diy solar

diy solar

Experience purchasing cells from Shenzhen Basen Technology Co. Ltd.

Tracking says mine are arriving today...
Not sure what to use to implement load testing without installing them in the RV. I don't have a spare inverter to hook up.
I was going to charge them all separately with a bench PS, then connect parallel for a final top charge to 3.65V.
Assemble the pack.
 
Tracking says mine are arriving today...
Not sure what to use to implement load testing without installing them in the RV. I don't have a spare inverter to hook up.
I was going to charge them all separately with a bench PS, then connect parallel for a final top charge to 3.65V.
Assemble the pack.

This is a duplication of effort with no benefit and decreased efficiency. Better to just parallel them and do it in one operation.

Following the top balance guide is an even better option. :)
 
This is a duplication of effort with no benefit and decreased efficiency. Better to just parallel them and do it in one operation.

Following the top balance guide is an even better option. :)

Charging the cells individually will take longer because of the human interaction delay in the loop.
The benefit is, your cells can settle individually which is another indicator of general quality and of how well the cells are matched.
Another benefit is each cell will stay in the high knee for a shorter amount of time as charge current is higher.
Finally individually charging the cells avoids the scenario where one or more cells spend a long time exposed to high knee voltage stress because the started out at a higher state of charge than their peers.
 
I read several how-to's that suggested charging in steps, getting them all to 3.5 or so, then connecting parallel and top balancing at 3.65.
I got one of those user-adjustable bench power supplies, up to 10A. Adjust...THEN connect and start...got it.

Is discharge testing done with individual cells, parallel, or series?
I could hook up a 12v headlight for discharging on the latter, but would still only be like 5A or something. Or pull my inverter out of the coach - a big hassle but do-able I guess.

Don't mean to thread-jack, but seems the same subject - cell prep before pack assembly.
 
Is discharge testing done with individual cells, parallel, or series?
You can capacity test by discharging or charging individual cells or as a battery.
Capacity testing cells in parallel is not particularly informative.
The quickest way to top balance is to assemble the cells into a pack with bms and charge at battery charge voltage until the bms trips.
Then top off the individual cells if required.

The quickest way to capacity test is to discharge the pack through the inverter at a rate representative of your usage model.
The battery capacity is determined by its weakest cell.
 
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Charging the cells individually will take longer because of the human interaction delay in the loop.
The benefit is, your cells can settle individually which is another indicator of general quality and of how well the cells are matched.
Another benefit is each cell will stay in the high knee for a shorter amount of time as charge current is higher.
Finally individually charging the cells avoids the scenario where one or more cells spend a long time exposed to high knee voltage stress because the started out at a higher state of charge than their peers.

IMHO, the time variable renders cell settling variation meaningless unless you're willing to kill additional time.

8 280Ah cells, 14 hours average each to charge @ 10A. Assuming 1 charged every day. Cell 1 has 8 days of settling. Cell 2 has 7 days, etc. What does that tell you? I guess if you're willing to let all the cells sit for another 8 days. Now all cells need to be hit again individually to ensure they're at peak SoC because 8 days between charging could matter in terms of balance.

In parallel, could shave off a day or two and then let them sit un-paralleled for 7 days and have all of them settling over the same period. A little simpler.

As alluded to in the guide, the time spent in the leg is a small portion of the total charge time. The C rate of parallel charging is so low, there's almost no leg when viewed on the total time scale... just a little tick up at the end. Additionally, these big 280Ah+ cells have a very high settling voltage - essentially in the leg.

My experience with 20A charging of 280Ah Eve cells had the leg occurring during the last 20 minutes out of a 14 hour charge (2.4% of total charge time):
1641243410454.png

At 10A, that would be even smaller.

Assuming worst case that the ultra-low C rate takes the same % of the total time, 8P charging at 10A for 112 hours might spend a couple of hours in the upper leg. I can't imagine this can cause any meaningful issue with top balance or cell longevity.

At some point, precautions have diminishing returns. IMHO, this is one of those situations.
 
I read several how-to's that suggested charging in steps, getting them all to 3.5 or so, then connecting parallel and top balancing at 3.65.
I got one of those user-adjustable bench power supplies, up to 10A. Adjust...THEN connect and start...got it.

There is only one guide:

 
IMHO, the time variable renders cell settling variation meaningless unless you're willing to kill additional time.
OP has a charger/discharge rig that does sequences with hi and low voltage cutoff plus tail current at up to 40 amps.
I think you and @Browneye are talking about a different scenario.
8 280Ah cells, 14 hours average each to charge @ 10A. Assuming 1 charged every day. Cell 1 has 8 days of settling. Cell 2 has 7 days, etc. What does that tell you?
Check the settled voltage at 1 hour and 48 hours.
I guess if you're willing to let all the cells sit for another 8 days.
I might leave them 2 weeks or even a month but I don't expect others to.
 
OP has a charger/discharge rig that does sequences with hi and low voltage cutoff plus tail current at up to 40 amps.
I think you and @Browneye are talking about a different scenario.

Check the settled voltage at 1 hour and 48 hours.

I might leave them 2 weeks or even a month but I don't expect others to.

I left mine for 5 months... :)
 
Is Shenzhen Basen the same as Docan?
I may have confused the two.
Mine arrived - all good except for one terminal is not threaded.
All 4 are 3.290V matching.

 
@Browneye Docan is a different vendor. I would contact them about threading issue on your post. Most reviews of Docan are favorable so keep us posted on how they handle your issue.

@RCinFLA Only had time to check 4 cells. 2 that I full cap tested and 2 new. Interesting results and I believe you saved me a ton of initial quality testing time.

Cleaned and polished terminals and bars. Clamped sense lead on nut as recommended and verified voltage from post shoulder to lead with DVM before, during, and after load. Set tester to 40A load for 3 minutes.

All 4 plots overlay and reduced time to first 20 sec.

20220104_010935.jpg

Cell 1
Start 3.293 @40A start 3.272 @end 3.235 known cap 315.08AH

Cell 4
Start 3.294 @40A start 3.275 @end 3.235 known cap 311.8AH

Cell 6
Start 3.294 @40A start 3.273 @end 3.235 unknown AH test

Cell 8
Start 3.294 @40A start 3.272 @end 3.235 unknown AH test.

All 4 settled to 3.279 after 5 min rest.

Looks like I want to see ~20mV slump +-2mV at full load start to be satisfied all cells will reach capacity and charge/top balance them from where they are at. Geek in me will probably still randomly verify cap...

@smoothJoey running Cell 1 (already tested @315.08AH long way) overnight from current soc to 2.5 then charging cv 3.65 @40A to 15A tail. Interested to see how many AH tester records inbound. Will do same tomorrow for Cell 4 to verify results.
 
Thanks for the tips here…I will continue on with the other supplier thread.
My product says “Shenzhen”. Docan Technology must be the reseller. [shrug]

I was able to tun a tap in and cut threads, grub screw in and locktite. It’s solid.
 
@Browneye Shenzhen is the city in China. Docan and Basen are company or business names. Have noticed some suppliers (companies) with same name but will differentiate from each other by adding city name first. Not really sure if they are the same business or competitors. Dongguan is another city that has numerous suppliers.
Glad you had tools and skills to tap your post. Now the Fun starts! Still amazed by the amount of power these little things hold. My 6 volt gc2 bank is stone age compared to these!
 
Spent most of morning doing slump tests and compiling data. All cells appear to be within 2mV of each other in testing at 40A load and sampling voltage at 2, 4, 30, 60, 120, and 180 seconds. Overlaying plots leaves a thick smooth curve across 3 minute test. Really don't see any anomalies that raise concern. I agree with @RCinFLA and am confident as I spot check capacities all cells will test above rated capacity as first 2 full tests indicate.

Have moved on to testing @smoothJoey hypothesis that I can skip full charge to 3.65V tail of 15A and simply take cells from current shipped storage state to 2.5V with short rest and charge to 3.65V with tail of 15A. Would expect slightly higher AH reading but based on efficiency of cells should be close enough. Plus...save a ton of time!

Cell 1 tested to 315.08 AH after full charge, rest, discharge, rest, partial charge to 3.3V tail 2A.
After 10 hour rest Cell 1 was again discharged to 2.5V (73.2 AH removed), rest, then charged to 3.65V tail 15A. Tester registered 315.6 AH into Cell. Higher, but not as high, as expected.

Duplicate test in process for Cell 4 and interested to compare results.
 
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@Browneye >snip Still amazed by the amount of power these little things hold. My 6 volt gc2 bank is stone age compared to these!

My M6 tap was pretty knackered, but got it started, then ground the end off to some good threads, and cut it all the way to the bottom. The stud threaded in nicely - they're nice and hard (SS) so I locktited it in. I'm never taking it out anyway. I marked it to beware not to over-torque especially this one - it's liable to pull the threads right out.

This is my hope as well. My costco/interstate GC2's have a 2014 sticker on them. One cell has dropping gravity. So it was time to do something either way. I figured FLA 215A at 50% usable, plus sagging voltage over discharge, was no match for 230A with 90% usable with no sag. So nearly twice the capacity at half the weight and footprint. Probably the last battery this coach will ever need. Or I might just get four more cells and park another one next to this one just for shits and giggles (capacity and redundancy). ;)
 
Cell 4 tested to 311.8 AH after full charge, rest, discharge, rest, partial charge to 3.3V tail 2A.
After 10 hour rest Cell 4 was again discharged to 2.5V (72.02 AH removed), rest, then charged to 3.65V tail 15A. Tester registered 312.7 AH into Cell. .9AH more than discharge test.

Cell 1 charge test registered .52AH more than discharge test.

Looks like I need one more cell to verify an average...here we go again!
 
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