Inter-PCB signal fusing - Page 1
Forum section: electronics / beginners

author: FlyingSquirrel
author_rank: Contributor
timestamp: April 27, 2017, 11:08:25 pm
content: hello every one!ive been spending some time optimizing some drone designs and theres one thing im not sure if there might be a solution at allso here goes "nothing"most drones usually have the speed controllers for the motors on separate PCB's that are connected to a power distribution board and the flight controllerin my case:- i have two 14AWG wires for the power (up to 24V/35A)- and another two 26AWG 5V digital signal wires to the flight controller- power and signal have a common ground- and not connecting the signal ground can apparently lead to issues with the signal integritynow heres the problem:if for some reason (usually crashes or tree branches) the power ground wire gets disconnected, the power will find its way through the signal cable and therewith cause a meltdownwhich doesnt just kill the wire/s but also the speed- and often even the flight-controllerand i cant just use a thicker wire for the signal, since the flight controller wont tolerate more than 1-2A eitherso ive been wondering:is there a way to somehow integrate a fuse or similar, that will prevent stuff from being blown up?or would a fuse lead to signal issues as well?thank you!!

author: james_s
author_rank: Super Contributor
timestamp: April 27, 2017, 11:15:38 pm
content: You could protect the signal leads, zener clamp with a resistor to limit fault current perhaps. Seems like it would be simpler to make robust connections in the power distribution though. I've had a few pretty hard crashes and I've never had the problem you describe.

author: FlyingSquirrel
author_rank: Contributor
timestamp: April 27, 2017, 11:44:20 pm
content: i know and im already avoiding bullet connectors or similar for that reason, but ive already had two meltdownsi have to admit i couldnt trace the issue with much certainty, since there wast much left that could have been tracedbut this is the only plausible explanation i could findif i understand you correctly i could add a 30ohm resistor in series with the signal cable, to lower the current to roughly 800mA?and wouldnt this increase the minimum power required, to get the motors spinning? ie when just giving it very little throttle for landing etc

author: james_s
author_rank: Super Contributor
timestamp: April 28, 2017, 12:32:48 am
content: The throttle signal is not based on current, it's PWM and varying the pulse width controls the speed of the motors. The work is all done in the ESCs.Are you getting power from your FC from a separate BEC regulator or drawing it from one built into the ESCs?

author: FlyingSquirrel
author_rank: Contributor
timestamp: April 28, 2017, 12:40:37 am
content: the FC power comes from the PDB/BEC

author: Ian.M
author_rank: Super Contributor
timestamp: April 28, 2017, 01:03:36 am
content: You could try a 50mA polyfuse in the flight controller to ESC signal ground wire, to prevent the wiring loom burnup, but without clamping the signal at both ends and series current limiting in the signal wire, loss of ESC ground will still blow the flight controller and ESC. Retrofitting such protection would be moderately difficult, and would probably require a PCB at the flight controller end. It would make far more sense to try to find ESCs and a flight controller with built-in clamping.

author: FlyingSquirrel
author_rank: Contributor
timestamp: May 01, 2017, 09:41:39 pm
content: cheers! didnt think it would be such a hassle, ill rather try and find components that already have some kind of protection then