Frequently asked questions are about powering an APM2.5 or why the same does not work or why it has failed.
Here is a simplified schematic showing the major components of the 5V/Vcc circuit on the APM2.5
Target Audience: Readers who do not have Eagle or are confused about using it.
You Need: Basic electronic schematic reading ability
Note that I have separated the PWM Output section into the upper left corner with a heavy purple line that is bridged by the jumper JP1 on the APM2.5. This is to emphasize that diode D1 passes current through JP1 (and drops voltage). The remaining energy is then called 'Vcc'. Everything outside the purple corner is Vcc.
This is why the USB will power the APM2.5 when connected to a computer/USB hub. Note the fuse on the APM2.5 side of the USB connector AND another fuse on the output of D1. Another change from APM2.0 is the D4 6.0V Zener diode. If an over voltage is applied to the board, D4 will crowbar what it can to protect devices.
As with APM2.0, any 5V source connected to any of the indicated Vcc/5V points outside the purple corner (with GND of course) will power the APM2.5.
Also of note is the 'Mystery Port'. This port takes 5VDC before D1 and the fuse and is called 'JP_VCC'. Other clues to the mystery are the lines to 'ADC 12' and 'ADC 13'. A mystery indeed!
Any errors in this drawing from editing are mine.
I hope this can be used as reference for solving problems.
-=Doug
27-FEB-2014 Eagle files are now located HERE
Replies
A UBEC will need more input voltage than the output.
example: +12VDC ---> UBEC ---> +5VDC
If using APM power module, JP1 should not be connected.
USB power should only be used for log file transfers and other PC/APM related work.
Having the PM and USB supply on at the same time could lead to a ground loop if you wiring is incorrect.
Could you provide a sketch of your wiring?
-=Doug
Thanks for the reply Doug,
With the PM supply only, JP1 not connected, mis behaves, I'd be inclined to say that something is receiving marginal voltage! Meanwhile voltage at the input pins is 4.8v
Now add usb supply (I guess connecting this is ok because USB v is not far off input pin v) Now works reliably! Meanwhile voltage at the input pins is 4.83v. Ie only 0.03 higher than without usb connected.
Supplying only input pins with full 5v = mis behaves, just don't make sense!
Its as if usb +v is supplying something differently!, will scope it tomorrow, see what difference there is, will also supply the apm with an ultra smooth supply, see if that works!
Meanwhile still scratching my head! It's not a duff PM either, I have 4 here!
Ground loop could come into play when USB is connected but we are only talking about 140mA or so!
The logs can/could also be analyzed for dropout/brownout conditions.
Though not a direct 5V sample, it is/was done by an algorithm used in Arduino code groups and implemented in APM Copter...at least before the last release. I've been running fixed wings for months now and dust is collecting on my rotary wing birds so.. not sure what is current regarding logs.
-=Doug
Have had chance since to test again with apm 2.6, apm 2.5, different esc's and it seems the cause is a bug in the 3.2 code! Loaded v2.9 worked fine, loaded v3.1 fine! 3.2 same old problem...
so currently running on v3.1
If I get time I will look into the code changes between the two!
That's nuts!
I have no clue why the older versions would impact Vcc.
Have you checked the other forum for information?
-=Doug
I don't think that it is voltage related anymore!
The apm is disarming after being armed for about 10 secs, some times unable to re-arm, have to do a reboot!
But if plugged into usb then works fine every time, thinking now its something to do with usb signal lines rather than pure usb voltage.
NUTS? Yes I agree!
There's one big thing I think we're all missing here. Imagine I"m using one battery to power the plane, and a BEC on the output rail. Even if I have JP1 open, the servo return current, can still go back to the battery via the ESC leads OR the APM ground traces. THIS IS A GROUND LOOP! I think there should be a way to disconnect the ground between the output rail and the rest of the APM board, in the same manner as JP1 disconnects the supply voltage.
Hello
I'm still studying and setting up my APM 2.6 ,but after reading the last few lines of your problem
it seems to me that's exactly what has happened you supplied to much voltage to the board -if you
had the jumper installed and used the USB and the ESC lipo if I read it correctly that is a possible
risk of burning out the board or components like I first said I'm still learning so I maybe WAAAY off
the mark ,or just wrong -I hope you can get it working again without a lot of trouble
Good Luck
Thanks for that post.
So, I never quite understood why I cannot power an APM 2.6 from both the servo side and the power module side.
The diode is there to make sure power module power doesn't flow to servos, so I don't understand why you'd ever want to remove JP1 and get into a non redundant power situation.
Do you happen to know?
Thanks
The power module is directly connected to the 5V Servo rail with JP1 installed.
The diode D1 stops servos from being powered from the USB port.
The diode D4 shorts to ground with a voltage over 6V, the main load being dissipated with the 500mA (now 1.1A) solid state fuse F2 (as current goes up, its resistance increases, having a larger voltage drop across it)
see http://copter.ardupilot.com/wiki/common-apm25-and-26-overview/#Powe...
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