How Does Phone Fast Charging Works?

R

rg12

100 kW
Joined
Jul 26, 2014
Messages
1,591
New phones have 9V chargers while the battery for all I know of is a single 3.7V lipo.
First of all, how is it possible to charge a single cell with such high voltage and second thing is, if it is converted back to 4.2V or something and some phones advertise crazy 50W and even over 100W charge speed, then that means that the current is supposed to be huge.

How do they do that?
 
The phones would have some kind of efficient DC/DC converter to step down to the battery voltage. Indeed, the current would be huge if you charge a single 3.7V cell with 100W. I'm surprised a phone would do that, but there must be lithium cells out there that can take such high charge rates.
 
All computer type devices have circuitry under host control to regulate the charging process and optimize battery lifespan.

Whether 1S (3.6-3.7Vnominal) or 2S or higher is up to the manufacturer's system designers.

USB standard input has been 5V, only recent "PD" variants of the USB-C standard go higher.

Most laptops have used 19Vdc input, with a lot of leeway.

As mentioned, DC-DC buck or boost conversion is standard circuitry to increase or decrease voltage as needed between circuits, nowadays very efficiently.

Even 200W is no big deal these days.
The C-rate, amps relative to the battery Ah capacity is what really counts for longevity.

Getting up to say 80% SoC at a high rate does not cause much loss of longevity, so long as the "topping up" stage getting to 100% is gentler.
 
john61ct said:
All computer type devices have circuitry under host control to regulate the charging process and optimize battery lifespan.

Whether 1S (3.6-3.7Vnominal) or 2S or higher is up to the manufacturer's system designers.

USB standard input has been 5V, only recent "PD" variants of the USB-C standard go higher.

Most laptops have used 19Vdc input, with a lot of leeway.

As mentioned, DC-DC buck or boost conversion is standard circuitry to increase or decrease voltage as needed between circuits, nowadays very efficiently.

Even 200W is no big deal these days.
The C-rate, amps relative to the battery Ah capacity is what really counts for longevity.

Getting up to say 80% SoC at a high rate does not cause much loss of longevity, so long as the "topping up" stage getting to 100% is gentler.
Click to expand...

Can the battery and small internal of the phone handle 20A to even 35A?
 
Amps current level is not pushed by the source

but pulled by the load.

The source only makes a max current available.

Without the control circuitry discussed above, the too-high CAR of the battery would be very destructive.

But with it, the phone will only allow a certain current rate to protect the battery - current limiting feature.

Hopefully allowing fewer amps as the battery capacity and health decline.

Of course they don't always get it right.

What specifically are you trying to do IRL?
 
john61ct said:
Amps current level is not pushed by the source

but pulled by the load.

The source only makes a max current available.

Without the control circuitry discussed above, the too-high CAR of the battery would be very destructive.

But with it, the phone will only allow a certain current rate to protect the battery - current limiting feature.

Hopefully allowing fewer amps as the battery capacity and health decline.

Of course they don't always get it right.

What specifically are you trying to do IRL?
Click to expand...

Yes, I'm aware that there is a control circuit but they still allow a 4.5Ah battery to be charged to full in 15m on this phone I read (I think one of the new Xiaomis), so it means it has to be above 20A since it lowers the charging speed at the top.
The thing is, even when it's controlled, how can 20A run inside the phone? is that a ton for such a cramped and closed circuit?
 
rg12
how can 20A run inside the phone? is that a ton for such a cramped and closed circuit?
Click to expand...

Either they have multiple traces to handle 20A on the pcb board, with additional via's for cooling (usually fets)
DCDC would do, but takes up to much space and probably a lot of leakage so its taken outside into the charger if its done that way I dunno.

I'd think 20A along a trace would interefere to much with everything near the trace. I really dont know much if anything about cell phone circuitry.
 
First off, the way they get a measurement of 4.5Ah is at a very very slow discharge rate, nothing to do with a higher charge rate

Second, the protective circuitry likely leaves 10% off the top end certainly at the higher rates, maybe even more off the bottom for longevity.

So 3.2-3.5Ah is more realistically what we're talking about.

And I may be wrong but I call BS on "charge to full in 15m". Maybe from when the user readout says 10-20% (actually 20-35% of 4.5Ah) and getting to a user readout of 80-85% (actually 65-80% of 4.5Ah)
 
It reduces cycle lifespan no matter what,

so use only when needed is better.

just that better quality you still get decent cycles even with the abuse.

Phone makers only need it to last 3-4 years anyway

then user gets a new phone
 
You must log in or register to reply here.

Similar threads

M
Help with first pack build
Replies
10
Views
487
mynameisjoe
M
E
Any galaxy-brain solutions to fast-charging ebikes, motorcycles, and light cars at level 2 chargers in the US?
Replies
2
Views
328
ElectricBikeSquatch
E
J
Connect battery holders together
Replies
1
Views
546
jatgm1
J
S
How unsafe are custom batteries?
Replies
15
Views
1,226
calab
C
C
The Charging Standards Thread
Replies
2
Views
578
CONSIDERABLE SHOUTING
C
Back
Top