[R-390] Power Supply, Capacitors, and Dead Horses
Dan Merz
[email protected]
Thu, 14 Mar 2002 08:27:53 -0800
Scott, there's always some resistance (wire in transformer, wire leads
etc) so current is limited by this but no doubt the initial current
surge can be very high, and this increases with input capacitance.
Sometimes a resistor is put in to limit this surge. On my 25 volt
supply for my R 392, I used brute capacitance filtering and I always
blew the 3 amp 110 fuse when I turned it on unless I brought it up with
a variac to limit the initial surge. I think I'm using about 20000
mfd. My solution was to wire in a relay that switched out a surge
resistor once the voltage came up - this was my solution because my
transformer (about 18 volts ac as I recall) didn't have enough extra
volts to accomodate the voltage drop in the surge resistor if I left it
in the circuit. There's probably a better way, but I had the relay on
hand. Dan
"Scott, Barry (Clyde B)" wrote:
>
> Sometime during the night last night, I happened to think of something relative to the power supply filtering thread. With a single cap across the rectifier, when power is applied, isn't the current demand on the transformer and rectifier components nearly infinite? Is this a potential problem? Should there be some kind of current-limiting resistor (or other component) in series with the cap?
>
> So far, it works okay and I realize this sudden current demand is short, but is this something to be concerned about?
>
> Thanks again,
>
> Barry(III) - N4BUQ
>
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