HV-isolated filament supply without transformer or battery

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Rich Feldman
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HV-isolated filament supply without transformer or battery

Post by Rich Feldman » Mon Jun 21, 2010 2:17 am

Just for fun, I thought I'd try a motor-generator with insulating drive shaft.
That method was used for HV DC power transmission starting in the 19th century (even then, more than 1 megawatt from series-connected, physically insulated HV generators).

First glimpse of calibration chart:
Verb Filament_voltage
----- -----
Stir 1.9
Whip 2.3
Blend 2.9

The blender speed control has more range when there's a significant mechanical load, and I wasn't equipped to put a fan on the drive shaft. So there's a 1-ohm shunt resistor across generator, as well as a 1.8-ohm R in series with x-ray tube filament.

This was an after-dinner project, but the upper shaft connection was inadequate & its design was changed the next day. No blender parts were damaged, but the cordless drill has made its last hole and driven its last screw.

The only cutting tool used to mount drill onto blender was a hacksaw. I love serendipity in mechanical fitting! With the drill's chuck and gearbox removed, the 2-piece body is a good fit around nominal 1-1/4" PVC pipe, augmented by 1 layer of electrical tape. A PVC coupling at the bottom perfectly fits the ID of blender jar's base gasket. A PVC adapter bushing has flange that snugly fits ID of the blender's jar's rubber lid.

Drive shaft is 9 inch length of 1/4 inch fiberglass rod, which is stiff enough to handle the maximum RPM without center support.
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David D Speck MD
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Re: HV-isolated filament supply without transformer or battery

Post by David D Speck MD » Mon Jun 21, 2010 3:12 am

The system works on a larger scale, too.

When I toured Fermilab last summer, I saw that in the antiproton source room, they used a 5 HP motor to spin a three story high vertical insulating shaft that drove a generator that supplies 120 VAC power for instrumentation inside the Faraday cage of the antiproton source. The source cage is driven at about 750 kV above ground as the first stage in the accelerator chain.

First photo shows the motor end of the chain on the chamber floor. The drive shaft is driven with a right angle drive and goes up through a hollow insulating support member visible as the center support leg in the second photo.

The third photo shows the generator as the gray vertical cylinder just to the left of the copper colored equipment rack, and behind the person in the photo. Sorry for the blurry shots, but we were moving fast and my old camera didn't have image stabilization. The hydrogen ions are generated at the left side of the chamber in the third photo.

Fantastic place!

Dave
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Steven Sesselmann
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Re: HV-isolated filament supply without transformer or battery

Post by Steven Sesselmann » Mon Jun 21, 2010 4:22 am

Rich,

Nice experiment..

I recall once upon a time doing the inverse, when we were baking a cake and we didn't have a blender on hand

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

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Chris Bradley
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Re: HV-isolated filament supply without transformer or battery

Post by Chris Bradley » Mon Jun 21, 2010 6:27 am

There was an age before silicon in which an inverter was a device consisting of a motor and generator, back-to-back. (And you got a much better sine purity out of them than silicon inverters, as well!!)

Jerry Biehler
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Re: HV-isolated filament supply without transformer or battery

Post by Jerry Biehler » Mon Jun 21, 2010 6:47 am

Those still exist to this day as power conditioners. Massive three phase motor spins a 3 phase alternator with a big flywheel between the two.

Something akin to that is a Ward-Leonard Drive or an Amplidyne. Monarch Machine used Ward Leonard Drives for infinite variable speed control in the 10EE series lathes. I had one in my 10EE but yanked it and replaced it with a brushless servo.

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Rich Feldman
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Re: HV-isolated filament supply without transformer or battery

Post by Rich Feldman » Fri Jul 16, 2010 3:10 pm

The Oster-drill kluge just served in my first x-ray dosimetry success.
Perhaps this belongs in the Radiation Measurement forum -- certainly when I follow up with numbers.

Previously I had run Coolidge tubes with anode voltages up to 11 kVp, cathode grounded, using half a NST. Characterized filament I/V curves and anode currents. It was easy to get qualitative and scary detection of x-rays with a Geiger counter, but their energy was apparently too small to measurably penetrate a pen dosimeter's ionization chamber (from the side or from either end).

The motor-generator set allowed me to run with full NST potential, about 22 kVp, with less additional trouble than setting up a battery. No resistors this time -- blender runs from a Variac, and is started with the rightmost button (Liquefy). HV is turned on momentarily from about 10 feet away, with the rocker switch on a power strip. My first shot with the pictured setup sent the dosimeter offscale (200 mR), so I had to dig out the charger.

This Coolidge tube has a thick cylindrical shield with 1/2 inch exit aperture. Here, the ends are crudely masked to block light from filament, in a successful effort to -see- the glow induced in a plastic scintillator rod. With the narrow aperture and point-blank range, I located the dosimeter's sensitive section, and confirmed that the system response is down at least 100x when anode voltage is halved.

Radiation safety measures include knowledge, instrumentation, shielding, distance, and short exposure time.
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