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V8 charging to only 86%


Kael

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So for about 2 months my V8 has only charged to 97% battery. The LED light on the charger would always remain green and the bars on the wheel wouldn’t become full, no matter how long the wheel was left on charge. I figured hey, maybe the battery has degraded slightly, no big deal. I’ve done a couple of rides where I fully depleted the battery thinking maybe that would reset it, but that hasn’t helped.

This weekend it now seems my V8 gets ‘stuck’ at 86% and won’t charge any further than that. That’s a bit of an unreasonable jump and I haven’t exactly done huge amounts of riding recently to warrant that. Pretty sure you should get 300-600 cycles of 100% charging with Li-Ion batteries. Barely used my wheel over winter so I can’t have done more than 80-100.

So I’m wondering if it’s the BMS or the charger.  Anyone else had similar problems?

Edited by Kael
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So it seems like you didn't really reach any kind of solution, but you're pretty sure it's a problem with the charger itself? The charging light was green at 86% charge today.

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5 hours ago, Kael said:

So it seems like you didn't really reach any kind of solution, but you're pretty sure it's a problem with the charger itself? The charging light was green at 86% charge today.

Yes, I believe it is. Although somehow my chargers miraculously work again for now. Full charge with green light brings my V8 to 84.5 - 84.6V again now. So it still remains a mystery for my case. :ph34r:

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That seems weird for sure. Just measured mine. It still only charges to 85% and 80.9V after running it totally flat and recharging. Messaged my support rep and will see what he says.

I honestly don't think the V8 is the ultra reliable wheel it's cracked up to be sometimes.

Edited by Kael
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  • 3 years later...

sorry to wake up an old topic, just bought a brand new V8F, and after a night of charging, it is only charging to 85%, so I am still looking on the web for a tip - I measured the voltage that comes out from the charger, it seems a bit low at only 84.2V with no load (electronics designer nerd here)

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4 hours ago, LaurV said:

sorry to wake up an old topic, just bought a brand new V8F, and after a night of charging, it is only charging to 85%, so I am still looking on the web for a tip - I measured the voltage that comes out from the charger, it seems a bit low at only 84.2V with no load (electronics designer nerd here)

84.2V no load from the charger is perfect, as the V8F is an 84V wheel!

Most likely your battery came DOA - seems like some dead cell group or a malfunctioning BMS.

Best to get in contact with your reseller and get some replacement!

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4 hours ago, Chriull said:

84.2V no load from the charger is perfect, as the V8F is an 84V wheel!

Most likely your battery came DOA - seems like some dead cell group or a malfunctioning BMS.

Best to get in contact with your reseller and get some replacement!

@LaurV Adding to this: it’s worth emphasizing that a dead cell or malfunctioning bms is what’s consistent with the issue you described. This is further indicated after confirming the charger is working as normal, which you already have.

Do not treat this matter lackadaisically. Get a replacement or refund for this worked out as soon as you can. It is not safe to ride your wheel as it may shut off mid ride without warning. A wheel that turns off mid-ride will not slow down gently, it will go immediately slack and likely cause an accident. Furthermore, I would not try and charge it anymore either. Not to say that yours will, but on rare instances electrical issues like this have preceded eucs catching on fire when ignored.

I don’t want to alarm you, but I do want to ensure you’re informed so you can meet the situation with an appropriate timely response. Best of luck to you sorting this out. 

Edited by Denny Paul
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  • 3 weeks later...
  • 4 months later...

Updates to the topic, sorry for the long sleep, I had other things to do than browsing these forums, my money here are all on a firmware bug. I work as a firmware developer and electronic designer for industrial electronics, so, believe me that I know how to use a multimeter. I have used that V8F wheel since I bought it in February, and the fact that it won't charge to 100% didn't bother me so much. I mean physically. It bothered my OCD and my pride a lot. At the time I bought this wheel with the hope that my wife will learn to ride (she is a small person), but it seems that I am the only loco guy in my family, haha, she is not interested, and no way to convince her. I use this wheel sometimes in the evening when I come from the job too tired to wrestle with a larger wheel, and I really love it. I also modded it to change the angle of the footrest plates (from flat to V-shaped like for larger wheels) and it became a totally different wheel after that (no more scratches of the tips of the "pedals" when turning). I also use it when it rains, as it stands the water better than the larger wheels I have (RS for example, totally sucks when it comes to rain). In this period it rains a lot here around (northern Thailand). Meantime I measured the charger with an electronic load, and measured the batteries, which seem balanced enough, and charged enough (but indeed, not to 4.2V). As said, I believe there is a firmware bug. The charger is quite "stupid", in the sense that there is just a normal AC to DC converter, and voltage stabilizer, few poer ICs, no microcontroller or what we would call "intelligent". Yes, I played with the potentiometers that control the voltage or the current, too. There is a LED which turns red if the load (that is, your unicycle) sucks more than 400mA, or stays green otherwise. But how much current to suck is decided by the wheel's firmware, according with the charging status of your battery. The current is cut immediately, and it does not decrease in time as it would happen if the charger can't give, or the batteries are not balanced. Also, I am a heavy guy and easily push (and keep) this wheel to the "tilt limit" (which is about 30-33km/h in my case, for my weight), and in these conditions, starting from the "full charge" of 89%, I still get a range of about 30km (flat, asphalt), which is similar to what famous youtubers with similar weight and riding style get from their V8F wheels, starting from 100% riding style. The last 3 to 5 km I ride with the wheel showing 0% battery, till it gets the dead tilt and I need to push it home walking it like you would walk the dog. I am still curious if anybody solved this issue by a firmware upgrade, or other way. As I have close to 1000km on this wheel, I "feel" I would open it soon and do a battery pack change, or separate charge with a power supply, to clarify this dilemma once forever.

 

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58 minutes ago, LaurV said:

Meantime I measured the charger with an electronic load, and measured the batteries, which seem balanced enough, and charged enough (but indeed, not to 4.2V)

They are all just charged to ~4.0V.

You are sure you measured 20 times ~4.0V? It's very common in such cases that one or two cell group has some much lower voltage and 18 or 19 cell groups have a bit less then 4.2V.

Batteries viltage is 84V like the charger no load output or just ~80V?

58 minutes ago, LaurV said:

The charger is quite "stupid", in the sense that there is just a normal AC to DC converter, and voltage stabilizer, few poer ICs, no microcontroller or what we would call "intelligent"

Yes. It's a simple Ac/dc converter with current limiting. Exactly what's needed to charge li ion cells. Just instead of just showing the green led the charge should stop...

As simple as they are, they are either working and maybe misadjusted or not working.

1 hour ago, LaurV said:

As said, I believe there is a firmware bug.

The bms only cuts off once one cell group gets charged beyond ~4.25V.

Some euc motherboards cut charging off if the charging current is too high.

There is nothing within the bms or motherboard (neither as electronic components or firmware) to stop charging before cells are full.

Some (?newer?) inmotion wheels can calibrate the battery voltage measurement by firmware. So this calibration could be off, if the battery has 84V and the motherboard reports 85% ~80V...

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  • 3 weeks later...
On 8/10/2022 at 8:17 AM, Chriull said:

Some (?newer?) inmotion wheels can calibrate the battery voltage measurement by firmware. So this calibration could be off, if the battery has 84V and the motherboard reports 85% ~80V...

Sorry, could you elaborate a bit more on that? I just acquired a lightly used (less than 200km) Inmotion V8F, and the device stops charging at 85%, 80.5V. Is it likely a calibration issue, dead cell, charger issue, or something else?

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Try a different charger (it's best if you can borrow one).

Try leaving it on the charger for a few hours and see if there's a difference in charge level compared to shorter time.

V8 packs are relatively easy and safe to open up and measure with a multimeter. That would be step three. 20 cell group values. See how much they deviate from eachother.

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5 hours ago, EternalEnigma said:

Sorry, could you elaborate a bit more on that? I just acquired a lightly used (less than 200km) Inmotion V8F, and the device stops charging at 85%, 80.5V. Is it likely a calibration issue, dead cell, charger issue, or something else?

As @alcatrazwrote trying a different charger is the easiest option.

Otherwise the steps would be:

measuring the chargers no load voltage

measuring the battery pakjs voltage and comparing it to the reported voltage

 

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On 8/26/2022 at 7:33 PM, alcatraz said:

Try a different charger (it's best if you can borrow one).

Try leaving it on the charger for a few hours and see if there's a difference in charge level compared to shorter time.

 

On 8/26/2022 at 7:51 PM, Chriull said:

As @alcatrazwrote trying a different charger is the easiest option.

Otherwise the steps would be:

measuring the chargers no load voltage

 

I measured the charger's no load voltage and it shows 83.5V. It doesn't look like a charger problem, but I'm hoping it is...

I've left the unicycle plugged in for a couple hours but it stays around the 85% 80.5V range.

I've followed advice from another thread to gently ride it down to 80V and charge it back up, but it only goes back up to 85%, and light on the charger turned green after around half an hour.

I'll try to find another charger to test it out. Thanks.

 

Edit: I borrowed a charger and my wheel went to 95% before I had to return it. Seems like the charger is the culprit.

Edited by EternalEnigma
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  • 2 weeks later...
On 8/27/2022 at 2:10 AM, alcatraz said:

83.5v without load sounds a bit low. I'd imagine it should show 84.5-85.0v. But I suppose it's also within error margin of the multimeter.

I purchased a charger from YZPOWER. It's rated for 84V, 3.5A, and shows 84.0V on my multimeter.

This one charges up my V8F to a max of 82.2V (98%) as shown on EUC World (about an hour after it turns green), then drops down to 81.9V (96%) when I leave it on the charger for several more hours.

Is that enough for battery balancing purposes, or should I purchase yet another charger?

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6 minutes ago, EternalEnigma said:

Is that enough for battery balancing purposes, or should I purchase yet another charger

It's unlikely that you have a charger issue... I would suspect that your battery pack is starting to fail. You really want to be somewhere above 83ish volts (there is some measurement error).

You can open the wheel, disconnect the packs and measure them directly to confirm. But I'd keep a really close eye on the wheel when it's charging, and would try to charge and store it outdoors or someplace where a fire is inconsequential (fireplace with screen and the flue open!).

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1 minute ago, Tawpie said:

It's unlikely that you have a charger issue... I would suspect that your battery pack is starting to fail. You really want to be somewhere above 83ish volts (there is some measurement error).

My original Inmotion charger that measures 83.5V with my multimeter only charges my V8F up to 80.5V (85%).

A borrowed original Inmotion charger charged my V8F up to 81.8V (96%) before I had to unplug it as the group ride was starting.

This new YZPOWER charger that measures 84.0V with my multimeter charges my V8F up to 82.2V (98%).

 

It's looking a lot like a charger issue to me? Unfortunately the guy with a V8F that lent me his charger came from out of town for the group ride, and I can't find anyone else with an original charger to borrow.

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Yeah... I'm super paranoid about large packs of Li Ion batteries, used to work in portable power and gained a healthy respect for what happens when things go wrong. I'm pretty positive that there are many people with wheels that behave similar to yours and quite honestly, disaster is fairly rare.

But I don't think it's the charger, so I wouldn't spend more money on chargers.

See, your original charger either gave up or the wheel said "enough" when it wasn't fully charged. The borrowed charger also terminated charge 'early', well before the individual cells in the pack would have had a chance to balance charge. You new charger can't get it fully charged either, the fact that voltage dropped when you left it on charger indicates the charger has stopped charging the batteries.

There are two basic reasons that a charger will stop. First is when the current it is delivering falls below a set threshold, this happens when the pack is unable to accept any more charge and with a healthy pack this won't happen until right around 84V. Second is when the battery management system signals the charger to stop charging, this is usually due to the BMS detecting a fault in the battery pack but is sometimes caused by a bad BMS.

If the battery pack won't accept additional charge at or below 83V, it is usually a sign that one or more of the cells in the pack are starting to die, either from age or a myriad of other reasons. If you continue to use cells in this dying state they will get worse and worse and eventually become fire hazards, it's how the chemistry works. Anytime the BMS says "stop charging" and the battery isn't at 84V (and the BMS isn't broken), you do have a serious problem with the pack and I wouldn't ride it or let friends or family ride it AND it would be stored in a fire safe place with the batteries disconnected until I could get the packs replaced. Like I said though, I'm overly paranoid.

Edited by Tawpie
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7 minutes ago, Tawpie said:

See, your original charger either gave up or the wheel said "enough" when it wasn't fully charged. The borrowed charger also terminated charge 'early', well before the individual cells in the pack would have had a chance to balance charge. You new charger can't get it fully charged either, the fact that voltage dropped when you left it on charger indicates the charger has stopped charging the batteries.

The original charger consistently charges to 80.5V, while the YZPOWER charger I recently purchased consistently charges to 82.2V. Well, as consistent as two charges can be since I just received it today. There's definitely something going wrong with the original charger, whether or not there's something also going wrong with the battery is another question.

The borrowed charger terminated early because I pulled the plug as the group ride was starting!

I think it's too early to rule out charger issues until I have a chance to try a known-working original charger to see if it goes to a higher voltage.

 

 

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Be careful before you've confirmed that you don't have a dead cell group. If two chargers can't get it to 100% and it actually stays at that level 1h after you've stopped charging, then something's wrong.

My V8 won't turn on with groups under 3v so I'd just guess there could be two or more groups that are low.

OR the voltage meter in the wheel is way off, reporting the wrong voltage/charge level.

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