Blown Mega2560 or?

Ramps1.4, 4 steppers, drv8825, 1 hotend-heater, 1 cooling fan, no bed heating. Driving a homemade delta.

I was printing happily when suddenly a poof and smoke, then all heaters and fans went on full..

The 5v regulator on the mega2560 had exploded.. So i hoped it was just that, soldered in a regular 7805 and plugged in the mega again (only mega board) . Nothing..
The powerled lights, and the AREF led lights. Nothing recognized on USB on the computer. The mega chip gets really hot, 60c in 20sec, then i cut power.
Removed 7805 and tried again.. same result.
I had been running the ramps1.4 on 13.5V as i really think it would be safe as the regulator on Mega states max 15v input. All diodes mounted on ramps.

Is it just to throw it and buy a new Mega2560 board ? And hope that nothing is wrong with the ramps board?
Typically it happens JUST as easter begins with some days off work.

If the CPU chip is getting hot the thing is dead. You will need a new board.

5V regulators don't normally explode, so I suspect that you have or had a short between +12V and one of the Arduino pins. If that is the case then you will indeed need a new board, but I suggest you check your wiring too. In particular, check that the 12V hot end heater wires can't short against the thermistor wires.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
AndersE
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I had been running the ramps1.4 on 13.5V as i really think it would be safe as the regulator on Mega states max 15v input. All diodes mounted on ramps.

...

You have the explanation for your "poof and smoke" right there.

13.5V on RAMPS 1.4 = bad idea. The RAMPS 1.4 is designed for 12V operation.

Now you have to change your Arduino, possibly change the RAMPS and some or all the stepper drivers, and you were lucky because apparently you didn't damage your PC and nobody got hurt.

Edited 1 time(s). Last edit at 04/03/2015 12:30PM by AndrewBCN.

Quote
AndrewBCN
13.5V on RAMPS 1.4 = bad idea. The RAMPS 1.4 is designed for 12V operation.

That's a myth. Arduino/RAMPS is perfectly capable of running from 13.5V, provided that you don't put excessive load on the 5V rail. Excessive load on the 5V rail will cause the 5V regulator on the Arduino to overheat. If that happens, it should go into thermal shutdown - not explode.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

From the wiki:

Quote
RepRap.org wiki
The safest way to power a RAMPS board is to just supply it with 12 volts, which is an easy voltage to generate. This will avoid you frying things that shouldn't be fried by trying higher voltages than are really needed.

From the Arduino Mega 2560 datasheet:

Quote
Arduino website
The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.

Edited 1 time(s). Last edit at 04/03/2015 08:54PM by AndrewBCN.

The key word is "may". Whether the regulator will overheat depends on the product of the voltage it has to drop and the current passing through it. What the Arduino team should do is to specify a maximum power dissipation for the regulator and tell us how much current the Mega itself takes in typical use, with no loads connected to the pins. Then it would be easy to work out the maximum input voltage for a given application. Sadly, the Arduino team doesn't provide that information. Arduino is aimed at novices, who typically connect LEDs, relay boards etc. to their Arduinos, thereby increasing the current passing through the regulator and thereby the heat dissipated. In that context, the advice to avoid exceeding 12V input is reasonable, given the reluctance of the Arduino team to provide the figures and explain how to use them.

A RAMPS board takes very little additional power from either the 5V rail or the pins of the Mega, so it does not add significantly to the current taken by the Arduino Mega itself. I have measured the current draw of a Mega+RAMPS at 90mA. I have also determined that I can run this combination at up to 15V without the regulator getting too hot to keep my finger on. The top surface of the regulator can get hotter than that before it overheats.

OTOH if you connect an LCD control panel to the RAMPS which draws its backlight power (perhaps 50mA) from the 5V rail, then even at 12V input the voltage regulator may get too hot for comfort.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks everybody.

I got a new mega, the rampsboard and stepperdrivers are all ok. So i am printing again now. On 12V ..