Earl's Corner

[Earl]

My progress has been severely delayed due to computer failure and many days of rain with no Sun (I am off-grid, solar energy only).
Hopefully in a week or two I will be cooking at full speed.

I have received a sortiment of SMD resistors, so am in good shape for a 10:1 HF home-brew probe.

Earl

[Earl]

My new notebook is up and running, but it will take another 2 weeks surely before it is running to my satisfaction.  The seller didn't include the recovery disk so will see what happens when that arrives as the notebook was delivered with XP Home instead of XP Pro.  I may decide to leave it the way it is.  I first need to burn a HDD image to a DVD, but I'm not sure if it will fit on a DVD.  Don't want to go gung-ho on reinstalling software until I've got an image backup.  Can't even look at PDFs yet.  And worse I can't generate PDFs.

I've received some more various avalanche-rated diodes and transistors so will have enough to blow up for my sub-nanosecond HV pulse experiments.  I will need to build a transformer (DC/DC converter) to generate avalanche voltages and I had a bizarre idea.  When I was welding the shelve supports for the laboratory, I grabbed one of my NEO magnets to hold pieces in place in order to spot weld on the ends, then remove the magnet before it got too hot, then continue.  One time I forgot and noticed the (ex-)magnet sliding down the steel.  So now I have a NEO unmagnetized core; it went way over its Curie temperature.  I can't resist winding a transformer on this "just to see what happens".  Will measure the AL of this and an identical magnet, wind transformers on both and will see.  As far as I understand such a core contains mostly iron powder with small amounts of rare-earths pressed together under high pressure and maybe a very small amount of binding glue.  If the powder is fine enough, it should have good HF & pulse characteristics.

That's what's happening here, regards, Earl.

[Earl]

I had a lot of trouble trying to measure AL of my 10mm NEO cores.  Didn't have the proper size plastic to turn on the lathe, but finally got a coil form for the 10mm dia NEOs.  With 10 turns the air core had a L= 2.0 uH.  Didn't seem to make much difference whether NEO core was magnetized or not: L dropped !!!! to about 1.48 uH.  A steel tube raised the L slightly, but a 8 or 10mm threaded steel rod dropped it a bit.  A solid ALU 10mm rod dropped the inductance the most, down to 1.2 uH.  Used an L meter where a uprocessor most likely uses frequency of osc to measure either L or C.  At turn on it calibrates itself.

So I am very confused, nothing makes much sense.  I can try winding a lot more turns and see what happens - or take a CMOS gate and build a quick and dirty Collpits oscillator.  I know that a brass core can decrease inductance, and therefore maybe ALU also, but anything ferrous whether NEO, steel rod, or threaded stock should raise the inductance.  This did not happen.

I found a ferrite bar and have some steel or iron fence wire, so will continue testing tomorrow.  I am very puzzled.

Earl

[Earl]

Hi All,

Have had my lab time reduced due to bad weather and zero Sun for some days.  The Sun is now back and tomorrow will put another 4 solar panels up to boost my energy resources.

Used some more turns on the coil and found out that a NEO slug does not have extraordinary AL value compared to METGLASS or ferrite antenna rod.  It looks like I will be using a ferrite pot core to make the HV pulse transformer.  Would like to have the minimum turns as possible; e.g. just one single turn for a 12V primary winding.  Therefore a secondary with only 10 turns gives 120V out and 20 turns gives 240V out.  Will be starting off with the primary being driven by just a CMOS IC with AC coupling capacitors with a stroke of 12V.  If necessary, will migrate to a MOS driver, and if this is still too weak, then driver and power FET.  I don't need nor want much power since the secondary will only be zapping a diode or transistor with a HV pulse to cause the semiconductor to go into avalanche.  My idea is that by keeping pulse width down I can keep the number of transformer turns down while keeping current very low and core flux level also minimal.

To keep fall time from increasing too much, I suspect that an output resistor of 50 Ohms will have to be used.  I may try somewhat higher like 200 Ohms since this would give 4 times the output voltage.

Should have time to start soldering and testing this week.  I would like to have a HV sub-nanosec pulse generator as soon as possible.  Will see how difficult it is to cook this soup.

Earl

[Bob Boyce]

I can certainly relate to the no sun. I recently upgraded to a new OutBack GVFX 3648 inverter/charger and have only had 1 partial day of sun since. Best day since then was only 6 A/H into my battery bank from all day. Typically had ony 3 or 4 A/H per day since installing it. Figures huh? I have a set of 5 panels, 125W 12/24V nominal ea. Still in storage, for lack of a decent mount. During summer I can lay them out, but the rest of the year the shading is too high.

If current requirement is real low, can't you use some really fine wire in your ferrite pot core? This should allow you to keep drive requirements low.

Bob