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Author Topic: Inductive Kickback  (Read 156572 times)

synchro1

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Re: Inductive Kickback
« Reply #15 on: November 20, 2015, 04:06:45 PM »
Synchro,
The current that flows when the switch is open is not from the battery. Isn't an inductor an energy tank? How that energy manifests itself during a field collapsing?

@Jeg,

The energy that appears in the coil from the collapsing field is new energy and has an opposite polarity.

tinman

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Re: Inductive Kickback
« Reply #16 on: November 20, 2015, 04:09:03 PM »
@Jeg,

The energy that appears in the coil from the collapsing field is new energy and has an opposite polarity.

The voltage across the inductor invert's,but the current continues to flow in the same direction. The energy from the collapsing magnetic field is not new energy,it is stored energy from the initial input energy.

Jeg

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Re: Inductive Kickback
« Reply #17 on: November 20, 2015, 04:09:53 PM »
@Jeg,

The energy that appears in the coil from the collapsing field is new energy and has an opposite polarity.

And where the stored energy goes?

woopy

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Re: Inductive Kickback
« Reply #18 on: November 20, 2015, 04:33:00 PM »
Hi all

Youp seems not to be so easy this flyback spike understanding.

For me what i see on the scope is that at the end of the pulse, when the reed sharply opens, the current trace goes to almost  instantly (verticaly) to zero. And only AFTER this shut down,  begins the flybackspike.

So to me the current who build up the magneticfield is gone , totally dissipated, finished at the end of the pulse. He was totally used to precisely build the magnetic field. So he has no more direction at all.

Than it stays the expanded magnetic field around the coil (??) and what exactly happens at that point is ?? But  on the scope ,  suddenly a strong narrow  "high negative voltage" trace appears  and also a strong very very narrow and strong current trace (not shown on the pic) also. What does create this event is still puzzling to me.

If it is the collapsing of the magneticfield please explain the process with simple words if possible.
But anyway to me that is a new current who has nothing to do directly with the one that created the magneticfield. It is what i call hes "son"

Youp, please don't shoot me down it's only an idea.

Laurent

synchro1

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Re: Inductive Kickback
« Reply #19 on: November 20, 2015, 04:35:45 PM »
And where the stored energy goes?

@Jeg,

The coil energy is stored in the magnetic field. The inductor can't store electricity. A capacitor can store electrical energy. Where does the new reversed polarity "Flyback" go? To the reverse pole.

synchro1

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Re: Inductive Kickback
« Reply #20 on: November 20, 2015, 04:42:05 PM »
Hi all

Youp seems not to be so easy this flyback spike understanding.

For me what i see on the scope is that at the end of the pulse, when the reed sharply opens, the current trace goes to almost  instantly (verticaly) to zero. And only AFTER this shut down,  begins the flybackspike.

So to me the current who build up the magneticfield is gone , totally dissipated, finished at the end of the pulse. He was totally used to precisely build the magnetic field. So he has no more direction at all.

Than it stays the expanded magnetic field around the coil (??) and what exactly happens at that point is ?? But  on the scope ,  suddenly a strong narrow  "high negative voltage" trace appears  and also a strong very very narrow and strong current trace (not shown on the pic) also. What does create this event is still puzzling to me.

If it is the collapsing of the magneticfield please explain the process with simple words if possible.
But anyway to me that is a new current who has nothing to do directly with the one that created the magneticfield. It is what i call hes "son"

Youp, please don't shoot me down it's only an idea.

Laurent

@Woopyjump,

Thanks for the test results. They confirm everything I've been saying!

Faraday's Law (loosely) states that current is generated when a magnetic field moves across copper windings. The collapsing magnetic field is moving across the coil windings as it shrinks inward. Like a balloon: You blow air in, it expands. You release the air and it blows out the hole with a force. This force blows across the coil wraps from outward to inward. This is in the opposite direction from the initial field expansion. 

tinman

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Re: Inductive Kickback
« Reply #21 on: November 20, 2015, 04:59:12 PM »
@Woopyjump,

Thanks for the test results.

Faraday's Law (loosely) states that current is generated when a magnetic field moves across copper windings. The collapsing magnetic field is moving across the coil windings as it shrinks inward. Like a balloon: You blow air in, it expands. You release the air and it blows out the hole with a force.

Quote
They confirm everything I've been saying!

What they confirm is that you are wrong.

Quote
This force blows across the coil wraps from outward to inward. This is in the opposite direction from the initial field expansion.


It is also opposite to that which created it. This is where you are lost. Power was supplied to the inductor to create the magnetic field.Then the magnetic field returned the energy which created it in the first place.

Let me try and explain it this way Synchro.
Lets say a motor vehicle is our inductor,and the wheels are the current. The engine is our power in when the switch is closed. When we use the engine(power input) to move the car forward,which way will the wheels rotate. Now,we switch the engine off,and with the car stationary,we move the road backwards under the car-which way are the wheels rotating?. Thats right-in the same direction.

citfta

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Re: Inductive Kickback
« Reply #22 on: November 20, 2015, 05:08:29 PM »
Synchro,

Let's take things one step at a time.  Which way does the current flow "inside" a battery?  Now which way does it flow outside of the battery.

synchro1

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Re: Inductive Kickback
« Reply #23 on: November 20, 2015, 05:18:06 PM »
@Tinman,

"It is also opposite to that which created it. This is where you are lost. Power was supplied to the inductor to create the magnetic field.Then the magnetic field returned the energy which created it in the first place".

What is this some kind of attempt at burlesque?

tinman

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Re: Inductive Kickback
« Reply #24 on: November 20, 2015, 05:18:32 PM »
Synchro

Please look at the diagram below,and note the scope probe placements.

Question 1- What wave form will be seen on channel 1-->an AC or DC wave form?.
Question 2- What wave form will be seen on channel 2-->an AC or DC wave form?

citfta

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Re: Inductive Kickback
« Reply #25 on: November 20, 2015, 05:25:12 PM »
Synchro will you please put together the simple circuit Tinman has provided?  I have reattached it here.

Now short out the cap to make sure it is fully discharged.  Then momentary tap the switch closed and then leave it open.  Now check the voltage on the cap.  If you are correct about the current reversing then the top of the cap should be positive and the bottom negative.  However you will see the bottom of the cap is positive and the top of the cap is negative.  This is because the coil has become a source for the short time it takes the magnetic field to collapse.  Please answer my question about which way the current flows inside of a battery.

Carroll

tinman

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Re: Inductive Kickback
« Reply #26 on: November 20, 2015, 05:28:36 PM »
@Tinman,

"It is also opposite to that which created it. This is where you are lost. Power was supplied to the inductor to create the magnetic field.Then the magnetic field returned the energy which created it in the first place".

What is this some kind of attempt at burlesque?

The collapsing magnetic field is what inverts the voltage across that inductor. Although the magnetic field is collapsing around that inductor,and this inverts the voltage,the magnetic polarity remains the same,and this maintains the current flow direction,so as it is the same as it was before the power source was interrupted. In order for the current flow to change direction,the magnetic field polarity would also have to invert-which it dose not.

MileHigh

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Re: Inductive Kickback
« Reply #27 on: November 20, 2015, 05:48:04 PM »
I think there is a lot of confusion around the "reversing voltage" and the explanation for that is quite simple.

When you energize the inductor you have an external voltage source across the terminals of the inductor.  So an external power supply defines the voltage across the inductor.

Then when the switch opens, the external voltage source is gone - it has no influence at all on the voltage across the inductor.

When the switch opens the inductor now acts as a power source.  The inductor as a power source outputs current.   The inductor works to keep the current flowing in the same direction.  The load creates the counter-EMF under the imposed current flow from the inductor.

So, in the truest sense, the inductor is just a hapless rag doll along for the ride when it comes to the voltage across its terminals.   In the first case, the external power supply is imposing its voltage across the terminals of the inductor.  In the second case, the load itself is imposing its voltage across the terminals of the inductor as the inductor discharges a current flow into the load.

In both cases, the inductor is a "follower" when it comes to the voltage across its terminals - like a hapless rag doll.

MileHigh

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Re: Inductive Kickback
« Reply #28 on: November 20, 2015, 06:16:27 PM »
An entire cottage industry is built around the "secrets" of the inductor.

Here is a fun thought demonstration:

In one hand you have a one-farad capacitor with one volt across it discharging across a one-ohm resistor.

In the other hand you have a one-henry inductor with one amp traveling through it discharging through a one-ohm resistor.

If you put a scope across the resistor in both cases you would see an identical exponentially decaying voltage waveform.  Since it is a one-ohm resistor, you would also be looking at an identical decaying current waveform.

For the capacitor circuit, as you decrease the value of the load resistor, it starts to discharge faster and faster with higher and higher currents through the load resistor.

For the inductor circuit, as you increase the value of the load resistor, it starts to discharge faster and faster with higher and higher voltages across the load resistor.

If you can wrap your head around this then you will have an understanding about how capacitors and inductors work as energy storing devices and how they discharge their stored energy into a load.

Jeg

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Re: Inductive Kickback
« Reply #29 on: November 20, 2015, 06:26:14 PM »
Hi Tinman :)

There is really no sense for voltage to change polarity while the field is collapsing. Voltage and current have a strict relation between the two. Current always flow from higher voltage potential to a lower one and never the opposite even momentarily. As current keeps going the same direction after collapsing, the same is with voltage. Not only it doesn't alter its polarity, but also becomes magnitudes higher also momentarily like current does.