5 ms·
48Vdc is supposedly the highest voltage that is still considered safe. (https://electronics.stackexchange.com/questions/267789/how-safe-is-48v-dc https://electr
by elp 3y ago
48Vdc is supposedly the highest voltage that is still considered safe. (https://electronics.stackexchange.com/questions/267789/how-safe-is-48v-dc https://electronics.stackexchange.com/questions/267789/how-s...)
It certainly sounds like a smart move on the copper savings alone.
- jauntywundrkind 3y agoExtra low voltage is 50v ac or 100v dv. https://en.wikipedia.org/wiki/Extra-low_voltage https://en.wikipedia.org/wiki/Extra-low_voltage For some reason people assume it's 48v DC or 50v dc. But it's double that. That said, I feel significantly more scared dealing with 100v DC than I do 48 or 24v.
- myself248 3y agoThat's for IEC. Under OSHA it's 50 volts, AC or DC.
- sheepshear 3y agoELV is not a fundamental definition of "safe". The limits of what's safe depends on the application and your risk tolerance, and ELV is just a name for a couple of definitions out of many. Also, those numbers are for ripple-free DC, which you're not going to find in a car. They're cut roughly in half for ripple peaks.
- amluto 3y agoI find 48V a lot less scary when cars are involved than 12V. Neither is particularly likely to electrocute me, but 48V comes with fuses that will trip at 1/4 the current, giving 1/16 the resistive heating if something shorts, which is a lot less likely to melt or ignite things. Also, the wires are much smaller :)
- thot_experiment 3y ago> 1/4 the current, 1/16 the resistive heating Really underappreciated safety aspect. The currents required for your average doodad at 48V leave you with a MUCH lower chance of unscheduled welding. Remember folks, everything is a fuse if you put enough current through it, as a rule of thumb it's good to keep "enough" pretty low.
- dreamcompiler 3y ago"The job of the transistors is to protect the delicate fuses." --old EE lore
- shermantanktop 3y agoI used to work on vacuum tube power amps. 400v+ B+ with big caps is stressful to deal with. And doing it a lot can lead to complacency. We used to call getting shocked "getting a taste" - like getting a taste of ice cream, except it's more like a microsecond blackout.
- reportingsjr 3y agoI have been shocked by 110V DC and let me tell you, it hurts. A lot. Would not recommend.
- SigmundA 3y agoRemember a fully charged lithium battery with nominal 48v can be close to 60v just like 12v in your car is actually closer to 14v.
- wongarsu 3y agoHowever there is a lot of leeway on the "48V is the highest safe voltage" statement too. 48V has a special place in regulations because of its use in telco, but 60V DC is still very safe.
- hinkley 3y agoDoubling again to 96 is not safe, however. I’m not sure why they settled on powers of two. Something perhaps to do with noise filtration, and fewer new tricks to learn?
- myself248 3y agoIt's convenient to build things in multiples and powers of 2 and 3. A nice two-tier or four-tier battery rack full of 2-volt cells just works out nicely.
- hinkley 3y agoSmaller transformers with whole numbers, right? But why 4 and not 3 or 6?
- eternityforest 3y agoWe seem to stick with 7-smooth numbers, and really extra prefer highly composite numbers (https://en.m.wikipedia.org/wiki/Highly_composite_number https://en.m.wikipedia.org/wiki/Highly_composite_number) for things we chose before the age of calculators. 3 and 6 were the standard voltages for consumer stuff back in the days of people needing to buy multiple packs of AA cells every year
- eqvinox 3y agoIt's a bit of an arbitrary determination; 60V is the international common denominator on what various legal or civic (e.g. insurance) regulations consider safe; https://en.wikipedia.org/wiki/Extra-low_voltage#Separated_or_safety_extra-low_voltage_(SELV) https://en.wikipedia.org/wiki/Extra-low_voltage#Separated_or... 48V is somewhat of a dinosaur from the days when you designed things with a 20% margin since that's what was cheaply attainable. Regular PoE is 54V these days (10% margin), and some more specific applications creep even closer to 60V. (I've seen 57V and 58.5V, which is of course 5% and 2.5%)
- dmix 3y agoWhat's a commonly produced thing that's 48v? I don't know much about this subject. Is it most industrial type stuff or is there consumer tier products using it?
- somedudetbh 3y agoebikes, phantom power in audio equipment...
- stephen_g 3y agoBasically the whole telco industry runs off 48V, and has for a very long time. You'd have a rectifier box that would take the AC and output 48V, and then everything would run from that. A lot of the satellite and wireless equipment I've worked on has inherited that and runs off 48 too.
- p1mrx 3y ago240W USB-C uses 48V, so that should eventually become common for stuff like gaming laptops.
- dharma1 3y agoPro audio - most condenser microphones (except electret) run off 48v provided via the mixer/audio interface through XLR cables
- NotYourLawyer 3y agoWith wet hands, even 48v hurts.
- dade_ 3y agoOn my tongue, 9V hurts. There is pain, but no harm.