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## Can use ipad charger to charge iphone?

493643 Views 342 Replies Latest reply: Sep 10, 2013 3:00 PM by ronhenderson2 Branched to a new discussion.
• Level 7 (24,420 points)
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Apr 11, 2013 6:08 AM (in response to kelvinnguyen)

kelvinnguyen wrote:

Very simple.

1Ah = 3600 C (coulomb)

1 mAh = 3.6 C

Your iPhone needs total charge Q = 1440 mAh = 5184 coulombs

Your iPhone has a fixed battery inside. So capacitance is constant. C is constant.

C = charge/voltage = Q / V

V is constant (iPhone/iPad charger supplies 5V)

Q = charge_current x charge_time = I x t

So:

C = Q / V = (I x t) / V

=> charge_time  t = ( C x V ) / I

in this equation we have C constant, V constant (5V).

Therefore, higher charge_current will reduce charge_time.

There is no other side effect from this equation.

TOTAL BS. You understand nothing about how the charger circuit works in the iPhone. The current that the source is CAPABLE of supplying has ZERO to do with the amount of current that is supplied to the battery by the charging circuit in the phone.  I could connect a 5 volt supply capable of supplying 100 amps to the phone and it would still only draw 1 amp from it because the charging circuit IN THE PHONE regulates the current (or coulombs if you will) going to the battery.. Translating it to coulombs is mere smokescreen, and adds zero value to the discussion; it is just a units change.

Why don't you go look at the video further back in the thread that demonstrates that the phone draws excactly the same amount of energy whether you use a 1 amp or a 2.1 amp charger?

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Apr 17, 2013 12:42 PM (in response to emfung)

Hi All,

I've come to this discussion quite late and only read a few pages then jumped in so forgive me if this has been resolved.

Merlin and Lawrence Finch - You are both right to an extent.

Mostly Lawrence Finch by the way.

Merlin - Your test no doubt did produce the results you claim, you error was trying to explain and rationalise the results.

The ah huh moment?

Of course if you slow charge the iPhone Battery and provide a current LOWER than the internal regulator requires then yes your battery will last longer and perform better on average (however the test you described with such and small sample CAN NOT provide a statistically significat result - you got lucky or it was battery variability).

The Iphone and Ipad chargers both supply more current than the iPhone self regulating circuit requires (only just in the case of the Iphone charger) and charging the iPhone with either will NOT alter the battery life or performance at all. Any "excess" current (if you excuse the simplification) is stopped by the self regulating circuit.

By the way this same circuit also constantly reads and adjusts the amps fed to the battery according the battery temperature and charge state so that near the end of the charge the amps being fed to the battery might only be 20% of maximum.

But wait there is more -

Free steak knives anyone?

No? ... Ok ... Apple chose the maximum current that a cool battery at approx 5% charge will receive for a reason. They traded off charge time v battery performance / length of service. It was a consumer / sales decision.

Those of you like Merlin who prefer to charge your iPhone with a noticeabily lower current than the internal regulator serves up to the battery will avoid the battery warming cycles that the iPhone and Ipad charger produce and this (all other circumstances being equal) will result in better battery performace by most metrics.

At the cost of inconveniently long (as determined by Apple) charging times and of course if the battery is flat, insufficient current to plug in, power up, and use the phone straight away (and who of us has not needed that at some stage?).

Now I'm not going to flash my bio / resume on here to justify common sense but if anyone wants to take me on please feel free.

Or just play nicely?

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Apr 17, 2013 1:02 PM (in response to emfung)

Oh ... This is fun!

I just read kelvinnguyen's post - Now I see why this discussion is so addictive!

Fixed battery so capacitance is constant? Please!!!

While that is correct in itself that is so not the circumstane inside the iPhone, the variable circuit that monitors charge state and battery temp in the iPhone is constantly adjusting the amps fed to the battery (yes up to the arbitary maximum Apple chose as the trade off point for battery performance vs charge time).

So in effect capacitance is not constant.

I could waste hours on here!!

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Apr 17, 2013 1:04 PM (in response to Bigapples)

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Apr 17, 2013 1:15 PM (in response to emfung)

Why? This is so fun ..

Waiting to see who finds the little variables that I haven't addressed ..

Cause and effect people ..

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Apr 17, 2013 3:22 PM (in response to emfung)

Bwahaha. This thread is too much. I made the pleasent mistake of commenting on page 2. This has been 13 pages and about a year and a half of bickering. You guys are nuts.

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Apr 30, 2013 11:37 AM (in response to Bass12)

Bass12 wrote:

I plugged in two iphones one to USB and one to ipads charger, and indeed using the ipads charger is charging at a much faster pace, maybe its my USB thats not putting out but its what I have infront of me.

You have it correct. The facts well support the fact that the wall charger can supply more current than a USB port. The iPhone charge circuitry takes all the current it can get, up to its self-selected charging limit, and recognizing the limits of its supply.  It behaves differently on a high-power USB port (plugged directly into an iMac) vs. a medium power (a Macbook on battery) vs low power (unpowered hub) vs "unlimited" current (more current available than it wants to draw).  My iPad does the same thing when I plug it into an unpowered hub, it says "Not Charging" even though it will fully charge in 24hrs.

If you think Apple's self-selected charging limit is abusive to the battery, you certainly can "slow charge down" by plugging it into a weaker source.

Control System Guy wrote:

I love this thread; it’s where engineering meets new age science. ...  The impedance of the receiving device determines the amount of current drawn.

Now I going to tread on scared ground and say that some regulator circuits might not have been designed properly. There are “smart” (I personnel hate this term) chargers. My guess is that one of these devices when it found a rich source of current, it lowered its impedance to speed up the charging process. But said device wasn’t smart enough to recognize that it was going to overheat the battery at that rate.

With smart devices, saying the device smartly "changes its impedance" doesn't really do justice to what's going on.

If the battery  you could be right for one of two reasons.  First, Apple's design choice may be more aggressive than your preference.  Second, your particular phone may have be malfunctioning, notably the battery itself.

>>>> Kelvin's math which was meant for capacitors

No no no.  Batteries are completely different animals and capacitor math just doesn't work on them.  Second, as different as battery physics are, a charge-controlled battery even different from that.  "Battery meets switching supply meets smart controller" and you expect this to follow normal maths?  Good luck.

The only physics you can still rely on is this:  loads DRAW the current they want, and don't care how much current is available.

>>>> Battery overheating upon charging is definitely not a good sign

Probably means the battery is shot (at its end-of-life) and needs to be replaced.  If the phone is in warranty, get er done.  If not ---> Amazon and an hour of careful work.

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May 3, 2013 8:40 AM (in response to merlin1128)

Wow people ... A simple yes or no would do.

• Level 7 (24,420 points)
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May 3, 2013 11:44 AM (in response to pmassy)

Apple says "Yes" you can use an iPad charger with an iPhone.

Several controlled experiments reported in this thread demonstrate that you can.

There's also a lot of nonsense from people who don't know what they are talking about.

So you can believe Apple or not. Your choice. If you are into conspiracies you won't believe Apple, on the basis that Apple sells more phones if the iPad charger destroys your iPhone.

• Level 6 (15,675 points)
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May 3, 2013 11:50 AM (in response to Lawrence Finch)
If you are into conspiracies you won't believe Apple, on the basis that Apple sells more phones if the iPad charger destroys your iPhone.

The real reason is that the combination of the iPhone with an iPad charger sets up an electromagnetic flux that sends subliminal commands to buy more Apple products.

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May 3, 2013 11:54 AM (in response to modular747)

That would be

modular747 wrote:

The real reason is that the combination of the iPhone with an iPad charger sets up an electromagnetic flux that sends subliminal commands to buy more Apple products.

Quick! Buy stock in a tin foil hat manufacturer.

• Level 6 (15,675 points)
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May 3, 2013 11:56 AM (in response to Lawrence Finch)

It just so happens I just set up a tinfoil hat factory in Bangladesh!

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Jun 3, 2013 8:25 AM (in response to Lawrence Finch)

Mr. Finch.

I guess you are right.

Now, I guess that people can't see what they can't experiment.

So to make them experiment the truth, they should charge their phones while they are OFF, so no other factors gets into the the charging process.

Other thing as stated previously, is that either a FAULTY charger circuit (which may be under APPLE warranty) can also cause that behavior, and it will only be seen using a charger with more than 5W capacity

I bet that most people use the phone while charging and that's why to feel the heat with their hands (not using the proper instrument), and for sure it will be higher using a iPad power source (10w or 12w) than a iPhone power source (5w), because when using the ipad charger the phone will pull 1 amp for charging and  another ammount of amps for its active proceses and hardware (screen, gps, signal etc etc).

That only will happen using the iPad power source. So those still having doubts in Mr. Flinch claims, either can try to charge the phone OFF and see, or take the iphone to apple for an exchange or repair.

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Jun 15, 2013 7:04 PM (in response to emfung)

There are people here with valid points,,, but what I don't think people realize is that even though Apple states an ipad charger CAN charge an iphone,,, they are not going to say that it is at the expense of decreased battery life. The way I see it, WHY would Apple volunteer this information if it meant losing revenue from more frequent battery replacements ?

• Level 8 (49,785 points)
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Jun 15, 2013 7:05 PM (in response to monkeyhead0305)

Nonsense.

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