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Jack A

Sat Jul 30 2011, 10:37AM

Registered Member #2975 Joined: Wed Jul 07 2010, 12:19AM
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Posts: 28

Hi, I just wanted to run a homopolar generator design I found past you guys, please give any feedback you have.

I dont know why the image is mirrored, but I assume it is irrelevant. The article is here (http://amasci.com/freenrg/n-mach.html)

Cheers, Jack

Nmchcyl1

Ash Small

Sat Jul 30 2011, 10:45AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Jhackulon wrote ...

I dont know why the image is mirrored, but I assume it is irrelevant. .

At first glance it looks like if you reverse the direction of rotation, you reverse the polarity of the terminals.

Presumaby something to do with the 'left hand rule' (or is it 'right hand rule'?)

Proud Mary

Sat Jul 30 2011, 11:20AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hi there Jack!

Faraday disc generators are just another way of converting kinetic energy into electrical energy.

They were used in early synchrotron experiments because of their ability to generate millions of amps of DC at a few volts - if they be built on a grand scale that is!

As with much that looks simple at first sight, the devil is in the detail. Reliable ultra low resistance slip rings needed to take off low voltage at very high current are not easy to make, though few here would have any difficulty making a small demonstration model.

Stella

Conundrum

Sat Jul 30 2011, 05:50PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Ga-In alloy could work.

Hold it in place by mixing in a small quantity of iron particles (300 mesh) precoated with tin using electroless plating to prevent corrosion and it might work.

A

Proud Mary

Sun Jul 31 2011, 10:17AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Conundrum wrote ...

Ga-In alloy could work.

Hold it in place by mixing in a small quantity of iron particles (300 mesh) precoated with tin using electroless plating to prevent corrosion and it might work.

If we have one million amps flowing, and total circuit resistance is just 1 Î¼Î©, we will have a voltage drop of 1 V - half of the 2 V that our Faraday disc generator can produce.

This 2 V limit is what has prevented them from finding a permanent niche in the generator firmament, though all sorts of patents have been issued for them in the past.

Disc generators might bounce back from obscurity should cheap room-temperature superconductivity ever become available. Who can say?

Fraggle

Sun Jul 31 2011, 04:16PM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

Is it a fundamental limit? The back of this envelope is telling me that rpm and field strength determines the voltage. I realise that a couple of volts is probably the practical limit though.

Ash Small

Sun Jul 31 2011, 04:45PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Fraggle wrote ...

Is it a fundamental limit? The back of this envelope is telling me that rpm and field strength determines the voltage. I realise that a couple of volts is probably the practical limit though.

From Wikipedia:

"The voltage is typically low, on the order of a few volts in the case of small demonstration models, but large research generators can produce hundreds of volts"

Proud Mary

Sun Jul 31 2011, 05:04PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The output voltage is proportional to the speed of rotation, so I should have said typically a few volts, or a low voltage, though if you are prepared to go the extra mile you can get 200V out of one, as this description of a proton synchrotron PSU built in the 1950s makes clear:

"The power supply is a large homopolar generator which has 4 steel disks each about 139" in diameter and 19 tons in mass. These, rotating at 900 r.p.m. in a magnetic field of 16000 gauss have an energy of 5 x 10E8 joules and develop an e.m.f. of 800V when in series."

Brush contacts "are made with liquid metal (sodium-potassium alloy) jets" .... "the gaps are chosen so "vertical forces are balanced within 40 tons" ... A 1000 kW motor generator is used as the primary power supply to turn the discs.

Source: Blamey JW The Orbital Magnet and Power Supply of the 10 GeV Proton Synchrotron At the Australian National University

which you can download in pdf from the Cern site here:

Jack A

Tue Aug 02 2011, 11:58AM

Registered Member #2975 Joined: Wed Jul 07 2010, 12:19AM
Location:
Posts: 28

ah, maybe a capacitor is less complicated coil gun supply after all! I guess the advantage of the homopolar generator would be its ability to give off bursts rapidly (rapid fire).

cduma

Tue Aug 02 2011, 01:56PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300

I think that this would make a great power supply for a railgun if the rails were made of a super conductor or maybe even made of normal materials

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