Video on 80% charging, "Good or Bad?"

[Richardo]

Off topic: One of the surprises for me in this thread is how you mentioned a single cell does benefit from the 80% charge cycle, I think you mentioned that cell phones can benefit from this because they run on a single cell. 

So that got me wondering, what voltage does a cell phone run? Aren't electronics generally geared for 12v? Not phones! A phone does all that computation on a single cell with 3.7 or 3.8 nominal voltage!  Remarkable 

[Planemo]

40 minutes ago, Richardo said:

So that got me wondering, what voltage does a cell phone run? Aren't electronics generally geared for 12v? Not phones! A phone does all that computation on a single cell with 3.7 or 3.8 nominal voltage!  Remarkable 

The only 'general' thing I can think of that runs 12v is cars.

Don't forget that semi-conductors are designed to run very low voltage, even PC CPU's are often specced at 3.3v despite the system being powered by 240v mains.

 

[mrelwood]

On 9/26/2021 at 8:16 PM, Eucnhtusiast said:

I have to make a small correction, our chargers are CV(constant voltage) only and will not supply a lower than *insert wheel specific peak voltage here*. What you described, is that our chargers would have smarts that allows them to sniff the battery voltage and adjust accordingly, which they don't, otherwise the video is ON POINT.

I don’t know where or how you got the impression that any charger even could be CV only, but it is incorrect.

To be able to apply full 100V to a battery depleted to 75V would require an immense amount of current. Way past what any charger can provide, and way more than the batteries could take without exploding.

Voltage = Resistance * Current, so Current = Voltage / Resistance. Battery resistance doesn’t really change while charging, so changing either Voltage or Current changes the other one as well.

 There’s not much point on me explaining further here how the charging process works on all lithium-ion batteries, since I already did that on the video.

Scroll down to “Charging and Discharging” for further reading:

https://en.wikipedia.org/wiki/Lithium-ion_battery?wprov=sfti1

Or Google “li-ion charging” and pick the source you like or trust the most.

 

56 minutes ago, Richardo said:

Off topic: One of the surprises for me in this thread is how you mentioned a single cell does benefit from the 80% charge cycle, I think you mentioned that cell phones can benefit from this because they run on a single cell.

There’s a catch though, which is why percentage is a completely wrong measure here:

 What is the voltage of your phone battery when it is charged to 100%?

If it was 4.2V, then charging to 80% only would be beneficial. But I’d bet a few cases of beer that it isn’t exactly 4.2V.

See, absolutely nothing I explained in the video is news to anyone who knows a bit more about lithium batteries. It’s all public knowledge, and common to them who have dealt with these things. Phone manufacturers have a huge list of professional engineers and electricians designing the phones that they sell millions of units every year, like they have already done for decades. I’m pretty sure that they know pretty darn well how to utilize the li-ion battery voltage range with an extreme amount of detail. A retired sound engineer from Finland has absolutely nothing to say to them about batteries that they wouldn’t already know a million times over.

 So no, I don’t think anyone should charge their mobile phone only to 80%. But also, trickle charging a phone though every single night is well known to be harmful. When my phone battery gets to 100%, I unplug it usually right away.

Laptop batteries don’t die because they are charged to full either. They die because they are way too often trickle charged 24/7, and not consumed. I’ve seen several laptop batteries that have been in use for years, yet have less than 10 charge cycles. And that’s why they can only power the laptop for 10 minutes.

56 minutes ago, Richardo said:

So that got me wondering, what voltage does a cell phone run? Aren't electronics generally geared for 12v?

Electronics aren’t geared for any one voltage. One single electronic circuit often has many operating voltages for different parts of the circuit. Just like the EUC mainboard. And especially a computer. It is standard for the preamp sound sections to work with +-5VDC, since the most suitable IC op amps use that. But the power amp bias voltages can be whatever the specific circuit was designed for, with a wide range.

56 minutes ago, Richardo said:

A phone does all that computation on a single cell with 3.7 or 3.8 nominal voltage!  Remarkable 

So do desktop computers actually…  The maximum operating voltage of a CPU is usually 3.3V, or thereabouts.

[mrelwood]

1 hour ago, div said:

Speaking of which; 3.8V (nominal) smart phones batteries: 

I hate the word “nominal”, because it doesn’t say very much. Especially on li-ion batteries, where the maximum voltage is extremely important and precise, while the minimum can be loosely chosen between 2.5-3.5V for the specific application.

Gotway (and it’s descendants AFAIK) uses an average voltage range of 3.3 - 4.2V per cell. KS 18XL uses 3.0 - 4.2V. Are their nominal voltages then 3.75V and 3.6V per cell? MSX 84V has a nominal voltage of 75V, and the 18XL has 72V? Argh!

 Speaking of “nominal”, not many things irk me as much as “nominal power”. Be it on an EUC or any device that produces audible sound. Especially when people who are not into these things compare products based on different “nominal power” values. There’s nothing wrong in not knowing, which is why there is definitely a lot wrong in purposefully creating faulty assumptions to those who don’t.

Edited September 28, 2021 by mrelwood

[Chriull]

34 minutes ago, Eucnhtusiast said:

The charger can't apply the full 100V to the battery because the voltage sags and that is not due to any electronics doing CC, but because of the difference in voltages.

Interesting thought.

The voltage sags by some miracle. So the current stays within limits, but the charger is not involved in this...

35 minutes ago, Eucnhtusiast said:

Eucs(or atleast Gotway) have NONE of these sensors and logic built in to either the bms or the chargers.

They have. Typically current sensing is performed via some (low value) resistor, called shunt. The voltage drop over such an resistor us used in the feedback loop of the switched mode power supply to reduce the output voltage and keep the current at some constant limit.

Letting the "voltage sag" from 100.8V to around 80V (empty battery) at some low charging current of about 2A would need something consuming a power of 20V*2A=40W - a very nice heater. This can never happen within the small plastic chargers we use.

[Chriull]

1 hour ago, Eucnhtusiast said:

Well, I believe that is what is happening as the chargers are really dumb.

If they have that current sensing capability, why isn't it used to shut down the charging procedure at the peak voltage when the current comes down to the range of 0.01-0.03C?

No idea. Especually as they already have this functionality implemented - they have the led changing from red to green once the current drops below some threshold.

Some chargers have only adjustment potentiometers for voltage and current, but some/many also for this threshold:

Quote

Have you felt a gotway charger during charging? They get very warm even with the fans blowing full tilt.

All/most chargers get very hot. Even if they have some great efficiency of some 95% they'll burn 5%. For a 250W charger that's still 12,5W transformed into heat. That's already about a (very) small soldering iron..

This why "stronger" chargers are in aluminium cases acting as heatsink instead of plastic cases.

58 minutes ago, Eucnhtusiast said:

Maybe I shouldn' have said EUCs, only gotway, as I would find it reasonable that IM and KS would include the basic lithium charging methods in full. I've got experience with only GW, which is know for their ridiculously simple bms and electrical "engineering". 

Gw, IM, ninebot KS use the same chargers.

Shermans had imho the sane, too - as @divwrote they seemed to have changed? Could be that the cutting off is performed on the mainboard - the Sherman has an unique bms/motherboard design.. afaik the motherboard measures charging current and battery voltage.

Ks and gw have very similar bms. KS just always had overcurrent/short circuit protection in the bms. Gw just with the newest models? And maybe with the old ones?

About IM bms was afair not too much written and ninebot have a bit smarter bms. With cell voltage reporting and joule counting. Afair the im v12 has cell voltage reporting, too? (Edit: mixed this up with pwm duty cycle reporting...)

Edited September 28, 2021 by Chriull

[Planemo]

4 hours ago, div said:

Some of them do, mostly (only?) third party chargers.
The cutoff current has to be right though, if too early it will shorten the balancing phase.

Here is my (third party) Sherman charger, cutting current after having tapered down to 0.4A or so. EUC shut down by itself, as it should.

(edit, BTW here is RagingGrandpa mentioning the chargers that never stop)

 

Its got nothing to do with the 3rd party charger, and everything to do with the Sherman, which will turn itself off and block input current whatever charger you use (as long as it hits peak voltage).

[Planemo]

5 minutes ago, div said:

No, with the stock charger it never turns off. It powers off only when there is no current.

Thats weird, mine did. The same as it does with my 'cheapo' aftermarket YZ 6A charger, whether I have it set to output 3A or 6A.

Maybe not all stock chargers are outputting quite enough peak voltage to hit the mobo cut-off point?

[Planemo]

19 minutes ago, div said:

I shared the picture of the Sherman to illustrate that the C1200 charger do have a cutoff threshold.

Just to make sure we are not talking cross purposes, are you saying that in the picture the Sherman shut down because the charger shut down, or because of the Sherman itself shutting down?

[supercurio]

18 minutes ago, div said:

The Sherman shut down because the charger stopped delivering current, contrary to the stock charger that goes on for ever. The point was the charger cutoff threshold, the powered off Sherman was just to illustrate that the current was cut.

I observe a different behaviour with the 5A stock charger (YZPower branded Leaperkim) as well as with a 3A Gotway stock charger on mine.

At the end of the CV phase, and after draining down to approx 22W from the socket, the wheel shuts off while the charger stays on with a green LED. The charger keeps using 2-3W (wasted) as the wheel remain off.
Unplugging the charger and plugging it again has no effect, as the wheel refuse to take charge, being already at "full" voltage.

Take note that it's with a very recent Sherman board running the 10.0.58 firmware and voltage calibrated so it ends up at exactly 100.8V.

Edited September 28, 2021 by supercurio

[Planemo]

28 minutes ago, div said:

The Sherman shut down because the charger stopped delivering current, contrary to the stock charger that goes on for ever. The point was the charger cutoff threshold, the powered off Sherman was just to illustrate that the current was cut.

Ok, I dont want to bang on about this but can we quantify it. The Sherman can be seen to shut down for two reasons:

1. It reaches full saturation.

2. Input charge is terminated.

Are you confident that the charger switched off totally thereby causing the sherman shutdown or:

That the Sherman got saturated, shut down and gave the impression that the charger had shut down.

Unless you were probing the output of the charger at the time of sherman shutdown or the charger has some sort of visible indication to show it is indeed 'off', I'm not sure how you could be sure it was one or the other.

10 minutes ago, supercurio said:

At the end of the CV phase, and after draining down to approx 22W from the socket, the wheel shuts off while the charger stays on with a green LED. The charger keeps using 2-3W (wasted) as the wheel remain off.
Unplugging the charger and plugging it again has no effect, as the wheel refuse to take charge, being already at "full" voltage.

Yep, exactly the same as mine. Also the same with my friend, using the stock charger on one of the earliest V1 Shermans.

My point being, although the charger is still 'on' and sending out a very small current, its irrelevant as the Sherman isnt accepting any of it. So the fact the charger is 'dumb' doesnt matter, at least on the Sherman. I believe its the same with my Z10 too as it happens.

[Planemo]

33 minutes ago, div said:

I was answering the question regarding if chargers can cut the charge on their own..

Out of interest, have you tried this charger on a Gotway for example?

[Planemo]

40 minutes ago, div said:

There is a display on the charger, it shows the current being 0.00A, just look at the photo I posted.

Oh and just for clarity/consistency, my 'non auto shutdown' charger would also show 0.00A if plugged into a fully charged sherman that had shut itself down..

[Planemo]

Just now, div said:

I don’t understand why you care so much about my charger and what you are trying to get to.

I'm simply interested in your charger. No idea why that would be a problem. But either way, no problem, we'll forget it. No offence intended!

[Richardo]

tell me to beat it if these electronics newbie questions are annoying... but if a CPU runs on 3.3v, and like a new Ryzen 3970 uses 280W, does that mean it's an 85 amp part?! 

[Planemo]

44 minutes ago, Richardo said:

tell me to beat it if these electronics newbie questions are annoying... but if a CPU runs on 3.3v, and like a new Ryzen 3970 uses 280W, does that mean it's an 85 amp part?! 

Good point! That said, I read a thread of someone overclocking a 3970X and using liquid nitrogen cooling so.... maybe 

[mrelwood]

14 hours ago, Richardo said:

tell me to beat it if these electronics newbie questions are annoying... but if a CPU runs on 3.3v, and like a new Ryzen 3970 uses 280W, does that mean it's an 85 amp part?! 

Ryzen 3970X seems to run on core voltages below 1.5V.

https://www.anandtech.com/show/15152/asus-rog-zenith-ii-extreme-review/8

 But a computer processor is much more than the core(s). Wikipedia can surely tell much more than what I know/remember, but unless I’m badly mistaken, there are several sections of the processor that use a significant amount of power as well.

[mrelwood]

On 9/27/2021 at 9:13 PM, EUC Endurist said:

would be interested in what happens when the cells are fully outbalanced and the charger is still plugged it? would there be some kind of bypass?

Why don’t we discuss the technical matters in it’s own topic? Link below. These won’t be answered in a short single posting.

 

[Chriull]

5 minutes ago, mrelwood said:

Why don’t we discuss the technical matters in it’s own topic? Link below. These won’t be answered in a short single posting.

Splitted these posts over to here - unfortionately it is sorted in by date...

On 9/27/2021 at 8:13 PM, EUC Endurist said:

would be interested in what happens when the cells are fully outbalanced and the charger is still plugged it? would there be some kind of bypass?

If cells are fully outbalanced they'll stay at exactly one 24th of the charger voltage (in case of a 100.8V wheel).

If everything is adjusted perfectly this would be 4.2V per cell, just before bleeding resistors are "applied".

So they'll trickle charge forever and build up some platings/dendrits over time.

As nothing is 100% perfect the charge voltage will be at bit above or below this threshold. If all resistors are applied trickle charging current will be a bit lower for the cells as some current is bypassed.

As all resistor voltage threshold are not 100% equal there also could be the case that some resistors are applied and some not. This could lead to some very slight balance by different trickle charge currents. But should not really change too much...

[mrelwood]

On 9/27/2021 at 9:13 PM, EUC Endurist said:

would be interested in what happens when the cells are fully outbalanced and the charger is still plugged it? would there be some kind of bypass?

I’m not sure what you mean by “outbalanced”. Do you mean fully balanced out, or fully out of balance?

[Jason McNeil]

It's a good video, but the explanation of the causes of cell/pack failure is to simplisitc & far from complete. Over the past 5 years, we've sold many thousands of Wheels, of the couple hundreds of pack failures that we have dealt with, >90% had been using the stock charger & following the standard manufacturing practice of charging to 100%. 

The strongest correlation evidence of premature pack failure is the cell-brand, followed by BMS fault & then shock/trama events—where single cells break from the nickel strips in the series.

Another consideration, that is somewhat unique to the electric unicycle, is that during hard braking, the amount of regenerative transient surge current will be far & beyond that of a 'normal' lab cycle longevity test. Partial charging will give your Wheel some buffer space for packs to absorb the converted kinetic energy without over charging beyond spec. This effect is also offset by the number of parallel packs in the Wheel & is not linnear in nature, i.e. it is logarithmic over a certain threshold. A host of other factors come into play as well: ambient temperature measured against the individual load factor of the cells, a cell's internal resistance, charge rate, depth of discharge frequency, etc. 

In response to Mrelwood's concerns last year, I had instructed our charger supplier to implement a CV phase into the partial charging modes to potentially minimize cell drift, & a Wh counter into the LCD output for Customers to be able to monitor the pack health/capacity.  

I agree that this topic needs further research to try to address the questions of:
1) What is the degree of cell imbalance if the charge cycle is terminated during the CC/CV transition?
2) Does tapering down the current in partial 80/90% modes reduce drift? In theory it should, but it ought to be demonstrated
3) Collect pack samples from both a control group (100%) & frequent partial charge usage to see if there's any descernible longevity effects, measure the IR of each cell 
4) Future BMSs ought to have an interface to view individual cells & cell-groups for monitoring those that are out of sync—this is something we're working on with our battery partner LiTech on the Begodes
5) Evaluation of active-balancing so that cells remain balanced over the whole charge cycle

In the larger context of targets for mfgrs to improve, battery issues consistute a minor rounding error to controller & motors issues.  

 

Edited September 30, 2021 by Jason McNeil

[meepmeepmayer]

@Jason McNeilWhat are the chances of convincing the manufacturers to use a BMS that always balances the cells (at least when the wheel is off) regardless of charge state? Assuming that would make sense, but balancing only in some states seems like an arbitrary and unnecessary technical holdover.

[Jason McNeil]

3 minutes ago, meepmeepmayer said:

What are the chances of convincing the manufacturers to use a BMS that always balances the cells (at least when the wheel is off) regardless of charge state? Assuming that would make sense, but balancing only in some states seems like an arbitrary and unnecessary technical holdover.

With LiTech, almost certain, but these projects take time, especially if it's something that's relatively novel.

[Marty Backe]

On 9/24/2021 at 12:26 AM, mrelwood said:

I finally got this video made. I hope that the crucially important information spreads better this way.

 

Late to the game, but I really enjoyed your video. I've been charging to 100% for years on all my wheels, and I typically don't get around to unplugging the charger for probably 8+ hours after the charging is complete.

I am guilty of leaving all my wheels at 100% and some of them will sit fully charged for over a month. I do notice many of the newer wheels are consuming some amount of power even when off. Many of the control boards have at least one tiny LED that will be flashing all the time. For instance, a Sherman that's left alone for over a month may be down ~1-volt. So I wonder if the "store at 40-60%" is as important now???

[RockyTop]

I am old school knowledge on batteries, yet I don’t see why this would not apply here. When you run batteries in series they are only as strong as the weakest cell. From day one, one of the cells is the weakest link. That cell is then damaged by the good health of the other batteries. The weak cell is over drained and charged every cycle. The BMS does what it can to minimize the damage. The point is that any abuse will be directed to the weakest cell. The damage is compounded. This also backs up Jason’s statement on poor quality batteries as being a major factor in failure.