Short Between VBAT and GND, FC Burnt.

[rafareusch]

Hey guys,

I have a Nazgul5 which I was installing My receiver. After and before the instalation everything was working fine.
Then I was troubleshooting A failsafe problem, so I was pluggging the battery and the usb cable on and off the drone, testing failsafe and other stuff.

Out of nowhere I plug the battery and I saw smome coming off the underside of the FC. Went to look and there was a Short between BAT and GND on the pin side of the connector that comes from the ESC, the ESC seems to be fine(didnt tested but no apparent damage to it) The only I think could have any relation is that 2-3 times I had to plug the battery out while the drone was armed with motors running (no props) and was not entering failsafe. The only thing I changed was the 5v,gnd and signal pad. Could a short in 5v do that?

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(I tested receiver and vtx with external supply and they work fine)

 

[wafflejock]

Yup if the 5V regulator can put out enough current to cook a given wire or component then 5V can be enough to cook something. Lets say 5V 1.5A regulator is able to deliver more current for a brief period it might up the amps to lets say 2A then 10W of power is available to bleed off as heat or use to light something or move something (essentially that energy is going somewhere), if nothing useful is happening with that power then it is just becoming heat in a wire/resistor, if enough heat builds up the component cooks. Resistors have a max wattage which is effectively the max heat they can dissipate (usually like 1/4W or 1/2W for small resistors) in a given time the same holds true of wires which are effectively very low resistance resistors, if the current gets high enough I^2xR = P then things start melting.

In terms of avoiding the issue I generally just continuity check VBat/GND and everything else I touch with a soldering iron to make sure things aren't shorted unexpectedly and things are connected where I want them to be but sometimes things happen, solder blobs fall or a little flake of wire can fall between things and short them out (very thin wire is high resistance and more likely to toast itself but not as likely to allow enough current to flow to toast thicker leads). You can also use a "smoke stopper" which is effectively a current limited power supply (or get/build a bench power supply, buck converters with current limiting capability are around $30-40) any current/wattage limiting can help to avoid cooking things though not sure you would be able to get the right balance of enough power to test things here while limiting it to a "safe" level for everything.

Another little tip, either work on your boards completely away from the frame (test initially before installing each part) or have it mounted fairly securely on the frame/screws and make sure any CF from the frame is covered in electric tape since the frame itself can and will conduct electricity

 

[Dugdog47]

In layman's terms you let out the factory installed magic smoke.

 

[rafareusch]

hahahaha, Well, since this is My first quad, I'm trying to find what I did wrong to cause this, can't see anything wrong other than these pins. I Could use another 5v regulator to power the board, as the 5v rail seems to be fine.
How can I test the ESC? I've had no problem powering it with a lipo, It makes a very very low hissing sound (everything unplugged) , but all voltages seems alright.

 

[wafflejock]

Just about all the ESCs I've encountered will accept a "servo signal" or 50hz PWM pulses with a width of 1000-2000 us or 1.0-2.0ms, that's to say you can hook them up directly to the output of a receiver that gives PWM signals for controlling servos and have it also control an ESC so can skip the FC. The only other way I've tested ESCs is through the FC sending control signals or acting as a passthrough and connecting with BL-heli-suite to the underlying ESC to flash things or change config and can test individual motor output there somewhat bypassing/passing through the FC. I know you can flash arduinos to act as the control device for those too but have just never had the need myself since always have had at least one working FC around to test with. Grab BLHeliSuite32 though and check out docs around it if want to try and connect to a BLHeli32 based ESC more directly to diagnose things.

My 2 cents if my electronics are hissing at me it's a bad sign