Maybe I'm crazy, but it sure seems like when I plug my electronics (iPhone, iPod, etc.) into a car charger it gets up to a full charge MUCH faster than if I use a regular charger and an outlet.

Do these devices charge faster from car adapters, or am I imagining this? If so, why?

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    Do you have any data to support your suspicion? Have you tried running the gadget down then timing a full charge on both? I suspect it may be a case of watched pots... – Rich Seller Aug 1 '10 at 16:06

The answer to this question is that "it depends" and it is actually quite possible that your car charger is charging your devices faster than the AC charger you use at home. In both cases, there is significant power available at the source to do the charging relative to the number of watts being used to charge the device. That is, both the AC wall outlet and the cigarette lighter socket are both going to have "hundreds" of WATTS available if not more whereas the device being charged is only going to be consuming maybe "tens" of WATTs at the most during peak charging rates.

Therefore what makes the difference is the amount of power being OUTPUT by the particular charger itself....you just need to check the ratings of the charger and see how much power than can each OUTPUT. The output power is simply VOLTS times AMPS for the DC power that your device is likely to be using.

Some wall chargers that are very inexpensive have very small power supplies in them and only put out a limited amount of charging current at the rated charging voltage for your device. Others may be quite a bit beefier and will be output up to or above the maximum the device will take. Similarly for the car adapter.

Given that the DC source from the car is directly available and a very low cost regulator can be used to generate a regulated charging voltage without having to convert using a switching power supply from an AC line, it seems more than likely that you have a car charger that charges quicker than your home unit. Also, it is possible that the device accepts a variable input DC voltage and can take the 9V to 12V range from the car directly. In this case, it is quite possible that the car charger will end up delivering significantly more charging power than the AC charger.

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The amount of power you draw from cars is quite limited, so it must be your imagination. The reason is probably because you are doing something instead of going back and forth checking. So it's more your sense of time that's different.

A more detailed explanation:
Typically what you get from a car at it's raw state, is something like 9-12 volts. What you get from your house is around 200-300 Volts, it depends where in the world you live. When you're changing a small gizmo, like iphone/ipad, that has a small power usage, 9-12 volts is just fine. However if you were to charge a laptop you would see what I mean. You would have to convert the 9-12 volts to 200-300, (a factor of 20-30) and would thus have to decrease the amperage with the same factor. The result would be that your laptop could hold power for a longer period of time, but would eventually go flat.

So there is a limit to how much power (Walt) you can draw from a car, and it will always be a lot lower than what you can get at home. If you are a skilled electrician you could raise the amount of power by accessing the car battery directly.

Now why isn't it a lot faster to charge your iphone at home?
Well it easily could be, but charging a battery at a very high pace, will also create a lot of heat. Apple have probably taken this into consideration when they created the charger for the iPhone. A balance between having a low charge time, without heating the battery too much which could risk the health or just the durability of the phone.

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    There's plenty of power available from a car to power a phone or iPod charger. – Dennis Williamson Aug 1 '10 at 4:48
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    @Dennis Williamson: plenty of power to charge it at a decent pace, but not plenty of power to charge it MUCH faster than at home. – googletorp Aug 1 '10 at 10:36
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    A typical gadget draws 300-500 milliamps while charging. A typical cigarette lighter socket is fused for 20 amps. You can run a 150W (120V AC output, about 15A DC input) inverter from a cigarette lighter socket. Believe me, there's plenty of headroom for a quick charger. I have an AC powered quick charger that will charge 4 AA batteries in an hour. It only pulls 18W (120V AC)... – Dennis Williamson Aug 1 '10 at 15:49
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    Just because you have 1800 W available in a home AC outlet, that doesn't mean you can jam that down a cellphone's throat. The biggest DC adapter I have is 2250mA and it only draws half an amp on the AC side. A DC-DC adapter that's 12V in and 5V-500mA out is only going to draw about 200mA plus whatever's lost to inefficiency. – Dennis Williamson Aug 1 '10 at 15:50

I'll disclaim this post by stating upfront I am no sort of electrical engineer, but two things stick out to me as possibilities:

  1. Phones operate on DC power. Any charging effort has to ensure the power is being delivered in DC form. This means charging from the AC outlet has to do a conversion, where as the power from the outlet on your car only has to be regulated. Which brings me to my second point..

  2. The power from your car is already in DC form. If regulated correctly, it should be no different from the wall charger. If you're seeing drastically different charging times I would suspect either the wall charger is limited to prevent too much heat buildup, or your car charger is allowing more direct charging to occur (maybe at the expense of your battery?)

Maybe batteries are 40VDC in Denmark, but they are (mostly) 12VDC in the US (which seems to be where the OP is from). Any car should have more than enough power to charge a phone. My Blackberry charger is only 5V 700mA. My truck has 12v with 30amp circuits... if not regulated I would probably have a fireball on my hands in a matter of seconds. ;)

Just something to consider...

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My iPhone charges twice as fast when being charged with a 3rd party after market charger in the car (DC), as opposed to the Apple AC charger.

In my case DC is definitely faster

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My experience is the car charger I use restores my iPhone battery at a FAR GREATER speed than does any device at home: my USB charger in the wall, my USB charger at my computers, and my iHome and other stereo docks. It's not even close—maybe as much as 4 or 5 times fewer minutes to full recharge.

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  • It would be interesting to check the current supplied by each charger with an ammeter. – daviewales Dec 4 '12 at 6:50

Ok... I'm going to put this in simple terms... most car chargers, especially the cheaper ones, don't have voltage regulators on them. This WILL cause them to charge your phone faster. Some CHEAPER chargers don't have them either and will do the same. HOWEVER, you should know home chargers are designed to be slower and "trickle charge" your battery because this is safer. Speed charging damages the battery in time and will limit your battery's charge capacity even though it will read full. If you look on your home charger it will state this.

For example: my home charger says on it,
input 100-240v Output 5.1v

Why would my BRAND NAME MOTORLA CHARGER want to lower the voltage output? Because it prolongs battery life. This link has a little more tech talk in it on the subject... slightly. http://chris.pirillo.com/are-mobile-car-chargers-good-for-phone-batteries/

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I think it's because we're charging straight from USB and there's no Adapter involved. May not be how we're intended to charge...

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