I bought a car adapter charger with two USB ports for charging iPhone 5s and iPad 4 in my car. The charger has a rating of 3.1 AMPS. I assume if the two are connected at the same time the 3.1 AMP is divided equally until one or the other is charged, then the full 3.1 AMPs would go to the remaining port! WOuld tht be ok if you dont leave it on for extended period of time? I would try to disconnect as soon as charged!
The charger is in the phone. It will limit the current to the battery to 1 amp or less, depending on the state of charge of the battery. Typically it will charge at 1 amp to approximately 80%, then reduce the current to the battery linearly until the battery reaches 100%, at which point it will stop charging entirely. Thus, it is safe to leave it plugged in after it reaches full charge. The amount that the power source can supply is irrelevant as long as it is greater than 0.5 amp.
The charger is in the phone. It will limit the current to the battery to 1 amp or less, depending on the state of charge of the battery. Typically it will charge at 1 amp to approximately 80%, then reduce the current to the battery linearly until the battery reaches 100%, at which point it will stop charging entirely. Thus, it is safe to leave it plugged in after it reaches full charge. The amount that the power source can supply is irrelevant as long as it is greater than 0.5 amp.
amps is a max being able to supply measuring
you can use a 31 AMP or 310 AMP charger without any problems a device draw amps as they see fit it's not pushed on them same with your dog being able to drink from a 10000 liter basin without drinking it all
Oh, God, is this starting over again? The "expert" in the Apple store apparently knows NOTHING about electricity or how it works. He is making it up as he goes along. There is no way an iPad charger can "detect" what is connected to it. ANY device draws as much current as it needs. No more. No matter how much is available. Your house probably has 150 amp service. One 60 watt light bulb (conventional) requires 0.5 amps. A computer requires typically 3 amps. If the current available is what goes to each device then every light bulb and piece of electronics in your house would instantly explode the moment you turned on the main circuit breaker. Current NEVER gets FORCED; it gets drawn to meet a need. It is such a shame that basic electricity no longer appears to be taught in middle school Science class. Or were you too busy texting to pay attention?
For the other thread you are referring to I tested a number of USB adapters using a USB power meter (this one: http://www.amazon.com/Centech-USB-Power-Meter/dp/B00DAR4ITE/ref=sr_1_cc_1?s=aps& ie=UTF8&qid=1400794264&sr=1-1-catcorr&keywords=century+usb+power+meter), not just Apple's adapters. I tried adapters up to 5 amps. For EVERY SINGLE ONE OF THEM the iPhone drew 1.0 amps or less.
Stop spreading misinformation. The ONLY requirement for a USB adapter (don't call it a "charger"; it isn't - it is a 5 volt source with a USB output) to charge an iPhone is that it is reasonably high quality and has a "clean" output.
if as you indicate there is a current limiting circuit in the phone and iPad that would definitely answer my question and within reason almost any 5v source would be safe,, but wpuldn't a current limiting devive get hot/
The charger is in the phone. It is not in the adapter. The charger in the phone limits the current to the battery regardless of what the supply current is.
My USB power meter is quite happy to tell me that my iPad charges at 2.1 amps, so it can clearly show above 1 amp. It also shows the current tapering after the SOC reaches about 80%, linearly to zero at 100%.
As backup I used the same AC wattmeter on the AC side of the adapter that was used in the video, and it showed a maximum of 5 watts going into the adapter. As I'm sure with your MIT degree you understand the laws of thermodynamics, so if only 5 watts goes in to the adapter no more than 5 watts can come out of it. And, as the voltage (which I also measured is 5 volts, the current out cannot be higher than 1 amp. Charging an iPad the wattmeter shows 11 to 12 watts, which is consistent with 2.1 amps and 5.1 volts.
However, you win on credentials; my EE degrees are only from Stevens and NYU with some additional study at RPI.
Gregory Lazarchik wrote:
After some thought your comment really doesn't end the discussion. Yes the battery willl draw current it needs but it is a function of rate. A fully discharged battery will draw at whatever amps are provided until its voltage approaches the charging source at which point it will gradually slow down to a trickle. THe problem is heat. LiPo batteries have ratings and some can take a fast charge and some cannot. Normally with the 10 W charger it takes several hours to charge an iPad and with the iPhone apple suipplies a 5W charger. I am wondering,since the 3 amp charger will charge the battery much faster and generate heat, if the battery and the equipment can take it?
You're not an electrician may I assume.
After some thought your comment really doesn't end the discussion. Yes the battery willl draw current it needs but it is a function of rate. A fully discharged battery will draw at whatever amps are provided until its voltage approaches the charging source at which point it will gradually slow down to a trickle. THe problem is heat. LiPo batteries have ratings and some can take a fast charge and some cannot. Normally with the 10 W charger it takes several hours to charge an iPad and with the iPhone apple suipplies a 5W charger. I am wondering,since the 3 amp charger will charge the battery much faster and generate heat, if the battery and the equipment can take it?
excuse those typos....wouldn't a current limiting device get hot?
No
After reading these replies an following another thread on this subject that was full of apparently erroneous info some posted by folks claiming the be electrical engineers, I was in the Apple Store in Pittsburgh yesterday and here is the scoop from a so called "genius" there.
There is a uTube video that shows an iPhone drawing the same 1 Amp whether connected to an Apple iPad 2 AMP charger or the Apple 1 Amp iPhone charger. Conclusion was in the video that the iPhone had a current limiting circuit and you could not force too much current into it...This is wrong! The Apple iPad chargers, according to the Apple Store Genius, have a sensor in them that can detect an iPhone and in that case will only put out 1AMP.
Other third party chargers that output 2 amps or more (some are 3Amps) will cause the battery to charge faster but the battery will get hot and its life will be deteriorated from regular charging that way.
I understand that the LiPo battery in the iPhone is rated at 1440 mahr. , in that case, 1.44 amps would be considered the max safe charge rate assuring normal battery life and minimal heating.
Without coming down too hard on me with my engineering degree from MIT. Perhaps your USB power meter cant measure above 1 AMP current, or, is inaccurate. I note there are no specs on the reference you gave and there was this comment from a user of that device:
__________________________
Q: What's the maximum current/power that this will safely measure?
I connected my iPhone 5S that was at 30% charge, powered off, to a car lighter USB port rated at 3.1 AMPS. It charged to 100% in under an hour and got quite warm to the touch. I took the same iPhone powered off and discharged to 30% inside and connected it to the Apple 5W USB port that came with the phone and it took about 3 hours to charge and never got warm to touchl
It would seem to me that the faster charge rate and heat generated would indicate more current was going into the phone with the car USB port rated at 3.1 AMPS.
Further more your comment ...
"Any device draws as much current as it needs. No more. No matter how much is available."..
while true is out of context here and does not apply to charging a LiPo batterywhich I have had considerable experience. They come with different ratings and we set the max current levels from our chargers according to the duty rating of the battery. We charge most at what is called 10C,which is a function of their rated capacity, as I said that would be about 1.4 amps for a 1440 miliamperehour battery which someone reported was in the iPhone in the other thread you mentioned,. We have variable chargers and the battery will take all the current you give until it approaches its rated voltage and too much current will cause the battery to overheat and swell up, they have also been known to catch fire although I have not had that happen.
While in your oinion I am spreading misinformation, I have accurately reported what an Apple repair rep told me and what I have observed from my own experience, not sure how that can be mis-information.
USB chargers have pull-down resistors connected to the USB data lines. The resistor values tell the phone the maximum current that the charger can provide. It is up to the phone as to how much of the available current is used.
It seems that iPhones designed after iPad chargers were available can use more than one amp.
Malcolm J. Rayfield wrote:
USB chargers have pull-down resistors connected to the USB data lines. The resistor values tell the phone the maximum current that the charger can provide. It is up to the phone as to how much of the available current is used.
It seems that iPhones designed after iPad chargers were available can use more than one amp.
But they don't. As measured by many people.
BTW, that iPad charger is incredibly smart! In addition to knowing to charge an iPhone at 1 A, an iPad at 2.1A, it also knows to charge my Q2 BT headset at 50 ma, and my Zik stereo headphones at 320 ma and my portable scanner at 200 ma.
Explain please from a thermodynamic point of view, why the iPhone5s gets hot and charges in much less time on the 3 amp adapter than when on the apple 1 amp adapter.
the ios device could in parts detect what source it was connected to the same way one measures the barrery
you lower the internal resistance until you draw enough current for the volt to lower a fixed amount of millivolts
the 10watt charger would be able to keep the 5volt with a lower resistance in the ios device then a 5watt charger
I stand by one can't push any type of current into a device
if an ios charge faster as in draw more amps when corrected to a charger with more watt then it's
1. it was made to be able to do so
2. it has 100% no limitation as to how much current it can draw in which case a higher watt device would make it explode
option 2 is unlikely as a company like apple would not risk that type of approach
option 1 is pretty likely but apple made it so it's current limitation system could charge with more current then was good for the battery it would again be poor design on apples part
likely real cause is that apple allow the ipad charger to charge faster for iphone but never drawing more current then not damaging the battery
the "genius" are sales people they are trained for selling and supporting apple stuff
the cheap knock off chargers need just send volt spikes and the ios dies the "genius" likely seen devices which died from that but to expect the "genius" to explaine or understand why the charger killed the ios device is asking for way too much of him or her
Is a 3.1 AMP Charger OK for iPhone and iPad?
