Non-changing current with C-EMF

[Gryd3]

I pretty much got what I needed. My misconception of the additional power to increase voltage has been adjusted, how constant current works(kinda getting the idea), the rate of reaction which I believe is equal to counter-emf induction OR quicker? I mean, would it be fast enough to maintain current during the whole time?

What I mean is, induced -V starts to "oppose" the current is the constant current really fast at reacting and increases the supply voltage to keep the current the same never decreasing during the whole time?

Again, thank you guys for the help! It's amazing finding experts helping out.

You should grab

What do you mean by the ideal world , is there a catch?! If I try to work on a model?

There is always a catch
In an ideal world, a multi-meter would have an infinite resistance when measuring voltage, 0 resistance when measuring current. Oscilloscope leads would have 0 capacitance...
With many components, there are characteristics such as slew-rate http://en.wikipedia.org/wiki/Slew_rate that dictate how fast something will react.
That of course could be used to your advantage to to prevent c-emf from propagating through certain components.

 

[Arouse1973]

Every component is ideal. Remember in the real world every component has LCR.
Adam

 

[XRZ]

@Gryd3, @Arouse1973

As long as current is constant 90% of the time(which I think it would be with a CCS) I think that's "idea" for me, nothing can be 100%.
I know there are losses, and efficiency issues... But as long as current is constant most of the time that's great for this experiment. I know that the constant current source would react to maintain current, but how fast? I guess it's fast. Equal or a bit less than counter-emf's induction.

 

[(*steve*)]

What do you mean by the ideal world , is there a catch?! If I try to work on a model?

In theory there is no difference between theory and practice. In practice there is.

 

[XRZ]

In theory there is no difference between theory and practice. In practice there is.

"Practice = losses"
Well most components nowadays are high in efficiency so I assume I can have the current constant like 95% and more possibly...?

 

[XRZ]

So...how fast would the constant current source react to induced-counter emf?
Also in both my example the range of voltage would be the applied EMF + counter-emf for the constant current correct? So for example if the applied voltage prior to counter emf was 2V and CEMF is 1V the voltage range would be 1V - 3V?

@BobK @(*steve*) @Gryd3 @Arouse1973

 

[Gryd3]

So...how fast would the constant current source react to induced-counter emf?
Also in both my example the range of voltage would be the applied EMF + counter-emf for the constant current correct? So for example if the applied voltage prior to counter emf was 2V and CEMF is 1V the voltage range would be 1V - 3V?

@BobK @(*steve*) @Gryd3 @Arouse1973

I can't give you an answer, as it is heavily dependant on the components in the circuit, and in the constant current supply..

 

[XRZ]

@Gryd3 Yea that's right... say you had such a system and you picked the components(by choosing the components you feel are right), could you guess/ or approximate it?

I mean, I know we can't put a time frame here(could we guess it?), is it possible to have the constant current source change it's voltage fast enough to maintain current? Having it react fast enough to respond to the change in voltage due to the induced-counter emf?

 

[XRZ]

Anyone know the price range of such power supplies, or how much the components could cost at the end(estimations anyone)? If I'm interested in building/buying them?
@Gryd3 @Arouse1973 @(*steve*)

 

[Gryd3]

@XRZ, it's a lot of theoretical work that would most likely be useless... I think it's time for a real-world test.

As far as buying them is concerned. They could be anywhere from $3-4 to $100s...
Google is your friend mate

The biggest difference for you when you look at them is the current they are set to, and the upper limit of the input/output voltage.

 

[BobK]

@Gryd3 Yea that's right... say you had such a system and you picked the components(by choosing the components you feel are right), could you guess/ or approximate it?

I mean, I know we can't put a time frame here(could we guess it?), is it possible to have the constant current source change it's voltage fast enough to maintain current? Having it react fast enough to respond to the change in voltage due to the induced-counter emf?

"Fast enough" is a useless description. Any constant current source will track changes in the load and compensate within some amount of time. This might be 1uS or it might be 1S. Either of these are "fast enough" for someone's application. What is your requirement?

Bob

 

[XRZ]

One of the reasons I asked about "adding" voltage to a circuit(in another thread), is because I was wondering of an idea to just have a high voltage source(with exceptionally low current) aside from the constant current source that's purpose is just to cancel out with induced counter emf.

So that now there are multiple power source, which I assume can add up? P1(constant current) + P2(voltage source) = total Power in the circuit?

 

[(*steve*)]

Nope. What you say makes no sense.

 

[XRZ]

Nope. What you say makes no sense.

Can't there be a secondary power source that just adds high voltage?
A secondary power supply that has a high voltage and low current to deal with counter-emf.

 

[(*steve*)]

Nope. What you say makes no sense.

 

[XRZ]

What's wrong? What don't I understand that seems to make no sense?
I'm pretty sure you understood what I meant, but to a circuit it's nonsense?

 

[(*steve*)]

There is no way to "add" a high voltage, low current source and a low voltage, high current source to get both high voltage and high current at the same time.

 

[XRZ]

2- The obvious way to hold the current constant is, as Arouse said, to balance the circuit. For example have a second identical slab of copper in the same field but wired into the circuit in the reverse direction. The emfs will exactly balance out and leave the current constant....

How is this possible?
A diagram:

The first conductor and second, are in a changing magnetic field. From the diagram above it seems that they increase current in opposition while having the same induced counter EMF.

Yet in this diagram without the PS, the cancel out:

Of course both of them in a changing magnetic field.

 

[(*steve*)]

From your PM:

Well let me explain my motive, this is just an experiment to answer a question that came to my mind when I started to study the physics of electric motors, and rail guns, and many other applications that had current reduced due to back-emf which is something natural. I wondered what if we required current to stay the same say in an electric-motor for example, So it lead to me to ask the question: Is it even possible to have current maintained when there is changing in the magnetic field? And the magnetic field has to be there(similar to an electric motor, or other applications, we can't cancel it out).

It seems that it can, by applying a higher voltage from the supply(inspired from constant current source), and thought there was no other option until I reviewed merlin's post and studying the idea of twisted pair wires. And when I read your response(you had a lot to share thank you!) I had to know what you think of his post.

Now, voltages could be cancelled or reduced(two equal power sources in opposition maybe?, and an example of reduced voltage is back-emf). In my experiment I have a conductor fixed next to a changing magnetic field. Based on Faraday' law, we know that there is induced-emf and from Lenz's law we know it's in opposition to the supplies input, so I was wondering if merlin's post is correct, having those two conductors cancel out their equally induced voltages.

The main issue that I see is that you absolutely want the current to vary in an electric motor.

If you always had the stall current flowing, even when the motor was running with no load, you would be very sad.

 

[BobK]

Yes, that has come up before. People think back EMF is a bad thing. It is not, electric motors would not be practical without it.

Bob