Ufobox's pressure-contact 18650 fused connections

Batteries, Chargers, and Battery Management Systems.
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Ufobox   1 mW

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Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 11 2019 11:24pm

Hi all, I'm working on my 18650 battery holder project, I red some relevant issues I face and trying to solve being discussed here. Below are some of the features I built into my battery holder :

- Cell Level Fuse (just positive ends). Negative ends are all connected.
- Stainless Steel Springs (just positive ends) apply cells contact pressure only, insulated, DO NOT function as conductor.
- Durable Materials, fiberglass and aluminium (functions as frame structure and bus bars).
- Easy to Open Battery Pack, for maintenance or inspection, bad cell/fuse/BMS replacement.
- Modular Design, one module is 12V (4S), scalable to 24V 36V 48V or higher.
- Easier To Build battery packs, eliminate the soldering/spot welding on cells contact.

Image
Image

I'm still waiting for some parts to complete the "module extension" (12V to 24V 36V 48V...so on), I try not to create "bottle neck" for current flow when scaling up the voltage of the modules. I hope the parts arrive soon and I'll show how to stack up the modules.

I have some short info on my blog which is still under development
https://leanmakes.wixsite.com/18650-battery-holder

Feel free to let me know if you see any flaw in the design at this stage. Thanks!
Last edited by Ufobox on Jul 15 2019 7:37am, edited 4 times in total.

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Re: New weldless battery system crowdfunfing project

Post by 1N4001 » Jul 12 2019 3:00am

Interesting. Are you using thread inserts as contacts? Those are made of brass, aren't they? You might want to consider making your own contacts out of copper, maybe even with one end closed for more contact surface. Brass has only 1/3 the conductivity of copper. For low-current situations that'll be enough, but for anything above 5A or so I'd definitely want copper contacts.

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Re: New weldless battery system crowdfunfing project

Post by Ufobox » Jul 12 2019 3:49am

Yes, in theory close-end nut will have more surface contact compare to hollow nut. But at the same time I found that there are many spot weld bumps on recycle 18650 even after cleaning/scraping.
Image

When placing a flat surface on the cell contact, the bumps create a gap in between result in less area of contact.
Image

When I place a hollow nut on the cell contact, there's no gap in between, maybe we have more contact in this case?
Image

Therefore I decided to use hollow thread inserts with the max diameter without touching the cell's negative.

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Re: New weldless battery system crowdfunfing project

Post by Matador » Jul 13 2019 7:19am

1N4001 wrote:
Jul 12 2019 3:00am
Interesting. Are you using thread inserts as contacts? Those are made of brass, aren't they? You might want to consider making your own contacts out of copper, maybe even with one end closed for more contact surface. Brass has only 1/3 the conductivity of copper. For low-current situations that'll be enough, but for anything above 5A or so I'd definitely want copper contacts.
Copper is quite soft and threads would easily strip. You're right, brass only has a third or so of the conductance of copper, but look at the wide surface area of contact... The bottle neck is not at the brass contact.

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Re: New weldless battery system crowdfunfing project

Post by Matador » Jul 13 2019 7:21am

Ufobox wrote:
Jul 11 2019 11:24pm
Hi all, I'm working on my 18650 battery holder project, I red some relevant issues I face and trying to solve being discussed here. Below are some of the features I built into my battery holder :

- Cell Level Fuse (just positive ends). Negative ends are all connected.
- Stainless Steel Springs (just positive ends) apply cells contact pressure only, insulated, DO NOT function as conductor.
- Durable Materials, fiberglass and aluminium (functions as frame structure and bus bars).
- Easy to Open Battery Pack, for maintenance or inspection, bad cell/fuse/BMS replacement.
- Modular Design, one module is 12V (4S), scalable to 24V 36V 48V or higher.
- Easier To Build battery packs, eliminate the soldering/spot welding on cells contact.

Image
Image

I'm still waiting for some parts to complete the "module extension" (12V to 24V 36V 48V...so on), I try not to create "bottle neck" for current flow when scaling up the voltage of the modules. I hope the parts arrive soon and I'll show how to stack up the modules.

I have some short info on my blog which is still under development
https://leanworkshop9.wixsite.com/18650-battery-holder

Feel free to let me know if you see any flaw in the design at this stage. Thanks!
Quite a nice project. The use of threaded inserts and nylon scews is brilliant

Matador

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Re: New weldless battery system crowdfunfing project

Post by Ufobox » Jul 13 2019 8:06am

Matador wrote:
Jul 13 2019 7:19am
1N4001 wrote:
Jul 12 2019 3:00am
Interesting. Are you using thread inserts as contacts? Those are made of brass, aren't they? You might want to consider making your own contacts out of copper, maybe even with one end closed for more contact surface. Brass has only 1/3 the conductivity of copper. For low-current situations that'll be enough, but for anything above 5A or so I'd definitely want copper contacts.
Copper is quite soft and threads would easily strip. You're right, brass only has a third or so of the conductance of copper, but look at the wide surface area of contact... The bottle neck is not at the brass contact.
Fuses are the bottle neck so I fuse the positives end only instead of both ends.

Copper nuts are costly compare to brass nuts. I try to make the best possible design and keep the cost low at the same time.

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Re: New weldless battery system crowdfunfing project

Post by 1N4001 » Jul 13 2019 8:23am

Matador wrote:
Jul 13 2019 7:19am
1N4001 wrote:
Jul 12 2019 3:00am
Interesting. Are you using thread inserts as contacts? Those are made of brass, aren't they? You might want to consider making your own contacts out of copper, maybe even with one end closed for more contact surface. Brass has only 1/3 the conductivity of copper. For low-current situations that'll be enough, but for anything above 5A or so I'd definitely want copper contacts.
Copper is quite soft and threads would easily strip. You're right, brass only has a third or so of the conductance of copper, but look at the wide surface area of contact... The bottle neck is not at the brass contact.
That depends on the alloy, you don't have to use pure copper.

Image

(and yeah, I realize that tensile strength isn't hardness)

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Re: Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 23 2019 10:07pm

Video : The making of the fiberglass bracket to lock and extend the module into higher voltage

https://youtu.be/QjZbZJz3t28



Image

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Re: Ufobox's pressure-contact 18650 fused connections

Post by neptronix » Jul 23 2019 10:15pm

Very interesting, thanks for sharing with us.
I think that as battery density increases, things like this which add weight, but provide all sorts of other interesting benefits will become more accepted. You are ahead of the curve with this idea.

Right now, it'd be a hard sell to convince me to add this much bulk/weight to my battery. It'll be another story when we get into 400whrs/kg and beyond. :)
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Re: Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 23 2019 11:40pm

Thanks for reminding on the weight issue.

This is the weight of one module (32 cells) -
1.082 lbs (pound) or 491 g (gram)

Image

Replacing the fiberglass bottom with carbon fiber will bring down the weight by quite some margin but it will bring up the cost. Now I realized that losing weight can be quite expensive.

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Re: Ufobox's pressure-contact 18650 fused connections

Post by neptronix » Jul 24 2019 12:43am

So 2-3lbs for a typical ebike pack. That's not too bad, i would have thought it would be more.

I find the idea very interesting and kind of charming in a way. Remember old portable stereos and things that had to have 4.. maybe even 8 batteries put in parallel-series? this is the monster size version of that :lol: :bolt:
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Re: Ufobox's pressure-contact 18650 fused connections

Post by peters » Jul 24 2019 1:36am

I like the structure but I think spring contacts would be necessary on both ends of the cells.
I had a flashlight with 1 spring only that I used on a road bike (thin tires) and it frequently switched off on a bumpy road because the cell lost the contact for a moment due to its inertia. It could also switch off by hitting one end by hand. It was not a regular flashlight, I fabricated it and its circuit with some transistors and resistors and it did not turn back on automatically after the cell contact was restored (unlike the normal flashlights), but it convinced me that 2 springs/cell are required in any case.
You could test it: for example put just one cell in the bottom row and hit the Al section from the bottom with a rubber hammer while measuring the voltage with an oscilloscope.

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Re: Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 24 2019 1:42am

neptronix wrote:
Jul 24 2019 12:43am
So 2-3lbs for a typical ebike pack. That's not too bad, i would have thought it would be more.

I find the idea very interesting and kind of charming in a way. Remember old portable stereos and things that had to have 4.. maybe even 8 batteries put in parallel-series? this is the monster size version of that :lol: :bolt:


Yes, a 10S (36V) will need 3 modules, weight 3 lbs.

1 module is 4S
3 module will be 12S
for a 10S there will be 2 empty slots available as reserved space for a BMS.

Spot on, it looks very old school, very analog indeed. The good thing is I can easily replace most of the parts, like when I screw up on welding a fuse I can simply unscrew and take out the plated copper piece and replace with a new one, and solder again.

To give a slight of modern touch to the pack, maybe I'll go with a polycarbonate enclosure/box, will learn to bend some polycarbonate sheet later.

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Re: Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 24 2019 2:46am

peters wrote:
Jul 24 2019 1:36am
I like the structure but I think spring contacts would be necessary on both ends of the cells.
I had a flashlight with 1 spring only that I used on a road bike (thin tires) and it frequently switched off on a bumpy road because the cell lost the contact for a moment due to its inertia. It could also switch off by hitting one end by hand. It was not a regular flashlight, I fabricated it and its circuit with some transistors and resistors and it did not turn back on automatically after the cell contact was restored (unlike the normal flashlights), but it convinced me that 2 springs/cell are required in any case.
You could test it: for example put just one cell in the bottom row and hit the Al section from the bottom with a rubber hammer while measuring the voltage with an oscilloscope.
:thumb: I like the suggestion of hitting the aluminium busbar and checking the voltage with an oscilloscope (yet to get one).

I did come across whether to have both ends with springs or just one end. As I didn't use the springs as conductor I'll have to fuse both ends (if both ends are springs installed) which I think this will create a lot of resistance in the current flow. I guess fusing both the negative and positive ends is not necessary.

Another concern is will it be difficult to insert cells into a holder with springs on both ends?

One more down side with both-ends-springs is it will increase the length of the battery holder result in a less compact design.


My solution is to compress the spring coil to almost the max, just enough gap to insert the cells. Attach is a pic showing the springs before and after compression. Will do some real riding test for sure after the pack is fully installed.

I'm using stainless steel springs with thicker wire diameter compare to the springs in an ordinary battery holder. Will increase the thickness of the wire diameter if necessary.

Image

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Re: Ufobox's pressure-contact 18650 fused connections

Post by Drunkskunk » Jul 24 2019 2:37pm

This looks awesome.

I'm not sure I would want to use this in a permanent battery, but for prototyping and experimenting with different configurations it would be awesome to have something like this.

A carbonfiber backing would be conductive. With a spring loaded mount, the cells would vibrate and could eventually rub through their sleeves, shorting out against the backing. Fiberglass or polycarbonate are non conductive. I'd rather have that.

As an end user, I'd 3D print off a few cell dividers that would prevent side to side movement and keep the cans from touching the edge of the aluminum part. But not everyone would need that.
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Re: Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 24 2019 8:10pm

Cool suggestion on the cell divider/spacer. I quickly grab a generic 18650 holder/spacer and did a simple test as in the videos below :

https://youtu.be/Wac7ImBHmDA


Slightly rougher test

https://youtu.be/BMTe8kdWYKM

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Re: Ufobox's pressure-contact 18650 fused connections

Post by spinningmagnets » Jul 24 2019 8:35pm

For the casual viewer who is new to 18650 cells, the bottoms and sides of the 18650 format is all one shell that is charged with the negative. The small nipple in the center of the positive end is the only place to draw the positive. There is a narrow space between the positive nipple and the shoulder of the shell where a catastrophic short can occur, and that is why these plastic cell holders are only being added on the positive end.

I think this is a great addition. Well done!

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Re: Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 24 2019 9:06pm

Just a visual presentation of a 18650 battery polarity.
Image

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Re: Ufobox's pressure-contact 18650 fused connections

Post by whereswally606 » Jul 26 2019 7:51am

I'm sure you have already thought of this but if not... the design looks like you could use the back side and double the numbers in parallel very easily. I really like this design. very easy for the home hobbyist. Then the double sided layers could be stacked for more in parallel at the edges by paralleling bus bars across the stacks.
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Re: Ufobox's pressure-contact 18650 fused connections

Post by flat tire » Jul 26 2019 12:47pm

This is like the worst idea ever. Unnecessary complication for no reason that I can tell.

I'm not sure what circumstances anyone would ever use this besides seeing it and not knowing any better.

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Re: Ufobox's pressure-contact 18650 fused connections

Post by Drunkskunk » Jul 26 2019 1:54pm

Looks like those cell holders work great in the videos.

The reason I was thinking of those is I see a use for this design where you might only have 4 parallel cells in a row, and the next 4 would be in series to them, causing a difference in voltage between the outside shell of some of the cans.

I have this idea for a trike running recycled cells that may benefit from this design. Is this something you plan to sell as a kit? it would probably be a year before I get started on it.
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Re: Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 26 2019 10:34pm

whereswally606 wrote:
Jul 26 2019 7:51am
I'm sure you have already thought of this but if not... the design looks like you could use the back side and double the numbers in parallel very easily. I really like this design. very easy for the home hobbyist. Then the double sided layers could be stacked for more in parallel at the edges by paralleling bus bars across the stacks.
Superb observation :bigthumb: Yes, I can scale this module in parallel as well. I have ordered some copper/brass bracket for parallel connection, need to finalize the length of the bracket.

Beside powering my ebike (36V), I would like to try using this pack (in 24V) to power my tools with a DC to AC inverter.

It's a versatile modular design.
Last edited by Ufobox on Jul 27 2019 12:43am, edited 4 times in total.

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Re: Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 26 2019 10:53pm

flat tire wrote:
Jul 26 2019 12:47pm
This is like the worst idea ever. Unnecessary complication for no reason that I can tell.

I'm not sure what circumstances anyone would ever use this besides seeing it and not knowing any better.
Visually it looks complicated, the idea behind is fairly simple. In short, small cells together make a big cell, fused at positive ends (for safety) as depicted in the picture. But simple doesn't mean easy, it's the precision and the use of right materials that make the idea works.
Image

I hope I can compile a video to show everyone how to use the module soon.

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Re: Ufobox's pressure-contact 18650 fused connections

Post by flat tire » Jul 26 2019 11:01pm

"How a battery is born 101" well no shit, but your thing won't be cheap and it's less effective and secure than spot welding or even soldering + a little tape adhesive glue etc. Those things are cheap effective and just as accessible to noobs as an overpriced prototype style frame.

Or if you're smart you can use braid and rubber bands like Zero MC used to do. Dirt cheap canned cell interconnections with huge current capacity.

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Re: Ufobox's pressure-contact 18650 fused connections

Post by Ufobox » Jul 26 2019 11:09pm

Drunkskunk wrote:
Jul 26 2019 1:54pm
Looks like those cell holders work great in the videos.

The reason I was thinking of those is I see a use for this design where you might only have 4 parallel cells in a row, and the next 4 would be in series to them, causing a difference in voltage between the outside shell of some of the cans.

I have this idea for a trike running recycled cells that may benefit from this design. Is this something you plan to sell as a kit? it would probably be a year before I get started on it.
Hey thanks for the suggestion Drunkskunk, it really secure all the cells in place. If the cells are bricks, it's like cement added onto bricks.

It's a versatile module, I think its quite user friendly as well. If the test result is great, yes, I will sell this as a kit.

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