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Garrie Lim

Fast Charging: Dispelling the Myths

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And if you want your battery to last "forever" never charge over 80% or discharge under  40%  cycles go up exponentially when the battery is kept in this range.  Full charge and storage causes capacity loss, full discharge causes more loss. 

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21 minutes ago, Brian Morris said:

And if you want your battery to last "forever" never charge over 80% or discharge under  40%  cycles go up exponentially when the battery is kept in this range.  Full charge and storage causes capacity loss, full discharge causes more loss. 

I only charge to 100% when I'm just about to go out for a ride i never leave it full for long ,i only fast charge when I'm out when i need a quick to up , if i need the feel to go for another ride I'll grab my other wheel 😁😁

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In other topic, you can find that self-balancing battery circuit is important and works only when charged to 100%. So you need to charge to 100% every x cycles, or you risk your pack...

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Posted (edited)

From what I know, this is true, the amperage is hardly a problem for the modern wheels with multiple packs in parallel. Some years back, most of the wheels had just one or two packs and there it could have become an issue. Nowadays, the limiting factor is the charge connector (such as a GX16) and the wiring, which can become very hot with high amperage, still, 5A for a GX16-3 or such should be within limits (the maximum given by manufacturers is 5A or 7A, depending where you look, and seems to go down the more pins the connector has). The newer plugs used on some wheels (don't remember the name, the rectangular one) are probably meant for higher amperage, and even the other wheels could be retrofitted with thicker wiring and multiple charge ports in parallel. I think 1RadWerkstatt used to sell a kit with 8A charger with two outputs (4A each) and secondary charge connector to fit in the wheel...

Edited by esaj
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1 hour ago, LucasD said:

In other topic, you can find that self-balancing battery circuit is important and works only when charged to 100%. So you need to charge to 100% every x cycles, or you risk your pack...

source?

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Posted (edited)
1 hour ago, Brian Morris said:

source?

You can probably find a ton more just by a quick google search for something like  lithium ion cell balancing , but here's a couple:

https://www.batterypoweronline.com/blogs/why-proper-cell-balancing-is-necessary-in-battery-packs/

https://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing

 

Wheels don't seems to have "active" balancing circuits, rather they just bypass shunt cells that reach the full voltage, thus the "balancing" on the wheels works by charging it to full and then leaving it still on the charger for the rest of the cells to catch up (even after the charger light turns green to indicate "full" battery, there is still current running, many of the chargers turn the light green somewhere around 200mA). I use Charge Doctor to monitor this, and wait until the current drops to very near zero (10-20mA).

I recall seeing a screenshot from the app of some wheel (Ninebot Z, maybe?) that showed the individual cell voltages, wonder whether they have an actual active balancing scheme?

Edited by esaj
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2 hours ago, LucasD said:

In other topic, you can find that self-balancing battery circuit is important and works only when charged to 100%. So you need to charge to 100% every x cycles, or you risk your pack...

 

48 minutes ago, Brian Morris said:

source?

The importance of balancing seems to be "discussionworty" - at least as the articles at batteryuniversity.com express it.

Much more important seems the cell matching - this seems to be the number one factor.

But cell balancing could /should be able to at least delay the end of a battery pack.

Balance voltage threshold is normaly specced at 4.2V for the BMS i've seen. Balancing could start at any other (lower) voltage, but would not make much sense to bypass by this all cells in the end as the they are charged to 4.2V.

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4 hours ago, Brian Morris said:

full discharge causes more loss

debunked here:

 

 

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Posted (edited)
3 hours ago, esaj said:

From what I know, this is true, the amperage is hardly a problem for the modern wheels with multiple packs in parallel.

The point is that amperage is a meaningless notion in this context without giving further information. On the other hand, C-value or charge time to achieve a full charge seem to be meaningful. That is, a charge time of two hours or above (EDIT: to charge from 0% to 85%) will not harm the battery and a charge time below one hour is likely to impact its life expectancy.

Edited by Mono
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9 minutes ago, Mono said:

That is, a charge time of two hours or above will not harm the battery and a charge time below one hour is likely to impact its life expectancy.

According to todays "state of the art". 1C is about the "border", and a bit less recommended. Most manufacturers today specify 0.5C or even a bit less.

But maybe we could hope for serious improvement to come:

"One assumes that all charge energy goes into the battery, whether charged slowly, rapidly or by ultra-fast method. Batteries are nonlinear devices and most chemistry accepts a fast charge from empty up to about 50% state-of-charge (SoC) with little losses. NiCd does best and suffers the least amount of strain. Stresses occur in the second half of the charge cycle towards top charge when acceptance of lithium ions in the anode of Li-ion becomes labored. An analogy is irate drivers fighting for the last parking spot in a shopping mall to catch a sale special.

Applying an ultra-fast charge when the battery is empty and then tapering off the current when reaching 50% SoC and higher is called step charging. The laptop industry has been applying step charging for many years. The charge currents must harmonize with the battery type as different battery systems have dissimilar requirements in charge acceptance. Battery manufacturers do not publish charge rates as a function of SoC. Much of this is proprietary information.

Research companies claim to achieve benefits with pulse-charging Li-ion instead applying the regular CCCV charge as described in BU-409: Charging Lithium-ion. The scientific community is skeptical to alternative charging and takes the “wait-and-see” approach."

from https://batteryuniversity.com/learn/article/ultra_fast_chargers

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Posted (edited)
41 minutes ago, Mono said:

The point is that amperage is a meaningless notion in this context without giving further information. On the other hand, C-value or charge time to achieve a full charge seem to be meaningful. That is, a charge time of two hours or above will not harm the battery and a charge time below one hour is likely to impact its life expectancy.

True, it's probably easier to understand it as the time it takes to charge than a value of current. Still, in real-life circumstances, actually charging from empty to full in one hour would mean that the charge rate is actually far higher than 1C, because the amperage (and thus charging "speed") drops towards the end, as the charger voltage reaches the maximum and stops raising it. To keep going at 1C until the end, the charger would have to raise its voltage above the maximum battery voltage and then somehow "know" when the battery itself has reached the maximum value and stop abruptly. Thus even a 2-hour charge may be using close to or even more than 1C before the CV-phase begins.

With the large capacity of most current wheels, probably nobody actually reaches the "1C" -values... imagine something like 20S/1600Wh pack at nominal 74V (3.7 * 20), that would be over 20Ah. Likely the charge port or wiring will melt, or the BMS components will die before that high current can be reached.

Edit: Oh right, for the unitiated, the "C"-rate for charging speed is explained here: 

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

 

Edited by esaj
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