Duemilanove power requirements

Hi, When connecting extra goodies to the 5v source on Arduino board i need extra current, im using a 7.2v sub C racing pack, my question is

Why does the onboard 5v regulator get hot? Is it ok to have USB & external power connected at the same time?

im running a Micro VGA board, the 5v the Arduino board supplies doesn't quite carry enough current and uVGA resets alot unless i add the external power but then the onboard regulator gets hot

Thanks

The onboard regulator gets hot because its drawing a lot of current. The difference between your supply voltage (7.2 volts) and 5V is dissipated as heat. The uVGA board is first suspect. The arduino uses very little (around 18-25 mA) and the regulator won’t get hot just supplying its own needs. USB can supply 500 mA and that isn’t enough so its certainly is using a lot of power. I’d use an external power supply that can supply clean 5V at a couple of amps.

The duemilanove automatically switches power , so it doesn’t conflict, it doesn’t use both, it will just be using the external power if its connected.

OK, Thanks for that, mainly i was wondering if it was ok to have USB and external power connected at the same time and it's not going to fry anything

Short answer : Yes, although the Duemilanove will only use one of them at once.