan 02, 2015 1:44 am

999zip999 wrote:Are you using any protection on the pos. end to keep that solder wick from shorting on the neg. Case ? Like a gasket ?
What would you use as gasket material, or is there a ready made source?
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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Re: 18650 battery pack build Kepler style

Post by Mike Allred » Jan 02, 2015 4:41 am

It's a work of art and instantly impressive. I want to build my own 13S 1000W battery (therefore it won't be so beautiful), to fit my bike, but have trouble finding a compact BMS. Could you give me a clue on the brand and source of your controller ?

Mike

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Re: 18650 battery pack build Kepler style

Post by Mike Allred » Jan 02, 2015 4:45 am

It's a work of art Kepler and instantly impressive. I want to build my own 13S 1000W battery (therefore it won't be so beautiful), to fit my bike, but have trouble finding a compact BMS. Could you give me a clue on the brand and source of your controller ?

Mike

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Re: 18650 battery pack build Kepler style

Post by pendragon8000 » Jan 02, 2015 4:49 am

Thanks for the detail on this one Kepler. That's some nice clean work.

The solder wick trick is cool. Your idea?
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