Hi all,
a while ago I pulled the stock Vin Regs off of my 2560's. Seemed a good idea
at the time. Now I need to replace them but don't know what the max amps
need to be. I can get LM1117 800ma over the counter or wait several weeks
for 1.5a version to come by post.
Can someone cast some light on my slightly idiotic dilemma?
Many thanks,
Andrew
How much current do you need? (The Arduino itself doesn't "pull" 800mA, but I don't know exactly how much current it takes with nothing connected.)
Maximum current doesn't tell the whole story. The power dissipation is often the limiting factor. With a linear supply, the power dissipation is calculated as Current x Voltage dropped across the regulator. i.e. With a 12V supply, there is 7V across the regulator, which means the regulator is dissipating a little more power than the rest of the circuit. And, the higher the applied voltage the hotter the regulator will get.
The bottom line is that you probably can't get anywhere near 1.5A from the Arduino board anyway.
USB 2 will only supply 500ma?
DrProblem:
I can get LM1117 800ma over the counter or wait several weeks for 1.5a version to come by post.
As DVDdoug points out, it depends on your current requirements. If you don't have a specific requirement in mind, then you'll probably be fine with something that works at 800mA.
The regulator that comes on the board is a LT3480EDD, which is rated for 2A max. However, you are unlikely to get that full amount, even with a low Vin.
For reference, the Uno boards use the NCP1117 series.
cjdelphi:
USB 2 will only supply 500ma?
What does this have to do with the regulators? They aren't connected to Vusb.
Hi, cn anyone tel you what the part number of the ones you removed were, apart from what the board needs for supply, you also have to keep in mind that the track widths will also govern the maximum current allowable.
Tom..... 
Merry Christmas
Mega R3 schematic shows NCP1117ST50T3G
49 cents
Hi everyone,
thank you all for the replies. I suspected I only needed to worry about fitting a
reg that could supply 800-1000ma, but wanted to double check.
I'll probably fit the 1.5A version anyway, it's about 50c more and that
extra margin for 0.5 or so amps might come in handy even if I never need
more then 800mA. A dodgy 800mA reg is probably going to start playing up
at 600mA or so, whilst the 1.5A reg wont even notice it.
I'll have to drop a spare heatsink on it as well as it's going to be in a space
with poor ventilation 
My thanks again,
Andrew
The reverse polarity protection diode after the barrel jack is only rated to 1A.
Don't try getting 1.5A thru it.