Review of Capacity and Terminal Temperature - cells from Shenzhen Luyuan (Amy Wan)

RGIvy

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Hi folks

I thought I'd share the results of our first two tests of cells purchased from Shenzhen Luyuan (Amy Wan).

We wanted to know three things:
  1. What are the individual cell capacities and how evenly matched are they.
  2. What is the capacity for a a reasonably high-C - in our case this would be around 160A so around 0.6C
  3. What temperature do the terminals go to. These are the new welded-stud terminals with worryingly small surface contact area.
We have found in the past that anything up to around 120A is fairly forgiving - terminals not tightened correctly tend to not heat up that much. Above 150A and it's a very different story. Approaching 200A and your margin for error is fast disappearing.

The cells are 280ah, and we tested four of them.
We asked Amy for the official torque and were told 10nm.
We used the bus bars she provided, which are 19.8mm x 1.9mm = 37.62mmsq. We would have been keen to double them up but she only provided four bars so went with single. We wanted to know if the terminal was up to the task, not the bus bars. So I guess we got to test both.
Ambient temperature of the room was 21°C. We'd normally test with the cells in a temperature-controlled cabinet at 25°C but we wanted to make it easy to observe temperature.

3FFC9F09-B3C1-4662-8C14-E0944CE1AD37-61338-00000C2BFAD2FB33.JPG
We top-balanced the cells and then did tests of individual cells at 15A. We used decent cables fastened well to prevent too much voltage loss.
Screenshot 2021-05-07 at 15.26.35.png

All four cells came out at between 289ah and 290ah. All exceeded capacity by about 10ah. Well pleased.

Connected the BMS and charged at 20A, within the knees the delta was very low - about 0.001v, again we're pleased with the results. Set the BMS to HV 3.65v and LV 2.5v.

Once fully charged we let the battery rest for about two hours and then connected a 2kw Giandel that had a 1.7kw heater attached. This drew about 160A for most of the test.
We used two shunts to measure amps and ah just out of curiosity to compare a non-cheap Victron smart shunt (£120-ish) vs an inexpensive Juntek shunt (£30-ish). Because we were drawing high currents there was a reasonably high voltage difference between the two shunts (12.54 closest to the battery vs 12.42 furthest from the battery at some stage), but amps were within 1% of each other and very similar to the BMS reported amps. Due to the voltage difference there was a reasonable difference in kwh.

The capacity got to 281ah before the BMS prevented further discharge. Again, happy with the results.
The test ran for about 01:49:00

Now for the terminal (and cable) temperature.
IMG_2634.jpeg
IMG_2631.jpeg
We had four temperature sensors in an ambient temperature of 21°C:
  1. On the negative terminal. This got to a maximum of 38.1°C towards the end, it got to around 28°C quite early in the test and slowly worked it's way up.
  2. On the positive terminal. This got to a maximum of 38.8°C towards the end, it was always a few °C warmer than the negative terminal except towards the end when they became very similar.
  3. On other terminals and on the bus bars. We moved this around a bit. The temp was always a couple of degrees cooler than the main terminals. The middle of the bus bar was nearly a degree warmer than the terminals it was bolted to.
  4. On the positive cable, 35mm assembled by ourselves. This started out as several °C warmer than the terminals but eventually they all came to about the same temperature. We didn't officially measure the negative cable (came with the inverter) but it was definitely warmer than the positive. At it's hottest the positive cable was just under 40°C
Prior to the test we were concerned about terminal surface area. After the test we're not at all concerned. The 5-6nm extra toque more than compensates for the reduced surface area. We've had other cells terminals heat up to much higher temperatures.

Not many people need to draw anything like 160A. In our own vehicle the most we usually draw is around 90A for our Nespresso coffee maker.

Coming next ... we'll do a low-C test which we hope will hit 290ah. We're thinking around 20A for the test.

On another note we're well pleased with our Giandel 2kw 24v inverter. It's around 88% efficient which isn't at all bad.
 

SoundinSpirit

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Very well written overview and testing! Thank you... I have 32 of these cells coming- someday... Lol. Been two months already. Thankfully, not in a rush at all.
 

HRTKD

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No way I would be putting 10Nm of torque on regular terminal threads. That can't be right at all. But you've got welded on studs, so that's a different matter. Still, the EVE spec says the terminal itself should not see more than 8Nm. But that's rotational force. If you're not rotating the terminal with all that force then maybe it's OK.

Is the entire perimeter of the stud surface welded? I tried to zoom in on your picture, but it lost resolution.
 

Gazoo

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Hi. Thanks for the review many of us have been waiting for... :) Interesting how much torque is recommended on those studs. In one of the spec sheets EVE says no more than 8nm torsion on the terminals. I am not so sure applying 10nm torque vs 5nm torque is going to make a huge difference? I honestly don't know. 4nm torque is equal to 700 pounds of clamp force.

The concern was not only the surface area of the pedestal, but the contact area of the weld, and the contact area between the bottom of the mount and the cells terminal since there is no torque to speak of applied to that area when the mount is welded to the terminal. Thanks to your testing, this does not seem to be concerning.
 

RGIvy

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Is the entire perimeter of the stud surface welded? I tried to zoom in on your picture, but it lost resolution.
If by that you mean is it welded all the way round then yes. Seems pretty strong. I went with 10nm and it was fine.
 

guerby

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Thanks for this detailed test!

What charger and discharger model did you use?
 

Leon

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Very glad to see some actual testing of the welded terminals. Thanks very much for sharing your results.
 

RGIvy

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Thanks for this detailed test!

What charger and discharger model did you use?
We have a few chargers but use this on a fully assembled battery:

We use this or the Victron smart shunt to measure discharge for high-C rates:
 

RGIvy

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Confirm those are m6-1 threads?
Yes

Any kind of surface preparation?
No, and deliberately so. Normally we'd prepare copper busbars with a flat diamond sharpening pad. These are tinned copper bars, and we wanted to see how they would do out the box. Bear in mind the very small contact surface area .... not much point in levelling the whole of the busbar.

Does the contact surface with welded-on studs seem identical to the cell terminals themselves?
Not sure I understand the question. A "traditional" terminal has a big surface but you use a very low torque. These new terminals have a much smaller surface are by comparison.
 

Hedges

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Not sure I understand the question. A "traditional" terminal has a big surface but you use a very low torque. These new terminals have a much smaller surface are by comparison.

<Does the contact surface with welded-on studs seem identical to the cell terminals themselves?>

When busbar is clamped using welded-on stud, is contact surface provided by stud bare aluminum just like the tapped terminals people were using?
In which case, I would expect same issue with native oxide. Possibly, higher pressure breaks through that.
 

RGIvy

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<Does the contact surface with welded-on studs seem identical to the cell terminals themselves?>

When busbar is clamped using welded-on stud, is contact surface provided by stud bare aluminum just like the tapped terminals people were using?
In which case, I would expect same issue with native oxide. Possibly, higher pressure breaks through that.
I believe the contact surface is a much harder/tougher metal, certainly not the butter-soft aluminium. Not sure what it is exactly.
 

Bob B

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Great information and testing @RGIvy ..... I'll be seriously considering this on my next set to get away from those soft threads.
 

Hedges

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The higher torque capability is a big improvement.
I'd want to know if the contact surface is still non-conductive Al2O3/AL(OH)3 and needs special treatment, or if it is a conductive material.
Ideally these weld-on studs would have a tin plated or similar surface.
 

MattiFin

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Dec 31, 2020
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Hi. Thanks for the review many of us have been waiting for... :) Interesting how much torque is recommended on those studs. In one of the spec sheets EVE says no more than 8nm torsion on the terminals. I am not so sure applying 10nm torque vs 5nm torque is going to make a huge difference? I honestly don't know. 4nm torque is equal to 700 pounds of clamp force.

The concern was not only the surface area of the pedestal, but the contact area of the weld, and the contact area between the bottom of the mount and the cells terminal since there is no torque to speak of applied to that area when the mount is welded to the terminal. Thanks to your testing, this does not seem to be concerning.
Smaller surface area could be also good thing. There is probably a sweet spot of force per area or pressure. You want to flatten the minuscule ”mountains” on the contact surface, othervise the actual contact area is only tiny fraction of the joint area. This also helps to create air tight joint that prevents further oxidation.
IIRC there is a industry standard recommendation for the joint pressure and ”chinese m6 screw terminal” is like 1/10th of that.
(really flat and smooth surfaces stuck together by itself like gauge blocks ”wringing”)
 

mike95490

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bare aluminum oxidizes in seconds into Aluminum Oxide. That is used in sandpaper and is very tough. The anti-ox compounds both seal air from the aluminum and helps displace the oxide. It also has a mild anti-size effect so you can unbolt the connection years later without frozen threads.
 

RGIvy

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Low-C test (at 30A) yielded 287AH so all-in-all we're pleased with the cells and would recommend them and Amy.

I didn't give you any details on the transaction itself - suffice to say that nothing unusual to report. Our biggest frustration was the lack of shipping info, but this is not Amy's fault (it's the way it is). It would be really great to be able to do all the tracking ourselves.

I found out too late that if I had used the DIYSolar code she would've included double busbars. Pity .... seeing as we've already ordered and paid for another 100 cells.

I have asked Amy for more info regarding these welded terminals. She mentioned that the new contact surface area is stainless steel. She's getting more info. I guess we'd all like to know a bit more ....
 
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