Corona and insulation Q

The one I most remember is the spark plug on the lawnmower.

That really hurt.

I remember getting across the ends of a TV power transformer, something like 700 volts at low impedance. I shook for a day afterwards. That could have been fatal.

I worked with two brothers, down in New Orleans. I designed automation gear, and the older brother died falling off an antanna tower on an oil rig, installing my stuff. The younger brother died about a year later, putting up a ham radio antenna, when it hit a power line.

You are an idiot.

You are a complete and total retard.

You ain't real bright, boy.

That is a DC pulse. A standing field on a transformer winding collapsing.

Same direction every shot.

No. It's a damped ringing oscillation, with an average value near zero. Get an oscilloscope and see for yourself. Or do the math.

You are AlwaysWrong.

You are always wrong, Jackie.

--

John Larkin Highland Technology Inc

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators

You calculate correctly. My design makes the whole 25KV stack affordable to a hobbyist.

I used to use that red corona dope when i was young and messing around with HV; very good stuff. Paraffin? Am surprised at that spec. And melting/burning is not a problem if sealed inside the Corotron(TM). Well worth considering because it is so cheep and available.

But what's it for? Fixing old TV sets? What else is a 25KV pseudo-zener useful for?

Yea, heard then seen those ultrafine holes being created - and once it starts, they grow and then carbonize and then zzzAAAaP! Well, that gets into the mystery of WHICH potting glop will do the job at a reasonable price. Too many out there for me to judge adequately.

How about a Teflon tube with 1/8" wall thickness? You might be able to use less thickness or shrink the boards. The problem with this might be the power dissipation. You've got to dump a few Watts, the old regulator tubes could handle the temp rise.

Jon

I always used 'General Cement Corona Dope' for HV work.

AKA: 'Canning Wax' at the supermarket.

NO, it isn't. Modern systems in CARS are electronically pulsed coils.. But a lawn mower was a 12V (design target) pulse, delivered by the permanent magnet dynamo, making a standing field on the coil from a charged capacitor being released by a set of points.

The collapsing field through a transformer (the coil) induces a huge spike on the secondary. The pulse is always in the same direction.

Try again, you know nothing dork.

It's not really suitable as a potting compound, but works well for coating exposed metal parts in a Hi-V circuit.

Sorry, I should have been more specific. I forgot that in some countries, paraffin also refers to gasoline, mineral oil, kerosene, and other hydrocarbon compounds. I'm suggesting you look into using solid paraffin wax.

Avoid the candle making, therapeutic, casting, etc variety and get the pure food grade wax using in canning. The others contain fragrances and additives that might cause complications.

I would be seriously concerned about melting and fire. If your device isn't sealed, the heat from the rectifier stack might melt the wax, which will make a mess on the PCB. This is common with overheated flyback transformers, which are often coated or potted in wax. Also, paraffin tends to be brittle, so you'll need some manner of outer coating to prevent cracking.

Rewaxing Flyback Transformer (23 mins, yawn...) He doesn't say what type of wax he's using, but from the photo of the block, it looks like beeswax from a toilet ring seal or a honey bee farm. I couldn't find anything on the dielectric strength of beeswax.

Put an oscilloscope probe near a spark plug wire. You'll see a damped ringing oscillation.

Most lawn mowers use magnetos. There's no 12 volts anywhere. They are not capacitive discharge systems.

Later colour TV sets used PD500/9ED4 style power triodes (25 kV, 35 W) as shunt regulators across the EHT line. I guess it might be easier to use such tubes instead of building 50 element semiconductor stacks.

Idiot. A collapsing standing field on a coil always looks like a single damped half wave pulse.

The "magneto" (dynamo is the term I used) generates the dc pulses. The design target for the dynamo output was 12V. The points capacitor stores the energy in DC form, and the coil releases it when the points open. That collapsing field generates ONE SINGLE PULSE in the coil secondary.

The crap you spew in here is a dumbed ringing oscillation.