Inductor current can't be suddenly cutoff if no freewheel diode is attached

What else is new? (:(

Just to be pedantic: Inductor current can't be suddenly cut off even with a freewheel diode. The purpose of the diode is to give a decaying inductor current a path when the driving source is suddenly cut off.

It is more than that. Free wheeling rectifier combinations such as bridges, allow more efficient charging of capacitors by efficiency while the capacitor has almost no charge. Diodes still dissipate some power. Remember, repetitive charging and discharge from a non-inductive dc source delivers V*I/2 while drawing power V*I. V is peak capacitor voltage while I is the average (dc) current.

My sarcastic point is that sudden changes in current in a conductor gives large voltages should be learned very early by anyone working with electrical circuits. I found that out early in life using dry cells and my mother's motorized mixer.

I also learned that by fooling around with a 6V dry cell and an old Ford ignition coil (the kind in a nice wooden box- ). It takes skill (or ignorance) to hold a wire in each hand and energize the primary but still get said hands across the secondary.

You may have also discovered that even the primary when the voltage was disconnected would give a good kick.

It does not take all that much skill to get a shock because you do not need to touch the secondary at all. I am not all that familiar with modern ignition systems, but when points were in vogue, all you had to do was pry apart closed points with your fingers to find out just how high primary voltage could go. After all, preventing point contact spark prevention was why a capacitor was used.

At one AIEE lecture I attended on the subject of electrical shock, I got an idea of how stupid a person can be. The lecturer said that someone wanted to see what kind of shock could be obtained from a 22.5V battery. He wet his hands with salt water before grasping wires to the battery. He managed to kill himself.

Ordinarily, the lecturer said, that death from dc came because of inductive kick (ventricular fibrillation) or just getting cooked.

At one time, I was using a photoflash battery (510V I think) to power a phototube. It was unpleasant to get across it but not truly terrible. Very occasional shocks like that didid not deter me from soldering to the battery's c contacts.

Voltage of 22.5 volts across a wet hand possibly could be felt but it would be lethal in a very, very, small percentage of cases. Ventricular fibrillation from a 22.5 volt shock to the hand would not be very likely.

I think I recall feeling a shock from a 90V B battery with dry hands. I certainly knew it when I went across a photoflash battery with dry hands.

Mt recollection of that lecture was that lecturer indicated how difficult it would be to die from a 22.5V battery. I vaguely remember that the "victim" may have been in a bathtub. Death was not from ventricular fibrillation. The lecturer was saying that inductive kicks from opening a dc circuit could set off ventricular fibrillation.

I think it would be safe to take a battery powered ohmmeter, such a Simpson meter, and measure your body resistance. I have done so. With wet skin. that resistance can be markedly low. Even dry skin can have low resistance after an electrical burn wets it. If you do such an experiment on yourself in a stupid, don't blame me if you wake up dead.

I think that you and Tom are right. My recollection of just where my hands were (other than one was on each lead from the battery) are nearly

70 years old. At that time it was just a box, obviously with electrical parts and I had a 12V battery and no knowledge of di/dt

There is your memory playing tricks on you again. 12 volts in a 6 volt world would be pretty unusual. :=)

You are right- the battery would have been of the mid-40's vintage. It was a fairly large dry cell (6"x9"x2") or thereabouts) ostensibly used for an electric fence power supply (problem here would be short life -so it could have been intended for something else-). The ignition coil was "OLD" -well potted in a wood box, "trembler coil" type. Did I risk fibrillation? -apparently not- some insulation as well as being bypassed by the battery itself -limited current and let-go wasn't a problem.

I am not an expert on this. My guess is that the high voltage output for an electric fence would come from such a high impedance source, that there would be insufficient energy in a pulse to do much harm. Do you know of animals killed by an electric fence? I have heard from a reliable source that cattle could be killed through a barbed wire fence from a lightning strike--but that is something else entirely.

Recently, I read a brief biography of Charles Kettering. I think he is the one who introduced the ignition point breaking system in the primary of an autotransformer. He probably also introduced a storage battery, starter, generator recharger, and self-starter into automobiles. I think, but do not know, that before that, dry cells were used for ignition. Also,I think that Ford coils ran continuously with a distributer. That should not be a hard thing to find out, but that is for another time.

Yes, as far as I know, the source was high impedance and was not continuous in that the pulse rate was slow -about 1/sec-so energy demands would be low. Direct experience with an electric fence- startling but not harmful pulses. That wasn't the case with the Ford coil- which was a different experience- one shot was enough.