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
This look like it should be fine and if you not are experiencing any issue, I say fly it!
Log analysis is good if you have problems....IF the parameters show the issue.
Putting the radio on a separate BEC should allow you good performance.
-=Doug
Dear Doug,
thanks for your comments..
Dear Doug and Bill,
so if i understand correct, if my fuse is 500mA the only solution is to use a BEC??? If it is a 1A fuse I could use the usb to power my 500mW radio module. Correct?? Is there a way to check what fuse I have ??
If I have to use a BEC is there somewhere a schematic or a video available that shows how to connect the BEC with the radio telemetry module?? I see that the BECs have a 3 pin servo connector.. How can I connect this with the 5 pin molex connector of my radio telemetru module ???
Thanks and Regards,
Bill, thanks for the update on the fuse change for the USB. Clearly the 1A device (silicon fuse as Bill pointed out) would be another variation of use for the USB connector. At this time, USB electrical limits are defined as:
As the current rating of the source goes up, the wire size must be appropriate to deliver the current.
DN, Bill mentions connecting directly to the PM (theoretical source current from the PM is 2.25A). This would require custom wiring from the PM to the USB connector or the nearest pcb pad/trace that can handle the current - this is the same as wire size mentioned previously. If the pcb trace is too small, it will overheat and possibly melt with excessive current.
We will have to dig around the boards for information on connecting your HK radio. I looked on the HK site and there was little that hasn't been taken from this site. The 'PM to USB direct path' might be the simplest solution.
THIS page from the Arduplane group shows an ESC powering the Output rail with an Xbee radio (older unit) and the +5 VDC to the Xbee noted as disconnected. Scroll down to the section called 'Example Wiring Diagram'.
-=Doug
Dear Doug,
I have created a schematic of how the radio telemetry, the BEC and APM should connect to each other... Is is correct ??? If yes, where should the negative line of the BEC's output be connected ???
Thanks and Regards,
Bill beat me to it.
The important part is not having the 5 VDC from the BEC going to the APM.
The 5 VDC from the HK radio could be cut or de-pinned from the APM connector.
I find lifting the latch on the connectors and pulling the pin easy and clean.
-=Doug
Dear DOug,Bill
in order to conclude, according to your notes the final schematic I should follow is this ??
Is this BEC's characteristics appropriate for my case ??? --> http://www.ariesrc.gr/6302-dys-sp-3a-5v-switching-bec.html
Thanks a lot for you valuable help
Yes, the power connections look correct. I have not confirmed the data connections, but if you are only modifying the power wires of the original cable, the data lines should be fine.
The BEC looks fine. You will have to confirm the input settings for your BEC. They may not be automatic and some BEC have outputs that are adjustable. Your choice looks fixed at 5V.
The 3 Amp rating (3000 mA) significantly exceeds the need of 500 mA of the radio.
Let us know how this works out. Good luck!
-=Doug
Dear Goud,Bill,
I have installed the BEC as we said according to the schematic of my previous post, and here are my findings..
When I connect APM to Mission Planner, my hwvoltage value is now almost steady playing between 4.90V and 4.94V. So everything good.. Before the BEC install the hwvoltage used to fluctuate between 4.45V and 4.81V..
However when I measure again with the voltmeter in the same points as I used to do before installing the BEC, you can see in the following pictures my new measured values...
SO it seems like the hwvoltage value has been fixed but the voltmeter values have been damaged...
Please give me your comments...
Thank you
The ground (neg) is the common reference point for *all* electrical signals or power sources.
Essentially the PM point you are referencing *should be* the same as directly on the APM. If it continues to provide a difference after all grounds are connected, suspect resistance in the wiring.
Resistance (unwanted) is usually a bad crimp or solder joint - a quality issue.
Resistance is *intentionally* added in electrical circuits with a component called a resistor.
Good Luck!
-=Doug
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