Concerned about New EVE 3.2V 280Ah LiFePo4 Cell Manufacturing Design Change

[JimStLaurent]

First off, I've been lurking here on the forum since mid March, reading learning a lot from everyone that contributes . For this I'm very grateful and thank you!


Now my concerns, I recently receive a set of 4 Grade A 3.2V 280Ah cells from Shenzhen Luyuan Technology Co., LTD via Alibaba.

In an attempt to fix a mechanical problem with the terminal stud posts, they recently opted to weld M6 studs onto the existing terminals. A base was added to the M6 stud that now reduces the battery terminal to lug area interface to about 20% of what is was, best case guess is 25%. This will increase the current density (amps/unit area) and with it goes temperature. My intuitive thoughts are this is bad because of the potential for premature end of life due to increased temps at this sensitive interface area x8. I don't think the threaded post is contributing much to the 150A current dispersion because I believe the SS washer and nut resistance is much higher than aluminum terminal and welded post. But this is me guessing the material composition of these components.

I've raised my concerns with Amy (Alibaba sales support), intermediary to manufacturer engineering. Their response was to be care if drilling out the posts and report back any testing results. I told them I purchased a set of Grade A batteries and they are responsible for all the testing to ensure this manufactering change has no impact the expected cell life cycle.


My goal here is multi-pronged.

Get a discussion doing with the experts on this forum for their collective options on the situation. I'd like feedback on my assumptions of pumping 150A at .5C through an area ~ 1/5th of what is was before this change. This is one of those times I'd really like to be disproved.

If I am correct, to leverage the weight of forum to hold the manufacturer accountable to remedy the problem. This is my first purchase from both Alibaba and EVE, hopefully it’s not my last.

To make others who have recently purchased or about to receive new cells from Shenzhen Luyuan Technology aware of the potential problem. And to see if anyone else with this new manufacturing build has noticed hotter than normal terminal post connections. I've done nothing with mine yet, except mechanical measurements.

Here are some images to support my concerns.

First image - Shows original (old) cell terminal post suface area



Second image - show (new) elevated, reduced area welded stud cells next to aluminum bus bar with elongated mounting slot


Third image - 2D CAD scaled drawing showing contact interface area changes.



thanks in advance,

Jim

 

[bladetoyshop]

I'm not sure I like the looks of that change, to be honest. At least the previous design enabled full contact of the bus bars to the battery terminal.

 

[curiouscarbon]

Watching this thread because I was thinking of buying luyuan 280Ah cells because of the stainless steel laser welded stud. This issue of available terminal cross sectional area being reduced interests me and I hope OP finds a satisfactory solution.

 

[Thorium]

Good thread topic, I got 16 of these cells on order.
I wonder why they added the additional base piece and couldn’t just find a way to add a permanent stud without changing the base contact area.

 

[sparrowhawk]

I think the critical point is how you're going to use the batteries. If you are going to charge & discharge at high c rates on a regular basis then perhaps over time it will cause problems. I choose to have enough batteries configured so that none of the individual cells are paralleled together. I currently have 2-24 volt banks with seperate BMSs paralleled on a bush bar. I plan on adding 2 more 24 volt banks done the same way. That way I spread the load over more cells and taking some of the strain off of them.

 

[Bob B]

I was skeptical about the welded studs and the reduced surface area when I saw them also .... but, so far the reports I have seen have been positive.
It seems that the ability to torque to a higher pressure may overcome the reduced contract surface.

I think Michael Caro is also experimenting with a washer of the correct thickness to increase the surface area ....I was skeptical about this approach also, but it has received some good reviews.

 

[Steve_S]

I have both with Welded studs and just normally taped M6 holes, I have pulled 200A hard & nasty as well as pushed 140A Charge during the Thrash Testing I ran, there was no significant temp differences to note, no weird issues or unusual reading by the cell monitoring.

A welded contact with a solid base like this will carry the current without issues due to the Bond unlike just a mechanical contact only. Technically the "pad" is to carry the current to the busbar but with welded posts the actual post is also carrying that full current to the busbar.

Others have done hard tests and thermal test monitoring and no one has noted issues. The only exception would be if there was a Bad Weld and that would be pretty obvious.

Sadly, in 2021 there is a major propensity to go all Chicken Little "The Sky is Falling" mode on minutia. There is absolutely no need to make mountains out of mole hills, there are actual REAL Things to be far more concerned over. IF anyone thought that 100's of us would buy these cells with welded posts and not report any issues, you'd have to be barking mad.

 

[JimStLaurent]

Some great testing done by RGIvy can be found at the link below. Thank You, RGIvy!
https://diysolarforum.com/threads/r...ure-cells-from-shenzhen-luyuan-amy-wan.22371/
Executive Summary : 4S configuration test at 160A, highest terminal temp measured just under 40C from with Tambient =21C,
Much higher torque spec of 10Nm, the standard aluminum bus bar is a descent heat sink.

Steve_S, I pleased to hear your reporting good results. And I'm happry to report my Angst meter is back in the comfort zone!

I'll work on improving on the aluminum bus bar with the elongated slots. Thinking of using a much heavy braided copper bus bar. To reduce the slot area, I'll try a silver solder fill with hi temp kapton tape on the underside to contain the re-flow, followed by polishing the bottom and re-drill the M6 mounting hole. This will improve the current density area issue by 2x. And the larger copper thermal mass will dissipate more heat.

Jim