Its 230v
Good by quartz halogen bulbs, are we ready?
- Thread starter ericmark
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OK.
Fair enough.
Was it ever demonstrated that changing back to an axial type made a difference? As I said, I found it hard to believe that, with either type of lead arrangement, there would not be enough inductance to have a significant reactance at VLF.
Kind Regards, John
It isn't VLF ( Very Low Frequency ) that is the problem, it is the very fast rising and falling edges that the reactance prevents from entering the capacitance
Not as far as I am aware in the case I posted about. Some tests were made in the lab of a radio communications company and the inductive reactance was measured and it's effects were found to be less than significant when considering UHF sine waves inducing noise onto DC power PCB tracks and/or rack cables.
Fair enough, but if the design is such that such "very fast rising and falling edges" are a known component of the waveform, then there surely should be a capacitor of an appropriate type and value (in addition to the electrolytic 'smoothing' the VLF) (or, as below, a ferrite bead) to deal with that, shouldn't there?
From VLF to UHF is quite a conceptual jump ('sublime and ridiculous' come to mind) :- )
Are you suggesting that the "very fast rising and falling edges" (which you believe were fast enough for the leads of an electrolytic to have significant reactance) has faster rise/fall times than a UHF sine wave (when reactance was, you say, "less than significant")? In any event, if the answer were 'yes' (which I would doubt), then (a) would not other parts of the wiring/PCB track etc. have even more reactance than the electrolytic's leads, and (b) would not the answer be a ferrite bead or two, rather than a capacitor of any sort?
Kind Regards, John
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It is not the capacitors leads that contribute the majority of the inductance. It is the spiral wound foil electrodes in the capacitor.
In a radial capacitor there is one point of contact from each lead to the corresponding electrode so the length of the spiral forms a distributed inductor along the electrode. The current has to flow along the length of the foil
In an axial capacitor the entire length of the edges of the electrodes can be connected to the corresponding lead wire. The current only has to flow across the width of the electrode
In a radial capacitor there is one point of contact from each lead to the corresponding electrode so the length of the spiral forms a distributed inductor along the electrode. The current has to flow along the length of the foil
In an axial capacitor the entire length of the edges of the electrodes can be connected to the corresponding lead wire. The current only has to flow across the width of the electrode
If that's true, I don't see why it needs to be, since it would seem trivial to make both in essentially the same way. At the most, 'converting' an axial one to radial (i.e. both leads at same end) would require just a wire the length of the capacitor but, if it was in an aluminium 'can', one wouldn't even need the wire, since one could use the can as the conductor to the 'other lead'.
Having said that, anyone who relies on an electrolytic capacitor (of any type) to filter 'spikes' with rise times of the order seen in a sinuoisoidal UHF signal, they are probably rather daft - as I said, one would surely add a capacitor of appropriate type/value and/or a ferrite bead to achieve that?
Kind Regards, John
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