Coil Spring connectors ?

Hello,

Has anyone come up with a practical way to use spring coils as serial connector between cells in large battery packs ? It's quite common in cheap 1 to 4 cells holders, but I have never seen a large pack built with such a system. The reason I'm thinking about building one is because the current battery geometry I'm facing would favor stacking cells atop another instead of next to each other like in a classic rectangular box. Using coil springs between the cells seems like an option, especially based on brass wire (or fancy beryllium Cu!).
Open questions remains though, like how to easily connect the coil to each other (parallel wiring for balancing) and more importantly, is there a real risk of contact braking in high vibration or shock environment ? After all, the coil would only push against the cells, and not be soldered to it.

Thanks for for your feedback,

qwerkus

how about 2 little magnets opposing each other

qwerkus said:

...fancy beryllium Cu!...

Click to expand...

I'd prefer to stay away from that stuff based on its nasty negative health issues.

99t4 said:

qwerkus said:

...fancy beryllium Cu!...

Click to expand...

I'd prefer to stay away from that stuff based on its nasty negative health issues.

Click to expand...

Fun fact: More people involved in the Manhattan Project died from beryllium poisoning than from radiation poisoning.

I've machined stuff from beryllium copper alloy before. Despite being 98% copper, it's only about 25% as electrically conductive as pure copper. Kind of a letdown, really.

goatman said:

how about 2 little magnets opposing each other

Click to expand...

I worked with magnets before, and I would not recommend it. In a relatively stable environment, you can use magnets to clamp a copper foil on top of cells - plenty of examples in this forum. Now once you try to serially join cells its a different story. It's actually the only pack I had balancing issues with, because the contacts between cells where not reliable. A big issue also is how brittle magnets are: a few tougher shocks and they easily split in half, with tiny particle suddenly roaming the place and causing all kinds of problems. And finally assembly / disassembly is super tricky. Those things are strong and keep attracting each other. Couple it with loaded cells and you'll have guaranteed fireworks. At least that was my experience - hence the search for something softer, like springs.

Thanks for pointing out the beryllium toxicity; brass was my favorite anyway. Good enough conductivity and corrosion resistance, plus easy to work and strong enough to survive reasonable abuse.

qwerkus said:

Thanks for pointing out the beryllium toxicity; brass was my favorite anyway. Good enough conductivity and corrosion resistance, plus easy to work and strong enough to survive reasonable abuse.

Click to expand...

Beryllium toxicity is mainly an inhalation hazard, and it's difficult to get inhalation exposure from beryllium copper alloy. If it's the right material for what you're doing, you should consider using it. However, between being expensive, not easy to work, and not especially conductive, it's probably not the right material for your idea.

Has anyone ever used those little metal tactile domes they put on PCBs to make buttons? You can get fairly large ones i recall with about 2mm travel. Put them between the cells?

Tbh, this not welded or soldered contact thing scares me. If you lose contact under load, surely you're going to instantly punch holes through your cell casing and then... Bang.

I'm interested to know how you envision stacking the cells. I have had similar thoughts to yours, but built nothing, I have envisioned cells stacked like in a flashlight, in a thin-walled tube--preferably plastic, but metal like electrical conduit or copper plumbing pipe could be used with proper precautions. Any number of cells could be stacked end-to-end with a single spring at one end just like a flashlight, the spring not intended as a conductor. No springs between batteries. Parallel connections could use a small copper tab between each two cells, soldered to a small wire, with only the tab separating the cells. The wires could exit the tube through a small hole drilled at the point of each battery junction, or possibly run within the tube, diameter permitting, with suitable insulation precautions.

Usinng springs as conductors has a bunch of problems.

Is any of this relevant to your concept?