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KS14S Stops charging before 100%

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Hi all!

So, I will try to explain what the issue is as good as I can. The wheel is a ks14s, 840Wh battery.
 

I have a wattmeter between the wheel and the charger. The wheel (through the app) and the wattmeter agree on the voltage with just a 0.2V difference, so I would say the board READS WELL the voltage (important point here).

The wheel has stopped charging at about 63V, the wattmeter says 67.2V and the light is green, 0 amps are flowing. It has stopped all of a sudden.

My sense is that there is a cell that has reached 4.2V and the BMS is cutting the current. (this has been after searching a little bit)

 

Suggestions, alternative explanations, solutions?

Thanks,

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I had a similar issue with 4V "missing".

If your wheel has 2 battery packs, then one might have a dead cell. You could try opening the wheel up and trying to charge one pack at a time. Before connecting both packs together, make sure their voltage is the same.

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Posted (edited)

But I do not want to open it
:(

Anyway, the wheel board and the charger agree on the battery voltage, until it stops charging, and since there is no current flowing, the charger goes back to 67V.

I am thinking on leaving the wheel on with music playing on the speakers until the battery is empty, and charging from there. But I guess this could be days...

 

EDIT: The wheel has 3000km on it and is 1.5 years old, is there any problem with the guarantee?

Edited by Struck

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Lithium ion battery packs do not get fixed by discharging and charging again.

From your description it seems you have a problem. The wheel could be unsafe (faceplant while riding or fire at home) and someone will need to open it for diagnosis. If it's under warranty, contact your seller, if not, then find someone who will repair it for you.

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Posted (edited)

leave it plugged in all day.. at least 12 hours after the green light,, if you have not been charging it properly there is a chance one or more of the cells are out of wack.. you need to let it trickle charge for a long time to let the bms balance it out and hopefully it can be brought back up.. just use the standard charger and leave it for minimum 12 hours and then see what it's at.. if that doesn't fix it then you have a problem that's going to need to be diagnosed by someone who knows what they're doing.. this has the potential the be dangerous to you, most likely bad case is a cutoff if you ride it too low and one of the bad cells goes below 3.0.. it shouldn't happen because there are safeguards but it's not unheard of.. btw don't drain the battery that will only worsen it, it's not good practice to drain lithium batteries as it can damage them

Edited by Rywokast

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17 hours ago, Struck said:

I have a wattmeter between the wheel and the charger. The wheel (through the app) and the wattmeter agree on the voltage with just a 0.2V difference, so I would say the board READS WELL the voltage (important point here).

The wheel has stopped charging at about 63V, the wattmeter says 67.2V and the light is green, 0 amps are flowing. It has stopped all of a sudden.

My sense is that there is a cell that has reached 4.2V and the BMS is cutting the current. (this has been after searching a little bit)

Is my understanding of this situation, too.

The BMS cuts off the charging input once one cell reaches t/about 4.28V - a normal cell overcharge protection all wheel BMS have.

Quote

Suggestions, alternative explanations, solutions?

Thanks,

As there are about 4.2V "missing", you have (a) bad cell(s).

Solution : Replace the cells or buy a new pack.

As the Ks14c 840Wh has two similar packs chances are given that only one pack is bad.

34 minutes ago, Struck said:

But I do not want to open it
:(

Without opening you can just sell this and get a new wheel...

Or get it repaired - but most presumably with shipping and repair costs a new one will be the much better(cheaper) option.

34 minutes ago, Struck said:

I am thinking on leaving the wheel on with music playing on the speakers until the battery is empty, and charging from there. But I guess this could be days...

Won't change anything...

Theoretically but unlikely it could be that one cell stopped the charging at 4.28V and the other 15 cells stayer equally at 3.9V.

But in every case the BMS could not balance your pack till now and more important it let the cells go out of balance! So it won't have any chance to balance it in the future - cells only get worse over time, there is no "magical" selfhealing...

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20 minutes ago, Rywokast said:

leave it plugged in all day.. at least 12 hours after the green light,, if you have not been charging it properly there is a chance one or more of the cells are out of wack

Could maybe be a last chance, if @Struck did charge the wheel too short till now...

But the batteries need to be as much discharged before, that the BMS does not cut off. (Wattmeter showing no current)

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I hate complaining to the store :( But it looks like I have to send it

 

7 minutes ago, Chriull said:

Could maybe be a last chance, if @Struck did charge the wheel too short till now...

But the batteries need to be as much discharged before, that the BMS does not cut off. (Wattmeter showing no current)

I did not fully understand your last sentence.
There are literally 0.0 Amps flowing to the wheel once it reached the 63V. I don't see any balancing there, right? Something should flow in. And 67.2 - 4.2 = 63 makes total sense, there is a "row" gone bad :(

 

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17 minutes ago, Struck said:

I did not fully understand your last sentence.
There are literally 0.0 Amps flowing to the wheel once it reached the 63V. I don't see any balancing there, right? 

Yes - the BMS cuts off once the first cell reaches about 4.28V. Then no balancing can happen anymore.

So one has to discharge the pack a bit and then recharge it. Since balancing (normally) just starts around 4.2V not too much discharge is needed.

Once the BMS cut off again rinse abd repeat.

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okay, will try that. And just spoke with my store. They will give me a good price on a replacement if it is needed. They are on holidays now, so until september I will try a little bit this process, which I assume is not the best for the battery, but worth trying

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This has happened twice to my 16S, once in each pack. I’m certain you also have a dead pair of cells in one of the battery packs.

As explained by @Chriull above, as one of the healthy cells reaches the overvoltage limit, BMS disengages the batteries. No charging happens after this. Leaving it in the charger does nothing, as you noticed, no current flows. This is why balancing can only happen if the cells are fairly close to eachother, so they don’t trigger the overvoltage cutoff.

If you still ride the wheel, do it carefully! The wheel doesn’t have anywhere near the power or range it used to. Only accelerate peacefully.

Replacing one battery pack is not too difficult to do. It’s the only option if you want to keep riding the wheel. If you feel unsure about doing it yourself, you could probably find a fellow wheeler or someone with knowledge in electronics to help you out.

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4 hours ago, Chriull said:

Yes - the BMS cuts off once the first cell reaches about 4.28V. Then no balancing can happen anymore.

Just leave the wheel for ~8 hours, cells above 4.2 V will be discharged to 4.2 V. Lower voltage cells will not be discharged. That is how passive balancing works.

Please correct me if I'm wrong.

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44 minutes ago, Tadas said:

Just leave the wheel for ~8 hours, cells above 4.2 V will be discharged to 4.2 V. Lower voltage cells will not be discharged.

They all should settle a bit - the overcharged cell presumably a bit more.

I would not reccomend trickle overcharging a cell on purpose.

44 minutes ago, Tadas said:

That is how passive balancing works.

Every cell starting from about 4.2V gets a bleeding resistor in parallel, so it gets charged slower then the other lower voltage cells.

So discharging the whole pack a bit seems much safer then doing the settle and trickle charge thing.

44 minutes ago, Tadas said:

Please correct me if I'm wrong.

 

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Thanks to you all!!

I am not afraid of replacing the battery, I am afraid of breaking some plastic "tabs" when opening the wheel.

 

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1 minute ago, Struck said:

Thanks to you all!!

I am not afraid of replacing the battery, I am afraid of breaking some plastic "tabs" when opening the wheel.

trust me you wont.. ive opened many wheels many times, especially kingsongs and though it may sound like its going to break, it definitely wont.. and luckily the 14S has brass inserts and not self tapping screws so you can take it apart as many times as you like without fear of it not staying back together after

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That sounds great.

 

Last question, we are saying here that now the safeness of the wheel has gone down quite a bit.
But we are talking about a 2x420Wh battery packs, one of them presumably damaged, the other one presumably ok.

The "safety level" shouldn't be about the same of the ks14d 420Wh?

Thanks!

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Assuming you have 15S pack on one side and 16S pack on the other.. 15S pack is constantly being overcharged, that will kill the pack eventually. 16S is never getting balancing, which will kill one cell eventually by letting it discharge too much.

Long-term this setup is unsafe and unreliable. How dangerous is it? No one knows, but is it worth to risk a faceplant or a fire?

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That sounds like a horror movie. Will replace the thing very soon. In the meantime speeds of 10kmh / 6mph with my hands prepared in front :p

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Posted (edited)

 

Quote

The "safety level" shouldn't be about the same of the ks14d 420Wh?

I don't think so. The charging is stopped by the BMS whenever any single cell gets past 4.2V. At that point the overall charge will be down at least the 4.2V of the died pair of cells. When the battery gets depleted, the low battery tilt-backs will start based on the total voltage, but the cells will have a variance of at least 0.28V and in my understanding the voltage drop during acceleration will be larger due to the dead pair of cells being a burden to the healthy ones.

Edited by mrelwood

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What happens if I charge separately one battery to 67.2V, and the other stays at 63?

I guess the BMS will shut the current for the one that is at 63, until both reach 63V, am I right?

 

Thanks!

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11 hours ago, Struck said:

What happens if I charge separately one battery to 67.2V, and the other stays at 63?

I guess the BMS will shut the current for the one that is at 63, until both reach 63V, am I right?

No! If you connect battery packs with a large voltage difference, there will be a huge spark as the higher voltage battery will try to ”charge” the lower voltage battery instantly. That means overvoltage for the cells in the faulty pack.

Melted connectors and burnt fingers is a sure outcome, permanent battery damage is probable, and a fire from a battery meltdown is possible.

Edited by mrelwood

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1 hour ago, mrelwood said:

No! If you connect battery packs with a large voltage difference, there will be a huge spark as the higher voltage battery will try to ”charge” the lower voltage battery instantly. That means overvoltage for the cells in the faulty pack.

Melted connectors and burnt fingers is a sure outcome, permanent battery damage is probable, and a fire from a battery meltdown is possible.

So they are connected straightaway? There is not such protection in the BMS / motherboard?

So what happens if one pack suddenly dies? Faceplant? Is the wheel not separating  both energy sources?

Thanks!

 

Edited by Struck

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5 minutes ago, Struck said:

So they are connected straightaway? There is not such protection in the BMS / motherboard?

The S series from KS has some third wire connection between the battery pack?

Could be, that by this the packs are somehow syncronized?

But, if not (or the battery voltage wires get contact while connecting the plugs before the sync wire) one could get fireworks as @mrelwood wrote.

I would not never try to connect two packs with such a voltage difference.

I would also never use a pack with a bad cell - you should replace it!

5 minutes ago, Struck said:

So what happens if one pack suddenly dies? Faceplant? Is the wheel not separating  both energy sources?

In such a - very rare - case one battery should shut down and the other one works on.

Never was really into the function of this third wire between the batteries. And can't really remember a detailed report. I am also not 100% sure if all the S models have this sync wire?

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Thanks Chriull,

I have seen a very thin red wire, next to a bundle of three, where two of them are very thick (red&blue)

The battery pack is labelled "KS-16S", 7Ah, 403Wh (where have my other 17Wh gone?)

I will not try the fireworks think, of course. I am waiting for the replacement of my shop (they say they will try to fix the battery pack first)

In the mean time I have decided to just go with the "safe" one, riding only when needed and slowly.

 

thx,

 

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Hello to everybody and thanks for keeping here with me :p

Finally decided to open the battery pack and measure voltages across.

There are exactly 0V between V7 and V8, all the other dV read 4,18V

The result is this:

battery_V7V8faulty.thumb.jpg.85719371cd065b7ad217c317bace747d.jpg

My shop promised to have somebody experienced in batteries to take a look at it, but apparently that expertise is not coming.

Any suggestions on how to proceed? Should I buy two lgebmj11865 (which I think is the cell being used here) and take it to a shop?

Can I test somehow if the BMS is at fault? A problem similar to what @Tadas had.

Thanks!

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