Follow Slashdot stories on Twitter

 



Forgot your password?
typodupeerror
Polls on the front page of Slashdot? Is the world coming to an end?! Nope; read more about it. ×

Comment: Re:Impractical (Score 5, Interesting) 582

by Phreakiture (#49791209) Attached to: How Tesla Batteries Will Force Home Wiring To Go Low Voltage

This is largely what I was thinking.

As it currently stands, commercial buildings often have 277V lighting circuits (this is in the US) because it involves installing less copper in the ceilings.

From this, one can intuit that lowering the voltage will significantly increase the amount of copper, but let's take an example and make it more solid.

Let's say, for the sake of example, that we were considering 48V DC as an alternative to 120V AC (I personally would not want to consider anything lower than 48V in a home environment). If you need to deliver 1200W from point A to point B, it will require 10A at 120V, and 25A at 48V.

That 10A could be safely delivered on a 14 ga. wire in most domestic contexts, but will probably be delivered on 12 ga. For 25A, however, you're going to need 10 ga.*

A 250' roll of wire is ~$43 for 14 ga, $95 for 12 ga., and $138 for 10 ga. See the problem?

For the next challenge, you will also need to use different, more expensive switches and circuit breakers, or drop back to using fuses. This is because an AC arc self-quenches in half a cycle or less, and won't re-establish until the contacts are brought close enough together. The DC arc, on the other hand, is continuous, and requires additional effort to quench. Just for the record, there is an arc every time that a circuit breaker or switch is opened under load. This is the reason why you will often see switches and breakers labelled "AC Only".

Now, this is not to say that these problems won't be overcome or that a different variant might come about. Who knows? Maybe they'll gravitate towards 120V AC or some such, in which case it will be 1915** all over again.

(*For the non-Americans and uninitiated, US wire gauge is backwards: larger numbers are smaller wires. 14, 12 and 10 gauge are ~2.1, 3.3 and 5.3 mm^2, respectively)

(**There is nothing special about 1915, but I live in a house that was built in 1915 and was electified from day one. It would have had DC delivered to it in those early days, courtesy of Mr. Edison's various efforts in my current home town of Schenectady.)

Comment: Re:Impressive... (Score 1) 150

Cheap and good can be done together. I am in upstate New York and my car is insured with GEICO. I switched to them for the reason they typically advertise: it's cheaper. The delightful surprise is that their customer service people are super-polite, sufficiently trained, sufficiently empowered, and on the two occasions when I have filed a claim with them, they have been fast about getting things back in order.

On a side-note, I've been to the Philippines. I think their English is more EN_ca than EN_us. I'm sure that's a lot like arguing EN_au vs. EN_nz, but there are some little bitty details that stick out if you are a native speaker of either. I've heard a lot of both, having lived in a border town.

Comment: Re:Markets, not people (Score 1) 615

by Phreakiture (#49719967) Attached to: The Economic Consequences of Self-Driving Trucks

Drivers need to be able to do things like hear breaks screeching, feel the thump when they lose a retread from their tire, feel a flat tire pulling them, etc.

The sensors for these problems are already pretty well available and many of them are even common. Every modern consumer car has TPMS on it (Tire Pressure Monitoring System) that tells you if your tire is low. If the retread flies off of a tire, it will get low right away because inward pressure on the inner tube will fall. Measuring engine temperature, oil pressure, oil level, coolant level, fuel level, etc. are also things that are already done by consumer vehicles. The auto-drive will already be gathering the data necessary to determine if there is an alignment problem or something else causing the vehicle to pull, and this can be identified by computing the trend of any adjustments it makes to its course. Transmission temperature is a no-brainer, using the same general tech as used to measure engine temperature. Brake and bearing temeratures are the only thing left that I can think of, and you just need to look to the railroads for a solution to that one, involving inexpensive infrared thermometers (though in this case, they would likely be traveling with the vehicle rather than stationary on the road).

Comment: Re:IAADP (Score 1) 37

by Phreakiture (#49641375) Attached to: FAA Program Tests Drones Flying Beyond Pilot's Line-of-Sight

Works poorly because of operator limitations?

I'm going to go out on a limb here and say it may very well be technological limitations, not operator limitations. I'm thinking that there is probably some lag in the feedback. Whether or not this can be fixed is, at least partially, going to be dependent on how far out of site the drone will be.

Comment: Re:Does This Make Sense? (Score 4, Insightful) 318

by Phreakiture (#49640519) Attached to: Tesla To Unveil Its $35,000 Model 3 In March 2016

There is also one more benefit that you sort of touched on a little, but maybe could use some elaboration.

One gasoline-powered car runs on gasoline. You can bend the gasoline a little by putting something somewhat comparable like ethanol in it, but in the end, you can't stray far from the basic formulation, and that formulation is made not just from fossil fuels, but from one specific fossil fuel. Synthesizing gasoline from coal or natural gas is theoretically possible, but expensive and impractical barring a crisis.

One electric-powered car runs on electricity. You can bend the "formulation" of electricity a number of ways (AC vs. DC; various frequencies, voltages, currents, phase counts) and interchange them pretty efficiently. The electricity itself can come from coal, several grades of oil, natural gas, wind, solar, nuclear, hydro, biomass, whatever. Effectively, an electric car runs on whatever is available.

For bonus points, an electric motor has torque where it counts: at the bottom of the curve. You need the torque to get the car moving, preferably before the motor has come up to speed. Electric motors will do that. ICEs, on the other hand, need you to temper your load by feathering the clutch, or using a torque converter or hybrid drive system.

Electric cars also have features in common with hybrids, to wit, regenerative braking and no idling.

Comment: Re:Screw 'em (Score 1) 87

Perhaps, but realistically we now know two things:

Thing the first: there is a vulnerability to these locks, and we should be using something else. This goes double since the company has demonstrated that they are more interested in hushing it up than fixing it.

Thing the second: there is a vulnerability to these locks, and it would be interesting to try to find it. In essence, this event has enabled those amongst us who like to tinker with such things to narrow the search.

Comment: All this fuss over 50 micronewtons?!? (Score 1) 416

by Phreakiture (#49619819) Attached to: No, NASA Did Not Accidentally Invent Warp Drive

Does anyone even realize how little 50 micronewtons is? It is approximately the amount of force that a 5 microgram mass exerts on the ground due to gravity. It takes more force than this to discernibly move a speck of dust. The background noise in just about anyplace in the world exerts several orders of magnitude more than this on your eardrums. You can't feel it.

An error of 50 micronewtons has a name: it's called "noise".

"Our reruns are better than theirs." -- Nick at Nite

Working...