Introduction: Build a Variable High Voltage Power Supply
I needed a variable 0 to 50KV high voltage power supply for my high voltage experiments that wouldn't break the bank, so I built my own.
With just a few parts from old microwave ovens, TV sets, and an oil burner, you can build an affordable instrument for whatever you wish to snap,crackle, or pop!
The key component is the voltage multiplier, which I covered in the High Voltage Multiplier instructable. Build it first, then drop it into this project for a variable output.
Step 1: Theory of Operation
The diagram shows the supply in the de-energized condition and the case closed.
Mains voltage is applied to the power supply thru a 120 VAC Panel connector. With the case closed, current passes through a 5 Amp fuse, F1 and through the case safety switch, S1 causing the Ready indicator, I1 to light when the power switch S2 is placed in the ON position to energize the supply.
At this time, the power supply is NOT ON but in a state of readiness to enegize the high voltage stage.
When pushbutton S3 is pressed, relay K1 energizes and remains energized after S3 is released.
Current passes through Variac, VT1 which adjusts the input voltage to the OBT. The OBT steps up the input voltage to a maximum of 6,000 VAC. The output of the OBT is fed to the high voltage multiplier, HVM where it is multiplied to 51,000 VDC output.
To de-energize the supply, place S2 in the OFF position. K1 will de-energize and remove power from the OBT and HVM and all indicators will extinguish.
The case safety switch and the power contactor are not necessary for this supply to work. I thought the ability to power on and off by using a pushbutton was cool. Thats all. The second schematic shows them removed.
Step 2: Gather the Parts
All the parts with the exception of the variac used for voltage control came from my junk collection or Ebay. Here's the list:
CHASSIS - Texas Instruments TI99 Computer case. Any metal box will do as long as there is enough room for the parts. An electrical box will do just fine. The computer case had a switch, an AC plug adaptor, and a removable lid so it was perfect.
F1 - 5 Amp fuse with holder (Radio Shack).
HVM - HV Multiplier - This is a build it yourself part made up of (6) 12KV High Voltage Diodes and (6) 470 picofarad 20KV High Voltage ceramic doorknob capacitors. You can buy all the parts on Ebay. I have already posted an instructable on this. Just search for High Voltage Multiplier.
I1 - READY Indicator - GREEN 120 volt Neon lamp (Radio Shack). An old 120 volt Neon indicator from a microwave oven is what I used here.
I2 - HV ON Indicator - RED 120 volt Neon lamp (Radio Shack).
K1 - Contactor - 120VAC 10 Amp DPST Relay with a 120VAC coil.
OBT - Oil Burner Transformer salvaged from an old oil burner from a mobile home rated at 120VAC @ 2.25 Amps on the input and 6Kv 20Ma on the output. The single pole type was used here. This can be purchased from a burner service company for about $65.00
S1 - SPST N.O. Cherry Microswitch for case safety.
S2 - DPST Toggle or rocker switch for power on.
S3 - SPST N.O. 120VAC Pushbutton switch.
VT1 - A variac was purchased for $60 from an electrical supply house. Any dimmer that can handle inductive loads up to 5 amps will work. The variac can control 2.5 amps. Just enough for the OBT.
MISC - You will need some wire lugs and various colors of wire scavenged from power cords for the internal wiring.
Step 3: Lay Out the Chassis
If your box has stuff in it, gut it. Take everything out of it except essential parts. I kept the power switch and the AC Adaptor. Everything else, GONE!
If your box has HANDSIZED holes in it, patch em. You don't want little ones (or a nosey neighbor) sticking their paw in the box with power on. Mine needed a cover for the back and a new face plate made of sheet aluminum. It would have cost me less to just use an electrical box instead.
Next, layout all the parts in the approximate locations shown giving yourself plenty of room for wiring. Space is essential in this project because we want to limit the possibility of arcing between high voltage components.
Drill holes where needed for mounting the parts and secure your parts using whatever hardware you have for working with sheet metal.
Step 4: Wire the Low Voltage Side
Decide if you are going to include a power contactor and case safety switch. If so, use the first schematic. If not, then use the second schematic.
Wire the supply starting with the AC connector, fuse holder, switches, variac and power contactor.
Test each stage of your build to make sure your wiring is correct.
Next wire up the OBT and test the range of the variac.
To test the output of the OBT, hold a GROUNDED screwdriver near the OBT output terminal.
If you see an arc, good. Power off the supply and disconnect it from Mains and move to the next step.
Step 5: Complete the Build
Depending on how you built your multiplier, you need to mount it to the chassis so it doesn't move around. In my case, I made a pair of homemade U shaped wooden mounts and glued the multiplier to the mounts using contact cement.
When dry, mount the multiplier in the chassis and wire it to the OBT and ground.
For the output, I passed the 50KV lead through the chassis using a 2 inch large rubber stopper as a grommet and some corona dope to prevent arcing. This worked until I passed the 35KV mark and then it arced over.
So I bought a screw on PVC plug and passed a 2 inch brass screw through the center, then filled it with 30 minute epoxy and let it cure.
I secured the feed through to the chassis with a piece of threaded PVC pipe to match. I then cut my 50KV lead to length and soldered it to the screw head on the back of my feed through.
I coated the whole assembly with corona dope, let it dry, and tried again. This time I succeeded and got to the 50KV mark at 100 percent without any arcing
Step 6: Power UP and Test It
*** WARNING ***
THESE NEXT STEPS ARE DANGEROUS.
Connect the power to the supply and turn on the main power switch. The "Ready" Indicator should light.
Set the voltage to 50 percent and press the HV ON pushbutton.
The HV ON Indicator will light and you will hear a slight hissing sound. This is okay. If you hear any snaps or arcing, determine where the problem is, shut off the supply, and dope the area. When it dries, test again.
With a grounded screw driver, bring the tip of the screw driver in close proximity to the output stud and watch for sparks.
*** WARNING ***
DO NOT TOUCH THE OUTPUT STUD WITH THE SCREWDRIVER. PERMANENT DAMAGE WILL RESULT.
If you are confident in your building skills, or hungry for sparks, SLOWLY ramp up the voltage to 100 percent and test again with the screwdriver.
Success will be indicated by the 2 inch long spark that you get from the supply.
*** WARNING ***
DO NOT ATTEMPT TO MEASURE THE OUTPUT OF THIS DEVICE WITHOUT SPECIAL TEST EQUIPMENT OR THE PROPER SAFETY EQUIPMENT.
*** DANGER DANGER DANGER DANGER DANGER DANGER ***
THE CURRENT PRODUCED BY THIS SUPPLY ALONG WITH THE HIGH VOLTAGE MAKES THIS DEVICE DANGEROUSLY LETHAL! DO NOT TOUCH THE HIGH VOLTAGE STUD DURING OPERATION. THIS THING WILL KILL YOU! GROUND THE STUD AFTER EACH SHUTDOWN TO DRAIN ANY REMAINING POTENTIAL.
Step 7: Safety Rules, and Disclaimer
ALWAYS wear rubber safety gloves and stand on a rubber safety mat when operating this supply.
ALWAYS wear protective goggles when power is on. Especially if you plan to power a laser with this unit.
NEVER touch anything or device that is connected to the supply while it is in operation without adequate protection.
NEVER defeat the safety switch on the case or operate this supply with the lid removed.
DISCONNECT the supply from power before opening or working on it.
FOCUS your attention on what you are doing with this device. Eliminate any distractions or annoyances in the area where you use this device.
DO NOT ALLOW others to operate or work in the same area of this device without adequate supervision or safety training.
REMEMBER, Smokey says, only YOU can prevent People Fires!
*** DISCLAIMER ***
You, the builder and user, bear the responsibility for your own safety in building, testing, and using this supply. By building this device, you acknowledge the risks involved in it's operation and accept those risks as a result. I will in no way be held responsible for your actions, including your death by this instrument and you accept these terms by building and using this device.