Picture of Build a Variable High Voltage Power Supply

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.
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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.
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Will this be able to drop the voltage on the load (virtually) instantaneously to zero, or will there be some drain time? I need the load to ramp to high voltage and then cut to zero for testing purposes.

There'll always be drain time, I think what you need to add is thyratron and another transformer to instantaneously cut the voltage to zero.

miicchhii12 months ago
"Multiplier for raising the 6000 volt to 50000 volt at the same current"?
So you get more power out, than you put in or am i getting something wrong?
jpayton1 year ago
What is the output current of this?
My load has very high impedance so I need virtually no current (<< 1 mA) but I would like to reduce the ripple on the output so it is negligible.  A simple RC low-pass filter with a resistor and a capacitor in series across the original output should do the trick. I don't want to have to find a 100 kV cap so I'll just join a few 20 kV caps in series to create a cap unit that will handle the voltage. My new + output will come from the junction of the resistor and the + end of the caps (the low-pass filter output).

Member Machine mentioned earlier that a front panel meter would be nice and I agree. He had some concerns about using a voltage divider so the meter could work with some reasonable voltage like 0 to 10 V instead of 0 to 50 kV. I've done the resistor voltage divider thing successfully at 50 kV using a 5000:1 voltage divider. I then connected the divided voltage output to an analog DC voltmeter calibrated to 0 - 10 V.

One final comment.  I plan to use a 3PDT relay for K1 so the third pole can be used to discharge the HV output through an appropriately sized current limiting resistor.  I plan to connect the HV output to one end of the resistor and the other end of the resistor to the common of the third pole on K1.  The NC contact of the third pole goes to ground.  Whenever K1 is not energized, the HV output is routed to ground through the current limiting resistor.

Do you see any problems with any of the above enhancement assuming I use appropriately rated components and good HV insulation practice?
corbonzo1 year ago
Sorry if this is a stupid thing to ask.but i dont have money for a variac, i was wondering if a 120vac light dimmer used in houses would work. it says rated for 600 watts which would mean 5 amps right? sooo would that work? a reply would be great!
prini1 year ago
oh ok thank you for answering me,alls i needed was a power supply that could power a minimum of 400 amps
burningsuntech (author) 1 year ago
This device is for sale. If you would like further details, please contact me at
prini1 year ago
is this really strong ? would this say power a house? im looking for a very strong power supply for somthing im building wich requires as much power as a house maybe more lol
burningsuntech (author)  prini1 year ago
This is a HIGH VOLTAGE power supply and cannot be used to power a house which is low voltage (120 volts AC). This is also a low current supply (20 milliamps) and a house requires high current (200 Amps). So, no. This will not suit your needs.
Hey, I'm looking for something on the scale of 50kv 10 milliamps. would i be able to adjust or modify this to get 10 milliamps? any help would be appreciated
luismasino2 years ago
Hi, I am needing to build a project of the variable power source 0-40kV can walk, I need if I you can send information to build the source as you did, since I can not download the pdf, you made me the source would come very well. please if you can send me information on the value of the component and the names and designing things. any information will be very welcome
thank you very much
Machine2 years ago
I like the quality internal layout, it looks professionally done. A meter on the front panel could be good.

It'd be hard to measure directly the output volts as a high-voltage divider would be needed (more cost, insulation difficulties).

So a meter calibrated in kV but measuring the output volts at VT1 would be an easier method to indicate final voltage.

wespow12 years ago
i cant seem to get the image up so i'll give you a URL to the burner
wespow12 years ago
Hello i was wondering if a OIL BURNER TRANSFORMER 110 HIGH VOLTAGE 10,000 WEIL MCLAIN GOLD BURNER BASE NEW would work here is a images of the burner
Is this -50kv or +50kv?
+50kv i think
If you connect the leads reverse it will be -50 as well
Yes it will be -50 wrt the other lead but not -50 wrt earth ground.

How can you make it -50 wrt earth ground? This will allow it to be used as a negative ion generator.
weldor2 years ago
I have a sneaking suspicion that this could be turned into some sort of a welding device (TIG or Spot). Possibly a device that was both CC and CV capable. Possibly ac/dc with cc/cv for the TIG and some sort of variable control for the spot welder too. all of the above could be assembled in one unit.

Automatic trans fluid is supposed to work well and it has an operating temp of well over 100 deg F.

An aluminum housing with heat sink fins (or even tubes) with air being circulated over/ through them. H2O running through external copper tubes and then into a heat exchanger (auto heater core or ac condenser) would improve your coolin effect also. This could lead to more efficient over all operation. (water cooled TIG torch??)

Great Instructable!!!! please keep it up.
ifrit2 years ago
will there be enuff power in this powerbox to serge my invisability cloak and will there be enuff power in this box to channel me for teleport and download me at any power source ?
infinity112 years ago
Is this a positive currant you are producing and if it is how could I make it negative.
aweis3 years ago
if i only want a killavolt (1000 volts) from a 70 volt alternating current generator, would i be able to do that for around 50 dollars?
burningsuntech (author)  aweis3 years ago
Possibly. As to specifics, I can't say. Most likely, you will be using 1N4007 diodes for the diodes. And caps will be .001ufd 2 KV minimum, but any voltage up to 10Kv will be fine.

There has been a lot of questions concerning the math I used to figure out the voltages. So I will refer you to the link that I found concerning Cockroft-Walton Voltage Multipliers.

And here is a blurb about the output voltage characteristics of the multiplier:

Good luck in your build.

Moo_cow3 years ago
If I were to take out the multiplier, would if work for 0-6000 volts?
Wanting to use this for part of my science fair but I do not need to go over 6000 volts.
burningsuntech (author)  Moo_cow3 years ago

If you only want 0 to 6000 volts AC, then the answer is yes.

If you need 0 to 6000 volts DC, then you must add a single 12KV Diode to the output of the transformer.

Good Luck in the science fair.

ewpwrqlty3 years ago
I only need a 100-700 VAC variable supply. Can I modify your design to achieve this goal?
burningsuntech (author)  ewpwrqlty3 years ago

without knowing details like how much current you want the device to provide and at what voltages, I wont be able to help.

More info is needed besides "can I modify your design to achieve this goal?"

Thanks for your quick response.

The device does not need to provide any current. I only need to provide variable voltage potentials between 100-700 VAC. I am attempting to create a voltage calibration set for my BMI 8800 power disturbance analyzers.

The required voltage (Vrms) calibration levels are:

1. 0
2. 7.6-8.4
3. 30.2-33.4
4. 75.5-83.5
5. 150-170
6. 200-225
7. 300-335
8. 604-670

I am using a 0-140VAC Variac to produce the first four levels.

I tried using a hipot tester to produce the last four levels and was successful up to level 8. The hipot unit that I own is a Hiptronics HD5 0-5KV at 5 mA.
The impedance of the BMI voltage input channels during calibration is 1.01 Megga Ohm. At approximately 500 VAC the leakage current light was glowing and the unit was vibrating and ready to fail on leakage. My Hipot tester would need to have at least a 20 mA output capability in order to complete the calibration series
burningsuntech (author)  ewpwrqlty3 years ago
On second thought... You would need a 0 to 800 volt Transformer and use the variac to supply the variable voltage to it.

With a vernier dial on the Variac, you would have a calibrated settings range. If you need finer settings, say in millivolts, you would need a twenty-five turn vernier instead of a ten turn vernier.

Hope this helps.
burningsuntech (author)  ewpwrqlty3 years ago
You could use a switch to select one of two ranges. The first range would be what is supplied by the Variac. The second range would be addition of another step-up transformer connected to the output of the variac.

With a Vernier knob attached to the variac and a volt meter, of course, you could tune the output of the step-up transformer to the appropriate ranges based on where the vernier is set.

That would give you your ranges and the desired voltages though it might be a bit cumbersome.

One other possibility would be to calculate the output of a transformer given the input voltage and the number of turns on the output. If you are adventurous enough, you could design and wind your own transformer for the desired output ranges beyond the output of the variac and use a selector switch to select the output tap for the given range you desire.

It takes some doing and a bit of knowledge of transformers but it can be done.

Lastly, you could also have a special transformer built for this purpose which would give you all the ranges based upon which tap you choose.

There are other methods but I do not build devices for people nor do I have the time for these projects as i am currently busy running a business.

Good luck. i hope this helps.
ewpwrqlty3 years ago
I need to build a variable AC power source from 0-700 Vrms for calibrating my BMI 8800 power disturbance analyzers. There are 8 voltage ranges that the power source needs to provide: 0 Vrms, 7.6-8.4 Vrms, 15.1-16.7Vrms, 30.2-33.4 Vrms, 75.5-83.5 Vrms, 150-170 Vrms, 200-225 Vrms, 300-335 Vrms, and 604-670 Vrms.

Hi, i think that your source cannot supply that much current (20milis) because that depends on your load resistance.. mmm how do you know you can hold that much current in your design? thx..
burningsuntech (author)  CharlesBarret4 years ago
CharlesBarret Technically true. The problem is with the type of transformer used in this supply. The specs of the OBT state that it will supply .02 Amps at 6000 volts. This transformer does have a load in the form of an air gap approximately 1 cm in length. With the resistivity of air equal to anywhere from 10^8 to 10^9 ohms per meter then resistivity of a one cm gap is 10^6 to 10^7 ohms. This assumes that the air has not ionized. (which is the point of an OBT anyway). After ionization of the air, the conductivity increases dramatically to the point of a near short circuit. To prevent that from becoming a dead short, there are current limiting windings built into the transformer to limit maximum draw to 20 ma. So, the maximum draw from this device is limited to 20 ma. But if there is a resistive load placed on this supply, it will be somewhat less based on Ohms law. Hope that explains the specification. Thanks for the question. RA
silicacat64 years ago
Would you please assemble and sell me a high voltage DC power source? Input either 24 V DC or 220VAC, your choice. (I would prefer to use 24V DC input). The max voltage required ~900V and max current 5A. Name your price, and have a guess at when you could deliver. Thanks
skeric174 years ago
hello i was wondering if u could please give me a few pointer on making a 0-12v variable power supply i dont know where to begin thanks for ur time and help=]
burningsuntech (author)  skeric174 years ago
I can point you in the direction of either the internet or Radio Shack engineering booklets which would have circuits that would work for you. Do a Google Search for 12volt power supply schematic. There is tons of them out there. Good luck with your project. RA
simondodd4 years ago
Great job!! I am thinking of building this with myNST and using it for my Tesla Coil.  However all the plans I have seen for Tesla coils require both the hot and cold output from the NST. Would this be the HV output and the case/ground or would I have to wire it up slightly differently?

Thanks in advance

Hi, very nice idea, five stars!
I don't have an six KV Oil Burner Transformer, but I do have a five KV Neon Sign Transformer. Would that work just as well?
Yes it will.  In fact even AC (mains) passed thru a standard transformer (ie 120VAC in and 120VAC out) will give you a high voltage based on the formula in the multiplier design.  Thanks for the 5 STARs.  enjoy the build.

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