Fast charging has finally become truly fast, Xiaomi's 100W system demonstrated

mrk · 27 Mar 2019 at 11:19

https://www.facebook.com/wangxiang.xiaomi/videos/337246410239405/

18V 4.5A pumped into the phone. 17 minutes to charge to full whereas the 50W competition only reaches 65% as the Xiaomi one reaches 100.

I feel this will be a stop-gap solution until Graphene batteries hit the mainstream (Samsung recently announced they have finished their development of them). Quite remarkable though and be interesting to hear how they tackled the heat generated by that much voltage/current. It's not fast charging that reduces battery health, but the heat it generates, be it wired or wireless. Which is why OPPO's Super VOOC works so well as all the heat resides in the charger block and not the phone.

d_brennen · 27 Mar 2019 at 11:21

Do you dial 999 before or after plugging it in?

cu3ed · 27 Mar 2019 at 15:41

d_brennen said:
Do you dial 999 before or after plugging it in?

I'd say before...considering you're about to blow up your phone.

PooKer · 28 Mar 2019 at 10:15

If it doesn't blow up. realistically how many cycles will the thing last?

Then again I remember the days when you'd take a battery from being 5% up to 100%.... by swapping the battery.....

mrk · 28 Mar 2019 at 10:43

It's the heat from the charger circuitry that weakens batteries the most, like with wireless fast charging too, the system generates heat. Take the heat away and you retain battery health like with Oppo's Super VOOC and so on.

Some higher end laptop batteries charge up to 100W IIRC, but they have big power bricks external to the laptop to avoid quick cell degrade.

DarkBahamut · 29 Mar 2019 at 00:18

mrk said:
It's the heat from the charger circuitry that weakens batteries the most, like with wireless fast charging too, the system generates heat. Take the heat away and you retain battery health like with Oppo's Super VOOC and so on.

Some higher end laptop batteries charge up to 100W IIRC, but they have big power bricks external to the laptop to avoid quick cell degrade.

Laptops also don't have a 15W/h battery either. While battery temperature is important you can't just ignore the C-rate either. Pushing charge rates to something like 6C is definitely going to reduce cycle life no matter what temperature you keep it at. I'd guess Xiaomi bank on a few hundred cycles as enough as most users will upgrade after a couple of years anyway.

Something quite interesting is that over time Samsung for example has been slowing down their 'fast charging'. The Note 9 has a lower battery input current than the Note 4 does - slower charging. And the S10 is even lower still on most fast chargers. Quite telling that a manufacturer of batteries has been pulling back charge rates despite years of battery advancements.

mrk · 29 Mar 2019 at 08:22

Samsung have only been slowing dome some elements or keeping it the same since the Note 7 issues. This week the Samsung CEO made a statement that they might unlock the 25W fast charging ability of the S10 series with a firmware update, for example. Otherwise Samsung fast charging has been at 0V 1.67A since the very early days of around the S6+/edge IIRC for all flagships.

So the chipsets certainly support it, and in the past QualComm have been quoted saying that batteries engineered for fast charging are safe for exactly that.

We already have phones charging up to 40-50W anyway and they'e been fine!

DarkBahamut · 29 Mar 2019 at 10:10

They haven't exploded, you mean?

I'm sure they can apply that current without a failure event occuring but that's very different than viewing this from a reliability and cycle life standpoint. Samsung chargers support 9V 1.67A yes, but you can't just look at the number on the charger as the device directly decides how fast it's going to charge it's battery. So 9V @ 1.67A = 15W

Yet what is actually delivered to the batteries on the actual devices when fast charging is enabled...

Galaxy Note 4 = 4.4V @ 3.15A = 13.9W [12.4W/h battery // 1.12C max charge rate]

Galaxy Note 9 = 4.35V @ 2.85A = 12.4W (if battery <300 cycles, otherwise lower) [15.4W/h battery // 0.8C max charge rate]

Galaxy S 10+ = 4.35V @ 2.85A = 12.4W (if battery <300 cycles, otherwise lower) [15.8W/h battery // 0.78C max charge rate]

So Samsung who even spoke about faster charging on the S10, once you start looking at the device you find it's no faster at all and once you take into account the larger battery the effective charge rate is actually even lower. All this talk about 25W charging for the S10 and yet they don't even max out the 15W charger

This is also unrelated to the Note 7 issues. We can see from the earliest Galaxy S6 source code that Samsung were already reducing charge voltages and charge currents as soon as they moved to non-user replaceable batteries. They did it for cycle life performance reasons and a long time (~18 months!) before the Note 7 came along. Samsung are one of the few companies that actually try to protect your battery cycle life. No press releases or news articles, we just need to look at the black and white of the charge control to see that Samsung actually are trying hard to balance battery performance with ultimate charge capacity. Something I bet any phone company shouting "100W charging!" isn't doing.

I'd love a fast charging device once battery tech has moved on, but we still ultimately have the same batteries now that we did years ago. The refiniements will allow slightly higher capacities and slightly higher charge currents, but there's been no charges that will sudddenly make a 6C charge as good for the battery as a <1C charge or at least any more than it would have been to do this 3 or 4 years ago.

james.miller · 29 Mar 2019 at 10:22

Where is that extra energy going? Heat? are samsung pulling back charge current to save battery life even knowing they are generating extra heat?

DarkBahamut · 29 Mar 2019 at 13:57

Nowhere, the phone only pulls as much power as it needs from the charger. Phone chargers just work in the same way as power supplies for PC's. Just because you have a 650W PSU in your PC doesn't means it pulling 650W all the time

On a Samsung phone with fast charge enable they configure the phone to pull up to 1.65A @ 9V from the wall (15W) and put up to 2.85A @ 4.35V (12.4W) into the battery. If the phone is otherwise drawing no current (ie: it's turned off) then only 12.4W + some charging lsoses is drawn from the wall. If the phone is powered on and actually drawing power then the phone can use the excess amount of the AC power supply can provide (the extra 2.5W) to not reduce charge speed at all. If it doesn't need it then it's not used. If it needs more than the spare 2.5W then battery charge current is reduced and the AC adapter powers the phone directly via the PMIC.