Can use ipad charger to charge iphone?

I love this thread; it’s where engineering meets new age science. I happen to be in the engineering camp. I am boring engineer with a “put you down” number of years’ experience. I have used lots of DC power supplies in many different configurations. I agree completely with Lawrence Finch at the beginning of this thread and his legion of followers and still do. 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.

So my advice is if the phone is getting hot to the touch don’t use the higher wattage supply as an everyday charger. It’s okay for emergencies but the effect is cumulative. (Oh, I forgot to mention, I deal with battery backup systems too.) Heat is their enemy. We air condition all our major battery systems. Depending on the battery, you can cut the life by way more than half by raising the battery temperature by less than 5°F.)

So the second take away my children (there I go again, being patronizing) DON’T leave phones, etc. in cars during the summer. Also, store your battery powered tools in the house not the garage. One more passing comment, batteries don’t like the cold either. They don’t lose power but they won’t give up the power as easily so stuff can stop working at cold temperatures.

This discussion is awesome, I respect and believe everyone might be right on his/her own, I'm not technical but only pondering... being COMPATIBLE and what Philip Schiller says "... CAN be used..." instead of "iPad charger REPLACES the iPhone charger" then it would really be a legal battle involving Apple lawyers if the iPhone can be proven damaged by the iPhone charger guys... a battery overheating upon charging I believe is definitely not a good sign... There must be some other underlying factors inside the iPhone or iPad circuit not discovered in this discussion yet, 'cos we know at least by now that the "charger" is only an energy/electric provider. Someone (our technical engineers) should dissect these two products circuitry and let us know!

Gotta agree with Finchy here. Don't have an electrical background, just in I.T. but what Finchy says falls in line with what I read a couple years ago:

Anyone with a Mac with both OSX and Windows will notice their iDevices charge much faster on OSX. This is because OSX is programmed to recognise the power requests from the iDevices and dishes out the correct amount accordingly.

edit: to clarify, it sort of backs up the idea that the iphone/ipad is capable of adjusting power. It doesn't just simply lie back and receive it.

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.

Your iPad charge gives 2.5 amps (compared to 1amp charger), it will charge your iPhone faster.

There is no other side effect from this equation. 🙂

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.

Your iPad charge gives 2.5 amps (compared to 1amp charger), it will charge your iPhone faster.

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?

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?

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!!

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.

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.

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.

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.

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.

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 ?

Well, as I said somewhere around a billion posts ago.....I've been charging my iPhone 4 with my iPad charger for the last 5 years and 10 months, and the battery is still going strong.

Also, my tinfoil hat has prevented me from being coerced into replacing my iPad 1 with a newer iPad model, but, I did purchase a Macbook Air. I don't think this was a defect in my tinfoil hat, however, since I did not have a previous Mac laptop (or desktop, for that matter - I used my husband's Macbook Pro until I got my own - so I don't think that counts).

Do you think it is real? Or is it Memorex?

GB

I have read half of the posting on this subject and I do have an engineering degree But, let's be honest... the engineering degree means nothing if you do not understand how a device works. It seems logical that the charging circuit is in the device and controls the allowable amount of amperage. However, we do not know that the allowable amount of amperage needed is equivalent to what is listed on the power supply.

In other words, the iPhone charger is capable of 1A maximum. But, it is possible that the Phone will allow 1.8A (an arbitrary number). If that is the case, then the battery life will be dimished by constant quick charging. Every battery retains best charging performance when it is occasionally slow charged. Constant quick charging will diminish the life. So what is the end result?

I was looking to purchase a car charger that would be sufficient for all devices. I spend a good deal of time in the car, so I will be using the charger quite a bit. I was considering a charger with dual 2.1A ports. Based on my findings here, I will be getting a dual charger, 2.1A on on port and 1.0A on the other port. This will allow me to charge the devices in their intended amperages.

Thank you all for the information. I know this is an old thread, but I hope my analysis helps someone seeking the same answer as I.