Another No Solder/Weld 18650 Build (Updated 03/09/2014)

[Lurkin]

Really, really impressed with the creativity and quality of finished product.

I will be making something similar in the coming months, based on, and inspired by, your packs.

 

[bowlofsalad]

HOLY WATTHOURS BATMAN!! IT'S, IT'S, ANOTHER SNATH PACK!!

Do you use any sort of thread locker on your compression packs?

 

[snath]

I don't use any thread locker. The Nylon or PVC that I make the spacer bars out of grips the screws grips the screws very tightly..

 

[Vanarian]

Snath you made a pretty wonderful job too (been looking around solderless packs).

 

[spinningmagnets]

I am fascinated by this style of housing. I am also intrigued by the thought of making a small triangle pack like this. If I made a few of them and sold them as kits (to pay for the development costs), that might alleviate the issue of liability, if a buyer inserted one or more cells in backwards and had a rapid melt-down. I briefly considered arranging the bus bars so that all of the cells are inserted all facing one way, and the contacts that are intended to press against the flat negative anode ends would have a small hole in the center, so that if a cell with the positive "button" was in upside-down, there would be no contact until it was inserted in the proper direction.

Thoughts?

 

[Lurkin]

An excellent idea if decent contact can still be made.

 

[Skrzypas]

Great idea, safety is important, especially when you sell stuff to someone not experienced.

 

[snath]

Sounds like it could prevent an "oops" moment.

The potential product liability is why I never pursued making kits. Too bad, the packs are really simple to build and maintain.

 

[Punx0r]

Trademarks for polycarbonate are Lexan and Makrolon. I don't think it's known by a common acronym.

 

[liveforphysics]

Trademarks for polycarbonate are Lexan and Makrolon. I don't think it's known by a common acronym.

PC.

 

[Swe]

Is it correct 0,25mm copper should be used?

So you are bending two stripes and solder them together?
What do you think of copying the "2S" strips like the link below? Or maybe cut out even bigger unevenly pattern if you have like 0,25mm copper paper sheet, if you want more than 5P but are limited to 5 in a row. Do you see any problem with this? Except making the square form holes...

http://www.aliexpress.com/item/18650-li-ion-battery-pure-nickel-strip-3P2S-4P2S-5P2S-nickel-belt-lithium-battery-nickel-plate/32366776392.html

 

[Swe]

No one knows if 0,25 mm is enough for 5-7P (50-60A) ? (short periods)

Or if 0,5 mm is better? Or is it to hard to work with? Maybe too hard so the contact surface on the cells is even worse?

 

[Matador]

Hi everyone

This is my very first post on this forum. Hopefully I'm posting in the right thread.
I was stunned to see all the detailed valuable information available here and all the knowledgeable people!
I wish I had found this forum before, as it would have save me some mistakes and trouble in my builds.

I started tinkering with laptop 18650 cells last November 2015, as I wanted to build a battery for my thermoelectric Peltier cooler. Then as I bought more and more old 18650s, and I thought why not make an e-bike battery and then buy an ebike motor kit (I finally bought a Bafang BBSHD with the 30A controller) ?

So, now I have 202 cells... Took me about 8 months to test them all: I checked many parameters and discarded all the bad cells. I got one of those Foxnovo 4S charger that measures the discharging mAh capacity (at 0.5A/cell dschg) and I used some 3.7Ohm 5W resistor to do voltage drop tests and calculate the internal DC resistance of each cell. I also kept record of the salvage voltage of each cells. Included in this post is an Excel file with all my cells data.View attachment Li-Ion.xlsx

I excluded cells with:
a) Residual capacity of less than 80% of original rating
b) DC Internal resistance of more than 250 mOhm (DC resistance... not the impedance). Most of my cells have around 140 mOhms.
c) Cells that dropped voltage by more than 0,20 volts in 6 months, after being initially charged to 4.20 volts.

I had only 126 good remaining cells. So even though I originally designed my battery box for a 14S13P LiCoO2, I had to settle for a 14S9P battery.... Kind of a stretch since laptop battery are not very good at 2C and my oldest cells are (4.4A at 2C).

Anyways... I'm still working on that battery, but today I tried it on my bike (without a BMS and the celllogs that I plan to install) and it was Fun (50 km/h easily). The goal of my post is to share my battery build progress... And since laptop cells sometimes fail, I wanted to avoid soldering cells. I build everything from Plexiglass (2.5 mm thick acrylic sheets). I flattened copper pipe and drilled them to make bus bars, and used BCC-ND battery springs (from digikey.ca) and brass nuts and bolts (from Reno depot) for battery contacts.

But images tell more than word…
View attachment 18View attachment 12View attachment 8View attachment 5

 

[Matador]

I still have to wire the BMS, a fuse, 2 cellLoggers, a shunt and a PoweMeter (V, A, W, Wh). I'll also do a thick plexiglass casing for the whole thing afterwards. Today, I just wanted to try my ebike for the first time. It was a blast.

I also want to say hi to Marcel, another e-biker that I met on St-Jean Street today while we stopped a bit to talk about our ebikes.

I'll have to concentrate on my coming exams from now on, but I'll keep posting in the coming weeks.

This forum is just absolutely awesome!

Jonathan

 

[rowbiker]

Thank you Jonathan, and Welcome! It was a very constructive and useful post.

Two questions:

1) how much does the pack weigh in its current 14S9P configuration?

2) How/where are you mounting the pack on your ebike?

 

[Matador]

In this 14S 9 P config, the whole thing is 20.2lbs (9.2kg) : 7.2lbs case + 13.0lbs for the 126 cells.
So I can assume that the 14S 13P battery would weight around 26 pounds... But then again, I want to build a box out of 6mm thick plexiglass and also have to add BMS, fuse, shunt, Powermeter and 2 CellLog8M.... So it'll be closer to 30 pounds in the end.... but I need to make the thing sturdy.

Yesterday was just preliminary testing, so I took the battery, wraped it in bath towels, shoved it in a backpack and off I went.... Reaching 58.5 km/h on flat tarmac with 46T front gear and 14T rear gear and 700c wheels (Bike 28lbs alu, Motor 11.6lbs, Rack 2 lbs ?, Me : 150lbs).

I havent figured any mounting solution yet. I was thinking of using my rear rack for the battery... It's a Zephyr rack, rated for a max of 50 lbs...

Imagine if I could fill up the case with 14S13P 3600 mAh cells, that would be 2.424 kWh of capacity ! It's 1/35th of a Tesla 85S capacity !!

I have to say though, the springs in my build are a limiting factor for current... I did a test and by passing 3 amps through the spring in the air, it would reach 35°C after 30 minutes... Not exactly high current rated... The springs are made of 0.9mm thick, 18 cm long nickel plated springsteel wire... It's the tickest springwire I could find... I wish copper would have such a good elastic recoil !

As it is now (14S 9P), I only have 1075 Wh of capacity and a potential current of around 39.6A at 2C... But my controller maxes out a 30A... Still I'd rather have a 13P battery and use it at 1.05C when the controller maxes out at 30amps. As it is now in 9P config, a 30 amp max draw would translate into a 1.5C draw on the pack... A bit high for laptop cells...

Hope this helps,

Jonathan

 

[kwabdul]

Good build man, I too am looking to building something more for my house thou, and i do not want to solder, as i'm like well if you have a 4 cell 18650 battery holder you just need to multiply that by say whatever and you get a large enuff storage cap. so i'm thinking i will be going down that route, when i'm done will post what i came up with looking for something simple as i don't have access to tons of 18650 cells so each cell is very precious to me and i need to be able to replace the cells as one would the tv remote batteries so that's my plan just joined up to get some ideal, simple i like that word, so i'll be looking something simple, thanks

Hi everyone

My name is Jonathan, I'm from Quebec City in Canada (sorry for my rusty English). This is my very first post on this forum. Hopefully I'm posting in the right thread.
I was stunned to see all the detailed valuable information available here and all the knowledgeable people!
I wish I had found this forum before, as it would have save me some mistakes and trouble in my builds.

I started tinkering with laptop 18650 cells last November 2015, as I wanted to build a battery for my thermoelectric Peltier cooler. Then as I bought more and more old 18650s, and I thought why not make an e-bike battery and then buy an ebike motor kit (I finally bought a Bafang BBSHD with the 30A controller) ?

So, now I have 202 cells... Took me about 8 months to test them all: I checked many parameters and discarded all the bad cells. I got one of those Foxnovo 4S charger that measures the discharging mAh capacity (at 0.5A/cell dschg) and I used some 3.7ohm 5W resistor to do voltage drop tests and calculate the internal DC resistance of each cell. I also kept record of the salvage voltage of each cells. Included in this post is an Excel file with all my cells data.View attachment 19

I excluded cells with:
a) Residual capacity of less than 80% of original rating
b) DC Internal resistance of more than 250 mOhm (DC resistance... not the impedance). Most of my cells have around 140 mOhms.
c) Cells that dropped volted by more than 0,20 volts in 6 months, after being initially charged to 4.20 volts.

I had only 126 good remaining cells. So even though I originally designed my battery box for a 14S13P LiCoO2, I had to settle for a 14S9P battery.... Kind of a stretch since laptop battery are not very good at 2C and my olded cells are (4.4A at 2C).

Anyways... I'm still working on that battery, but today I tried it on my bike (without a BMS and the celllogs that I plan to install) and it was Fun (50 km/h easily). The goal of my post is to share my battery build progress... And since laptop cells sometimes fail, I wanted to avoid soldering cells. I build everything from Plexiglass (2.5 mm thick acrylic sheets). I flattened copper pipe and drilled them to make bus bars, and used 211 D battery spring (from digikey.ca) and brass nuts and bolts (from Reno depot) for battery contacts.

But images tell more than word…

 

[Matador]

Cell holders would do it.
Make sure it's the kind with thick enough wires to be able to pumps enough amps out of them.

In my case 182 cells mean 46 cells holders, so I though why not build my own 13 cell holder and make them stackable...
In the end, my choice is more expensive (plexiglass is expensive, and brass bolts and nuts too), but I've learned a lot of stuff from this build and design.

 

[rowbiker]

Jonathan - thanks for the additional info! Trying to get my head wrapped around the idea that your bike is lighter than your battery pack. I have two ebikes, both with rack mounted battery packs. One is standard off-the-shelf, while the other is a custom ("hack") mount. Neither battery is over ten pounds, though. I'd be interested in hearing your assessment of having that much weight up that high over your back wheel.

Your test of the battery contact springs was very useful, with the results being surprising. I use a similar setup for doing 18650 capacity tests, but I typically don't push more than half an amp through the spring, so I've never worried about it. It's good to know what the limit is. Just a wild thought: would it add to the spring's current carrying capacity if you used an electroplating type process to add copper layers to the springs? I have no idea if you can plate over zinc, but some googling should answer that. I only suggest that since it seems obvious you are both willing and able to engineer whatever it takes to make a solid pack. :wink:

 

[Matador]

Jonathan - thanks for the additional info! Trying to get my head wrapped around the idea that your bike is lighter than your battery pack. I have two ebikes, both with rack mounted battery packs. One is standard off-the-shelf, while the other is a custom ("hack") mount. Neither battery is over ten pounds, though. I'd be interested in hearing your assessment of having that much weight up that high over your back wheel.

Your test of the battery contact springs was very useful, with the results being surprising. I use a similar setup for doing 18650 capacity tests, but I typically don't push more than half an amp through the spring, so I've never worried about it. It's good to know what the limit is. Just a wild thought: would it add to the spring's current carrying capacity if you used an electroplating type process to add copper layers to the springs? I have no idea if you can plate over zinc, but some googling should answer that. I only suggest that since it seems obvious you are both willing and able to engineer whatever it takes to make a solid pack. :wink:

My pleasure !

Yeah it's kind of funny the battery weight almost more than the bike ! I guess we need something even lighter than Lithium cobalt oxide cells (the cobalt is probably responsible for much of the weight as Lithium is just 6.94 g/mol but Cobalt is a huge 58.93 g/mol ...). I think I'd be great if they could make a stable Lithium Silicium cell (Silicium is very light at 28.09 g/mol), with graphene instead of graphite anode... That would be mad capacity to weight ratio and mad power to weight ratio!!!

I will get the casing done and wire everything up... but it might take a few weeks if not months as I will be in another city for a month very soon (work). When I'm finished I will do some testing... You're right : having such weight at such a high height is a bad idea for having a good handeling. The thing is... I started to build the pack even before buying the bike and motor kit lol... Though I'd make a good battery first. But now i'm stock with a high center of gravity... Anyways still fun !

Copper plated springs would probably work better (but custom plating can become pricy). The thicker the copper plating, the better. I think it's indeed possible to plate copper on nickel... About the springs, I tried 2 kinds. At first I bought some cheap alkaline D cell holders and took these springs (I think the spring wire was 0.8 mm diameter measured with calipers)... These springs were no good, not more than 0.5 amps and they would get hot... The steel core was probably of lower grade (Resistivity of steel can vary a lot, from 1.6 x 10-7 Ohm.m to 7.5 x 10-7 ohm.m depending on steel grade). The nickel plating was soo thin on these springs, it would flake off sometimes when I inserted my brass screws.

The BCC-ND springs I ordered from digikey.ca were better (sping wire was 0.9 mm diameter mesured with calipers) to push amps... But keep in mind, there still is a bit of voltage drop and heat generation. I wish I could get copper plated, but I think I'll just settle for what I have now.

Took my ebike again today, 61.9 km/h top speed (flat) with battery charged to 90% (57.1V). Left a digital thermometer in the battery the whole time. In the end the max temps was 51.7°C.

This electric project is just so fun !

 

[spinningmagnets]

Consider the option of having the springs and the current-carrying elements be separate parts? (copper strips in-between the spring and cell?). Nice work, thanks for posting the pics here...

 

[Matador]

For my copper bus bars made of 1/4inch OD copper pipe. The outer diameter is 0.64 cm while inner diameter is 0.43 mm. So the conductive residual area is 32.2 - 14.5 = 17.6 mm2.
So these buss bar are equivalent to 5 AWG copper wire (should support 80 Amps no problem)...
Copper resistivity is 1.68 x 10-8 ohm.m, so with a conductive area of 1.76 x10-5 m2, and a length of buss bar of 0.23 m, the resistance of the copper busbars is only [1.68 x 10-8 ohm.m] x [0.23 m] / [1.76 x 10-5 m2] = 0.22 milliOhm per bussbar That means with these buss bars, I'd only get a 0.02 voltage drop if I pull 100 amps !

Did the same kind of calculations for the brass bolts...
Resistivity of brass is 7.10 x 10-8 Ohm.m
Lenght of brass bolt (between spring and busbar) is 0.015 m
Surface area of brass bolt core is 8.04 mm2 (or 8.04 x10-6m2)
So I get a resistance of 0.13 milliOhms per brass bolt (meaning I'd get a 0.013 V voltage drop if I pulled 100 amps throught this small lenght brass bolt).

My problem is with the contact springs.... Resistivity of carbon steel, springwire steel or stainless steel is not good. In the best case I think I can expect a 1.611 x 10-7 Ohm.m resistivity

Resistivity of good springsteel (a kind of carbon steel) : 1.611 x 10-7 Ohm.m
Surface area is 0.6362 mm2 (6.362 x 10-7 m2)
Lenght of spring wire is 18 cm (0.18m)
So with the same calculations, i'd get 45.6 milliOhm resistance per spring. That's huge ! Of course, I'm not facting in the nickel plating here (well I have no clue of the plating thickness so I can't make calculations for here). But nickel plating probably helps a lot to pull current since it's resistivity is much better than steel !
Anyhow, if it was just made out of steel with no plating, 45.6 milliohms means I'd get 0.05V voltage drop for every amps I pull through that spring.

Note If I downgrade the spring wire diameter from 0.9 mm to 0.8 mm, the wire section area downgrades from 0.6362 mm2 to 0.5026 mm2... Meaning more resistance (57.7 milliOhms) !!!

Copper by itself is too malleable to make springs out of this element. Copper springs would loose their elastic recoil over time. But I guess we could plate them... Gold plating is actually a bit less conductive than copper plating, but gold plating has one major advantage, it does not oxidise ! That's why it's used in high fidelity applications. But money money here...

EDIT : More info on the copper bussbars made of 1/4 inch OD copperpipe : https://endless-sphere.com/forums/viewtopic.php?f=14&t=84791&hilit=tags&start=25#p1274130

 

[parabellum]

Consider the option of having the springs and the current-carrying elements be separate parts?

Copper by itself is too malleable to make springs out of this element.

What he means is cooper sheet over springs, connected to terminal.
Se my early intent I have in my garbage pile.

 

[Matador]

Consider the option of having the springs and the current-carrying elements be separate parts? (copper strips in-between the spring and cell?). Nice work, thanks for posting the pics here...

That's an excellent idea spinningmagnets!!! I'd love to thinker more on this and try to put a copper piece soldered to the top of the spring and a copper wire soldered, going from that spring tip piece, to the brass bolts... I must admit that I'm very busy at work these days, so my project is going very slowly and free time is cruelly lacking... I'm just an amateur having fun thinkering on sunday mornings, not a real engineer
I Might try it one day though, as it is the logical thing to do next in order to increase efficiency by lowering resistance thereby minimizing energy dissipation in the form of heat (and it wouldn't add soo much weight to the whole build)... but for now, it still works out for me with nickel plated steel, so I'll concentrate more on making the box so I can mount the pack on my bike and make it more practical than a 20 pounds backpack... Man, my shoulders hurt so much from that last 29 km run :x ...

This forum is just awesome !! Looking forward to hear from you all and your great ideas!

 

[Matador]

Just for correction, I checked again on digikey.ca, the springs I bought were BCC-ND model rather than 211 D. And the're not zinc plated but rather Nickel plated...
I Made corrections to previous post buy editing them. As I said, I'm just an amateur, but this is soo fun !