Hi Bob, All,

I'm surprised about your Florida comments, I thought FL was sunny almost all the time.
I am going to separate computer, lab, and frig and put each on their own string.  I do have an emergency 1kW gasoline generator with load-controlled RPM, but I don't like to use it unless absolutely necessary.  My hot water is solar heated.  In Winter a bit more difficult, but I really try to be 100% solar.  It teaches one to conserve energy.  I won't change even if FE becomes available; don't like to waste.  My fridge has no side door, it opens on the top.  I have plans in my head for water-cooled fridge and freezer using Peltier elements and 8 cm thick insulation on all sides, but didn't have enough time this year to build them.

Since NEO powder makes such super magnets, I thought an unmagnetized NEO slug must by definition be very ferromagnetic.  I was surprised to find its lower A_L value.  Just for kicks I will also measure a ferrite ring magnet to see how it compares.

I am going to grab a pot core, which I should have in my junk box, and start winding.  Will start engineering from only gut feeling and change course depending on measurement results.  Most avalanche pulse generators use 2 to 4 pF (or a short coax stub) on the collector, charged through an R or L.  I am going to use no C, but instead the energy from a magnetic field.  It is my own idea; don't yet know how things will turn out.  Will write a detailed report on it, whether it works great or not.

Earl

Hi Earl,
   Just looking in. I have some circuits and simulations to add soon also. Looks like fastest transition times are achieved with IXDD414 driver and IRF820 for output. I just have to do some final experimental tests to confirm the latest designs and see if I can stop blowing driver chips.

You should also check out the IL710 isolator chip from www.nve.com  -- very fast (fastest availble) and does level shifting as well -- great for driving floating supplies.

cheers

mark.

@Mark, @All,

My present avenue is to "jump around" the usage of FET drivers and FETs.
In other words, go from a coil and switching element over to an avalanche breakdown.  Switching is at best in the lower nanoseconds or tens of nanoseconds.  By using avalanche breakdown, there is a possibility to drop to say 50 to 350 picoseconds and this in a real-world practical result.  IF and this is a big IF, I could generate sub-nanosecond pulses with amplitudes of say 100 to 400 Volts and IF these have phase stability without lots of jitter, then this would be a quantum step forward.  When a semiconductor is near breakdown, the electric field gradient is so high, that when an electron smashes into a neighboring atom, it knocks several electrons loose, which then proceed at high velocities to smash into other atoms.  It becomes a classical chain reaction and the semiconductor becomes a short circuit in a matter of picoseconds.  This is what I desire to master and harness in order to shock the environment.  I have decided it is worthwhile to pursue this route and will follow it until I decide that the results are not beneficial enough for the time invested - or until I have my beautiful pulses.  Since I want to admire a FE generator before the end of this year, I am going to force this with all my possibilities.  The desire is there, don't know whether a rendezvous with destiny is on the agenda though.

Earl

Earl @all

I think I am getting a handle on what thee minimum pulse time and rise times may be. I have done some simulations of the coils as transmission lines -- much more accurate and revealing than lumped analysis. In summary the results are:

Pulse width and amplitude: The primary outcome of varying pulse width and amplitude is to control the amount of power delivered into inductive load (straight wire or coil). The pulse width is varied such that the back EMF rises to the maximum permissable by the driving device. The longer the pulse width the more energy and the higher the BEMF. You dont want the shortest pulse width possible -- that yields to small a BEMF. You want just the right length pulse width to achieve maximum dv/dt and peak BEMF.

Pulse rise/fall time: The primary target here is fast enough such that the rise/fall time exceeds the capacity of the driven device to respond. When driving transmission lines there are maximum slew rates that are easily determined. A I show below for the particular device I am testing that looks to be 6ns transition time as an absolute minimum required... and faster wont help at all.


Practical considerations:

1. When driving very fast pulses into the sorts of loads we are considering (air cored and iorn powder core coils) the peak currents required to generate BEMF's of 500V or so are tiny - under 1 amp. This permits use of lower current mosfets which switch much faster then high current devices.
After a lot of looking around I chose the IRF820A -- this has simillar ratings to the IRF840 many people are using. The difference is that it's peak current capability is 8A but it is *very* fast and has only 360pf gate capacitance.

2. Drive the mosfet gate as hard as you can. The IRF 820A can take 30V gate drive. Even with only 360pf gate capacitance the limit to switching speed is peak current from the driver. I am using IXDD414 which can work up to 40V and deliver peak current of 15A -- I only need to drive at 22V to reach peak current limits. It is the peak current that is limiting speed -- you need very good bypassing on the driver supply. Faster switching speeds could be obtained with high gate drive voltage but would require going up to IXDD430 to deliver more gate current -- and analysis shows that we are probably far exceeding the shortest switching time required.



The simulations show that driving an IRF20 hard results in switching times 4x faster than IRF840 in our applications.
The simulations show that transition times are just below 1ns at the coil... however, we are limited to the rise time of the real world transmission line we are driving -- in the circut I am about to test the BEMF rises to 500V happens in about 25ns in the simulations -- a slew rate of 20V/ns !!

In the full simulation of the transmission line there is a full 6ns from the time the IRF840 switches of to the time the BEMF starts to rise. This sets a conservative maximum rise time of 6ns -- something that is not hard to achieve at all.

In the representative circuit I am about the test (lab experiment) the simulation shows that with a 44V high side supply (I am using 22V for the gate drive) a 600ns pulse into my 69uH coil will result in a BEMF peak of 450V 55ns after the IRF840 is turned off.


Although every circuit is different the guidelines are the same:
1. Drive a low gate capacitance mofset hard.
2. Start with a shor pulse width (50ns) and keep increacing it untill you reach a safe maximum BEMF.

This simple aproach maximises dv/dt and peak voltages while minimizing power input at the same time.


I'll post the sims and experimental results soon.

cheers

mark.

Mark @All

My present line of thinking is not to go with BEMF to generate the environment shocking potential.  Instead, I will use avalanching in semiconductors to produce the pulse directly by discharge of a HV-charged capacitor (or magnetically-stored energy).  Instead of using a coax stub as a capacitor, as some people use, I intend to use microwave-rated hi-Q ceramic chip capacitors.  For an idea of a home-brew avalanche pulse generator see:
http://www.holmea.demon.co.uk/Avalanche/Avalanche.htm

With an avalanche pulse generator, you are continually and repetitively "blowing up" the semiconductor, but it survives because the avalanche energy level is being controlled.

My first experiments will use a pulse-by-pulse HV generation with no rectification.  I will control the avalanche energy by means of pulse width.  Voltage will be set by means of turn ratio.  Thinking of using 2 independent secondaries to avalanche 2 semiconductors at the same time:  1 for one side of the parallel transmission line, the other connected with reverse polarity to the other side of the parallel transmission line.

Attached is a very preliminary idea.

Earl