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Topic: Apply External Vin Power Backwards on Arduino Mega 2560 R3 (Read 2025 times) previous topic - next topic

rodolf0

The title of my topic says it all.

I was desperately testing different codes for my mobile robot, all of a sudden I hooked up the wires from my 7.4V  @ 1Ah LiPo battery in the Vin and GND pins backwards and then my board crashed  :smiley-eek:. I didn't look up at the wires polarity properly cause I had been doing that for days but s**** happens. :smiley-red:

Fortunately I could use it again, powered it via USB cable, but given the circumstances I'll need an external power source. The thing is that I don't know what component has been damaged; thought it could be the voltage regulator, but if anyone could give me an advice on this, I'll truly appreciate it.

And even more if there is a way of fix it, even though it sounds pretty difficult.

Thanks in advance
Rodolfo Aguilar

retrolefty

If the board presently works using USB power but does not work using Vin power because of your reverse polarity 'brain fart', then the two likely components to change is the voltage regulator and the 47ufd cap on the input to the regulator.
See schematic, upper left section.

In the future you might consider wiring your external voltage source to a DC power plug and just connect it via the DC power connector on the board, that would have protected you from reverse polarity as it has a series polarity protection diode.

Lefty


rodolf0

Rodolfo Aguilar

rodolf0

https://www.dropbox.com/s/w80uupelq1m968l/voltageregncap.jpg?m
Rodolfo Aguilar

retrolefty


https://www.dropbox.com/s/w80uupelq1m968l/voltageregncap.jpg?m



Correct regulator but not correct cap. It would be a larger 47ufd electrolyic cap near by, called PC-1 on the schematic.

http://arduino.cc/en/uploads/Main/arduino-mega2560_R3-schematic.pdf

Lefty

rodolf0

Thanks again,

This one...

https://www.dropbox.com/s/fxf7sy8mvlho0z0/47uFdcap.jpg?m

Right? Sorry I shoulda noticed thats a cap before.

Cheers
Rodolfo Aguilar

retrolefty


Thanks again,

This one...

https://www.dropbox.com/s/fxf7sy8mvlho0z0/47uFdcap.jpg?m

Right? Sorry I shoulda noticed thats a cap before.

Cheers


Most likely seems to be the one.

Lefty

rodolf0

The voltage regulator should be at 3.3V or 5V? I already replaced for one at 3.3V. And its not working yet with my battery... I'll apreciate your response.

Thanks
Rodolfo Aguilar

retrolefty


The voltage regulator should be at 3.3V or 5V? I already replaced for one at 3.3V. And its not working yet with my battery... I'll apreciate your response.

Thanks


The 5V one, and it feeds the input to the 3.3v one, so the 3.3v one can't work if the 5v regulator is bad.

Lefty

rodolf0

#9
Mar 05, 2013, 12:59 am Last Edit: Mar 05, 2013, 01:05 am by rodolf0 Reason: 1
Like I told you in the last post I replaced the original NCP1117 voltage regulator for a generic one. I thought the problem was the output voltage that seemed to be at 3.3V but turns out there's a wide voltage range that works for.

The problem was that the one I replaced it for has a different pin configuration and that was the reason it didn't work at the first try.

Today I got a new voltage regulator with the same pin config than the original, replaced it and No, it's not working yet. =(

So I don't know whatelse can I do? I think I'm out of ideas.

Regards
Rodolfo Aguilar

rodolf0

Anyone could give me a hand on this?

Please!!! I'll really appreciate it

Cheers
Rodolfo Aguilar

Docedison

What is the part number of the replacement part, what is the voltage at both it's input and output? does it still operate from the USB cable?...
IN OTHER WORDS, WHAT CHANGED? WE CAN'T READ MINDS AND MY CRYSTAL BALL IS BROKEN...
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

rodolf0

Here is the datasheet of the replacement part...

https://www.dropbox.com/s/4cwzfn4evx2c4u8/ds1117.pdf?m

Haven't checked the voltage at the input and output yet, Im out of town this weekend,

And Yes, its still operating from the USB cable.

Nothing seems to have changed by replacing the voltage regulator

Thanks for your time
Rodolfo Aguilar

zoomkat


Anyone could give me a hand on this?

Please!!! I'll really appreciate it Cheers


I've externally powered my aduino just using a standard 7805 regulator chip connected to +5v pin and ground. Not sure how this would play with the USB power source connected at the same time.
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