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

RGIvy

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Amy has corrected what she told me, the contact surface is aluminium, the stud is stainless. TBH 10nm seems a bit much for stainless, but we had no problems.
 

RGIvy

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This is the one I use. I have others and I've tested them against each other, found them to be very accurate.

tempImageeIqlgr.jpg
 

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Gazoo

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I think it's about time I bought one of those.
I bought one of those from a different manufacturer and returned it. I couldn't hear the click on anything I tried it on. So then I bought a beam torque wrench. I believe it's fairly accurate but it can be a bit difficult to handle. I like the bicycle torque wrenches I have seen but they are only good for torqueing the nuts to the cells.
 

RGIvy

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I believe it's fairly accurate but it can be a bit difficult to handle. I like the bicycle torque wrenches I have seen but they are only good for torqueing the nuts to the cells.
Isn't that why we use a torque wrench anyway? :unsure:
 

Just John

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I can add that the old style cells without the welded studs will rise about 5 degrees Celsius during the last 40 to 50 amp hours of discharge (at a 40 amp discharge rate). This has been very consistent, leading up to that final 40 amp hours, 2 degrees Celsius is the temperature rise. I am measuring the cell body temperature with a cheap temperature gun, and compare it to ambient.
 

Just John

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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 ....
My reading of the latest spec sheet indicates they rate capacity at 0.33C (a little over 92 amps) and de-rates by a small percentage for 0.5C and 1C.

I discovered this when capacity testing the newest Eve 105AH cells, tested half at 34.65 amps, and half at 40 amps. I couldn't see any real difference in capacity.

Yes, use the code, the extra busbars come in handy to top balance.

I'm actually waiting on delivery of a thermal camera to better evaluate if the temperature rise is due to the cell chemical reactions or the resistance of the connections. Even with a thermal camera, it will be difficult to get definitive results.
 

Hedges

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I'm actually waiting on delivery of a thermal camera to better evaluate if the temperature rise is due to the cell chemical reactions or the resistance of the connections. Even with a thermal camera, it will be difficult to get definitive results.

If you can probe cell terminals themselves, voltage drop from cell to cell through contacts and busbar will tell you watts dissipated in the metal. More difficult to decide if heat is flowing into cell or transferring to air (unless convection, emissivity etc. are part of your vocabulary) but it should give a qualitative understanding.

Down to whatever millivolts your DMM reads, unless you have a fancy bench DMM with microvolt sensitivity. We're using op-amps or instrumentation amps to resolve microvolts - in our case to determine ripple. That lets us use scopes with sensitivity a bit better than millivolt. You might be able to use an eval board or breadboard as preamp to get to microvolts.
 

Just John

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If you can probe cell terminals themselves, voltage drop from cell to cell through contacts and busbar will tell you watts dissipated in the metal. More difficult to decide if heat is flowing into cell or transferring to air (unless convection, emissivity etc. are part of your vocabulary) but it should give a qualitative understanding.

Down to whatever millivolts your DMM reads, unless you have a fancy bench DMM with microvolt sensitivity. We're using op-amps or instrumentation amps to resolve microvolts - in our case to determine ripple. That lets us use scopes with sensitivity a bit better than millivolt. You might be able to use an eval board or breadboard as preamp to get to microvolts.
I can use my 4 wire Yaorea meter (I also have a Fluke 87 V). It can measure quite low resistance, the biggest problem is being able to get at the terminal surface with a busbar in place. I do know some of my temperature rise is due to my testing with 40 amps with 10 gauge wire, just started switching to 8 gauge. Using Ancor wire and crimp connectors (Ancor again). Being anal retentive, I had to order the Ancor crimp tool to go above 10 gauge, probably my 10 gauge crimp tool would work, but it would bug me if not perfect. Of course you can also use battery lugs and even heavier gauge wire (or even lugs with 8 gauge wire). Ancor makes some very high quality products, and everything is already tinned.

Like you say, how much is transmitted due to the wire, and how much is from the cell itself is the question, hopefully I can get some more accurate readings soon.

But I don't have any welded studs to test with. I will likely order some soon, my initial objective is to be able to run a 12,000 BTU mini split heat pump from 3:00 PM to 6:00 PM Monday through Friday (SRP charges a lot extra then, it accounts for 50% of my electric bill in the summer).

Eventually I want to be able to run it for at least 8 hours, before having to fire up the generator during any extended power outage.
No solar yet, but already planning on grid tied solar next year. Load shifting is a bonus.
 
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Hedges

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I would like to store cold in an ice chest and duct air for cooling during peak rate times. Freezer with jugs of water and blower is one idea. Possibly ducted air heat exchanger to deal with condensing/icing issue. But freezer compressor running 16 to 18 hours isn't anything like the wattage/BTU of a central A/C running 6 to 8 hours; seems sufficient to replace a window air conditioner but need heavier equipment for whole house. Haven't evaluated whether a 20 cubic foot freezer is enough ice. Could be, as my freezer ran continuous several days to re-freeze contents.
 

Just John

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I would like to store cold in an ice chest and duct air for cooling during peak rate times. Freezer with jugs of water and blower is one idea. Possibly ducted air heat exchanger to deal with condensing/icing issue. But freezer compressor running 16 to 18 hours isn't anything like the wattage/BTU of a central A/C running 6 to 8 hours; seems sufficient to replace a window air conditioner but need heavier equipment for whole house. Haven't evaluated whether a 20 cubic foot freezer is enough ice. Could be, as my freezer ran continuous several days to re-freeze contents.

My objective is to be able to survive an extended power outage without having to check into a hotel. Certainly the 12,000 BTU air conditioner wouldn't cool the entire house (I have a 3 ton SEER 16 unit), but would keep the downstairs cool enough to not force me out. The 8 hour runtime objective is to allow it to last through the night without annoying the neighbors by running the generator. Besides, the mini split is SEER 21, and frequently the downstairs has a 5 degree temperature differential to the upstairs (poor 25 year old ducting sizes).

My 3800 watt dual fuel Champion generator is quite loud, as hurricane Irma when we lived in Florida proved to me. I plan on getting two much smaller and quieter dual fuel inverter generators as well, they could be paralleled if necessary.
 

Hedges

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For that capacity, how about a chest freezer making ice during the day, with its heat dumped to room air which is cooled by A/C. Then at night, blow air through it to cool the downstairs.
 

RCinFLA

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The one thing I dislike about the newer welded posts is the reduced surface area of the terminal shoulder. The shoulder should be the main interface for current flow. Reducing the surface contact area just increases the current density over the contact interface.

Cell internal heating begins to show above about 0.5C current. This cell design has thick LiFePO4 cathode, meaning they have a lot of capacity for given weight and volume, but suffer more from ionic layer starvation at higher currents which gives more terminal voltage drop and lower efficiency at the higher C rate currents.

These cells work best (and last longer) below 0.5C so if you need more current consider adding another bank in parallel.
 
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Hedges

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I wouldn't worry about reduced area because force from bolt is so low, pressure isn't as high as desired with a large area. Reduced area could even be an improvement considering pressure for high points to break through. The actual cross section which carries current is orders of magnitude less than the apparent cross-section; only scattered high points make contact and carry current.

If welded stud allows twice the torque, that is a 2x improvement which outweighs almost any reduction in total area.

The smaller area does mean the contact points aren't distributed over as large an area, so more current crowding.
But how does the remaining cross section compare to ampacity charts for aluminum wire? (even if less that isn't necessary a problem, because it is just a brief pinch point and heat can escape in 3 dimensions.)
 

Just John

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These cells work best (and last longer) below 0.5C so if you need more current consider adding another bank in parallel.

I agree 100% with that. That is also my plan. I don't want power that only lasts for 1 or 2 hours, so additional parallel batteries running at reduced current rates is required. Avoids a lot of problems that way, although then it adds how to best distribute the current draw evenly. Tradeoffs in everything. Certainly surges can be handled better by more parallel batteries as well. But I should desist, we're hijacking this thread.
 

Alkaline

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May I ask what you paid for them? You can message me if you want to keep it private.
 
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