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.



27-FEB-2014 Eagle files are now located HERE


Tags: (UAV)-autopilot-hardware, APM2.5

Views: 47227


Reply to This

Replies to This Discussion

I never quite understood why I cannot power an APM 2.6 from both the servo side and the power module side

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)


Aaah, the power module isn't protected from powering the servo rail with the diode when JP1 is installed?

Ok, not sure why it would be designed that way, but now that makes sense, why you'd have to remove JP1 if you use the power module.


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.  

Hi all,

I have a question that's bugging me.

In some places including arducopter site (compassmot specifically) it's saying we CAN connect both BATTERY and USB at same time

In a case where I use a power module and no JP1 installed is this true or not ?

Thank you for your question.

If everything is wired correctly - we have seen many cases where this is not true - having battery (to power module) and USB should not harm anything. It is discouraged because the ESC are then powered and if you are working via USB to the APM, testing system parts, we certainly do not want the props to spin up.

The USB port is fused. I wish there was a power removal jumper for the +5 but, Pixhawk is the future and this entire thread may one day be retired when the hardware is no longer supported.



© 2014   Created by Chris Anderson.

Badges  |  Report an Issue  |  Terms of Service