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The story of a little powerwall
#11


It's a mix of a bit of scary and a bit of exited.

One pack done, made with 32 cells.
216 Wh of energy. One mile of an electric car's range.
The coldness of it, the weight, the size, the danger and the unseen potency all add to the mix.
That i'll be wrapping it in heater wire does not help either.


A few days ago i came across another used laptop battery seller, and made a mistake of asking how many he got.
Turns out he got a whole box...
So now i have a box full of batteries, and am slowly going through them.

I've ordered PCBs for more cell exercisers, and for the month it'll get them to get here i'll be designing and making frames, heaters, controllers and the rest of the things while painfully attaining 8 cells a day...

The plan is to make a 7s32p system, which will probably be a separate project from the existing chaotically grown 2s20p one.
You can follow my projects at https://orbides.org
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#12
The PCBs have arrived.
Soon i will no longer be limited to 8 cells a day. Smile

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#13
And they are assembled.
And they are working.

Well, not all of them, some are only looking nice.
9 out of 24 slots are dead, 3 of which were due to an assembly miscalculation, 4 due to a mysterious bug that turned out to be flux residue under the resistors, 1 due to a crappy part, and one due to me not wanting to test a single cell on it's own.

The whole assembly also features a UPS made out of the "protected" cells (which had to be amputated once i realized they trip from the just the capacitor charge surge), mostly for the ability to move it from socket to socket without having to wait for the cycles to finish.

...can i sleep now?

[Image: 181112-chargers.jpg]
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#14
Wow, need some close up dude - great work
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#15
(11-13-2018, 11:49 PM)hbpowerwall Wrote: Wow, need some close up dude - great work

Like that? Smile

[Image: re_20181115_025302.jpg]

I've been contemplating making this thing open source, but the design was quite a slap-it-together so i'm a bit ashamed of it.


Meanwhile, after re-testing all the cells from before (3 weeks worth in 3 days!) and debugging the setup i'm about to start increasing the cell count again.
Sadly, the good cells box is on the right and the bad ones are on the left.
Out of 114 cells in there only 56 that are decent, of which 28 are good.
It's going to be a long trip... :/

[Image: re_20181115_030412.jpg]
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#16
Yep, that works lol well done - looks neat enough to a noob ake me
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#17
Despite the lack of snow, it's well below freezing outside here.
And Li-ion does not like being charged in the cold.

Let's make some winter-grade batteries.
-Get the battery pack assembled
-Apply thermometer
-Wrap it in fiberglass tape
-Apply nichrome heater wire and a power out for BMS
-Wrap it in insulation material, secure with duct tape
Done.

Should work down to -20*C based on my earlier tests...
Hopefully.
The BMS logic would be "if below +5*C and sun is on, heater on. If above +5*C or no sun, heater off. If Tb<0*C, charge off".

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#18
Hmm, not sure I wanna comment about pack #4 on the right Tongue
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#19
Nice work on the gear you made :-)

Seems like a very high rate of "bad" cells? Are you sure they are bad? Maybe worth a 2nd test?

re heating, is there a way you can have the battery system inside a warmer area of the house?
Running off solar, DIY & electronics fan :-)
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#20
(11-20-2018, 11:57 PM)Korishan Wrote: Hmm, not sure I wanna comment about pack #4 on the right   Tongue

In that case, here is the full battery. Smile


(11-21-2018, 02:13 AM)Redpacket Wrote: Seems like a very high rate of "bad" cells?  Are you sure they are bad? Maybe worth a 2nd test?

Bad is relative...

77 laptop packs, out of which 61 contained non-dead cells, where dead is anything leaked, corroded or showing under <1V.
That gives 297 cells.

Out of them, 41 ended up dead in testing, as in either heaters or have a capacity under 1000mAh.
That leaves 256 usable cells.

In further sorting, 100 of them were sorted into the "bad box" meaning they are high self discharge, high variance (capacity drops between discharges), high ESR, high degradation (under 60% from rated if known) or have a capacity below 1500mAh.
That left 156 cells in the "good box".

These are further sorted by the same parameters into 85 good, 59 mediocre, 8 low and 4 missing.

Finally, 128 of the best of the good and mediocre were selected to form the 4 32p packs shown here.


So, how much of a bad ratio this is?

(11-21-2018, 02:13 AM)Redpacket Wrote: re heating, is there a way you can have the battery system inside a warmer area of the house?

No, they will be sitting in a place that is rarely occupied during winter, so no heating to be expected most of the time.
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