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Make an inductance coil
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quentief:
Hi everyone,

Thank you for all your replies. I just would like to precise that I am using the MOT as a coil, I do not use its secondary to make high voltage. To be honest, I prefer to stay at 230 volts for the moment. Despite the risks, I assume this voltage is safer than the 2000 or more volts produced by a high voltage transformer.

The aim of the coil used in my setup is to make a high-voltage spike when I spread the electrodes, to start an arc. Furthermore, the inductance is used to smooth the current and to stabilize the arc. According to my tests, the primary coil of the MOT (again, used as a simple coil) has made very good results. I am not sure about its inductance but by considering the nominal voltage, the frequency of the line and the no load power consumption of the transformer, I have estimate an inductance of about 900 mH.

I am now trying to replace this transformer, and I would like to design a coil in that respect. I have made some researches about inductances with iron core but I do not know how to calculate the maximum current before the saturation of the core. I have already read that air gap was used to avoid saturation but I do not know how that works, neither how I can size a gap in that respect.

I hope I have not make any mistakes this time, and made my explanations more clear. Please, let me know if some of my sentences are not clear, I have to improve my English, comme vous l'avez fait en Français Jonpaul :)
jonpaul:
Bonjour encore Monsieur! Alors, j'ai plus des questions, votre project:

1/ Arc is in air or gas or an arc lamp?

2/ Carbon arcs like cinema projector?

notes:

3/ MOT will have 2kV on sec even if that is not used, beware.

4/ Most air arcs with carbon or metal electrodes do not need any HV to start, the electrodes are touched momentarily and then gaped open

5/ Any current limiter will work, even a big power resistor.

6/ if are is in arc lamp eg Xenon or metal halide a different type of HV ignitor is used.

7/ All arcs emit powerful and invisible ultraviolet light, capable of corneal or retinal damage, use welders mask and goggles to protect eyesight!

8/ Metal or carbon electrode arcs in air cause nitrogen to react and produce noxious compounds, as a gas or fine particles. Professional applications must use a hood, duct with fan to exhaust the fumes, eg cinema projectors. Beware the smoke of the arcs!



Nous pouvons contacter a Paris quelquefois, habitez-vous a Troys?

Bon journée; Jon
quentief:
Bonjour Monsieur

1/ The arc is produced through the air, between two iron electrodes (two nails)

2/ No, I am trying to establish electric arcs between metal parts. I know it is easier to establish electric arcs between carbon electrodes (I have already tried), but I want to understand how electric arcs can be made between metal parts.

3/ I used a modified MOT : I replace its secondary to make a spot welder (the voltage is around 2 volts), so don't worry about that

4/ Well according to my tries, when the electrodes are made in metal, a coil is needed to make an electric arc. I don't know if that is because a high-voltage spike is needed to start an arc, or because the current needs to be smoothed, or maybe both, but without a coil with an inductance enough strong, that doesn't work.

5/ An electric kettle is used as a power resistance, the R.M.S. current is limited to 10 Amps.

6/ No discharged lamp devices is used in my setup.

7/ UV glasses are used at ever attempts.

8/ Every attempts is done at the outside.

Je suis à Troyes et je suis désolé mais je n'ai pas la possibilité de me déplacer jusqu'à Paris pour l'instant. Mais nous pouvons correspondre par mail si vous le souhaitez.
chris_leyson:
Maybe you could use something similar to an arc welder ignition transformer.
EDIT: https://patentimages.storage.googleapis.com/ea/c6/5d/70433111f93ace/US6156999.pdf gives a little background information on arc welder ignition transformers
quentief:
For the moment, I just just want to know more about inductances, and the saturation phenomenon. I would like to know how I can size an iron core inductance, and especially how I can size a air gap to avoid the saturation phenomenon. I cannot find any information on this subject on the Internet.
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