Dear all hello,

this is my first appearance and question since I am a new in the electronics, and I need some help which I believe I can find here. I have a HV ignition transformer at 6kV, which I want to limit the current from 25mA which is now at 5mA. The reason is I want to have no arcs, just corona discharge. Any idea how to do it? By a resistor maybe?

Many thanks for your help

 

1.2 million ohms will limit the current to .005 amps. The difficulty is that the power could be as high as 30 watts on the resistor. It is difficult to find 1.2 million ohms in a 30 watt size, and the usual safety rule is to use a 60 watt resistor.

In addition, a single resistor will be so small that 6,000 volts will arc right across the outside of it. This calls for several resistors in series.

More likely to limit the current on the input side, but you're still looking at 30 watts of heat to get rid of.

 

If you have the option to change your circuit, a voltage multiplier is a good way to get a steady DC current at a high voltage, i.e., for a slow discharge to get a corona.

 

Many thanks, I know there are HV transformers that give 5mA max. I was wondering how they are doing that. Can a transformer be manufactured that is having a limitation in current?

 

Many thanks, I know there are HV transformers that give 5mA max. I was wondering how they are doing that. Can a transformer be manufactured that is having a limitation in current?

Yes...............................................
Another way to simulate the magnetic shut is series resistance or reactance in the primary. (if memory serves)

 

Yes.
Some are built with very tiny wires so the resistance and wasted heat is distributed throughout the windings. This is what is meant by, "impedance protected" which you often see on small motors.

 

HV transformers use magnetic shunts to limit primary magnetic flux that couples the secondary, which in turn limits output current. These shunts cannot typically be changed.

 

So the only way for my project is to find a special HV transformer which limits by construction the currnet at the secondary. Trying to modfiy one, by adding resistances or capacitors at the primary or secondary is waste of time?

 

So the only way for my project is to find a special HV transformer which limits by construction the currnet at the secondary. Trying to modfiy one, by adding resistances or capacitors at the primary or secondary is waste of time?

I wouldn't say that. I think like #12 mentioned, you could use some number of series resistors so you don't over power or over voltage them. A typical prototyping resistor is probably rated for 100V or 200V, so you would need quite a few in series.

 

Any idea where I can find such a transformer?
many thanks

 

Corona discharge comes from high voltage, so why do you want any current flow at all? Why not run the transformer with the secondary open?

 

just in case someone or something touches it to limit the current could flow

 

Find an old electrostatic plain-paper copier [ mita - savin - kyocera ] as salvage at an office store, a dedicated repair facility, or wherever you can locate one... There are a ton of other nice "toys" in the machines...

The copier, to place the image on paper for the toner to be attracted to, uses a specifically designed corona transformer, that puts up very near the voltage you need, some give you a choice of AC or DC with very small amps --
listed on the units anywhere from .01 mA to .08 mA .

I was going to say I have a couple available, until I noted you are in Greece... Shipping would be horrendous, as these units are around 5 -15 pounds Avior depending on source...

Good hunting... picture pending

 

So the only way for my project is to find a special HV transformer which limits by construction the currnet at the secondary. Trying to modfiy one, by adding resistances or capacitors at the primary or secondary is waste of time? ..........Not at all..........

Not at all difficult.

Here is some information.
Tesla builders do it all the time.

Search.........transformer current limit for tesla

http://www.richieburnett.co.uk/ballast.html

 

Many thanks to all of you. I have plenty of info to dig in, and start and hopefully complete my project. I will inform you at the end. it will take a couple of months I believe. great help, excellent forum.
Many thanks again