I'm putting together a UAV using an APM 2.5, the APM power module, and the 3DR 915 Mhz radio system.  When I first put it together, the RC electronics were not functioning properly.  When I started to look into what was wrong, I hooked everything up through me E-Flight power meter to see what kind of current I was drawing to see if I could use a power supply instead of running down my batteries.  The power meter showed that the plane was drawing about 50 amps, without the motor plugged in.  I was able to figure out why the flight controls weren't working, but I still don't know why everything is pulling so much current.  If I unplug the telemetry air module, the current drops down to about .1 amps, right where I thought it should be.  Does anyone have any ideas on why the radio would be drawing so much power?  I don't want to hook this up to my batteries like this, they are not rated to handle that much draw.  I'm currently using a 12 volt sealed lead acid battery to power everything on the bench.

Thanks for any help you can give.


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A current draw of ~50amps would have smoked the telemetry air module if it indeed was drawing that much current.

Are you sure that the E-Flight power meter is reading the right current?

Did your battery get hot with that kind of current draw?

Since you are powering the APM with the PM, have you removed the J1 jumper?

How are you powering your servos on the APM output?

I think that you should perform a thorough inspection of all your interconnecting wiring and verify that it is correct and there are no shorts to ground anywhere in the interconnections.



I can not be completely sure that the E-Flight power meter is reading an accurate current.  I am pretty confident though.  Before I started hooking up all of the APM equipment, I took the plane out and was doing taxi tests with no wing to test a new prop size.  I had the power meter hooked up, and it was reading 22 amps when the motor was at full throttle, right where I expect it to be.  The ESC I'm using has some data logging capabilities, and it confirms the reading.  The battery capacity that the meter showed is right where the battery is rated, so I think it should be fairly accurate.

I didn't leave the battery plugged in that long to see if it got hot.  When I saw the current that high, I unplugged it immediately.

Yes, the J1 jumper is removed.

The servos are powered by the ESC on the output rail of the APM.

I guess I just need to pull the air module out of the plane and give it a good look over on the bench.  I also might borrow a friends air module and see if it causes a similar spike in current draw.

3dr telemetry draws about 0.303Amps 

W=V x A => 100= 3,3 x X=> X = 0.303Amps 

i would suggest to check the telemetry cabling, but if you draw 50A.. possibly its fried or even Apm could fried even for a second!

Well, I took out the radio and it all looked fine. I have it all hooked up through another meter. I'm using the E-Flight and an Actron that I believe I got from AutoZone.  Right now the E-Flight is reading about 24 amps, while the Actron fluctuates between .19 and .21 amps. I'm wondering if the E-Flight meter might be picking up some RF interference from the telemetry radio. Looks like it might just be the meter though. Thanks for all your help

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