hi everyone,

i was finishing up with building my first drone and for some reason, drone only connects to the radio when on usb. when i connect it to the battery, rx gives the constant green light like its paired but wont pair with the radio at all. 

it connects with the radio when i first plug FC with usb cable and then supply the power via battery.

i had a successful smoke test and has set all the possible config via betaflight.
could anyone please tell me what is happening? 
any hint is much appreciated ?

btw, my specs are as follows:
Speedybee f7v3 stack with latest firmware
Battery: 1300mah 6s
Dji O3 air unit
Radio: (jumper-t-pro w/ elrs module
Rx: Jumper 2.4GHz ExpressLRS ELRS AION-RX-MINI


thank you

Have you put a meter to it to see if you're getting 5V with the battery? A lot of flight controllers will pipe the 5V from USB to power up various modules in place of the BEC. If you don't see any voltage with your battery plugged in, it's possible you have a bad BEC on there.

When plugging in a LiPo without a USB cable connected, check to see if there is any LED activity on the FC. You should have at least one constant LED and one flashing LED.

If the FC isn't powering up with just a LiPo connected then that is the typical symptom of a fried 5V voltage regulator on the FC. With a USB cable also plugged in, that will be providing 5V power to the FC from the your computer and bypassing the 5V supply from the LiPo as Suros said, which is why it works when you connect a USB cable.

Below is a crude circuit diagram showing how 5V power is provided to an FC from either the USB connection or the LiPo. The Schottky diode is there to act as a one-way gate which allows 5V in from either the USB connection or the LiPo without allowing that voltage to be sent back out down the USB or LiPo 5V supply lines. It will be the 5V BEC directly after the VBAT(LIPO) connection that will be fried.

(16-Jan-2024, 08:25 AM)Suros Wrote: Have you put a meter to it to see if you're getting 5V with the battery? A lot of flight controllers will pipe the 5V from USB to power up various modules in place of the BEC. If you don't see any voltage with your battery plugged in, it's possible you have a bad BEC on there.

it looks like voltage is fine. please check the attached link below. 

power via battery https://streamable.com/p1a9bg
power via usb https://streamable.com/ppg7e2

thank you for your prompt response.

(16-Jan-2024, 10:42 AM)SnowLeopardFPV Wrote: When plugging in a LiPo without a USB cable connected, check to see if there is any LED activity on the FC. You should have at least one constant LED and one flashing LED.

If the FC isn't powering up with just a LiPo connected then that is the typical symptom of a fried 5V voltage regulator on the FC. With a USB cable also plugged in, that will be providing 5V power to the FC from the your computer and bypassing the 5V supply from the LiPo as Suros said, which is why it works when you connect a USB cable.

Below is a crude circuit diagram showing how 5V power is provided to an FC from either the USB connection or the LiPo. The Schottky diode is there to act as a one-way gate which allows 5V in from either the USB connection or the LiPo without allowing that voltage to be sent back out down the USB or LiPo 5V supply lines. It will be the 5V BEC directly after the VBAT(LIPO) connection that will be fried.

Light pattern in the FC looks fine when connected with both usb and battery. ?

light when connected via battery: https://streamable.com/pke10a
light when connected via usb: https://streamable.com/486hp8

thanks

This thread fixed my problem. https://intofpv.com/t-rxloss-when-dji-o3...controller

I appreciate youse help. Thanks