Barebones GE X-Ray Head Driver

It is possible to reliably drive most General Electric and Gendex X-Ray heads on the used hardware market via a relatively cheap and simple minimalist driver circuit.

Let us assume you understand safety with x-ray radiation and high voltages(65kv to 110kv), and that safety is your own responsibility.

Why is this useful knowledge?

Most OEM/proprietary controllers for medical/dental x-ray heads available on eBay and other resell marketplaces seem to have been damaged internally by unskilled users attempting repairs. It is much cheaper and less time consuming to build this minimalist circuit than to take the chance buying a used controller box. If you don't have the time and shipping money to try 2-5 orders on potentially broken controller units, building your own simple driver may be the only viable option for your project.

Common Specifications

Please do not assume these specifications apply to your X-Ray head model, they do vary, but the electrical specs and pinout for the GE1000 head are described by SiliconPr0n(Mcmaster). The labeling convention and abbreviations for the 6 terminals on an X-Ray head tend to be universal. What may change are the maximum and minimum acceptable voltage, current, and timing of the power supplied to the correct terminals.

Preparation

Materials

The materials used in my particular build were as follows:

-Scrap Wire

-A handful of 'acorn' wire couplings

-A scrap 10a breaker from a blow dryer cable in my parts boxes

-A 2-5 gallon(a few litres) bucket with a resealable lid.

-Table salt or baking soda (technically safer if you use baking soda, or another basic electrolyte)

-Water (technically better to use distilled. I used tap water, and may eventually have to recalibrate my waterload sooner than with distilled)

-2 wall AC lighting dimmer switches/dials. DO NOT USE DIGITALLY CONTROLLED DIMMERS, as they do not use resistance as the primary means of power drop / time, and do not cause an output that we want

-2 relays. Make sure they are rated at much higher than the target current draw if possible, mostly to account for mistakes calibrating the waterload and potentiometers. I used a few high current solid state relays (a 40a 240v max for the filament rail, and a 400v 120a model for the HV rail), but SSRs often fail to closed circuit. Feel free to try conventional/mechanical relays. If you calibrate the circuit incorrectly, it may chunk a relay or two before you have it dialed in. *You need the HV relay to be reactive enough to time exposure accurately. I expose my GE100 for only 3/100 of a second, and there is more than enough radiation to acquire detailed images through a test grating from any x-ray sensor I have tried

-Aluminum Tubing. I used maybe 3 ft of 3/4 inch x 1/16"(thickness) tubing from my parts boxes. It's just a convenient material for the electrodes in the waterload.

-A few bolts(and a handful of nuts and washers) suitable for making the terminals on the waterload

-A cheap microcontroller and some jumper wires. I used an Arduino Uno clone with the following overly simple script uplooaded from Arduino IDE(exposes on a timer on boot, roughly 12 seconds+ 2.5 seconds to warm the filament):

-Some would want a capacitor and/or varistor somewhere to buffer out any voltage spikes, but I have found that they aren't really an issue with a waterload. Don't blame me if you burn out your head here. Clearly some may see me as a reckless tool abuser. My x-ray head seems to be reliable without these protections.

Tools

- A vice, a 'vice-grips', or a hammer. (You need to flatten the ends of the aluminum tubing electrodes. this will also allow you to forego actually cutting the aluminum, because you can just break it off to length where flattened).

-A decent drill, and a drill bit(use a twist bit) compatible with the diameter of your bolts for the waterload terminals. You'll be drilling plastic and aluminum, so most conventional steel twist bits will work fine.

- A multimeter that can read AC Voltage, AC Current up to 10A, and Resistance. If you aren't careful, you will burn out the high(ish) current rail in your multimeter. I did, because I am not careful, and I use cheap multimeters for stuff like this.

- Screwdrivers

- Spanners(what you imagine when someone says the word, "wrench") to lock down the nuts and bolts you use on your waterload.

- Razor blades

- A wire stripper(optional, since you have razor blades)

- A medium or high temp glue gun(optional, if you have a high viscosity removable adhesive to use instead. wax would likely be fine). Used for locking the dials on the dimmers once they are set/calibrated.

-Insulative gloves. You absolutely need good gloves. Dry them before turning anything on if they get wet. duh.

Making the circuit

- Step 0) Adding a cheap resettable breaker:

The very first thing you need to do is provide some protection to the rest of your circuit. I do not have access to my own breaker box, because my landlord breaks fire code. To avoid having to email the landlord to reset the breaker, and have a 1-2 day delay any time that happens, I opted to use the 10 amp breaker from a blow dryer in my parts boxes that had already been gutted for the diodes and nichrome heating element. There is no need to open the casing - it is easy enough to simply cut the cable and it can act as the power cable too. Mine was already destroyed, so you may notice that mine has no housing and is coupled in.

- Step 1) Building the Waterload:

You could probably get away with a lot smaller dimensions, maybe even just some parallel wires sealed in a bottle, but I used the dimensions I chose to give myself more room for error when adding electrolyte to calibrate it in. I don't want to burn out an x-ray head just because something minor happens. Shipping costs suck on replacement x-ray heads!

Under most applied conditions, an electrolyte solution acts like a large resistor and can be treated as a resistor in circuit design. The way I will describe my waterload, there will be no significant voltage drop, but it will ballast current when connected in series with a load - not exactly how we would normally expect a big resistor to behave, right? You will likely find that it is not easy to get a waterload with specifications similar to mine to even yield a voltage drop.

Occasionally, I stick weld using a larger and different water load connected to a 240v 50a rail, that waterload DOES act as expected, with a voltage drop - I use a different set of dimensions, materials, and concentration of electrolyte for that.

Let's begin with the bucket. You will want to choose two locations for the terminals, above the future fill line. The electrodes will hang from the location of the terminals, down from the rim of the bucket. The approximate fill line, and the distance between your electrodes will matter, but the length of the electrodes, and the height and overall volume of the solution will be secondary. The surface area of the electrodes matters some, but as long as they aren't an extremity, the water load will likely be possible to calibrate to spec. I'll list my bucket's approximate dimensions below:

<----------------- Bucket, Electrode, and fill line dimensions here --------------------->

To make my terminals, I used cheap zinc coated steel machine screws, with a few nuts and flange/flat washers to lock everything down in the right spot, and act as spacers to hold the electrodes at the flattened tip. You will want to mark and drill the bucket with a hole diameter just large enough to feed the bolts through the hole for each terminal. You can use a small amount of waterproof adhesive on the washers mating to the plastic of the bucket, to seal the terminal, but I chose to simply cinch down the washers.

My terminals won't last forever(due to galvanization), but I might get a few years out of this waterload if lucky.

-Flatten your aluminum tubing to length, and then simply bend off excess until it snaps apart. it also makes an easy way to trim the length down if you make it too long. This is much easier with a pair of "vice-grips' and a vice(or another pair of vice-grips).

-Smack a pointed object, such as a nail or punch tool, into the flattened part of the tubing to mark the hole you will drill. Drill your hole, to the same diameter as the hole you made for the terminals in the bucket.

-Bolt your aluminum tubing into the terminal locations on the bucket, and add some wire. It needs to be tight enough to conduct electricity well, or it will introduce inconsistent variables to your circuit.

-If you used adhesive and it has cured, you can now fill your bucket to a fill line that corresponds to the total length of electrode that approximately matches mine. It does not have to be a precise length match with mine, but within 1/2 inch or less would be prudent.

-At this point, it would be prudent to dissolve several tablespoons/grams of tablesalt or baking soda into a glass of hot water. You want it to be dissolved when you test current spec, and predissolving will save a lot of time. Consistency is key here, because a solution with undissolved electrolyte will be less conductive than when it is further dissolved.

Since your bucket has a large volume in relation to the glass of hot salt/baking soda water, you need not cool it to room temperature before adding.

-Time to clean up your area, make sure nothing outside the bucket has any moisture, especially yourself and the floor, and put on your gloves.

Make sure your bucket is difficult to spill, but breathes if under pressure, as it will produce Hydrogen and Oxygen gas if you use saltwater as the electrolyte. Be safe accordingly. This is mostly only relevant when you are calibrating it in. I simply left the lid off during calibration, and did it in an area with ventilation and no open flame. I suspect that not enough hydrogen or oxygen is produced per time to actually pose a serious danger unless it collects on your ceiling, or the circuit is left running for a long time. Once calibrated, you are only running it for a small fraction of a second at a time, to operate the high voltage rail to the x-ray head. I test a lot of different hardware with it(safely from another area of the building), and might need to vent mine once every month.