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#### Cantafford

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When I have a DC voltage source and connect it to an inductor and resistive load, the inductor will oppose the change in current untill the change of current will become 0(therefore current will be steady) and at this point the inductor will be just a piece of wire.

So far so good. But when I disconnect the power source, the inductor has some kickback voltage. I'm aware of this but I don't understand why it kicks back voltage since it's tendancy is to keep current going in the same direction. So my question is why does it kick back voltage instead of 'kicking it forward' and trying to maintain the current flowing in it's last direction.

#### Vintage Sounds

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An inductor stores energy which it discharges in an attempt to oppose the change in current caused by turning the power off.

#### JRaef

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More laymans terms:

The phenomenon is based on what is called the "inductive time constant" which dictates that you cannot change voltage or current flow in an inductor any faster than a given rate. So when voltage is increasing, it slows down the increase, smoothing out the response which is the desired effect. It's because as you start current flowing in the inductor, the magnetic fields you are creating in the coils and iron core are themselves cutting the lines of force on each other conductor and creating a counter EMF that is opposing the increase. The faster the increase, the stronger the counter EMF. But it works both ways, so when you cut off the voltage input, the energy stored in the magnetics of the inductor core cannot instantly stop either. The magnetic fields will be collapsing instead of expanding, but still cutting the lines of force in the conductors, which then creates its own voltage potential. So if that energy has nowhere to go, it just charges up the circuit, sort of like a capacitor. It's not really that it forces the energy to go the other way, it's just that the charged circuit will find the easiest path in which to discharge back to equilibrium. So if you have a little contact opening into that inductive circuit, and somewhere on the other side of that contact is a path for energy flow, that charged inductor will try to get to it, often by jumping the gap of that contact. Likewise if you have a FET or something doing the switching, that device has leakage, which to the charged inductor looks like a path and it tries to use that, which can destroy it. Hence the surge suppressor is added to the circuit to give it a safer alternative path toward equilibrium, and/or a diode to just block it from taking the path you don't want it to.

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Is this same principal how an HID igniter works? The triac (I forget its real name) rapidly cuts the current flow causing the coil to produce a high voltage output.

#### xpertpc

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I don't know about HIDs but it is how the ignition system on cars work, remember the older points and capacitor systems - the points opened the coil causing the field to collapse and the capacitor kept the dwell of the arc on long enough for ignition to occur.

#### JRaef

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Is this same principal how an HID igniter works? The triac (I forget its real name) rapidly cuts the current flow causing the coil to produce a high voltage output.
I don't know about HIDs but it is how the ignition system on cars work, remember the older points and capacitor systems - the points opened the coil causing the field to collapse and the capacitor kept the dwell of the arc on long enough for ignition to occur.
Originally, they were both very similar circuits. One part that the capacitor played was that in charging and discharging faster than the coil fields could collapse, it caused the inductor (coil) to act like an autotransformer to build up voltage until it was high enough to discharge across the gap, either in the spark plug in the engine or the HID lamp to excite the gas molecules and create plasma, which gave off light. Both systems have gone electronic now however, using PWM firing into an actual transformer to increase the voltage. But of course, a transformer is an inductor too, it just has two sets of windings.

#### Moonshot180

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often times a large inductor will have a resistor diode connected in paralell...these resistor diodes are also known as snubber diodes.

#### RIVETER

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More laymans terms:

The phenomenon is based on what is called the "inductive time constant" which dictates that you cannot change voltage or current flow in an inductor any faster than a given rate. So when voltage is increasing, it slows down the increase, smoothing out the response which is the desired effect. It's because as you start current flowing in the inductor, the magnetic fields you are creating in the coils and iron core are themselves cutting the lines of force on each other conductor and creating a counter EMF that is opposing the increase. The faster the increase, the stronger the counter EMF. But it works both ways, so when you cut off the voltage input, the energy stored in the magnetics of the inductor core cannot instantly stop either. The magnetic fields will be collapsing instead of expanding, but still cutting the lines of force in the conductors, which then creates its own voltage potential. So if that energy has nowhere to go, it just charges up the circuit, sort of like a capacitor. It's not really that it forces the energy to go the other way, it's just that the charged circuit will find the easiest path in which to discharge back to equilibrium. So if you have a little contact opening into that inductive circuit, and somewhere on the other side of that contact is a path for energy flow, that charged inductor will try to get to it, often by jumping the gap of that contact. Likewise if you have a FET or something doing the switching, that device has leakage, which to the charged inductor looks like a path and it tries to use that, which can destroy it. Hence the surge suppressor is added to the circuit to give it a safer alternative path toward equilibrium, and/or a diode to just block it from taking the path you don't want it to.
I love a simple answer...but you are right.:thumbsup:

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