Inductive Kickback

[Magluvin]

If you look back at the Ossie motor, he used 2 reed switches to disconnect both ends of the source. The purpose of that is that now you can have 2 diodes send the bemf back to the source directly, where with only 1 switch or reed that cannot happen directly.

Mags

Well now that Im thinking a lot lately , here is a way to overcome the single switch problem.

In a typical situation, putting a diode across the single switch to try to direct bemf back to the source, it does not work, due to the bemf actually being forward emf, opposite the direction of the diodes conductivity function.

But, if we put a tiny cap across the coil and put the reverse diode across the switch, when the switch opens, the bemf/femf will charge the cap. Then the cap reverses the current in the coil and the coil will charge the source through the diode across the switch.

Just ran it on sim. It works.

Mags

[Magluvin]

The resistor in series with the cap is necessary in sim because when the switch closes the program cannot calculate infinite current flow to the cap. So in real life that res is not necessary.

The cap can be very small to perform the current reversal in the inductor and the process happens much faster.



Mags

[Magluvin]

The resistor in series with the cap is necessary in sim because when the switch closes the program cannot calculate infinite current flow to the cap. So in real life that res is not necessary.

The cap can be very small to perform the current reversal in the inductor and the process happens much faster.



Mags

Correction.  The lower right res does the function of current limiting for the sim to process properly. So no res in series with cap necessary in the circuit shown.   

Mags

[forest]

Well, I can see from your scope shots that you always have current flowing in the coil.  Personally I find that to be a more complex measurement problem as compared to pulsing the coil with voltage, and then during the OFF time you observe the coil completely discharge its stored energy.  That should be a simpler measurement problem to tackle.   With current always flowing in the coil during the energizing cycle and during the discharge cycle, two things are happening at the same time during the energizing cycle, - 1) the energizing of the coil, and 2) the discharging of the coil though the LED.  I would have to think for a while on how to make the energy measurements in a case like that.   Although the LED appears to be clamping the coil discharge through the LED to a fixed voltage, we know it's not truly doing that.  I also see how your function generator output (?) droops s bit as the coil current increases which also introduces nonlinearities.  It all depends on how accurate you want your measurements to be.

Your observations are all good.  You are getting the feel for how you can play with the coil excitation voltage and the ON time for the excitation to literally "dial up" any final current for the coil you want.   Likewise you can "dial up" the discharge time through an LED + resistor or just a resistor by choosing whatever components you want for the load.   By playing with the inductance of the coil, the ON energizing time, and the ON drive voltage, and the nature of the load, you can dial up just about any type of pulse that you want.

For example, if someone said to you that a certain battery can be pulse charged from a coil, but the maximum initial current flow at the start of the pulse was one-half amp, you can design your pulse to do exactly that.

MileHigh

I agree, and that's what I'm refering to. Investigate the situation where there is no current flowing into coil, simply because coil is disconnected from power source and connected to the led.

[synchro1]

"The direction of *current* flow is opposite to the direction of *electron* flow".

"First of all, current doesn't flow. Charge flows. The conventional direction of the current is from + to -, and this direction can be the same as the direction of actual charge flow or the opposite, depending on the type of the charge carrier. As you know, the formula of definition for the electric current is I = dq/dt. Now, if we consider a conductor, in which the charge carrier is the electron which is a negative charge, the dq term will also be negative and so will be I in the direction of the electron flow. That's why the direction in which I will be positive is the opposite direction of actual electron flow, meaning that the electrons actually flow from - to +. If we consider a semiconductor, in which there are two charge carriers - the electron and the hole (which is a positive charge) - the electric current will be given by the flow of both (electrons and holes). While the direction of the actual electrons flow will be from - to +, the direction of actual holes flow will be from + to - (the same as the conventional current direction) because for the hole current the dq term is positive. So, yes, charge can flow from + to - and from - to + in the same time (for example in a PN junction) but the direction of the electric current is from + to -".