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J_Mack58

Member
Joined
Apr 7, 2021
Messages
92
Breaking down packs be it laptop, scooter, modem or these 26650 packs I’m getting is no fun. Then capacity testing, IR and sorting is a pain. Every now and then one has to have fun. In 45 minutes a fashioned some good old 10 AWG into ghetto bus bars and slammed an additional 4.1 kWh to my 14S80P and now I can make it around the clock on solar and battery.. Relax… the battery packs have their own BMS and they work nice. I hand balance some packs with my handy halogen car light 5 days in and the pack has balanced itself far better then I was doing with the light. Which lead me to think and question myself… if these batteries are good, why am I tearing them apart just to test them and find out they are good? Anybody else building power walls from original battery packs?
 

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J_Mack58

Member
Joined
Apr 7, 2021
Messages
92
When I first got the packs here is the initial voltage readings, sorted.
 

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Korishan

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Joined
Jan 7, 2017
Messages
6,572
If the packs are new, or barely used, then just randomly testing a pack would be sufficient. Voltages don't tell you much except if they were severely depleted for some reason.
If the packs have been in storage for years, have been used in a UPS or similar application off/on over years, or were used in high drain applications, then testing each pack would be recommended.

You can have a brand new cell/battery be drained to <1V, then do a careful recharge, and it will perform almost like new, as it may loose a little capacity. For example, when new it could be 2400mAh, but after the deep discharge, it now is 2350mAh. Not a deal breaker, but there is a little loss.

The biggest thing that determines if a cell/pack is good, is the IR and cycle capacity. @Wolf has done extensive tests and posts about this subject. Capacity testing is pretty straight forward. Overall, you are looking for any anomalies in the readings.

3000 - 3500 mAh is a pretty wide spread. Especially if that spread was in a single pack/battery. If you are able to pull the packs out of the housing, and then use some kind of clamp to hold leads to the parallel groups, you can decrease the time required to test. One of our cell reviewers used a bar clamp to hold two heavy leads to either side of the cells. You could something similar to this and that way you could not only measure voltages per parallel group, but also combined capacities of that group. You could also do an IR reading this way, but it would be the average of the cells in parallel, unless you were able to disconnect one side of the cell w/o damaging anything.
 

J_Mack58

Member
Joined
Apr 7, 2021
Messages
92
If the packs are new, or barely used, then just randomly testing a pack would be sufficient. Voltages don't tell you much except if they were severely depleted for some reason.
If the packs have been in storage for years, have been used in a UPS or similar application off/on over years, or were used in high drain applications, then testing each pack would be recommended.

You can have a brand new cell/battery be drained to <1V, then do a careful recharge, and it will perform almost like new, as it may loose a little capacity. For example, when new it could be 2400mAh, but after the deep discharge, it now is 2350mAh. Not a deal breaker, but there is a little loss.

The biggest thing that determines if a cell/pack is good, is the IR and cycle capacity. @Wolf has done extensive tests and posts about this subject. Capacity testing is pretty straight forward. Overall, you are looking for any anomalies in the readings.

3000 - 3500 mAh is a pretty wide spread. Especially if that spread was in a single pack/battery. If you are able to pull the packs out of the housing, and then use some kind of clamp to hold leads to the parallel groups, you can decrease the time required to test. One of our cell reviewers used a bar clamp to hold two heavy leads to either side of the cells. You could something similar to this and that way you could not only measure voltages per parallel group, but also combined capacities of that group. You could also do an IR reading this way, but it would be the average of the cells in parallel, unless you were able to disconnect one side of the cell w/o damaging anything.
Thanks for the reply, IR and cycle capacity is what I will be looking at. Now I will let the cat out of the bag. These cells are 2018 and a few late 2017 cells that come out of smart parking meters. Two 12 vol,t 16ah batteries per parking meter. My friend work for the city and there are pallets of used batteries in which they have not found a place to dispose/recycle them. Some are changed because the battery is low others get change because they are on a Preventive Maintenance (PM) schedule. The city can afford this because revenue from these meters is very good. So some will work hard because of lack of sun and drain low till they can get some sun, others will soak up the sun and stay charged. Some may over charge should the BMS in them fail. (I seen a few). Overall I'm trying to convince my friend who only wants to build a 120 ah powerwall from these batteries (16S40p) that we should develop a good test for the battery as a whole and use it and all bad batteries we can break down and reclaim good cells if there is any. I won't be mad if I drive through the city and see all the smart parking meters sawzall off now, I ask that you cut them high at the meter so the city can replace them easily and no tripping hazards.
 

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Korishan

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Jan 7, 2017
Messages
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I don;t think we have any solar powered ones here. They still run on battery, just not lithium, that I am aware of.

Pretty good haul to get a resource like that. Koodos on saving them from destruction. PM schedule makes a lot of e-waste, unfortunately. They could save a lot of battery waste with meters by just putting a phone home system in place when the capacity drops below a certain amount. Wouldn't be that hard. Or a red light on them or something.
 

J_Mack58

Member
Joined
Apr 7, 2021
Messages
92
Scratch that ideal of taking these batteries and adding them to my powerwall. After making a quick 4.1kWh, 80ah battery and adding it to my existing powerall it actually worked very well and I could tell I had a boat load more capacity. I measured the batteries for 2 weeks at 3pm when the my powerwall is full at 55.5 volts and every morning at 4:30am where my powerwall should be discharged to some lower voltage. Use to be between 46-47 volts but with the add on it was 50 volts. Each of the 20 batteries I measured and logged in excel. I could see I had three that acted strange so I remove them and made some swaps now I have a 3.3kWh add on battery. I carefully open the bad batteries so that I could measure the raw cell pack before the BMS. WALA! Voltage at the battery terminals 7.xxx volts, voltage before the BMS 12.065! so I unplugged the BMS and the battery terminal voltage came up to 12.065 volts. Plugged the BMS back and the terminal voltage stayed. Powerwalls can't be unreliable. I disassembled the 20 cell pack, Scraped the BMS. Tested 8 cells so far and capacity and IR are great. If I test all 20 and they are good then these batteries are being taking out of service due to BMS failure. That's how my Powerwall got started, I noticed a e-waste barrel full of Stihl and Echo leaf blower packs at work. I took them all. 30 and 28 cells per pack. I was not keen on testing then so I charged them and if they did not get hot and they did not self discharge after charging they went into my powerwall. Hundreds of good cells only a few bad and those bad may have been my fault. Overcharging and popping the CID. So many power tool batteries discarded because of bad BMS and not the cells. China "atpow" brand BMS is mated with China "Heter" brand 26650 cells in these batteries. The Atpow BMS is giving Heter cells a bad name. As advertised below "Using a good BMS is the difference between a dangerous battery & a great one". Let me add "and one that the cells will end up in a DIY powerwall".
 

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