my 18650 frame pack build

Batteries, Chargers, and Battery Management Systems.
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izeman
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my 18650 frame pack build

Post by izeman » Jan 29, 2018 10:18 am

my lipo battery is aging, and is about 4 years old now. it's down to 80% capacity, and it is time to replace it. i never had a single issue with any lipos over the years, be it in my bike or in the quadcopter, rc car ....
still the 18650 cell looked interesting to me, and i thought how a switch could happen.

the current configuration is 8 packs of 6s 5.000mAh zippy 20c rc-lipos cells. the pack weighs around 6.2kg and has a nominal capacity of 3,7V * 12s * 5.000mAh * 4p = 888Wh.

i took a lot of measurement of the available space in my self-made frame, and the space available is 370x50x110mm. thanks to the great help and support of maddin88, we found a very good solution which uses the space ideally. totally i can fit 150 cells into the frame. 2 packs of 75 cells in a 15s3p configuration. the cells will be arranged in a 3s5p honeycomb layout and then folded. this will give a long pack of 50x105x350mm.

150 cells will make the capacity much larger. from 888Wh to 3,6V * 15s * 3.000mAh * 10p = 1.620Wh (almost double the capacity), at 6.8kg. the pack is more heavy because it has more volume, and fills the room much better then the lipos which needed a connection pcb in the middle.

the sag will be much worse than before, but due to higher voltage (44.4V compared to 54.0V) the current will come down and range may be doubled.

this is what the bike looks right now:

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Re: my 18650 frame pack build

Post by izeman » Jan 29, 2018 10:26 am

the new batteries from nkon have arrived. 150x samsung 30q and some meters of 25mm and 10mm wide 0.15mm thick nickle. and some heat shrink and end cap's savers as well as kapton tape.

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first of all they were arranged in groups of 5 and glued together with hot glue. i 3d printed a little box where the batteries fit in quite tightly and are perfectly aligned before fixing them in 5p packs.

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then some kapton tape is wrapped around each end to reinforce the very thin heat shrink:

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these are the 10x 3s5p packs that will make the two big packs

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Last edited by izeman on Jan 29, 2018 10:40 am, edited 1 time in total.

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Re: my 18650 frame pack build

Post by izeman » Jan 29, 2018 10:34 am

a friend of mine bought a spot welder from Aulakiria https://endless-sphere.com/forums/viewt ... &start=250.
after some initial issue of too weak welds, and the great support here we found out that the battery was too weak. it's important to use a strong battery directly connected to the welder - no adaptors, no long wires in between.

after that, the welds came out beautifully and very strong:

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each cell got a little black self adheasing paper ring. the whole cell is the negative pole, so if the heatshrink anywhere is damaged there is a high risk of a short circuit.

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the batteries where stacked and glued together with regular silikone glue and let cure over night

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then i could start welding the packs together:

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you may notice some different color heat shrink. these are all the same cells from the same charge. but during glueing them together, i did it too slowly or used too much pressure, and the hot nozzle of the heat gun destroyed the heat shrink. so i had to replace some.

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Last edited by izeman on Jan 29, 2018 10:37 am, edited 1 time in total.

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Re: my 18650 frame pack build

Post by izeman » Jan 29, 2018 10:35 am

the big pack has solder fins for the balance wires:

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Last edited by izeman on Jan 29, 2018 10:39 am, edited 1 time in total.



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Re: my 18650 frame pack build

Post by e-beach » Jan 29, 2018 10:55 am

Looking very nice so far! Subscribed.

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Favorite Quote: "This is L.A., sugar. There is no 'over the top." --- Chris Erskine

Current build: Liahona w/ cheap front suspension and suspension seat post. Yescomusa 36v 800w generic front hub motor. 15ah Headway triangle mounted pack. Tronsung 30 amp,

Previous Build:1992 Trek Antelope 800 - Bone Crusher (no suspension) - Yescomusa 800 watt 36 volt front wheel kit. Don't do it! Get suspension!!!

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Re: my 18650 frame pack build

Post by izeman » Feb 02, 2018 9:34 am

so it goes on. i made the mains connection. a 10mm wide 0.15 nickle strip.
first i cut of 5cm of insulation of the awg12 silicone wire and divided the wires in two parts, twisted those and tinned them.
then i pre-tinned the nickle and soldered the wire to it, pressing it down with a screwdriver bit by bit.

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safety first. it's really important to isolate wires under voltage.

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pre-tinned the battery tabs as well. with a good soldering iron and 400°C this takes less than a second. so not much heat transferred into the battery.

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welded the strip to the battery. i don't know why, but there were some sparks flying and burnt holes in the nickle. so it doesn't look that nice, and i had to weld at some more points to have 6 valid welding dots.

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all done, ready to test :) those are not the final wires. just for testing, to see if the BMS is working - which it does! all cells are within 7mV. not what i expected, but good enough. i thought that 5 parallel cells would level each other out closer than that.

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Re: my 18650 frame pack build

Post by 999zip999 » Feb 06, 2018 2:24 am

What amp rate are you going to use this pack at ?


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Re: my 18650 frame pack build

Post by e-beach » Feb 06, 2018 11:36 am

Do you worry that the positive solder fins will be a potential short if they cut through the plastic wrapper and ground to the negative battery outer case?

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Favorite Quote: "This is L.A., sugar. There is no 'over the top." --- Chris Erskine

Current build: Liahona w/ cheap front suspension and suspension seat post. Yescomusa 36v 800w generic front hub motor. 15ah Headway triangle mounted pack. Tronsung 30 amp,

Previous Build:1992 Trek Antelope 800 - Bone Crusher (no suspension) - Yescomusa 800 watt 36 volt front wheel kit. Don't do it! Get suspension!!!

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Re: my 18650 frame pack build

Post by izeman » Feb 06, 2018 2:08 pm

I don‘t really worry, but there is a) extra capton tape b) paper rings and c) i will add some tape to the inner side after soldering as well. This should keep the risk to a minimum.

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Re: my 18650 frame pack build

Post by 999zip999 » Feb 06, 2018 4:16 pm

Maybe there was a small air gap between the stiffer pos. End with mutli strand and solder combo. Giving a spark gap blow out. Maybe hold down with a chop stick if you have a third arm with hand attached.

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Re: my 18650 frame pack build

Post by izeman » Feb 10, 2018 3:59 pm

today i made the isolators. 0.7mm thick gfk. cut into 50x102mm pieces, then sanded and rounded the edges. i also made a slot for the wires.

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then those were glued to the battery with silicone

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before that i attached some additional isolation to the balance tabs. just in case ;)

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then the parts were folded together and held down by clamps to straighen the hole battery out.
now it's time to way for the silicone to cure.

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Re: my 18650 frame pack build

Post by Animalector » Feb 11, 2018 10:01 pm

looks great, nice work.

Andy

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Re: my 18650 frame pack build

Post by izeman » Feb 12, 2018 10:25 am

printed endcaps last night, they guide the wires and protect the ends of the battery

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added some extra protection tape. you can never have enough protection, right? ;)

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lots of silicone to glue the caps to the battery. they stick nicely, even with uncured silicone

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i also cut 0.5mm gfk sheets for the sides. they are absolutely necessary as they give stability and also isolate the nickle tabs (at the places were the battery was folded, the nickle sticks out)

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and finally the clamps again. it's vital to make the battery as small as possible as the battery space is very limited. internal width is around 52mm, which is exactly the width of the battery with side covers.

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