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Apr 09 2010

Myth: iPad charger blowing up iPhone

Published by at 11:29 pm under Uncategorized

I just heard of an iPad customer who asked their Apple tech whether it was safe to charge their iPhone with an iPad charger.  The iPad has a charger with greater capacity than the iPhone.  The tech said no, it might blow up their iPhone.

Maybe this reflects the sad state of science education in this country, but this is bunk.

It’s like plugging a lamp into a 20 amp circuit instead of a 15 amp one.  The lamp isn’t going to blow out because the circuit has greater capacity.  The amperage used is based on the device’s demand, and as long as its less than the capacity of the circuit, its fine. The iPad’s wall charger is 10 watts, the iPhone is 5 watts, and the USB port is 2.5 watts.  The higher the wattage, the faster the charge, presuming the device can use draw what it needs.

What could do damage is if they used a different voltage… but since they all use USB, the voltage is the same.

Here’s how to think about electricity like a water hose:   Voltage is like water pressure on a hose.  It can have a lot of pressure with the valve off, but no flow.  Amperage is like the amount of water flowing.  Attaching a narrow nozzle keeps the pressure up but the amount of water restricted.  A wide open nozzle lowers the pressure but allows more water.  Wattage is a measure of the flow times the pressure.  Watt-hrs is like gallons per minute… the amount of flow over time.

Connecting a iPhone to a 10 watt charger is like connecting a sprinkler to a 2″ pipe instead of a 1/2″ pipe with the same water pressure.  If the sprinkler’s demand can be handled with the 1/2″ pipe, then it doesn’t matter if you connect it to a 2″ pipe.  If the 2″ pipe had more pressure (the equivalent of voltage), then things would change.  (but the iPhone and iPad use the same voltage).

So, its an urban myth…

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