John, look at your formula! it is the 'current' that remains unchanged, but N1=5000 and N2=2500; so by your own formula the field is more.
but since you preficed your statement with "I don't think so." is ok.
You are absolutely correct. I is constant, but N changes. Thanks for your correction.
On Tue, 11 Nov 2014 12:52:54 +0000, John Devereux Gave us:
Silver, both solid form and SPC gets used (or used to) in RF amplifier designs. Most were air core tank circuits.
Silver is too expensive for consumer products, and the actual gains over copper are pretty small.
But we see folks in the electric car realm fighting to transfer every last electron from their batteries to their motors, and "audiouphools" who think their speaker wires are going to make better sound for them, if they are one milliohm lower in resistance.
Does it work?
In transformers, YES. Operation is almost identical, but heating over time is lower for the same driving and loading. Very minimal gains, but they do exist.
In the E-cars, YES... every little bit counts, and a few hundredths of a volt drop on your connector cables is just unacceptable!
The audiophools are just that though. Any white, pink, shot or other noise they claim they can hear are artifacts of the amplifier, not the damned interconnect link between it and the load (speaker). They are even bigger fools to pay so much for so little. Then they go and do the same stupid shit on their AC power cords! They are a huge joke on intelligent man!
If the 2500T coil + resistance has a total series resistance of 12 ohms, yes.
The magnetomotive force has units of ampere-turns for a reason.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Carry his line of reasoning far enough and *Money* makes the field!
-- Rick
It should be added that the voltage over the 2500T coil is half of the voltage of the 5000T coil at the same current.
-- -TV
(snip)
Easy to remember formula- B = (0.899 mu N I)/R
B in gauss, mu is permeability of air (most Helmholtz coils are air-core), 0.899 is a constant to make the units happy with the geometry, N is turns, I is amperes, R is (radius and coil separation in) meters.
By inspection field strength is linear with the product of N and I, and inversely linear in radius.
Want more field? Use more N, more I, and/or less R.
Easy-peasy.
Mark L. Fergerson
One of the handy results is that if you have two coils of the same dimensions but different wire sizes, then to the extent that the packing efficiency is the same, the magnetic field vs. power will be the same.
You'll often see this in motor catalogs, where they'll have an (e.g.) 100W motor with windings from 6V to 24V or more, with torque constants that are roughly inversely proportional to the rated winding voltage, very similar RPM at rated voltage, etc. -- basically, the current scales down as the voltage scales up, but the response of the various motors per watt stays the same.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
LOL!!!!!
Jamie
Absolutely. This assumes you are adjusting your supply voltage to achieve the same current, as you have indicated. The higher DC R will just cause more heating and side effects with non air cores.
Jamie
and, just how much volume does that equation hold to say, 1%? Actually, it's 'exact' for the center spot and then goes downhill from there.
** Now hear this: the efficiency of an (air cored) coil depends on its shape and the use of a low resistance conductor - nothing else.
A near ideal shape is where the cross section of the coil is square and the centre hole diameter is close to half the outside diameter.
Here is an example of such a coil with only 6 turns.
All that changes when you use the SAME shape with more turns is the ratio of voltage to current to get a particular magnetic field strength.
Capice ??
.... Phil
On Tuesday, 11 November 2014 12:16:01 UTC+11, DecadentLinuxUserNumeroUno w rote:
Much though I hate to admit it, DecadentLinuxUserNumeroUno is almost right here.
The SI unit of magnetic flux is the weber, which is just the product of vol tage and time (in seconds). The unit of magnetic flux density is the weber per square meter, which is why the specifications for magnetic cores always include the smallest cross-sectional area, where the magnetic flux density is going to be at it's maximum and where the core material would saturate if you pushed the assembly too hard.
The voltage in question is the magnetic "back emf" of the coil to which - i n real life - you have to add the ohmic drop in the resistance of the wire making up the coil. In a lot of cases it's a vector sum, which can make lif e more complicated than some designers want to recognise.
-- Bill Sloman, Sydney
I think "almost right" means "wrong". The volt is produced when the flux changes. It is not a feature of the flux itself. That is why it is Volt?seconds and not Volts.
In an electromagnet the flux is proportional to the current flowing. If there is no resistance there is no voltage which actually happens in superconductors.
-- Rick
On Tue, 11 Nov 2014 20:30:34 -0500, rickman Gave us:
That is in a secondary, idiot.
Ummm, I think that's just an upside down way of looking at it.
For example, a perfect inductor would have zero resistance so therefore could not have any voltage across it. People who are around fusion reactors will appreciate low resistance, and would like to get rid of it all actually.
And then technically, if there is no voltage, there is no power.
This is one of those f***ed up things like the scientific definition of work. You can get damn tired holding something up in the air, but unless it moves against resistance or accelerates/decelerates, no work is performed.
So magnetic force is produced, technically without power consumption, but no work is actually done unless it moves something. When that happens though, there will be a back EMF.
Maybe take this over to the physics department...
On Tue, 11 Nov 2014 18:06:22 -0800 (PST), snipped-for-privacy@gmail.com Gave us:
You are performing work as you "holding it in the air" is you overcoming the gravity of the Earth. That IS "work" performed.
Were in micro gravity Earth orbit or less, THEN there would be little measurable work performed.
e
ght here.
voltage and time (in seconds). The unit of magnetic flux density is the we ber per square meter, which is why the specifications for magnetic cores al ways include the smallest cross-sectional area, where the magnetic flux den sity is going to be at it's maximum and where the core material would satur ate if you pushed the assembly too hard.
- in real life - you have to add the ohmic drop in the resistance of the w ire making up the coil. In a lot of cases it's a vector sum, which can make life more complicated than some designers want to recognise.
No. He did say "voltage makes the field", which is an inversion your statem ent that voltage is produced when the flux changes. He hasn't expressed him self all that precisely or clearly - this is DecadentLinuxUserNumeroUno - b ut what he's said isn't wrong.
"Makes" can be understood to be the process of creating the field, rather t han the process of sustaining it.
But there's still "back emf". You need to apply volts to change the current flowing through a superconducting coil.
-- Bill Sloman, Sydney
It isn't. You may be expending effort holding something up in the air, but that's just because you can't be bothered to stick something solid under it .
Something in orbit around the earth presents a rather more complicated situ ation. Two objects starting off at different distances from the centre of t he earth are in different orbits. If they are going to stay inside the same space craft they are both going to have to be in slightly different ellipt ical orbits that have the same average distance from the centre of the eart h, and will look as if they are orbiting around each other.
-- Bill Sloman, sydney
On Tue, 11 Nov 2014 18:54:48 -0800 (PST), Bill Sloman Gave us:
You ain't real bright. It most certainly IS.
No shit, Dip Tracy. WORK IS being PERFORMED. It has NOTHING to do with whether or not a stand is available or to be used.
HIS HAND IS SOLID, idiot. The WORK is performed AGAINST the FORCE of gravity.
It is so simple, in fact, that math is not even required for proof.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.