Hi Dimitrios, yes those should do the job. I suppose that you need a
situation with paralleled caps where any one can carry the peak current. It
is probably a bit marginal if you really have to rely on current sharing in
this situation. I used up to 3 in parallel in the C2 position without
problems....I seem to remember the peak current was about 15 amp. I did a
simulation usig a switch mode power supply model.
Good Luck with it.
Alan
G3NYK
----- Original Message -----
From: "Dimitrios Tsifakis" <[email protected]>
To: <[email protected]>
Sent: Thursday, August 09, 2012 1:34 AM
Subject: Re: LF: Re: Caps for Class-E amp
Hi Alan,
thanks for the tip, I will keep an eye open for RIFA PHE428 or PHE450
which seems to be the newer version of that capacitor type.
In my PA, I used two .1 uF caps in series to make .05 uF, then three
of these in parallel to make .15 uF hoping that the currents will be
distributed, however I think, once one of them gave up the ghost, the
others immediatelly followed suit, so I ended up with one in every
two-in-series capacitor being busted.
By the way, that self-healing effect is quite useful if you ever want
to create a bunch of lower value caps with non standard values :-) I
now have a77 nF, 45 nF, 16 nF and even a 0.3 nF out of my .1 caps! I
am kidding of course. :-)
73, Dimitris VK1SV
2012/8/9 Alan Melia <[email protected]>:
Hi Demitris, I am not sure of the types codes but I used 1000v or greater
rating, the problem often is that the caps are not rated for high pulse
currents. The best kind of caps that are used are rated for pulse
operation
in switch-mode power supply. Normal caps will not take the current
pulses.....the individual plates get disconnected from the lead wires.
One of the caps I used has come to hand its a RIFA PHE428 rated 2000v. I
used this on 36v Class E running about 300W. I believe WIMA make similar
caps but I am not sure of their type numbers.
Alan
G3NYK
----- Original Message ----- From: "Dimitrios Tsifakis"
<[email protected]>
To: <[email protected]>
Sent: Wednesday, August 08, 2012 11:03 PM
Subject: LF: Caps for Class-E amp
Hello LF group,
I am building a 200 W Class-E transmitter for LF but keep killing the
capacitors in the output circuit (both C1 and C2 according to the
schematic in Sokal's QST article). I have used a mixture WIMA
polypropylene MKP10, MKP4 and FKP1 caps and I haven't damaged any FKP
ones so far. Should I not bother with MKP and use only FKP caps or is
there any other type of capacitor what will do the job? I need a
couple of hundred of nanofarads. The voltage rating of the caps I
destroyed was 400 VDC or 250 VAC. I can see that these caps have a
decreasing AC rating as the frequency goes up, but that's what I had
in the junk box at the time...
The mode of failure of these MKP10 0.1 400 VDC caps is interesting
too, they seem to go down in capacitance as the damage progresses.
Any advice is appreciated.
73, Dimitris VK1SV/SV1DET
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