Holy grail of solderless 18650 is close but not idiot proof.

[jdevo2004]

And that is why I am going to abandon this potential business project.

However, my loss might be the communities gain. After about $500 spent on materials I have come away from the project with some knowledge that could bring about the holy grail of a relatively cheap, extremely strong and capable 18650 solderless battery solution. The only problem is, does anyone really want to spend the extra $3000 it will take to actually fully test the thing and then market it to all the idiots of the battery world who will muck it up and burn down their homes. Then blame you!

OK on to the product. Simply put, just take two printed circuit boards and squeeze some batteries in the middle. Using printed circuit boards provides an easy solution for all the different battery combinations that one can think of. Printed circuit boards are also easily designed and procured from any number of sources for a very reasonable cost in lower quantities. Printed circuit boards also offer a wide array of copper thickness and trace size solutions to handle very high power.





The problem: Finding a suitable battery contact that can solder to the circuit board. The ideal contact would be nickle plated copper to offer excellent conductivity a good mating surface that stays clean and does not corrode.
The solution so far: After several different products including designing my own nickel plated copper buttons that I had shipped in from china, I settled on tacks... But not just any type of tacks. These are retail security tacks that are used to pin RFID tags to expensive products. These tacks are flat, are only slightly larger than ideal size and are nickel plated. Importantly, they provide a soldering point for through hole PCB use. They are however made of steel rather than copper, but that can be compensated for by using pads and thick vias. These tacks come in boxes of 1000 and can be had for as low as 3.5 cents each, perfect for a low cost solution.





Now on the the biggest and most expensive challenge: How to squeeze those batteries together.
The solution: delrin plastic stands....a forest of them. These stands are 66mm long, and 7.7mm in diameter. This allows a grid of 18650 batteries exactly 18.5mm on center. They are light and very strong. By using a stand on 4 sides of a battery, you can create a very strong contact between the pcb and the battery for every single battery. They are threaded on the top and bottom to allow the use of screws to attach to the pcb boards. These single stands are also very versatile in that they allow an infinite number of possible pcb battery designs. I have had 9 manufactured at a cost of around $300!! just to test how they would work with 4 batteries. Worry not because you will need a lot of these things and that means that a mold will have to be made. A mold will cost about $1000 and after that each piece will be about 30 cents to make. To put that into perspective, if you created a 100 battery solution, you would need a forest of about 120 stands which would cost about $36. They only weight 2.25g each.


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The final product ended up being much stronger than I ever imagined. Even with only 4 batteries and 9 stands the structural integrity was excellent. The stands and batteries themselves act like struts and end up forming a solid immovable brick. I can only imagine the strength of dozens of stands and batteries will be. The contact between the battery and the board is excellent and would be almost impossible to move as more stands and batteries are used. Initially I thought that I would have to use .93" or .124" FR4 board, but my prototype is using .62" and it is definitely strong enough. I was also worried that the delrin plastic stands would strip easily, but they are actually very resilient, and very tough to strip if you use the right length of screw. 5/8" #4 hex machine screws work perfectly. If this project were to continue, I would suggest 3x8mm screws to make it more international friendly.



Fusing proved to be a challenge. My initial plan was to use extra small low profile blade fuses like they use on motorcycles. One for each cell but that proved cost prohibitive. After being inspired by the Tesla Motors battery pack, I settled on fuse wire which can be found in Europe. While this approach works, it is far more time consuming to implement than I had imagined. If the project were to go forward, I would suggest ditching this route in favor of designing PCB fuse traces. This will not be an easy task since PCB fuse traces do not allow a lot of consistency and can not be easily repaired. However, I feel it is the only route to allow a low cost easy to produce solution. If a trace is burned away, the customer should use fuse wire to repair it.




Why am I abandoning this project? Well honestly it worked much better than I ever thought it could. However, as I was putting batteries in I realized how easy it would be for someone to either electrocute themselves, improperly install a battery and severely burn themselves, improperly install a battery and possibly burn down their house. There are tons of scenarios that can end up very bad and the blame will fall not on the customer, but on the kit manufacturer. After watching some 18650 exploding battery videos I decided this project was too much risk for me and I was out. Yes you can limit liability by incorporating and having people sign wavers, but the thought of someone hurting themselves or losing a home because they could not build the battery properly was too much for me to bear. Fortunately there are braver people than me out there and this project might live on. I would be glad to answer any questions.

All my progress is available to purchase at a small fraction of the cost to make plus shipping to a VERY SERIOUS buyer only. Includes all materials and CAD designs and quotes.




.

 

[Teh Stork]

I could write a wall of text explaining why this is a bad idea and design, but read this feedback instead: Just, no.

A cheap china spot welder, nickel stip and hot glue is better than your mess.

 

[spinningmagnets]

I'm glad you posted this. I imagine some will like it and others may not, but you have actually done something and posted the pics. I really like this idea, but I wonder if some small modification could help with heat expansion (a small issue, but it should be easily allowed for). That was one of the reasons that using closed-cell foam as a compression blanket on one end of the cell-groups is one of my top default methods (for the purposes of discussion).

I believe spot-welding is a very good method to use for factory packs, but I believe the benefit to the recent batch of solderless designs from ES mean that when the cells wear out, they can be replaced easily by ordering bare NIB cells. A spot-welded pack would require new strips and all the welds to be repeated.

 

[jonescg]

I like it. I agree, there are problems with compression straining the terminal ends, but you are right - it's not idiot proof. If you were to build them for people as a complete unit you can avoid a lot of the issues, but shipping complete packs is expensive.

I really appreciate the fact that you came up with a design and tested it - more of that around here is always a good thing.

You're right though - you were very close, but I can't think of a good way to make that final cell-to-PCB connection nice and solid, while not compressing the cell.

 

[Ypedal]

Well done !!

I think about half the forest would be enough to provide a solid connection, along with some of the high conductivity grease project idea

http://endless-sphere.com/forums/viewtopic.php?f=14&t=61542

but i agree fully, DIY battery pack assembly is a messy business .... soooo many ways for it to go wrong..


Edit : if the boards were made for each parallel group to be assembled first, then could be bolted together with traces made to overlap only in series.. maybe ?

 

[liveforphysics]

The key to making any of the solderless designs work is independent and adequate spring force designed into contacts that allows the cells to wiggle and shift a bit from stress events and still remain a low resistance electrical connection to each cell.

Solderless has many advantages over spot welded tabs. Snath's battery design is my current favorite for round-cell pack designs.

 

[jdevo2004]

The key to making any of the solderless designs work is independent and adequate spring force designed into contacts that allows the cells to wiggle and shift a bit from stress events and still remain a low resistance electrical connection to each cell.

Solderless has many advantages over spot welded tabs. Snath's battery design is my current favorite for round-cell pack designs.

Yeah I guess compression is one of those things that the community would have corrected me on if I had shown off a working prototype. I think an easy solution to too much compression with my design would be to use thick soft rubber washers for each screw to provide an even low pressure compression for each battery allowing it to expand and move a bit. I also like the conductive grease idea further up. Oh well. Let the next guy figure it all out.
It was a fun project even if it was a dead end.

 

[jonescg]

I think an easy solution to too much compression with my design would be to use thick soft rubber washers for each screw to provide an even low pressure compression for each battery allowing it to expand and move a bit.

I was just going to suggest a rubber washer underneath each thumbtack. Something like this:

 

[Honk]

This is actually a very good weldless approach. Congratulations jdevo2004 !!!

I have also designed a similar PCB design holding 108 pcs of 18650 cells in paralell.
The main difference between our designs is that mine has built-in fusing by
thin copper tracks from each cell. No messy fuse soldering afterwards.
The second thing is that I added individual cell monitoring for safety.
If any cell goes bad in the pack I'm told which by an array of small SMD leds.
The third difference is built-in low voltage detection for safety.

I have planned a heavy duty 10kW pack 108p12s.

Each cellpack with 108 cells is individually charged, no need for built-in overvoltage protection.
The charger handles this as it has 20 separate channels with monitoring.
Each channel capable of 10 or 30 amps (selectable) charge current.
The charger is my own design.

 

[Everett]

That looks like a very interesting design. Seems like it should work very well, but you are right, put one cell in backwards, and boom. I suppose that would be the reason to have each cell fused, so that if a completed pack gets put together with one backwards cell, then its an easily replaceable fuse, or 4.

 

[friendly1uk]

I can see the problem, but I don't see how a working legal system could hold you responsible. . The battery manufacturer supplies the dangerous bit. They should make sure the buyer knows what they are getting. You may presume the person with the batteries knows what they have. It's not your duty to tell everyone with batteries that they are dangerous. It is your duty to tell anyone you give batteries to that they are dangerous. So the person with the batteries always knows. It's a pretty solid case.


It's an interesting design. If the tree's were wavy they might offer some compression. The board would have to be a bit flexible but it could work. It is very fussy though.
How about something like these, but stackable and higher capacity. http://www.ebay.co.uk/itm/5-Pcs-Parallel-Series-Connection-4-x-3-7V-18650-Battery-Plastic-Holder-Box-/360981845206?pt=UK_ConsumerElectronics_Batteries_SM&hash=item540c31d4d6

 

[flathill]

Neal already figured it out. Would not it be funny if Zero licensed his solderless battery tech after they got rid of him?

In general, the present invention is directed to the construction of a robust, high conductivity, inexpensive, and easy to assemble and servicable battery contact for battery cells. More specifically, the present invention is directed to battery contact comprising a thin flat, and highly electrically conductive metal configured to be attached to a circuit board. The high conductivity battery contacts may allow for the utilization of high energy density battery cells, such as but not limited to lithium ion cylindrical cells that may be used in high power applications.

A tab 120 may be electrically connected to the electrical pathways on the PCB 110. Tab 120 may be formed from or comprise, at least in part, copper or other high conductivity metals. It is contemplated that tabs (for example, those made of copper) may be plated to prevent corrosion. Materials such as tin, gold, or silver may be used alone or in combination for plating materials. The exemplary tab 120 shown in FIGS. 1 and 1A in profile view may be substantially in the shape of an oval or a racetrack: a hollow shape with two flat sides with rounded semi-circular ends connecting each flat side. One flat side may be formed by the overlapping ends of the strip. Alternatively, there may be a gap in the oval or racetrack shape, where the ends of the strip do not reach each other. The overlap or gap may be located on the side of the tab 120 proximate to the PBC 110, or may be on the side of the tab proximate to the battery cell 140. The other flat side is approximately midway between the ends. There may be a bend radius at each semi-circular bend to form a parallel gap in middle of the section.

An elastomeric pad 130 may be located inside of the tab hollow space. The pad comprises elastomeric material so as to have the quality of being compressible and preferably with minimal compression set. Additional material qualities such as high temperature resistance and resistance to aging are also desirable. Materials such as those comprising silicone in either solid or foam structure are suitable. Silicone foam comes in either open or closed cell structure.

---

 

[jdevo2004]

It's an interesting design. If the tree's were wavy they might offer some compression. The board would have to be a bit flexible but it could work. It is very fussy though.

This is a very smart idea. The compression strength would have to be tested under cold and heat as well as time, but it is doable. Manufacturing cost would stay the same. It would look something like this:

 

[Hillhater]

That is a over engineered solution. Too complex and expensive to be commercially viable.
The next generation of Tesla packs are rumoured to be printed pressure contacts using a segmented , flexible, PCB , and a pressure "blanket" .

 

[parabellum]

That is a over engineered solution. Too complex and expensive to be commercially viable.
The next generation of Tesla packs are rumoured to be printed pressure contacts using a segmented , flexible, PCB , and a pressure "blanket" .

Maybe, but it is a solution, and not difficult on mass production scale.

 

[mistercrash]

This newb does not like it. It is to complicated with too many parts that are custom made for this application. Way too expensive and ends up being too heavy. Can anyone come up with a solder-less/weld-less solution that does not require the use of machining equipment or having custom parts made at great expense? Can a no solder/no weld battery be made of off the shelf, inexpensive parts that anyone can find, buy and put together with a few simple tools?

I guess I'll have to come up with something myself.

Those Tesla packs I see, are those little fuses welded to the cells? Because they look like they are some springy wire that just makes contact with the cell with little pressure.

 

[amberwolf]

Can a no solder/no weld battery be made of off the shelf, inexpensive parts that anyone can find, buy and put together with a few simple tools?

Yes. There's a few ways it's been done here on ES already; Leamcorp's comes to mind.

EDIT: no, wait: I think his pack used some holders that arent' made anymore. BUt they could probably be 3d-printed.

 

[parabellum]

This newb does not like it. It is to complicated with too many parts that are custom made for this application. Way too expensive and ends up being too heavy. Can anyone come up with a solder-less/weld-less solution that does not require the use of machining equipment or having custom parts made at great expense? Can a no solder/no weld battery be made of off the shelf, inexpensive parts that anyone can find, buy and put together with a few simple tools?

I guess I'll have to come up with something myself.

Those Tesla packs I see, are those little fuses welded to the cells? Because they look like they are some springy wire that just makes contact with the cell with little pressure.

Donono but i can see kind of discoloration and grovs on them.

Edit

 

[Hillhater]

.
Those Tesla packs I see, are those little fuses welded to the cells? Because they look like they are some springy wire that just makes contact with the cell with little pressure.

Yes, fusible links welded to the cells. Either laser or ultrasonic welding is used.
Plenty of detail documentation of the pack construction is available on line .

 

[friendly1uk]

A lot of people seem to want to reinvent the wheel. What is wrong with a normal battery holder?

http://www.ebay.co.uk/itm/5-Pcs-Parallel-Series-Connection-4-x-3-7V-18650-Battery-Plastic-Holder-Box-/360981845206?pt=UK_ConsumerElectronics_Batteries_SM&hash=item540c31d4d6

Forget the pins, they are just in the way. Chop them off and solder to the springs. 50 cents a cell.

 

[riba2233]

There is 15 up to 25 mV drop at 1.3A on those springs, according to my measurement.

 

[jdevo2004]

LOL of course I researched springs. They are expensive, and they are not suitable for anything more than 2 amps. They are made of steel and even the thickest small springs are too thin. They would heat up like an incandescent filament under the types of current that we would need. You want to keep the terminals of the battery as cool as possible to ensure long life.

 

[parabellum]

LOL of course I researched springs. They are expensive, and they are not suitable for anything more than 2 amps. They are made of steel and even the thickest small springs are too thin. They would heat up like an incandescent filament under the types of current that we would need. You want to keep the terminals of the battery as cool as possible to ensure long life.

Not if your cooper strips are on top of the spring in direct contact to cell.

 

[jdevo2004]

Custom copper strips are expensive. Remember, they need to be nickel plated. Copper oxidizes relatively quickly in the air and even the thinnest layer of oxide will impede the batteries performance. I am aware of what you mean by leaving one of the contact sides "springy", there are other ways to do that besides actually using expensive springs. The "compression blanket" that other people have mentioned is just a thick piece of soft rubbery silicone which is super cheap and easy to use. That is the best direction for solderless 18650 imho.

 

[parabellum]

Custom copper strips are expensive. Remember, they need to be nickel plated. Copper oxidizes relatively quickly in the air and even the thinnest layer of oxide will impede the batteries performance. I am aware of what you mean by leaving one of the contact sides "springy", there are other ways to do that besides actually using expensive springs. The "compression blanket" that other people have mentioned is just a thick piece of soft rubbery silicone which is super cheap and easy to use. That is the best direction for solderless 18650 imho.

Yeah, blanket solderless is nice. Holder packkaging atractives are: Reconfigurable, resizable, reshapable, segmentable, extendable in small and big and almost shape independant. Any line can be shifted for exotical shapes. It is worth to consider.
Happy new year!!!