Have you checked your cell terminals lately?

[Skypower]

I was shocked(astonished ?) by the looseness of a number of my cell terminal nuts even though I had re-torque them days after the original assembly. Three different 16s batteries but two had similarities and similar issues. None of the batteries had any electrical issues(yet), beautiful balance and performance, I just now simply checked out of a whim and curiosity six months later. The two problematic batteries have cells are the CATL 302 Ah welded terminals type that have the small contact diameter on top. The last battery that’s only been in service a few months is an EVE LF280K double hole post with flexible buss and exhibited very very slight nut loosening and of those it was only the ones with balance eye terminals and the positive and negative Selterm cable lugs. The CATL cell were from two different sources with two different types of welded terminals. One with taller posts and no stud and one with stud. The taller posts allowed me to use a longer grub screw that facilitated the use of a Belleville washer and flat washer beneath it but of course above the conductor. On all batteries the nuts used are flat smooth bottom, not the common serrated concave, balance lead eye terminals are plated hard brass, not soft copper. During assembly the oxides were removed from from both contact surfaces without compromising flatness or plating, “NO-OX ID A special” applied to contact surfaces while avoiding the threads and nuts torqued to 4Nm.
My realizations: #1 Stainless Belleville washers( two different brands) are useless as these were the loosest. These flatten out well before full torque and do not recover in shape after being used especially with time. #2 And most importantly to understand is, copper busses, lugs or jumpers will flow when there is a confined point of contact (small terminal area) and this yielded space must be taken up until it subsides as needed. The metal will flow the most initially. #3 The large mounting surface LF280K with a flexible buss(resistance welded ends) tho the youngest, seemed to be more solid in terms of torque, so far and will factor greatly in any future purchases.

If you haven’t checked lately, perhaps you should. Please report back on your results, experiences and thoughts.

 

[sunshine_eggo]

I was shocked(astonished ?) by the looseness of a number of my cell terminal nuts even though I had re-torque them days after the original assembly. Three different 16s batteries but two had similarities and similar issues. None of the batteries had any electrical issues(yet), beautiful balance and performance, I just now simply checked out of a whim and curiosity six months later. The two problematic batteries have cells are the CATL 302 Ah welded terminals type that have the small contact diameter on top. The last battery that’s only been in service a few months is an EVE LF280K double hole post with flexible buss and exhibited very very slight nut loosening and of those it was only the ones with balance eye terminals and the positive and negative Selterm cable lugs. The CATL cell were from two different sources with two different types of welded terminals. One with taller posts and no stud and one with stud. The taller posts allowed me to use a longer grub screw that facilitated the use of a Belleville washer and flat washer beneath it but of course above the conductor. On all batteries the nuts used are flat smooth bottom, not the common serrated concave, balance lead eye terminals are plated hard brass, not soft copper. During assembly the oxides were removed from from both contact surfaces without compromising flatness or plating, “NO-OX ID A special” applied to contact surfaces while avoiding the threads and nuts torqued to 4Nm.
My realizations: #1 Stainless Belleville washers( two different brands) are useless as these were the loosest. These flatten out well before full torque and do not recover in shape after being used especially with time. #2 And most importantly to understand is, copper busses, lugs or jumpers will flow when there is a confined point of contact (small terminal area) and this yielded space must be taken up until it subsides as needed. The metal flow most initially. #3 The large mounting surface LF280K with a flexible buss(resistance welded ends) tho the youngest, seemed to be more solid in terms of torque, so far and will factor greatly in any future purchases.

If you haven’t checked lately, perhaps you should. Please report back on your results, experiences and thoughts.

Aluminum has a bad habit of "relaxing." Steel has an infinite endurance limit, but Aluminum does not. A certain aluminum alloy was banned from use in SCUBA tanks because of what amounted to zero cycle fatigue, i.e., even though all the calculations said this pressure vessel should be good for X cycles, simply holding gas at pressure without cycling could result in tank rupture.

In other words, under constant stress, Aluminum yields by small amounts over time and re-torquing may be necessary.

 

[Skypower]

Aluminum has a bad habit of "relaxing." Steel has an infinite endurance limit, but Aluminum does not. A certain aluminum alloy was banned from use in SCUBA tanks because of what amounted to zero cycle fatigue, i.e., even though all the calculations said this pressure vessel should be good for X cycles, simply holding gas at pressure without cycling could result in tank rupture.

In other words, under constant stress, Aluminum yields by small amounts over time and re-torquing may be necessary.

Yes you are correct it also could very well be the surface of the aluminum, threads in the aluminum and the head of the stud inside the welded terminal giving some too. A combination of all things.

 

[chrisski]

I prefer dial torque wrenches on the low inch pound torquing.

I have one similar to above I got used from a neighbor.

I found a loose nut on a battery terminal when the cell voltage on the BMS was off. Although no damage was caused, still too late.

 

[740GLE]

I’m also not a fan of huge gauge inter cell connections, just doesn’t seem to be the easiest on the terminals.

 

[Alkaline]

You need to replace those with M6 bolts, those tall screws with nuts never torque down properly.

 

[Skypower]

When you have soft material it’s best to use studs. You can have the most length of thread engagement in the weaker material. I toss the bolts as they are a good way of ripping out threads in the old pre-welded terminals

 

[Skypower]

I’m also not a fan of huge gauge inter cell connections, just doesn’t seem to be the easiest on the terminals.

?

 

[740GLE]

I’m curious if those 2/0 cables are causing undo stress to your terminals. Maybe it’s just the picture but looks like those lugs have some odd angles.

 

[Skypower]

They are crimped in a pre-bent arc so they literally drop on the studs. The arc is to eliminate any tension component in use.

 

[740GLE]

Nice! Must have just been how the picture skewed the view.

 

[rhino]

They are crimped in a pre-bent arc so they literally drop on the studs. The arc is to eliminate any tension component in use. View attachment 163553

What is the gauge of the strands in that cable? Just wonder if the stiffness in that cable that would cause any heating and cooling of the cable to flex slightly and put pressure on the terminals. I found some 2/0 with 36AWG strands for battery will be building and you can't pre-bend it because it acts like rope.

 

[sunshine_eggo]

You need to replace those with M6 bolts, those tall screws with nuts never torque down properly.

There you go again. Spouting silly.

 

[Skypower]

What is the gauge of the strands in that cable? Just wonder if the stiffness in that cable that would cause any heating and cooling of the cable to flex slightly and put pressure on the terminals. I found some 2/0 with 36AWG strands for battery will be building and you can't pre-bend it because it acts like rope.

It’s fine strand and crimping lugs so close does make it stiff. I’m pretty certain that the temperature range that it operates in has little effect on flexing. Because of the shared current of multiple batteries it will never see a continuous high load that could warm it. The stiffness of the cable is not only determined the number of strands but what the jacket is made of. Silicone is the easiest bending then rubber and vinyl is the stiffest(Ancor). Unfortunately 2/0 silicone jacketed cable is excessively expensive so it would probably be more economical for flexibility to use say, four #4 silicone cables into a crimp. I found out that for some reason that multiple conductors should equate a single larger one, it turns out that the multi is a bit better, I did some testing on conductivity on 2/0 cable:

Surprising cable/buss test results

I was watching Madi on Digital Mermaid assemble some flexible buss (jumpers), four #8AWG I believe and noticed how low the resistance readings were. This had me confused because I had bigger a cable and my reading were higher. Could tinned cable make the difference? YES!!!!!! My test...

diysolarforum.com

 

[Alkaline]

There you go again. Spouting silly.

Put me on your ignore list I know what you are trying to do, its not going to work.

 

[sunshine_eggo]

Put me on your ignore list I know what you are trying to do, its not going to work.

LOL. Paranoid much? Just pointing out silly when I see it.

 

[featherlite]

They are crimped in a pre-bent arc so they literally drop on the studs. The arc is to eliminate any tension component in use. View attachment 163553

Those are some very nice looking crimps on those Selterm cable lugs. What kind/brand of crimper did you use?

 

[Brett V]

I’m not a mechanical engineer but I’ve played one. Because of the slight bow in the flexible bus cables, as they expand and contract, there will be a very small rotational force on the studs. The serrated flange nuts grab better in one direction and will have a ratchet effect with each heating and cooling cycle. Solid bus bars won’t have this problem.

 

[740GLE]

LOL. Paranoid much? Just pointing out silly when I see it.

You guys are too cute!!! ?

 

[Skypower]

Well I got lucky with these, but another forum member bought them and was unlucky and got junk. It’s hit and miss with these things. They probably come from the same manufacturer in different brand names, different colors and two different sizes 12 & 16 and I bought both because of a back up and one being a bit smaller and less bulky. This brand does come with a repair kit. My suggestion is, what ever you buy, test it immediately on a tougher challenge. If they fail, 80% of the time it does so very early. Then it’s time to utilize the Amazon guarantee. Regardless of crimper I’ve bought I usually end up modifying the dies to get the perfect crimp by reducing the area marked with an X a little at a time. What I look for on the lug is a semi flattened hex with crisp corners and almost or very little flash at the gap. I file a small radius on the 12 hex corners, not the gap corners.
I also experimented using the same methods with a mix of two dies #6 & #8 for crimping on a #7 cable( JK bms) and a # 6 Selterm lug. The cut away was to see how successful the radius was to not overly thin or compromise the lugs cross section. I didn’t want to crimp into one lug because two separate leads are much more maneuverable. I highly recommend these cable cutters.