Arduino MEGA getting super hot while running

I'm using a RAMPS pcb on top of a MEGA 2560. I'm powering the RAMPS with a 12V PSU rated @ 320 watts. Everything is connecting fine, I've tested almost everything, but I think I fried at least one of my megas. The megas run fine plugged into the computer with no RAMPS board attached, and then again with the board attached but carrying no drivers. When there's no drivers on the RAMPS, I'm getting the expected 3.3v on the 3.3v header, and 4.7v on the 5v header. All is peachy there.

When I plug in the RAMPS board with even one driver on it, and the 320W psu *not* plugged in, the 5v reading immediately drops to 3.6v or so. The board will still work, however, If I plug in more than 1 driver, the LED just flashes continuously when I plug it into the USB port. However, if I plug in the 320W psu, and then plug in the mega to the USB port, I can have all 4 drivers on the board no problem, and everything works well.

Here's the problem though - the MOSFET next to the external power input jack on the mega gets BLAZING hot. Like, untouchable hot. I didn't notice it previously, but I think that's what fried my other mega. Anyhow - I'm assuming everything is working well because the board is taking power from the Vin pin, which is supplying a full 12v, and it's then able to maintain a steady 5V on the 5V header, which I confirmed with a multimeter.

My question is, I guess, is how hot can this component get without having issues? And secondly, the other mega that I think I fried will actually have the power light lit when I plug it into the USB port, it just won't communicate at all. The TX / RX lights never light. Is there someway to reset this thing to get it to work again, or is it screwed?

Thanks!

naPS

Do you have the diode installed on the RAMPS. If so, cut it.

jcabrer Wrote:
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> Do you have the diode installed on the RAMPS. If
> so, cut it.


I do, and I've thought about that, but then the problem comes in that the 5v signal from my USB port drops to 3v when I plug in more than 1 driver, and the board doesn't run. I guess I need to provide the board with external power.... I believe 5 volts / 1 amp is the max I can use, correct?

Or you could use a powered USB hub, which should be able to power the Mega.

It's actually not, not with the 4 drivers. The max USB power is 500ma at 5v, which is not enough for this particular MEGA and the 4 drivers. It's enough for 1, sometimes 2 drivers, but not all of them.

Test each of the drivers individually in each socket. See if you have shorts in the soldering. Cut that diode though. I don't recommend using it.

The drivers should only take about 10ma from the 5V rail so you must have something wrong.

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[www.hydraraptor.blogspot.com]

jcabrer Wrote:
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> Test each of the drivers individually in each
> socket. See if you have shorts in the soldering.
> Cut that diode though. I don't recommend using
> it.

Yeah, gonna nuke the diode for sure.

Each of the drivers works individually in each socket. Tested all of them.

nophead Wrote:
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> The drivers should only take about 10ma from the
> 5V rail so you must have something wrong.

I think it might be because I'm using the A4988 drivers, not the A4983's. They have their own pull-down resistors in them which I think is causing the increased current draw.

They are two 100K and one 50K, which will take a grand total of 200uA.

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[www.hydraraptor.blogspot.com]

Can you take a picture of your board, from the top down, with the Pololu's removed?

IMBR, but it sounds like you have either a wrong component on the board (eg: different FET or a BJT), or something s backward.

Also, check for a short somewhere, usually between an output pin and a voltage rail and/or ground.

So, basically this boiled down to the diode. I'm using a large 12v power supply, and it was providing too much power through the D1 diode. So, it's clipped off the board now. I ended up nuking a Mega and 4 Pololu drivers in the process - I imagine it was applying >5v to the board due to the high power being fed into the regulators, and it fried it. Oh well. The drivers themselves were responsible for pulling the high amperage after they had fried, thus the resultant drop in voltage on the 5v side of the board when I was plugging the drivers back in.

Got a new Mega, 4 new drivers, and am just powering it off the USB now. Works great. Now if I could just get repsnapper working...

dont feel so bad i did pretty much the same thing trying to make my own ramps board, that damn blue genie likes to escape

what version of the mega do you have, i know with my 2560 there is a bug there with repsnapper, i can only get it to connect if it is the first time after i plug in the usb chord. and if i close repsnapper, i have to unplug it and plug it back in again.

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[mike-mack.blogspot.com]

Yeah, that's the same version of the MEGA I have as well. It's annoying, but I just keep it plugged into an accessible USB port so I can easily plug and unplug it.