Power issue

Pixhawk
1

Hi. I have Pixhawk 2.4.8 board (well, actually it’s Pixhack, but there should not be much difference) powered from Li-Pol 3S 6000 mAh battery via this power module - www.aliexpress.com/item/32545395023.html. There’re several peripheral devices connected: compass/gps, sbus radio, beeper, telemetry (see below). All motors and servos are unplugged.
The telemetry cable is connected to Orange PI Lite board which goal is to send the telemetry over a vpn link. The PI requires 5V to work properly.

When the battery is fully charged (>12V), everything works just great. But when the battery voltage goes below 12V (for example, 11.8V; measuring at the far end of the power module), the PI board is not starting up. It’s b/c the voltage in the telemetry port is ~4.6V instead of 5V.

Do you have any ideas why the voltage is lower than 5V and what needs to be done to make it 5V?

Your help is kindly appreciated.

2

There is nothing you can do that output is not really meant to power anything.
You will have to add a BEC to power the pi.

3

@jimdgit, thanks for your prompt reply! I’ve just connected back one of my motors with the ESC (https://aliexpress.ru/item/32955454285.html, it has BEC inside). 3-wire cable goes to the Pixhack PWM8. And checked the voltage:
ESC’s VCC - 5V
Telemetry VCC - 4.76V
AUX1 VCC (measured to make sure the power from the ESC comes to the Pixhawk w/o issues) - 5V

4

So where did you connect the PI to?
Telemetry VCC will never be 5v it has a current limit resistor so as you draw current the voltage goes down.
You need to connect the PI to the BEC 5v not the telemetry VCC, if you have not done so already.

5

According to Pixhawk Overview — Copter documentation
image
telemetry VCC should be 5V (at least, w/o a connected consumer). That’s why I decided I could use the power from the telemetry output.
The voltage 4.76 was on the telemetry VCC pin w/o the PI connected. Isn’t that weird?

Anyway, I gonna follow your suggestion and connect the PI to the BEC. Do you think I can use the servo rail (which is currently powered from the ESC BEC) to get the power for the PI?
image
(added telemetry connection)
Is this correct?

6

Well like I said I noticed the VCC pins on the telem port do not provide a full 5V.
I power my receiver from the SBUS port and the voltage is 4.5V which is ok for a receiver but not a pi.
So yes if you are driving the servo rail from the BEC that should be fine.

1 Like
7

Thank you very much, @jimdgit!