Can this battery be revived?

[saneagle]

Something wrong with your maths or measurement.
Cell pack is 56.6v
13 x 4.04v + 1 x 0v = 52.52V
14 x4.04v =56.56v, so all good. Maybe check your switch, or just unplug the multi-pin connector and plug it back in again. You did remember to switch it on, right?

 

[RichB]

Something wrong with your maths or measurement.
Cell pack is 56.6v
13 x 4.04v + 1 x 0v = 52.52V
14 x4.04v =56.56v, so all good. Maybe check your switch, or just unplug the multi-pin connector and plug it back in again. You did remember to switch it on, right?

I didn't have it switched on, but then that wouldn't make any difference would it as I measured it at the battery?
I'm out at the moment, so can't check. But if everything is all OK cells wise, why would it not take a charge and it is still outputting 30 something volts at the battery connection (ie, where you plug it into the motor)

 

[WheezyRider]

I didn't have it switched on, but then that wouldn't make any difference would it as I measured it at the battery?
I'm out at the moment, so can't check. But if everything is all OK cells wise, why would it not take a charge and it is still outputting 30 something volts at the battery connection (ie, where you plug it into the motor)

It sounds like there is an issue with the BMS. As people have said, if you are getting 13 x 4V, the last bank must be doing something more than zero in order to get 56.6V.

A BMS can output less than the pack voltage if there is a fault. This happened to me when I had a loose connection on one of the sense wires. Voltage from the pack was only a fraction of what it should have been, but when you squeezed the pack, the BMS gave the right voltage. It turned out to be a frayed sense wire. Once resoldered all was well again.

I would disconnect the sense wires from the BMS and carefully measure the voltages you get from each of the sense wires going into the BMS connector.

 

[WheezyRider]

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.

I don't think that's the case, it would tend to put the pack out of balance. Also, most MOSFETs need more than 4 to 6V to fully saturate. If a cell bank is only 3V, the MOSFET would not turn on fully and a lot of power would be dissipated in the BMS.

 

[RichB]

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:
View attachment 49565

Yes, that looks like the same set up as mine and using a meter on B14 as it is on that diagram, shows zero volts.
I'm going to recheck all the wiring tomorrow but certainly couldn't see anything obvious today.

 

[saneagle]

I didn't have it switched on, but then that wouldn't make any difference would it as I measured it at the battery?
I'm out at the moment, so can't check. But if everything is all OK cells wise, why would it not take a charge and it is still outputting 30 something volts at the battery connection (ie, where you plug it into the motor)

You can measure something like 18v to 30v leakage charge on the output when it's switched off. That's how you know when your BMS is switched off. The only question is why the BMS is switched off. It could be because you didn't switch it on, or it went to sleep.

 

[Nealh]

Just got in from work so not seen the updates until now, as I said earlier and as D8ve has also reiterated the cell pack appears fine. We need to see the actual 14 voltage readings in writing.
56.6v / 14 = 4.04v each which is pretty good, with 56.6v if a cell group was 0 then the others would read 4.35v which is bad. One suspects one didn't probe correctly for a good contact.
If the BMS has gone to sleep remove the thin sense wire multi connector then refit it to see it the BMS wakes up.

The pack is to good to bin , it simply may need new BMS if all the cell groups read ok and the BMS cant be woken up.

As mentioned the 30v reading is because the BMS has shut down.

 

[Nealh]

Whether a battery can be charged via the discharge wiring depends on the mosfet type used. P types aren't for reverse charging whilst N type are.
One can apply a 10/15 sec reverse charge to try and wake up a BMS or disconnect & re connect the multi wire jst connection .

A few reasons not reverse charge as a matter of course if a seperate port BMS is used.

• Applying to much current.
• Connecting polarity incorrectly.
• Damaging a good BMS.
• Not knowing mosfet type used.

I have never taken much notice of the mosfet designation but should do.
For sure a same port BMS must be a N type and it may be that some separate port BMS may be N type but unless one is sure then mosfet damage may likely occur.

 

[RichB]

Just got in from work so not seen the updates until now, as I said earlier and as D8ve has also reiterated the cell pack appears fine. We need to see the actual 14 voltage readings in writing.
56.6v / 14 = 4.04v each which is pretty good, with 56.6v if a cell group was 0 then the others would read 4.35v which is bad. One suspects one didn't probe correctly for a good contact.
If the BMS has gone to sleep remove the thin sense wire multi connector then refit it to see it the BMS wakes up.

The pack is to good to bin , it simply may need new BMS if all the cell groups read ok and the BMS cant be woken up.

As mentioned the 30v reading is because the BMS has shut down.

Thank you for the comprehensive reply, especially straight after work, much appreciated.
I will take a look again today and write down the actual voltages and take it from there. Good to know that all may not be lost.
I did unplug the BMS and plug back in and that has not made any difference though, so doesn't look like that will work to bring the BMS back to life. If the last resort is a reverse charge, how would I do that? A direct connection to the charger with the battery output connections?

 

[Nealh]

Yes direct charging via the discharge connection but only for 10/15 secs to shock the system , of course polarity has to be correct and an adapter from charger to battery made up.

 

[egroover]

Just got in from work so not seen the updates until now, as I said earlier and as D8ve has also reiterated the cell pack appears fine. We need to see the actual 14 voltage readings in writing.
56.6v / 14 = 4.04v each which is pretty good, with 56.6v if a cell group was 0 then the others would read 4.35v which is bad. One suspects one didn't probe correctly for a good contact.
If the BMS has gone to sleep remove the thin sense wire multi connector then refit it to see it the BMS wakes up.

The pack is to good to bin , it simply may need new BMS if all the cell groups read ok and the BMS cant be woken up.

As mentioned the 30v reading is because the BMS has shut down.

Off topic, forgive me, but is WheezyRider aka D8ve aka vfr400? If so, glad you have returned with your helpful knowledge and experience. Blame Nealh for blowing your cover lol. Anyway a belated welcome back

 

[Nealh]

Off topic, forgive me, but is WheezyRider aka D8ve aka vfr400? If so, glad you have returned with your helpful knowledge and experience. Blame Nealh for blowing your cover lol. Anyway a belated welcome back

I don't know, tbh I haven't even thought about WR as being D8veh not that it matters.
Some of us though know another alias being used.

 

[WheezyRider]

Off topic, forgive me, but is WheezyRider aka D8ve aka vfr400? If so, glad you have returned with your helpful knowledge and experience. Blame Nealh for blowing your cover lol. Anyway a belated welcome back

No, I'm certainly not D8ve or vfr400. If you look back in the history you will see we have had our fair share of - "discussions". Sorry to disappoint

 

[egroover]

No, I'm certainly not D8ve or vfr400. If you look back in the history you will see we have had our fair share of - "discussions". Sorry to disappoint

Sorry Wheezy, I think I went all Columbo and failed miserably. It was Nealh line earlier in the thread mentioning D8ve that prompted the thought D8ve/VFR400 was back on the forum under a new alias, clearly not the case. As Nealh says, it matters not either way.
I'll get my (Trench) coat

 

[Nealh]

As I metioned d8evh/vfr is on the forum and posts but not as much as previously, the alias used is one that belonged to a late friend of his.

 

[RichB]

Hi all,
Sorry for the delay, just been out this morning with the multimeter again.
Pack in total (at first and last cell) is showing 56v .
I then measured each point on the plug in point, points 1 to 13 are showing 4.1volts on every point from 1 to 13. Point 14 is still showing 0v.
So 13 x 4.1 = 53.3, so I'm missing some volts somewhere!
I checked all of the wiring from the battery to the plug and all appears good with no obvious breaks or weak spots. However, just putting the meter on just the cells on the last pack also shows zero, although putting it on the last TWO packs then shows 8.3v, so I'm fairly certain that the last pack has power in it but I just cant work out why it is not showing?
I have plugged the BMS sensor plug back in and still no difference, when charger is connected still 'clicking' on and then off constantly.
Is a reverse charge worth a try or does the unplugging/pluging back in of the sensor wires normally wake it?
Thanks again

 

[matthewslack]

I'd keep looking for those missing volts first! If you can understand that issue, it may be related.

You have 14 cell groups, so 15 places that your meter probes need to go to measure all cell groups. There should be 14 red and one black wires on the balance connector. Those should give access to the points you need to probe.

 

[RichB]

I'd keep looking for those missing volts first! If you can understand that issue, it may be related.

You have 14 cell groups, so 15 places that your meter probes need to go to measure all cell groups. There should be 14 red and one black wires on the balance connector. Those should give access to the points you need to probe.

Yeah, I agreee, it's that B14 point that is the issue, I feel like if I could get a voltage through that point it would solve the issue but I can't work out why the wire/first group of cells isn't showing a charge?

 

[flecc]

is D8ve aka vfr400?

Don't mix up D8ve and D8veh, they are two different people.

in This Post D8ve thanks D8veh for his help.

Many believe D8veh became vfr400 and then later on, Saneagle.
.

 

[matthewslack]

Yeah, I agreee, it's that B14 point that is the issue, I feel like if I could get a voltage through that point it would solve the issue but I can't work out why the wire/first group of cells isn't showing a charge?

My cheap multimeter probes sometimes have to be pushed very firmly to get a good contact.

I would start at the cells, and get 14 valid voltages measured directly there, which must be possible because of the overall 56V or so. Then repeat measuring on the balance connector wiring.

It should be possible to get the same reading whether you probe directly on the cells or on the wiring. Anywhere it isn't the same, then inspect really closely, or double check meter probe contact quality.

I would not do anything else until the voltage measurements at cells and connector are understood and correct. There will be a reason.