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Lithium ion packs without balancing

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Siwastaja:

--- Quote from: BradC on February 13, 2022, 11:21:20 am ---I've also seen quite a few advertised as "B" grade, so in some way shape or form they probably exist.

--- End quote ---

The manufacturers do not advertise the cells to the general public. You need to buy in millions and qualify as a customer. All we mere mortals get are from grey market. It can be any mix of A, B or whatever grade, and fakes.

If you can buy known B grade from the actual manufacturer, I'm sure there's an NDA in the process, and the cells are still good for use, and the suitability is assessed with the customer.

BradC:

--- Quote from: Siwastaja on February 13, 2022, 11:31:23 am ---The manufacturers do not advertise the cells to the general public. You need to buy in millions and qualify as a customer. All we mere mortals get are from grey market. It can be any mix of A, B or whatever grade, and fakes.

If you can buy known B grade from the actual manufacturer, I'm sure there's an NDA in the process, and the cells are still good for use, and the suitability is assessed with the customer.

--- End quote ---

Not disputing any of that. I'm sure a Chinese company making something like a USB power bank and wanting cheap cells can tap the B grade market. Anyway, given the obvious specification disparity with these they're not B grade but counterfeit.

BradC:
Righto. Replaced cells with 8 x Panasonic NCR18650B. Bloody expensive at $15/ea + GST, but at least I know they are genuine and I'll hopefully only do it once.

If this works I'll do the other one (I have 2 of the same power bank).

BradC:
My gear arrived to allow me to do a load test on these power banks.

I have 2 power banks. Unit 1 was purchased in mid 2020 and failed (due to a mechanical failure of a connection) in early 2021. It was "replaced" by Unit 2 in mid-2021 and then repaired. Unit 1 saw quite a good heavy and deep cycle load before it failed. Unit 2 hadn't been used anywhere as much when I tore it down to find the pack badly out of balance.

The tests were done using a USB-C PD trigger supplying 20V and loaded with a SkyRC BD200 at a configured 25W constant power load (turned out to be an average of 22.7W) until the battery shutdown the output.

Unit 1 (un-touched) tested to 88.08Wh (4.40AH at 20.02V) and Unit 2 (with the new cells) tested to 96.26WH (4.78AH @ 20.14V).
Based on the rated discharge curve and capacity for the new cells, that gives an output efficiency around 96%. Nice.

Back calculating, that puts Unit 1 batteries at about 3050mAH. I hooked up the cells I replaced from Unit 2 to an iMax B8 balance charger and gave them a full cycle with a discharge load the same as performed on the other sets and they measured out to be 2700mAH rather than the 3200mAH they are specced at. That gives roughly 80WH and at 96% efficiency an output capacity of about 77WH, which is roughly what I measured with my previous imprecise methodology.

That, coupled with the disparity in characteristics resulting in the pack going out of balance indicates they are perhaps "not genuine".

Unit 1 is considerably older and has far more cycles on it than Unit 2 and it still showing a credible capacity, so it'll be interesting to monitor them both over the next couple of years to see how well the new Panasonic cells stay in balance as a whole.

This is the unit : https://www.auspowerbanks.com.au/product/apple-macbook-power-bank-87w-pd-with-magsafe-gen-2/


Great unit, but a complete bitch to get apart.

BradC:

--- Quote from: BradC on February 25, 2022, 01:56:35 am ---Back calculating, that puts Unit 1 batteries at about 3050mAH. I hooked up the cells I replaced from Unit 2 to an iMax B8 balance charger and gave them a full cycle with a discharge load the same as performed on the other sets and they measured out to be 2700mAH rather than the 3200mAH they are specced at. That gives roughly 80WH and at 96% efficiency an output capacity of about 77WH, which is roughly what I measured with my previous imprecise methodology.

That, coupled with the disparity in characteristics resulting in the pack going out of balance indicates they are perhaps "not genuine".
--- End quote ---

12 month update. The re-packed unit appears to be still well balanced and I still get > 95Wh out of it. I'm not going to pull it apart to check each set of cells this year as it's not easy to get into without risking damage and requiring more glue to put it back together again. I might do it next time around.

After the tests last Feb, the removed cells were all charged to ~3.85V and left on the shelf as an assembled pack with only a balance lead connected to them. A check this morning sees 3 sets of cells all > 3.8V and one set at 3.5V. So a marked difference in self discharge over a 12 month period. Just for giggles I'll do a balance charge and discharge test again.

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