Pixhawk servos power options/clarification

Archive
21

I tested the zener with the UBEC putting out 6v and I measure 5.9v across the rail. I thought it would hold it at 5.6v. Perhaps it’s because it’s continuous rather than a transient spike.
It does heat up as predicted.

22

You might have fried it already. It’s not a good idea to use even a 5W Zener for constant regulation.
For low power applications, zeners are commonly used as regulators, so not only for transients.

23

I used a fresh Zener and a 10v 1000uF cap together like this. [attachment=0]ImageUploadedByTapatalk1402515793.800111.jpg[/attachment]

24

I wish you would not double post on DIYDrones and Ardupilot. It makes a lot of work for the people providing support.

The instructions read to not use >5V servos as backup power and to install a Zener diode to prevent the rail from going about 5.7V

Starting at 6V is not going to work. May I suggest spending some time reading about how a zener diode works as part of your DIY electronics education.

Cheers

25

I apologize for the double post, I don’t make a habit of it. I appreciate your help and patience, this is an area of weakness in my knowledge base and I am working to remedy that.
I take it you approve of my diode/cap arrangement in the photo above?

26

Yes. it looks fine

27

After reading different “interpretations” of the zener / capacitor combo, I am more confused than I was before. I get that the Zener is cutting the power above 5.6V, but what good is the capacitor? There are two (non-exclusive) options:

  1. Reduce ripple
  2. Provide backup power when zener is active (overvoltage)

Then I wonder, if the capacitor does not just bypass the zener diode in case the voltage spikes!? Which would of course render the zener quite useless…

I check wikipedia for the zener, but found that for voltage cut-off a resistor is used and not a capacitor…

Any pointers would be much appreciated!

28

Powering/backup off the servo rail,

Thank´s for good info.
but…total newbie with electronics here :open_mouth:
So far only flying with basically rtf quatros for coupple of years, and now on my first build.

I have been reading and reading and i´m getting there.!
The picture above about zener&cap…is the whole connection done like in my attatched higly sophisticated blueprint :smiley:
[attachment=0]pixhawk power.jpg[/attachment]

I read somewhere that capasitor is not reguired with opto esc´s ??

thanks

Mikko

29

[quote=“scubari”]Powering/backup off the servo rail,

Thank´s for good info.
but…total newbie with electronics here :open_mouth:
So far only flying with basically rtf quatros for coupple of years, and now on my first build.

I have been reading and reading and i´m getting there.!
The picture above about zener&cap…is the whole connection done like in my attatched higly sophisticated blueprint :smiley:
[attachment=0]pixhawk power.jpg[/attachment]

I read somewhere that capasitor is not reguired with opto esc´s ??

thanks

Mikko[/quote]

Edit to my previous post,

…and of course… a 12 to 5V bec after 12v output from esc.