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Harvested cells analysis.
#21
(03-08-2019, 07:33 PM)100kwh-hunter Wrote: I think i will end up this first experiment with 1/15 laptop and 14/15 powertool/ebike cells, so no need yet for laptop cells.

Speaking of to jumpstart the car....that buzzer that is warning you, that you left your lights on, is broke, stopt working two months ago.
I had to jump start several time's, i am not kidding!

That's great if you have so many powertool batteries then yes I would just go with them alone and not even put the laptop cells in there.
In my case I have maybe 150 powertool batteries compared to 1400 "good" ones out of 3051 laptop cells so far.

LOL on the jumpstart. 

Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 5/23/2019
Total Number of Cells                          5354
Cells  >80% of Capacity                      3801
Cells <80% of Capacity                       1553
Cells ≥2200mAh & ≥ 80% & ≤75mΩ    2645 (155) to go
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#22
My goals are 48v@20kwh useable + long life (20yrs - to get ROI) but one thing I don't see discussed much is this chart from Battery University vs $$ for new/better cells vs $ for used-but-good cells.    Here's the web page link that contains the chart below: https://batteryuniversity.com/learn/arti..._batteries


Based on the chart above I've sized my battery to consume all my PV array can produce at  an average of 50% DOD per year.  That's a 40kwh battery (5,000 cells) for my situation.

In the beginning (first 1500 cells) I went with more expensive/more-capacity but the $$ killed me so for the last 2,000 cells I went with 2200mah LGDAS31865 "modem cells" @ aprox $1.20 each from alarmhookup (very trusted source on ebay).   I harvested an average 2150mah @ 130millohms w/average 5yr-old-date-code. 

My Question:
Is this chart from Battery University reflective of real life at all? - e.g. can cells actually go 5,000 or 7,000 cycles (1 per day) at low DOD and still retain 80% of their capacity?


If you look at it as 20yrs and still have 70% power - then mah per cell is probably not the key issue. It might be manufacturer or in my case $/cell vs 20yrs vs return on investment. At $3.00/cell I would never get my money back. I'm currently at 22.23 years for system to pay for itself @ .12c/KWH where I live Smile
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#23
20 years?!!? With LiIon? They degrade faster than that Im afraid. Dont forget their degradation per year :/

LiFePo4 on other hand is possible. I calculate 10 years on my Life bank and ROI 8 years.
The Ultimate DIY Solar and build place
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
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#24
Offgridinthecity, you made the mistake of overpaying for cells. The chart above must be for Tesla Panasonics because most cells are rated for only 300 or 500 cycles. With the money you spent, you should really have gone for LiFePo4 or LTO, those are rated for 1000s of cycles.

Also about time degredation: The oldest cells I recovered are Sony 1500s with a 1998 date code. They still tested at around 85-90% capacity. Most of my new old stock cells are from 2011 and are testing right around their original capacity. So I dont really buy that time degradation unless someone can point me to some proper research. Now if you store at full charge, that's where you get time degradation. I've found that good cells (90%+) will lose 3% capacity in a year at full charge, ok cells (75%+) will lose 10% capacity per year, and bad cells(50%) will lose 33% per year.
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#25
Dallski - 300-500 cycles.
Daromer - 3000 cycles (8yrs * 365) requires LifePo4

Well I did ask.      

I'm hoping that middle range charge/discharge at pretty soft demand (150ma discharge, 300ma charge) will greatly extend usability.

Specifically - I have set the charge to top out at 4.02v (88%) and cut-off at 3.39v (28%).   This is a 60% DOD range; however, it will only go all the way to 4.02v about 1/2 the year because winter/clouds/smoke reduce PV array output.     For example, today it topped out at 3.71v charge which will only be a 30% DOD as Inverter burns off the power down to 3.39v thru the evening.  

Overall I'm expecting a 48% average DOD.    Over time, I can expand the voltage range to compensate for loss of capacity to maintain my original power needs of 20kwh (out of the 40kwh battery) as long as cells hold out / degrade gracefully.

So far I have done 225 cycles with average 50% DOD and the original packs seem OK - but I didn't get system fully implemented with Batrium and Database recording till 50 cycles ago so I didn't have data to detect loss of capacity till now.

Over time the proof will be in the pudding and there will likely be new generations of cells in another couple of years and I can buy differently Smile

Again, thanks for info as I know you guys have actual experience!!!
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#26
Can your batteries last 10 years? Why not? I don't think anyone here has had their 18650s longer than a few years, and no one has posted benchmark showing the degradation is much worse than that chart. The battery university chart is shows its possible, even with just regular 18650s to get 10 years. Figure you are never always going to have a full cycle every day anyways, so it's not exactly 3650 days = 3650 cycles = 10 years. The Battery University chart shows plots of different degradation based on different ranges, so I'm still optimistic on possibly getting 3000 days (not cycles) out of my batteries based on a 60% DoD.
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#27
(03-09-2019, 02:14 AM)not2bme Wrote: Can your batteries last 10 years? Why not? I don't think anyone here has had their 18650s longer than a few years, and no one has posted benchmark showing the degradation is much worse than that chart. The battery university chart is shows its possible, even with just regular 18650s to get 10 years. Figure you are never always going to have a full cycle every day anyways, so it's not exactly 3650 days = 3650 cycles = 10 years. The Battery University chart shows plots of different degradation based on different ranges, so I'm still optimistic on possibly getting 3000 days (not cycles) out of my batteries based on a 60% DoD.

Yes - you are echoing my thought process that has shaped the goals of my system.   The data seems very sparse and I'm not even sure what actually matters.  For example - are some 18650's built to die quickly while others target a longer life?..  have not seen any facts on this.   Does low % DOD expand life as dramatically as Battery University shows?

Tesla Model 3 literature says 70% capacity at 8yrs.   
Powerwall 2 has 10yr warranty in their literature. 

Deep Cycle Marine are supposed to be good 4-5yrs and conventional wisdom is Lithium-ion will easily double that? But of course the battery industry is buyer beware for sure.

What are fundamental differences between Tesla cells and say LG 2200mah LGDAS31865 that affects cycle/capacity over time - e.g. chemistry, quality of manufacture, hi charge/discharge amps, secret sauce...
----

In any case, my system is fully operational, batteries are already purchased and built (too late for me)...  so I plan to maintain 50% DOD (or less) daily operations and record things and see what happens Smile
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#28
You have great questions!

For every cell, I think the four most important things that determine its useful life are (1) Storage state of charge; (2) Temperature both in storage and during use; (3) Depth of Discharge; and (4) rate of charge/discharge.

For specific cells, mostly it is the chemistry and the electrolyte used.
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#29
newby speaking:
I think: if your bank is large enough, then there is no cycle?
If u charge 1000w a day and you consumption is also a 1000w a day, you have every day one cycle, with a bank that can holds 1000w.
But what if you have 1500w charge a day, with your consumption of a 1000w a day, and a bank that holds 5000w.
Than the bank is in a "float" state and have no cycle?

get an second opinion about this, also asking for myself
Still learning English. Learning Li ion and solar technology.
+/- 3500 Li ion cells harvested, none checked and counting.

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
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#30
The question is just how much capacity left after x time is considered ok? IF its 10% sure they can last 10+ years....

Tesla count on rather low average dod. Most People here dont build big enough battery banks... During Summer here i got at most 15% dod..... That Will ensure longer span.

There are many cells today that do show faster degradation after x cycles. This is something i also have confirmed by a big manufacturer that its the case.which cells i dont know though but it have been seen here to happen after around 60% degradation.

IF above input matters for you thats Up to you but without setting some values its Hard to even calculate how it willlast.

Just look at degradation for liion at 20c per year at full or almost full Charge. Its easy between 2-6%. 6% is alot Smile
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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