Follow Slashdot stories on Twitter

 



Forgot your password?
typodupeerror
×

Comment Re:"using a lot more fossil fuels than they save"? (Score 1) 685

Not to mention that they would cost a lot more if this were actually true. A little research reveals that shipping costs for a 4-pack of CFLs is much less than $1USD, and more like $0.05 to $0.25. That's pennies per bulb, and fuel costs are a fraction of that amount.

Since I expect to save $20-40 per bulb in electricity, I think that it is unlikely that more fuel is consumed in shipping over the life of the bulb.

John

Comment Re:That's an incredibly good dielectric plastic (Score 2, Interesting) 603

The electric field strength of dielectrics is a function of material thickness, with thinner materials generally exhibiting a higher field strength. Thus, a thinner dielectric has a higher breakdown field.

A common rule o' thumb is that to double the voltage breakdown of a given sheet of insulator, one needs to multiply the thickness by a factor of 4. The exact exponent used depends on the material type, quality, etc, but the gist of it is that thinner materials can have much higher breakdown strength than one would expect from testing a thicker material.

Many other factors play an important role, such as field strength enhancement due to small radii, voltage rate of change, material defects, humidity, temperature, and so forth.

Finally, there is evidence to suggest that certain concentrations of nanoparticle fillers may increase dielectric strength.

Disclaimer: IANAMS (I am not a material scientist), but I have done some high-voltage design. Dielectrics are still a black art, if you ask me. If you don't believe me, ask a dielectrics expert a quantitative question sometime, and see how long the answer is.

Comment This is probably not "Witricity"... (Score 1) 221

Note the requirement for the charging station.

There are a number of ideas for "charging pads" or "charging mats" with a matrix of planar coils. The power receiver would be in the back of the item to be charged and rest directly on the pad. They are transmitting power via magnetic coupling, but over much shorter distances (mm, not m). This can actually be done with reasonable high efficiency (>90%). Sorry, I don't have the references on the top of my head.

On the other hand, Witricity is a dog because they are trying to transmit power over a distance on the same order of the coil's radius or farther. Without a winding with much better conductivity than copper, this cannot be very efficient (60-75% is pretty poor). The resonance aspect does not affect the coil transfer efficiency in theory, but it helps in practice because power electronics components are, alas, non-ideal.

If you ever have a chance to see someone demo this, ask them to put the coil axes at right angles to each other and see what happens...

John

Slashdot Top Deals

UNIX is hot. It's more than hot. It's steaming. It's quicksilver lightning with a laserbeam kicker. -- Michael Jay Tucker

Working...