2.1 mm jack DC plug

I found one of the 2.1 mm plugs and its works for my mega,

1) It operated slightly higher temp so i wanted to check if i have missed something

2) can i safely carry 28 V DC supplied to the MC from the DC jack in and out from the Vin pin to supply other IC's and circuit's power? (external to MC)

Read the voltage specifications for the input jack and you will find it is much higher than recommend.

The range is 7 to 24 (?) with recommended 9v.

Weedpharma

12V is the practical upper limit unless you actively cool the on-board regulator anyway.

If you have a 24V SLA system as your power find a DC-DC converter to bring this down to either about 8V for the jack/Vin or direct to 5V even. You'll have no problems with heat dissipation as a DC-DC converter from 28V will be about 80% efficient compared to 18% obtainable from a linear regulator going from 28V to 5V

MarkT, its 24 V but ive got it in its own enclosure with a cooling fan. still risky?

arduidiot: 2) can i safely carry 28 V DC supplied to the MC from the DC jack in

Considering that the input filter caps used on the Mega are rated for 25V and you're driving them with 28V, it'll work for about a month or so. Then they'll fail. So I would say, no.

arduidiot: MarkT, its 24 V but ive got it in its own enclosure with a cooling fan. still risky?

Yes. The on-board regulator has very little heat sinking. At 24V in, the 50mA the board requires to run itself will burn 0.95W alone.

yep ok thanks im going to take this situation ive run into as a "sign" i need to leave the wires alone for a few weeks and keep my head in a few books.