I have another 48v pack and three 36 SLA's, so no need to rush. If the Volgood BMS is messed up, what then? There are just too many cells for running without a BMS. Correct, the pack at 47 or 48, charger will go green right away. Otherwise, charging it takes longer. The pack doesn't seem to want to charge up fully. For what reason may be the 64,000 question?
Volgood 48V20Ah LiFePO4 Repair by Amberwolf
- Thread starter amberwolf
- Start date
Well, I'll tell ya one thing...
The BMS to start with needs some going over...
I got the last group to 2.7v, so I decided to try to charge again...
After many times of plugging and unplugging I noticed a bunch of weird things (and especially with the last group and during charging)..
Sometimes the voltage DROPS on that last group while charging..
Sometimes the voltage shows 5.83v on the last group at some point in the charge process...
Voltage of last group via the charge balance leads is different then from pack itself..
The BMS to start with needs some going over...
I got the last group to 2.7v, so I decided to try to charge again...
After many times of plugging and unplugging I noticed a bunch of weird things (and especially with the last group and during charging)..
Sometimes the voltage DROPS on that last group while charging..
Sometimes the voltage shows 5.83v on the last group at some point in the charge process...
Voltage of last group via the charge balance leads is different then from pack itself..
ther is almost surely a dud cell in that group just like before. you'd hacve to cut the group in binary serarch like i did to find it. as soon as you disconnect the bad cell from others still good, then thye will begin climbing in voltagew.
the bms stuff may be caused by the resistance of that bad cell, so it develops a large voltage across it whenever there is any current flow.
could also be a bad channel in bms, which is easy to check by just not connecting the balance leads and then single-cell charging that geoup after you find the dud cell, and watching behavior of groups at that point. but suspect it is just the cell.
if you can get any spare cells, you could just replace the whole group.
bms works like mine, so it cuts off charge or discharge with thowe fets on the heatsinks, whnever lvc or hvc is hit on a group. i dont remember what i found lvc hvc to be per cell, but i probably noted it in one of the 2 repair threads.
the bms stuff may be caused by the resistance of that bad cell, so it develops a large voltage across it whenever there is any current flow.
could also be a bad channel in bms, which is easy to check by just not connecting the balance leads and then single-cell charging that geoup after you find the dud cell, and watching behavior of groups at that point. but suspect it is just the cell.
if you can get any spare cells, you could just replace the whole group.
bms works like mine, so it cuts off charge or discharge with thowe fets on the heatsinks, whnever lvc or hvc is hit on a group. i dont remember what i found lvc hvc to be per cell, but i probably noted it in one of the 2 repair threads.
dnmun
1 PW
"the bms stuff may be caused by the resistance of that bad cell, so it develops a large voltage across it whenever there is any current flow."
this is so true. the internal resistance to charging causes the voltage to climb rapidly as it has current flowing into it, which causes the BMS to turn off the charge as that cell climbs above 3.9V.
this is such a crucial insight AW.
this is so true. the internal resistance to charging causes the voltage to climb rapidly as it has current flowing into it, which causes the BMS to turn off the charge as that cell climbs above 3.9V.
this is such a crucial insight AW.
While I'm charging that most negative cell group, I decided to test 4-cell groups with a 55w bulb..
P.S. I started all groups at 3.6xV
Took surface charge off so each cell read 3.3xV
Recorded amp pull at 4.25a (.3c) (V-below is 10 min into draw)
Cell groups 1-4 voltages during amp pull...
1.) 3.27v
2.) 2.95v <--- Ick!
3.) 3.28v
4.) 2.90v <--- Double Ick!
Groups 2 and 4 at no greater than .3C and their voltages are that low...
So far, not looking good...
I will check every so often and see which group craps out first..
EDIT AS OF 1:48am...
Welp, 1.5 hours in and cell group 4 starting dropping with cell group 2 right behind it.. (within minutes)
Cell groups 1 and 3 kept their 3.2xV While this happened..
So we are looking at about 6.5Ah for groups 2 & 4...
Onto next 4 groups...
EDIT AS OF 2:01am
Cell groups 5-8 (Again V's read 10 min in)
5.) 3.00v <---- Not happy
6.) 3.29v <---- THAT'S what they should all read!
7.) 3.29v <---- Yey!
8.) 3.01v <---- Again "not happy"
These groups will be my last for tonight, as I need SOME sleep
EDIT AS OF 4:10am
Ok final data on this second group..
Cell groups 5 & 8 started dropping at pretty much the exact same time..
(till they hit my self enforced 2.6v under load threshold.)
About 2 hrs and 20 min in.. So for groups 5 and 8 we're looking at about 9.9-10Ah.
P.S. I started all groups at 3.6xV
Took surface charge off so each cell read 3.3xV
Recorded amp pull at 4.25a (.3c) (V-below is 10 min into draw)
Cell groups 1-4 voltages during amp pull...
1.) 3.27v
2.) 2.95v <--- Ick!
3.) 3.28v
4.) 2.90v <--- Double Ick!
Groups 2 and 4 at no greater than .3C and their voltages are that low...
So far, not looking good...
I will check every so often and see which group craps out first..
EDIT AS OF 1:48am...
Welp, 1.5 hours in and cell group 4 starting dropping with cell group 2 right behind it.. (within minutes)
Cell groups 1 and 3 kept their 3.2xV While this happened..
So we are looking at about 6.5Ah for groups 2 & 4...
Onto next 4 groups...
EDIT AS OF 2:01am
Cell groups 5-8 (Again V's read 10 min in)
5.) 3.00v <---- Not happy
6.) 3.29v <---- THAT'S what they should all read!
7.) 3.29v <---- Yey!
8.) 3.01v <---- Again "not happy"
These groups will be my last for tonight, as I need SOME sleep
EDIT AS OF 4:10am
Ok final data on this second group..
Cell groups 5 & 8 started dropping at pretty much the exact same time..
(till they hit my self enforced 2.6v under load threshold.)
About 2 hrs and 20 min in.. So for groups 5 and 8 we're looking at about 9.9-10Ah.
remember that until the pack actually gets fully charged on each group which won't happen in a normal charge until the bad cell group is fixed, none of the voltage may look good.
slow trickle charge at say 100-250ma at 3.6-3.65v of each group (once duds are removed) could fix them, and then as long as the pack is put on the charger frequently even if not used they'll probably continue to be ok.
of course, if there are badly sagging groups after that, then there are probably other cells within those geoups that are higher internal ir and so they drop under load. (but during charge they will rise in v and possibly prevent full charge of them within normal time).
slow trickle charge at say 100-250ma at 3.6-3.65v of each group (once duds are removed) could fix them, and then as long as the pack is put on the charger frequently even if not used they'll probably continue to be ok.
of course, if there are badly sagging groups after that, then there are probably other cells within those geoups that are higher internal ir and so they drop under load. (but during charge they will rise in v and possibly prevent full charge of them within normal time).
All of the cell groups (except for the last one) were charged to 3.6x (and stayed there for overnight) after being single group charged...
Once the specific group's voltage starts to drop below 2.6 under load (especially this .3c load) that's gonna be the max AH ability until any errant cells are removed.. (and still won't improve by that much after)
I seriously doubt that a single bad cell or two is going to affect the group by that large of a margin...
According to IceCube he was only getting 16.5Ah out of it and after it got sent to you it only had 12.xAh (after your fixes)...
So there is at LEAST 4 to 7 cells in one or more of the 16 cell groups that already have problems...
As I've been going, I've updated what AH equivalents the (Lower AH'd) groups are...
2 groups have a max AH of about 6.5
2 groups have a max AH of about 10
8 groups tested, 8 more to go in these 4-cell group cluster tests.
When I'm done discharging them via 4 cell group clusters, I'll start the single group discharge on the ones that haven't been brought down to the 2.6v LVC threshhold. That will give me a basic idea of how many iffy cells are in each group.
Once the specific group's voltage starts to drop below 2.6 under load (especially this .3c load) that's gonna be the max AH ability until any errant cells are removed.. (and still won't improve by that much after)
I seriously doubt that a single bad cell or two is going to affect the group by that large of a margin...
According to IceCube he was only getting 16.5Ah out of it and after it got sent to you it only had 12.xAh (after your fixes)...
So there is at LEAST 4 to 7 cells in one or more of the 16 cell groups that already have problems...
As I've been going, I've updated what AH equivalents the (Lower AH'd) groups are...
2 groups have a max AH of about 6.5
2 groups have a max AH of about 10
8 groups tested, 8 more to go in these 4-cell group cluster tests.
When I'm done discharging them via 4 cell group clusters, I'll start the single group discharge on the ones that haven't been brought down to the 2.6v LVC threshhold. That will give me a basic idea of how many iffy cells are in each group.
If it was at most 16ah when you got it and then 12.5ah after Amberwolf played with/fixed it, that is 6/10ths of the original AH of the pack.
6/10th of 26lbs or 4/10ths bad cells or 26 X .4 or 10.4lbs of iffy/icky/bad cells right there.. Take just those out and you're looking at ~ 15 or so lbs (but that would be only 48v 12Ah in the worst case scenario..)
It's beginning to look like, in order to get the most AH out of it, I'd have to remove most of the cells and re-solder like a crazy man...
Won't know exactly what the best case scenario could possibly be, until I figure out the best AH of each cell group, in it's current condition.
Will work on the next 2 sets of 4-cell groups tonight..
P.S. I got that most negative group to 3.0v and it's resting at 2.59v at the moment..
Will leave it for another 8 hours or so and see what it finally rests at.. If it's still close, I might be able to charge that group (with the pack) via the BMS after I've drained the rest of the groups to see how they will hold up under load..
So far about half of those cell groups are sagging by almost .4v under only a .3C load as opposed to what they should, maybe a .1v under those conditions.. So if that holds up, that would be 8 cell groups dropping pack voltage by 3.2v just with a .3c load.. (.3C load is considering only 12Ah capacity, not the 20Ah it was originally supposed to have.. Otherwise were talking a .2C load)
So if you were drawing 10-12a on a continual basis, we're talking a 1C load and I haven't tested that yet, so figure even worse sag... Maybe .8v per group or 6.4v out of 52.8v nominal or 46.4v (and that's not including the .1-.2v drop from the other "decent" cell groups so add another .8-1.6v) or avg it to be an additional 1.2v or pack voltage during a 1C load of 45.2v.
I'll check AW's data and see what he was getting..
And compare the two.
Edit: Just looked it up and it looks like AW's figures are close to mine... (At least in my guestimates of Vmin)
42.8V (10.0v under nominal V) under about a 58a load (4.5c) and that's after the fixes.. (e.g. At that time, most of the groups were probably much more reliable then they are now.)
6/10th of 26lbs or 4/10ths bad cells or 26 X .4 or 10.4lbs of iffy/icky/bad cells right there.. Take just those out and you're looking at ~ 15 or so lbs (but that would be only 48v 12Ah in the worst case scenario..)
It's beginning to look like, in order to get the most AH out of it, I'd have to remove most of the cells and re-solder like a crazy man...
Won't know exactly what the best case scenario could possibly be, until I figure out the best AH of each cell group, in it's current condition.
Will work on the next 2 sets of 4-cell groups tonight..
P.S. I got that most negative group to 3.0v and it's resting at 2.59v at the moment..
Will leave it for another 8 hours or so and see what it finally rests at.. If it's still close, I might be able to charge that group (with the pack) via the BMS after I've drained the rest of the groups to see how they will hold up under load..
So far about half of those cell groups are sagging by almost .4v under only a .3C load as opposed to what they should, maybe a .1v under those conditions.. So if that holds up, that would be 8 cell groups dropping pack voltage by 3.2v just with a .3c load.. (.3C load is considering only 12Ah capacity, not the 20Ah it was originally supposed to have.. Otherwise were talking a .2C load)
So if you were drawing 10-12a on a continual basis, we're talking a 1C load and I haven't tested that yet, so figure even worse sag... Maybe .8v per group or 6.4v out of 52.8v nominal or 46.4v (and that's not including the .1-.2v drop from the other "decent" cell groups so add another .8-1.6v) or avg it to be an additional 1.2v or pack voltage during a 1C load of 45.2v.
I'll check AW's data and see what he was getting..
And compare the two.
Edit: Just looked it up and it looks like AW's figures are close to mine... (At least in my guestimates of Vmin)
42.8V (10.0v under nominal V) under about a 58a load (4.5c) and that's after the fixes.. (e.g. At that time, most of the groups were probably much more reliable then they are now.)
Haven't even looked at this pack in a week..
Life happenings are getting in the way...
I did check the most negative group's voltage just now and it's back down to 1.23v...
Single charging it over night and see what it's at in the morning...
I did however charge up those 2 sets of 4 groups that I load tested to 3.6v each last week.. Most of them are at 3.4-3.5v each after a week...
Still trying to get to this pack, but I know it's gonna be a pain once I open it up, so I'm gonna wait until I have an entire day to play with it before doing that.
Still have to test groups 9-15 and get group 16 up to 3.x and holding until I even think about opening up the pack.
I'm hoping groups 9-15 fare better than the first 8.. Even then, I'm sure I have a lot of searching for bad cells...
I'm beginning to think I have a LONG way to go with this..
Life happenings are getting in the way...
I did check the most negative group's voltage just now and it's back down to 1.23v...
Single charging it over night and see what it's at in the morning...
I did however charge up those 2 sets of 4 groups that I load tested to 3.6v each last week.. Most of them are at 3.4-3.5v each after a week...
Still trying to get to this pack, but I know it's gonna be a pain once I open it up, so I'm gonna wait until I have an entire day to play with it before doing that.
Still have to test groups 9-15 and get group 16 up to 3.x and holding until I even think about opening up the pack.
I'm hoping groups 9-15 fare better than the first 8.. Even then, I'm sure I have a lot of searching for bad cells...
I'm beginning to think I have a LONG way to go with this..
The BMS works "ok" as far as I can tell..RTLSHIP said:
Although the most positive group always ends up "high" 3.8v or so (even if I drain it down further than the rest by over a .1v) and the most negative group is always low.. BUT... I keep charging it up and I get it to 3.4v or so, but letting it sit for a day and it drops back down below the 2.0v mark... That cell group is dunked up..
I tested the others.. Half of them give up about 12-13Ah, the other half, range from 6ah-11Ah (NOT including the most negative cell group.)
When I have a chance, I really need to open the pack and start, searching for and clearing out, the bad cells (via cutting the connections to the bad cells).
If I can "clear out" the bad cells, I'm guessing, I might be able to get it to about 8 - 10Ah..
(Battery will still be the same weight and size though.. and again, that's if I can get that most negative group to some reasonable level - which might happen if I clear out the "leaky" cells..)
Just an FYI, this battery is 3 years old, the original owner, at some point, charged up the cells to 4.2v each.
(I'm guessing on more than one occasion, By using a charger made for LiPo - I read it in his thread), then RTL had it and something flaky went down, AW "fixed/modified" it, RTL had an issue with it again... Ands now 3 years later, a good half of the cells are leaky/crappy/etc.. {I may even find a reversed cell or two}, I'm not sure until I open 'er up!)
icecube57
10 MW
I over charged certain cell groups to 4.2 once to try to bring up the low cells but even if you read through my thread It was only giving me 15 AH to begin with. Did the over charge push it over the edge i dont think so. It just a shitty pack all around i think. It was giving a solid 15-16 AH throughout the time I had it. First and last time i deal with a round cell pack of that scale.
sangesf said:I feel honored to be the first one you think of amberwolf...
Yeah, RTLSHIP, if ya let me know where in SF you are, maybe we can meetup and work on that battery for you.
Let me know.
After reading that long "PM session" you guys had, it seems to me, that he has a loose connection some where along the line..... If the voltage of the pack fluctuates that much (by 8v or so), then it seems obvious to me that there's some form of wire not making a good connection...
Actually, whatever it is, I'm sure I can figure it out...
Would actually need the battery in front of me and I could test it..
I would be honored if I could get my pack and charger back, Sangesf. Where have you been for past 3 months. That's my property, not yours.
