John Isaac

Two weeks ago an Apple store salesperson sold me an Apple 30 watt Brick Fast Charger and appropriate cable to fast charge my Iphone 8 (not Plus)

Today I went back to get another one for my wife's phone (same one as mine) and 2 different Apple techs told me I should buy the 12 watt because the 30 watt would work, but, if used too often it could put undo stress on the phone's battery.

That contradicts what I have read in several online articles. I am confused and need your advice?? Go with the 30 watt or 12 watt??

smc333

You should be fine with the 30. It is possible to damage a battery or shorten it's life by charging it too quickly but the battery management stuff built into today's phones will prevent that. If you were just sticking some AA's into a wall charger or charging up a car battery then yeah, I'd say go with the slower charger, since there's no 'intelligence' built into those things. But with your phone you should be fine.

It's worth noting that if you go to Apple's web site and look for a charger for an iPhone 8 then you ONLY get the 30w once you have the filters applied (I filtered by Product Type: charger and iPhone 8).

jerryhze

John Isaac

Thank you for your answers

Loren Pechtel

And plugging your 30W charger into an outlet that can deliver 1600W obviously will damage it!

(In other words, a properly designed piece of electronics will not be harmed by a power source that can deliver more power than it needs. Harm will only result if the power source does not deliver the voltage it's supposed to.)

gfunkdave

But as far as I know the iPhone can only charge at a maximum of 12W anyway, so buying a $50 30W adapter doesn't get you anything more than the usual 12W one.

smc333

I believe it uses around 19-20w from 0-10%, then drops down to something a bit lower from 10%-66%, the finishes off at a yet lower rate. I don't remember what the second two rates are, but I'm pretty sure it starts at 19 to 20 when you're battery is dead or very low.

gfunkdave

Ah, interesting. USB-PD fast charging was introduced with the iPhone 8. I had no idea.

CPRich

Looks like 18W is above the max. And the cheap 12W adapter gets you most of the way there. iPhone X family is the same.

HDQDD

People that work in Apple stores aren't always the sharpest knives in the drawer. First of all what they referred to as a "charger" is really a power supply. The charging circuitry is on the device. That distinction isn't important to most consumers, but someone who calls themselves a "tech" should know that. The current used is determined by your phone's charging system. It will take what it needs. The current *available* is irrelevant (as long as it's enough, I believe you need at least ~10W for most iPhones). I've used a 8A/40W Anker power supply for 4-5 years with multiple iphones/ipads/hotspot/bluetooth headphones/fitbit, etc. Works great.

I've done some USB amperage testing, and my iPhone 7+ pulls a little over 1.6A (8W) when it starts the charging cycle. This drops off as it gets closer to 100%. I believe Apple starts slowing it down at 90% so it doesn't overcharge. That particular curve (high initial and then dropping off) is common for other Li-Ion devices too. What I find interesting is that Apple gives out only a 1.0A power supply with new iPhones, when they can clearly take more amps. This is why iPhones charge faster with an iPad power supply (2.1A)

With an inline USB amperage meter, I've noticed that devices pull max amps around:
iPhone 7+: 1.6A
iPad Pro 2: 2.2A
Hotspot: 2.1A
fitbit: less than 1A
QC35s: less than 1A.

Nice thing about having 8A (40W) available, is that I can charge all of those above at their max rate at the same time with one 4 port brick.

TL;DR: The Apple store peep is wrong. Get a larger power supply.

docbert

In fairness, if the techs started calling it a "power supply" then their customers would start telling them they don't want a power supply, they want a "charger"!
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HDQDD

So true. Although I have noticed that some of the backup batteries are starting to call themselves "power banks".

deniah

Backup batteries are device/format specific. If it's generic source of power that can power many devices, it is power bank