7 Dec
2005
7 Dec
'05
3:02 a.m.
Subject: RE: Cap reformation question
From: "Joe R." <rigdonj at cfl.rr.com>
Date: Tue, 06 Dec 2005 21:48:03 +0000
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
At 06:25 PM 12/6/05 -0600, you wrote:
That's what I was thinking of doing. I keep a bunch of HP adjustable
voltage/ adjustable current supplies around and they've come in handy for
LOTs of different things. (I used one tonight to recharge and test some
lead-acid batteries for my HP 5315 Freq meter then used to same supply to
manually drive the VCO LO in a spectrum analyzer that I'm working on.)
Q: How high of a voltage do you use the reform the caps? I'm wondering
if it's necessary to apply full (or nearly full) rated voltage or if
they're fully reformed at say 5 VDC. Has anybody done any testing in this
area?
Joe
They need to be formed to at least the working voltage, it's better if
you can go closer to the rated voltage.
My trick has been a low current (120V pannel lamp) in series with whatever
supply was needed/handy. The lamp (under 1W) will limit current flow
and they are cheap.
Switch mode supplies are very risky at below rated voltage as the operating
currents in many (older ones) gies up with decreasing voltage. This are best
carefully, removing the caps and forming them out of circuit may be advised.
Allison
I take a bench power supply and a resistor and
bring the caps up that way-
sometimes you have to disconnect a wire or two, but not
always, and the
resistor gives you a degree of safety a straight variac wouldn't.
7 Dec
7 Dec
3:29 a.m.
These are big mambo-jumbo caps in a linear supply, specifically a
nameless S-100 system. I'm not sure if it's feasible to remove them.
They're screwed into the motherboard, and while I could disassemble the
motherboard from the chassis, it might still be a pain to get them out.
Controlling the voltage into them is pretty easy, via the Variac.
Limiting the current is a whole 'nother problem. Maybe a light bulb in
series with the Variac?
--jc
4:12 a.m.
J.C. Wren wrote:
These are big mambo-jumbo caps in a linear supply,
specifically a
nameless S-100 system. I'm not sure if it's feasible to remove them.
They're screwed into the motherboard, and while I could disassemble the
motherboard from the chassis, it might still be a pain to get them out.
Controlling the voltage into them is pretty easy, via the Variac.
Limiting the current is a whole 'nother problem. Maybe a light bulb in
series with the Variac?
--jc
For that case yes. Variac to come up slow and low wattage lamp to limit
current.
S100 linear supplies are unregulated (usually) before they get on the bus
so a load is NOT needed. Do insure the caps are discharged before inserting
any board.
Allison
4:34 a.m.
Sounds good. Last question (I think). Watt (!) constitutes
low-wattage? 4W and 7W nightlights are easy to find. 40 watt oven bulb?
--jc
Allison wrote:
J.C. Wren wrote:
These are big mambo-jumbo caps in a linear
supply, specifically a
nameless S-100 system. I'm not sure if it's feasible to remove
them. They're screwed into the motherboard, and while I could
disassemble the motherboard from the chassis, it might still be a
pain to get them out.
Controlling the voltage into them is pretty easy, via the Variac.
Limiting the current is a whole 'nother problem. Maybe a light bulb
in series with the Variac?
--jc
For that case yes. Variac to come up slow and low wattage lamp to limit
current.
S100 linear supplies are unregulated (usually) before they get on the bus
so a load is NOT needed. Do insure the caps are discharged before
inserting
any board.
Allison
6974
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