I'm old school also. WVDC rating and capacity--but with the newer, and
very compact construction of caps, this ripple current rating can be
important. I get that it is the rating the cap will handle passing the
AC ripple component to ground. Remember that there is an AC component
on the 13.8VDC line (ripple) the cap will pass that AC to ground thus
it is passing AC current. The current is the RMS ripple value divded by
the Impedance of the cap at the ripple frequency.
That being said, I have replaced ALOT of PS filter caps in 40 Years of
teching and have never worried about it. Pick a cap with same size for
mounting, and better than original temp rating and forget about it.
Just my understanding and .02
Curt
KU8L
K8AC wrote:
I changed out the caps in my PS-7 a couple of years back and used caps
from Mouser. Not sure why you're concerned about current rating -
that's not a factor. I think you'll find the caps rated only by
voltage and capacitance - oh yes, and by temperature max. In the
PS-7, you ought to worry more about the physical characteristics.
It's nice if you can find caps of the same diameter so you don't have
to change the mounting hardware. Also, the post height for the
terminals is a factor. I can't remember now whether the original caps
had the longer posts or whether or not I ordered the right height.
Before ordering, take everything off of one of the terminals and
measure the height.
My caps have been running several hours per day for a couple of years
with no problems. I may be able to dig out a receipt if you have
problems locating a replacement.
73, Floyd - K8AC
----- Original Message ----- From: "Don Cunningham"
<wb5...@martineer.net>
To: "Ron" <wd8...@yahoo.com>; <drakelist@zerobeat.net>
Sent: Wednesday, October 28, 2009 9:42 PM
Subject: Re: [Drakelist] Replacement caps for the PS7
Well, I hope since you asked this, it will bring on one of the
"guru's" that will explain ripple current. I have been seeing that
lately, and this old guy will admit to not knowing what the heck it
is!!!! I wouldn't think you would need the same rating as the power
supply current though!!!! What say experts??? I'm wanting to change
out my PS7 caps too.
73,
Don, WB5HAK
----- Original Message ----- From: "Ron" <wd8...@yahoo.com>
To: <drakelist@zerobeat.net>
Sent: Wednesday, October 28, 2009 8:34 PM
Subject: [Drakelist] Replacement caps for the PS7
Okay before everyone says Heathkit shop like they did last time,
note that the PS7 is the 13.8 volt power supply for the TR7 not the
L7 power supply. I need new filter caps, any thoughts on where and
which ones?
I spotted some on mouser, but I can not find their ripple current
ratings. Apparently Mallory has changed numbers slightly and all I
can do is guess given the size above and below that they are about
the correct current rating. On that subject, I presume the ones in
the supply are at least 12 amps each. That would get them close for
the 25 Amp constant current that the supply is suppose to be able to
run. With the fan cooling them, I would think 12 amp caps would be
about right.
TNX es 73,
Ron WD8SBB
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