Every year divisible by four with remainder one, adventurous geeks hold an outdoor festival in the Netherlands. This year, about 6000 people are expected to attend a long weekend.
Among them will be a group of experimenters who will be testing a 42 volt direct current grid. Specifically, a cluster of tents within the festival will receive approximately 50 × 4 Amperé supplies and 8 × 16 Amperé supplies. Hopefully, this will be run by solar power but there will also be a backup generator. Switching a high load of direct current is more complicated than alternating current and losses around the example MOSFET circuit are expected to be less than 0.2W per junction. Although people are expected to bring together previously untested circuitry, it is hoped that pieces of the project will inspire multiple direct current grids in more permanent locations.
Hopefully, electrocution or voltage drop doesn't halt electrical distribution at the festival.
(Score: 2, Disagree) by tekk on Sunday July 02 2017, @05:48AM (8 children)
DC's generally safer because you don't have a single 'live' wire, you have to actually complete the circuit, unlike AC. Plus at 42 volts I don't think that's enough to overcome the resistance of unbroken skin, is it? So unless you're like, bridging the wires across a pair of open wounds you should be pretty much fine.
(Score: 4, Informative) by Anonymous Coward on Sunday July 02 2017, @08:51AM (4 children)
Ah, what???? You always have to complete the circuit!!
Yes, there is.
https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html [ohio-state.edu]
Welders insulate themselves from their workspace too. Even stick welders, that work with 12 or 24V. AC or DC, doesn't matter. The difference is that if you are being electrocuted by an AC source, it is generally easier to guess by an external observer.
(Score: 0) by Anonymous Coward on Sunday July 02 2017, @11:57AM (3 children)
so no. you don't really have to 'complete the circut' like you do with dc.
just to be standing on the ground will do it.
(Score: 0) by Anonymous Coward on Sunday July 02 2017, @03:03PM
Same with DC.
(Score: 0) by Anonymous Coward on Sunday July 02 2017, @04:01PM
Which has completed the circuit because the second half of the circuit is the earth itself.
(Score: 0) by Anonymous Coward on Monday July 03 2017, @08:06AM
That's a property of the circuit, not of AC.
If you are using the ground as one half of the circuit, touching the other side while standing on the ground will complete the circuit, whether you are using AC or DC.
If you are not using the ground as one half your circuit, you need to touch both sides to complete the circuit, whether you are using AC or DC.
(Score: 2) by isj on Sunday July 02 2017, @12:44PM
DC's generally safer
It really depends on the expected failures.
AC has points in time (50 or 60 times a second) due to the waveform where the voltage is zero, so it is more difficult to sustain an arc. If you want to avoid arcs then go for AC (or use better spacing).
It is my understanding that DC tends to burn skin but not cause muscle cramps, while AC generally doesn't burn skin but does cause cramps.
So what is safer really depends on the environment, voltage and amps.
In either case: don't try to make Mr. Fork close friends with Mrs. Outlet. Don't lick live wires. Don't pee on electric fences.
(Score: 1, Insightful) by Anonymous Coward on Sunday July 02 2017, @03:00PM (1 child)
Correction, my friend: ANY electrical system, AC or DC, that uses one pair of wires has a SINGLE live wire. The other wire is neutral. Touch the live wire and you risk current travelling thru you as the electricity finds an alternate path other than the usual one. Most people call this "ground". Source: Electrical Engineer.
(Score: 2) by Osamabobama on Monday July 03 2017, @05:38PM
Would this be a good place to touch on capacitance as a factor in AC circuits? Higher frequencies exhibit less resistance across a capacitor (or, perhaps, an ungrounded human) than do lower frequencies. Not being (or having consulted with) and electrical engineer, however, I am not the best person to explain this.
Appended to the end of comments you post. Max: 120 chars.
(Score: 2) by Aiwendil on Sunday July 02 2017, @06:57AM (12 children)
Why 42V? I mean both 24V and 48V are the standards for DC in industrial uses and would make more sense (not uncommon to find industrial buildinga with several small 24V or 48V DC grids)
(Score: 4, Funny) by JNCF on Sunday July 02 2017, @07:13AM (2 children)
What do you get if you multiply six by nine?
(Score: 2, Touché) by rleigh on Sunday July 02 2017, @07:33AM (1 child)
54.
(Score: 2) by Magic Oddball on Sunday July 02 2017, @09:13AM
...which is 42 in Base 13. (I admit that AnonTechie's H2G2 Wikipedia link jogged my memory.)
(Score: 2) by AnonTechie on Sunday July 02 2017, @07:41AM (8 children)
Are you not familiar with:
https://en.wikipedia.org/wiki/Phrases_from_The_Hitchhiker%27s_Guide_to_the_Galaxy#Answer_to_the_Ultimate_Question_of_Life.2C_the_Universe.2C_and_Everything_.2842.29 [wikipedia.org]
Albert Einstein - "Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
(Score: 2) by Aiwendil on Sunday July 02 2017, @09:31AM (7 children)
I am, I even met D.A IRL (at a signing, but still).
I just am curious why they opted going for humor instead of following a standard where parts are readily available and where setup is a painfree standard since at least a few decades ago.
(Score: 4, Interesting) by Unixnut on Sunday July 02 2017, @09:47AM (2 children)
> I just am curious why they opted going for humor instead of following a standard where parts are readily available and where setup is a painfree standard since at least a few decades ago.
Because it is a gimmick, done for PR purposes more than any other reason. I don't see the point of it myself beyond attention seeking. We know you can use DC grids (indeed HVDC lines exist in quite a few places where it has benefits over AC), we know AC is the most cost effective (at the moment) method of long distance transport of energy. We also have entire datacentres running off DC at 48V, with only big, mains AC-DC converters at the transition point (I've worked in such places myself, and of course Google was famous for doing it).
And running DC off local generation is also done many times before, by anyone who is serious about camping, or lives off grid, or even truckers, who usually have all sorts of things running on their own APU (usually at 24, sometimes 48 volts).
So... there is absolutely nothing revolutionary, or even new, about what these people are doing, except they are running a non standard voltage, and seem to be keen to puff themselves up for attention.
(Score: 2) by LoRdTAW on Sunday July 02 2017, @05:01PM
The only reason I can think of for that number: https://en.wikipedia.org/wiki/42-volt_electrical_system [wikipedia.org]
But everyone else uses some multiple of the 12V number, derived from the 12V lead acid automotive battery where the cell voltage is roughly 2V per cell. 48V in telecom and mission critical communications equipment, 24V in industrial automation and European heavy duty trucks, 12V in automotive and many others. Solar battery systems use most of those 12V multiples voltages up to 60V.
It would be easier to pick a more common voltage like 24 or 48 as you can more easily find off the shelf power supplies, DC-DC converters, and devices that run on those voltages.
(Score: 2) by VLM on Sunday July 02 2017, @11:15PM
Its interesting that we're days/weeks away from ham radio field day which has a great pile of PR gimmick, mostly exists to camp drink beer and play with radios, and without any fanfare the hams set up greta thundering weird 12 volt DC networks at their camp.
Tons of standardized gear and techniques and frankly its boring and the DC bus is not the most exciting part of ham radio field day.
Part of what killed the great conversion to 42V car batteries a decade or two ago is cheap power supply technology. My wife's prius has multiple DC bus, the legacy 12V for the radio and not a heck of a lot else, some weird voltage for the electric air conditioner (not belt driven) and the main DC bank. Its entirely possible there will never, ever, be a standard DC bus for cars beyond maybe 12V at the radio port and 5V for USB charging because switching power supplies are just too cheap. Your alternator runs at highest efficiency at 90V, well let it. Your LED headlights run best at 3.2 volts? Cool dude, run then at 3.2 volts. Your engine computer CPU runs as 0.9V cmos or WTF? Cool, run at that.
(Score: 4, Informative) by bzipitidoo on Sunday July 02 2017, @04:31PM (3 children)
In the late 90s, there was a program afoot to move automobile electric systems from 12V DC to 42V DC. There is a 6V standard, but that was phased out in favor of 12V more than 60 years ago. They picked 42V because that was about the highest voltage that was not too dangerous for people. Yes, current kills, but voltage is what overcomes resistance. Would've liked to go higher, but 42 is high enough to realize a whole bunch of improvements. The wiring can be much thinner, and yet carry more power. Lot of components that have to be belt driven by the engine in a 12V system can instead be driven by small electric motors at 42V, as needed at any speed within its range, instead of being stuck with continuous operation at whatever RPM the combustion engine is running at, or having to work around the limitations with heavy clutches and the like. Would move the A/C, water pump, power steering, and the valves to electric, and combine the starter and alternator into one winding, and integrate it into the flywheel. The fuel pump and radiator fan were transitioned to electric decades ago, fuel pumps in conjunction with fuel injection to obtain the higher pressures needed.
But the program fizzled out, and manufacturers never made the change. One big problem was that the filaments for incandescent headlights have to be thinner at the higher voltage, which makes them very short lived. Too easy for a bump in the road to break the filament. It wasn't just headlights, it was all the lights. Of course, now we have LEDs. Meantime, electronics for changing voltage levels have improved, allowing more to be done with the 12V system, making the 42V system less of an improvement. We may be 5 years away from a mass switchover to electric cars, so there's little point in switching standards now.
(Score: 0) by Anonymous Coward on Sunday July 02 2017, @07:17PM
Good points. One you left out is that switches and mechanical relays wear out more quickly at higher voltages because arcing becomes more of a problem. Open a closed switch at 48 volts and there will be arcing. Not so much at 12 volts.
(Score: 0) by Anonymous Coward on Monday July 03 2017, @08:19AM
My mid-engined car has electric power steering (it's located about as far from the engine as you can get), so that's no problem.
As for the coolant pump, I would prefer it running at the same time as the engine, not on some electric motor on a separate fuse.
(Score: 1) by terryk30 on Monday July 03 2017, @10:35AM
And although 42 may sound a bit precise for an "about" quantity, it's peak V for 30 VAC (rms), which seems to be the "traditional" rule-of-thumb* for the safe/unsafe "threshold".
*A strong enough rule-of-thumb that it also seems to be the unofficial limit below which you do not require professional certification to work on systems (in some jurisdictions at least?).
(Score: 3, Informative) by c0lo on Sunday July 02 2017, @09:41AM
With AC, the advantage is the transformers and price to pay is the large diameter conductors due to skin effect [wikipedia.org]. DC doesn't show skin effect, but it's a pain to raise the voltage.
In any case, AC or DC is costly at low voltages - to draw enough power, one needs to crank up the current. And ohmic losses go up with the square of the current, which mean thicker wires for lower resistivity. Last time I checked. copper is not that cheap and the next contender, aluminium, is worse in respect with:
a. bend-fatigue - which matters a lot when connecting the ends. Also, the resistivity of bent regions tend to be higher
b. soldering - at least not as easy as copper (brazing can work)
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by FatPhil on Sunday July 02 2017, @09:24PM (1 child)
[1] https://www.nist.gov/pml/nist-guide-si-chapter-9-rules-and-style-conventions-spelling-unit-names
[2] https://en.wikipedia.org/wiki/Andr%C3%A9-Marie_Amp%C3%A8re
[Skitt's Law carefully observed in this post.]
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 0) by Anonymous Coward on Monday July 03 2017, @01:32AM
...when written out completely.
When abbreviated, however, they are capitalized.
Consistency is for small minds, apparently.
-- OriginalOwner_ [soylentnews.org]
(Score: 0) by Anonymous Coward on Monday July 03 2017, @07:27AM
ACs posting on AC and DC while listening to AC/DC...