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Registered Member #4659
Joined: Sun Apr 29 2012, 06:14PM
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Posts: 158
Pinky's Brain wrote ...
Magnetic potential does not have a linear relation with electrical power ... so Aturn/Watt is not a useful metric (try swapping the currents for both). At the same electrical power they have the same magnetic potential.
The force a solenoid exerts on another magnet or ferromagnetic object Force does have linear relation with electrical power though ... and a quadratic relation with magnetic potential.
Oh, ok. I'm thinking about coilguns here, so the force it exerts on a ferromagnetic object is the "force" i'm looking at. Measured in amp-turns.
On closer inspection, if i reduce the voltage (and thus the wattage) applied to both coils from 1v to (1/8)v, both coils get 8 times more efficient. It seems that coils are always more efficient at lower power.
...I think this is why multistage coilguns exist. It's more efficient to have many weak coils than one strong one.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Yanom wrote ... I'm thinking about coilguns here, so the force it exerts on a ferromagnetic object is the "force" i'm looking at. Measured in amp-turns.
No, force is measured in Newtons :) Also as I said, it has a linear relation with (amp-turns)^2. So in that respect it's still all about the copper, not about the turns ...
I expect multiple coils are used because the coils are more efficient when the slug is relatively close to the center. Not quite efficiency in the way you mean though, it's important to realise that the inductor isn't independent ... you can't just calculate the magnetic field in isolation ... the slug changes the magnetic field and the inductance of the coil, the losses are a bit more complex than the calculations in this thread assume.
Registered Member #4659
Joined: Sun Apr 29 2012, 06:14PM
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Pinky's Brain wrote ...
it's still all about the copper,
So more copper is better, eh? How about other conductive materials, like aluminium wire? In that respect, it's about conductivity vs. price. copper is expensive.
How do you measure conductivity of a metal, anyway?
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Aluminum's cheapness seems mostly theoretical to me since the availability of aluminium enamelled wire in small quantities is almost non existent. Soldering it is a bitch too.
How do you measure conductivity? With a multimeter :P
Registered Member #4659
Joined: Sun Apr 29 2012, 06:14PM
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Pinky's Brain wrote ...
Aluminum's cheapness seems mostly theoretical to me since the availability of aluminium enamelled wire in small quantities is almost non existent. Soldering it is a bitch too.
it does exist, though. I see what you mean by "not available in small quanitities"... the only place I could find it for sale was on the auction site alibaba, with minimum order 400kg (!)
There has to be some place to get small amounts second hand... maybe someone on 4hv has some.
wrote ...
How do you measure conductivity? With a multimeter :P
Well yes, but that depends on the length and thickness of the wire you're measuring. Is there some sort of standardized measure of how conductive a material is compared to other materials?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
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Place to get small quantities of enamelled alli wire?
Some microwave ovens, post cheap copper, but pre high frequency ferrite, use alli windings on the mains transformer. But you won't know until you've got into the oven. There aren't many about.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
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The electromagnet can also be rated in volts per turn. in this case, the resistance is taken of the table, and lumped with the internal resistance of the battery.
In a transformer, the voltage per turn, on the primary and the secondary will be equal and opposite.
If all the flux field produced by the primary winding, could be cancelled by the flux field of the secondary, there would be no magnetic field. So the amp-turns would be meaningless.
Registered Member #4659
Joined: Sun Apr 29 2012, 06:14PM
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Dr. Slack wrote ...
Place to get small quantities of enamelled alli wire?
Some microwave ovens, post cheap copper, but pre high frequency ferrite, use alli windings on the mains transformer. But you won't know until you've got into the oven. There aren't many about.
mmm. I'll look if I ever find one.
Here's another thought - you can buy thick (or thin) uninsulated aluminium wire for cheap lots of places. It's apparently used for electric fences. Would it be possible - to insulate it yourself? If I made a coil of a short length of thick wire, and designed my devices for such thick, low-resistance coils, I wouldn't have much length of wire to insulate. How do the factories insulate magnet wire? or regular wire, for that matter?
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
They run it through a bath of varnish. If you heat the wire/varnish it will dry very quickly. you just have a roller under the varnish, and roll it from one spool to another.
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More wire improves efficiency of a coil?
