Is Wrongway right about V8S BMS?

[mrelwood]

2 hours ago, rcgldr said:

What is the resistance of the Begode resistors?

At least some of the older ones had 120 ohms. But we can't make too many deductions based on a single component value. Balancing is performed by a network of components, many of which can affect the actual bleeding current.

My previous wheel was the 84V MSX. I let the cells balance for a few hours after every charge. I sold the wheel after 14 000 km with no notable reduction in range.

The balancing current in EUCs is generally low, that much has been observed. It is possible that it is even slower in Inmotion wheels than it is in Begodes. Which is further supporting the habit of letting the cells balance every single time you charge the wheel. I don't know what the balancing resistors or current is in the 16S, but balancing every tenth charge and 80% charging the rest only lasted me 4000km before a total pack failure (a cell group at 0V). Balancing every single charge on the V11, the cells were all within 0.01V after the same 4000km. I'd call that a successful balancing design, as long as it is used correctly.

[rcgldr]

1 hour ago, mrelwood said:

Balancing every single charge on the V11, the cells were all within 0.01V after the same 4000km. I'd call that a successful balancing design, as long as it is used correctly.

I'm just a hobbyist, riding about 50 miles | 80 km a month on my V8F. The dealer that sold me my V8F replied to me that balancing once a month would be good enough.

As for the bleeding resistors at 1000 ohms, I don't see how the resistance can be less due to circuitry. On the older ones with 120 ohms, it may be more than 120 ohms, but probably a lot less than 1000 ohms.

[v8nice]

the v5, v8, v10 were created before 2018, on a fairly similar layout, if there is a balancing circuit, this one is badly implanted or badly calibrated because it does not balance all the time or badly, even leaving the charger  long. Or it has a high failure rate. This is the only rational way to explain a high rate of imbalance on these models. I'm not talking about v11, v12, v13, I think they changed the logic  of the bms and the location of the components. It is an established fact that there is a lot of imbalance in the 3 models that I mentioned. I also have Xiaomi mi scooter pro batteries that have done a hundred cycles and which are not  not unbalanced. The new v8f is unbalanced on its own despite long charging each time I plugged it in, and it was already unbalanced when I received it. 83.6V while the load limit is more than 4.2v per  cells. The photos with the voltage readings of each cell, I have shown them.

[v8nice]

maybe someone here has already repaired an inmotion 84v charger? I have the charger of my v8f which does not turn on anymore, suddenly. Open, no trace of grilled components. Sometimes. when I plug it in it turns on in green for several seconds before going out again. I checked the capacitors, everything seems ok. The 220v primary circuit is working well. Do you have any idea, have you already repaired the same fault on a charger? inmotion which are of rather poor reliability, my v5f badly charged 4 days ago, 0.5v less than usual, I thought that again an imbalance was created, but no it was the charger which had slightly decreased its voltage. I opened and adjusted the potentiometer by 1/4 turn and then the charger was again at 84.4. I slightly increased the voltage between 84.5 and 84.6v. Now the wheel is charging up to 84.25v in total, so for the moment the imbalance does not return.

[Chriull]

2 hours ago, mrelwood said:

At least some of the older ones had 120 ohms.

Afair that's about the values used by many KS and GW bms. No idea if this is still the case - did not look at detailed pics of newer bms.

2 hours ago, mrelwood said:

But we can't make too many deductions based on a single component value. Balancing is performed by a network of components, many of which can affect the actual bleeding current.

Passive balancing consists of the following stages:

1) slowing down of charging: activation of the bleeding resistor during charge once a cell reaches about 4.2V. So this cell gets charged a bit slower and the other cells can catch up.

1a) If a cell reached about 4.25V bms cuts off to not overly stress the cell.

2) Bleeding these higher voltage cells downto 4.2V after the charge is complete (charger disconnected, bms cut off)

Now the lower the lower voltage cells are "untouched" and can be charged again for this up to about 0.05V the one cell was bleeded in step 2. This gives up to 19x0.05V ~ 1V balancing possibility!

But only if step 2 is "fully performed". If one discharges the pack by riding or turning on the motherboard _all_ cells get discharged and the 0.05V delta vanishes - no chance of this up to 1V balancing possibility with the next charge cycle anymore.

Step two should take with the 1kOhm resistors quite some time - discharging a 5000mAh cell with 1kOhm takes 1000hours... 2 in parallel 2000 hours.

According to https://batteryuniversity.com/article/bu-409-charging-lithium-ion 5mV with a cut off charge at ~4.2V should be about 2.5% of the capacity. So some up to 25 (50) hours could be needed for bleeding!

(These numbers seem very high and should be double checked?)

Could maybe be "veryfied" by @rcgldr and/or @v8nice by charging until green led shows with the original charger, then disconnect charger und shut off the wheel. After one (two) days same procedure again. Then some notable voltage gain after charging should be notable.

With the "common" bleeding resistances of ~140 Ohms these waiting times are much easier to maintain or to "just happen".

Also, with the "old" designs with charging input at the batteries and not with the mainboard interfering all this happened automatically - bms cut off and turned on again as needed...

Now with the motherboard/firmware taking over the control many things could go wrong...

[v8nice]

so according to your deduction, there is a balancing circuit but it is very often inoperative because of its operating logic. Inmotion never said or even wrote in its manual that the charger should be disconnected and reconnected again 2 days later. They weren't stupid enough not to put the balancing circuit on, but either they didn't check it in real condition, or they don't mind that some wheels won't work properly anymore. , probably after the 1 or 2 year warranty... For most users, charging a wheel is like a phone, we charge at night and hop in the morning, everything must be ok. Or someone to raise awareness of balancing cells, does a long charge from time to time. If it does not work in this way, it is considered faulty. It must be admitted that between no balancing circuit and a faulty balancing circuit, there is little difference. I will do your test over 1 week, charge at the indicator green , disconnected and recharge 2 days later, but how long? How many times do you have to do this? If inmotion told me to do this, I would tell them to send back a wheel that works normally....

[Chriull]

37 minutes ago, v8nice said:

so according to your deduction, there is a balancing circuit but it is very often inoperative because of its operating logic

Top level balancing is designed to equalize small differences of well matched cells.

Once one/some cells detoriate passive top balancing is soon overburdened - there are many reports from all wheel manufacturers with all slightly different designed bms. There are no obvious outliers so one could deduct easily a worse system.

Passive top balancing is not designed to keep mismatched cells balanced.

37 minutes ago, v8nice said:

For most users, charging a wheel is like a phone, we charge at night and hop in the morning, everything must be ok

If one charges the wheel until the green led shows, let it rest some short time before a ride, as normaly done everything is fine.

Imho the main reasons for imbalances are (random order)

- no balancing - "80% charging" to improve cycle count

- badly matched cells

- bad weldings of the nickel strips

- defective bms

- different working temperatures of the cells in a pack

- burdening "empty" packs. The worse for the cells the weaker they already are.

Once some cells are notable deterioated using the pack is not recommandable anymore. It needs manual care and knowledge.

I could not guess how much influence an 1 kOhm bleeding resistor vs an 140 Ohm could have on battery pack life. One can say that the 1kOhm cannot balance deterioated cells as the 140Ohm as easy. Everything else is imho pure speculation.

37 minutes ago, v8nice said:

. I will do your test over 1 week, charge at the indicator green , disconnected and recharge 2 days later, but how long?

Just until green light shows up again.

37 minutes ago, v8nice said:

How many times do you have to do this?

You should notice a voltage gain after the first charge after the first one to two days rest. Maybe 10h (one night) resting already could show results.

Otherwise it could be a defective bms for someother fault?

Edited March 14, 2023 by Chriull

[mrelwood]

 

34 minutes ago, Chriull said:

If one discharges the pack by riding or turning on the motherboard _all_ cells get discharged and the 0.05V delta vanishes - no chance of this up to 1V balancing possibility with the next charge cycle anymore.

Good point. True, if the wheel is ridden before the balancing resistors get to bleed out the overvoltage. The balancing time is a big unknown though.

34 minutes ago, Chriull said:

Step two should take with the 1kOhm resistors quite some time - discharging a 5000mAh cell with 1kOhm takes 1000hours... 2 in parallel 2000 hours.

The BMS only needs to bleed out a very small portion of that though, since there isn’t all that much difference in the amount of energy between 4.2 and 4.5V.

 But while there aren’t many obvious components in place for the balancing, there are several 20-40 pin ICs, whose exact operation (beyond switching the bleeding on/off I’d assume) or purpose is not known. And we don’t know if there are any parallel connections to the bleeding resistor. Or if it engages earlier during charging, etc. We just don’t know, and answers this detailed are impossible to get from the manufacturer.

 

13 minutes ago, v8nice said:

so according to your deduction, there is a balancing circuit but it is very often inoperative because of its operating logic.

That’s how I feel about passive top balancing in general, not just Inmotion.

13 minutes ago, v8nice said:

They weren't stupid enough not to put the balancing circuit on, but either they didn't check it in real condition, or they don't mind that some wheels won't work properly anymore.

A lot of the wheel features we see today are community requests. Smart BMS, cell monitoring, and better balancing have only been requested in the recent few years, so they are only now present in the few latest models. And I would assume that battery issues haven’t been a big enough problem for the manufacturers to improve the BMS further, since the bottom line is generally a big deal to any manufacturer.

13 minutes ago, v8nice said:

Or someone to raise awareness of balancing cells, does a long charge from time to time.

If you haven’t noticed, I’ve been pretty vocal about that in the recent years. My 80% charging video has 5.8K views. (Not that much for YT in general, but it’s my second most watched video.)

13 minutes ago, v8nice said:

If it does not work in this way, it is considered faulty. It must be admitted that between no balancing circuit and a faulty balancing circuit, there is little difference.

Absolutely. The passive top balancing system in almost all EUCs is insufficient for taking use of the cells’ full lifetime.

13 minutes ago, v8nice said:

I will do your test over 1 week, charge at the indicator green , disconnected and recharge 2 days later, but how long? How many times do you have to do this?

Depends completely on the level of the imbalance. 0-4 would be my wild guess that isn’t based on any actual testing or calculations.

I would keep the charger connected for a while after it turns green though, since they tend to turn green pretty early. 300-700mAh is still a decent current for balance charging.

13 minutes ago, v8nice said:

If inmotion told me to do this, I would tell them to send back a wheel that works normally....

The problem is though, that this is normal.

[Chriull]

3 hours ago, mrelwood said:

I would keep the charger connected for a while after it turns green though, since they tend to turn green pretty early. 300-700mAh is still a decent current for balance charging.

For a 4p config 300mA is just a bit above as specified from the manufacturer.

Personaly i'd adjust this current threshold instead on fiddling with the charge voltage like some report here.

If the led turned green because the bms cut off charging and the motherboard stays on discharging the battery the voltage difference for the balancing is again used up.

Some ifs in this last sentence - don't know how this wheel behaves in detail. Even some firmware versions are different... ;(

[Mono]

7 hours ago, v8nice said:

the v5, v8, v10 were created before 2018, on a fairly similar layout, if there is a balancing circuit, this one is badly implanted or badly calibrated because it does not balance all the time or badly, even leaving the charger  long. Or it has a high failure rate. This is the only rational way to explain a high rate of imbalance on these models.

These models have sold at least 20K times and I haven't seen many threads taking about an imbalanced or broken battery. What have I missed? I certainly wouldn't consider 1 in a thousand as "high rate".

[lagger]

14 hours ago, rcgldr said:

The other factor is more important, what has been observed is that V10|V10F BMS halted all charging once any group of parallel cells reached some maximum voltage, before balancing completed. The tech guy observed the halted charging on a V10|V10F BMS, but apparently didn't check to see if there was any balancing activity.

My opinion is that there is passive cell balancing, but the bleeding resistance is too high (too many ohms) to drain cells once they reach the balancing voltage threshold, only slowing down the rate of increase, allowing the voltage to continue to increase and halt all charging before balancing has completed. Mrelwood's video mentions there are 1 k ohm resistors on the Inmotion V11 BMS. What is the resistance of the Begode resistors? Apparently the resistance of the bleeding resistors on KingSong | Begode | Veteran BMS is low enough to drain voltage from any group of cells reaching some maximum voltage along with logic to drain those groups back to balancing voltage or a bit below, so that a single 100% | balancing charge would balance a pack (all groups charged to balancing voltage) no matter how imbalanced it was. The Inmotion BMS issue may be due to the balancing logic chips not being able to dissipate heat as much as the other BMS designs, restricting the bleeding resistors to 1 k ohms.

It could be that the Inmotion BMS is designed such that it is underperforming when the imbalance in cell groups is too high. The idea might be that they expect the groups imbalance in the range that only slight top charge balancing might be needed to keep the pack in a good state. When the battery gets in bad condition e.q. complete discharge while storage it might be that the design is not capable to handle this and the charging and balancing gets cut off faster than the balancing is able to balance the pack. On the other hand if you have a pack in that state maybe you just should throw it away. The idea of balancing and good battery handling practicies is to not get into that state in first place.
This could explain most of the issues that the tech guys, wrong way and the guys here discussed why they see imbalances but most of us dont.

TLDR
My opinion is that the inmotion design is different and doesnt have the capability to fully balance all the groups at one cycle and is designed for lower imbalance in cells qualities or voltage states.

Edited March 14, 2023 by lagger

[rcgldr]

15 hours ago, Chriull said:

Passive balancing consists of the following stages: 1) slowing down of charging: activation of the bleeding resistor during charge once a cell reaches about 4.2V. So this cell gets charged a bit slower and the other cells can catch up.

If you watch Wrong Way's video, there is an animation showing that activation of the bleeding resistor slowly decreases voltage for a parallel group of cells (~150 ohms), as opposed to just slowing the rate of increase (~1000 ohms).  Not mentioned is once a bleeding resistor is activated, there needs to be a second lower voltage trigger to deactivate an activated bleeding resistor. With this design, a single charge will balance a pack, even with a very unbalanced pack (within reason). 

This assumes that the charger doesn't shut off. My ewheels rapid charger shuts off once current drops below 300 ma, which is about 83.4 volts (reported) on my V8F. The stock charger doesn't shut off, so I use that to top off for a full charge, but then it's my V8F that shuts off charging, while still using some power for blue tooth and other circuitry, so pack voltage slowly decreases over time. Once I switch to the stock charger, I have to monitor the voltage and disconnect the charger from my V8F as soon as I see the voltage start to trend down.

Edited March 14, 2023 by rcgldr

[mrelwood]

6 hours ago, rcgldr said:

If you watch Wrong Way's video, there is an animation showing that activation of the bleeding resistor slowly decreases voltage for a parallel group of cells

You probably meant to type “series group of cells”.

6 hours ago, rcgldr said:

Not mentioned is once a bleeding resistor is activated, there needs to be a second lower voltage trigger to deactivate an activated bleeding resistor.

To our knowledge there is only one trigger. Whenever a cell group voltage is above 4.15-4.2V, the resistors are activated. If the voltage drops back below the threshold, the resistor is disengaged.

6 hours ago, rcgldr said:

With this design, a single charge will balance a pack, even with a very unbalanced pack (within reason).

Assuming that there was nothing else in the balancing circuit than the single resistor, a 120 ohm resistor would have a balancing current of 35mA while a 1K resistor would be 4.2mA. So roughly 8 times less, just like 1K is roughly 8 times more than 120 ohms.

So in practice the charging current will always be larger than the balancing current, even with 120 ohm resistors.

 If I’m calculating this correctly, the worst case scenario of bleeding a 2p cell group from 4.25 to 4.2V would take roughly 40 minutes (120R) or 5h 40min (1K).

@Chriull was exactly right, going for a short ride immediately after charging to full does prevent the balancing from doing it’s job. It does seem best to just let it be for the above amount of time, and then checking the voltage and trying charging again.

[v8nice]

my v8f charger no longer works, I ordered an adapter to plug into the ks18xl charger. I hope it's not a problem to use this charger. The only external difference is that there is no earth on the 220v socket.

[rcgldr]

3 hours ago, mrelwood said:

You probably meant to type “series group of cells”.

I meant a parallel group of cells. For a 20S4P, pack there are 20 bleeding resistors, one for each group of 4 parallel cells.

3 hours ago, mrelwood said:

To our knowledge there is only one trigger. Whenever a cell group voltage is above 4.15-4.2V, the resistors are activated. If the voltage drops back below the threshold, the resistor is disengaged.

There needs to be some hysteresis to keep the circuit from oscillating. The animation in Wrong Ways video shows this, once the bleeding resistor is activated, the voltage decreases until it reaches a lower threshold to deactivate the resistor. Something similar to a Schmitt trigger (which has two thresholds).

3 hours ago, mrelwood said:

Assuming that there was nothing else in the balancing circuit than the single resistor, a 120 ohm resistor would have a balancing current of 35mA while a 1K resistor would be 4.2mA.

I looked at some articles about e-bike BMS, with battery packs equivalent to smaller EUCs, and the passive cell balancing current is typically around 200mA. I'm wondering if somehow if the non-Inmotion BMS systems are able to get 200mA+ balancing current, which would more closely match Wrong Way's video animation.

Edited March 15, 2023 by rcgldr

[Chriull]

On 3/14/2023 at 9:29 AM, Chriull said:

 

12 hours ago, rcgldr said:

If you watch Wrong Way's video, there is an animation showing that activation of the bleeding resistor slowly decreases voltage for a parallel group of cells (~150 ohms), as opposed to just slowing the rate of increase (~1000 ohms). 

In my example in https://forum.electricunicycle.org/topic/22109-passive-balancing-a-simulation/

(3rd graph, blue line) one sees too that a bleeding resistor can reduce a cells voltage during the constant voltage phase.

If so depends on "quite all involved factors" as ?mainly? state of "weak" cell(s) vs "normal" cells, charging current and of course bleeding resistor value.

There is no reason why this should not happen with 1kOhm resistors - it happens just under different circumstances.

12 hours ago, rcgldr said:

Not mentioned is once a bleeding resistor is activated, there needs to be a second lower voltage trigger to deactivate an activated bleeding resistor

The following point from the same cited post 

On 3/14/2023 at 9:29 AM, Chriull said:

2) Bleeding these higher voltage cells downto 4.2V after the charge is complete

mentions exactly this? "Bleeding downto 4.2V" implies the second lower viltage trigger for deactivation.

5 hours ago, mrelwood said:

To our knowledge there is only one trigger. Whenever a cell group voltage is above 4.15-4.2V, the resistors are activated. If the voltage drops back below the threshold, the resistor is disengaged.

Many of the standard passive top balancing bms from aliexpress (visually similar quite to gw bms) have specified 4.2V for bleeding resistor activation and 4.19V for release. 4.25V for charge shut off.

All values +5/-0 mV.

As @rcgldrposted a hysteresis is good practice/state of the art.

Afaik this hysteresis is already implemented in about all used ic's. For some settable, some hard coded.

4 hours ago, rcgldr said:

I looked at some articles about e-bike BMS, with battery packs equivalent to smaller EUCs, and the passive cell balancing current is typically around 200mA. I'm wondering if somehow if the non-Inmotion BMS systems are able to get 200mA+ balancing current, which would more closely match Wrong Way's video animation.

200mA through a bleefing resistor would need 21 Ohm resistors dissipating ~0.8W...

[v8nice]

we wonder how this balancing works, it's good that it doesn't work normally, like all the others. Me on my v8f wheel that I got new and I've always respected balancing times with each recharge, it had nevertheless started to deviate. And on the batteries that I opened, no long charge could have restored the cells to equilibrium. On the v5f battery, the voltage reached 84.5v (real -1v) and then despite the charger still connected, green led, the voltage went down to 82.8v .... The bms became completely weak for a slight imbalance, that a normal bms could have corrected. After a light manual rebalancing, everything works correctly, the charge reaches around 84.9v, the light turns green and then the voltage rises slowly to 85.25v. The test has lasted for 12 recharges, for the moment the balance remains. the photos, this imbalance was not too big, but the bms did anything and especially nothing to remedy it... Only 0.09v between the lowest cell and the highest cell and the bms did nothing , I don't know why the charge went down again after an almost complete charge. And if nobody speaks of imbalance it is because there is no visibility of the cells, few people open the battery pack. unbalanced batteries have gone in the trash without anyone knowing...

[rcgldr]

From Inmotion service:

From: service@imscv.com [mailto:service@imscv.com] 
Sent: Thursday, December 29, 2022 9:37 PM
To: rcgldr <rcgldr@cox.net>
Cc: 孟翔宇 <leo.meng@imscv.com>
Subject: RE: V8F - Does the V8F have passive battery balancing?

no passive battery balancing on the V8F. 

Thanks & Best regards
Rachel

 - - - after asking what the 21 wires on the V8F BMS are used for:

From: service@imscv.com [mailto:service@imscv.com] 
Sent: Monday, January 16, 2023 9:39 PM
To: rcgldr <rcgldr@cox.net>
Cc: leo.meng <leo.meng@imscv.com>
Subject: RE: V8F - Does the V8F have passive battery balancing?

ok, but our techs still say there is no passive cell balancing on V8. 

Thanks & Best regards
Rachel
 

Edited March 15, 2023 by rcgldr

[rcgldr]

9 hours ago, Chriull said:

200mA through a bleefing resistor would need 21 Ohm resistors dissipating ~0.8W...

For this e-bike, the batteries max voltage is around 3.65 volts, not 4.2. It's a smart controller, that allows the balancing voltage to be adjusted, but not the balancing current, which is fixed at .2 amps = 200mA. The video is confusing, as he mentions current from a solar panel charger driving everything in the room, and the current from the e-bike charger, which eventually drops below the .2 amp balancing current.

https://www.youtube.com/watch?v=SleoqcKxVqI&t=298s

He then increases the balancing voltage to 3.5 volts, then decreases to 3.35 volts:

https://www.youtube.com/watch?v=ue9Xc9MCuvg&t=390s

 

[Mono]

This is just an observation how my several V8 behave differently than my V8F after they have reached the final voltage while charging (using the same charger): the V8 continues to draw 0.04A (apparently forever) whereas the current on the V8F drops below 0.01A (and it might be zero, I can't say for sure).

[rcgldr]

1 hour ago, Mono said:

the current on the V8F drops below 0.01A (and it might be zero, I can't say for sure).

The V8F stops the balancing, but still uses come current for blue tooth and other circuitry, and the voltage will slowly decline over time, I've seen it drop from 83.6 volts to 83.0 volts in about 2 hours. The only way to prevent this is to monitor when near peak voltage and disconnect the charger from the V8F once the voltage starts to decrease.

 

[v8nice]

1 hour ago, rcgldr said:

 

 

If the voltage slowly decline with charger on,i think you have unbalancing cells...

2 battery i have with this problem ,fixed with manual balancing...

Now the voltage max is the same 2 or 10 hour after green light.

The variation voltage is only 0.01v up or down after the peak charge.

Open your battery pack to verify.

Edited March 16, 2023 by v8nice

[rcgldr]

2 hours ago, v8nice said:

If the voltage slowly decline with charger on,i think you have unbalancing cells...

I agree, one or more of the pairs of cells is reaching maximum voltage, which causes the V8F to stop charging.

I don't have the skills, tools, space, ... , to take apart my V8F. 

[v8nice]

1 hour ago, rcgldr said:

I agree, one or more of the pairs of cells is reaching maximum voltage, which causes the V8F to stop charging.

I don't have the skills, tools, space, ... , to take apart my V8F. 

if mrelwood is true just charge and wait for balanced, which is not very true in reality, it does not work. Try several times to ride 2 minutes after each full charge and put the charge back. I doubt that it works but you have no other choice without opening the battery. The voltage must not drop with the charger connected, even if the bluetooth is active, the charger maintains the charge because it consumes very little.

[rcgldr]

I tried @mrelwood suggestion of leaving the charger on for about 3 hours, which lowered the voltage from 83.4 volts to 82.5 volts, then I disconnected my V8F from the charger, waited a few minutes, the connected the charger again, and the V8F still would not charge, both chargers led stayed green, the rapid charger showed 0 amps, and the voltage just kept decreasing. Apparently I have to ride the V8F in order to reset the charge disable trigger. Note both stock and rapid charger leds normally go green at 83.3 | 83.4 volts, but after leaving on stock charger for 3 hours with voltage down to 82.5 volts neither charger was charging.  A short ride fixed the issue, as both charger led's switched to red.

I tried @v8nicesuggestion of charging | short ride | charging | short ride | ... for about 6 cycles. Didn't seem to make any difference, peak voltage remained at 83.4 volts with intermittent display of 83.5 volts.

Edited March 17, 2023 by rcgldr