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  1. #21
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    Re: carbon arc modalities

    I doubt a typical LED driver could reach the striking voltage ( several kV - unless you touch the electrodes together and then unwind them a bit ) and then supply the 50A or so needed for a half decent arc...

    Any current limited 3kW 50A power supply can be used to make a carbon arc - the lads at work have done this with pencils ... ( graphite "lead" ) they do tend to catch on fire quite quickly due to the wood tho' - welding goggles needed.

    A very slight air flow past the arc ( usually vertically ) is helpful to carry away the gases and some heat ...

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    Re: carbon arc modalities

    Those 3kW 50A supplies are uncommon perhaps you have images of it in action with carbon electrodes?

    Its been well established the method to make arcs is contacting then separating the electrodes.

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  3. #23
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    Re: carbon arc modalities

    Its been well established the method to make arcs is contacting then separating the electrodes.
    I do not know the final application, but 3kW supply appears excessive. If you are happy with a small arc for experimental purposes, you can just use a 500W /1kW heater element in series (as a ballast) with the electrodes.

    If you are planning to use a 200W system, you should use 1mm leads (used for mechanical pencils). Also use a series ammeter to see the current. But the gap will be small and you need to manually adjust the gap continuously.

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    Re: carbon arc modalities

    A capacitor dropper series to the arc is better than a large ballast. Can be full wave rectified and filtered.

    But what high voltage constant current topology is most efficient?

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    Re: carbon arc modalities

    a capacitive dropper does not limit peak impulses drawn by the arc - a cap is a short to high freq impulses - this is why inductors are used - esp is a smooth steady arc is required ...

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    Re: carbon arc modalities

    Those impulses would be suppressed if the filter capacitor is large enough to supply most of the peak current.

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    Re: carbon arc modalities

    this is why inductors are used - esp is a smooth steady arc is required...
    If my memory serves me right, arc discharges are rarely stable or steady because of the negative dynamic resistance. For a really stable arc, you should use a well regulated constant current supply using DC.

    Arc lamps are used in many scientific instruments as a source of high intensity light and they are invariably powered by a DC constant current source.

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    Re: carbon arc modalities

    Quote Originally Posted by c_mitra View Post
    If my memory serves me right, arc discharges are rarely stable or steady because of the negative dynamic resistance. For a really stable arc, you should use a well regulated constant current supply using DC.

    Arc lamps are used in many scientific instruments as a source of high intensity light and they are invariably powered by a DC constant current source.
    How efficient are constant current sources powering the arcs?

  9. #29
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    Re: carbon arc modalities

    Most are high efficient switched mode power supplies.

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    Re: carbon arc modalities

    Whats the switching constant current topology which ideally suits the arc?

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    Re: carbon arc modalities

    Quote Originally Posted by Zak28 View Post
    Those 3kW 50A supplies are uncommon perhaps you have images of it in action with carbon electrodes?

    Its been well established the method to make arcs is contacting then separating the electrodes.
    I know with some types of welding equipment they use a high frequency arc stabilizer. This allows you to strike and maintain the arc without direct contact.

  12. #32
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    Re: carbon arc modalities

    Just about any toplogy can be controlled to be constant current - how 'bout a plain ol 20kHz full bridge switcher with a good sized o/p choke - don't even need to rectify if you don't want to ...

    By the way, do you have some science to support your original statement that constant current is no good for carbon arc?

    I would have said that constant current is the only way to power the arc ...

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  13. #33
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    Re: carbon arc modalities

    Quote Originally Posted by Easy peasy View Post
    Just about any toplogy can be controlled to be constant current - how 'bout a plain ol 20kHz full bridge switcher with a good sized o/p choke - don't even need to rectify if you don't want to ...

    By the way, do you have some science to support your original statement that constant current is no good for carbon arc?

    I would have said that constant current is the only way to power the arc ...
    What was meant by the claim constant current isn't ideal to sustain arcs is with linear constant current sources.

    I was simply going to employ fullwave rectified capacitor dropper with a lot of ganged high voltage MOSFETs driven by opamps with a shunt at their source terminal. But haven't found switching DC constant current sources which should be far more efficient.

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