AC, DC, and Superconductors

[Enola Straight]

In this thread over on the SDMB
http://boards.straightdope.com/sdmb/sho ... p?t=362072
I asked if a magnetic flywheel could be thought of as a DC transformer...simply a DC motor attached to a DC generator.

Is it?

[Isolder74]

In this thread over on the SDMB
http://boards.straightdope.com/sdmb/sho ... p?t=362072
I asked if a magnetic flywheel could be thought of as a DC transformer...simply a DC motor attached to a DC generator.

Is it?

no. It is not. Its is a mechanically coupled system. A transfromer works by the changing magnetic field in between the two coils and the diference in the number of coils from one to the other.

Here we have motor A -> Generator B -> Power out with friction and torsion losses.

If I read it roight you have Motor with large magnet spinning -> Spin metel wheel -> spins Generator -> DC out.

The only way to step down DC voltage is to use a voltage divider circuit. This circuit has a disadvatage of shunting some energy out of the ciruit wasting current. This is why they alway have a transformer that steps down the AC to the RMS of the DC you want and the rectify it into DC. Its actually easier to us an osolator circuit to turn the CD into AC and use a transformer to step up and down that to do it in DC.

[Braedley]

With regard to the question posed on the linked site, it's actually more efficient to transimit dc electricity through lossy lines because you don't have to worry about the inductances and capacitances. Not that a super conductor!=lossless. On lossless lines, it doesn't matter, and since most tx lines are almost lossless, it really doesn't matter what you use, from a theoretical point.

[drachefly]

The only way to step down DC voltage is to use a voltage divider circuit. This circuit has a disadvatage of shunting some energy out of the ciruit wasting current.

Well, yes and no; mostly no. You can use a very high impedance voltage divider hooked up to a transistor to regulate DC flow without having all the disadvantages of a voltage divider.