[Vagaboul]

Hello Community,
on my Quadrocopter I use a step down converter (LM2596S) as a power supply for the Revo and the other components that need 5V (GPS etc). The step down converter reduces the 22V from the 6S LiPo to 5V (I measured 5,3V under load). Between the LiPo and the Quadrocopter I use a lightning protection plug.

When I was calibrating the g-sensor I had the Revo connected to my Laptop by USB. The power supply (step down converter) was active, means the Revo was also powered by the LiPo.
This worked very fine for a while but after 10 minutes my Revo went dark. After this it is not possible to react it, no light, no connection to USB also when only power from USB is connected. Complete damaged I think.

My colleague at work (electrical engineer) had the Idea that the step down converter (LM2596S) could produce an oscillation. He said I should try to connect a capacitor behind the step down converter to stabilise the voltage (or some capacitors to stabilise a bigger frequenz range).

Bevor I try it and ruin the next Revo I want to know if anyone else hat the same problem.

Did anyone else damaged a Revo by connecting to LiPo and to USB?
Did anyone had problems with a step down converter?
What did you do? Any circuit to protect the Revo?

Thanks in advance,
Vagaboul

[Brian]

I would first suspect the power supply as well.  6S to 5V is a pretty large drop, although that voltage regulator should be able to handle it.  Is the voltage regulator still working correctly?  Where did you get the voltage regulator board from?

If you want to try adding a capacitor, I would add it after the voltage regulator, not before.  There shouldn't be much fluctuations on the battery voltage when the motors are not active.

It could also just be a bad regulator on the Revo board that went out on it's own.  Do you see any obvious damage that might show what component failed?  Did you happen to notice the board being hot just after the failure?

[TheOtherCliff]

"Internet Wisdom" has it that for this reason (oscillation mainly) you should not parallel a switching power supply with anything.  This is cited as a reason to remove the center red wire on all but one of your ESCs if they have switching BECs.

If it doesn't at least power up (no drivers needed) from USB on a different computer it is probably burned.  You could try connecting 3.3v to the internal 3.3v bus and see if it powers up (LEDs).  If it does, you might consider replacing some voltage regulators on the Revo (very very tiny soldering) if you are able.

[Vagaboul]

Thank you Brian and TheOtherCliff for the fast reply!

First Information my Quadrocopter is still under construction. I wanted to start the first flight but then I had this terrible mistake.

@ Brian:
1. The motors have not been active when the Revo has been damaged. So it can not be a problem of fluctuations on the battery voltage like you supposed.

2. I can't see any damaged components on the revo. ( I know how that looks like because: Before that I burnd down another Revo by using the wrong Voltage. There I could see that the voltage regulators (REG113NA-3.3/3K) on the Revo where damaged. I tried to change them but they are too tiny) I did not check the temperature after the failure.

@ TheOtherCliff:
The Like I wrote the motors have not been active when the Revo has been damaged. So it can not be an effect from the ESCs I think. To avoid voltage jumps in generell (to smooth the voltage) I plan to use one (ore more) capacitors parallel to the Revo input.


I'm not sure if the capacitor idea will work and I don't want to burn down the third (!!) Revo with the next try.
Is it in general no problem to power up the Revo by the LiPo (with regulator of course) AND USB? Could it be an effect of difference of potential on ground or something like that? 

[TheOtherCliff]

OP FCs are designed to be able to use flight power and USB at the same time.

I wasn't suggesting it was an ESC issue, but that it was your switching regulator which is technically similar to the switching BECs some ESCs have.  And mentioned problems people have with the switching BEC in some ESCs.

Verify the power coming out of the switching regulator.  To be honest, if that regulator is associated with two FCs burning up, I would hesitate to use it to power a third FC.  I would even hesitate to use that style in the future.  I have some of those 2596 regulators, but have never used them.  I will be leery of using them now.

[Vagaboul]

Thank you very much TheOtherCliff for the explanation! Now I understand what you mean with the BEC.

Under the proposition I have two options:
1. Looking with an oscilloscope on the output of my stwp down converter. If I see some oscillation maybe the solution with capacitors works.
2. Changing my power supply for the FC in general.

I will report what happened. :-)

[Vagaboul]

Hello,

I decided on the second option "Changing my power supply for the FC in general. ". Now I use a 5V DC/DC Converter from Würth Elektronik. The behaviour is very stable, I had no more damages on my FC. No problems also when LiPo and USB are conected. The two Euro extra charge are very worthwhile I think!

I did the first flight and it was great!!! :-)

Thanks a lot for your answers!