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


mrelwood

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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...

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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?

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@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.

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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???

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13 minutes ago, RagingGrandpa said:

The 'weak' cell will become discharged to about 3.0V. It's lower than the others, but still a perfectly healthy and non-damaging voltage.

So using one cell, the weakest cell more than the others, draining just a bit further is NOT going to weaken it even quicker than the good healthy cells? 

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51 minutes ago, RockyTop said:

using the weakest cell more than the others, draining it just a bit further, is going to weaken it even quicker than the good healthy cells

^ this, yes, but only slightly

It means: for every 100 full-cycles of the 'weak' cell, there are only 90 equivalent full-cycles of the strong cells. So the weak cell ages faster.

This is a small effect, because problems resulting from this usually don't matter until we're nearing 500 cycles. Since EUC's are not a high-cycle-count application, it's rare to find an example where this normal aging process makes a pack unusable. (500 cycles is 12,500 miles ridden for Tesla, and 33,000 miles ridden for Sherman!)

So when there's a failure, it's more likely that one of Jason's 1-2-3 is to blame ;)

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Would your 'weak' cell be in danger of getting pulled below the 2.5V damage threshold during large current draw events? Or do the individual cells have under voltage protection (in the olden days of primary lithium cells, each cell had over and under voltage protection and some had fused PTC—I don't know about individual LiIon cells).

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17 minutes ago, Tawpie said:

Or do the individual cells have under voltage protection

I don't believe any of our EUC's use packs with protected cells. Presumably the idea being that when used with a BMS, you shouldn't need them. Of course, the problem with this is that we are up to so many cells in our EUC's now, with silly amounts of them being paralleled, that each string monitored by the BMS has too many cells hanging off it for my liking.

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1 hour ago, Dogmaticjoe said:

so if I charge my wheel (the KS18XL) to 100% with my stock charger how long after it hits 100% should I leave it plugged in to let it balance?

TLDR: once the charger shows the green light.

If the KS18XL is (still?) using the NCR18650GA panasonic recommends:

"(5) Termination of Charging
The system will determine that the battery is full by detecting the charge current.
Stop charging once the current has reached 0.1 It to 0.07 It. Note that there will be some degree of
variation for each individual battery.
(6) Charge Timer
A total charge timer and a charge completion timer should be included"

in https://industrial.panasonic.com/cdbs/www-data/pdf/ACA4000/ACA4000PE4.pdf

For this specific cell they use/recommend for a full charge in their cell datasheet in one diagram 67mA as charge current threshold, 100mA in another.

With the KS18XL having 6 cells in parallel this translates to 6 x 67...100mA~400...600mA.

It's not secure how the charge current threshold of the individual chargers to show the green light are adjusted, but normally, from what us reported here this green led has chances to show at some a bit lower current thresholds.

The effects of charging downto 600, 400 or even 250mA should imho be minimal, but it is interesting and notable that panasonic in their dazasheet charges downto 67mA for the "performance graph", but only downto 100mA for their "cycle life graph"!

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I don’t have the 18xl at hand but in the case of the 16S (it’s about the same) the charger goes green before the voltage stabilises; so in the lack of current measuring I like going for the second. (Feels more right, no scientific backing)

(The selection point on the graph is when the charger goes green, at 67,43V, it stabilises at 67,59V)

Ultimately people don’t stand by their charger to see the second it goes green, so as a general rule (considering most won’t notice it until a bit later) it’s probably fine.

Edit: Chriull is certainly correct here, only as he mentions we’re not sure of the threshold of the individual charger to go green. Hence me estimating stable voltage as end of CV.

IMG_0915.jpg

Edited by div
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1 hour ago, div said:

(The selection point on the graph is when the charger goes green, at 67,43V, it stabilises at 67,59V)

Seems your green light really comes a bit early.

For comparison the charge graphs (with EUC Worlds "estimated" charge current via the HS110 plug) are from my KS16S https://forum.electricunicycle.org/topic/18317-battery-faq/?do=findComment&comment=307641 . Our batteries very likely have some different "internal state" by now, but in my graphs this last ~0,15 happen from ~0,5..0,7A on...

... and sounds plausible. Perfect internal 16s4p resistance (48mOhm per cell) would be about 0.2 Ohm. 0.7A * 0.2Ohm = 0.14V :)

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2 hours ago, Chriull said:

If the KS18XL is (still?) using the NCR18650GA panasonic recommends:

Panasonic doesn’t have recommendations for large packs in series with a passive top balancing systems though… I think that balancing even just a bit longer easily overrides the microscopic difference that the charging current cutoff can ever bring.

 

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I haven't been bothered with cell degradation due to I bought so many new wheels because the development went so fast. 

So far I have yet to see a problem. Well my V11 had a BMS state failure on one battery pack but beside that neither of my wheels showed any signs of degradation. 

Now going forward I suspect the upgrade cycle at least in my part will be much slower. I have the speed and in general the range I need. And the comfort of the V11 suspension too. 

That is not to say something better might make me want a new wheel. But having 2x V11 with winter/all season tire on I think they will outlast me for some time. And I can choose to use one for spare parts if any problems occur in one of them. But I am fairly sure most do not have a wheel similar just for backup. I chose this as I know how hard spare parts can be to come by these times. And I predict it will take a year maybe more before this get stabil. 

So far I charge as long my wheel get below 70% in battery. And I use EUC.WORLD to monitor the charging though a TP-link HS110 smart plug. 

It might degrade the battery over tid. On the other hand I am more worried of cells getting out of balance.

I am not a battery or charging expert at all. What I am doing could be all wrong. 

What I do think is very very interesting is the @Jason McNeil joined in. I think he will hold more data in view perspective what causes problems. But like @mrelwood said one thing is warranty resolved issues another is what happens outside warranty. That leaves a blank data sheet in most cases compared to what I know from my line of work.

As battery pack gets larger the impact of degradation might show more as it is less prone for people to buy a new wheel if the old one is sufficient if in working order.  Also charge cycles might show different because of different charging behaviours.

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 I have watched @mrelwood rack up excessive miles on many new wheels in just a year or two. ( 16s > MSX > v11 ) The DarknessBot tends to set him near the top of the mileage list. So I am going to trust his observations. 
 

As a hobby rider, weekend explorer, I will never put the miles on a wheel like the commuters. I have always assumed that my batteries are going to age out before they wear out. 
 

I thought that max battery preservation included a cycle of  4:1  Four times at 80% then a full charge. Is this not true? 

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1 hour ago, mrelwood said:

Stalker. :lol:

I like your voice. :wub:  

Hey it's not me. Blame Darknessbot. You are a Darknessbot celebrity.

RockyTop 136 miles this week. rank 995. So who is in the top 10?  mr.elwood. 

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1 hour ago, RockyTop said:

I like your voice. :wub: 
 

Someone said that I sound like Arnold Schwarzenegger! :roflmao: (But thanks! I made it myself!)

 

1 hour ago, RockyTop said:

You are a Darknessbot celebrity.

RockyTop 136 miles this week. rank 995. So who is in the top 10?  mr.elwood. 

It’s actually interesting, since I haven’t used DarknessBot for a year or two. I have connected it a few times though, so maybe it catches up for the long term charts. But It has been maybe a month since I last connected with it.

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On 9/29/2021 at 10:06 PM, Chriull said:

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

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...

thanks really much. so ill opt for 1-2hours green led and then cut the charger. you helped me many times chriull :)

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  • RagingGrandpa changed the title to Video on 80% charging, "Good or Bad?"

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