Battery FAQ

[Chriull]

The specific parts are mainly regarding Kingsong (KS) and Gotway (GW (13)). Maybe Inmotion/Rockwheel BMS work quite similar? Ninebot BMS (S1/2, Z6/8/10) are different - they use smart BMS!

What is (more or less) known:(6)

Passive Cell Balancing:

Works with comparators that switch with a Mosfet a bleeding resistor in parallel to individual (paralleled) cell (groups). (1) In this specific example they get activated above 4.2+/-0.025V and deactivated below 4.19+/-0.035V. 

These bleeding resistors stay active after charging for cells with voltages above the threshold - so they get discharged again to 4.19+/-0.035V (or whichever comparator is used in the specific wheels BMS)

Whilst charging (7) balancing happens by this paralleling of a bleeding resistor to each cell groups that exceeds this threshold voltage. So the cell gets less charging current and charges slower as the other cells with voltages below this threshold. This threshold (4.2V) can be reached about the transition of the constant current charge (stage 1) to saturation charge (stage 2, constant voltage charge).

Charging to ~80% by cutting off the charger once about max voltage is reached (only using more or less the constant current stage) prevents any balancing!

See (14) for some more thoughts/details on passive balancing.

Cell Overvoltage Protection:

This works with comparators too to monitor the individual (paralleled) cell (groups). If any of the comparators threshold is exceeded a mosfet cuts the charging input. If the wheel has more than one battery pack they are syncronized, so that all packs cut off charging simulatanously.(2)

The overvoltage protection threshold voltage lies somewhere in the 4.2xV region.(5)

Charger:

The commonly used chargers are ""normal" AC/DC converters with current limiting". So they provide some constant current for the first charging stage (6) until the max voltage is reached (saturation charge) (6).

Despite Li Ion cells should never be trickle charged, from reports here i strongly suspect that they do not stop charging once the current drops below about 3% rated current as recommended (6, li ion cells datasheets)!

So timer switches are often used to overcome this.

Chargers are normally no precission instruments and can be not working according to their assumed specifications! So they could deliver to low voltage (no balancing happening, battery not fully charged) or have a too low shut off current threshold.

Many Chargers have adjustment possibilities for voltage, current and shut off current threshold(8,9).

KS only:

The charge input is connected via the mainboard to the battery packs. So charge current could be/is monitored there (3). The battery outputs are connected individually to the mainboard (each has their own fuse, etc) and paralleled there.(4)

The BMS has some output protection. This is only for short circuit/overcurrent protection.

GW only: (as for KS wheels prior to S series?)

The charge plug is directly connected to the batteries charge input, the battery output(s in parallel) directly connected to the motherboard. There is no firmware interference (possible).

The GW BMS have no kind of output protection.

Cell undervoltage protection:

There is nothing like a individual cell undervoltage protection in any of these BMS! This used to be in the beginning and led to nasty faceplants by BMS cut offs. So riders are safe, but with bad consequences for li ion health/safety...

Individual cell voltage montoring:

Is not done by neither BMS. (just ninebot). KS18(X)L BMS have a connector in one corner of the PCB so one can access all individual cell voltages there with "just" a little cut in the shrink wrap.

Reported battery pack voltage:

The wheels measure internally the battery voltage and report them to the app. Do not expect this value to be overly accurate! Deviations of 1,5V are not uncommon.

Do not trust the charge % showing 100%! 100% cover a wide range - monitoring the reported battery voltage gives a much better picture! Charge % numbers are just calculated in FW from the battery voltage with some 4.1xV beeing 100% and 3.3V (GW) and 3.0V(KS) or 3.15V (KS) beeing 0%.

Consequences:

Cell Balancing:

is the key to a healthy, performant and long living battery pack!

Li Ion batteries are especially "stressed" with high and with low voltages. Any (longer) charge to over 4.2xV or discharge below 2.5V prematurely ages/destroys Li Ion cells. 

As all the used cell (groups) in a battery pack cannot be absolute identical they will differ more and more with each charge and discharge. With some bad luck  mismatched cells were assembled or cell (groups) were from the beginning at different charge states (voltages).

Whilst the saturation charge (6) this will be balanced out (a bit/more or less).

The worst possible extremes for an 20s/84V pack:

19 cell (groups) at ~4.2xV and one cell at 84V-4.2xV*19 ~ 2.7V!!

In such a case charging is prematurely stopped by the BMS (cell overvoltage cutoff). Although the battery pack shows full voltage directly after charging the voltage will drop (by the activated balancing resistors) to about 4.19V*19+2.7V ~ 82.3V.

1 cell will reach the 4.2xV overvoltage threshold and the other 19 stay about (84V-4.2x)/19~4.19V. This does not sound grave, but if this one cell (group) has less capacity and continously reaches low voltages and by charging reaches the upper etremes it will age prematurely and loose even more capacity. By this it will get to much lower voltages as the others. Until it goes below safe voltages and gets destroyed.

How to note battery pack problems:

As long as the battery pack charges fully nothing really is to be noted or can be diagnosed without knowing the individual cell voltages!

- Premature charge cut offs by the BMS are a first sign.

- Wheel reports less voltage after a full charge as used from prior full charges.

Note that there will always be a difference between maximum charging voltage to battery output voltage as there is some voltage drop at the input protection circuitry of the BMS (~some tenth of volts).

If this is just a low difference one can try to make some repeated full charges with just slightly discharging the battery inbetween (to about 80%?). So one has repeated stages with balancing - best battery aging versus balancing efficiency! Never do this charging unattended! Best in some "fireproof" enviroment!

- less range/performance

What to check once something seems "strange":

- Measure the charger output voltage! (10)(11)

- Check the wheels reported battery voltage. If one ever happens to have his wheel open this is a good time to check this value.(10)(11)

- If the wheel has two or more packs in parallel chances are high that only one of them is degraded/bad. So they should be checked individually and if so replacing just this bad pack is sufficient and recommendable. The degraded/bad pack will hinder the good packs from beeing balanced!

Easiest check is to charge them individually and each pack reaching full voltage is (hopefully) ok, the one not reaching the full voltage is the "bad" one.(12)

- The bad battery pack most probably has only one or two bad cell groups - so they could be replaced. In the forum are some reports of doing this, but this work needs experience and is absolutely not hazard free!

 

DISCLAIMER: No specific BMS was fully analyzed/reverse engeenered (to my knowledge) - there are some points just "best knowledge" but still speculation. Any specific wheel from any manufacturer could have some different BMS used inbetween and especially in any future version/revision. Resellers could use different battery packs. I'm no long time, educated battery expert - just gathered thoughts from discussions here, different internet links, batteryuniversity.com combined with (long time ago specialised) electronics school education.

This is the first draft - expect everything to change. Corrections, additions and restructurings (hopefully) come continously.

Any input is welcome - especially knowledge and experiences so faults/speculations/important missed topics/etc can be corrected and/or improved!

 

(1) Schematics: https://forum.electricunicycle.org/topic/2102-gotway-charging-questions/?do=findComment&comment=23539

(2) Since the packs are in parallel a single pack cutting off would be charged by the parelleled output connections.

This BMS syncronization wires were introduced for KS with the S series?

(3) KS16X for example continously beeps (with some FW's?) if charging current is too high.

(4) Did not hear of ony special "uses" by this like using the packs seperately as it is done/suspected for ninebot wheels. Could be checked by some mainboard analysis if the paralleling is "hard-wired" on the PCB.

(5) Have not seen any details reported which comparators are used in special and so don't know exact thresholds. Many on aliexpress seen BMS have a threshold of 4.28V specified.

(6) Anything can change with each new batch delivered! Seldomly BMS PCBs are analyzed and/or checked for changes.

(7) https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

(8) https://forum.electricunicycle.org/topic/2247-decrease-charging-time-5a-high-current-charger-mod/?do=findComment&comment=25662

(9) Be cautious opening electric devices operating at mains voltages! Even disconnected from mains they can still contain life threadening high voltages!

(10) Regard the digital multimeter accuracy! Only because some DMM show one or two digits after the decimal points this does not mean that they have any value! Even the first digit before the decimal point can be easily off:   https://forum.electricunicycle.org/topic/13629-multimeter-accuracy-needed-for-chargerbattery-measurements/?tab=comments#comment-233250

(11) Take care to not short anything. Be sure the multimeter is _not_ in current measure mode - any short circuit of the battery can melt the probe tips immedeately and send molten metal drops all around! Use googles to protect the eyes!

(12) Take care that the packs have good as the same voltage once they are reconnected again! Reconnect without hesitation. The longer it takes to get the connectors fitted the longer there will be sparks until the connectors are to be replaced... Anti spark plugs are available.

(13) Detailed 2015 GW MSuper V2 BMS teardown https://forum.electricunicycle.org/topic/18374-how-bms-works-gotway-pack-teardown/

(14) https://forum.electricunicycle.org/topic/22109-passive-balancing-a-simulation/?tab=comments#comment-359235

Edited March 24, 2021 by Chriull

[Chriull]

How to check the battery with EUC World and HS110

(TLDR -> jump to the next bold heading)

As i just got my newest gadget - a HS110 for charge control and logging with EUC World (1) i had to make some more graphs!

Especially as with the recent reports of burning wheels the question arose how to check if my battery is still ok?

So to start - here the log of my first charge with the adaptor to a fixed battery charge level of 70%: (Menu Point in EUC World Version 2.3.10: Charging Control/Battery Level Limit)

One sees the constant charge current (8A in my case), battery charge level nicely climbing from some 45% to the choosen 70% and then the charger stopped automacigly (Thanks @Seba ). In red one sees the corresponding battery voltage rising - just in a bit a bad zoom...

The next charge log while continuing after this 70% did not make it alive - somehow i fiddled around and the log never made it on the phone or was lost, or whatever...

Here is just the end of this charge:

The battery charge level is here already constantly at 100%, voltage "rises" from ~66,7V to ~66,95V with the current dropping from ~2.5A to 0.4A. So this shows the end of the constant voltage charge.

This ~0.4A is the charge stop if one chooses the EUC World Menu Point Charging Control/Disable Battery Balancing (as of 2.3.10). This makes the charging process being stopped at ~30W (30W/67.2V~0.4A). I like this number, as it fits about the battery university recommended charge end for my 14Ah battery!

 

This charging events are here again summarized in the normal log (which worked all the time), but just shows the battery voltage:

From 12.9h.. almots 13h the wheel was idling - once or twice shortly connected to the charger. At ~13h the 70% charge started. At ~13.25h i turned the wheel on again and one sees that the voltage "dropped" from ~62+V (while charger put in 8A) to ~60,5V. That's mainly happening in because of the voltage sag on the internal resistance - the higher the charging current, the higher this drop will be.

At ~13.35h the charging started again until ~14.35 when i interrupted charging (the small ditch is nicely seen at the voltage graph). That's the sequence were i lost the charge graph. Until ~13.75 was the constant current phase and from then on the transition to the constant voltage phase.

From ~14.35 on the above shown graph "Final Charge stage, level == 100%, Disable Battery Balance active" was recorded.

Next day i finalized charging without this option enabled -here (if i understood right) charging is continued about 1 hour after this 30W are reached.

 

Here the current settles more or less to a bit below 0,1A - the residual current the charger takes, some active balancing resistors and the basic consumption of the wheel.

So, until now some graphs and descriptions of the charge process - how does this help to check ones battery states?!

1) The battery charges nicely until the end == current is continously and steadily decreasing. This means that the single cell group overvoltage protection was not triggered - the cells are about balanced!

2) The battery show no elevated self discharge:

Here the battery voltage in the real timeline showing the different charging events from above and at the finish a "(almost)no load/no charge)" comparisson:

After the first charge (dark blue) in the beginning until ~0.4A the wheel rested about 20 hours (~~a day). This next charging (light blue, is shown in the log just above downto ~0.1A charging current) started a bit lower than the charge a day before ended. This is mainly because the charge ended with ~0.4A, so there is some voltage drop in the cells (not shown here, as the voltage was recorded only while charging). And directly after a charge some little voltage drop even without current is normal.

After this second charge downto almost no charge current was a break of about 2h. There no real self discharge is to be seen - as far as the noise of the internal wheels voltage measurement allows to see anything... The decreasing voltage at the end (middle blue) is the turned on wheels basic consumption. The scale of this graph is just 0.1V on the y-axis!

For healthy batteries the drop happening after charging (without the drop by the voltage sag!) and the self discharge after the first 24h are a quite direct measure for the battery health! Both should be in the very low % range. Depending on the "speed" of charging, the end charging current the first settling of the voltage can be a bit bigger.

At batteryuniversity.com numbers for this self discharge are given to get a feeling of the scale.

~5% in 24h, then 1-2% per month. (2)

This percentage signifies state of charge, not Voltage! According to (3) at the "high end" 0.1V are ~10%. So 5% are ~0.05V per cell. For a common 84V wheel, which has 20 cells this first voltage drop should not be higher than 0.05V*20=1V! After this the battery should not loose any more then ~0.2-0.4V per month.

In my example after the charge which stopped in the CV phase at ~0.4A and 66,9V.

The next day (after ~20h) the battery voltage was at 66.7V. A part of this drop happened by the voltage drop at the internal resistance of the batteries - this should accord to something like 0.4A*0.2Ohm = 0.08V. Roughly the rest of the difference of 0.2V-0.08V = 0.12V is this mentioned Voltage settlement after charging, which is well in the good range below 0.05V*16=0.8V.

As it seems the ranges from batteryuniversity are quite huge - either battery chemistry changed to much better inbetween or my cells are still very good...

For the ones living in areas with cold winter and not riding in the cold that's a perfect time to look at the self discharge of their batteries - just power on the wheel and take the voltage reading from the app. If it's below this 0.2-0.V per cell per month everthing should be fine.

As one sees in the last section of the Voltage trend diagram above - leaving the wheel turned on for hours leads to quite "significant" discharge compared to the self discharge of the cells!

3.) Internal resistance estimate:

From the datasheet my cells should have lower than 40 mOhm "initial AC impedance" - resulting in 0.16 Ohm for my 16s4p pack.

The voltage drop after the 8A charge at ~13.1h was from 62.3V to 60.3V, the charging current 7.9A at the end. This results to an internal resistance of (62.3-60.3)/7.9 ~ 250 mOhm.

Quite ok for the current measurement beeing an estimate, too.

 

 

(1) https://forum.electricunicycle.org/topic/21054-euc-world-charging-control-in-upcoming-24-release/

(2) https://batteryuniversity.com/learn/article/elevating_self_discharge

(3) https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries , Table 2

 

Edited January 14, 2021 by Chriull

[Chriull]

A bit more on cell degradation - had a friend visiting with his KS16S  (825Wh - 18650 ?lg mj1? 16s4p) with some ~~7'000km driven. Logged his charging with EUC World and the HS110 lead to the following graph:

Settings were "disable battery balancing" "no (100%) battery level limit" "disconnect on finish". So charging was stopped once the current dropped to ~0.33A.

CV Phase took about (17.1-15.2)h~2h.

CC phase from the 63.3V (79%) before charging took just ~(15.21-15.17)h~0.04h~2,4 min.

In my in the above post already shown charge graph for my KS16S with something around or less than 1000km and the same charge the CV phase took ~(15.25-13.75)h=1.5h downto ~0.33A.

My CC Phase from 60.3V (56%) took about (13.75-13.3)h=0.45h~27min.

So CC was much shorter (although the battery was fuller) - just CV phase took about 0.5h / 33% longer...

Friends Wheel reported a battery voltage of 63.3V (79%). The voltage jumped with the 8A charging current to 64.6V -> (64.6-63.3)V/8A=0.16 Ohm. 0.16 Ohm /16*4= 40 mOhm. 

"New Wheel" reported a battery voltage of 60.3V (56%). The voltage jumped with the 8A charging current to 61.35V -> (61.35-60.3)V/8A=0.13 Ohm. 0.16 Ohm /16*4= 32 mOhm. Is more or less like the original internal specified in the datasheet!

The datasheet speciefies <= 40mOhm "initial AC impedance at 1kHz after standard charge". So both seem to be in quite good shape? As far as this above estimate can be taken as some kind of measurement.

Reported end (max) voltages were 67.00V vs 66.95V - so "exactly" the same voltages reported by both wheels.

Seems to be an interesting "supervision tool" for ones battery - such a charge log taken every now and then! To discover premature charge cut-offs by single cell group overvoltage == ?first sign of/already serious? imbalance and charge time chage (CC phase shortens, CV phase takes longer with normal degradation)

https://batteryuniversity.com/learn/article/bu_409a_why_do_old_li_ion_batteries_take_long_to_charge

Edited March 4, 2021 by Chriull

[Bob Eisenman]

Despite asserting intellectual mastery on the topic I think your post is too long for the average reader on the forum. According to a word counting website

https://wordcounter.net/website-word-count

Your post has 1,902 words:

[Chriull]

2 hours ago, Bob Eisenman said:

I think your post is too long for the average reader on the forum

Most propably not only for the average reader... 

As there were some thourough discussion lately about batteries i just got the urge to assemble this content in one place, as long as it is fresh in memory.

It was still an unexpected amount of work. Got already while writing the impression this gets a bit monstrous - should be summarized with just links to the detailed descriptions/explanations for the interested reader. And/or split up in related parts. 

Maybe it happens sometimes i'll feel the urge again 

[Planemo]

Dont worry Chriull, I think its a great post 

[Bob Eisenman]

It was warm today.....I'd been riding twenty five to thirty or so miles for the he last 3 of 5 days. It was so warm that arriving in Boston/Charlestown I had only used forty one percent of the Monster's 1600 wHr fully charged capacity in 22 miles...mostly flat and at 11 mph average moving speed. My battery use habits are simplistic....Monster goes on the charger (standard) when not being used....it is unplugged when the LED turns green....leaving it on the charger with a green LED for hours while I sleep has never been a problem.

As a Ninebot One E+ rider, prior to the Monster, I grew tired of the BMS throttling after ten or so miles and never considered riding while on the BMS to be fun.

Gotway's Monster rides from 100 to 20 percent without making a piezoelectric beeping warning sound. Riding below twenty percent is a beeping constantly experience. I tend to plan not ride the Monster when the battery is below 10% and ride much more conservatively at that battery range....hopefully within a mile or two from home.

I don't really appreciate how the EUC is engineered to deliver this level of performance....Kudos to @Chriullfor posting his info.🙄

WARM WEATHER is for sure a positive riding factor for this all year long New England weather rider. 

A ride a few days ago took me past the strip club that remains closed due to CoVid 19

Today's ride went within a block of the Squire. An attractive buxom woman outside the Dunkin nearby wanted to know if she could take a photo of the Monster....😏 I wanted to ask if her boobs were real but thought it better to silently and softly stand beside her while she enjoyed imaging the Monster with her phone.

We all recharge in different ways....😁

My ride's purpose was to buy a computer storage device at a Cambridge electronics/computer store...thank you government stimulus payment!

I decided to continue to ride on through the gates of Harvard University before heading back to the commuter rail station in Boston.

Arriving back at the Commuter rail station early for the 5:30 pm ride (30 minutes back to my town) the miles travelled was 29 miles with lots of battery left...(forgot how much exactly). The rail station was almost empty, benches for sitting gathered together and roped off...it looks about the same weekdays due to CoVid 19.

Monster is back on the charger for the night. Some times I wake up in the middle of the night...notice that the charger's LED is green and unplug it in an abundance of caution.

 

[Dancer]

I charge my Monster the same way. After 25,000+ km I still have 83.7v on a 100% charge.

[Denny Paul]

22 hours ago, Bob Eisenman said:

Despite asserting intellectual mastery on the topic I think your post is too long for the average reader on the forum.

I will shamelessly say this stuff goes over my head. A TLDR or summary for us that are less than an intellectual master on the subject would make this post a great resource, possibly one worth pinning?

Edited May 17, 2020 by Denny Paul

[Lindsey]

23 hours ago, Chriull said:

Most propably not only for the average reader... 

As there were some thourough discussion lately about batteries i just got the urge to assemble this content in one place, as long as it is fresh in memory.

It was still an unexpected amount of work. Got already while writing the impression this gets a bit monstrous - should be summarized with just links to the detailed descriptions/explanations for the interested reader. And/or split up in related parts. 

Maybe it happens sometimes i'll feel the urge again 

It's really good information, and it's a useful post.

There is a lot of information in the current forum, but I hope there is more information about batteries.

I want to see more information that even beginners can easily understand. It doesn't matter if good information is long.

Please ask for more battery knowledge.

Thanks to you, I get good information.

[pico]

@Chriull   Nice write up!  May be some mentions of pro/con of fast charging?  

Edited May 17, 2020 by pico

[Chriull]

14 minutes ago, pico said:

@Chriull   May be some mentions of pro/con of fast charging?  Effect on balancing of fast charging?

Pfff... Not too much to say, known (by me)

Some points maybe:

- There is no fast charging done/available.

- cell capacity / (charge current / parallel cells ) should be below 0.5 (the C number specified in the cells datasheet) for most cells. Some are specified for 1C.

- much rumours about charging at 0.1C or below vs 0.5C or 1C charging. Haven't seen something serious/reliable. Also not really searched something

- charge plugs/wirings/BMS input protection circuitry could be/are the weak part and could be overburdened.

- CC stage proportionaly shortens, CV stage gets longer.

- in regard to balancing: could be affected both ways? Should be more or less without difference?

 

[pico]

As you said, unfortunately no much reliable data available.

My personal guidelines for my V10F: Fast charging (I have a 5A charger) only to 90% then top up at regular charging rate if needed (allowing the pack to cool down  a bit ). Attended balancing only on the company supplied charger, once every 10 charges or so.

My guess is that any weak cell in a pack will have a higher temperature when fast charged (higher internal resistance) and the higher temperature will cause that cell to degrade even faster...

 

Edited May 17, 2020 by pico

[Chriull]

3 minutes ago, pico said:

My personal guidelines for my V10F: Fast charging (I have a 5A charger) only to 90% then top up at regular charging rate if needed (allowing the pack to cool down  a bit ). Attended balancing only on the company supplied charger, once every 10 charges or so.

Balancing is about the same no matter which charger you use. In the constant voltage phase the current is not determined by the chargers capabilities.

There's not to much known about it, bit every tenth charge could maybe not be enough.

6 minutes ago, pico said:

My guess is that any weak cell in a pack will have a higher temperature when fast charged (higher internal resistance)

Just the higher current is enough.

6 minutes ago, pico said:

and the higher temperature will cause that cell to degrade even faster...

Could be.

But doing a faster 1st stage charge, letting the batteries cool down and then doing the 2nd stage charge could be done in about the same time with the standard charger?

[pico]

15 minutes ago, Chriull said:

But doing a faster 1st stage charge, letting the batteries cool down and then doing the 2nd stage charge could be done in about the same time with the standard charger?

I did not mean to stop charging to cool down , I meant top up at a lower rate (when needed), generating less heat...

[Planemo]

35 minutes ago, Chriull said:

Balancing is about the same no matter which charger you use. In the constant voltage phase the current is not determined by the chargers capabilities.

Very true! I monitored a charge the other day on my msx with my 6A charger. The current dropped off rapidly at around 99.5v IIRC. The CV stage took a lot longer than I thought as well, and long after the green light came on. Its the first time I have actually monitored voltage/current whilst charging and it was enlightenting to say the least.

[pico]

45 minutes ago, Chriull said:

Balancing is about the same no matter which charger you use. In the constant voltage phase the current is not determined by the chargers capabilities.

I understand that part(CC/CV), thanks! My case is a trust issue to balance cells with a cheap OEM $55  5A charger that has a loud fan for hours! 

Let me rephrase, for my own use.

Say I am in a hurry. I use the fast charger up to 90-95% charge and go ride. 

Every now and then when I have time, I use the silent/sealed IM stock charger for long charging and balancing.

 

[Chriull]

1 hour ago, pico said:

I understand that part(CC/CV), thanks! My case is a trust issue to balance cells with a cheap OEM $55  5A charger that has a loud fan for hours! 

Let me rephrase, for my own use.

Say I am in a hurry. I use the fast charger up to 90-95% charge and go ride. 

Every now and then when I have time, I use the silent/sealed IM stock charger for long charging and balancing.

 

There is nothing to discuss about loudness and trust.

To control the "quality/ability of balancing" afaik just the voltage of the charger in conjunction with the BMS is important. Quite out of scope to measure this without specialized equipment.

Maybe taking the charger with the higher voltage and monitoring charge current, that no premature BMS cutoff (4.2xV cell overvoltage cutoff) occurs could be an easy possibility.

1 hour ago, Planemo said:

Very true! I monitored a charge the other day on my msx with my 6A charger. The current dropped off rapidly at around 99.5v IIRC. The CV stage took a lot longer than I thought as well, and long after the green light came on. Its the first time I have actually monitored voltage/current whilst charging and it was enlightenting to say the least.

Your charger does not cut off at the "about 3% rated current" as often reported here?

Batteryunuversity states that full saturation charges do not differ too much in time. Just very slow charges should imho take longer just by needing to much time for the CC stage?

[Planemo]

9 hours ago, Chriull said:

Your charger does not cut off at the "about 3% rated current"

I need to do some more testing. Its so tedious sitting next to the charger for several hours logging the data every 10 mins! From memory I think the green light went off at around 700mA. The voltage and current curves looked about right though. I think these green lights are generally very rough guides, and they dont seem to have any influence on what the charger is actually doing.

[Chriull]

14 minutes ago, Planemo said:

I need to do some more testing.

+1! Let us know the results!

14 minutes ago, Planemo said:

Its so tedious sitting next to the charger for several hours logging the data every 10 mins!

CD was great for such cases! From eunicycles.eu's chargeman not really something was reported and @Inductores seems to need some more time for finishing his project...:(

14 minutes ago, Planemo said:

From memory I think the green light went off at around 700mA.

This could be around 3% for a 1C rated 6p 3500mAh pack. Would be a strange default adjustment.

14 minutes ago, Planemo said:

The voltage and current curves looked about right though. I think these green lights are generally very rough guides, and they dont seem to have any influence on what the charger is actually doing.

Could be the green led just show the low current threshold is reached and the chargers generally don't cut charging anymore?!

... and thresholds are adjusted to some value the assembler just liked this day...

Newer KS modells seem to measure charge current - they could report this value  or implement such battery "healthy" features.

Inmotion has/could have some charge features, too?

And ninebot with his smart BMS should control everything - if they care to do so and implemented it right...

[Planemo]

2 minutes ago, Chriull said:

+1! Let us know the results!

Certainly will. It should be mentioned though that my only data source is a £6 chinese volt/amp meter that I fitted into my charger so its probably not the most accurate!

2 minutes ago, Chriull said:

CD was great for such cases! From eunicycles.eu's chargeman not really something was reported and @Inductores seems to need some more time for finishing his project...:(

Yes the CD would make it so much easier. I did look at the chargeman and its looks nice but I just need to come up with buying something for £65 that wont do much other than satisfy my curiosity!

2 minutes ago, Chriull said:

This could be around 3% for a 1C rated 6p 3500mAh pack. Would be a strange default adjustment.

Well thats handy for me because I think the Sanyo GA are that spec

2 minutes ago, Chriull said:

Could be the green led just show the low current threshold is reached and the chargers generally don't cut charging anymore?!

I think thats exactly whats happening. I believe the LED is just set at a point where much of the CC phase has been completed. A serious example though for carrying on charging past the green light (on this charger anyway).

[Planemo]

Hi @Chriull

I couldn't find an easy way to download my excel graph as an image so I took a photo of my laptop screen. Not ideal but hopefully it gives you an idea. Data taken from MSX 100v 1865Wh with PM Battery 6A charger and cheap onboard Chinese volt/amp meter. The graph isn't as smooth as I would like but I blame the meter - I tried my best to average the readings but the meter is a bit 'jumpy'. Readings taken every 10 minutes. This was on a wheel that started at 45% charge. Hopefully I will repeat the test with a lower starting voltage some day. Main things I noticed were:

1. Time period from CC at 6A to CV 2A is around 50 minutes (A faster drop than I imagined).
2. Green light came on at around 750mA (higher than I imagined).
3. Current did not drop to 100mA until 1.5hrs after green light came on (later than I imagined).
4. Total time from start of CV phase until fully charged (100mA current) was 2hrs 40min (longer than I imagined - this is effectively the balancing phase as you know).

So the green light comes on earlier than I would like. I would like to adjust this to come on at 100mA to show a full and balanced charge but I'm not sure which pot to turn, nor do I want to possibly affect any other workings of the charger so I will probably leave it.

The charger does seem to be slightly low. On my handheld meter it shows 100.7v (no load). The same meter shows 101v on a friends stock Gotway charger.

[Chriull]

17 minutes ago, Planemo said:

Hi @Chriull

I couldn't find an easy way to download my excel graph as an image so I took a photo of my laptop screen.

Select the diagram, then "save as" pdf. (There one can assure under options to save "selected diagram") - and voila! At least at excel 2007 - maybe newer excel versions can already save bmp/png/jpg, too.

In Libre Office (?Openoffice?) Diagrams can be directly exported as graphics by right clicking the diagramm.

17 minutes ago, Planemo said:

Not ideal but hopefully it gives you an idea. Data taken from MSX 100v 1865Wh with PM Battery 6A charger and cheap onboard Chinese volt/amp meter. The graph isn't as smooth as I would like but I blame the meter

From what i've seen till now i'd blame the charger - the control loops don't seem to be to "sophisticated" (and don't really need to) and there are and will be "hops" in voltage. My graphs were recorded with just the internal voltage measurement of the wheels - which are reported to be with an to high ohmic voltage divider, so they measure all kind of noise/disturbances...

17 minutes ago, Planemo said:

- I tried my best to average the readings but the meter is a bit 'jumpy'. Readings taken every 10 minutes. This was on a wheel that started at 45% charge. Hopefully I will repeat the test with a lower starting voltage some day. Main things I noticed were:

1. Time period from CC at 6A to CV 2A is around 50 minutes (A faster drop than I imagined).

Can't follow that?

CV starts at about 14.10 to 14.20(100.1V). Why CV 2A? So ~60-70 minutes for CC?

Just as comparisson from batteryuniversity.com:

17 minutes ago, Planemo said:

2. Green light came on at around 750mA (higher than I imagined).

Your 1865Wh pack is a 24s6p configuration of 3,5Ah cells. So the pack has 6*3,5Ah = 21 Ah. The rated current, depending on cells should be either 0,5C or 1C. With 0,5C (3,5A/2=1,75A) * 6 3% would be 3,5A/2*6*3%= 0,315A.

The 750mA would be about the right time to stop for 1C rated charge current cells.

17 minutes ago, Planemo said:

3. Current did not drop to 100mA until 1.5hrs after green light came on (later than I imagined).
4. Total time from start of CV phase until fully charged (100mA current) was 2hrs 40min (longer than I imagined - this is effectively the balancing phase as you know).

100mA current is already trickle charging - recommended full charge should have been reached about an hour earlier (315-730mA).

My very personal feeling (without any reliable source) woul be that most balancing happens in the beginning of the CC phase. In the end the cells are just tortured...

Anyhow - if one wants to intensify balancing it should be best to repeat the CC phase some times (slight discharges inbetween) so one never trickle charges the pack.

17 minutes ago, Planemo said:

So the green light comes on earlier than I would like. I would like to adjust this to come on at 100mA to show a full and balanced charge but I'm not sure which pot to turn, nor do I want to possibly affect any other workings of the charger so I will probably leave it.

You have a nice description here from @Cranium:

On 5/14/2020 at 1:05 PM, Chriull said:

(8) https://forum.electricunicycle.org/topic/2247-decrease-charging-time-5a-high-current-charger-mod/?do=findComment&comment=25662

There have been in the meantime many other descriptions of these proceeds, too. Since you are well equipped with measuring devices there should not really be a risk to mess something up. Just turning all potentiometers at once without remembering their original positions could lead to troubles ... 

Should not be necessary to mention this, but as it's already prewritten:

On 5/14/2020 at 1:05 PM, Chriull said:

(9) Be cautious opening electric devices operating at mains voltages! Even disconnected from mains they can still contain life threadening high voltages!

 

17 minutes ago, Planemo said:

The charger does seem to be slightly low. On my handheld meter it shows 100.7v (no load). The same meter shows 101v on a friends stock Gotway charger.

So depending on your multimeter this should mean the "real values" are some +/- 0.5V to +/-1V? (With the relative difference beeing true.)

Even with just 100V (and maybe a little bit less with the voltage drop at the input protection) there would be still 100V/24 cells = 4,1667V per cell. Balancing should be enabled at 4.2V+/-0.035V. So in the worst case cells get only balanced once the first cell is about 0.07V off. Does not sound like anything to worry about to me?

On the other side, once one reaches "real" 102V at the battery charge input that'll mean 102V/24cells = 4.25V/cell and is "endagered" by premature BMS cutoffs due to single cell overvoltage! ( @RagingGrandpa found 4.25V as threshold in https://forum.electricunicycle.org/topic/18374-how-bms-works-gotway-pack-teardown/ )

 

 

 

[Planemo]

23 minutes ago, Chriull said:

Select the diagram, then "save as" pdf. (There one can assure under options to save "selected diagram") - and voila!

Great, thanks

23 minutes ago, Chriull said:

From what i've seen till now i'd blame the charger - the control loops don't seem to be to "sophisticated" (and don't really need to) and there are and will be "hops" in voltage. My graphs were recorded with just the internal voltage measurement of the wheels 

I agree, it may well be the charger that's causing the wobbly readings, I only pointed first at the onboard meter I retro fitted cos it was so cheap I hadn't thought about using the wheel measurement itself (via EUCW) because I didn't fancy leaving the wheel powered up for hours?!

23 minutes ago, Chriull said:

Can't follow that?

CV starts at about 14.10 to 14.20(100.1V). Why CV 2A? So ~60-70 minutes for CC?

Yes CV starts around 14:20, I only mentioned 2A as a reference point. I think someone raised concerns recently about using high amp chargers and how quickly they drop the current when heading into the CV phase. I only noted it as this period was quicker than I thought. 

23 minutes ago, Chriull said:

The 750mA would be about the right time to stop for 1C rated charge current cells.

100mA current is already trickle charging - recommended full charge should have been reached about an hour earlier (315-730mA).

OK thats great. Maybe I will disconnect the charger soon after the light comes on then Oh and maybe not adjust the light either.

 

23 minutes ago, Chriull said:

Even with just 100V (and maybe a little bit less with the voltage drop at the input protection) there would be still 100V/24 cells = 4,1667V per cell. Balancing should be enabled at 4.2V+/-0.035V. So in the worst case cells get only balanced once the first cell is about 0.07V off. Does not sound like anything to worry about to me?

I was slightly worried that if the charger was a bit low, no cells would actually reach 4.2v and therefore full balancing wouldn't take place. So you are saying that even if the charger only outputted 100v, balancing would still get enabled?

23 minutes ago, Chriull said:

On the other side, once one reaches "real" 102V at the battery charge input that'll mean 102V/24cells = 4.25V/cell and is "endagered" 

I totally agree, I don't want to really ever hit 4.25v on any string, but I also want to ensure full balancing which I thought only occurs once a string hits 4.2v, so I'm not sure? I must admit, as it stands I'm not desperate to adjust anything on this particular charger as it seems pretty good as it is.

[Chriull]

1 hour ago, Planemo said:

I was slightly worried that if the charger was a bit low, no cells would actually reach 4.2v and therefore full balancing wouldn't take place. So you are saying that even if the charger only outputted 100v, balancing would still get enabled?

The balancing resistors are applied if the cell voltage goes above 4.2+/-0.025V (remembered the tolerance wrongly in the last post) and get inactivated once voltage drops below 4.19+/-0.035 (at least with the 2015 GW BMS - others should work quite similar).

So, the lower the charger max output voltage the higher the imbalance has to get, before the first time such a resistor is enabled and some balancing happens. How grave consequences certain voltages could have is hard to say (and could be endlessly discussed) - would need severe testings...

... i hope we all will have new wheels with smart BMS reporting cell voltages by then 

1 hour ago, Planemo said:

I totally agree, I don't want to really ever hit 4.25v on any string,

Yes. But if it happens it's a sign (if one knows charge times and notes the premature cut off) that there are imbalances. And as the balancing resistor stays on until the 4.19+/-0.035V this particular cell (group) will get discharged nearer to the other cell voltages again.

1 hour ago, Planemo said:

but I also want to ensure full balancing which I thought only occurs once a string hits 4.2v,

Perfect for balancing would be every cell just going above this threshold and staying below 4.25V - and then after charging all get discharged to the lower threshold again and be perfectly balanced.

1 hour ago, Planemo said:

so I'm not sure?

Me neither. Is it better to have the cells perfectly balanced (with some higher stress by some higher voltages and a bit of additional discharge) or just some outliers gets forced back to more normal voltages?

1 hour ago, Planemo said:

I must admit, as it stands I'm not desperate to adjust anything on this particular charger as it seems pretty good as it is.

+1

Could be a nice feature for @Inductores charge monitoring device - to allow setting of a current threshold for charging cutoff (this 3% of rated current) and warn if before charge cutoff by the BMS happened (cell overvoltage happened).