Cell Terminal Strain Relief, bus bars, and compression

Colonel.lp

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Interesting thread. A couple of observations though...
1) No one has mentioned the use of Lock Washers on the busbars - I use & recommend Serrated Washers as they are superior to split washers and keep an even balanced pressure.

2) Properly Binding & Securing your cell blocks is essential it is the correct method to use with the cells. Please Follow the cell Specification Data sheet information. Different brands & casing types have varying requirements.

3) I should point out that if people look at properly assembled commercial battery packs, quite often the busbars are welded to the cell pads and that those same cell packs are properly bound and blocked. Not only is that shown in some of Will's teardown but others as well. Not talking about the cheaper Chinese pre-builts (even some of them are starting doing it now) but the Higher end stuff.

A thought on Cable/busbars, that is 2 lugs (2 crimps) per, 2 possible points of issue, resistance etc.
Lithium Based Batteries are Not "Brute Force" like Lead, remember they ARE MILLIVOLT Sensitive and that goes for their sensitivity to Resistance !
REMEMBER why everyone is so picky about Matched Cells and Equal Resistances ! KISS Rules are always Best ! Time Tested & True. Do consider consequences and the potentials, sometimes a Good Solution may not actually be because of the side-effects.

4) Flexible Busbars are a good idea IF properly made from the correct materials, relative to application & environment. In a Marine Environment, Tinned Pure Copper mesh & lug-ends with Insulation is the way to go. See below. You can buy tinned mesh, sleeving as well and DIY them. Same with untinned, BUT you have to be confident that the connections/compression is "perfect". A Solid busbar has no weaknesses. It's easy to say and not hard to do but it is not easy to Make Properly, look closely at the commercially made ones & you'll see. (errant copper strands wreak havoc)

View attachment 61879
View attachment 61880
These are identical flexbars from Erico
REF: https://www.erico.com/category.asp?category=R2918

These & Others available at:


Hope it helps, Good Luck
Steve
Very good points.

Re the cable lugs, considering the reliability of the cold weld in a properly crimped good quality lug and cable in a dry environment, I really don't see it as a problem unless you are working with huge amps. Every system has its issues and weighing it up solid busbars had more potential issues than cable and lugs, despite the fact I'd prefer to use them. I will be monitoring the cells and if I see discrepancies I will be checking the cables, but at my normal draw of 5 to 10amps, 20amps solar charge in my camper, and occasional 80amp hookup charge, I'm not expecting problems.
 

tim0shel

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I had big thick bus bars on mine and had the same thinking as you so I just went with 1/0 wire that can be more flexible. AlthoughIMG_20200711_144619.jpgIMG_20210822_174842.jpg I have mine in an aluminum tray very snug I have yet done the pallet straps around the center. This was going to be my solution to compression.
 

Colonel.lp

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Looks good. I really like that aluminium box.

For anyone questioning cable lugs, which are deemed as gas tight:

As a gas-tight connection is one where the conductors and connectors are so tightly deformed and compressed together that there are no cavities between them. Neither a liquid or a gas-type medium can permeate the crimp in normal atmospheric conditions.

Oxidation between the compressed individual wires is suppressed and any increase in the crimp transition resistance is almost impossible.

In the limit case it is possible that isolated cavities will still occur. As a result of the fact that the cable is twisted, however, these cavities may be regarded as self-sealed. A dense crimp can be tested using a section. The section level is ideally in the middle third of the conductor crimp sleeve and between the compressed grooves


And out of interest I just cut one open.


16300683095191006534864648529912.jpg
 

Steve_S

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Very good points.

Re the cable lugs, considering the reliability of the cold weld in a properly crimped good quality lug and cable in a dry environment, I really don't see it as a problem unless you are working with huge amps. Every system has its issues and weighing it up solid busbars had more potential issues than cable and lugs, despite the fact I'd prefer to use them. I will be monitoring the cells and if I see discrepancies I will be checking the cables, but at my normal draw of 5 to 10amps, 20amps solar charge in my camper, and occasional 80amp hookup charge, I'm not expecting problems.
Properly / Correctly done compression as described works well and has done so for over a century.. tried & true proven method. The average DIY non battery builder type encountered here on average won't have access to the crimping equipment to do to (hammer crimpers don't cut it, ever).

I've seen Submarine Lead Banks (yep Navy Sub) now there is serious wiring & gas/vapour protection to an extreme. Batteries made by "Rolls Surette" no less. hehehe.
 

Colonel.lp

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Properly / Correctly done compression as described works well and has done so for over a century.. tried & true proven method. The average DIY non battery builder type encountered here on average won't have access to the crimping equipment to do to (hammer crimpers don't cut it, ever).

I've seen Submarine Lead Banks (yep Navy Sub) now there is serious wiring & gas/vapour protection to an extreme. Batteries made by "Rolls Surette" no less. hehehe.
True, but judging by the comments by most folk on here, they research things to excess, me included.😝

A decent 10tonne crimp can be had for under £30 these days.

I bet those cables were impressive, and expensive. 😁
 

tim0shel

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Looks good. I really like that aluminium box.

For anyone questioning cable lugs, which are deemed as gas tight:

As a gas-tight connection is one where the conductors and connectors are so tightly deformed and compressed together that there are no cavities between them. Neither a liquid or a gas-type medium can permeate the crimp in normal atmospheric conditions.

Oxidation between the compressed individual wires is suppressed and any increase in the crimp transition resistance is almost impossible.

In the limit case it is possible that isolated cavities will still occur. As a result of the fact that the cable is twisted, however, these cavities may be regarded as self-sealed. A dense crimp can be tested using a section. The section level is ideally in the middle third of the conductor crimp sleeve and between the compressed grooves


And out of interest I just cut one open.


View attachment 61886
Appreciated sir and Thanks for the share and knowledge you added. I have been making sure mine is tight as I use the hydraulic crimper.
 

Bob B

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I may have a spark of inspiration and make braided busbars at some point, but Im not sure I can make them to the spec I'd like, the biggest problem being I'd like them tinned if they are going up against aluminium, and the only way I can see that working without making a soldered mess would be to have a solder pot.
Tinned copper ground braid is readily available ..... I've got some, but have forgotten where I got it.

Here is a quick Amazon search just for reference. https://www.amazon.com/s?k=tinned+c...+copper+gr,aps,218&ref=nb_sb_ss_ts-doa-p_1_16
 

Gazoo

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I am attaching an image of another way to build a pack if using cables or braided busbars for the interconnects. I forgot who posted it initially but credit goes to him.
 

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Steve_S

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I am attaching an image of another way to build a pack if using cables or braided busbars for the interconnects. I forgot who posted it initially but credit goes to him.
That is the proper example of doing so, the main reason to avoid large loops or tight bends - preventing strain.
 

ohthetrees

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I am attaching an image of another way to build a pack if using cables or braided busbars for the interconnects. I forgot who posted it initially but credit goes to him.
I'm struggling to understand this layout. Is it a..... 8S pack? I love the over-arching concept, but can't see how it would apply to a 4P4S
 

Gazoo

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I'm struggling to understand this layout. Is it a..... 8S pack? I love the over-arching concept, but can't see how it would apply to a 4P4S
Yes it is an 8S pack. Since the thread title is about terminal strain relief I thought I would post it for those interested in configuring their cells that way. It can also apply to a 4S pack.

I don't know if it's a good idea to put more than two cells in parallel. Many people make 4S packs and each pack has it's own BMS. This ensures the cells in series remain balanced and offers redundancy in case a cell or BMS fails. If buying binned capacity matched cells, balancing might not be as much of a concern in large all in one parallel packs. Personally I would feel more comfortable monitoring each cell.
 

shadowsteve

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I am attaching an image of another way to build a pack if using cables or braided busbars for the interconnects. I forgot who posted it initially but credit goes to him.
That would be a better layout if using heavy cable for the cell interconnects. My AGMs are done with 1/0 cable and that stuff is hard to bend into a U shape and would have an outward pressure on the legs which it supposed to avoid in comparison to the bus bars.
 

ohthetrees

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Yes it is an 8S pack. Since the thread title is about terminal strain relief I thought I would post it for those interested in configuring their cells that way. It can also apply to a 4S pack.

I don't know if it's a good idea to put more than two cells in parallel. Many people make 4S packs and each pack has it's own BMS. This ensures the cells in series remain balanced and offers redundancy in case a cell or BMS fails. If buying binned capacity matched cells, balancing might not be as much of a concern in large all in one parallel packs. Personally I would feel more comfortable monitoring each cell.
Thank you for your thought, but I'm very comfortable with the 4 parallel cells. I've thought over the pros and cons pretty thoroughly.
 

ohthetrees

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I had big thick bus bars on mine and had the same thinking as you so I just went with 1/0 wire that can be more flexible.
Nice. How was it to work with the 1/0 wire? I want the largest interconnects possible, but wire that is too thick can be so stiff that it might defeat the purpose, and will definitely be a pain to work with.
 

ohthetrees

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So after taking in all the helpful comments in this thread, I think I'll be spring clamping the cells, and using wire and lugs. I've attached a diagram of what I'm intending to do. All the small amperage numbers on it are my guesses about how much amperage will flow through each connection when pulling 100 amps, which came out of the good discussion on my other thread: https://diysolarforum.com/threads/calculate-amps-through-each-bus-bar.27440/
Screen Shot 2021-08-27 at 11.28.15 PM.png
 

time2roll

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So after taking in all the helpful comments in this thread, I think I'll be spring clamping the cells, and using wire and lugs. I've attached a diagram of what I'm intending to do. All the small amperage numbers on it are my guesses about how much amperage will flow through each connection when pulling 100 amps, which came out of the good discussion on my other thread: https://diysolarforum.com/threads/calculate-amps-through-each-bus-bar.27440/
View attachment 62006
OK so if you want to take this to a higher level you will need to calculate the resistance for each bar and connection. The connection path of least resistance will sustain higher current. Note in this diagram the lower four cells of each parallel set will have the shortest path with fewest connections and resistance and in theory will be worked a bit harder.
 

Marinepower

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This is an interesting thread. I would love to hear from other's experience who have EVE 280 cells (or other 6mm tapped AL cells, i.e. Lishen,) in mobile applications.

For those who using these or comparable cells in mobile applications , with locking nuts (serrated, double nuts, Nylock, Nordlock, etc) torqued at 35-40 inch pounds and compressed cells, what has been your medium / long term experience? Have you had issues with bus bars getting lose and needing attention?

I for one have had not problems with my bus bars but my main negative came lose the other day, tripped my BMS and needed to be re-tourqued. It's on a 1 AWG cable with strain relief.
 

Colonel.lp

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jwelter99

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Looks good. I really like that aluminium box.

For anyone questioning cable lugs, which are deemed as gas tight:

As a gas-tight connection is one where the conductors and connectors are so tightly deformed and compressed together that there are no cavities between them. Neither a liquid or a gas-type medium can permeate the crimp in normal atmospheric conditions.

Oxidation between the compressed individual wires is suppressed and any increase in the crimp transition resistance is almost impossible.

In the limit case it is possible that isolated cavities will still occur. As a result of the fact that the cable is twisted, however, these cavities may be regarded as self-sealed. A dense crimp can be tested using a section. The section level is ideally in the middle third of the conductor crimp sleeve and between the compressed grooves


And out of interest I just cut one open.


View attachment 61886

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.
 
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