Levitating a coil / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Levitating a coil

previous 1 2 3 4 next

Move Thread

LAN_403

Marko

Mon May 15 2006, 11:24AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

That 100v x 6.5A is not 650W of course, but 650VA. The actual power dissipated in the coil will be given through the DC resistance of the coil (at operating temperature) by I[sup]2[/sup]R. A measurement of true electrical power consumed at the terminals would give the heating in the copper plate as well as the heating in the coil.

Actually it seems that quite a bit of power is dissipated in a copper plate because of srong eddy currents.

Tesladownunder

Mon May 15 2006, 04:29PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Well, sounds like time to pull out the kW meter.
Readings below are 100.6V, 6.61 A (giving 665 VA)
Power meter shows 0.55kW (550W).
I presume this is a power factor of 0.82.

I guess it would be less without the load of the copper plate with the more pure inductance.

NeilThomas wrote ...

How long can you run it before that interesting smell prompts you to turn it off?

Lots of 2-3 second shots to get 20 - 30 photos. Took a few breaks to allow it to cool. Never got to the interesting smell stage.
I'm sure a clever person could work out using the specific heat of copper, how long it would take to raise the temperature of the 200g work coil to 220C from 20C given a total power input of 550 W with perhaps 30% (a guess) being transferred to the copper plate and not contributing to coil heating. Who will be the first to do so. I would guess 60 seconds.

Peter

Marko

Mon May 15 2006, 08:59PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I think it would take somewhat more for th e power to corrupt this coil.

Maybe few minutes.
I think you need to figure out power dissipated in the copper plate more accurately, does it get warm and how much..?

Tesladownunder

Tue May 16 2006, 12:16AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

OK here is a 30 second test.
Power was 540W dropping to 470W during the test.
Coil temperature rose from 22.4C to 108C peak about 10 secs after the test
Copper plate temp rose from 22.4 to 24.6C
Copper plate is 6mm x 254mm x 160mm
I should repeat this test with the coil thermally insulated from the plate but have to let it cool first.

External temperature rose 80C in 30 secs so 220C should be reached in less than 90 secs even allowing for increasing resistance and reducing power. The core temp would be expected to be even higher than the external temp though.

I will alter this post when I get to repeat it insulated but feel free to calculate the energy transfer from these data as they should be close.

Peter

Simon

Tue May 16 2006, 01:10AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

Tesladownunder wrote ...

I'm sure a clever person could work out using the specific heat of copper, how long it would take to raise the temperature of the 200g work coil to 220C from 20C given a total power input of 550 W with perhaps 30% (a guess) being transferred to the copper plate and not contributing to coil heating. Who will be the first to do so. I would guess 60 seconds.

Your blatant manipulation of board members has worked.

The specific heat capacitor of copper is 385J/kg/K. So raising .2kg of copper by 200C takes 385x200x.2 J = 15400J of energy. 550W at 70% efficiency is 385W, so dividing again by 385 gives 40s.

That's a lower bound, since heat radiation will make it take longer.

Tesladownunder

Tue May 16 2006, 05:30AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Oooh.. Spooky coincidence with the 385's.

Now can a clever person calculate the power loss to the plate from the second set of figures?

Peter

teravolt

Tue May 16 2006, 05:34AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Very neet Tesla Downunder I have seen disks of aluminuim levitated in this manor with field shaping.

Marko

Tue May 16 2006, 05:24PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Could you try to hook the coil up to a flyback core driven by andrineri driver?

Tesladownunder

Wed May 17 2006, 12:42PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Tesladownunder wrote ...

OK here is a 30 second test.
Power was 540W dropping to 470W during the test.
Coil temperature rose from 22.4C to 108C peak about 10 secs after the test
Copper plate temp rose from 22.4 to 24.6C
Copper plate is 6mm x 254mm x 160mm

Ok, no takers so here are the calculations.
Average input power = 500W
Total energy input in 30 sec is 15000J
Mass of copper plate is 9g/cc x 243 cc = 2.2kg
Temp rise of copper plate is 2.2C
Energy to raise 2.2kg by 2.2C is 385 x 2.2 x 2.2 = 1800J
Hence power transfer is 1800/15000 = 12%

Less than I thought but this will vary with the weight supported and how closely it is tethered.

Power remaining in the coil similarly is 385 x 0.25 x 86 = 8300J
(put weight as 250g copper)

Total energy accounted for by temp rise is 1800 + 8300 = 10100J which is less than the calculated input of 15000J. Presumably the difference is due to factors like air cooling and also the core of the copper coil is probably a lot hotter than 108 degrees. In fact, there would be energy balance at 126C.

Peter

Tesladownunder

Sun May 21 2006, 04:29AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Invoking the double post rules of 48h with new information here.

Two pics. One shows double coils elevating with only 2 support wires plus the effect of a large iron mass beneath it (none). Second shows the 2 coil setup and the 1.3kW to drive it.

Peter

previous 1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob