# Maximum amperage on power supply? [duplicate]

Possible Duplicate:
Can I feed the device with a current higher than 1A?

I've checked the RS and Element14 power supplies: `5V 1A`.

I've read a few posts here on power supplies and seen people use `5V 700mA`.

I found an old power adapter lying around home: `5V 3.8A`. Is that a bit much ? I haven't tried it yet, but a bit scared as I don't want to fry my Pi.

Thanks

## 3 Answers

The current rating is the maximum current that devices can draw from the supply. As long as the voltage is actually 5 volts and consistent you should be able to use that supply.

It will be fine as long as it's a regulated adapter. Some older adapters would just have a rectifier and sometimes a cap. They could output much more than the rated voltage when lightly loaded.

The current rating is just the limit that the adapter can supply safely. Beyond that it may get too hot, or the voltage may drop below 5V for example.

The current drawn by the raspberry pi much less than that so you wouldn't need to worry about damaging it unless you accidentally short something out. But that could cause damage even with a lower rated supply anyway.

The voltage regulator used for the Raspberry Pi is a linear voltage regulator. The input and output currents of the voltage regulator are essentially the same. The difference in voltage is dissipated as heat.

``````Vin =5V
Vout = 3.3V
hence Power dissipated as heat = (5-3.3)*0.7 = 1.19W
``````

The maximum output current of the Raspberry Pi's voltage regulator is rated to be 1A. It is safe to use the voltage power supply that you have.

• Safe, yes. Overkill, maybe. :)
– XTL
Nov 27 '12 at 7:41