Cell Terminal Strain Relief, bus bars, and compression

ohthetrees

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The issue is never the correctly done crimp!

The issue is the cable jacket! The jacket is sealed to the lug - heatshrink tube with self melting glue inside is typical - will always fail. In your picture where the cable is subject to a tight bend radius they will fail faster.

If you go with tinned copper this is not a big deal for "dry land" applications; the cables can live for many years without issues. For bare copper it will oxidize starting at the cable ends just past the nice crimps and moving inwards. Eventually the strands break, resistance goes up, and the cycle accelerates until you have a failure.

The issue is on a boat even the best tinned copper cables do not last long once salt water gets under the jacket. It then quickly corrodes the fine strand wiring causing high resistance and eventually failure. Once it starts under the jacket it is impossible to stop - replacing the cable is the only option.

I've seen all sorts of things used to prevent this and about the best is Permatex liquid electric tape in which you mask off the lug contact areas and then dip the entire end into the material to about 1.5 inches up the cable and then let it hang dry. Depending on cable size it might need several dip, dry, dips to get the desired thickness. This will last a good many years. But it is a slow and labor intensive process to do correctly.
Excellent point about a weakness of the wire interconnect approach. I will try to mitigate it by using top quality wire, and dipping the ends as you described. Lucky for me I have a pretty modern boat, with a dry bilge, and my battery box area tends to say quite clean and dry. I’ll also run my system under max rated load once a year and look for heat in connections.
 

Bob B

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How do you make ends? Tinned? Properly crimped? I'd love to make some but couldn't sort a good process in head.
I haven't done mine yet .... I have the braid, but don't yet have the copper are the electroplating stuff. I do have a 20 ton press in my shop.

Best thing is to search @upnorthandpersonal 's posts .... search for bus bar and posts by him.

edit .... HMMM the link didn't work right for some reason .... maybe best to just search for anything upnorthandpersonal has to say about bus bars.

 
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upnorthandpersonal

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The important bits are to use annealed copper pipe and a proper hydraulic press - you want 12 tons or more (metric), but it's possible with less (but definitely not cold welded in that case). To make them, use a (in my case) 18mm outer, 16mm inner diameter pipe, cut off 25mm (remove burrs, flange slightly out if possible so the edge doesn't cut the braid). Then compress this up to the point where you can slide the 25mm braid into the now squeezed pipe for the entire length of the piece. Compress fully after that.
I used a simple Nickel plating method (using nickel acetate) which just needs vinegar, salt, a power supply and some pieces of Nickel. There should be a few tutorials online for this.
 

Bob B

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The important bits are to use annealed copper pipe and a proper hydraulic press - you want 12 tons or more (metric), but it's possible with less (but definitely not cold welded in that case). To make them, use a (in my case) 18mm outer, 16mm inner diameter pipe, cut off 25mm (remove burrs, flange slightly out if possible so the edge doesn't cut the braid). Then compress this up to the point where you can slide the 25mm braid into the now squeezed pipe for the entire length of the piece. Compress fully after that.
I used a simple Nickel plating method (using nickel acetate) which just needs vinegar, salt, a power supply and some pieces of Nickel. There should be a few tutorials online for this.
For the copper pipe, is this the type of pipe used for refrigeration projects? Have you ever bought regular copper pipe and annealed it yourself?

I went to my local Lowes and asked them where the annealed copper pipe was and they looked at me like I was from another planet LOL
 
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upnorthandpersonal

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For the copper pipe, is this the type of pipe used for refrigeration projects? Have you ever bought regular copper pipe and annealed it yourself?

Yes, it's the soft one, usually sold on a roll instead of straight pieces. I have done copper annealing before, but when I can find annealed copper off the shelf I use that to save time.
 

Bob B

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Thanks .... I searched at refrigeration supply sites and found the annealed stuff .... so, good chance the local refrigeration supply places may have it.
 
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WalterM

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I'm sure everyone is tired of talking about cell compression. I know I'm tired of reading about it (I've read many posts on many threads about it).

What I'm hoping to discuss in this thread is compression and bus bars, but only as it relates to the integrity of the terminals. I have 16 EVE 280ah from Amy on the way, and I'm coming up with my pack design, which will be a 4P4S design. My original plan was to build a threaded rod box with aluminum end plates, snug them lightly at 50% SOC, and use the bus-bars supplied by Amy (2mm x 20mm). However, all this reading about compression has got me worried about the strain on the terminals when the cells expand and contract.

What I'm asking for is 1st hand experience or informed opinions on whether the fixturing discussed above would mitigate strain on terminals with solid bus bars. Since I'm building the pack for a boat, and I'm already slightly nervous about the physical durability of these big 280ah cells, my first priority is reducing any physical strain on the cells. Improved cycle life is far down the list.

I just don't have a sense of how much force the terminals would experience (Usually charging less than 0.2C and discharging less than 0.3C) with such a setup.

At this point, I'm getting so concerned about terminal strain that I'm leaning toward interconnecting with curved pieces of wire and lugs, maybe 1/0 or 2/0. Alternatively, I'm also thinking of putting spacers between each cell (corners and edges) and letting the middles of the cells "breath" even though I'd give up cycle life, maybe this would reduce strain and I could keep the rigid bus bars.
I read through these replies and I didn't see any mention of placing your batteries on a rubber mat for shock mounting. CALB recommends it in their installation instructions. Be safe with any up and down movements.
 

ohthetrees

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I read through these replies and I didn't see any mention of placing your batteries on a rubber mat for shock mounting. CALB recommends it in their installation instructions. Be safe with any up and down movements.
Thanks, and good point. Does anyone have a favorite material to recommend?
 

chrisski

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I used a simple Nickel plating method (using nickel acetate) which just needs vinegar, salt, a power supply and some pieces of Nickel. There should be a few tutorials online for this.
I found electroplating with vinegar to be much easier than I thought it would be. I’ve done zinc plating and am mixing a copper solution with vinegar, salt and left over busbar copper. I’ve got the power supply set at 15 volts and ,25 amps. WIthin a couple hours, the solution was a dark blue. I’ll let this go overnight. Tomorrow, I will make a batch of the nickel acetate you mentioned.
 
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shadowsteve

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Thanks, and good point. Does anyone have a favorite material to recommend?
If it's just for shock mounting you can find used yoga mats cheap. I've used the stuff in other applications where I need padding but I don't know how suitable it is for battery usage although I checked and ~15psi compresses it about 25% using my clamp and bathroom scale method
 

Steve_S

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What to use as a Liner got stuffed in the thread below.
"The "PROPER" Material for such an application is Epoxied Fiberglass Sheets, specifically, FR-4 thermosetting industrial laminate. This is readily available on Amazon/EBay/AliBaba/AliExpress and virtually every Electronic Components store."

 
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shadowsteve

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What to use as a Liner got stuffed in the thread below.
"The "PROPER" Material for such an application is Epoxied Fiberglass Sheets, specifically, FR-4 thermosetting industrial laminate. This is readily available on Amazon/EBay/AliBaba/AliExpress and virtually every Electronic Components store."

Won't be any shock/vibration absorption in that for a mobile application.
 

chrisski

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Won't be any shock/vibration absorption in that for a mobile application.
Suggestions?

After looking at the FR4 Steve suggested, seems to be the same material Circuit boards Are made of. If you need a lot it, like a sheet 3’ X 4’, it only costs $36, but shipping is $140, and definitely not available locally. I found some on E-Bay from china in a 8” X 8” sheets, which should cover two or three eve batteries once cut up From EBay shipped from China for $8.

Someone else suggested Poron, which is soft and would provide some shock absorption. It’s supposed to be heat resistant to 110C and $8 on Ebay for a 18” X 42” sheet.

I’m open to options. My small 25 ah milk crate battery will be 1mm neoprene, but I’m open to suggestions for a mobile application. I’m about six weeks away from my Eve cells showing up, and this “Spacing” material is getting me to think.
 

Steve_S

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I've bought FR4 at my local electronics supply house and it is pretty cheap for .5mm
It also the same thing commercial pre-built packs use, as can be seen on Will's teardowns as well.
It is simply the protective break for between cells and the cell casing and whatever box/frame etc you put the cells into. People are scurying looking for "what" to put between & around their cells, well, might as well use the right material for the job.
Shock/Vibration management is another separate matter.
 

chrisski

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I've bought FR4 at my local electronics supply house and it is pretty cheap for .5mm
It also the same thing commercial pre-built packs use, as can be seen on Will's teardowns as well.
It is simply the protective break for between cells and the cell casing and whatever box/frame etc you put the cells into. People are scurying looking for "what" to put between & around their cells, well, might as well use the right material for the job.
Shock/Vibration management is another separate matter.
I do have an electronics supply house. Fry's Electronics. Same as the supermarket chain, but they own a few stores. I'm sure there's more locally.

Thanks for the tip.
 

Steve_S

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people that play with Arduino, Raspberry Pi and board level goodies that go with it, often have such material in stock. It isn't that uncommon but not something the everyday average person would know about, let alone what it's called and what to look for.
 

shadowsteve

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Suggestions?
I suggested yoga matt material above. I'm building two 4s 12v packs for my trailer and they'll be in plywood boxes for compression and mounting. I have a mat I've been cutting up for other purposes so may use some of that under the cells. I'm not concerned about any fire rating or anything as the whole RV is made of flammable material (FR4 burns too). My 4 AGMs were tightly mounted in a plywood frame with plywood spacer and strapped down. After 30,000mi of travel the outside of the cases look like I took a palm sander to them so I know everything moves
 

chrisski

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I suggested yoga matt material above. I'm building two 4s 12v packs for my trailer and they'll be in plywood boxes for compression and mounting.
I think if I use yoga mat material, or something thicker than .5mm, I will be cutting about $40 of copper to make busbars. Something that thick probably won't fit with the busbars I have included with my shipment. .5mm may not even fit.

I'm not opposed to making more busbars. Just want to be sure that's the best. Does worry me what is under the shrink wrap on the cell and how that will hold up miles and miles of travel.
 

shadowsteve

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I think if I use yoga mat material, or something thicker than .5mm, I will be cutting about $40 of copper to make busbars. Something that thick probably won't fit with the busbars I have included with my shipment. .5mm may not even fit.

I'm not opposed to making more busbars. Just want to be sure that's the best. Does worry me what is under the shrink wrap on the cell and how that will hold up miles and miles of travel.
The initial question I was responding to was something to place the batteries on to isolate some of the vibration from travel so it doesn't reach the batteries as much. I wasn't thinking about space the individual cells with the mat material. I haven't decided yet if I'll find something thin to put between the batteries that still permits the use of the supplied bus bars for interconnect or whether I'll use built cables for that purpose.
 
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