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Discussion Starter · #1 ·
I posted this as a reply to an old thread but I think I will start a new thread.
I just received my pack of 40 -200ah small case, new old stock TS cells. They arrived with voltages ranging from 3.29 - 3.62.(checked with a second meter and they were between 3.27 and 3.58) 10 cells are around 3.5 and the rest are between 3.29 and 3.45. they have been off any charger for at least 2 weeks. I have no idea how they got this way,someone had to actually do it. I plan to do an initial balance in parallel using an adjustable 13.8V -50 amp bench power supply. My plan is to charge CC to 3.6V in parallel. My question is what special precautions(What amp setting, etc) should I take since my pack is all over the place .
Should I be concerned about a resting voltage of 3.58 ? Kimball
 

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Chances are you have cells from more than one batch there. So the older cells, which had been sitting longer, have been subjected to more self-discharge. That, or there was a difference in temperature when they were stored/shipped, which caused some loss of capacity.
 

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Discussion Starter · #3 ·
These cells are in fact yellow LiFeYPo4 in crates from the same batch. I have been able to determine using a small PS that some cells are at the upper knee and some are around 50%SOC or less. Why some one would randomly charge 10 cells in different blocks is beyond me but that is what I have.
At this point in my learning curve I feel more confident going up hill with a charge as the PS will cut back on current . I don't know how you individually fully discharge 40 cells with going too far.
Would it make sense too do a parallel charge putting the fullest cells at the far end of the parallel string (to avoid pushing too much current through a full cell?)?
Or should I just individually bring each cell up to say 3.5-3.6 V at 40-50 amps and then do a finish parallel charge to 3.65. Kimball
 

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I also had some cells delivered pretty far out of balance, but then worked great with full capacity after bottom balancing.

Another thought: Maybe you should just put them in parallel and leave things that way for a while (in other words, no charger). Some other threads were saying lithium doesn't like float charging, and I could foresee some cells getting steady current pumped through them while others are still discharging.
I posted this as a reply to an old thread but I think I will start a new thread.
I just received my pack of 40 -200ah small case, new old stock TS cells. They arrived with voltages ranging from 3.29 - 3.62.(checked with a second meter and they were between 3.27 and 3.58) 10 cells are around 3.5 and the rest are between 3.29 and 3.45. they have been off any charger for at least 2 weeks. I have no idea how they got this way,someone had to actually do it. I plan to do an initial balance in parallel using an adjustable 13.8V -50 amp bench power supply. My plan is to charge CC to 3.6V in parallel. My question is what special precautions(What amp setting, etc) should I take since my pack is all over the place .
Should I be concerned about a resting voltage of 3.58 ? Kimball
 

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Another thought: Maybe you should just put them in parallel and leave things that way for a while (in other words, no charger). Some other threads were saying lithium doesn't like float charging, and I could foresee some cells getting steady current pumped through them while others are still discharging.
I am at this point too, I have 18 used TS 160's that all tested out good, have reasonable resistance, and all came in at 3.30-3.33V when I bot them. I now have them all in parallel (bot lots of bussbars for this reason) and I charged them up to 3.45 or so. I left them alone since Friday off the charger and will disconnect them from parallel Sunday evening. Wait a day or two and see if HOPEFULLY resting voltage is all the same for each of them.

Update Sunday Evening: I checked voltage after resting off charger for 1 1/2 days and pack voltage is 3.359, then disconnected all from Parallel and each voltage was 3.358-3.359 after 5 minute rest. I will check individual cells tomorrow. So it seems to me that the cells DO float (together) as each cell before paralleling was all over the place 3.25 to 3.42. (hope this is relevant to you and I am not burglerizing your thread.)

Francis
 

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Discussion Starter · #6 ·
I am at this point too, I have 18 used TS 160's that all tested out good, have reasonable resistance, and all came in at 3.30-3.33V when I bot them. I now have them all in parallel (bot lots of bussbars for this reason) and I charged them up to 3.45 or so. I left them alone since Friday off the charger and will disconnect them from parallel Sunday evening. Wait a day or two and see if HOPEFULLY resting voltage is all the same for each of them.

Update Sunday Evening: I checked voltage after resting off charger for 1 1/2 days and pack voltage is 3.359, then disconnected all from Parallel and each voltage was 3.358-3.359 after 5 minute rest. I will check individual cells tomorrow. So it seems to me that the cells DO float (together) as each cell before paralleling was all over the place 3.25 to 3.42. (hope this is relevant to you and I am not burglerizing your thread.)

Francis
Thanks that is helpful information. You mention that the cells were all about 3.30-3.33V when you bought them ,How did they get scattered to 3.25-3.42V ?Please let me know how it all works out. Kimball
 

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Discussion Starter · #7 ·
Since I also did not receive any buss bars, I have been thinking of ways to string 40 cells together in parallel in a simple and safe fashion. Today I noticed my roll of perforated plumbers strap and thought why wouldn't that be a reasonable temp. buss? The holes need to be opened just a bit for the bolts. Anybody done this? What other simple solutions have folks come up with? Kimball
 

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I would strongly encourage you to bottom balance them instead. Parallel them, bring them down to 2.6V, seperate them and leave them for a few days. If any of the cells have internal shorts, the voltage will drop and you can see which cells are bad. If they're full in capacity, it's really hard to find internal shorts. If you have a few batteries with higher self-discharge rate, you can use them but you at this point have to have a BMS because they'll get unbalanced fairly quickly.

If they all float at 2.6V after a few days, put them inseries and charge them while watching each battery's voltage. When the first one hits 3.65V, it'll tell you that it has the smallest capacity and if it's too low, you can discard the cell. If the string is all fairly close in voltage when the first one hits 3.65V, measure the string's voltage and set your charger to finish at that voltage. Then you're good to go.
 

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Thanks that is helpful information. You mention that the cells were all about 3.30-3.33V when you bought them ,How did they get scattered to 3.25-3.42V ?Please let me know how it all works out. Kimball
I bought my cells used and they were used for different things and not all in one pack, so the voltages were all different. As I mentioned above, the resting voltage now after one day was 3.35v. I discharged one and got 162.801 AH out of the used 160ah battery. So 3.35 is really all a person needs to charge to. It is pointless to charge 3.7, 3.6, 3.5 or even 3.4. May as well stay on the safe side.

"How did they get scattered to 3.25-3.42V ?"
Because I started charging them in series when they were different voltages. Trying to learn what happens when cells are not balanced and charged. I found that high voltage ones WILL way overcharge while others are still be trying to catch up. DUH.


francis
 

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I decided to top balance... since I am not going to start w/ a BMS, plan to stay well clear of max DOD, and normal charge cycle should work fine at the top if top balanced. I wired in parallel with 16ga lampcord wire, and input juice from a inexpensive Mastech power supply (positive lead at one end, neg at other)... set to 3.8v, and just let it go until amps dropped to 0. I then let the pack sit in parallel for a couple days before un-wiring.
 

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Discussion Starter · #11 ·
I decided to top balance... since I am not going to start w/ a BMS, plan to stay well clear of max DOD, and normal charge cycle should work fine at the top if top balanced. I wired in parallel with 16ga lampcord wire, and input juice from a inexpensive Mastech power supply (positive lead at one end, neg at other)... set to 3.8v, and just let it go until amps dropped to 0. I then let the pack sit in parallel for a couple days before un-wiring.
Dan, How much current did you use? Kimball
 

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Dan, How much current did you use? Kimball
my (smallish) Mastech can go either CV, or CA up to its internal max. I set the CV to 3.8 figuring that would be further up the knee than I want my changer to go (set to 38*3.65v), and further up the knee should zero in on the balance closer than the flatter part of the curve. Initially, the Mastech was putting in about 10 amps at 3.8v for about a week, then started dropping slowly over the next couple days, and eventually read 0 amps holding steady at 3.8v.

after disconnecting Mastech, pack dropped to 3.6 pretty fast, and cells have levelled out at 3.38-3.39. no load has been applied to them yet, I am still re-building my racks and re-wiring a couple things that changed w/ voltage upgrade.
 

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my (smallish) Mastech can go either CV, or CA up to its internal max. I set the CV to 3.8 figuring that would be further up the knee than I want my changer to go (set to 38*3.65v), and further up the knee should zero in on the balance closer than the flatter part of the curve. Initially, the Mastech was putting in about 10 amps at 3.8v for about a week, then started dropping slowly over the next couple days, and eventually read 0 amps holding steady at 3.8v.

after disconnecting Mastech, pack dropped to 3.6 pretty fast, and cells have levelled out at 3.38-3.39. no load has been applied to them yet, I am still re-building my racks and re-wiring a couple things that changed w/ voltage upgrade.
On my Mastech, 30v-20amp I use 3.7V @20amps. When it reaches down to 10-12 amp I shut it off and it settles at 3.35 to 3.36 which seems to be about 95% charge. (for bench testing I can go down to 0amps, but will sure not want to have to wait around when charging the pack in the car, so trying to find a good amp rate vs voltage ~ equaling 90-95% charge.

(BTW: do I assume that TS 160ah is160ah? Since my Calbs are 180ah, but deliver 195ah, is that just unusual or is TS 160 the same 8% over as well, giving me ~173ah when new and fully charged?)

Francis
 

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Discussion Starter · #15 ·
I made the plumber strap busses yesterday and I think they will work pretty well. I wonder how much current they will handle ? I have to wait for my new PS to arrive and I will get to the job at hand. Thanks, this is all very helpful information for me! Kimball
 

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I made the plumber strap busses yesterday and I think they will work pretty well. I wonder how much current they will handle ? I have to wait for my new PS to arrive and I will get to the job at hand. Thanks, this is all very helpful information for me! Kimball
steel strap may work, but will have way higher resistance than even small 16 ga wire... and the uninsulated stretch of the strap between terminals presents a shorting hazard if you happen to drop a wrench. I would highly suggest you whip up some short lengths of insulated 16ga copper wire instead to make your jumpers.

or... at least consider taping the middle sections, or putting length of bike tube to protect from accidental shorts.
 

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Discussion Starter · #17 ·
steel strap may work, but will have way higher resistance than even small 16 ga wire... and the uninsulated stretch of the strap between terminals presents a shorting hazard if you happen to drop a wrench. I would highly suggest you whip up some short lengths of insulated 16ga copper wire instead to make your jumpers.

or... at least consider taping the middle sections, or putting length of bike tube to protect from accidental shorts.
I will put a long strip of tape covering the bolt heads also. kimball
 
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