This is an old issue but hoping to see if I can get an explantion or some help.
I have a Hitec Optima 7 Rx using something called the SPC port, basically the receiver has 2 power sources, 12.6V for the radio side straight from the flight battery and 5V for the servo's from a BEC or the ESC's. One of the fantastic features is of course the telemetry which sends the flight battery's voltage to the transmitter.
I am using this is on a quadcopter using APM2 (uses channels 1-5 on the Rx).
On the quad are 2 LED strips getting power from the balancing tap of the 3S LiPo so in parallel with the SPC port.
Everything works fine.
However, if I plug a servo into channel 6 or 7 on the receiver with the LED's connected, a SMT diode blows on the ArduPilot Mega board!
However a servo plugged into channels 1 thru 5 does not short or blow anything and works fine.
The diode is between the output rail (ESC's) and the rest of the board including the input rail which has 5 servo cables to the Optima 7.
I managed to replace the diode with difficulty, first with the same then with something better rated but it now shorts out the servo.
I don't quite understand how on earth can the Hitec Rx be wired internally so that just plugging a servo into ch6 or ch7 (but not into channels 1-5) causes a direct short (presumebly through the LED's)??
Can anyone explain why those two channels do this??
Or better still offer a way to prevent the problem? (I still want to use the LED's and not use a second battery.)
Replies
Thank you, Guy, I will do. I also use the CH7 function occasionally on the APM, so if I want to use the LED's, tilt servo and CH7 in the future I'll have to remove CH7's ground lead too so that the only ground to the Rx is the one from the SPC port?
@Darren, saw that too, my Rx however has no volts on the servo rail when just the SPC plug is in.
Thanks guys, here's the diagram, if the servo or LED's aren't there the APM2 is fine. The diode that blew is arrowed in red below:
This sounds like a classic 'ground loop' problem. Ground loops are when current flows in the GND wire as they show resistance to the other GND. GND is supposed to be a common point in the electrical circuit.
Looking at the manual for the RX I see that it has its own regulator. You may have more luck just powering the RX with the ESCs internal BEC, or make sure the ESC 5V power line is disconnected (PDB 5V)
Ground Loops are complex, especially when the setup involves circuits that are not documented. Like the internals of the Optima 7 RX.
Can you post a diagram how you have wired the RX is your setup? it may help in helping to solve the problem.
cheers Bill