MH's ideal coil and voltage question

[tinman]

Tinman,

I have always preferred using counter-EMF (CEMF) with regard to inductors and back-EMF (BEMF) with regard to the action of motors.  If used interchangeably, one must be sure to indicate which action is being referred to within the context of its usage. 

From the following Wiki:

https://en.wikipedia.org/wiki/Counter-electromotive_force

PW

PW
I dont see the difference between the two? BackEMF or CounterEMF.
Most everything i read,says the two are one in the same,and mean the same thing-a coil subject to a magnetic field that changes in time.
Quote wiki-The counter-electromotive force (abbreviated counter EMF, or CEMF),[1] also known as the back electromotive force, is the voltage, or electromotive force, that pushes against the current which induces it.

I do realize that the DC motors i used will have the coils(windings) see two changing magnetic fields-one self induced,and one from the PMs,but still,is not the same thing happening,as in,the coils will still be subject to a  magnetic field that changes in time?.

What is the outcome between a !Pushing! type DC PM motor,and a !Pulling! type DC PM motor? How dose that effect the terms being used?,and how dose it change the outcome,when both types will work as a generator as well,but each will subject the coils on the rotor to a different PM field.

One must also take care as to !what! PM field the coils are actually subjected to,in regards to the timing of the motor it self. There are a lot of people that dont actually know as to where each !two! coils are,that has the bulk of the current flowing through them,in relation to the two stator magnets(i am using my DC motors as reference,as they are two pole motors-two PMs)

For example here.
1-If we take a simple pulse motor,and we have our inductor producing a !north! field at the rotor end of that inductor,will the inductors CEMF value be changed if we have all the PMs on the rotor with there north field facing out(toward the inductor),so as the motor is a pushing motor,to that if we have all the south fields facing out(toward the inductor),so as the motor is a pulling motor.
We are to assume that the RPM will remain a constant between the two tests.
So what happens now is,one test,the field of the PM will be the same as the induced field,and so opposite that of what the CEMF wants to produce,and one will be the opposite that of the induced field,but the same as what the CEMF wants to produce.

2- Now,if i remove the rotor altogether,and i pulse that inductor with my FG,so as to simulate the switching of the coil to that of when the rotor was in play,will there be any difference in the efficiency or operation of that inductor?
This is something i can do,and have done many times on my bench.
The point being-how much difference do the stator magnets really make to the coils in that DC motor. Have people just decided that it is the stator PMs that are reducing the current flow,due to them(the PMs) being responsible for creating the backEMF,of have they just failed to realize that as the motor increases speed,that the coils are switching faster-much the same as raising the pulse frequency of a pulsed inductor?.


Brad

[tinman]

Yes, I do agree, that is a bit of a misnomer by Brad which he should acknowledge. Any load on a power supply of any sort (including a battery) that results in a current flow, be it a single wire or a coil across the terminals will create a full current loop within the supply and load.

Interestingly, a simple resistor connected directly across the battery will have the same voltage readings across it as the battery it is connected to and could be considered in parallel with the battery voltage, but the current from the battery through the resistor back into the battery is considered as taking a series path.

Cheers

I already did,in post 1385
Quote:  Even with a long straight piece of wire,you must form a loop to apply a voltage,and so now you have a single turn coil.

As we were talking about Kirchhoff's law at the time,i was referring to a single loop,as being one without a power supply attached-as it was in the tests i carried out with Poynt,where the current was induced into that loop by an external electric field that was not physically a part of the loop.


Brad

[picowatt]

PW
I dont see the difference between the two? BackEMF or CounterEMF.

Really?

The CEMF of an inductor causes the current to increase from a minimum after T=0

The BEMF of a motor causes the current to decrease from a maximum after T=0 (as the motor's RPM increases)

PW

[hoptoad]

I already did,in post 1385
Quote:  Even with a long straight piece of wire,you must form a loop to apply a voltage,and so now you have a single turn coil.

As we were talking about Kirchhoff's law at the time,i was referring to a single loop,as being one without a power supply attached-as it was in the tests i carried out with Poynt,where the current was induced into that loop by an external electric field that was not physically a part of the loop.

Brad

Sorry Brad, I missed that.
Cheers

[MileHigh]

The fat lady sings.