Can back emf be eliminated by...

[DARK0717]

can back emf be eliminated by using a spark gap to make the electricity independent after it jumps the gap? Well not really eliminate but to keep the back emf constant no matter the load?

Edited April 25, 2019 by DARK0717

[studiot]

2 hours ago, DARK0717 said:

can back emf be eliminated by using a spark gap to make the electricity independent after it jumps the gap? Well not really eliminate but to keep the back emf constant no matter the load?

Can you tell us why this would not be a good idea, even if you could do it, which you can't ?

Why do you think there is a negative sign in Faraday's equation and Lenz ' law?

 

The best you can do is to absorb it with something like clamping diodes, varistors or other surge arrestors.

Edited April 25, 2019 by studiot

[peterwlocke]

I did a quick search and it sounds interesting but quick question. is it kind of like the right-hand rule with magnetic field traveling opposite?

[John Cuthber]

Well, you can use gas filled tubes as voltage regulators and also as transient suppressors
https://en.wikipedia.org/wiki/Voltage-regulator_tube

https://en.wikipedia.org/wiki/Transient_voltage_suppressor
 

 

 

[DARK0717]

13 hours ago, peterwlocke said:

I did a quick search and it sounds interesting but quick question. is it kind of like the right-hand rule with magnetic field traveling opposite?

yes. If what I think is what you mean, then yea.

14 hours ago, studiot said:

Can you tell us why this would not be a good idea, even if you could do it, which you can't ?

Why do you think there is a negative sign in Faraday's equation and Lenz ' law?

 

The best you can do is to absorb it with something like clamping diodes, varistors or other surge arrestors.

This is a good idea (if it works) because overloaded generators would basically not happen as the load back emf stays constant (which is the spark gap being the only real load). 

One way I can think of is using a step up coil then a rotary spark gap to do so. Obviously, the output will be AC.

If my idea works, then power plants wont have to worry about the generators burning or breaking and a black out due to overload, but instead, devices using the electricity will only shut down due to not enough power and not cause further damage (further damage, by which I mean blackouts).

Edited April 26, 2019 by DARK0717

[studiot]

Thank you for your response.

Why did you not read mine?

 

I said you can't eliminate it, and implied that trying to do so was not a good idea.

Back EMF is used in electrical machinery (actuators, motors, generators, transformers etc)  to make them work properly.
Without back EMF transformers would burn out.

This is because the energy is already in the magnetic field and has to go somewhere, when you start to use electric machinery.

 

Edited April 26, 2019 by studiot

[DARK0717]

3 minutes ago, studiot said:

Thank you for your response.

Why did you not read mine?

 

I said you can't eliminate it, and implied that trying to do so was not a good idea.

Back EMF is used in electrical machinery (actuators, motors, generators, transformers etc)  to make them work properly.
Without back EMF transformers would burn out.

This is because the energy is already in the magnetic field and has to go somewhere, when you start to use electric machinery.

 

I know that EMF cannot be eliminated thats why I said "Well not really eliminate but to keep the back emf constant no matter the load?"

I was thinking of a much simpler way of doing so. Surge arrestors are too much of a hassle to operate or atleast, its more expensive that a rotary spark gap.

Edited April 26, 2019 by DARK0717

[studiot]

You are still not taking note of what is being said.

Back EMF is an integral and most t necessary part of the working of electric machinery.

It would not work correctly without it.

Do you understand how a transformer or sychronous motor works?

[DARK0717]

30 minutes ago, studiot said:

You are still not taking note of what is being said.

Back EMF is an integral and most t necessary part of the working of electric machinery.

It would not work correctly without it.

Do you understand how a transformer or sychronous motor works?

I do understand how sync motors work and transformers but thats not my point. Im asking if using a spark gap will make the current independent from the generator which, on the top of my head is, the spark gap is only the load that induces back emf.

An engineer told me that even if you put a generator in space, it will stop if you add a load coz of back emf. Its not perfectly accurate but you get the point.

Now, please answer this question. Can a spark gap be used to isolate a current from the generator after it jumps the gap which makes the load constant no matter how much the load is?

I dont know how back emf is required so please tell me why. What do you mean by "would not work correctly"?

Edited April 26, 2019 by DARK0717

[studiot]

23 minutes ago, DARK0717 said:

An engineer told me that even if you put a generator in space, it will stop if you add a load coz of back emf. Its not perfectly accurate but you get the point.

I get the point that if your 'engineer' actually said that then you need to speak to better engineers.

A generator is a device which is driven by mechanical means.
If something 'stopped' the generator then it would mean that the mechanical drive had in some way failed or been broken.

There is no other possibility.

 

The transformer is the easiest to understand.

Imagine a length of copper wire of resistance 4 ohms.

If you connected this across the mains here in the UK it would draw 240/4 = 60 amps of current and pretty soon melt.

But if you first wound this wire onto a suitable core forming a many turned coil, the current drawn, when connected to the same mains, would be reasonable and sustainable indefinitely.
I haven't given a figure since that depends upon the wire, the winding and the core.

Why is this, you might ask?

It's due to the back EMF induced in the wire which balances or very nearly balances the forward impressed EMF.

The small difference between the two is all that is driving the current.

If you attach further circuitry as a load then:

The current is always determined by the load.

That is part of the definition of an electrical load.

If the load varies, you (may) want to vary the current to keep the power or supply voltage constant.

So if you draw more current, then you must increase the difference between the impressed EMF and the back EMF.

 

It is as simple as that.

 

Variations on this theme are

A transformer has electrical energy input and electrical energy output.

A generator has mechanical energy input and electrical energy output.

A motor has electrical energy input and mechanical energy output.

But they all work on the sme principle of balance the forward and back EMF.

 

So any attempt to 'hold the back EMF constant will thwart the action of the machine.

 

 

A form of back EMF occurs when some circuits are connected or disconnected, as a result of the magnetic field collapsing.

This is sometimes called 'backswing' and can damage sensitive circuitry, weld or pit contacts in switches etc.

The faster this collapse occurs, the greater the backswing.

 

Absorbing this energy is the point of my original comment and the purpose of the devices John Cuthber and others suggested.

As regards a spark gap.
You need to supply a high voltage to create and maintain a spark.
Thus most of your supply would be wasted doing this, instead of supplying voltage to your load.

[DARK0717]

19 minutes ago, studiot said:

I get the point that if your 'engineer' actually said that then you need to speak to better engineers.

A generator is a device which is driven by mechanical means.
If something 'stopped' the generator then it would mean that the mechanical drive had in some way failed or been broken.

There is no other possibility.

 

The transformer is the easiest to understand.

Imagine a length of copper wire of resistance 4 ohms.

If you connected this across the mains here in the UK it would draw 240/4 = 60 amps of current and pretty soon melt.

But if you first wound this wire onto a suitable core forming a many turned coil, the current drawn, when connected to the same mains, would be reasonable and sustainable indefinitely.
I haven't given a figure since that depends upon the wire, the winding and the core.

Why is this, you might ask?

It's due to the back EMF induced in the wire which balances or very nearly balances the forward impressed EMF.

The small difference between the two is all that is driving the current.

If you attach further circuitry as a load then:

The current is always determined by the load.

That is part of the definition of an electrical load.

If the load varies, you (may) want to vary the current to keep the power or supply voltage constant.

So if you draw more current, then you must increase the difference between the impressed EMF and the back EMF.

 

It is as simple as that.

 

Variations on this theme are

A transformer has electrical energy input and electrical energy output.

A generator has mechanical energy input and electrical energy output.

A motor has electrical energy input and mechanical energy output.

But they all work on the sme principle of balance the forward and back EMF.

 

So any attempt to 'hold the back EMF constant will thwart the action of the machine.

 

 

A form of back EMF occurs when some circuits are connected or disconnected, as a result of the magnetic field collapsing.

This is sometimes called 'backswing' and can damage sensitive circuitry, weld or pit contacts in switches etc.

The faster this collapse occurs, the greater the backswing.

 

Absorbing this energy is the point of my original comment and the purpose of the devices John Cuthber and others suggested.

As regards a spark gap.
You need to supply a high voltage to create and maintain a spark.
Thus most of your supply would be wasted doing this, instead of supplying voltage to your load.

I see, If i understood correctly, the back emf is caused to balance emf which means one cannot exist without the other. and the current depends on the load, which i think means that if there is no load, there is no current which leads to the more load there is, the more current it draws out from the generator and since there is too much load, it results to more emf which then also results to more back emf. Is my understanding correct?

[studiot]

13 minutes ago, DARK0717 said:

I see, If i understood correctly, the back emf is caused to balance emf which means one cannot exist without the other. and the current depends on the load, which i think means that if there is no load, there is no current which leads to the more load there is, the more current it draws out from the generator and since there is too much load, it results to more emf which then also results to more back emf. Is my understanding correct?

Nearly.

Simplified, the sequence is this:

The electric current through the wire causes a magnetic field in the core.
The strength of the magnetic field depends upon the magnitude of the current.

If the current changes, as it does continually for alternating current or if the current is stopped or started,
then the magnetic field changes accordingly.

A changing magnetic field induces a current/voltage in a conductor (your wire).
This voltage is called the back EMF because it is such that it opposes the original voltage.
But what is important is how fast it changes, not just the amount of change.
The faster the change, the greater the induced (back) EMF).
This is why the 'backswing voltage' of a sudden disconnection can be many times the supply voltage and thus so damaging.

This rate of change is also the link to motion (motors and generators).

[DARK0717]

1 minute ago, studiot said:

Nearly.

Simplified, the sequence is this:

The electric current through the wire causes a magnetic field in the core.
The strength of the magnetic field depends upon the magnitude of the current.

If the current changes, as it does continually for alternating current or if the current is stopped or started,
then the magnetic field changes accordingly.

A changing magnetic field induces a current/voltage in a conductor (your wire).
This voltage is called the back EMF because it is such that it opposes the original voltage.
But what is important is how fast it changes, not just the amount of change.
The faster the change, the greater the induced (back) EMF).
This is why the 'backswing voltage' of a sudden disconnection can be many times the supply voltage and thus so damaging.

This rate of change is also the link to motion (motors and generators).

oh I see, thanks, so it means that using a spark gap would be very inefficient for the generator and for the device using that power from it due to the load being very low which causes very little current after the gap.