rchelicopterhub.com / rchelicopter.hu
10 May 2019

Scorpion BEC goes into protection mode with no reason
The issue and the fix for Tribunus 80/120

Apparently this title is not quite true, because there's a reason - even if it is not so obvious. Scorpion have investigated what can cause this "failure" of Tribunus ESCs at the BEC, and the problem found.

Scorpion BEC goes into protection mode with no reason

Actually the issue itself can be caused by some particular servos - as Scorpion reported. Few servos have high induction voltage, which can cause a back feed. This can be even 30% more than the output voltage of the BEC. It does not sound good, because this can push the voltage up by 2.5V on the system killing all the FBL or the receiver or both. Tribunus goes into protection mode preventing any damage on its circuit - at least.

Other variation, when the servo draws really high peak current for its operation. When the BEC detects this high current, it thinks, there's a short circuit somewhere, that's why it cuts down and goes into protection mode. 

Few servos produce both effects in combination, so the switching into protection mode is even more likely.

But what to do?
Is there any firmware update? 

No, there's no update because this is not a software problem, this is in the hardware. The fix takes a short time, and particularly cheap, few pounds all together. Only a capacitor is required around the FBL or the receiver on the supply circuit. Get a servo plug, and solder minimum 20AWG - or wider - wires to the red and black pins. They should not be longer than 5-6cm.

Then solder a 1000-4700μF 10-25V capacitor to the wires.

Warning! The capacitor is polarity sensitive. Minus goes to the black, plus goes to the red wire. Polarity indicated on the side of the capacitor. Plug it into the receiver or the FBL unit.

This capacitor can absorb the kick back voltage protecting other components, and can supply the extra current draw during the high peaks. 

If you have no free socket on your receiver, you can split an existing one, we advise the BEC lead.