If back in the day if they had DC at 120volts then to make everything vacuum tube work, unless it was series filament, anything low voltage would have had to use those "vibrators" to step down the current complicating all circuits that used low voltage like bias current? Now a days we would still need expensive(er) DC converters and make cheap SMPS;wall power supplies would be more complicated? Wastinghouse brand was a really good idea I think. I wonder if this played into their decision considering all loads were resistive or inductive at the time.
Most of todays SMPS would "just work" on DC lines. So not a big deal with those.
Of course, these cheap SMPS arrived one or two decades ago, before using a line frequency transformer was the usual choice.
You'd have other problems: E.g. your simple switch in the wall that turns on and off your lighting would be of "DC-proof" kind. Normal switches are designed to work on AC, for DC these would need additional means to extinguish the arcing that occurs when the switch is opened. Same issue applies for plugs, breakers and fuses.
Back in the time, the transformer was a great invention, because one could easily step up and down the line voltage. Less interesting for domestic use back then, since everything worked directly from the line voltage, but of great value for longer distance transmission of energy. At 120V / 230V the line losses are too high to brigde distances of more than a single digit number of kilometers.
Stepping up / down of DC voltages to a suitable value for longer distance transmission was simply not possible back then.
Today DC based distribution over smaller areas is discussed again, e.g. for factories and homes. For long distance energy transmission, HV DC already is proven in use.
One very good reason against adopting DC infrastructure: it's difficult to put out. DC fuses are expensive, ever more so as you go up in voltage.
The most common kind is very fast acting: they don't care whether it's AC or DC, they clear in under a half cycle. These are called "semiconductor fuses" because they can be used to protect semiconductors -- diodes and SCRs, the only kinds robust enough to withstand fusing current without severe derating. I see "traction fuses" up to 5000V, but maybe not anything above there, I'm not sure.
You wouldn't want to use these in normal infrastructure, because of that fast blow rating. One lightning hit and the building or neighborhood goes out! It may well be that slow-blow DC fuses aren't so hard to do. I suspect it's possible, but it's not necessarily an easy or convenient thing.
I would think vacuum reclosers would be reasonably useful, still.
General purpose breakers would need to be very different, and much more expensive.
The "duh" answer is, of course, the entire world is AC, so you have to spend a tremendous amount of money developing and producing equipment and infrastructure just to try something that's only marginally better than what's already out there. There's little enough money already to keep existing infrastructure running as it is.
There are also some possible gotchas, like the innate persistence of DC (except when it does go down) makes manufacturers less likely to build adequate hold-up or surge protection into their designs. A big honking electrolytic does wonders for both of these, and is a necessity when you have to deal with a normal 100-times-a-second dropout. But without that, a brief interruption (10s of ms) from a lightning strike or recloser operating, and every freaking thing reboots!
Same thing happens on a smaller scale in automotive equipment. There, restarts are fairly common (brownouts due to cranking voltage), so most equipment is made to handle that gracefully. On the other hand, complete outages are uncommon (it's usually assumed to be battery-backed, which... it is, after all), which is annoying when the battery does need to be disconnected...
I would think it very likely that any technologically advanced alien species would also be using AC. Mechanical systems can be more powerful, certainly -- consider the amount of power flowing through a hydraulic hose, or various parts of a jet turbine! But nothing else compares with the universal nature of electricity, that it can be connected to electric, magnetic, photonic, mechanical, acoustic, chemical and more systems. It's also king on transmission distance. The exact frequency chosen is fairly arbitrary. Alien frequencies would certainly be oddball frequencies to us, due to our arbitrary definition of the second (and likely their equally arbitrary equivalent), but anything from 20Hz to 200Hz should be pretty likely on an Earth-like planet with the same resources we have (even if in different proportions -- we may not have much copper, but we know exactly how to use it). It's very likely they'll use three-phase power: it's a symmetrical system, and electrical power only has two degrees of freedom, making any higher number of wires or phases redundant, and any fewer wires (i.e., two or one) cannot deliver continuous, rotating power. And any alien species will almost certainly develop magneto-mechanical systems (i.e., generators) long before solid state controls are developed, meaning their infrastructure will be built wholly in AC, before DC becomes feasible.
Tim
Say what? You’d need a bunch of noisy oscillators all over the place. The ham radio guys would love it
Vibrators were used to step up voltage for tube radios in cars, or battery operated farm radios.
You're implying there aren't already!
Distribution stuff tends to be much better built, to higher standards, including FCC limits of course.
That they'd be doing it at 1MW instead of 1W, for the same emissions, is somewhat impressive, but it's just that much more filtering, not a big deal.
Tim
how would you float stuff or filter it so you don't have HV on the terminals of the device when you disconnect it? it will also clench your muscles and kill you quick.
and have you ever played with DC plasma?
i dont want fire snakes and lethal stored charges everywhere.
how do you limit current with passives? you would need monstrous MU inductors, which would generate ridiculous magnetic fields.
everything would need to be complex multi failure mode active devices.
actually look at it with high current levels:
also shit would corrode like crazy for the same build quality.
It's not an "if", it actually happened.
https://en.wikipedia.org/wiki/War_of_the_currentsBack then, relatively little equipment was low voltage, and whatever was would be powered by batteries and not connected to the mains. The transistor hadn't been invented, vacuum tubes are fine operating directly from line voltage (no rectifier required for DC, nor any hum --- an advantage.) Remember, electricity was still a rather novel thing and its dangers yet to be fully known, it was the norm to design equipment to operate directly from mains voltage.
having alot more phases at lower currents would be even safer.
One thing not mentioned yet is
HVDC transmission which has become quite common for new major interconnects, both for a slight efficiency boost, but also to avoid the need for frequency synchronisation.
I thought of one. From the end of the valve/tube era, reasonably precise oscillators in all clock radios in the world that were taking a signal from the transformer secondary, and using the 50Hz as master clock would be at least millions, and maybe into the billions
Because DC is harder to distribute. DC works for long transmission in special "Pumped lines" but is not as useful generally. There are really specific and easy to learn about reasons for AC. It has a lot to do with Transformers and adjusting impedance. I suggest that you explore your own question. You will learn a lot.
This is a really great resource for this kind of thing. They debunk a lot of myths about early days of electrical power distribution and use. My favorite is how they cut tesla down to size (But that's a little off topic)
http://edisontechcenter.org/
DC wouldn't be as useful for electrocuting elephants.
(Who knows the reference?)
Westinghousing an elephant.
DC wouldn't be as useful for electrocuting elephants.
(Who knows the reference?)
There's a myth going round that DC is more dangerous, than AC, but it has been known that the reverse is true for a very long time.
From personal experience I find I get more of a shock from 30VAC, than I do from even 75VDC.
AC may kill you faster, but DC locks your muscles so you can't let go. The polarity might be a factor in that but I'm not sure. 75V might not be a big deal, but try grabbing 300V (that was..."fun").
Also, a lot of rural areas had private LVDC power. The company made appliances in both AC and DC versions.
http://www.delcolight.com
AC may kill you faster, but DC locks your muscles so you can't let go.
Another myth. Numerous studies have proven that the let go current is higher for DC, than AC. I don't know why the myth that the reverse is true persists today. Perhaps it's because AC crosses zero at 100 times per second, so some believe it allows the victim to release themselves? In any case that's not true because zero crossing is only a short period of time and the locking muscle spasms are worsened by the periodic changes in current.
http://www.wright.edu/~guy.vandegrift/wikifiles/Electric%20shock%20voltages%20Dalziel.pdfhttps://www.quora.com/Which-is-more-dangerous-AC-or-DC-powerhttps://www.allaboutcircuits.com/textbook/direct-current/chpt-3/ohms-law-again/The polarity might be a factor in that but I'm not sure. 75V might not be a big deal, but try grabbing 300V (that was..."fun").
How could the polarity make any difference? The human body responds to electric current the same, regardless of polairity.
And whilst I wouldn't want to be shocked at all, I'd feel a heck of a lot more comfortable around 300VDC, than even 230VAC. The only reason why I might feel less safe around such a DC circuit, than an AC one is large capacitors storing a charge when the supply is disconnected.
Also, a lot of rural areas had private LVDC power. The company made appliances in both AC and DC versions.
http://www.delcolight.com
DC power distribution is common in off grid setups and newer data centers.
It's neither here nor there but I've got a copy of "Edison and the Electric Chair" by Mark Essig. (found it in the leftover bin somewheres) It covers how Edison et al worked to get execution by electrocution to be made available and covers the first use. Pretty gruesome - It didn't go as expected and ended up being more of a barbeque.
I've got some fairly high voltage, high current contactors for DC that are quite a bit bigger than their AC equivalents. I think they have blowout magnets. When I think back over my experience with relays and switches, most of the trouble has been with switching DC. They either arc and damage or destroy their contacts or they stick closed. AC, for the most part, just works.
If we had DC mains our fridges would have had DC motors and probably wouldn't have hermetically sealed compressors. Imagine accidently unplugging a fridge from the mains while running- probably get a good frazap off the contacts. Maybe the receptacles would have had integral switches as in the UK to prevent this.
Would we have had fluorescent lighting with DC? They do work with resistive ballasts once started but that's none too efficient.
Cheers,
I've got some fairly high voltage, high current contactors for DC that are quite a bit bigger than their AC equivalents. I think they have blowout magnets. When I think back over my experience with relays and switches, most of the trouble has been with switching DC. They either arc and damage or destroy their contacts or they stick closed. AC, for the most part, just works.
That's the last largely unsolved problem with DC - how to cost effectively stop the arcing. But what about pulsed DC, so it has periodic interruptions just like AC does? It would have the advantage of being easier, cheaper, and more efficient to generate from plain DC.
If we had DC mains our fridges would have had DC motors and probably wouldn't have hermetically sealed compressors. Imagine accidently unplugging a fridge from the mains while running- probably get a good frazap off the contacts. Maybe the receptacles would have had integral switches as in the UK to prevent this.
Most likely they would use linear compressors with an external vibrating contact operating from a magnet on the piston, as some old RV refrigerators did. (Some refrigerators still work that way, but with a solid state switching circuit.)
Would we have had fluorescent lighting with DC? They do work with resistive ballasts once started but that's none too efficient.
Most likely they would be "hybrid" lights with a small incandescent bulb acting as a current limiter. At least until solid state becomes economically viable for that application. For that matter, why is it that CFLs are almost always AC inside? Wouldn't it be cheaper to just put in a voltage multiplier with capacitors sized to limit the current?
That's the last largely unsolved problem with DC - how to cost effectively stop the arcing. But what about pulsed DC, so it has periodic interruptions just like AC does? It would have the advantage of being easier, cheaper, and more efficient to generate from plain DC.
Yabbut, how are you going to keep those pulses together? "Pulses" implies tons of harmonics. Maybe we filter it, so there aren't many harmonics left; but then we're back where we started, with a lot of signal power in a more-or-less sinusoidal AC component, except we have a pesky DC offset we can't transmit through a passive transformer.
Tim
Hasn't DC become viable now that it can be effectively stepped up and down due to solid state electronics, and its awesome, super awesome, on resistance, giving little loss?
Hasn't DC become viable now that it can be effectively stepped up and down due to solid state electronics, and its awesome, super awesome, on resistance, giving little loss?
Creating tons of noise that radiates out from the devices and wires like antennas, requiring shielding and filtering that's $$$. That's why that whole "digital electricity" stuff is rubbish.
you still use a transformer (if you want isolation) or a inductor if you just wanna rely on fuses without hard limiting during a failure of a pass semiconductor (dumb, step down is way less safe and failed switches short means you can discharge a upstream capacitor down stream without a transformer isolator in a step up or in a step down you can just put HV across the LV side. it's hard to imagine a transformer growing turns vs losing them to isolate a core vs empower it
Yabbut, how are you going to keep those pulses together? "Pulses" implies tons of harmonics. Maybe we filter it, so there aren't many harmonics left; but then we're back where we started, with a lot of signal power in a more-or-less sinusoidal AC component, except we have a pesky DC offset we can't transmit through a passive transformer.
Limit the slew rate so that there would be little EMI at the frequencies that are particularly problematic.