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Author Topic: Inductive Kickback  (Read 157798 times)

MileHigh

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Re: Inductive Kickback
« Reply #30 on: November 20, 2015, 06:34:01 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.

That is not true.  Suppose that you have two batteries that have a common ground.  One battery is +1 volt and the other battery is +2 volts.

What will happen if you connect a 1-ohm resistor between the two batteries?

The answer is that one amp of current will flow into the +1 volt battery.  So in this example, current is flowing in the "opposite" direction through the +1 volt battery.

Jeg

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Re: Inductive Kickback
« Reply #31 on: November 20, 2015, 06:36:56 PM »
That is not true.  Suppose that you have two batteries that have a common ground.  One battery is +1 volt and the other battery is +2 volts.

What will happen if you connect a 1-ohm resistor between the two batteries?

The answer is that one amp of current will flow into the +1 volt battery.  So in this example, current is flowing in the "opposite" direction through the +1 volt battery.

Hi MH.
I said the same. Current flows from higher to lower potential always.

Ps. Ok MH I got it. Thanks.
  Inductor is now a power source itself, so yes Tinman is right. It changes voltage polarity but current flows the same direction inside the inductor. This is true.

synchro1

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Re: Inductive Kickback
« Reply #32 on: November 20, 2015, 06:53:45 PM »
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.

@Tinman,

Everything is everything!

Magluvin

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Re: Inductive Kickback
« Reply #33 on: November 20, 2015, 07:01:22 PM »
From what i have found in the past is that the output of the coil when input is taken away doesnt necessarily have to be a spike.  It depends on the load it is sent to.
Like putting a diode across a relay coil to recirculate the bemf, the the field collapse is slower than with a higher ohm load. Most relays are high ohm already so it does drop off very fast. But a very low ohm winding with high induction should slope while diminishing through the diode rather than a quick spike reaction of a higher ohm coil.

I have coils that I had shown in Lucs thread that are .5ohm 2mh.  The bemf from those coils will heat up a 5w 5 ohm resistor that you cant touch when hot. And its not due to quick spikes.


Mags

verpies

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Re: Inductive Kickback
« Reply #34 on: November 20, 2015, 07:41:53 PM »
When the current source to an inductor is interrupted, the current will continue to flow through the inductor in the same direction,but the voltage across that inductor will invert.
I agree.

I would add though, that the cause of current flow through an inductor can be:
- an external current source,
- an external voltage source,
- an external magnetic flux source,
- the inductor itself, since a current flowing through an ideal shorted inductor will flow forever.

synchro1

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Re: Inductive Kickback
« Reply #35 on: November 20, 2015, 07:51:52 PM »
I agree.

I would add though, that the cause of current flow through an inductor can be:
- an external current source,
- an external voltage source,
- an external magnetic flux source,
- the inductor itself, since a current flowing through an ideal shorted inductor will flow forever.

From Woopyjump:

"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 magnetic field 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 magnetic field. It is what I call his "son".

synchro1

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Re: Inductive Kickback
« Reply #36 on: November 20, 2015, 08:13:09 PM »
The current passes into the inductor; The inductor stores the current in a magnetic field; The current is cut off; The magnetic field collapses and a new current and voltage are generated; The new current and voltage share the same polarity! Stop trying to falsely maintain that the new voltage reverses polarity while the new current does something else!

Go back and look at Woopyjump's scope shots!

citfta

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Re: Inductive Kickback
« Reply #37 on: November 20, 2015, 08:21:15 PM »
Simple test for Woopy.

Put one channel of your scope across the coil and the other channel across the 10 ohm resistor.  Now pulse the coil and watch the two waveforms.  Please post your results.

synchro1

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Re: Inductive Kickback
« Reply #38 on: November 20, 2015, 08:26:39 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.

@Jeg,

Go back and have another look at Woopy's scope shots!

synchro1

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Re: Inductive Kickback
« Reply #39 on: November 20, 2015, 08:28:56 PM »
Simple test for Woopy.

Put one channel of your scope across the coil and the other channel across the 10 ohm resistor.  Now pulse the coil and watch the two waveforms.  Please post your results.

@Citfta,

What's the voltage of the power source? What's the inductance of the coil?

citfta

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Re: Inductive Kickback
« Reply #40 on: November 20, 2015, 08:30:56 PM »
The current passes into the inductor; The inductor stores the current in a magnetic field; The current is cut off; The magnetic field collapses and a new current and voltage are generated; The new current and voltage share the same polarity! Stop trying to falsely maintain that the new voltage reverses polarity while the new current does something else!

Go back and look at Woopyjump's scope shots!

Synchro, instead of just repeating what you believe please take the time to think about what we are saying.  You have never answered the question about which way the current flows inside the battery.  Jeg now understands what is going on because he took the time to consider that idea.

citfta

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Re: Inductive Kickback
« Reply #41 on: November 20, 2015, 08:33:13 PM »
@Citfta,

What's the voltage of the power source? What's the inductance of the coil?

It doesn't really matter.  The results will be the same.  A voltage of 12 volts or so is usually convenient.  And the higher the inductance the easier it will be to see the scope traces and follow what is happening.

synchro1

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Re: Inductive Kickback
« Reply #42 on: November 20, 2015, 08:34:11 PM »
Synchro, instead of just repeating what you believe please take the time to think about what we are saying.  You have never answered the question about which way the current flows inside the battery.  Jeg now understands what is going on because he took the time to consider that idea.

@Citfta,

I don't know anything about batteries.

synchro1

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Re: Inductive Kickback
« Reply #43 on: November 20, 2015, 08:35:52 PM »
It doesn't really matter.  The results will be the same.  A voltage of 12 volts or so it usually convenient.  And the higher the inductance the easier it will be to see the scope traces and follow what is happening.

@Citfta,

I can adjust the values to produce a spark across the Reed contacts.

citfta

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Re: Inductive Kickback
« Reply #44 on: November 20, 2015, 08:37:49 PM »
@Citfta,

I don't know anything about batteries.


OK.

If the conventional idea of current flow is for current to flow from the positive pole to the negative pole through the circuit then which way would the current have to flow inside the battery to complete the path of current flow?