Cell Terminal Strain Relief, bus bars, and compression

[Ampster]

Maybe try Nord-Lock washers?

I have been using Nord-Lock washers on various projects over the past ten years. I am very happy with their performance.

 

[Fpoet]

I have no way to measure.... but they seem as hard or harder than the lug connections on cables. Hope that helps.

Maybe try Nord-Lock washers?

It sure helps, thanks. Sounds good then.

I am already using serrated nuts, and the fact they all remained tight on the large cable lugs points to my braided busbars, which were not made for this purpose. Maybe I could go to a metal shop and have them hydraulically pressed harder, but at this point I am more inclined to try the ones you are using.

 

[Marinepower]

It sure helps, thanks. Sounds good then.

I am already using serrated nuts, and the fact they all remained tight on the large cable lugs points to my braided busbars, which were not made for this purpose. Maybe I could go to a metal shop and have them hydraulically pressed harder, but at this point I am more inclined to try the ones you are using.

Sounds good. I am also using serrated nuts. They seem to work fine for me, but I am on a sail boat so perhaps not as much vibration as a van.

I assume you are using a BMS and there are voltage sense wires on your terminals. I think that stacking ring terminals on top of the busbars reduces the effectiveness of the serrated nuts. Admittedly, this is purely conjecture on my part, with no data to back it up.

So I drilled my busbars and used a separate bolt/nut. Not sure if this is your circumstance....but if so, it might help.

 

[Fpoet]

Sounds good. I am also using serrated nuts. They seem to work fine for me, but I am on a sail boat so perhaps not as much vibration as a van.

I assume you are using a BMS and there are voltage sense wires on your terminals. I think that stacking ring terminals on top of the busbars reduces the effectiveness of the serrated nuts. Admittedly, this is purely conjecture on my part, with no data to back it up.

So I drilled my busbars and used a separate bolt/nut. Not sure if this is your circumstance....but if so, it might help.

Yes, I saw LithiumSolar do this on his packs and thought it was a good idea. I will steal that idea as well.

As an extra step, I might try using a touch of blue loctite in the serrated nuts. I do have a tube in paste form, and I am thinking that if I put the pack on the side when tightening the busbars and let the paste dry, it will not contaminate the contact area.

 

[chrisski]

As an extra step, I might try using a touch of blue loctite in the serrated nuts. I do have a tube in paste form, and I am thinking that if I put the pack on the side when tightening the busbars and let the paste dry, it will not contaminate the contact area.

I opted against the picture on the nuts for my RV build. Really came down to how would I take the nut off for any maintenance or even down the road to add a balancer. I’ve pulled studs out after using picture on the nut on top.

I have the 280 eves with welded studs.

If you do try this, I’d like to hear down the road.

 

[Fpoet]

I opted against the picture on the nuts for my RV build. Really came down to how would I take the nut off for any maintenance or even down the road to add a balancer. I’ve pulled studs out after using picture on the nut on top.

I have the 280 eves with welded studs.

If you do try this, I’d like to hear down the road.

I assume picture is a loctite equivalent?

I have epoxied grub screws in my Eve 280’s and tighten/loosen the busbar nuts with an Allen key in the grub screw and small wrench for the nut. I will do some testing to see if blue loctite is still too strong for the nut to be unscrewed safely.

 

[chrisski]

When you tighten or torque the nuts, do you somewhat come to a hard stop?

Don’t come to a hard stop. For things in inch pounds, I really need to pay attention to when the torque wrench “clicks.” At those light settings, the click is rather soft and easy to miss.

 

[TorC]

Thinking along these lines for the system I'm putting together. Batteries 32 EVE 280Ah as 16s2p. I've done quite a bit of looking at the braid, and generally not happy with the ampacity I find. Of the various braids for a 280Ah cell, the 1⅛" tinned copper from McMaster looks to be the only one I'm comfortable with the ampacity of in a reasonable width.

For the termination, a 3/4" type L copper is only a little smaller inside circumference than this braid (2.466" vs 2.813" braid perimeter). A couple legal plumbing alloys aren't listed for electric/electronic use, but they're still 999+, so for a thin terminal end I doubt this matters. Rather than pipe, soft sheet should be pretty available. Has the advantage in terms of cutting to exact size needed for the braid, but I suppose squeeze-out on the sides may be a problem when pressing.

After a test tonight, however, I might have to think differently. I don't currently have a press, and had hoped I might be able to achieve a similar effect with my jewelry rolling mill. A test with a couple small scraps of copper says no dice. I just end up with two thin pieces, not even pretending to stick together. Back to the drawing board I go.

 

[FilterGuy]

The important bits are to use annealed copper pipe and a proper hydraulic press - you want 12 tons or more (metric)

Reviving an old discussion....

What kind of press do you use for crimping the pipe onto the braid for your flex bus bars?

 

[upnorthandpersonal]

Reviving an old discussion....

What kind of press do you use for crimping the pipe onto the braid for your flex bus bars?

Something like a 10 to 12 ton (metric) press nowadays, something like this:

https://www.amazon.de/-/en/Hydraulic-workshop-press-tonnes-pressing/dp/B01MS6RAY7/

I also used a hydraulic vise in the past, and that works too - but I think a press as the one above is more readily available.

 

[Fpoet]

I assume picture is a loctite equivalent?

I have epoxied grub screws in my Eve 280’s and tighten/loosen the busbar nuts with an Allen key in the grub screw and small wrench for the nut. I will do some testing to see if blue loctite is still too strong for the nut to be unscrewed safely.

I opted against the picture on the nuts for my RV build. Really came down to how would I take the nut off for any maintenance or even down the road to add a balancer. I’ve pulled studs out after using picture on the nut on top.

I have the 280 eves with welded studs.

If you do try this, I’d like to hear down the road.

Well I did go that way, after testing blue loctite in gel form on grub screws (like I have on my cells) and serrated nuts. I feel it is safe to unscrew, especially that I can limit the torque using an Allen key on the grub screw. I am confident that I can easily disassemble the packs if need be.

I actually carefully put blue loctite in gel form on all screws in my packs: cell/busbar connections, BMS sense/active balancer wires (in the same ring terminals on separate connections) and even the BMS B- and C- connections.

While rebuilding the packs, I also replaced my braided busbars with the same flexible Webertech busbars as Marinepower showed above.

So far so good. I put the packs back in the van and I am happy with what I see under load. Time will tell how it works in the long run.

 

[Itohmamma]

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 have 16 Eve 304 cells, I intend to connect each cell consisting of the maximum rating of 300 A, even though 200 amp It’s probably what I will be max. Busbar capacity research as indicated that the bus bars which are provided by the manufacturer will handle only around 100A continuous. Therefore I have chosen 2/0 gauge welding wire, and will be using 3/8 copper rigid pipe to make my own busbars, which I intend to use Limeaway to clean then silver electro plate. I am still investigating either pad spacers for compression or springs, as the subject of determining precise Springs or pads is very confusing. The subject of pressure the subject of psi the subject of the optimum 12psi compression distribution still is not clear to me.
Any thoughts?

 

[HRTKD]

It's been a while since I've read of someone wanting to build bus bars from copper pipe. If these bus bars from pipe are intended to go on your terminals, consider that the bus bars need to be very, very flat to make solid contact with the surface of the terminal.

One forum member went down the road of building bus bars from copper pipe and eventually threw them in the trash. As I recall, they didn't make good contact with the terminal.