On Thu, December 1, 2011 12:09 pm, jim@jpes.com wrote: > > I'm not sure what the industry standard might be, or what is dictated > by whatever governing body, but my > preference would be to fuse both supplies individually. To me, it > makes sense to fuse each individually. > This might help troubleshooting later somewhat by possibly telling you > which supply was drawing too much > current, and therefore might tell you which circuits to concentrate on > if and when it happens. > If this is a very high volume product, fusing each might add enough > cost that it might be deemed > uneconomical. If it is a low volume product, the cost won't be as > scrutinized. > If it's a onesey - twosey product, the extra cost won't really be felt > at all. > > This is my take on your question. > > Regards, > > Jim > >> -------- Original Message -------- >> Subject: [EE] Fuses Required - 1 or 2? >> From: "Gordon Williams" >> Date: Thu, December 01, 2011 11:50 am >> To: "Microcontroller discussion list - Public." >> >> >> Darn, caught again. Tag added. >> >> >> > Hi, >> > >> > I'm going to be running a 48V (at 3W) boost converter and a 5V (at 5W) >> buck >> > converter off of a 12 V battery. >> > >> > Is it a good practice to have a fuse on both supplies' inputs or just >> 1 >> for >> > the system? >> > >> > >From a bit of research my understanding is that I should use a slow >> blow >> > fuse to handle the inrush current into the converters and I should >> size >> the >> > fuse at 150% the nominal rate. Is that in the right ball park? >> > >> > Gordon Williams A very important aspect of running multiple supplies is: what happens if one supply fails? With a single fuse, if it blows, all the power is off, if you have 2 fuses, (and the two circuits that the 2 power rails are connected), how will the circuits interact? Will you phantom power via an I/O? Do you need to provide additional circuitry to detect a power failure on the other supply. In my view, a good design is not just a circuit that works, but also one that can handle failures (definitely not a comprehensive definition of "good" ...) If you design in a failure mode (like a fuse), you gotta be prepared for the consequences. Matt Bennett Just outside of Austin, TX 30.51,-97.91 The views I express are my own, not that of my employer, a large multinational corporation that you are familiar with. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .