50% charge in 30 minutes?

i note that a decent cell like a Samsung 35E is to be charged at 1amp to ensure a long life, otherwise at 0.5C or 1.7amp for standard conditions; charging time to 50% will be 3 or 1 hour respectively. When I try to force a high charge current, the battery quite quickly hits 4.2v - opposite of sag.

How and why are these car manufacturers ignoring the advice of the battery manufacturers?

I can't speak for all the EV manufacturers, but it's my understanding that the packs in Tesla cars are actively cooled when they are being charged.

Also, the on-board BMS allows occasional "fast charges", but...it won't let you fast charge every time, because they have a warranty that guarantees a certain amount of range will remain during the first eight years, and frequent fast-charges will erode the packs life, even with the active cooling.

50% in 30 min is only a 1C charge rate which is not excessive fot quality cells....
But...remember that 50% is restricted to below 80% of full charge...IE never to max pack voltage which is where high charge rates likely cause problems and why all chargers reduce current towards full charge level.

The 35E is a low c-rate cell (the trade-off of high capacity) and not representative of typical EV cells.

James Broadhurst said:

How and why are these car manufacturers ignoring the advice of the battery manufacturers?

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They're not. EV cells are generally made specifically for EV's, and the EV manufacturer works with the battery manufacturer to make sure the specs are aligned. 1C charge acceptance is not that unusual.

billvon said:

They're not. EV cells are generally made specifically for EV's, and the EV manufacturer works with the battery manufacturer to make sure the specs are aligned. 1C charge acceptance is not that unusual.

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Oh, come on, they are! They're defending themselves against guarantee claims; guarantees which they have to give otherwise no one would buy them.

I'm still interested in knowing how it's done. Occasionally I would have liked to put a half charge in 30 minutes but the speed with which the pack hits 4.2v is just too quick. The quicker I taper the current, the longer the charge takes.

James Broadhurst said:

Oh, come on, they are! They're defending themselves against guarantee claims; guarantees which they have to give otherwise no one would buy them.

I'm still interested in knowing how it's done. Occasionally I would have liked to put a half charge in 30 minutes but the speed with which the pack hits 4.2v is just too quick. The quicker I taper the current, the longer the charge takes.

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Given a big enough charger, I can get a cell from empty to 4.2v in a matter of seconds, if not shorter. That doesn't mean it's 100% charged. That's just the voltage recorded at the charger, not the potential difference between the anode and cathode (which is again different from the voltage recorded at the cell ends).

So how do they do it? I don't know specifically, but here's my guess, since I see my EV charger occasionally dropping to 0W for a few seconds to a few minutes - They set a CC-CV charge method with two profiles - one with a high constant current when the SoC is < 50%, and one with a low current when the SoC is > 50%.

At first, they just set high constant current. The voltage will slowly rise, but it's ignored unless it hits 4.2v per cell. During the CC phase, voltage is not a reliable indicator of State of Charge. Once the battery is charged enough to hit 4.2v per cell, they go constant voltage instead, and the cell controls how much current is absorbed. Again, voltage is NOT a reliable indicator of State of Charge, because it's affected by the internal resistance of the cell.

Every <X> minutes, they disconnect the charger for a few seconds, and sees where the voltage settles to. THAT is the accurate measure of state of charge. Once that "settled" voltage indicates cells are >50% SoC, they probably do a much slower constant current charge to protect the battery.

James Broadhurst said:

billvon said:

They're not. EV cells are generally made specifically for EV's, and the EV manufacturer works with the battery manufacturer to make sure the specs are aligned. 1C charge acceptance is not that unusual.

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Oh, come on, they are!

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The Panasonic INR18650-20R is spec'd by the manufacturer to rapid charge at 2C, for example - and it's a five year old battery. Nowadays the tradeoff is generally between discharge (and charge) rate and energy - between power and energy, in other words.

If your charger is hitting constant voltage that fast then the cells either arn't that low and are mostly charged, you're charging with really high current limit, or the capacity is degraded.

Pretty much all cells can charge at 1C it's not that complicated. If you go from a pretty low SOC, at 1C you will have about 50% capacity added in 30 minutes.

The EIG NMC cells (p/n C020, IIRC) I have charge at 1C easily, and my quick charger does do at least 50% in half an hour, without heating the cells noticeably, or slamming the voltage up to "full". (it takes more than an hour to do a full charge, though, as it tapers off as it gets close to full.)

They are EV-rated cells, made for the purpose.

I don't run them down that far very often, though.


The 18650 pack I have (can't recall which cells) aren't like that, though--they're more like what the OP reports, cuz they're not really made for this purpose. (and they get hot in discharge as well as at least warm in charge).

I = V/R

If you want to stuff high amps into a cell with high internal resistance then you need high voltage to do it i.e. over 4.2V.

High capacity cells have high internal resistance, which is why they charge (and discharge) slowly (and make a lot of heat doing it).

flat tire said:

Pretty much all cells can charge at 1C it's not that complicated. If you go from a pretty low SOC, at 1C you will have about 50% capacity added in 30 minutes.

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A 25R charged at the "Rapid Charge" of 4amp should charge in 60 minutes with a 100mA cut-off. This battery conforms to the EV manufacturers claim. However, the charge voltage within a minute reached 4.19v and the charger then entered its CV phase with a current of 3 amps and falling. The charger is an iCharger and it will cut-off at C/10 or 0.4 amps which it did 81 minutes later having gained 1,975 mAhr. Setting the cut-off at 100mA gives another 279 mAhr after 68 minutes.

It took 150 minutes to put a full charge into the cell.

Sansung don't actually say what you should expect. The only data they give in this respect is the "Standard Charge" rate of 1.25 amps which will give the nominal capacity of 2,500mAhr.

You'd probably get somewhere near 80% in an hour but you'd have a seriously stressed battery.

The amount of punishment such a battery can take is pretty limited; do it for 250 cycles and you'll have less than 60% capacity.

I dunno what to tell you. I have had totally different experience with my 25R. Maybe yours are counterfeit or your charger has issues.

James Broadhurst said:

A 25R charged at the "Rapid Charge" of 4amp should charge in 60 minutes with a 100mA cut-off. This battery conforms to the EV manufacturers claim. However, the charge voltage within a minute reached 4.19v and the charger then entered its CV phase with a current of 3 amps and falling. The charger is an iCharger and it will cut-off at C/10 or 0.4 amps which it did 81 minutes later having gained 1,975 mAhr. Setting the cut-off at 100mA gives another 279 mAhr after 68 minutes.

It took 150 minutes to put a full charge into the cell.

Sansung don't actually say what you should expect. The only data they give in this respect is the "Standard Charge" rate of 1.25 amps which will give the nominal capacity of 2,500mAhr.

You'd probably get somewhere near 80% in an hour but you'd have a seriously stressed battery.

The amount of punishment such a battery can take is pretty limited; do it for 250 cycles and you'll have less than 60% capacity.

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So why are you using "rapid charge" at 4 amps ?.....that is not what was being discussed.
Why not limit the charge to 1C (2.5A) as suggested , and see what Ah you get after 30 mins.
Most folk here know that excessive charge rates are not a good idea to use regularly, and also that the last 20-25% of capacity doubles the time taken to charge ..because of the CC/CV profile.

Hillhater said:

So why are you using "rapid charge" at 4 amps ?.....that is not what was being discussed.
Why not limit the charge to 1C (2.5A) as suggested , and see what Ah you get after 30 mins.
Most folk here know that excessive charge rates are not a good idea to use regularly, and also that the last 20-25% of capacity doubles the time taken to charge ..because of the CC/CV profile.

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I think if the manufacturer in the datasheet already writes that it is possible to use 4A "rapid charge" one would expect that it will have practical use. Like you are able to charge at least 30% of capacity with that current before you enter CV mode.