Blue my MegaBoard - What did I do wrong?

I started my build like 6 months ago, but, had to set it aside for over 4 months. Got the table built, just hooking up the electronics
I went for the 24v power supply (will need some advice on stepper reference settings, but, later - i have BIGGER problem now).
So, I had the Mega powered up via the USB to my PC, was just about to download the program to the board, had the 24volt supply on (I had set the ref voltage, but, now i am wondering if i set it for a 12v supply, if it will be diff for 24v?)

Anyway, I was going to unplug it so i could move it, so I unplugged the USB cable - while the 24 volt supply was still on - on the Ramp board.
As soon as I unplugged the USB the Mega board began SMOKING… Totally fried by the time I got the 24v supply unplugged from the AC.

SO… is that “normal” ? I mean, will the Mega board totally fry if we have high voltage power on the Ramp board and turn off power to the Mega? That seems really bad.
I mean, i could see accidentally doing that unplug the use from the PC and not shutting off power to the stepper driver first - Or did i have a bad board? Which board would that be, the Mega or the Ramp? I don’t know if the Ramp board and the 8825 drivers are fried or not, i hope not, the smoke was on the Mega board, i think the power supply chip fried.

So, is this just the way it is, or do i look for something wrong in my set up ??? (I have another Mega board - but - i need to know what is what before i plug it in.

Is it the 24 volt supply?? Should i have used a 12v supply instead? (Hope not, i got 2 of the 24 supplies - the trimmer only takes it down to 19) it seems like the 24 volts fed over into the mega supply somehow?

I’m not an expert, but a quick google search turned up this post:,196602. It looks like you can run the 11A side of the board at 24v, but there are some specific things to consider, and the 5A side needs 12v regardless.

Maybe someone else will chime in who’s run 24v on ramps, but I think most of us are using 12v.

Good luck!

I’m pretty sure that mega is toast.I lost one to the magic smoke myself yesterday. I think the steppers and a heat bed would thrive on 24v but the arduino board can’t handle it. Did you cut the D2 diode on the Ramps board before you did this? If not then you definitely should to isolate the arduino voltage regulator from the 24v. If you do cut the D2 diode then you can run 24v but you’ll need to power the arduino from a seperate power supply or USB. People do this on3d printer setups with 24v heated beds all the time so lots of info online explaining the process. The 12v power supply is less hassle because you can power the arduino and the Steppers from same supply plus generic laser drivers use 12v too which leaves you set for laser add on later.

Hey, both of you , thanks for the quick response.
Yeah, i searched it more after i posted, i tried to delete post, but, see it stayed up. I saw the links about removing the Diode, etc. But, I decided i will just go with 12v instead. I’m going to use a PC powerSupply that has 12v 30a on a single rail, and if i need them, it has 5v supply also. (-12 and -5) Has plug in ac power cable, has power switch, cost less, and has 2 yr warranty. Hopefully it will work.
And, yes, a laser head looks interesting…

Now i have another problm went to use my other Mega2560 and can’t upload programs to it, timeout - looked that up and looks like the bootloader needs to be (re)installed on the mega board another headache to figure out I am making this build large, 3x4 feet have to take some pix when i can…

Got any old xbox 360 power supplies laying around? They’ll work great for an MPCNC.