6 Dec
2005
6 Dec
'05
10:12 a.m.
I've got a system with a couple large electrolytics that hasn't been
powered up in a number of years. I have a 5A Variac. What's the
typical procedure for the reformation process? Remove all cards (or
maybe leave a junk card in for load?), start the Variac at 0V, increment
by 10V every so often? How long per step, and/or is a different step
suggested?
I've seen lots of people say "you'll need to reform the caps,
first", but never a prodecure for it.
--jc
6 Dec
6 Dec
11:35 a.m.
JC,
AFAIK the issue with reforming old electrolytics is that the caps will
have very high leakage currents until they reform. The goal is to limit the
power dissipation of the cap to something low enough that it won't vent (or
explode!) until it's recovered.
Lots of people use Variacs for this purpose and they'll certainly do the
job, but they don't give you any way to measure the leakage current. I
prefer the simple technique of putting a light bulb in series with the AC
side of the supply - when it's bright, the current is high and as it
gradually dims and goes out, the current is low.
maybe leave a junk card in for load?)
If it's a linear supply then it's probably happy without a load, and
there's no sense in wasting even a junk board.
If it's a switching supply then it depends on the design, but most likely
it will require some kind of load on at least some of the outputs to
maintain regulation.
Bob
-----Original Message-----
From: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] On Behalf Of J.C. Wren
Sent: Tuesday, December 06, 2005 7:13 AM
To: cctalk at classiccmp.org
Subject: Cap reformation question
I've got a system with a couple large electrolytics that
hasn't been
powered up in a number of years. I have a 5A Variac. What's the
typical procedure for the reformation process? Remove all cards (or
maybe leave a junk card in for load?), start the Variac at
0V, increment
by 10V every so often? How long per step, and/or is a different step
suggested?
I've seen lots of people say "you'll need to reform the caps,
first", but never a prodecure for it.
--jc
7:03 p.m.
-----Original
Message-----
I've got a system with a couple large electrolytics that
> hasn't been
> powered up in a number of years. I have a 5A Variac. What's
> the typical procedure for the reformation process? Remove
> all cards (or maybe leave a junk card in for load?), start
> the Variac at 0V, increment
> by 10V every so often? How long per step, and/or is a
> different step suggested?
>
> I've seen lots of people say "you'll need to reform the
> caps,
> first", but never a prodecure for it.
>
> --jc
> JC,
AFAIK the issue with reforming old electrolytics is that the
caps will
have very high leakage currents until they reform. The goal is
to limit the power dissipation of the cap to something low
enough that it won't vent (or explode!) until it's recovered.
Lots of people use Variacs for this purpose and they'll
certainly do the
job, but they don't give you any way to measure the leakage
current. I prefer the simple technique of putting a light bulb
in series with the AC side of the supply - when it's bright, the
current is high and as it gradually dims and goes out, the
current is low.
I would recommend using a high quality Constant Current/Constant
Voltage bench supply. These have a 'current' and a 'voltage' knob
on them and two meters (someetimes one switchable meter). The
procedure I use is to set the voltage to the level that you want
the capacitor to reach while disconnected. Then turn the current
limiting way down and connect the capacitor. Monitor the current
while turning it up slowly and leave it at some comfortable low
level so the cap can form up. This process limits the current
while the cap forms up. You can watch the voltage meter, which
should climb up to what you had it set at, if the cap is any good.
Good CC/CV bench supplies aren't cheap when new, but they're an
essential part of any good test bench, and can be located for a
reasonable cost.
maybe leave a junk card in for load?)
If it's a linear supply then it's probably happy without a
load, and
there's no sense in wasting even a junk board.
If it's a switching supply then it depends on the design, but
most likely
it will require some kind of load on at least some of the
outputs to maintain regulation.
Bob
7:47 p.m.
On 12/6/2005 at 7:03 PM Scott Stevens wrote:
I would recommend using a high quality Constant
Current/Constant
Voltage bench supply. These have a 'current' and a 'voltage' knob
on them and two meters (someetimes one switchable meter). The
procedure I use is to set the voltage to the level that you want
the capacitor to reach while disconnected. Then turn the current
limiting way down and connect the capacitor. Monitor the current
while turning it up slowly and leave it at some comfortable low
level so the cap can form up. This process limits the current
while the cap forms up. You can watch the voltage meter, which
should climb up to what you had it set at, if the cap is any good.
Wouldn't this amount to the same thing as putting a hefty resistor in
series with a variac-controlled power supply with a voltmeter on the supply
side? Start low--the resistor limits the current--crank the variac up bit
by bit until the desired voltage is reached. A fuse isn't a bad idea
either, in case the dielectric just plain fails.
It's worked for me. And my power supply isn't anything more than a
transformer connected to the variac followed by a full-wave bridge
rectifier--no filtering needed.
Cheers,
Chuck
8 p.m.
Chuck Guzis wrote:Wouldn't this amount to the same thing as putting a
hefty resistor in
series with a variac-controlled power supply with a
voltmeter on the supply
side? Start low--the resistor limits the current--crank the variac up bit
by bit until the desired voltage is reached. A fuse isn't a bad idea
either, in case the dielectric just plain fails.
It's worked for me. And my power supply isn't anything more than a
transformer connected to the variac followed by a full-wave bridge
rectifier--no filtering needed.
looks around ... better add a big hefty cap to that power supply as I
know you have at least one
kicking around :) Don't forget get to measure final voltage to your
cap plus 10% 20% ??? safety
margin. I also feel safe with new cap rather than a patched one.
Cheers,
Chuck
8:24 p.m.
On 12/6/2005 at 6:00 PM woodelf wrote:
... I also feel safe with new cap rather than a
patched one.
Maybe not--a couple of years ago there was a minor scandal about bad
Taiwan-origin electrolytics causing numerous motherboard failures (I have
one of those boards here):
http://www.niccomp.com/taiwanlowesr.htm
Cheers,
Chuck
8:49 p.m.
Chuck Guzis wrote:
Maybe not--a couple of years ago there was a minor
scandal about bad
Taiwan-origin electrolytics causing numerous motherboard failures (I have
one of those boards here):
Well a quality cap then , not floor sweepings.
BTW the best electrolytic has been discontinued so the people in the
quality audio have to go back
the cheaper brands.
Now for the latest USB item of the day:
"LEDLoad, a USB controlled LED display. "LEDLoad is a device and
software designed to display many shades of colors from green to red on
your computer case LED. Colors are controlled completely by software and
can be updated in real-time.""
7 Dec
7 Dec
12:58 a.m.
woodelf wrote:
Chuck Guzis wrote:
Conceptually similar to blinkenlights. Now I'd *definitely* buy USB
blinkenlights, if it was a real working panel.
Gordon.
Maybe not--a couple of years ago there was a
minor scandal about bad
Taiwan-origin electrolytics causing numerous motherboard failures (I have
one of those boards here):
Well a quality cap then , not floor sweepings.
BTW the best electrolytic has been discontinued so the people in the
quality audio have to go back
the cheaper brands.
Now for the latest USB item of the day:
"LEDLoad, a USB controlled LED display. "LEDLoad is a device and
software designed to display many shades of colors from green to red on
your computer case LED. Colors are controlled completely by software and
can be updated in real-time.""
9:18 p.m.
On Tue, 06 Dec 2005 17:24:26 -0800
"Chuck Guzis" <cclist at sydex.com> wrote:
On 12/6/2005 at 6:00 PM woodelf wrote:
I've had a few of those boards, too. I think I may have a part or
two salvaged off them still. Not that much worth salvaging on
that era of mobo, though.
... I also feel safe with new cap rather than a
patched one.
Maybe not--a couple of years ago there was a minor scandal about
bad Taiwan-origin electrolytics causing numerous motherboard
failures (I have one of those boards here):
http://www.niccomp.com/taiwanlowesr.htm
6874
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8 comments
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participants (6)
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bfranchuk＠jetnet.ab.ca -
bob＠jfcl.com -
cclist＠sydex.com -
chenmel＠earthlink.net -
gordonjcp＠gjcp.net -
jcwren＠jcwren.com