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What brand new 18650 cells should I get for my 3 yr old battery to replace some 0v cells?

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sounds like an obvious answer to replace like with like, but i thought you don't want to mix new and old capacity. My battery has just one parallel pack of 4 that has all 0v cells that needs replacing.

 

  my pack consists of 3500mah LG MJ1's with around 1000miles of riding

is it better to get brand new MJ1's to replace these dead cells OR

is it better to approximate and get brand new 3000mah cells of something else like LG HG2's etc to match more closely the current capacity of these 3 yr old cells?

 

i guess there's at least one more option, but i don't know where to get used MJ1's.

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Posted (edited)

From having done this, it's potentially not a good idea.

The cells are spot-welded to each other, so cumulatively it's a lot of work to remove the dead ones and spot-weld in replacements, then seal up the battery pack.

Years back I took apart three old packs, harvested the best cells from each, and built a "refurb[ished] pack." The first 3 charges were great, but on the 4th charge forward it started losing power. Around the 9th charge the old cells started failing. It was at this point I realized that quality, brand-name cells are like people, although they're all a little different, they tend to age at the same rate and expire at about the same time. There are a few old codgers that last a long time, but they can't keep up with youngsters--they tire quickly and need a rest.

If your pack was not used much and always stored at the proper voltage, replacing the dead cells might work. If you have a moderate to heavily used pack or non-optimal storage conditions it might be an exercise in futility. 

Edited by WI_Hedgehog
changed "batteries" to "cells" in one spot for clarity

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Posted (edited)
11 hours ago, someguy152 said:

is it better to get brand new <3500mah> cells OR
is it better to approximate and get brand new 3000mah cells

Reusing old cells is a hack, no matter which option you choose... but you seem to have come to terms with it :)

I think adding a strong link is better than adding a weak link, so I vote: use original-spec cells.

Once the refurbished pack is charged and balanced, the new cells will likely never fully discharge, since the old cells will drop earlier and bring the pack voltage low enough that the wheel gives you alarms & tiltback. That's acceptable in moderation.

Edited by RagingGrandpa

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1 hour ago, WI_Hedgehog said:

From having done this, it's potentially not a good idea.

The batteries are spot-welded to each other, so cumulatively it's a lot of work to remove the dead ones and spot-weld in replacements, then seal up the battery pack.

Years back I took apart three old packs, harvested the best cells from each, and built a "refurb[ished] pack." The first 3 charges were great, but on the 4th charge forward it started losing power. Around the 9th charge the old cells started failing. It was at this point I realized that quality, brand-name cells are like people, although they're all a little different, they tend to age at the same rate and expire at about the same time. There are a few old codgers that last a long time, but they can't keep up with youngsters--they tire quickly and need a rest.

If your pack was not used much and always stored at the proper voltage, replacing the dead cells might work. If you have a moderate to heavily used pack or non-optimal storage conditions it might be an exercise in futility. 

@WI_Hedgehog based on ur opinion the way i see it, there are then 3 options that might or might not be feasible depending on my bravery of handling the battery

1) sell the battery as is, or break it up into individuals and sell by cell

3) ignore the last 4 packs in series, as the bad cell is the 12th one out of 16 https://ibb.co/album/hj68tv. and reroute the wiring so that i have a 10S or 11S battery, perfect for a low voltage bike or skateboard.  This seem easiest, but if i have to get another BMS because you can't use a 16S one on a 10S, then i could also shave off 25% of the weight   doing it properly by snipping the connections to the last 4 series packs.

 

3) reroute my bms so it ignores the connection between the dead cells and becomes a 15s to be repurposed as a bike battery or skate battery, (the dead cells essentially become a high resistance "wire". I feel everyone will say that's a bad idea but they're already at 0v and who knows how long i was already riding on them at 0v before i discovered the problem.   This seems second easiest

Alternatively it'd be more work,  but i could snip the connections to these 0v cells and remove them and then rewire it to get a proper 15s for a ebike.

 

am i missing anything?
 

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40 minutes ago, RagingGrandpa said:

I think adding a strong link is better than adding a weak link, so I vote: use original-spec cells.

@RagingGrandpa

that's what i was thinking, too. i thought i read somewhere that these new higher capacity cells just won't be full but the voltages should stay around the same as the other ones. Not sure i understand that

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7 minutes ago, someguy152 said:

reroute my bms so it ignores the connection between the dead cells and becomes a 15s

Yes that's nice from a practical standpoint, but raises two problems:

  • It's a 16s BMS- it will know one cell group is missing (0V). Given this, will the BMS still allow normal charging, balancing, and discharging?
     
  • You now need a 15s charger.
    Using your old 16s charger would rely on the BMS charge-shutoff to prevent fires- this shutoff is supposed to be "plan B," not "plan A" - relying on it leaves no safety net.
     
5 minutes ago, someguy152 said:

i read somewhere that these new higher capacity cells just won't be full but the voltages should stay around the same as the other ones. Not sure i understand that

If you were to replace one cell in a parallel group, its voltage would match the old cells in its group.

But you're not doing that; instead you're replacing an entire parallel group. So your new group (with its different capacity) is free to live at a different SOC (and voltage) than the other, old cells in your pack.

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Posted (edited)
13 hours ago, someguy152 said:

My battery has just one parallel pack of 4 that has all 0v cells that needs replacing.

3500mah LG MJ1's with around 1000miles of riding

From the terms you use I'm not sure if you have a 16S-1P or 18S-4P pack, though it does sound like you have just one pack. (S=cells in series, P=cells in parallel)

Generally you're safe replacing one series of cells (simplified examples):

5S-1P
+01-02-03-xx-05+ (replace all cells)

5S-3P
+01-02-03-04-05+
+01-02-03-xx-05+ (replace these cells)
+01-02-03-04-05+

Edited by WI_Hedgehog

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12 minutes ago, WI_Hedgehog said:

From the terms you use I'm not sure if you have a 16S-1P or 18S-4P pack

16s-4p.

EUC model is KS18S. (Not confusing at all, right?)

2 hours ago, someguy152 said:

 

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In my mostly humble opinion, that does not seem like a lot of miles on a 16S-4P pack that's been maintained.

4.12V (under-charged, okay) on one branch vs. 4.23V (over-charged, bad) on another is a huge swing, I have to wonder why this is.

You have a very nice wheel. Is the pack balance-charging correctly?

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3 hours ago, RagingGrandpa said:

es that's nice from a practical standpoint, but raises two problems:

  • It's a 16s BMS- it will know one cell group is missing (0V). Given this, will the BMS still allow normal charging, balancing, and discharging?
     
  • You now need a 15s charger.
    Using your old 16s charger would rely on the BMS charge-shutoff to prevent fires- this shutoff is supposed to be "plan B," not "plan A" - relying on it leaves no safety net

I don't have a problem buying a 15s bms or whatever bms that  i end up with and soldering the connections on. nor is it hard to find the right charger

the problem is avoiding welding and soldering of 18650's

still there are these "smart" bms that accept a wide range of series connections so how are they able to do it https://www.aliexpress.com/item/32997552090.html

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22 minutes ago, WI_Hedgehog said:

In my mostly humble opinion, that does not seem like a lot of miles on a 16S-4P pack that's been maintained.

4.12V (under-charged, okay) on one branch vs. 4.23V (over-charged, bad) on another is a huge swing, I have to wonder why this is.

You have a very nice wheel. Is the pack balance-charging correctly?

i agree, im very sad i didn't know enough about batteries (and still dont) before buying this lovely wheel perfect for my height for sitting

, and im pretty sure the problem is i never balanced them because ewheels website makes it seem that the fast charger does miracles by keeping it at 80% with every once and a while charging to 100%, but I found out too late that you have to leave at 100% for hours to get them balanced.

 

I took this pack out and left it out, and depleted some of the voltage.  My other two 420wh packs were good when i did so cuz they charged to 67.2, but now i'm getting the same issue, charger stops at 63ish, which makes me think one set of 4 cells is again at 0%.  haven't dissected the device yet.

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19 minutes ago, someguy152 said:

I took this pack out and left it out, and depleted some of the voltage.  My other two 420wh packs were good when i did so cuz they charged to 67.2, but now i'm getting the same issue, charger stops at 63ish, which makes me think one set of 4 cells is again at 0%.  haven't dissected the device yet.

As a note:

Quote

Li-ion must not dip below 2V/cell for any length of time. Copper shunts form inside the cells that can lead to elevated self-discharge or a partial electrical short. If recharged, the cells might become unstable, causing excessive heat or showing other anomalies.

This might cause the safety mechanism to activate.

18650-protection.jpg

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this stuff gives me a headache as  my lack of education results in fear.   i envy most buyers as i feel most arent active on any sort of forum and just spend more time riding and not worrying until the device dies or plummets in performance that they sell it. (but they won't know that their battery had a small chance of going nuclear). ignorance is bliss sometimes.

i often think about selling this wheel and be done with it, but the form factor and it being my first wheel gives me too much attachment. hopefully keeping it motivates me to learn more about how to build a battery.

I posted another thread that got no response from anyone on if i could just put out one of my ks14s or ks16s 420wh packs into the top pack of the 18s.

  I also asked Vicky and Tina at Kingsong and one said i could do it and the other said it wouldn't work.  I think i might just do it to see (outside!) making sure the voltages are the same on the batteries. 

 

 

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1 hour ago, someguy152 said:

there are these "smart" bms that accept a wide range of series connections so how are they able to do it https://www.aliexpress.com/item/32997552090.html

Ah but those are generic BMS, which detect the pack type according to how you install them.

HTB15141d3mH3KVjSZKzq6z2OXXaF.jpg

But your Kingsong EUC has a pack-specific BMS. This is lower cost and more compact... just not reconfigurable.

16 minutes ago, someguy152 said:

i envy most buyers as i feel most arent active on any sort of forum and just spend more time riding and not worrying until the device dies or plummets in performance that they sell it. (but they won't know that their battery had a small chance of going nuclear). ignorance is bliss sometimes.

Totally! And these products are sufficiently idiot-proof that it's only the outliers who find a way to catch wheels on fire ("3rd party fast charger that was rained on," etc). A testament to the manufacturers taking their reputations seriously.

But, you're about to embark on remanufacturing a pack, so good that you're making an effort to understand the systems.

16 minutes ago, someguy152 said:

I posted another thread that got no response from anyone on if i could just put out one of my ks14s or ks16s 420wh packs into the top pack of the 18s.
I also asked Vicky and Tina at Kingsong and one said i could do it and the other said it wouldn't work.  I think i might just do it to see (outside!) making sure the voltages are the same on the batteries.

If it's the same voltage (and you equalize voltages before installation), certainly worth a try!
Be sure it has all the same connections as your old pack (charging input, discharge output... anything else?)

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4 hours ago, RagingGrandpa said:

But your Kingsong EUC has a pack-specific BMS. This is lower cost and more compact... just not reconfigurable.

yes i realized i have almost 0 chance of using one of these bluetooth bms for the top pack of the KS18S as there's so little space and these things are huge.  ugh

 

thanks for the cautionary advice. gotta remember to think about all the variables.

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I have replaced 0V cells on both of my 16S battery packs, and I might soon have to do it the third time. I guess the KS packs aren’t able to perform good enough balancing for the packs to live as long as one would expect.

 Depending on how you see the usage value and usage habits of the wheel, I would probably just replace as many bad cells as I can find and keep finding. But if you want to use the wheel as your main one for a few more years and wish to have it perform as good as possible, you would do best just replacing all the packs with new ones and take your experience as a motivation to balance the new packs rigorously.

 Regarding the fear you mentioned: THAT IS GOOD! An EUC battery pack is a horribly powerful chunk of energy, and it is way too easy to hurt yourself, the wheel, or even t your house when working with the packs at this level. Your fear is what helps you avoid those stupid mistakes, and you will question every action you plan on doing a few times beforehand. This is helpful, but it still requires that you have the required knowledge on what you should do, what you can do, what can you touch, and WITH what can you touch it.

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@mrelwood what spotwelder are you using? have you thought about adding a balance board.  a passive one that you'd do manually every month or so vs an active one like this

or a bluetooth bms to individually monitor the cells?

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33 minutes ago, someguy152 said:

@mrelwood what spotwelder are you using?

I purchase the cells with soldering tabs spot welded by the seller company Nkon.eu. Saved me from trying to learn spot welding connections that absolutely must be secure even after dozens of tumbles and continuous shaking. Worked well, so I sticked to it.

33 minutes ago, someguy152 said:

have you thought about adding a balance board.

No I haven't. My 16S is just a spare wheel, so I don't wish to take much time to improve it. I also expect that now that I've learned about the cruciality of balancing, doing it much more often will prevent the same issues from happening on the MSX.

Given that I have gotten 11 000 km on my MSX in 20 months and that the packs still charge up to where they did when new, it seems that when done often enough, the BMS balancing just might be enough. But every 1/10 charge which was generally recommended is simply not enough.

 

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We don't know for sure that pack would have been fine if you charged it diffierently. It's possible the bms simply isn't balancing. Same happened on my wheel. It's ok to ride without balancing as long as you accept that you need to monitor the pack. By that I mean to solder some balance leads to it and do the 3 month check to see they are somewhat balanced. If not you can top up the low groups with a single cell charger. I use two dirt cheap usb to 4.2v 3A charge modules to quickly bring two self discharging groups into balance. A pack that a bms can no longer balance can be used for many more years this way.

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13 hours ago, mrelwood said:

But every 1/10 charge which was generally recommended is simply not enough.

are you more like every other or every third charge?

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Posted (edited)
13 hours ago, mrelwood said:

But every 1/10 charge which was generally recommended is simply not enough.

 

15 minutes ago, someguy152 said:

are you more like every other or every third charge?

The every 10th charge for balancing has absolutely no rational background. Somehow someone just started with this idea and it developed as recommendation.

In reality it depends on the state ot your cells - balancing every charge could be not enough...

As the ?KS18L/XL? BMS have a connector hidden under the plastic wrap allowing to measure each parallel cell groups voltage it would be recommandable to make some measurement possibilty oneself once one starts messing with a battery pack. Finally its the only way to see ones balancing strategy works or the pack is about to die...

Very comfortable are the "new" smart BMS which allow this per cell diagnosis per mobile telefone - one has just to integrate them properly to the "syncronisation design" of the wheel... :(

ps.: some profound reading in regard to cell matching and balancing: https://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing

Edited by Chriull

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5 minutes ago, someguy152 said:

are you more like every other or every third charge?

No one can give advice anywhere near that precise. The only thing I’m relatively sure about based on my own wheels and what I’ve read on this forum for the last few years is that every 10th time isn’t enough. At least for many if not all KS models. Others could be just fine with that, or then again not. Going any further than that would be just wild guesswork.

What I still haven’t seen though is a wheel that has lost a notable amount of its range due to battery degradation, or from being stored at 100% for too long. Kind of ironic, people bust their batteries at 2000-4000km because they try to extend the battery lifetime upwards from 20 000 km. Which they would never reach anyhow.

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1 hour ago, alcatraz said:

We don't know for sure that pack would have been fine if you charged it diffierently. It's possible the bms simply isn't balancing. Same happened on my wheel. It's ok to ride without balancing as long as you accept that you need to monitor the pack. By that I mean to solder some balance leads to it and do the 3 month check to see they are somewhat balanced. If not you can top up the low groups with a single cell charger.

most of the cell balancers i've seen are for 8s max or else they get prohibitively expensive.

How do you wire up two 8s leads to a 16s battery?

does the 2nd lead's battery negative go to the middle of the pack or go to the total battery negative terminal aka where the first lead would start?

 

1 hour ago, alcatraz said:

I use two dirt cheap usb to 4.2v 3A charge modules to quickly bring two self discharging groups into balance.

any hope of clueing me in on what these are.  I keep debating from using the active balancers i showed above that stay on all the time or the passive ones that you seem to be talking about

i was looking at getting two of these

https://www.aliexpress.com/af/isdt-q8-battgo.html

or two of these bg-8s balancers

or even cheaper cellmeter8

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1 hour ago, Chriull said:

 

The every 10th charge for balancing has absolutely no rational background. Somehow someone just started with this idea and it developed as recommendation.

....

:thumbup:

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