Mx Nano Multiwii 1.31 burns ESC

[lucas1414]

Hello everybody,

I bought a super-x quad copter a year ago and everything worked fine until I plugged a Turnigy nano-tech 750mah from Hobbyking that had polarities inverted...
This mistake burned two of my four esc but the multiwii looked fine, conection via the fdti worked and all the sensors as well. So I bought two new esc and all good for a few minutes, until I try instead of the 260mah the 750mah 1s with the polarities changed to not make the same mistake.... and burnt again... only one though.
So I try to understand why?
- Is it the hight amperage from a bigger battery?
-Is my multiwii board dead , how can i check that? Output from the board to the esc gives 3.8volts, same as the battery output.
-maybe I wasn't lucky and the new esc was fragile?

Thoses esc are incredibly expensive so I post to see if someone has a solution before doing my own test.

Cheers!

[edsimmons3]

You have probably got a short circuit somewhere... Use a multimeter set to measure resistance and check what the reading is when you measure between 5v and gnd. You have probably damaged a reverse polarity protection diode or something that has gone dead-short.

You can find which board this is on by unplugging things one by one and measuring again. Once the resistance becomes higher, the short has been removed. It is possible that the short is on the multiwii board itself, you may be able to find the defective part if you have a good eye for electronics and a sensitive meter

Edit: I just re-read your post - since it's working with the FTDI lead you probably have a short that is connected to the block of connectors for the ESCs. My multiwii board has a thermal fuse and diode protecting the 'inner' 5v supply for the MCU and sensors (and sensor regulator for the 3.3v stuff), the reverse protection diode is connected between the ESCs 5v and GND rails... If this is what is shorted, you will probably get the symptoms that you mentioned... The FTDI will still work and the ESC power will be shorted, thus either damaging or shutting down ESC BECs.

If it is a protection diode that has broken, removing the broken one and soldering a replacement will bring your board back to life. Hopefully, the part that has failed shunted enough current to keep the reverse voltage very low (at expense of it's own life and the ESC).

Hope that helps...
Ed

[lucas1414]

Ok,

I do have a proper multimeter, but I'm not so sure about what i'm looking for, everything is tiny on this board maybe my best option is to buy a new board.
How can I check if something is going wrong on the esc output.

Thanks for your time!

[edsimmons3]

If your meter is really sensitive on the low ohms range, you can probe round everything that looks like it's connected between 5v and gnd until you find the lowest resistance. I'd guess you'd have settled on a diode that's fairly chunky in comparison to the rest of the small SMT parts. Since it seems to be a power short it has to be connected between 5v and gnd somewhere.... You already eliminated the sensors and MCU as possible culprits by testing with the FTDI lead, this doesn't leave very much on the board unchecked!

I work with SMT electronics all the time and can swap a part easily enough, sorry for assuming this is easy for everyone!

Here is a slightly over-exposed phone photo of the relevant part of my multiwii board... https://goo.gl/photos/hCVphVnAtC7H75Wi8 the diode I'd expect to be causing the short is the black cased component to the left of the gold PTC fuse. You might be able to see that it's connected to the ground plane copper at the far left, the other terminal is connected to the PTC fuse. This diode shorts out a reverse polarity to keep the voltage very low.

Hope that helps...
Ed

[lucas1414]

Ok I'm gonna try finding that, I'm not so sure to know what a micro diode looks like, I'm more used to bigger stuff. Are you sure that we can see what you describe on your picture I can't see more left than ptc fuse (if ptc fuse is what I think ) .
Any way there are not many components on the micro wii board, I will test that.
If I find the wrong component do you know where I could buy thoses micro diodes?

[edsimmons3]

The PTC fuse is the very reflective thing in the middle of the photo. The two black things either side of it are diodes, the left one has a track that joins the pad to the ground fill of the board, the other end is connected to the 5v on the PTC fuse.

The yellow/orange thing on the very far left by the reset button is a tantalum capacitor, just so you know...

The diode is a small rectifier diode probably, but unless I see the one you've presumably blown up I can't help source a replacement!

I hope that helps...

[lucas1414]

https://goo.gl/photos/g2jtANmjRvnMLLmv9 here is the back of my board I've test the two diodes the first one by the B jumper is giving 12.820 Kohms and the second one on the bottom right written JA gives 1.06... Mohms and in-between the vcc and gnd of battery connector 10.60kohms.

Here is the sensitivity of my multimeter :

Range : 0.5 - 5 - 50 - 500 kΩ,5 - 50 MΩ
Resolution: 10 mΩ to 1 kΩ
Basic accuracy: 0.1%R + 3D (500 Ω to 500 kΩ)


Here is the front side of the board but I think this side concern the sensors, arduino...
http://uav-review.com/wp-content/uploads/2015/01/SKU16395502.jpg

I'm wondering something, If the drone has worked for a battery time, is it possible that the diode is not shortcutting all the time?

[edsimmons3]

I'm surprised you didn't find a short! I would suggest that you got another board at this point... Sorry!