The Barncat Battery- No weld/no solder

[Chalo]

I think this style of battery is fated to have deterioration and poor continuity at the terminals, possible physical damage to the battery casings, and progressive looseness. I'm sure it works fine when new, but vibration directly affects the electrical contacts in a way it doesn't with welded or soldered packs.

Unlike some no-weld batteries, this one allows the cells to hammer directly on each other's terminals.

 

[Barncat]

Chalo- did you not read the very first sentence of this entire thread?

After about 1750 and 250 street miles respectively on these two packs, they're as tight as the day I built them with zero corrosion, degradation, or cell damage. You know what was hiding under cover on my Mongoose Girder, OCC Stingray, and Mongoose Blackcomb builds? These two battery packs.

You're entitled to your opinion as the resident skeptic on site, but spare us the drama. The cells are not "hammering" on each other...

I'll put these up against anything else out there. 'Nuff said.

 

[Hillhater]

I've not done any experimenting with pouch cells. They're heavier and you still need to safely contain and attach them to your ride.

I respect your efforts and admire your results, ...but that comment re pouch cell weights is wrong.
Individual cell energy density will be very similar, but finished pack weight is what matters.
What is the “ready to ride” weight of those packs ?
Pouch cells are available in higher capacity ..10, 20, 30+, Ah ...with connections being simple the end result is a compact light pack with few connections.
If the high capacity ,Multi cell flight packs are used, a pack can be just “plug and play” with inbuilt cell level balance leads etc for monitoring.
The total pack weight will be similar if not less than any “loose cell system” pack.

 

[SafeDiscDancing]

Re my reversed screw contact system: it works, so there's no arguing with that . Sturdy, optimal surface area/electrical contact, and it utilizes the inherent but subtle "springiness" of the positive cell cathodes. Fortunately they can be safely compressed in series without passing (or probably even nearing) their yield point. This works both with the thin copper paralleling strips or the even more vibration damping flat braid copper.

That's a good point.

All metals are flexible to some degree and behave as a spring.

So the 5 Series cells each add a small spring function when collectively they are given an overall pressure.

In a sense the cells "self correct" as springs, but you do need to find that ideal pressure that gives good contact but not too much that might actually damage the cells.

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Welded cells are stacked sideways and have no pressure holding things in place.

So if a weld let's go there is no spring waiting to push it back.

It would seem that welded packs are either 100% connected or they fail. (a sharp jolt could make the difference)

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As long as pressure exists in the series cell design the connectivity will only get BETTER over time simply because the contact point will act to grind the interface smoother over time.

This idea that pressure contacts get worse over time runs counter to logic as I see it.

I really don't think much pressure is necessary. Just a firm contact seems enough.

 

[SafeDiscDancing]

I've not done any experimenting with pouch cells. They're heavier and you still need to safely contain and attach them to your ride.

I respect your efforts and admire your results, ...but that comment re pouch cell weights is wrong.
Individual cell energy density will be very similar, but finished pack weight is what matters.

I found a trick for pouch cells but it's high labor and not many people have the skill set for it.

Wrap each pouch cell with a thin layer of fiberglass cloth and add the resin and let it harden.

That instantly creates unbreakable compression and it's very light weight.

But if you aren't skilled in fiberglass work you are facing a steep learning curve if it's your first try.

 

[Barncat]

(from 3 posts ago)
Hillhater- more pressingly- why are you so opposed to elevation changes? Just kidding .

We may be talking about apples and oranges; high power commercial lipo hobby packs are as you say lighter per energy density but I was shooting from the hip and referring to DIY pouch cell packs that then need to be enclosed/ protected and somehow attached to a machine.... if you can show me some examples of that approach that are pretty bombproof, please do.

I have no accurate means of weighing the packs but they certainly don't exceed 2.5 lbs tare weight, plus the spec weight of (100) 18650 MJ1 cells or (75) 21700 p42a cells.

At any rate, belaboring a few ounces here and there is not the point and if I was wrong I stand corrected.

 

[eMark]

Chalo- did you not read the very first sentence of this entire thread?

After about 1750 and 250 street miles respectively on these two packs, they're as tight as the day I built them with zero corrosion, degradation, or cell damage. You know what was hiding under cover on my Mongoose Girder, OCC Stingray, and Mongoose Blackcomb builds? These two battery packs.

You're entitled to your opinion as the resident skeptic on site, but spare us the drama. The cells are not "hammering" on each other...

I'll put these up against anything else out there. 'Nuff said.

. . .

No matter how secure/stable is the end-to-end cell contact there will always be those that prefer spot-welding vertical cell fabrication. IF for no other reason than it's supposedly more secure and more "Manly" ... requiring more expensive equipment, more skill and more labor intensive to fabricate. More time consuming then your horizontal fabrication with spot-welding more frustrating if and when it's necessary to remove and replace a faulty spot-welded parallel cell or cell group; moreso true when using salvaged cells.

Your concept lends itself more to a cargo etrike than it does to an ebike. My next project when my 30Q experimental Vruzend 10S3P is no longer viable (after 2-3 more years with 500-625 c/d cycles). Will be a similar flat end-to-end configuration secured against the vertical front wall (but easily removal) of my Plano cargo container (see photo).

Two adjoining flats of 5 series cells in length with 5 parallel cells so that it can be split into two 5S5P packs for bottom balancing and bulk charging (with balance leads and no BMS). Y-cable charging as a 5S10P with my 2S-6S HTRC Balance Charger. Then reconnected as one flat cell dimension as a 10S5P pack and rehung in Plano container. Five 18650 cells in length and ten cells in height mounted on front wall of existing Plano Cargo container. Enuf space for a 12S5P battery configuration (two 6S5P packs) for more speed.

Will use salvaged cells when i can secure a seemingly good deal from Battery Hookup. Only charge to 41V with average discharge to 34V. Will also carry UPP 36V 10Ah backup battery in original battery comparment housing that's located under Plano Cargo container modification. It's a Liberty Trike ... https://www.libertytrike.com/ ... i'm 77 yrs young and being retired 12mph is AOK as i'm seldom in a hurry

 

[SafeDiscDancing]

Wikipedia talks about it:

For given physical and mechanical material properties, parameters that govern the magnitude of electrical contact resistance (ECR) and its variation at an interface relate primarily to surface structure and applied load (Contact mechanics).[8] Surfaces of metallic contacts generally exhibit an external layer of oxide material and adsorbed water molecules, which lead to capacitor-type junctions at weakly contacting asperities and resistor type contacts at strongly contacting asperities, where sufficient pressure is applied for asperities to penetrate the oxide layer, forming metal-to-metal contact patches. If a contact patch is sufficiently small, with dimensions comparable or smaller than the mean free path of electrons resistance at the patch can be described by the Sharvin mechanism, whereby electron transport can be described by ballistic conduction. Generally, over time, contact patches expand and the contact resistance at an interface relaxes, particularly at weakly contacting surfaces, through current induced welding and dielectric breakdown. This process is known also as resistance creep.

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So basically as long as pressure exists then as I suspected resistance DROPS because the current tends to break up things in it's way.

Sort of like a stream flowing downhill will break up debris that slow the water flow.

After a heavy rain a small stream might be slightly wider than before.

 

[calab]

Any spring loaded/friction fit no weld configuration will have problems once you hit bumpy ground, once a slight problem occurs its avalanches very quickly from there, for me its not worth the risk or investment but I always think its cool people try new ideas, so there is more then just one skeptic lurking around.

The cool thing with new ideas comes the lego style battery modules such as Grintech, or cheaper and cheaper tab welders on the market. For me its best to stick with what works and lasts.

 

[SafeDiscDancing]

Any spring loaded/friction fit no weld configuration will have problems once you hit bumpy ground

But realize that is based on an assumption about how contacts actually work.

In reality a pressure connection actually improves with BOTH vibration and current.

That was the whole point I was making... we need to think in the ways things actually work.

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And let me add that the current acts as like it's own welder. At the microscopic level the current wants to break through and find a wider path to transfer energy.

This means if you have pressure then current will bond the contacts more tightly... but if nothing is holding the contacts together then the current starts burning away everything it gets it's hands on and creates a void.

Current and vibration can either work FOR you or AGAINST you.

 

[Hillhater]

Wrap each pouch cell with a thin layer of fiberglass cloth and add the resin and let it harden.

That instantly creates unbreakable compression and it's very light weight.

That may work for narrow (<2”) wide pouches,and prevent them from “bloating” , but isnt going to give much “compression” to wider pouches unless the glass/resin is quite thick and hence heavy.
Whilst i do believe there are some gains in capacity etc from effective compression on pouches, personally i dont bother with it.
I invariably overspec my packs for both capacity and discharge amps, so i am not looking to maximise performance or capacity.
I have pouch RC packs that are 10+ yrs old that still hold shape and balance even if down on capacity
And for reference , i also have several 18650 packs,.....but i do not like the bigger voltage loss with SOC

 

[Barncat]

SafeDisc- yeah we're on the same page here re the metallurgy of the series compression stack. If the steel cathode had to be deformed to achieve good repeatable contact, that would be a deal breaker. Trust me, I was very concerned about that.

I've ridden the green pack hard the equivalent of Tampa to Santa Fe with zero issues and still good as new.

My very first prototype iteration had the screws pointed in the conventional direction, and that could deform cathodes. Not good. You need surface area.

 

[Hillhater]

Any spring loaded/friction fit no weld configuration will have problems once you hit bumpy ground

But realize that is based on an assumption about how contacts actually work.

In reality a pressure connection actually improves with BOTH vibration and current.

That was the whole point I was making... we need to think in the ways things actually work..

Please remember you are not the first on this dance floor of solderless construction !
You are assuming that all your pressure points remain in contact ALL the time.
What if after a bump , one or two cell tops deform and you loose a few connections ?..that friction theory goes out the window , and as you say , that current starts working against you ......and some cells start to go out of balance.
There are good reasons no commercial pack assemblers use these “dry” assembly methods...they cannot afford to have pack defects to respond to.

 

[eMark]

SafeDisc- yeah we're on the same page here re the metallurgy of the series compression stack. If the steel cathode had to be deformed to achieve good repeatable contact, that would be a deal breaker. Trust me, I was very concerned about that.

I've ridden the green pack hard the equivalent of Tampa to Santa Fe with zero issues and still good as new.

My very first prototype iteration had the screws pointed in the conventional direction, and that could deform cathodes. Not good. You need surface area.

They do go out of their way to find fault based as much on bias than fact. Reminds me of the DNC and their fault finding with the GOP, or is it the other way around ? :wink:

If it works for a multi-cell flashlight without any problem than what's the beef?

 

[Barncat]

calab- my experience thus far does not align with your assessment above. Would I beat the crap out of these off road? Probably not, but even that prospect concerns me less than it used to.

For the record I have NOTHING against welded cell construction. Just figured I'd crack the nut on what I submit is the optimal no weld drop in case concept for those so inclined.

 

[SafeDiscDancing]

What if after a bump , one or two cell tops deform and you loose a few connections ?..that friction theory goes out the window

You do notice that the cells are laid essentially flat (30 degrees?) in a 5S and 5P layout per layer.

So unless you do things weird where you go off a jump and crash off the front wheel or throw the bike away off a jump and it lands on it's back wheel the normal forces will work SIDEWAYS to the cells. (and in those crashes a welded pack is doomed to break apart anyway)

See what I'm saying?

It's not like the cells were stacked up and down.

If the pressure was correctly set and the cells not pushed near dimpling the bumps are not oriented in the direction to cause damage.

 

[Barncat]

10-4 eMark.

 

[Barncat]

To the skeptic camp- I get your reservations but please go back and read all my posts. The idea here is super tight case tolerances in an inherently anti-vibe enclosure, and after the cells are carefully compressed in series, the lid then locks everything in place from the top down.

 

[SafeDiscDancing]

To the skeptic camp- I get your reservations but please go back and read all my posts. The idea here is super tight case tolerances, and after the cells are carefully compressed in series, the lid then locks everything in place from the top down.

Well, I guess I'm your biggest fan.

Yeah... I caught the tight tolerances talk at the beginning and think that is very important.

Speaking more generally about the issue of "flexibility vs rigidity" one must essentially pick one and be dedicated to it.

My pouch cell pack is designed with fiberglass which is a funny material because it can flex in some directions but then be quite rigid in others. Carbon fiber is even more extreme that way.

If something is subjected to extreme jolts then it either must naturally flex and react to the assault or it must be so rigid and strong to be able to withstand a direct hit without failing.

People can become almost religiously obsessed with "just one way" because they know only that way.

 

[calab]

Yeah but flashlight is not the same as 50a and if its a gamble you are willing then so be it.
Seen to many problems with those no weld/friction fit.

Point three is interesting after a cursory search. I guess I will do a quicke 3 minute search for liveforphysics which is very interesting.

In the 10 last years i have built dozens of battery packs ofvarious engineering level.

For all those i have kept the same common rules:

1: Good current sharing across every cells,
2: good thermal management
3: good mechanical resistance against vibration and moisture


For the point 1, this is one very important that most people pay attention to, however some very stupid errors can ruin the pack very easy.
For exemple, for my mongoose 2.3kWh buld in 2008, i have used parallel connections that connect in serie to each other by connecting them to both end of each row.. but did not used serie connections in the middle and thre is a perticular reason for that: the current is function of the cell internal resistance, and internal resistance is function of cell temperature. The cell temp at the end of each paralle row is lower than the temp in the middle. Think about it, this is very simple! if the Ri of the cell in the middle is lower due to higher temp, it will conduct MORE current and cell that are at both end will be colder and conduct less current... The serie connections made closer to these colder cell actually compensate and make the total curent share over the entire paralleled cells to be uniform. This pack ran over 16500km and only required few rebalancing and it does not have any BMS.

So YES current share and thermal management ARE IMPORTANT :wink: and if well made the pack last longer.

The second point: the thermal management is also very important. as well for mechanical tolerance and cell health... Hot glue is the cheap chineese PROBLEM.. I have dissassembled hunderd of OEM ebike battery that all had problem with bad cell connection due to vibrations due to hot glue that just unstick from the cell... Hot glue is bad for lower temp it become harder and break. Then the cell only rely on the cell connection to mechanically stay in place witch is bad.

Point 3: Good Mechanical resistance. i have dissassembled thousand of Makita packs.. yes thousand! and i also say the improovement made over the various version and years.
I can conclude that the packs that have the most problem are due to: Bad cell (bad apple), and bad cell connections due to hard environment where they are used at. and cells had completly broken spoweld... over teh years Makita have reduced the thickness of the nickel sheet and extanded the surface to allow flexion to take vibrations.. but these cells are now also very nicely hold together by plastic structure witch take most of the mecanical vibrations.

DIY Pack fail due to short circuit between cell case because people think the thinny green skin is strong enough to isolate between cells. ERROR!.. cell wirring is also something to think about... the place where the wires path is is also VERY critical.. that wiring must be secured correctly for any temperature and not rub against other sharp electrical connections... the weight of the pack must not be supported by balance connections wires too... all fact that seem an evidence for some is often completly forgot by others...

This IMPORTANT thread will get alot pages over the month i feel! 8)

Doc

in applications where it matters you dont rely on a single cell bond.

and i said it before: in theory you are right. in practice it does not matter one bit.

More welds on the bottom = more thermal damage

In practice for me, thermodynamics has been painfully reliable and merciless irregardless of my opinions. For this reason I'm happy to agree to disagree with you that it's good practice to raise places on the floor of the can to >1200degC.

Everyone's knee-jerk reaction is to hate on a weld-less design, and point out the shortcommings of the thousands of awful little battery holders in your TV remote controller or toy. This doesn't mean it has to suck, it would be a huge advantage to DIY EV builders to have something that can be assembled and reconfigured without needing specialty equipment. If we encourage and support efforts like that they will be more likely to happen and mature into something good for the community.

https://endless-sphere.com/forums/viewtopic.php?f=14&t=99012&hilit=weld+battery&start=25#p1450396

https://endless-sphere.com/forums/viewtopic.php?f=14&t=99012&hilit=weld+battery&start=50#p1453461

https://endless-sphere.com/forums/viewtopic.php?f=14&t=99012&hilit=weld+battery&start=50#p1453461

The trick is to make a pack that is still squishing against the cell contacts hard enough for a good electrical joint after years of sitting compressed.

This is why solderless packs aren't a mechanical design problem to solve as much as a materials tech challenge to select things that won't let force creep down to nothing after sitting a while.

 

[Chalo]

Chalo- did you not read the very first sentence of this entire thread?

After about 1750 and 250 street miles respectively on these two packs, they're as tight as the day I built them with zero corrosion, degradation, or cell damage.

Imagine someone saying exactly that about a car.

Either one of my e-bikes has a whole lot more miles on it than the sum total of what you have.

I know I have to spin around the batteries in a TV remote control every so often to restore continuity. That's milliamps. And my remote control doesn't have to bump down the road every day.

 

[SafeDiscDancing]

I know I have to spin around the batteries in a TV remote control every so often to restore continuity. That's milliamps. And my remote control doesn't have to bump down the road every day.

A flashlight uses the spring itself as the electrical conductor and this is possible because the current is so minimal.

What we deal with in these cylindrical cells is massive currents in the order of 5C (potentially 10 amps per cell) and that's a whole different world to exist within.

At that kind of current each contact acts like a welder or even a spark plug.

So I restate the observation I made earlier and was reinforced by the Wikipedia text:

"Current will either improve connectivity if under contact pressure or get worse if lacking contact pressure."

Let me add that you CANNOT pass significant current through a spring because the spring will quickly lose it's shape.

Any design for pressure contact must place a copper contact ahead of the spring mechanism.

Rigid bolt based pressure like done in this example (this thread) relies on the internal spring nature of the cells which have a small natural spring capability by default.

I think the overall design is logical, but I'd add a spring on the ends with a copper contact point. But that's my idea and not related to this present invention.

 

[footloose]

Existing design may do just fine in real world use.
Doing more may be gilding the lilly as they say.
But ... with simple tooling, really just a drill press, if working with copper bolt and copper rivet, something like this would be possible and, once jig was set up, pretty easy to create in needed numbers. Would eliminate what seems to be the possible design achilles heal of no spring compression.
Take a large copper bolt. Drill out the core of the larger bolt. Insert a coil spring. Insert flat-top copper rivet. Ideally, a snug slip-fit.
Might want a fairly large bolt to give enough material that there would still fairly strong threaded walls after boring out the core. Have to figure out exact sizing.

 

[SafeDiscDancing]

This is another way.

Just solder a 10 AWG wire to a copper disc.

 

[spinningmagnets]

The pack looks to be already complete, so please don't take all of these suggestions as an insult about your design choices.

I think this has a high chance of success, so I hope you continue to post the field-testing.

Many small devices run off of 1.5V to 4.1V, so intermittent lack of contact can occasionally be an issue.

A pack that uses 48V or more would be unlikely to suffer these types of problems, as higher voltages can flow through "less than perfect" contacts.

Higher currents need a broad contact patch, using connectors that are sized to handle peak currents.

If someone lived near the ocean, you should expect corrosion issues that would reduce the area of the contact patch thay can flow current. In that situation, the smaller contact patch would result in a hot spot, where the full current has a smaller contact.