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
DN, In regards to your questions:
1) This should be the same as using the molex, just a different path. You are still connected to Vcc and will still draw more current with the 500mW unit vs the 100mW unit. From the APM side, Vcc is still connected to the USB port via fuse, F1. The intended use of the USB is connector is not to source current/power. The intended use is for the PC to supply power with no battery/PM connected to the APM. I cannot explain why your values are good after changing cables -- unless there is a significant difference in the USB connection of the 500mW radio. In fact, if you use the USB as a power source, you are double fused from the PM to the device connected to the USB.
PM--->D1--->F2---Vcc---F1---->USB
2) The section you show, I believe, refers to maximum input voltages *applied* to those pins, not sourced from the pins. Any device supplying power to those pins is restricted to the values listed.
This problem is simply one of power budgets.
The PM limits are discussed HERE. I made some quick grabs of features on that page and specs of your Telem and FrKsy Rec...
The two devices alone can load 530mA. The Rcv is probably powered off the PWM input rails, but if you power through the USB port, F1 is only a 500mA fuse. That is a risky situation to be in.
You use the USB to source power at your own risk, especially at near the rating of the 500mA fuse. I recommend a separate BEC for the 500mW Telem radio.
-=Doug
It's 1A fuse in later boards, though the 2.5.2 schematic its 500mA. I'm not sure whats in the HK boards.
If you connect the USB power directly to the PM 5V out you bypass the fuse, and stop it voltage drop across it from being as large. That's the real issue with the 500mA part is that it drops quickly if your near the limit.
(A silicon fuse is a diode that has really high resistance at cut--off current. the 500mA part has quite the incline, hence the voltage drop, the 1A part is much flatter, before the cut-off (knee))
UPDATE for later firmware versions - the CLI had been removed.
This will not work depending on your code.
-=Doug
Hello,
I have bought from a local shop in Greece an APM 2.8 and in my logs I see low Vcc voltage...
- So, when I have only the APM and the RC receiver connected, my Vcc reading is 4.81V and if I put some throttle it fluctuates between 4.81V and 4.45V
- If I have the APM, the RC receiver and the GPS module connected, again I see the same Vcc value of 4.81V and about the same fluctuations.. 4,45 to 4.81
- If I have the APM, the RC receiver, the GPS module and the radio telemetry (http://www.hobbyking.com/hobbyking/store/__76950__HKPilot_500mW_Tra...) connected , my Vcc reading is 4.65V and if i put some throttle it fluctuates between 4.1V and 4,65V.
I also measured my power module output voltage with or without putting some throttle and it always shows a steady 5.27V..
So what is wrong here ?? Is it my APM faulty and needs to be replaced ??? What did you do guys to solve the same problem that you had with me ??
Thank you....
A drawing or detailed photo or your wiring situation is needed.
What kind of vehicle is this? Multirotor, Rover..?
-=Doug
Dear Doug,
it is a quadcopter with the following specs:
DJI F450 frame
DJI E310 tuned propulsion kit ( 2312 motor 960KV, 420S ESC, 9450 props)
APM 2.8 flight controller with gps module and power module
Multistar 10000mah 4S 10C battery
TURNIGY 9XR radio with FRsky DJT transmitter and V8FR-ii receiver
Hobbyking HKPilot 500mW Telemetry Radio v2 433Mhz
connection_diagram.jpg
Excellent feedback, thank you!
Other than the log voltage issue, is the aircraft operating properly?
In troubleshooting, I like to simplify the conditions as much as possible.
You might try removing items absolutely not necessary for basic operation; telemetry, switch inputs (leave rudder, elev, throttle, ail in place).
You did not mention where you are using a DVM to measure the PM output.
I recommend modifying a servo cable/connector and using it as a connection to the PWM inputs - use a DVM connected to the (+ red) and (-black) wires of the servo connector.
This measures Vcc directly on the pcb. Remove the propellers and then manipulate the controls as if you are actually flying. If the Vcc is actually dropping as low as the logs indicate, this allows you to be safe protect your investment, and see if the log voltage is correctly represented.
It seems to me that the *log voltage* - if I remember correctly - is not a 'real' voltage measurement, but a derived value based on an circuit performance. I will have to go back on a look at some old posts to be sure of this.
-=Doug
Yes, Vcc in the logs is not an actual measurement, but a derived one based on the 1.1V internal reference in the Atmel.
http://diydrones.com/forum/topics/quad-apm2-5-2-9-1b-it-disarmed-re...
Thought I remembered that correctly.Vcc in the logs is code based, not direct.
Arducopter code is mature enough at this point that I might suspect a quality issue with the components used on the APM or the Atmel chip/clone.
Did the aircraft fly well or was it misbehaving and you found this issue in the logs?
-=Doug
Dear Doug,
my quadcopter is flying nice in terms of performance. However, I think I experienced just once a brownout. I was hovering luckily at 2m above ground and suddenly everything turned off and felt to the ground without damage.
As you proposed, I have already tried to remove things one by one for troubleshooting. I mention this in my previous post.
- So, when I have only the APM and the RC receiver connected, my Vcc reading is 4.81V and if I put some throttle it fluctuates between 4.81V and 4.45V
- If I have the APM, the RC receiver and the GPS module connected, again I see the same Vcc value of 4.81V and about the same fluctuations.. 4,45 to 4.81
- If I have the APM, the RC receiver, the GPS module and the radio telemetry (http://www.hobbyking.com/hobbyking/store/__76950__HKPilot_500mW_Tra...) connected , my Vcc reading is 4.65V and if i put some throttle it fluctuates between 4.1V and 4,65V.
Regardless of what is connected on my APM if I have the battery connected and at the same time I connect the usb cable to my APM, the Vcc voltage is 5.05V and it is steady regardless of the throttle.
My PM voltage measure always shows 5.27V. In the attached image you can see how I measure the voltage. I hope it is correct. Also the measurements I take for the VCC using the DVM is between any pair of the top and bottom output pins. Isn't this measurement correct?
I discovered my low Vcc voltage and fluctuation by looking the logs and the real time values during flight. In terms of flying performance its looks OK... Do you think my APM needs replacement ?? In the past there were times that I connected the APM through Usb with my PC and at the same time I had the battery connected. Afterwards, I read that powering the APM through usb and battery at the same time should be avoided.. Is that true ??
Thanks and Regards,
You should see a slight difference between the output of the PM and the Vcc points on the APM. It should only be the drop across D1. F2 should not drop voltage -- in a perfect world.
It could be that your F2 and/or D1 is dropping voltage. Leave your meter at the (-) neg connection of the PM and measure base on this point of reference. Move the (+) pos lead to the input of D1 first. It should be the exact same voltage +/- .001V . If not, then there is some bad connection in either the neg PM lead or the pos PM lead going to the APM.
If good going into D1, then check the output of D1, it should be slightly less than the input. Then move to the output of F2. Again, only move the pos (red) lead, leaving the neg (black) lead at the same reference point.
I suspect a poor solder joint due to quality issue.
Do you have a good magnifier or microscope to inspect the components?
I have marked up the simplified schematic to indicate how the power module is supposed to relate to the APM. The area circled in green above is where I suspect you are losing voltage.
You can do this test with nothing plugged into the APM except the PM.
If there is a bad connection in either the JP_VCC path or the GND path (not likely) you will drop voltage across it, but I still think it is being lost in the D1 F2 area.. probably.
-=Doug
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