Forums

Spice modelling of back EMF

Started by Cursitor Doom March 22, 2016
On Saturday, March 26, 2016 at 1:21:13 PM UTC+11, Bill Bowden wrote:
> <bill.sloman@ieee.org> wrote in message > news:55e6d941-777f-4c06-964f-579d049511c8@googlegroups.com... > > On Friday, March 25, 2016 at 10:15:31 AM UTC+11, Bill Bowden wrote: > >> <bill.sloman@ieee.org> wrote in message > >> news:0865199c-0749-46a3-b9c9-25ac8724fb30@googlegroups.com... > >> On Thursday, March 24, 2016 at 9:28:48 AM UTC+11, Bill Bowden wrote: > >> >> Interwinding-capacitance causes eddy currents in the wire and lowers > >> >> the > >> >> Q > >> >> of the inductor. > >> > >> >The current that charges the inter-winding capacitances runs through the > >> >windings. If you bank wound an inductor, so it had lower interwinding > >> >capacitance it >would be self-resonant at a higher frequency, so the > >> >inductive reactance would be higher and the winding resistance less > >> >important. > >> > >> >> This is why Litz wire is used to wind antenna > >> >> loopsticks.for higher Qs and narrower bandwidths. > >> > >> >Wrong. Litz wire is better because at higher frequencies, current tends > >> >to > >> >flow on the surface of a wire. Litz wire has a lot more surface area > >> >spread > >> >over a >number of parallel windings. If you look at the manufacturers > >> >notes > >> >on Litz wire, you will find that progessively finer-filament Litz wire > >> >is > >> >recommended for >progressively higher frequency applications. > >> > >> >Interwinding capacitance doesn't come into it. > >> > >> Apparently, interwinding capacitance determines the upper frequency limit > >> where Litz wire has no advantage.This article says the upper limit is > >> about > >> 5 MHz. > >> > >> http://www.kerrigan-lewis.com/use-litz-wire/ > >> > >> "At frequencies > 5 MHz, Litz wire becomes less practical. The > >> capacitance > >> effects between the strands are the reasons for this high-frequency limit > >> on > >> the use of Litz wire." > >> > >> <snip> > > > > This sounds like total nonsense. The skin depth for copper at 1MHz is 66 > > micron, and 21 micron at 10MHz. You can't make wire strands that fine, > > which is why Litz wire stops making things better at around 5MHz. > > > > The whole point about Litz wire is that there is no voltage difference > > between the strands in a bundle (and the strands have to be distributed > > rather carefully to make sure that this is true) so the capacitance > > between the strands should be a non-issue. > > I don't know if Litz wire is used for multi-layer inductors. If it is, the > voltage will be different between the layers and the skin effect is wiped > out by the capacitance between the layers. If you take things to the limit, > the surface area and capacitance becomes very large between layers.
You can work out the capacitance between layers. It's typically of the order of a few hundred pF, which can be inconveniently large, but not "very large". Litz wire is used for multilayer windings - the logic for using it is based on the distribution of current within individual strands of wire and isn't any different between multi-layered and single-layered windings. -- Bill Sloman, Sydney
On Saturday, March 26, 2016 at 12:02:19 PM UTC+11, John Larkin wrote:
> On Fri, 25 Mar 2016 12:00:53 -0500, John S <Sophi.2@invalid.org> > wrote: > > >On 3/25/2016 11:08 AM, John Larkin wrote: > >> On Fri, 25 Mar 2016 13:39:38 -0000 (UTC), Cursitor Doom > >> <curd@notformail.com> wrote: > >> > >>> On Thu, 24 Mar 2016 10:39:04 -0700, John Larkin wrote: > >>> > >>>> We call it "voltage". Voltage isn't a force. > > > >There is a force between two objects caused by the voltage (EMF) > >difference between them. > > > >>> So are you saying the term "EMF" is a misnomer? Or is this just an > >>> argument about semantics? > >> > >> All I'm saying is that we don't use the term "EMF" when we mean > >> voltage, and we don't use "back EMF" to refer to the voltage across an > >> inductor's terminals. I suppose some people do. DVMs aren't called > >> DEMFMs. Too hard to pronounce. > > > >You are correct. The common usage these days is to refer to EMF as > >voltage. However, Voltage is the *units* of EMF. > > > >> We do use "potential" occasionally, generally to refer to fields, in > >> electrostatics, things you can't measure with a voltmeter probe. It > >> sort of means "what the voltage would be here if you could measure > >> it." Even that is kind of tricky. > > > >Not really. Electrostatic meters do that quite well. Note that they use > >force for the indicator positioning. > > > >So, if "potential" (energy) isn't a force, what is it? > > > >> Working engineers have their own language, and I'm sure engineers in > >> other countries or industries have their own dialects. Just words. But > >> electronics engineers in the USA have a pretty consistent communal > >> vocabulary, and we can spot amateurs and outsiders quickly by the > >> terms they use. > > > >Why are you interested in spotting amateurs and outsiders? Why not try > >to understand and work with them? > > > >This whole thing is prompted by your statement that "Voltage isn't a > >force." You are wrong and you should have your wrists slapped with a ruler. > > Volts are measured in volts. Force is measured in newtons.
One way of defining a voltage difference is in terms of the force (in newtons) acting on a test charge (in coulombs) moving across the voltage difference. You have to do work to move a test charge across a voltage difference. One way of expressing work/energy is as newton.metres John seems to have slept through most of his physics lectures at Tulane. -- Bill Sloman, Sydney
On Saturday, March 26, 2016 at 1:16:12 PM UTC+11, John S wrote:
> On 3/25/2016 8:02 PM, John Larkin wrote: > > On Fri, 25 Mar 2016 12:00:53 -0500, John S <Sophi.2@invalid.org> > > wrote: > > > >> On 3/25/2016 11:08 AM, John Larkin wrote: > >>> On Fri, 25 Mar 2016 13:39:38 -0000 (UTC), Cursitor Doom > >>> <curd@notformail.com> wrote: > >>> > >>>> On Thu, 24 Mar 2016 10:39:04 -0700, John Larkin wrote: > >>>> > >>>>> We call it "voltage". Voltage isn't a force. > >> > >> There is a force between two objects caused by the voltage (EMF) > >> difference between them. > >> > >>>> So are you saying the term "EMF" is a misnomer? Or is this just an > >>>> argument about semantics? > >>> > >>> All I'm saying is that we don't use the term "EMF" when we mean > >>> voltage, and we don't use "back EMF" to refer to the voltage across an > >>> inductor's terminals. I suppose some people do. DVMs aren't called > >>> DEMFMs. Too hard to pronounce. > >> > >> You are correct. The common usage these days is to refer to EMF as > >> voltage. However, Voltage is the *units* of EMF. > >> > >>> We do use "potential" occasionally, generally to refer to fields, in > >>> electrostatics, things you can't measure with a voltmeter probe. It > >>> sort of means "what the voltage would be here if you could measure > >>> it." Even that is kind of tricky. > >> > >> Not really. Electrostatic meters do that quite well. Note that they use > >> force for the indicator positioning. > >> > >> So, if "potential" (energy) isn't a force, what is it? > >> > >>> Working engineers have their own language, and I'm sure engineers in > >>> other countries or industries have their own dialects. Just words. But > >>> electronics engineers in the USA have a pretty consistent communal > >>> vocabulary, and we can spot amateurs and outsiders quickly by the > >>> terms they use. > >> > >> Why are you interested in spotting amateurs and outsiders? Why not try > >> to understand and work with them? > >> > >> This whole thing is prompted by your statement that "Voltage isn't a > >> force." You are wrong and you should have your wrists slapped with a ruler. > > > > Volts are measured in volts. Force is measured in newtons. > > > > And argumentativeness is measured in Larkins.
Arguments have content. Larkin generates evasive hot air, not arguments. -- Bill Sloman, Sydney
On 3/25/2016 8:02 PM, John Larkin wrote:
> On Fri, 25 Mar 2016 12:00:53 -0500, John S <Sophi.2@invalid.org> > wrote: > >> On 3/25/2016 11:08 AM, John Larkin wrote: >>> On Fri, 25 Mar 2016 13:39:38 -0000 (UTC), Cursitor Doom >>> <curd@notformail.com> wrote: >>> >>>> On Thu, 24 Mar 2016 10:39:04 -0700, John Larkin wrote: >>>> >>>>> We call it "voltage". Voltage isn't a force. >> >> There is a force between two objects caused by the voltage (EMF) >> difference between them. >> >>>> So are you saying the term "EMF" is a misnomer? Or is this just an >>>> argument about semantics? >>> >>> All I'm saying is that we don't use the term "EMF" when we mean >>> voltage, and we don't use "back EMF" to refer to the voltage across an >>> inductor's terminals. I suppose some people do. DVMs aren't called >>> DEMFMs. Too hard to pronounce. >> >> You are correct. The common usage these days is to refer to EMF as >> voltage. However, Voltage is the *units* of EMF. >> >>> We do use "potential" occasionally, generally to refer to fields, in >>> electrostatics, things you can't measure with a voltmeter probe. It >>> sort of means "what the voltage would be here if you could measure >>> it." Even that is kind of tricky. >> >> Not really. Electrostatic meters do that quite well. Note that they use >> force for the indicator positioning. >> >> So, if "potential" (energy) isn't a force, what is it? >> >>> Working engineers have their own language, and I'm sure engineers in >>> other countries or industries have their own dialects. Just words. But >>> electronics engineers in the USA have a pretty consistent communal >>> vocabulary, and we can spot amateurs and outsiders quickly by the >>> terms they use. >> >> Why are you interested in spotting amateurs and outsiders? Why not try >> to understand and work with them? >> >> This whole thing is prompted by your statement that "Voltage isn't a >> force." You are wrong and you should have your wrists slapped with a ruler. > > Volts are measured in volts. Force is measured in newtons.
As I said, EMF is measured in volts. How many newtons of force between two electrodes of 1 cm^2 each spaced 1cm apart with an EMF of 100V difference? Check your 1st semester physics book for help.
On Fri, 25 Mar 2016 23:15:03 -0500, John S <Sophi.2@invalid.org>
wrote:

>On 3/25/2016 8:02 PM, John Larkin wrote: >> On Fri, 25 Mar 2016 12:00:53 -0500, John S <Sophi.2@invalid.org> >> wrote: >> >>> On 3/25/2016 11:08 AM, John Larkin wrote: >>>> On Fri, 25 Mar 2016 13:39:38 -0000 (UTC), Cursitor Doom >>>> <curd@notformail.com> wrote: >>>> >>>>> On Thu, 24 Mar 2016 10:39:04 -0700, John Larkin wrote: >>>>> >>>>>> We call it "voltage". Voltage isn't a force. >>> >>> There is a force between two objects caused by the voltage (EMF) >>> difference between them. >>> >>>>> So are you saying the term "EMF" is a misnomer? Or is this just an >>>>> argument about semantics? >>>> >>>> All I'm saying is that we don't use the term "EMF" when we mean >>>> voltage, and we don't use "back EMF" to refer to the voltage across an >>>> inductor's terminals. I suppose some people do. DVMs aren't called >>>> DEMFMs. Too hard to pronounce. >>> >>> You are correct. The common usage these days is to refer to EMF as >>> voltage. However, Voltage is the *units* of EMF. >>> >>>> We do use "potential" occasionally, generally to refer to fields, in >>>> electrostatics, things you can't measure with a voltmeter probe. It >>>> sort of means "what the voltage would be here if you could measure >>>> it." Even that is kind of tricky. >>> >>> Not really. Electrostatic meters do that quite well. Note that they use >>> force for the indicator positioning. >>> >>> So, if "potential" (energy) isn't a force, what is it? >>> >>>> Working engineers have their own language, and I'm sure engineers in >>>> other countries or industries have their own dialects. Just words. But >>>> electronics engineers in the USA have a pretty consistent communal >>>> vocabulary, and we can spot amateurs and outsiders quickly by the >>>> terms they use. >>> >>> Why are you interested in spotting amateurs and outsiders? Why not try >>> to understand and work with them? >>> >>> This whole thing is prompted by your statement that "Voltage isn't a >>> force." You are wrong and you should have your wrists slapped with a ruler. >> >> Volts are measured in volts. Force is measured in newtons. > >As I said, EMF is measured in volts. How many newtons of force between >two electrodes of 1 cm^2 each spaced 1cm apart with an EMF of 100V >difference? Check your 1st semester physics book for help. >
The most important first semister freshman Engineering course was Engineering Design Analysis, taught by the Dean of Engineering. It was basically dimensional analysis, how to get the units right. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Fri, 25 Mar 2016 18:02:06 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>On Fri, 25 Mar 2016 12:00:53 -0500, John S <Sophi.2@invalid.org> >wrote:
>>This whole thing is prompted by your statement that "Voltage isn't a >>force." You are wrong and you should have your wrists slapped with a ruler. > >Volts are measured in volts. Force is measured in newtons.
I prefer foot-pounds but I won't quibble the point. The two are directly related. Let's see if you can show us the math. spoiler: http://www.electrical4u.com/electrostatic-type-instruments-construction-principle-torque-equation/ John John DeArmond http://www.neon-john.com http://www.tnduction.com Tellico Plains, Occupied TN See website for email address
On Fri, 25 Mar 2016 22:21:37 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:


>The most important first semister freshman Engineering course was >Engineering Design Analysis, taught by the Dean of Engineering. It was >basically dimensional analysis, how to get the units right.
We covered that the first semester of UPC - Unified Physics and Chemistry. In the 10th grade. John John DeArmond http://www.neon-john.com http://www.tnduction.com Tellico Plains, Occupied TN See website for email address
On Sat, 26 Mar 2016 07:13:46 -0400, Neon John wrote:

> On Fri, 25 Mar 2016 18:02:06 -0700, John Larkin > <jjlarkin@highlandtechnology.com> wrote: > >>On Fri, 25 Mar 2016 12:00:53 -0500, John S <Sophi.2@invalid.org> >>wrote: > >>>This whole thing is prompted by your statement that "Voltage isn't a >>>force." You are wrong and you should have your wrists slapped with a >>>ruler. >> >>Volts are measured in volts. Force is measured in newtons. > > I prefer foot-pounds but I won't quibble the point. > > The two are directly related. Let's see if you can show us the math. > > > spoiler: > http://www.electrical4u.com/electrostatic-type-instruments-construction-
principle-torque-equation/
> > John
John Larkin, you stand accused of talking nonsense. How do you plead?
On Sat, 26 Mar 2016 07:18:21 -0400, Neon John <no@never.com> wrote:

>On Fri, 25 Mar 2016 22:21:37 -0700, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > > >>The most important first semister freshman Engineering course was >>Engineering Design Analysis, taught by the Dean of Engineering. It was >>basically dimensional analysis, how to get the units right.
The problem is that some like weird units and some have similar names.
>We covered that the first semester of UPC - Unified Physics and >Chemistry. In the 10th grade. >
Ditto (though just HS physics).
On Sat, 26 Mar 2016 07:13:46 -0400, Neon John <no@never.com> wrote:

>On Fri, 25 Mar 2016 18:02:06 -0700, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > >>On Fri, 25 Mar 2016 12:00:53 -0500, John S <Sophi.2@invalid.org> >>wrote: > >>>This whole thing is prompted by your statement that "Voltage isn't a >>>force." You are wrong and you should have your wrists slapped with a ruler. >> >>Volts are measured in volts. Force is measured in newtons. > >I prefer foot-pounds but I won't quibble the point.
Do you measure force in foot-pounds?
> >The two are directly related. Let's see if you can show us the math.
Actually, I can't manage that. -- John Larkin Highland Technology, Inc lunatic fringe electronics