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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I have a 6kv and 12kv 1000pf ceramic capacitor. I can't find any mention on the datasheet how much current it can handle (peak and rms). I did find this information for a 1000v/1000pf mica capacitor (9A rms, 1500A peak). The only thing I found was a temperature range.
Does anyone know how much current a high voltage ceramic can handle?
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Typically this depends on the thickness and type of the metals used within the capacitor and the interconnects.
Normal failure mode for a ceramic capacitor is failure of either the dielectric (punch through) or the interconnects burn out completely because they are in one location. Capacitors are designed to spread the current over the entire edge using silver or palladium compounds but these do have a finite resistance so they will heat up under high dv/dt and eventually melt, normally fracturing the capacitor in the process.
A good way to test them is to apply a known load (i.e. run in series with an inductor and tune to resonance) and monitor the current into the system. If it begins to fluctuate or resonance is suddenly lost then chances are that the capacitor is running too close to failure.
Typically you would also want to use a high value resistor across the capacitor to limit the peak voltage but this can affect the results.
I have run into commercial products such as flat screen CCFL drivers where ceramic capacitors are placed in parallel to share current, this may be an option here if a single capacitor cannot take the load reliably.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
RF power ceramics should have a kVAr rating: you can calculate the RMS current rating from this.
If your capacitor doesn't, then it may be a DC block or laser pulse type, not intended for RF power at all. Usually these can handle a fair amount of power anyway, but their capacitance varies a lot with temperature. A resonant circuit built with one will retune as the cap heats up.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Steve McConner wrote ...
RF power ceramics should have a kVAr rating: you can calculate the RMS current rating from this.
If your capacitor doesn't, then it may be a DC block or laser pulse type, not intended for RF power at all. Usually these can handle a fair amount of power anyway, but their capacitance varies a lot with temperature. A resonant circuit built with one will retune as the cap heats up.
Meh, I've tried those Kvar-unrated doorknob caps in tank circuits before, they are completely useless. The losses are just so large that I couldn't even start an oscillation.
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Current handling for a ceramic
