How to Revive a Dead battery that was sitting for a couple years

[fechter]

I don't think it's a big deal to go a little over 4.2v. It's just not ideal for battery life. As long as the charger shuts off when it's done, it won't be a big deal. I've seen many small devices that charger the cells to 4.3v to get a faster charge. The voltage you are reading from the charger may be a bit off if there is no battery attached. If you put a small load (resistor, 12v light bulb, etc.) on the output, the reading will be more accurate.

 

[From-A-To-B]

So far I haven't been able to get the charger to charge past 4.225 volts.

This is your BMS doing its job and preventing overcharge. Many BMS’s are set to stop charge when a group hits 4.25V. Sounds like charge shuts down, and cells relax to 4.22V.

I don't feel like baby sitting the charger all the time, it's annoying...

I recommend you invest decent money (more than $5) into a charger so you don’t have to babysit it.

... Why won't it charge up to 12.45? perhaps the BMS won't let the battery charge beyond a certain point? I am doing independent research on this diode charger thing as we speak.

Your BMS is doing its best to thwart your attempts to overcharge these cells. Take it easy, there, pal.

 

[MarkJohnston]

To A to B

I am stress testing this battery. It will need to do heavy duty cycle on my bike. It will be getting knocked around a bit. I need to be sure its safe. Charge and discharge a few times in a fire safe environment. See what happens if left on the charger, etc. All tests

One thing that is a little strange. Maybe its just when the battery at fullcharge, but the BMS BaLANCES, the cell groups like this. 4.21,4.20,4.19, a little weird if you ask me. Maybe its just because its overcharged slightly.BMS does have an included balance circuit at 100 MA. Quite slow.

Edit: so far after discharging again, the BMS now had all cells evenly at the same voltage. Knock on wood, this will last and it was just a temp thing while it was overcharged

 

[MarkJohnston]

Ok.

I managed to get the battery up to 50 volts. But it got cut off right there. The bad cells got pretty warm. Battery it suppose to charge up to 54.6 volts. The cell group that got warm is the one that can't seem to hold it's voltage. keeps dropping more every day.

Time to part the battery out?

 

[fechter]

If the cells are getting warm and self-discharging, they're toast. The ones getting warm are in danger of catching fire.

 

[MarkJohnston]

If the cells are getting warm and self-discharging, they're toast. The ones getting warm are in danger of catching fire.

Ok..

My question is now whether I should disconnect the BMS from the battery for storage? Im pretty sure the BMS drained the cells to begin with.I dont have time to part out the battery right now.

I dont want.the good cells getting drained too. If you Dont Recommend disconnecting BMS, is it safe to charge the battery to keep the good cells healthy?

 

[nicobie]

I'm not even close to being as technically knowledgeable as fechter, but I never trust any BMS. I don't think it will hurt anything to disconnect it. And might save you from a big problem.

 

[MarkJohnston]

I'm not even close to being as technically knowledgeable as fechter, but I never trust any BMS. I don't think it will hurt anything to disconnect it. And might save you from a big problem.

YEah both BMS seems to be working, though with the new one it seems to me that one of the parralel groups will go pretty quit. THat's fine, I am an 18650 hoarder.

 

[MarkJohnston]

YEah both BMS seems to be working, though with the new one it seems to me that one of the parralel groups will go pretty quit. THat's fine, I am an 18650 hoarder.

Why on some BMS's there is a balance cable for the negative and positive side of the parralel cell group going to the pin connector ? So basically one group of six cells is two in series? I can't see the top of the groups to confirm till I dismantle

 

[fechter]

It's a fairly common failure for one or more BMS channels balancing shunts to get stuck on. This places a small but steady drain on the cells which will cause the voltage to drop over time. This can be tested by just watching the voltages over time. If a cell group is dropping, disconnect the BMS and see if it continues to drop. You can also disconnect the BMS and use an ohmmeter across each connection to look for any that have about 100 ohms showing.

 

[MarkJohnston]

It's a fairly common failure for one or more BMS channels balancing shunts to get stuck on. This places a small but steady drain on the cells which will cause the voltage to drop over time. This can be tested by just watching the voltages over time. If a cell group is dropping, disconnect the BMS and see if it continues to drop. You can also disconnect the BMS and use an ohmmeter across each connection to look for any that have about 100 ohms showing.

is it safe to store a battery without the BMS connected? I don't want a fire started, while in storage. do you mean an ohm meter in series with the negative and positive of the cell groups ? I still don't understand why the this battery, there is a balance lead on the positive and negative of the cell groups.

 

[fechter]

Yes, you can store a battery with the BMS disconnected. This eliminates any parasitic drain from the BMS, which is always present.

The BMS will typically have a row of wires that are in order from B- to B+. With the batteries disconnected, you can measure every pair of adjacent wires in the row to look for any that are "stuck on", showing the resistance of the balancing shunt. Normally the resistance should be very high, but the actual reading you get may vary depending on the BMS circuit and the meter being used. If all the pairs look the same, it's probably OK. If one or two pairs are showing something like 100 ohms, that's bad.

 

[MarkJohnston]

Yes, you can store a battery with the BMS disconnected. This eliminates any parasitic drain from the BMS, which is always present.

The BMS will typically have a row of wires that are in order from B- to B+. With the batteries disconnected, you can measure every pair of adjacent wires in the row to look for any that are "stuck on", showing the resistance of the balancing shunt. Normally the resistance should be very high, but the actual reading you get may vary depending on the BMS circuit and the meter being used. If all the pairs look the same, it's probably OK. If one or two pairs are showing something like 100 ohms, that's bad.

Ok I got the same reading on each pair except for the last pair. I got .800 which I think means 800 ohms for all except the last which was .500 or so. testing with a different meter I got 800 for some and 700 for others. the last pair again being lower.

The voltage did drop significantly. It went from 50 volts to 44 without being discharged. Yeah those groups are definitely toast.

Edit: IT's still at 44.50 volts and holding after I disconnected BMS. Will test again in a couple weeks to make sure it will not drop more

 

[Lucifer]

It's a fairly common failure for one or more BMS channels balancing shunts to get stuck on. This places a small but steady drain on the cells which will cause the voltage to drop over time. This can be tested by just watching the voltages over time. If a cell group is dropping, disconnect the BMS and see if it continues to drop. You can also disconnect the BMS and use an ohmmeter across each connection to look for any that have about 100 ohms showing.

Hi there

Trying to find the best place for this BMS question, this looks close (ish). I have just refurbed a few pouch cell batteries. No Q on that hoping its job done. Got to field testing a battery worked up to a four mile run (up reasonable hill) yesterday came back measured each cell, theres is a variation in cell voltages, Not massive but being a newbie, not sure if this is normal. The batt is 10 pairs of pouch cells, all were 4.1 volts when starting off. On returning..... starting from the -ve of the batt the voltages are (in order 1,2,3 etc..... 3.89, 3.89, 3.90, 3.90, 3.94, 3.93, 3.93, 3.94. 3.93. 3.94. so overall the differential is only .05 v (which is hardly anything now I think about it). So I'm think that's hopefully nothing to be concerned about?

Looks like a voltage gradient between -ve end and +ve end of battery beginning to appear, Is that normal?

All the components were used (got about 10 identical batteries v cheap, all had something wrong, but knew I that, So I did a bit of mix n match to produce 4 which "appear" perfect). atm the battery isn't cased yet so I can keep a better eye on it, and easier if I have to do more work on it.

As a bull park at what point would a cell voltage variation indicate a problem that needs attention?

keith

 

[fechter]

0.05v difference isn't anything to worry about. 0.1v is where I would start to worry. The resting voltage is only one thing to look at. The voltage sag under load is possibly more important, but hard to measure. The ultimate capacity of the cell group from fully charged to fully discharged is another one.

 

[Lucifer]

0.05v difference isn't anything to worry about. 0.1v is where I would start to worry. The resting voltage is only one thing to look at. The voltage sag under load is possibly more important, but hard to measure. The ultimate capacity of the cell group from fully charged to fully discharged is another one.

Thanks, did the run again, obviously more overall decrease but this time the max variation was only .04V (all round about 3.75 to 3.79) so looking good at least when resting. At least it's useable, so have not wasted my time, prob call this one ok, but will do a few more trips with it the get a better idea of the range it will give me, then prob call it a day, as I have three more to work through. But for now a happy bunny

Thanks for confirming what I suspected, and giving me a benchmark of .1v as a warning that will be useful as I work through the others, as I still have plenty of spare parts if anything is obviously suspect I can swap it out.

I did buy 2 of these BX100 battery monitors used by RC guys, they only cost a couple of pounds, obviously cheap and basic, but I thought I could rig them up to monitor the cells when in use lead to handle bars. Prob have an accident while I'm trying to read them, LOL needed two cos they only go up to 8 cells (but any number). So I thought 5 cells on each..... Better than nothing and you can set an voltage alarm if any cell drops below Xv.

K

 

[fechter]

I have some similar cheap battery meters. Just be sure to disconnect them when not riding as they drain the battery.

 

[Lucifer]

I have some similar cheap battery meters. Just be sure to disconnect them when not riding as they drain the battery.

I did a quick experiment and found if you disconnect the first wire (-ve) it turns them off. so was just looking on eday for a 2 pole small switch (there are plenty just choosing one)to put in that wire of both then I could turn them both on and off at same time wo having to unplug them, might even make it a momentary switch (push to make) still thinking which would be best.
k