Build a Variable High Voltage Power Supply

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.

Comments

[Machine]

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.

[wespow1]

i cant seem to get the image up so i'll give you a URL to the burner http://www.ebay.com/itm/OIL-BURNER-TRANSFORMER-110-HIGH-VOLTAGE-10-000-WEIL-MCLAIN-GOLD-BURNER-BASE-NEW-/120811839341?pt=LH_DefaultDomain_0&hash=item1c20f25f6d#ht_1543wt_1163

[wespow1]

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

[aweis]

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]

Aweis,
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.


http://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator


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

http://www.allaboutcircuits.com/vol_3/chpt_3/8.html


Good luck in your build.

RA

[Moo_cow]

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]

Moo_cow

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.

RA

[ewpwrqlty]

I only need a 100-700 VAC variable supply. Can I modify your design to achieve this goal?

[burningsuntech]

Possibly.

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?"

RA

[ewpwrqlty]

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]

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.
RA

[burningsuntech]

ewpwrqlty
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.
RA

[CharlesBarret]

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]

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