What does "current limited" mean?

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jlheidecker
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What does "current limited" mean?

Post by jlheidecker » Wed Sep 24, 2003 11:08 pm

Why must I output a certain amount of current from my supply before
I can increase the voltage? Why can't I set it to 1 mA, and then get
20 kV out?

Thanks,
Jason H

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Frank Sanns
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Re: What does "current limited" mean?

Post by Frank Sanns » Thu Sep 25, 2003 4:27 pm

The resistance of your fusor depends on pressure (and the type of gas in it). At any given pressure and gas, you will have a particular resistance. Since voltage divided by current equals the resistance(V/I=R), then for any given pressure, there will be a unique resistance between the inner and outer grid. That means there will be one and only one ratio of Voltage to Current at a given pressure.

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Richard Hull
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Re: What does "current limited" mean?

Post by Richard Hull » Thu Sep 25, 2003 5:24 pm

In any current limited and current settable supply, once you dial in a current, let us say, 2ma and attach a load, then you may advance the voltage up to the point where the 2ma is reached and from that point, BY DESIGN, the supply will never advance the voltage farther. THAT IS WHY THEY CALL IT CURRENT LIMITING. Continuing to advance the voltage would try and draw more current than you set it up for and that is not allowed, so the voltage ceases to rise even if you twist the voltage knob off to max.

If your supply is rated up to 10ma max output and you set the current for max, (10ma), then when 10 ma is reached by turning up the voltage then, again, the voltage ceases to move higher. You have exceeded the design limits of the entire supply even though you never got close to the rated maximum voltage. Your load attached to the supply output terminals is just too much for it to handle.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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