It's 1:35 AM and I am just now getting some time to myself to work on this a bit. Checking in, as it were, here first. See that I have missed quite a bit over the last day or so.
Glen, on the glass, make sure you allow for the thermal expansion, it will get hot fast and if the thermal conduction is too low you will get uneven expansion leading to fractures which lead to breaks in the thermal conduction which destroys the test in short order. The wire and the glass and the adhesive need to 'grow' together as much as possible during the expansion. Separate growth rates lead to problems unless expansion material is included.
Aaron, the 10K 10-turn pots from Radio Shack could be used by padding either side of them with 22K resistors as needed, or removed entirely if the desired resistance is below 10K. This gives a much better resolution of 1K per turn rather than 5K per turn but does require a course tuning by fixed resistance. I did see some 50K 10-turn trim pots online - could have been at Quest, don't recall. But a dual pot setup could be used also, for course and fine adjustment.
.99, getting a good battery model in spice would be a worthwhile endeavor. The voltage or current sources supplied generally don't allow changes in the source. Some sort of conditioner between the source and the circuit may be the ticket. Perhaps a series diode, resistor, and inductor feeding in and out of a rather large filter cap to simulate the battery impedence for the 140K - 250K frequency range. This would then allow the back EMF to recharge the cap similar to what we see in the real life battery. I don't know if we are going to be able to get the simulator to self trigger and produce the Hartley type oscillations. I tried a variety of approaches including capacitive feed back to the gate etc. with no joy. It is possible that we are inflecting the 555 ground circuit badly enough that the negative rail for the 555 is above the off threshold for the gate - hard to tell. Putting an inductor between the 555 ground pin and the simulator ground source may allow the similator to do that. I am only thinking out loud here as we have not yet conclusively determined from where the oscillation originates from.
Rosemary,
Power that is sent back to the grid is done with phase transformers or synchronized inverters. When the extra energy is present on the line it will flow to where the demand is, either local or back past the meter into the grid. The meter may or may not react to a back flow of power. Here in the states, the meters will run backwards and deduct from the readings. Our local energy companies will not buy the energy back, but they will extend credit against future energy use. The spikes in this circuit are very narrow but there are a lot of them during the oscillation periods. How much power they contain is still a matter of the calculations. Classically, they will not contain any energy that wasn't already provided. A pure inductor will return 100% of the power provided to it - they don't exist. This is why inductive components are not rated in watts, but instead they are rated in Volt/Amps. A watt infers that power has been dissipated whereas a Volt/Amp infers that power has been moved. The inductive portion of your load resistor tends to work in that way, attempting to return the energy, that is the ringing. When current flows through an inductor, it builds the magnetic field until it is saturated and can build no more, at that point the current flows through as if it were just a wire. When the current stops flowing through, the field attempts to keep it going by collapsing in on the wire. If there is a path, then current will flow until the field is fully collapsed. But when there is no path for the current to flow, all that energy is converted to voltage across the terminals of the inductor. Theoretically, the field is infinite and the voltage is infinite, but since a perfect inductor does not exist, neither is true, but the voltage will be quite high. This high, very transitory voltage has and electrochemical reaction in the battery. For a brief instant, the battery post will be at that potential and free electrons in the acid will accumulate at the positive terminal internally, but when the voltage collapses, those electrons are pushed away toward the negative terminal. This rapid back and forth disturbance in the chemicals can encourage other electrons to become free and accumulate at the negative terminal in a condition known as 'overcharging' where we get a larger charge than would normally be possible from the chemical reactions alone. This would be a true usable and persistent charge. Another effect that can occur is where the energy never actually affects the acid. Instead, the battery post acts as an ion collector and only the surfaces of those nearby plates and post material have a static charge on them. The charge has no depth in this case and is easily depleted - this is the 'fluff' that has been hashed about of late. Either condition could be true in your circuit - it really depends on the dynamics of the battery and the resonance of that portion of the circuit.
Bleagh - after several interruptions, it is now 2:40A and I am exhausted - the construction will have to wait till tomorrow.
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