doubts regarding circuit protection fuses
October 22, 2012
So, overall I know what a circuit protection fuse is and what it's purpose. I also know that are several types of fuses, in many shapes and forms, one-time-only and resettable (self, or non-self), slow and fast acting and some of rules of thumb for when using one or the other. However, my personal experience is only limited to often trigger the circuit breakers of my mains power supply (by either drawing to much current or shorting stuff [as a kid *cough* long time ago]) and blowing a few glass fuses.
From my research I read that slow blow fuses are indicated to protect things like motors or batteries/power supplies? And well, fast blowing fuses whenever any? spike in current could lead to catastrophic consequences? I recently equiped my multimeter with a fast blowing fuse, but what I read is that catastrophes can happen "when making reading on ovens something something main power" but, anyway I'm not planning to mess around with main (AC) current as of the moment.
What concerns me mostly, as of the moment, is fuse protection when using LiPos. So far I've only used LiPo batteries with "certified safe" circuits, that is not designed or built by myself, so besides the normal precautions handling LiPos plugging such battery was never a concern to me.
I've also read that the fuse value to be used should be the expected/measure current usage of the whole circuit plus a margin but many questions still linger in my mind for instance:
- how flexible should that margin be? what main variables to consider?
- should I use just one fuse directly after the battery? should I use several fuses trying to protect the most valueable/costy parts of my system? one fuse per "sub-circuitry"? that is I have vreg rated for 1A to feed the microcontroller and radio module, should I have a 1A slow blow fuse before it?
- for instance, I've built a couple of motor drivers/h-bridges and use diodes for protection, that way the motors should be protected, no? the only foreseable problems would be... diodes current rating being overcome or stray conductive material causing a short?
Also, I have no idea how often would a LiPo "overfeed a power spike without being asked for it".
I'm probably being overthinking it and being overparanoid and furthermore expressing myself badly because I also feel that the information I've gathered on fuses it's a jumble on my mind.
So I also issue a sort of challenge, if someone out there savvy enough to write up a compreensive tip/walkthrough regarding fuses and typical application within robotics, I at least, would appreciate it very much.