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KS18s won't charge beyone 78%. How safe to ride?


someguy152

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I'm having a similar problem described in these threads. see context for all the details i have
 
Unfortunaety i'm going to mexico for 10 days and wont' be able to troubleshoot. I've emailed Jason from ewheels, and he says it should be safe to ride but be more careful at lower voltage.  I'm concerned my packs will become more out of balance or some of the cells might be charging beyond 4.2v to make up for a possibly bad cell (if that's what's causing the issue).   I can live with my beloved 18s even at 80% capacity and going at a max of 16-18mph if need be. but if my concern is right, i should eventually open it up and diagnose.
I'm a little concerned about dissaseembling it, but I know someone here probably knows of a good guide on this forum or video to look at to help.
 
Do you think my problem below is one easily enough solved by a college electrical engineering student?
 
thanks very much
 
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CONTEXT
 
I've had the wheel for 1 yr now, I purchased it from somebody who purchased it from ewheels, but likely the warranty is over.
 
In my year of having the unit, I have charged it to "100%" two or three times (but im not sure how long extra i kept charging when the green leds came on), while mostly keeping it charged around 75 to 80%
 
This just started happening last week, and I've reproduced the problem at least twice (after discharging and riding the wheel and recharging)
 
 
  •  

 here some additional information:

1) The charger shows the green LED
2) Connected via Wheellog App it shows 77% charged and 62.4V
3) the wheel itself shows 8 bars
4)  I've checked it with TWO ewheels smart chargers at various amps and various % settings. I cannot get it to charge beyond this point at any of the settings

5) the Charger got to around 64.1 or 64.2 v (i've always noticed the charger is 1 to 1.5v higher than what wheellog reports) before the green led on the charger lights up and then it showcases 67.2 - sometimes 67.8v

6) I have not checked the voltage on the prongs of the charger yet.

7) i have not opened the device and measured voltage on the battery pack itself

8) I've charged it in two different places/two different outlets using one of the smart chargers

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@someguy152

15 hours ago, someguy152 said:

here some additional information:

...

5) the Charger got to around 64.1 or 64.2 v (i've always noticed the charger is 1 to 1.5v higher than what wheellog reports) before the green led on the charger lights up and then it showcases 67.2 - sometimes 67.8v

...

- So your charger(s) seem to be fine - two of them showing to deliver full voltage.

- The 1-1.5V difference between charger and wheels reported voltage seem "fine" - that's "just" voltage measurement inaccuracies and a bit BMS protection circuitry.

- at ~64V the charger was cut off by the BMS - ( it showef again full voltage of 67.2V and no current). So most presumably one cell (pair) is dead. 15*4.28=64,2V

So i would not risk any charging, especially unattended anymore.

Chances are high that only one of the two battery packs has dead cells. You could try removing/disconnecting alternately one pack and try to charge the single pack in the wheel.

(Much) more careful driving should be possible with one pack - still has 800Wh. 

PS.: Dont't reconnext the batteries once the have different voltages!

 

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Forgot to restore and send my reply after my phone battery died. But I agree with Chriull completely, it sounds very much like the battery has developed a dead cell group. This is not a very big of a surprise since the battery has not had the possibility to balance the cells, as it mostly happens only after the charger light has turned green. Unfortunately this is not mentioned in any EUC user manuals I’ve seen, despite it being a purposefully designed and a crucial feature.

How it happens is that the cell voltages have slowly drifted out of balance, and the cell group with the lowest charge has eventually dropped below what a li-ion battery can survive. Once the 15 functioning cell groups reach 4.2-4.3V during a charge, the BMS stops the charge in order not to overcharge the rest of the cells. 15 * 4.2V = 63V, matching the current behaviour of your wheel very closely.

A big issue in using the battery in it’s current state is that it can’t balance the remaining cells either, since the BMS has to interrupt the charge to prevent a severe overvoltage. So we don’t know how bad some of the other cells currently are, and when more of them will die and decrease the power output even further. Due to this and the additional burden of the dead cells, the voltage drop under stress is a lot larger than it’s supposed to, at every charge level. Risk of overleaning the wheel is already many times higher.

Also, since the charge is only interrupted by the BMS, the batteries may get a slight overcharge every time you charge it to the BMS limit. I wouldn’t make a habit out of it, as I think it also degrades the cells.

The healthier battery alone might provide better power without a significant drop in range than with the bad one dragging along, since the healthier one can probably still be charged to 100% and balance the cells.

I would disconnect both batteries, measure the battery voltages and only connect the higher one (and tape the remaining connectors shut!) to see if it charges to 100%, and leave it on for at least 3 hours after that.

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8 hours ago, Chriull said:

PS.: Dont't reconnext the batteries once the have different voltages!

that's a great tip! maybe woulda forgot that. But wouldn't a .2 v difference maybe be too small of a difference to hurt it? it's just ohms law right so if i know the resistance of the batteries i could figure out the current?

 

Everything you said was basically what Jason said, with the exception of ur calculation of 15x4.28....and that's worrisome.  Jason said i should be okay riding it at least not to crazily at low voltage, but i guess i shouldn't be charging to 64.1v anymore either.

 

as far as the comment about much more careful driving on one (good) battery pack? is that referring to that battery pack might not have neough juice to supply the motor what it needs now?

 

have u seen any guides on disassembly of the ks18s here?

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2 hours ago, mrelwood said:

Forgot to restore and send my reply after my phone battery died. But I agree with Chriull completely, it sounds very much like the battery has developed a dead cell group. This is not a very big of a surprise since the battery has not had the possibility to balance the cells, as it mostly happens only after the charger light has turned green. Unfortunately this is not mentioned in any EUC user manuals I’ve seen, despite it being a purposefully designed and a crucial feature.

How it happens is that the cell voltages have slowly drifted out of balance, and the cell group with the lowest charge has eventually dropped below what a li-ion battery can survive. Once the 15 functioning cell groups reach 4.2-4.3V during a charge, the BMS stops the charge in order not to overcharge the rest of the cells. 15 * 4.2V = 63V, matching the current behaviour of your wheel very closely.

A big issue in using the battery in it’s current state is that it can’t balance the remaining cells either, since the BMS has to interrupt the charge to prevent a severe overvoltage. So we don’t know how bad some of the other cells currently are, and when more of them will die and decrease the power output even further. Due to this and the additional burden of the dead cells, the voltage drop under stress is a lot larger than it’s supposed to, at every charge level. Risk of overleaning the wheel is already many times higher.

Also, since the charge is only interrupted by the BMS, the batteries may get a slight overcharge every time you charge it to the BMS limit. I wouldn’t make a habit out of it, as I think it also degrades the cells.

The healthier battery alone might provide better power without a significant drop in range than with the bad one dragging along, since the healthier one can probably still be charged to 100% and balance the cells.

I would disconnect both batteries, measure the battery voltages and only connect the higher one (and tape the remaining connectors shut!) to see if it charges to 100%, and leave it on for at least 3 hours after that.

thank you for the advice, I think Jason said my 1600wh has three parallel packs 

do u think it's wired like   this:

|controller| ---removable connector----|battery1| ---removable connector----|battery2| ---removable connector----|battery3|

so i have to just unplug and test each battery? Hopefully no soldering is necessary.

 

also, have you seen a disassembly guide? i've seen vids for the ks16s, and theoretically should be the similar process, but having the actual ks18s would keep my mind in a better place when it's actually time.

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53 minutes ago, someguy152 said:

that's a great tip! maybe woulda forgot that. But wouldn't a .2 v difference maybe be too small of a difference to hurt it? it's just ohms law right so if i know the resistance of the batteries i could figure out the current?

Yes. 0.2V difference should be no real prob!

But if one pack really has a bad cell there is no reason to reconnect the bad pack. Although liion cells normaly behave very well even when bad there is still some chance for desaster...

53 minutes ago, someguy152 said:

as far as the comment about much more careful driving on one (good) battery pack? is that referring to that battery pack might not have neough juice to supply the motor what it needs now?

With one instead of two packs (2 instead of three?)  you will have a more "shallow" limit line - so at the same speeds with the same cells charge state ("no load" voltage) you will overlean at lower burdens. (~1/3 or 2/3...)

53 minutes ago, someguy152 said:

have u seen any guides on disassembly of the ks18s here?

Sorry, no.

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Hey guys, 

Can you tell by looking at the eWheels charger that it's balancing? 

Before when I've charged to 100%, once it reached full charge, I've seen the amps fluctuate at a very low level, at a fraction of an amp. Is this the BMS doing the balancing? Then the last time I charged to 100%, the amps read absolute zero for a couple hours, and I'm guessing that means it finished it's balancing?

Edited by erk1024
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26 minutes ago, erk1024 said:

Hey guys, 

Can you tell by looking at the eWheels charger that it's balancing? 

Before when I've charged to 100%, once it reached full charge, I've seen the amps fluctuate at a very low level, at a fraction of an amp. Is this the BMS doing the balancing? Then the last time I charged to 100%, the amps read absolute zero for a couple hours, and I'm guessing that means it finished it's balancing?

In the first phase the charger delivers the full current. Once the battery reaches the full 67.2/84.2V it keeps the voltage and current decreases. In this second phase the balancing happens. Once the current reaches some threshold (usually ~0.1-0.2A) it stops. (Have no idea what is shown on the display then).

If the cells are (too) unbalanced and one cell reaches the upper threshold (~4.28V) the BMS cuts off and the charger shows just full voltage and 0A.

So full voltage and some current decreasing/below max shows balancing, premature charger cut off by BMS mean battery probs (to come?)

 

Edited by Chriull
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As @Chriull wrote. Charging a healthy battery the amperage will slowly drop from the charger maximum to near zero, but never actually reaches zero even after 24 hrs after the charger led turned green. An actual 0.000A indicates a disconnect, most likely by the BMS overvoltage protection.

But if the display only shows two digits after the perioid, it only shows down to 10mA (0.01A), the current may be below that without a disconnect. But it definitely should take several hours to get there.

If the BMS did cut the charge, I’d leave the charger on for several hours every time I charge, to give the BMS a chance to balance the cells for as much as possible. Not sure if that’s the best way to save a badly unbalanced battery though, but it’s the best I can think of.

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It's a newer wheel, had it since August. I was charging from 80% up to 100%. The amps tapered off at some point after about two hours, and then the 3 digit amp display showed zeros for a couple hours. Next time I'll leave it on the charger for more hours. But it's probably balanced, as I charge it up to 100% once a month. The last time I left it on for 9 hours.

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1 hour ago, erk1024 said:

I was charging from 80% up to 100%. The amps tapered off at some point after about two hours,

What was the Battery Wh, max voltage and charger current setting?

But two hours should be anyway a but short according to batteryuniversity's charge graph...

1 hour ago, erk1024 said:

and then the 3 digit amp display showed zeros for a couple hours.

With an decimal point? With max 5A the last digit should be 0.01A? LiIon chargers should stop charging at around 3%C which normaly more in the 0.1A range...

The charger has no special display once he stopped charging?

1 hour ago, erk1024 said:

It's a newer wheel, had it since August

Then everything should be quite fine - but quality issues happen and some (cells start to get misbalanced) packs already are not "perfectly" balanced at manufacturing.

1 hour ago, erk1024 said:

Next time I'll leave it on the charger for more hours. 

If the charger shows zero and this means <0.01A nothing is really going to happen but stressing the cells. Just repeat such full charhes from 80%(90%).

Edited by Chriull
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1 hour ago, Chriull said:

What was the Battery Wh, max voltage and charger current setting?

The wheel is 100V (actually 100.8V right?) 1845wh battery. The eWheels charger is 4+ amps, and the charger was set to 100%. There is a green light when it's done charging. The charger has two decimal points for the amps. There is a silver button to "reset" the charger and start it charging again. After a couple hours, it was reading 0.00, and it stayed like that for a couple more hours before I pulled it off--during which time the light had been green.

Before when I've charged my 84.2V Kingsong, I seem to remember watching a different eWheels charger fluctuate around a quarter of an amp when I was charging to 100%, and I assumed it was busy balancing.

 

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9 hours ago, erk1024 said:

The wheel is 100V (actually 100.8V right?) 1845wh battery. The eWheels charger is 4+ amps, and the charger was set to 100%.

So thats about 18 Ah, so ~18/4=4.5h CC phase + 2..3h CV phase for a full charge .

20% should then be around 1h CC and 2..3h CV.

.... very very roughly estimated ...

So showing 0A == charge stop after only 2h could indicate some misbalanced / factory mismatched cells!

Maybe you note voltage/current every ~10..15 min the next time you charge the wheel?

9 hours ago, erk1024 said:

There is a green light when it's done charging

Imo my charger goes green after the first (CC) phase is finished. Have to examine this once in detail.

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  • 4 months later...
On 10/29/2019 at 4:07 PM, erk1024 said:

It's a newer wheel, had it since August. I was charging from 80% up to 100%. The amps tapered off at some point after about two hours, and then the 3 digit amp display showed zeros for a couple hours. Next time I'll leave it on the charger for more hours. But it's probably balanced, as I charge it up to 100% once a month. The last time I left it on for 9 hours.

currently on my ks16s,

the 5th gen ewheels charger shows 0.00a but the voltage keeps fluctuating from 0.67 to 0.71

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5 hours ago, someguy152 said:

currently on my ks16s,

the 5th gen ewheels charger shows 0.00a but the voltage keeps fluctuating from 0.67 to 0.71

Then it it's not charging anymore (0A) and voltage limiting is a bit "rough"...

Nothing to worry..

Voltage shown is 67 to 71V, i'd assume.

Edited by Chriull
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