Can this battery be revived?

[Richtea70]

Hi all,
Had a 52v 20ah downtube battery that I hadnt used for some time (6 months plus), was doing a new a new build yesterday so thought I’d use the battery.
Put it on charge for the charger to click from red to green almost instantly. Checked the voltage of the battery and it was showing just over 22 volts, which i know is very bad.
I was working outside all day so just left the charger on it for about 4 hours. During this time the charger continued to keep clicking between red and green in approximately 30 second intervals. I also have another 52v charger which showed the same behaviour.
I didn’t want to leave on charge without me being there, so turned off and checked voltage again which was then showing as just over 34v.
Is the pack completely wasted or is it worth persisting with the charging? Ive never opened a battery pack before so if there isn’t a simple fix I think I will just bin it,
Thanks for any advice,
Rich

 

[WheezyRider]

Assuming nothing has gone wrong with the internal wiring connections or a BMS failure, the BMS has probably drained the cells below the point where the BMS will do anything. Cells will probably be recoverable.

I would open it up and have a look at the voltages of the individual cell banks.

It could be something as simple as a poor connection on the sense wires to the BMS.

How easy is the pack to open up?

 

[RichB]

Assuming nothing has gone wrong with the internal wiring connections or a BMS failure, the BMS has probably drained the cells below the point where the BMS will do anything. Cells will probably be recoverable.

I would open it up and have a look at the voltages of the individual cell banks.

It could be something as simple as a poor connection on the sense wires to the BMS.

How easy is the pack to open up?

Not sure how easy it is to open up? It's just a standard 'shark' type case. I have a multi meter, so is it as simple as just taking the casing off and then measuring each individual cell? What should the voltages of the individual cells be or am I just looking for one that's obviously lower than all the others?
Thanks
FYI - I am Richtea70, just logs me in as Richb depending on what device I'm on!

 

[matthewslack]

Sounds like a generic two wire battery? If so, then if it is just low voltage on all cell groups, it can be brought back up to a voltage the BMS will work with by charging via the output connection.

But you need to open up the case very carefully and check the cell group voltages first. Perhaps do that and report back. There will be 14 cell groups, and ideally each will measure 1/14 of the full pack voltage. Any major differences is cause for concern.

 

[WheezyRider]

Not sure how easy it is to open up? It's just a standard 'shark' type case. I have a multi meter, so is it as simple as just taking the casing off and then measuring each individual cell? What should the voltages of the individual cells be or am I just looking for one that's obviously lower than all the others?
Thanks
FYI - I am Richtea70, just logs me in as Richb depending on what device I'm on!

Post some pics, that will help people advise you what to do.

When you do open it up, make sure you do it on an clear insulated surface, taking care that nothing can cause a short between anything. Doing this in a shed or outdoors is a good idea, in case the worst happens, you don't want to burn the house down

There is also a Richtea99 on the forum...so plenty of rich tea here!

 

[RichB]

OK, so I've taken it apart very carefully.
And this is what I've got, I'm cut back done of the plastic to show (what I think) is the BMS?
Strangely the battery indicator on the pack, still shows full?

 

[Nealh]

If any cells have dropped below 2.5v each then the effort isn't worth it for ebike battery use.
Take a proper pack reading by removing all the shrink wrap and probe the first and last cell group.

 

[RichB]

If any cells have dropped below 2.5v each then the effort isn't worth it for ebike battery use.
Take a proper pack reading by removing all the shrink wrap and probe the first and last cell group.

Thanks, I've got no issues with binning it as want to be safe.
But by cell group, do you the individual cells?

 

[Nealh]

Take a pack reading first in case the BMS has gone to sleep.
Probe the first cell group end with thick Black wire attached and the last /14th cell group end with thick Red wire attached. If you get a reading of 58.8 v or a little under then the BMS is at fault or a sleep.
To wake up the BMS disconnect the multiplug with all the thin wires, one will have to clean off the silicone first. Then reconnect the multiplug and take a proper discharge reading from the battery output.

Some say reverse charge the BMS via the discharge however I wouldn't as this could damage the BMS unless it is a same port BMS and this one isn't as it utilises a separate charge input.

 

[Nealh]

Cells are panasonic either PF or 18650b, pretty reasonable cells so they shouldn't fail unless the BMS has drained them.

 

[RichB]

Probed the first and last cell group as above, shows 56.6v? Is it worth a BMS reset or is it cooked?

 

[Nealh]

56.6v says that IF all cell groups are equal then they are at 4.04v each which is good.
Though it is likely possible that one or two cell groups may be at or under 3v.

One will have to probe each cell group individually and write down the 14 results for us to see.

 

[RichB]

56.6v says that IF all cell groups are equal then they are at 4.04v each which is good.
Though it is likely possible that one or two cell groups may be at or under 3v.

One will have to probe each cell group individually and write down the 14 results for us to see.

Bad news, all showing about 4v other than the last group which is showing 0v (zero). Checked all the wiring on the group and all looks good, so I presume there's nothing else I can do?

 

[matthewslack]

Might be game over as a 52V 14s pack, but could be reworked as 48V 13s.

 

[RichB]

Can I 'remove' the bad cells, ending up with a 48v or something, or is it best to just bin it?

 

[RichB]

Might be game over as a 52V 14s pack, but could be reworked as 48V 13s.

How would I go about doing that? Just disconnect the bad cells? Would BMS need changing? And I guess a new charger?

 

[matthewslack]

The battery builders here are better placed to advise, but in summary a 13S BMS instead of the existing 14S, with the major connections to the cell pack in the right places, and a matching charger.

With 13 out of 14 cell groups looking OK, would be a shame to scrap it.

 

[Bikes4two]

Bad news, all showing about 4v other than the last group which is showing 0v (zero). Checked all the wiring on the group and all looks good, so I presume there's nothing else I can do?

I'm suspecting that that last reading of zero volts might be down to not connecting the multimeter to the right point as although I'm far from being as knowledgeable as some on here, surely a duff cell would give some sort of reading?

I'd advise you to get a reasonable understanding of the various connections to be found in an ebike battery - balance wires, charging port and so on. A google images search on something like '52v ebike bms schematic diagram' will improve your understanding at what you're visually looking at.

Here's a typical schematic:

 

[Bikes4two]

Some say reverse charge the BMS via the discharge however I wouldn't as this could damage the BMS unless it is a same port BMS and this one isn't as it utilises a separate charge input.

Hi Neal, does what you say above always hold true? I ask as:

• my bottle battery has a charging port and after a BMS charging problem, I did out of desparation start charging through the discharge port
• I also reconfigured the wiring for 'discharge byepass mode' as my TSDZ2 controller looks after LVC and discharge current management.
• I routinely check the cell group balance and after 4,000Km of use the cell groups are still within one tenth of a volt of each other.
• It would seem that my BMS still balances as surely after many charging cycles through the discharge port would have lead to imbalance otherwise would it not?
• My BMS is below - it is a mystery to me (at the moment) as to why all is well so far - I have a new BMS in the tool box but I haven't found a reason to install it - every day's a school day it seems!
• 

 

[matthewslack]

I don't know, but suspect BMS takes its power needs from the bottom cell group, which is why that one is 0V and the rest OK.