Fast Charging: Dispelling the Myths

[Garrie Lim]

I realised there are a couple of people who are against fast charging or worry that it will damage the battery very quickly. I’ll just like to share with you all that it is not always the case and that “fast charging” for our large capacity wheels these days is pretty safe and not really “fast charging” at all. 

 

Im gonna demonstrate it by using the Gotway MSX as an example. So bear with me. 

 

The Gotway (84v)MSX is a 72V 20.7ah 1490wh Wheel, with its cells arranged in a 20S 6P configuration. 

Before we carry out “fast charging”, it is first important to know the config of our battery pack, and also what cells we are using. 

The MSX uses the Panasonic/Sanyo GA cell, with a max capacity of 3.45ah per cell, and since it is arranged in 6P as mentioned, the total capacity of our wheel is 20.7ah.

Next we need to find the data sheet for the cell and find the standard charge rate for the cell, most of the time it is 0.5C  

1C is 3.45amps discharged in an hour 

therefore 0.5C ~1.7amps

However, the manufacturer has stated a lower standard charge rate of 1.475amps instead(https://www.orbtronic.com/content/Datasheet-specs-Sanyo-Panasonic-NCR18650GA-3500mah.pdf) so we shall use that  

 

Now when we use a 5a charger, assuming 100% efficient, those 5 amps will be spread over the 6 parallel packs in the msx  

Each parallel group will receive 5/6=0.83amps, way below the standard charge rate of 1.475amps.

 

so don’t worry, “fast charge” away because it isn’t even fast charging!

 

[Brian Morris]

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. 

[stephen]

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 😁😁

[LucasD]

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...

[esaj]

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 May 19, 2019 by esaj

[Brian Morris]

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?

[esaj]

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 May 19, 2019 by esaj

[Seba]

49 minutes ago, Brian Morris said:

source?

Working principle of so-called bleeding balancing circuit. It kicks-in only when cell is over 4.2 volts by shunting that cell with relatively high, paralell resistance. It is simple but quite limited in the way it works. It's also cheap and this is why it's the only type of balancing circuit used in EUCs (if any at all, because there are EUC s without balancing at all). So by charging to even 90% you never allow the pack to even start balancing.

40 minutes ago, esaj said:

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?

No, they just have an individual cell voltage readout. By the way very useful feature. Really helps to manage the charging regime and monitor how balancing works.

6 hours ago, Garrie Lim said:

so don’t worry, “fast charge” away because it isn’t even fast charging!

Nice post. I would only add one warning - although battery configuration may allow much higher charging current, you may be limited by MOSFET switch on the BMS charging side or even at EUC control board. So it's possible that you won't damage your battery, but you will damage the BMS/control board circuitry. As an example - King Song KS-18L/XL have additional MOSFET circuit (so-called "ideal diode" used as a reverse-polarity protection) in control board. With charging currents over 8 amps at about 20 °C ambient, temperature  of this MOSFET package quickly reaches 100 °C... Charging during hot summer day could cause this transistor to fail even if you charge way below the pack allowed current. So it's not just black and white...

Edited May 19, 2019 by Seba

[Chriull]

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.

[Mono]

4 hours ago, Brian Morris said:

full discharge causes more loss

debunked here:

 

 

[Mono]

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 May 19, 2019 by Mono

[Chriull]

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

[esaj]

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 May 19, 2019 by esaj

[samzed]

My friend had a Nissan Leaf EV and the handbook said not to quick charge past 70 percent very often in order to get the most life out of the Lithium batteries as possible. Does this hold true with our PEV's? Maybe that's why my Z10 only came with a slow charger and that's why Ninebot made it difficult to quick charge my Z10? Are people damaging their battery packs by quick charging their batteries past 70%?

[alcatraz]

Batteries wear out. Some habits accelerate wear.

It's not a secret that you get more cycles out of a cell if you don't charge or deplete it completely, or overheat it.

What is considered "quick charging"? The cell manufacturer specifies a standard charge rate. Faster will wear out the cell, slower should increase life.

So the charger is just a rate that the manufacturer has settled on using. It doesn't mean it's right for everyone. Some might accept a reduced life if they can charge faster, some don't.

Some chargers are so slow that a quick charger is still well below the standard charge rate that the cell manufacturer specifies. "Quick" is relative.

[mrelwood]

3 hours ago, alcatraz said:

"Quick" is relative.

Exactly, this is the key.

I'm to lazy to dig up the cell model for the Z10, but usually 18650 cells have a 3-3.5Ah capacity. For a 4p pack (not sure what the Z10 has) that would mean 1C charge rate of 12-14A. Standard charge has been mentioned as 0.5C, so 6-7A. Anything below that is a slow charge. And the charging connector is usually rated only at 5A. So even charging the Z10 at 5A wouldn't be "quick charging".

When reading battery advice from anywhere, especially outside of the EUC community, you have to remember that:

- EUC batteries REQUIRE 100% charging (+ 1 to 2 hours) to keep the pack healthy. The BMS only balances the cells after the highest cell has reached 100%.

- Without balancing an EUC battery is known to have failed before 2000km.

- 300 full Li-ion charge cycles equal roughly 15000km of riding on the Z10. To change one's charging habits in order to gain more battery lifetime very rarely makes logical sense. Especially if it means disabling balancing.

- EUC battery at 0% is still at 30-50% of the cell's usable voltage range. Percentage sucks as an advice.

More info on 80% charging an EUC battery:

 

[Funky]

Don't know about cars... And their battery system...

But in EUC's - You want to charge 100% every time. +Some time left after charger turns green. (My wheel beeps when it's done charging/balancing.. It normally takes 1-2 extra hours after charger have turned already green.)

And i charge my wheel when battery has dropped down to 40-50%. Normally over several days of usage.

Roughs numbers: With quick charger you may lose 10-15% of overall battery life? What 25k miles vs 22k miles? Is the ~3k miles worth? And by that time you may have lost about 15-20% of battery capacity.. You still can continue riding, but with little bit les range.

Ride till you batteries die.. Be 2k miles, be at 25k miles or at 100k miles. 

 

Edited October 7, 2022 by Funky

[Planemo]

4 hours ago, mrelwood said:

Exactly, this is the key.

I'm to lazy to dig up the cell model for the Z10

Z10 is 14s3p x2

OP: I have used 5A on mine many times. Zero problems. As others have said, 5A is NOTHING like a 'quick charge' on the Z10 or many other wheels. Ninebot supply a 1.5A as standard only because they are cheap.

Most EV cars run intelligent charging systems that can balance the packs throughout the charge phase, meaning that it can be beneficial to battery life to not charge past 70% if you don't need to.

Our wheels only balance towards the very end of charging. Balancing is critical. Far more critical than any downsides associated with charging to 100%.

So if you need to charge, go to 100% if possible.

[dycus]

One reason manufacturers supply low-amperage chargers is probably due to the limited amount of power the balancing circuit is able to bleed off.

Let's say you have one cell that's 0.2V higher than the rest. So during charging, all cells will eventually come up to 4.0V, while the high cell will reach the max voltage of 4.2V. The balancing circuit connects a resistor across the high cell to bleed off some of the charge. The charging current must be low enough that the bleed resistor can "keep up", so the high cell doesn't go over 4.2V while the rest of the cells come up. It basically shunts some of the charging current around the high cell.

These resistors don't bleed a lot of current (usually no more than 100mA) because they have limited power dissipation capability. A 100V pack with twenty-three 4.0V cells and one 4.2V cell is only at 96.2V, still well in the constant-current phase of the charger. If it's a 4P pack and you're charging at 4A, that's 1A through each cell, and the balancing resistor won't be able to keep up.

However, in practice, the wheel should stop charging once any cell reaches too high a voltage and only start again once it's bled off enough charge. Even charging at 1.5A on a 4P pack is 375mA per cell, well over what the BMS could bleed.

This also assumes a huge imbalance (200mV). For much smaller imbalances (~20mV) the charger should reach the constant-voltage phase, where charge current drops off exponentially, before any cell gets too high. But with a fast charger this could still be a large-ish current.

[YCC]

Guys, does high charging current make the lifetime of battery decrease?

In respect to not considering the safety issue and the charging current is under the safe margin of the charging current, do you know any evidence or theory to support that high charging current is bad for battery?

For instance, the 3A charging current used in one charger port is longer than 16A in two charger port for the lifetime of battery(8A for each charger port), or there is no significant difference.

[RagingGrandpa]

14 hours ago, YCC said:

high charging current make the lifetime of battery decrease

Not directly.
The problem is elevated cell temperature.
If we could keep the cells near 25°C, one-hour charging would be possible... but EUC packs are sealed with no cooling, so a one-hour charge is not realistic.
 

14 hours ago, YCC said:

evidence or theory to support that high charging current is bad

That's the cell aging data, collected by numerous admirable hobbyists and vendors.
https://endless-sphere.com/sphere/threads/cycle-life-tests-of-high-power-density-cylindrical-cells.114473/
 

14 hours ago, YCC said:

3A charging current used in one charger port
16A in two charger port (8A for each)

The ports are connected together directly, immediately, inside the EUC. 
The cells have no idea which ports are connected, so "one port" vs "two ports" doesn't matter to cell aging.

KS 16x is 20s6p 18650 MJ1. 
Using a 3A charger with the EUC means 3/6 = 0.5 amp per cell. A very slow charging rate. 
Using a theoretical 16A charger mean 16/6 = 2.7 amps per cell. Still within the cell's rating (3.4 amps max charging), but it would cause warming (which you could feel and measure), and thus accelerates aging. 
(But KS 16x's controller will not permit charging above 8 amps I think.)
 

Edited December 21, 2023 by RagingGrandpa

[Patrick Robert]

Always charged my OG Sherman at its maximum rated 10A, with at least one balancing charge up to 100% at the end of the day. 

Still charges to 100.4V like it always did after three years. No degradation. 

[Seba]

On 12/21/2023 at 4:03 PM, RagingGrandpa said:

But KS 16x's controller will not permit charging above 8 amps I think.

It will, but will also beep above ~6A of charging current.