Depending on your actual power throughput needs- PTCs can be a challenge as Bob mentions. You will have a tough time meeting the power requirements of a Thunderbolt with many you'll see. Now efuses (think TPS24/25xxx) or mosfets with a controller (think LTC43xx) can be a good choice but don't hesitate to use a real honest to god fuse that blows out and waits for you to come replace it if that is what you would need
I personally do as suggested in the thread above to some degree- I do AC to DC conversion once for all my time and frequency stuff then have batteries local to important gear and (in older stuff) a diode(s) or (in newer stuff) a real hotswap controller. But whenever something is really important there's whatever fuse is needed. Finally if you are of the type to be adventuresome - http://cds.linear.com/docs/en/datasheet/4110fb.pdf or - Google for Freescale's, ON Semi's or TI's *offline* UPS Reference designs. Yes they invert DC to AC, but you can drive the inverter gates with a microcontoller's PWM output. meaning no matter how jagged your utility's wave may be you can create a perfect, beautiful 50 or 60 Hz sine of your own - devoid of most noise. NS On Wed, Oct 14, 2015 at 12:01 AM Bob Camp <kb...@n1k.org> wrote: > Hi > > One option for the “fuse” part of the DC supply system are PTC resettable > fuses. You *do* indeed need to be careful about voltage and current ratings > on these gizmos. If the only objective is to “not have smoke” when there > is a short, > that can reduce the variables to a manageable level. If your wire will > handle 20A for > long enough to get the gizmo to limit and your load is typically < 5A > there are > parts you can find. > > A few cautions: > > The trip points are very temperature dependent. If you need to handle -20C > in the winter > and +40C in the summer, that will narrow things down quite a bit. > > Mounting matters quite a bit. If you go with SMD parts, be careful of > traces that act as > heatsinks. This is one case that the part needs to get hot. > > There are to many variables on most of the spec sheets to simply pick one > and move on. > The only good way to do it is to get several and run repeated tests on > them Min carry current > will occur at your highest temperature. Worst case trip will occur at your > lowest temperature. > > Consider that the “carry current” may not be the real limitation. > Resistance in the supply lead > of an OCXO is a bad idea. This may limit your current well below the point > that the fuse actually > trips. > > This sounds like a pretty scary list. To some degree it is. These parts do > have their place. That > does not mean they work everywhere and anywhere. > > Bob > > > On Oct 13, 2015, at 2:54 PM, Poul-Henning Kamp <p...@phk.freebsd.dk> > wrote: > > > > -------- > > In message <4FD0F30EBAEF49609DF207E3EE61C15B@pc52>, "Tom Van Baak" > writes: > > > > > >> I used to rely on one massive UPS (along with natural gas generator) > >> for my entire lab. Eventually I found it more reliable and convenient > >> to have localized power backup. By local I mean backup for a single > >> shelf, or even a single instrument. > > > > The big gain is avoiding the DC->AC conversions. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.