Advice sought for self build 15kV 50Hz 150mW supply

[jonnie]

Hello,

I would be grateful for any shared wisdom regards a project to build a 15kV 50Hz 150mW supply?

Mains supply here is 230/240V 50Hz.

My only previous experience with high voltage was when I built a jacobs ladder device working off a 9V dry cell, I have a good Physics and general electrical background but not electronic or high voltage specialist.

I wish to investigate findings in a scientific paper that used a dielectric barrier corona discharge (DBCD) to create a hydrophobic (water hating) coating on glass the authors state that their supply was 50kV (max) but it seems that they were typically working at 15kV the authors detail a power output of only 150mW (50Hz).

I would very much like to use dry cell batteries as a power source for safety reasons, my understanding is that the current limited nature of such batteries would result in a similarly current limited high tension supply although my understanding is that larger capacitors or inductances in the mix would probably nullify this safety blanket.

So basically wish to build a cheap "relatively safe" current limited 15kV device at mains frequency 150mW.

My initial idea was....

12V dry Cell => 12 V DC to 240 V AC inverter => Neon Sign Transformer

Assumptions:

1. That the devices are able to function at my low amperage/power.
2. Safety feature of using dry cells is not totally nullified by the presence of any large inductors or caps.

I would be grateful if someone more knowledgeable or experienced can make suggestions, particularly on the relative "safety", tell me if my initial suggestion is horribly or dangerously naive and perhaps make more sensible suggestions.

Happy to post a link for the research paper if anyone is interested - didn't risk posting a link in my first posting here.

Thanks in advance....

Jonnie





 

[profdc9]

High voltage transformers for mains frequencies usually are large because they both need many turns and relatively large cores.  You could certainly use a neon sign transformer with a low current mains voltage input for this purpose.  However, modern neon sign power supplies are usually switched-mode power supplies, and so limiting the current to such as a supply would not have the intended effect, the power supply simply wouldn't function.  You would need to find an old neon sign transformer, but you can generally still find those being sold on e-bay, though they are becoming more scarce.

A television flyback transformer is a fairly decent alternative as well as inexpensive.  You wrap four or five turns around the primary of the flyback transformer, and then drive this with a MOSFET (such as a IRF540) turned on and off by a 555 timer oscillator.  This would be powered directly by 12 volts DC.    The flybacks usually have a built in high voltage diode which will produce DC high voltage, which may be needed for your experiment.  You could extra inductance in series with the primary if you wanted to limit current further.  The duty cycle or frequency of the oscillator can also control the output power to a limited extent.  Like the neon sign transformer, the flyback transformer is a source of high voltage and can be driven to produce dangerous amounts of current at high voltages, or can potentially charge capacitors with lethal amount of energy.  So this approach does not completely eliminate the risk, but can be used to generate high voltages with low currents.

Auto or motorcycle ignition coils can also work well too, but generally do not have built-in rectifiers.  Both flybacks and ignition coils can be bought easily on ebay.

[ritaismyconscience]

I second using a flyback as your supply. You can easily find stuff like this on google:
https://rimstar.org/science_electronics_projects/high_voltage_power_supply_w_flyback_transformer_builtin_diodes.htm
If its too much power you can always add a resistor to the output.

You can also buy a ready made HV module for a few dollars off ebay that run off 3.7V lithium battery. (They advertise numbers like 400000V but are actually around 15-20kV. There is also a capacitor inside so you should probably use a HV resistor to limit the current)

[Mads Barnkob]

If 50 Hz is an absolute priority, which I assume it is as many electrical properties change effect as frequency goes up. I think you should look into getting a neon sign transformer, iron core and then use a range of resistors to limit the current to the level you need and you could use a variac on the input side to vary the output voltage.
 

[jonnie]

If 50 Hz is an absolute priority, which I assume it is as many electrical properties change effect as frequency goes up. I think you should look into getting a neon sign transformer, iron core and then use a range of resistors to limit the current to the level you need and you could use a variac on the input side to vary the output voltage.

Hi Mads, thanks for the reply. Yes at this stage I believe a frequency of around 50hz is a priority although I am still gaining understanding of the principles involved in dielectric barrier corona discharge (DBCD) but for now it seems wise to try and follow the paper written by the researchers as closely as possible.

High voltage transformers for mains frequencies usually are large because they both need many turns and relatively large cores.  You could certainly use a neon sign transformer with a low current mains voltage input for this purpose.  However, modern neon sign power supplies are usually switched-mode power supplies, and so limiting the current to such as a supply would not have the intended effect, the power supply simply wouldn't function.  You would need to find an old neon sign transformer, but you can generally still find those being sold on e-bay, though they are becoming more scarce.

A television flyback transformer is a fairly decent alternative as well as inexpensive.  You wrap four or five turns around the primary of the flyback transformer, and then drive this with a MOSFET (such as a IRF540) turned on and off by a 555 timer oscillator.  This would be powered directly by 12 volts DC.    The flybacks usually have a built in high voltage diode which will produce DC high voltage, which may be needed for your experiment.  You could extra inductance in series with the primary if you wanted to limit current further.  The duty cycle or frequency of the oscillator can also control the output power to a limited extent.  Like the neon sign transformer, the flyback transformer is a source of high voltage and can be driven to produce dangerous amounts of current at high voltages, or can potentially charge capacitors with lethal amount of energy.  So this approach does not completely eliminate the risk, but can be used to generate high voltages with low currents.

Auto or motorcycle ignition coils can also work well too, but generally do not have built-in rectifiers.  Both flybacks and ignition coils can be bought easily on ebay.

Hi profdc9,

Thanks for the reply - I actually need the output to be AC, I am trying to follow the researchers experiment as closely as I can and they were using -20kV to +20kV output at 50Hz they describe their supply as a testing transformer. Would the flyback suggestion be applicable to AC output given an AC input derived from dry cells?

Kind regards
Jon

[ElectroXa]

(Sorry for late reply)

I have an idea: using capacitors to limit current on an Oil burner transformer
for example, use a 0.1uF to 1uF cap on input, with a discharge resistor, and/or a ceramic high voltage cap on the output side.

stay safe when using caps, always discharge them before handling, as they retain a charge that can be dangerous.