iPhone charging - interesting discovery

[NSquirrel]

Our iPhone 8s and iPad are pretty picky about the voltage drop along a charging cable. Our bedside clock has a USB in, to power it, and a USB out. I haven't bothered or needed to use the USB out, but last night one of our phones was low and I tried to charge it via the USB out; it didn't work. At a guess the voltage out, coupled with voltage drop along the cable was too much.

I then had a thought: recently I bought a couple of spare wireless charging pads. I plugged one of the pads in to the clock and popped my iPhone onto the pad; charging started. So this suggests that wireless charging is far less picky in terms of USB voltage. I also tried a USB inline voltage meter between the USB out and the pad. which indicated 4.75V - far too low a voltage for my iPhone via direct cable. In fact the drop across the meter to my iPhone will not charge direct from a standard Apple wall charger.

No guarantees that this will be the same for other iPhones or perhaps different models of wireless charging pad, but it is useful to know.

 

[dmoskaluk]

Actually do use a USB out on the bedside lamps which are plugged into mains via surge - fir the QI chargers on the tables. That has always worked well.

 

[dmoskaluk]

Our iPhone 8s and iPad are pretty picky about the voltage drop along a charging cable. Our bedside clock has a USB in, to power it, and a USB out. I haven't bothered or needed to use the USB out, but last night one of our phones was low and I tried to charge it via the USB out; it didn't work. At a guess the voltage out, coupled with voltage drop along the cable was too much.

I then had a thought: recently I bought a couple of spare wireless charging pads. I plugged one of the pads in to the clock and popped my iPhone onto the pad; charging started. So this suggests that wireless charging is far less picky in terms of USB voltage. I also tried a USB inline voltage meter between the USB out and the pad. which indicated 4.75V - far too low a voltage for my iPhone via direct cable. In fact the drop across the meter to my iPhone will not charge direct from a standard Apple wall charger.

No guarantees that this will be the same for other iPhones or perhaps different models of wireless charging pad, but it is useful to know.

How long are the cables you are using?

 

[NSquirrel]

Standard 1m Apple USB to lightning cable, as supplied with phones/ iPad. I found a few years back that even a short USB to USB extender is enough to drop the voltage to below that needed for charging.

 

[dmoskaluk]

Standard 1m Apple USB to lightning cable, as supplied with phones/ iPad. I found a few years back that even a short USB to USB extender is enough to drop the voltage to below that needed for charging.

Absolutely shouldn't be. First I'd try maybe a friends or other family members phone using same cable and charger. Then have some diagnostics done on your phone & charger.

 

[NSquirrel]

Thanks dmoskaluk, although I do not think that any of my components (iPhones, iPad, cables, chargers) are out of Apple Spec, whatever the specs may be.

At a guess, the charging current for a fairly discharged iPhone is around 6/700mA and possibly double that for an iPad. As I am sure that we have all found, any dust or dirt on the connectors is enough to increase the ohmic resistance and hence reduce the voltage – even enough to stop the item charging. Hence keep connectors clean and free from dirt and dust.

I found that the additional resistance of a 1/2m USB-USB cable was enough to drop the voltage out of spec and hence stop charging when using a standard 1m Apple USB to Lightning cable. Using the standard cable there is no problem charging, it was simply a few years ago I was looking to extend the charging cable.

What I posted above was what I found with a USB to wireless charging pad. This seems, in my case anyway, far more tolerant of the voltage drop between the charger and pad as the charging pad circuitry converts the DC input to AC between 110 and 205 kHz. (I didn’t check, but for power transfer, I assume that the 5V USB charging current is roughly unchanged.)

Incidentally, I just put a 3m USB extender cable between the charging pad and one of my Apple chargers and my iPhone started charging with no problem.

 

[dmoskaluk]

If & when I use a cable ( normally travel involved with iPad - pre- covid) and there is an issue, I give the ends ( both 'lightning' and the charger side terminal) a spritz & wipe down with a contact- cleaner spray. It's always resolved what infrequent issues I've had.

 

[NSquirrel]

Good policy

 

[Henfield]

I have a low power wall outlet. Initially I thought the usb was really weak. Unable to start charging. Then discovered, it would charge but only if the device was off when plugged in.
Device wakes up and charges just fine