I’m not aware of that being true anywhere. Aircraft do use 400 Hz electrical systems to reduce transformer and generator mass, but at 115 volts.
Some modern commercial airliners (Airbus?) are using a ±270 VDC system, thus providing 540 VDC to some loads.
No, Sam is correct, although it would be more accurate to say that some electrical systems on some large aircraft run at 400 volts, usually at 400 Hz.
ISO 1540 governing aircraft electrical systems covers the following, in addition to lower voltages usually used on smaller aircraft:
nominal 115/200 V rms and 230/400 V rms AC, both one-phase and three-phase, at either a nominal 400 Hz constant frequency (CF), or over a variable frequency (VF) range which includes 400 Hz.
400 Hz is much more of a standard than 400 V, so I guessed that Sam may have been thinking of that. The reasons for the weight reduction are different but it has a similar net effect.
I guess when they say “400 V”, they are actually referring to a three-phase system, 230 V on each phase, but measured across two of the phases. That’s a pretty weird way of stating a system voltage IMO. So it’s not just some systems on some aircraft; you also have to interpret the voltage in a particular way to come up with the 400 number. It would be like calling an industrial three-phase line system in the US “208 V”.
And what’s even worse: Up to 50% or more off.
And there was a diet pill on Canadian television that advertised: “Lose up to 20 pounds or your money back.” I could just see some person calling them: “Hello, I lost 21 pounds - I want my money back.”
Yeah, this one makes me shake my head.
It draws around 18 amps at the wall outlet, 9 amps per motor. Registers about 1000 watts per motor. (My plug in power meter could only handle one motor at a time.) This is on a dedicated 30 amp line.
But advertises itself as 4 HP per motor, 8 HP combined, which would be a draw of nearly 6000 watts per motor, 12000 watts total. They “peak” at that power, whatever that means.
That one is the one that always makes me laugh. So, basically, you’re saying any price is possible from retail to free.
Even with the explanations given above, I don’t have a problem with the regular 50% off, but perhaps it’s because I’m cynical about the “of what”? part. I assume it starts with the suggested retail price. That said, there is one store around here that infuriates me. During the holidays they will often have sales like “Buy 1 get 2 free,” but then you’ll see the marked price at some ridiculous one that they do not charge on regular price days. For examples, there may be a rack of ribs that is normally $4/lb and it’s clearly marked on the package as $11/lb during the sale (so still a little bit of a sale, but also remember you get charged regular price for the heaviest item, so optimally you need all three to be exactly the same price to get the most of the meager savings.) And sometimes they’re sloppy about it, as you’ll see the new sticker over the old price sticker. But this is going beyond the scope of this thread, and beyond percentages. I think most people understand what 50% off means literally, it’s just the start point that can be manipulated.
Maybe it really does mean it “peaks” at that power (at 50% speed or whatever), but that is not the operating point.
Jewel should be ashamed of themselves for this. It’s so transparent and hard to see how anyone is fooled.
Circle gets a square!
I don’t know about Airbus, but the newest Boeing – the 787 Dreamliner – departs from the traditional 115V 400 Hz produced by the engine generators of most jets in favour of a doubled voltage (actually, 235V). The reason is precisely the one we’ve been discussing in this thread, namely cable and equipment weight and the consequent ability to more efficiently provide a more powerful electrical system. At its core, it’s for much the same reasons as the move from 6 V to 12 V in cars.
The 787 uses a variety of different voltage systems and both AC and DC, but that’s what the generators produce in both the main engines and the APU. Also departing from tradition is that the generators are directly coupled to the engine shaft, eliminating the usual constant speed drive, so instead of the usual 400 Hz they fall under the ISO category of “variable frequency (VF) range which includes 400 Hz”, producing AC power in the range of 360 to 800 Hz depending on engine speed.
It’s 'technically" illegal in the UK but we have a chain of furniture stores that have an almost perpetual sale with huge discounts and always “Last Few Days”.
At the back of each store, there is a display of items at ridiculously high prices. The purpose of this is to show that somewhere, in at least one of their many stores, the discounted goods are being offered at the full price.
Watts = amps x volts. so I suppose using the water analogy, it’s more along the lines of the force that the water is flowing with.
Maybe explaining it in terms of batteries might make sense. If you have a 40v battery with say… 7.5 amp-hours of capacity, that battery can kick out 300 watt-hours of energy, which would run a 100 watt light bulb for 3 hours at full brightness (theoretically). But if you had a 7.5 amp-hour battery that was 12 volts, it would only power that 100 watt bulb for about 54 minutes.
Another way to look at it is that the electrical wiring in your house is all 120v, but each circuit is rated for certain amperages- say 15 amps. So the most you could draw at any given time through that circuit is 1800 watts. Which in practical terms means that you could hook up 180 100 watt light bulbs before you would overload the circuit. But you couldn’t hook up more than one 1000 watt microwave that draws 8.33 amps (amps = watts/volts) because two would draw 16.66 amps and overload the circuit. And so on.
To break it down to what’s important to a consumer:
The power of an appliance (measured in watts or horsepower) definitely matters. That’s what determines how quickly it’ll be able to do whatever it is that it does.
The voltage an appliance runs on mostly matters to the extent that it tells you what battery you need to use with it. Different voltages will mean various difference in the internals of the device and of the battery, but as long as you’re using the right battery, no voltage is inherently “better” than any other (though voltage may or may not be correlated with power). Things that plug in to the wall will either run at the voltage you have in the wall (120 V in the US), or will have a transformer to step it down to some other voltage (often 5 V nowadays). In the case of a step-down transformer, you need to match that voltage, too, just like you would with a battery.
The current drawn (measured in amps) by the device matters in that the battery, or whatever other power supply you’re using it with, needs to be able to handle at least that much current. Using a source which is rated for a higher current is fine. Running multiple things off of the same power source (for instance, multiple things plugged into the same circuit in your house) means you need to add up all of those current draws, which might be too much (thus flipping a breaker) even if every individual device is below the limit. If you don’t have a breaker or fuse, then trying to draw too much current from a source can lead to overheating and possibly a fire. Other than that, the current is mostly used in combination with the voltage, to determine the power: Power is voltage times current.
The energy (measured in joules, watt-hours, or kilowatt-hours) stored in a battery, along with the power, determines how long you can use your device before you need to recharge: The time is the energy divided by the power. For things that plug in, the energy is mostly what you’re paying the power company for.
The charge of a battery (most often measured in amp-hours, but could also be measured in coulombs) is mostly relevant in that, when multiplied by the voltage, gives you the energy the battery stores (see above).
To be honest, I was actually thinking of 400Hz. Stupid brain fart. But thanks for the support. There are 400v systems as you say, but 400Hz is more universal.
One thing that should be mentioned, when talking about battery-powered tools is: TANSTAAFL.
Battery energy, within a given battery chemistry type (LiIon, NiMH, etc.), is pretty much directly proportional to the volume of the battery. So, if you have a battery pack that is 3”x2”x2” and it runs a tool for 30 minutes, doubling the number of cells to double the voltage will make the tool twice as powerful, but it will only run for half the time. This is a good tradeoff for tools that use energy in short, high-power bursts, but is not so good for those that need to run for a long time at a lower power.
Modern motor controllers are pretty good about conserving battery life at reduced motor power, but nothing is perfect.
Most of the points I could have made about batteries have been made already. So I’ll just say that I wasn’t trying to be a dick.
Some background:
I’ve been on about this whole “electromagic” advertising thing since they used to market air compressors with HP ratings(sore subject) that couldn’t possibly be powered from a standard 120v 20A outlet, yet they worked just fine from them. Then they had the nerve to use motors on them with a nameplate stamped “special” in the HP field. Yeah, those are “special” motors alright, we’re all “special” consumers and those are special nameplates. They weren’t just fudging the numbers. They were straight up lying. The bastards. ::End Rant::
What I see a lot of is manufacturers quoting inrush current on startup, which can be several times the steady-state current. The circuit breakers are designed not to trip in this situation, and it’s a short enough time to not overload the conductors.
It’s utterly stupid, of course. The inrush current is irrelevant to the performance of the device. It’s not quite straight-up lying, since there is a fraction of a second when the device is pulling that “peak horsepower” number, but it’s so deceptive that it might as well be lying.
Nobody really gets it. These numbers are not a reliable predictor of performance or reliability or … These are the days where manufacturers can “hack” any performance metric to the point that they are meaningless.
Join a local group of like minded individuals or come to this board and ask how to select a specific product.
Maybe the math does work if you run the inrush numbers. Inrush on a piston compressor has got to be six times FLA for at least a significant fraction of a second but there is lots of torque there at startup they could advertise next years product lines with too. Utterly stupid indeed.