I am not an electrical engineer and so I could use some help here.
We are a bit concerned about the speed controls pumping too much voltage into our APM2.
It appears our ESC's are outputting nearly 6 volts. Is this too much?
We started looking at some options. A little voltage regulator LM7805C came to mind, but it appears most suck up quite a bit of voltage (drop out voltage) ~ as much as 2 volts ~ so then the board would only get nearly 4 volts. And it sounds like that too could be a problem....yes?
So we found what is called a Low Dropout Regulator (see link). It appears this guy has a drop out voltage of only 0.15 volts at 100mA (did I read that right?) (How many amps do our APM2's need?) see specs at link below
So it sounds like if the ESC's produce anything more then 5.1 volts we could be assured of a safe 5 volts. Of course if the voltage from the ESC's gets down to 5 volts, our board would only get 4.9 volts etc.
I think I would like this little bit of insurance....am I on track or way off the wall ?
Thanks for your input.
I have some cheap speed controls....
I am concerned about hooking them up to a new $200 APM2.
It seems like the voltage regulator would provide a bit of insurance against any weird voltage spikes these ESC's might spit out.
Would a diode do the same thing?
Maybe I should just get some nicer ESC's :) !!
I would recommend investing in an better ESC for your entire aircraft or a separate BEC to supply dedicated 5V just for the APM. For ESC, I use Phoenix ICE LITE 50 Brushless ESC. For BEC, I use the phoenix Castle Creations CC BEC.
So are you talking these ?
Thanks for your help, Rick
Yes. I have both and I love them both. You can precisely control what the voltage output. The ESC also has build in logging for various parameters. Good stuff.
For what it's worth, I supply the APM with 5V via an LM7805 powered directly from a 3S lipo. No problems, works well.
Ha...Yes!! It is worth a lot....:) This is exactly the kind of info I was looking for. :)
So we go from a slightly variable 11.1 volts to a constant 5 volts for a few bucks :)
Tell me more if you can. Does the little guy get hot? Did you add a heat sink etc? How long have you been doing this? Do you know... are others using the little LM7805 on their APM2?
Thanks so much.
Yes this will work and not be any problems but this is a linear regulator, so not as effiecient as a switching regulator, and the wasted energy will be converted to heat, and the hotter it gets the more is wasted.. Perhaps this wastage is very slight it depends on whats going in and whats being used?
Perhaps I am being a bit anal about it? I will run some tests and find out how many mah are wasted using a linear regulator in comparison to a switched one.. :)
O.K using a regulator such as the 7805 on a 3s lipo, with 1amp draw, which 1 servo could use on its own without anything else would waste 7.6w of energy if you are only powering the board and nothing else you would waste 1.52w of energy.. So in terms we all understand drawing 1amp would cost you around 603mah and just powering the board will cost you around 121mah.
Hey Dean, thanks for your time :)
What is a switching regulator that you are talking about....can you give a link to one. Then can you show the calcs you used above and did you calculate what the switching regulator costs us in mah to power the board? :)
The 5-6V output from your ESC and the BEC that I was talking about are all switching regulators.
To calc the power draw, just connect an Amp meter in series to the 3s to the 7805 and check the current. The (actual) W1=V1 * A1 that you measure is the total power being used. Then you can check the actual current on the APM. The actual W2=V2 * A2 on this side of the ESC/BEC would be the power actually delivered to the device.
Power wasted is W1-W2. And the wasted mA is (W1-W2)/V1*1000