iPhone 12 iPhone 12 only drawing 16-17 watts when charging

[biglilsteve]

I have two USB-PD chargers at home. One 30w and one 45w. My wife’s 12 only draws 16-17w with a nearly depleted battery. My 12 Pro Max draws the full 20, as it should.

These are our first iPhones. Am I missing something here?

 

[Givmeabrek]

That sounds about right. The Phone will draw the current it's designed to draw. A 100w charger would give the same result. The output wattage rating is a maximum. The phone charging circuit decides the current draw. That's why the Apple fast charger is rated at 20w.

 

[biglilsteve]

That sounds about right. The Phone will draw the current it's designed to draw. A 100w charger would give the same result. The output wattage rating is a maximum. The phone charging circuit decides the current draw. That's why the Apple fast charger is rated at 20w.

16-17 is not 20 though.
As I said, my pro max draws 20 as it should. Why doesn’t the 12?

 

[Spudlicious]

Being my usual positive self I note that 17 is 85% of 20, so pretty close? And might we expect the larger battery to charge faster (circuitry permitting) due to greater cell area?

Whatever, the quoted charging rates appear fierce enough to me. Charging at 16W must mean charge current in excess of 4A and I would not be looking for more.

 

[Tenkaykev]

Don’t the phones charge at the maximum for only a short period of time before dropping the charge current.?

 

[now i see it]

Bigger batteries can charge with more current. The iPhone 12 mini will draw even less current when charging than the 12/12 Pro.
I have a 12 watt iPad charger. The most current I've ever seen it push into an older plus iPhone is 6.5 watts... because that's the max the charging circuit in the phone will allow

 

[doboy]

16-17 is not 20 though.
As I said, my pro max draws 20 as it should. Why doesn’t the 12?

You have a bigger battery and bigger heat sink to dissipate heat. Probably designed to draw more amp to match the charging times with the smaller units.

 

[biglilsteve]

Being my usual positive self I note that 17 is 85% of 20, so pretty close? And might we expect the larger battery to charge faster (circuitry permitting) due to greater cell area?

Whatever, the quoted charging rates appear fierce enough to me. Charging at 16W must mean charge current in excess of 4A and I would not be looking for more.

Amperage never exceeds 2.

Don’t the phones charge at the maximum for only a short period of time before dropping the charge current.?

They charge at Max speed until 40-50%.

Bigger batteries can charge with more current. The iPhone 12 mini will draw even less current when charging than the 12/12 Pro.
I have a 12 watt iPad charger. The most current I've ever seen it push into an older plus iPhone is 6.5 watts... because that's the max the charging circuit in the phone will allow

I was just under the impression that Apple advertises 20w charging across the entire lineup.

 

[Spudlicious]

Amperage never exceeds 2.

They charge at Max speed until 40-50%.

I was just under the impression that Apple advertises 20w charging across the entire lineup.

If amperage never exceeds 2 and everywhere I look tells me the voltage across a lithium cell's terminals should never exceed 4.2, how are we seeing 20W charging advertised?

 

[biglilsteve]

If amperage never exceeds 2 and everywhere I look tells me the voltage across a lithium cell's terminals should never exceed 4.2, how are we seeing 20W charging advertised?

Because voltage is around 10. Even when charging my old iPhone 7, voltage is around 7-8. Just look up the USB-PD charging standard.

 

[jdlnmia]

Which charger(s) were being used to charge the 12 & the 12 Pro Max?

The 20W USB-C Power Delivery standard is 9V @2.22A, which is a relatively new standard. This standard is supported by the new Apple 20W USB-C charger and updated versions of the Anker Nano, etc. If you use another charger that does not explicitly support this standard, you will see around 18W max, even if you use a 100W PD charger. Check the Power delivery standards supported by the charger(s) you are using to see if 9V @ 2.22A is listed.

The phone will negotiate with the charger as to its current state of charge as well as other factors such as internal temperature, etc. to determine how many watts it will consume.

Another thing to consider is if the battery management feature is active on the phone. This might explain the discrepancy.

 

[biglilsteve]

Which charger(s) were being used to charge the 12 & the 12 Pro Max?

The 20W USB-C Power Delivery standard is 9V @2.22A, which is a relatively new standard. This standard is supported by the new Apple 20W USB-C charger and updated versions of the Anker Nano, etc. If you use another charger that does not explicitly support this standard, you will see around 18W max, even if you use a 100W PD charger. Check the Power delivery standards supported by the charger(s) you are using to see if 9V @ 2.22A is listed.

The phone will negotiate with the charger as to its current state of charge as well as other factors such as internal temperature, etc. to determine how many watts it will consume.

Another thing to consider is if the battery management feature is active on the phone. This might explain the discrepancy.

Very good point!!! That standard is not listed on either charger. One is a 45w Samsung PD charger I already had for my Note 10+ and the other is an Aukey 30w PD charger I just bought. I must be getting lucky to draw 20 from both with my Pro Max. I’ll return the Aukey and make sure I purchase one that’s more compatible. Cheers!