23 Dec
2010
23 Dec
'10
9:11 a.m.
I've recently acquired a Variac (220V 10A) and was wondering what the
collectives views are on using them to revive long dormant power supplies.
Previously I have removed the electrolytics and reformed them with a bench
power supply setup, slowly ramping up the voltage (as per
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm). Am I right in
thinking I can use the Variac to effectively reform the capacitors in
circuit?
I'm currently rebuilding one of my PDP-8/E's which has a linear PSU which I
believe is ok, but will it also work with later DEC switchmode PSUs?
All the best,
Toby
23 Dec
23 Dec
11:05 a.m.
> From: toby at pdp11.co.uk
I've recently acquired a Variac (220V 10A) and was
wondering what the
collectives views are on using them to revive long dormant power supplies.
Previously I have removed the electrolytics and reformed them with a bench
power supply setup, slowly ramping up the voltage (as per
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm). Am I right in
thinking I can use the Variac to effectively reform the capacitors in
circuit?
I'm currently rebuilding one of my PDP-8/E's which has a linear PSU which I
believe is ok, but will it also work with later DEC switchmode PSUs?
All the best,
Toby
Hi
Don't use it on switchers. It is sure to either cause a failure
or for those that have brown-out feathers to not work
as expected.
If you want to bring up capacitors for switchers, remove
them from supply and use bench supply with a limiting resistor.
This is the better way, even for a linear supply.
Tinker Dwight
1:31 p.m.
Tobias Russell wrote:
I've recently acquired a Variac (220V 10A) and was
wondering what the
collectives views are on using them to revive long dormant power
supplies.
[...]
but will it also work with later DEC switchmode PSUs?
No! You should never run a switching supply on a variac, except within
the supply's rated input voltage range. Definitely do not plug the
supply into the variac and dial it up from zero!
1:42 p.m.
On 12/23/2010 01:31 PM, Eric Smith wrote:
Tobias Russell wrote:
Agreed! My favorite is a series lamp in the 40-300W range to limit
current and run the SMPS
with a light load (10% of rated). If there is a short the lamp lights
to limit current and all is good
it's dim or no glow.
Cheap and fairly simple, insures the start voltage is near 100% if the ok.
Allison
I've recently acquired a Variac (220V 10A)
and was wondering what the
collectives views are on using them to revive long dormant power
supplies.
[...]
but will it also work with later DEC switchmode
PSUs?
No! You should never run a switching supply on a variac, except
within the supply's rated input voltage range. Definitely do not plug
the supply into the variac and dial it up from zero!
3:37 p.m.
Agreed! My favorite is a series lamp in the 40-300W
range to limit
current and run the SMPS
with a light load (10% of rated). If there is a short the lamp lights
to limit current and all is good
it's dim or no glow.
Yes, I do that too. I also use a ;series light bulb' with unknown linear
supplies, it saves my nerves if the transformer has shorted turns or
womething. IT may also protect a lienar supply's transfdofmer from
further damage if there's a shorted rectifier or similar.
For SMPSUs I have a pair of240V bulbs in seres which I connect in the +ve
DC line between the mains smoothing caapciotor and the chopper circuit.
This will limit the chopper current if something goes very wrong, andf
while it may not save the chopper transistor, it will stop tracees
getting blasted off the PCB.
Of course owing to daft EU regualtions, cuitable ight bulbs are getting
harder to find. Idiots!
And as I said in my messag,e I'm with you andEric, I would never try to
'run up' an SMPSU on a variac.
-tony
2:06 p.m.
Ok, I suspected as much.
So for a linear supply such as the 8/E's is a Variac a valid way to go or
should I reform the capacitors individually as I've done previously?
All the best,
Toby
On 23 December 2010 18:31, Eric Smith <eric at brouhaha.com> wrote:
Tobias Russell wrote:
I've recently acquired a Variac (220V 10A)
and was wondering what the
collectives views are on using them to revive long dormant power
supplies.
[...]
but will it also work with later DEC switchmode
PSUs?
No! You should never run a switching supply on a variac, except within the
supply's rated input voltage range. Definitely do not plug the supply into
the variac and dial it up from zero!
--
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.
2:14 p.m.
New subject: Byte magazine is making a comeback
5:42 p.m.
New subject: Byte magazine is making a comeback
We'll see about that ..... so far they hired one "personality" and they
haven't said a single word about how Byte.com will be different from any
other gadget site. My guess is they're out of new ideas to be
competitive, so they're throwing poop at a wall to see what sticks.
6:07 p.m.
New subject: Byte magazine is making a comeback
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Evan Koblentz
Sent: Thursday, December 23, 2010 2:42 PM
To: On-Topic and Off-Topic Posts
Subject: Re: Byte magazine is making a comeback
We'll see about that ..... so far they hired one "personality" and they
haven't said a single word about how Byte.com will be different from
any
other gadget site. My guess is they're out of new ideas to be
competitive, so they're throwing poop at a wall to see what sticks.
It's such a strange feeling to find myself agreeing with Evan :-) but I can't see
anything but an attempt to spray-paint a once venerable name onto a fresh turd. By the
time Byte died, it was a mercy killing; as has been stated elsewhere, most of the computer
magazines, and Byte in particular, had transmogrified into PC magazines, despite the fact
there wasn't that much "there" there.
While there has been a lot of conversation as to why - some of it laced with various
conspiracy theories - I opine that it's simply that the general marketplace had moved
on from the heady early days of computing and, like it or not, publishers need to appeal
to that "general marketplace" in order to make money and stay in business. I
will acknowledge and embrace one conspiracy theory, namely that the Intel hegemony wiped
out a lot of meaningful discourse about computing because, well, if it wasn't x86 it
wasn't... happening. (I am so glad to see how ARM processors are creating a
competitive marketplace again.)
Wired has devolved to being little but a commanding presence in the gadget magazine genre
- to the point that I've allowed my subscription to expire, as I don't find their
content interesting (or accurate, in many cases, or readable, given their
"interesting" typeface and color choices). I really wonder how the folks hoping
to "revive" Byte can think they will find a market. -- Ian
7:30 p.m.
New subject: Byte magazine is making a comeback
We'll see about that ..... so far they hired one "personality" and they
haven't said a single word about how Byte.com will be different from any
other gadget site. My guess is they're out of new ideas to be competitive,
so they're throwing poop at a wall to see what sticks.
That was my first response, but after rereading the press release, they
might have an angle that works. The difference between the new BYTE and the
gadget publications is that BYTE appears to target only the enterprise
market--the people who evaluate and implement new technology in big
companies. If they don't just focus on features and do meaningful deep dives
not only into the technology, but how it integrates with existing systems,
they could offer unique value in the same mold as the old BYTE.
That's a big if, but I'm withholding judgment until I see what they produce.
24 Dec
24 Dec
11:21 a.m.
New subject: Byte magazine is making a comeback
Frankly, this seems like a rather cynical use of the Byte name. I'd
much rather see some sort of deal to make the contents of the REAL
Byte magazine available online (rather like the deal that Google seems
to have to make old InfoWorlds available) than some new website aimed
at CTOs on a budget.
5:21 p.m.
New subject: Byte magazine is making a comeback
Given the amount of time that's passed, shouldn't they call it DWORD?
--
"The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download
<http://legalizeadulthood.wordpress.com/the-direct3d-graphics-pipeline/>
Legalize Adulthood! <http://legalizeadulthood.wordpress.com>
23 Dec
23 Dec
3:31 p.m.
I've recently acquired a Variac (220V 10A) and was wondering what the
collectives views are on using them to revive long dormant power supplies.
Some people swear by the Variac for such things, I am not sure why...
Previously I have removed the electrolytics and
reformed them with a bench
power supply setup, slowly ramping up the voltage (as per
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm). Am I right in
thinking I can use the Variac to effectively reform the capacitors in
circuit?
Maybe, maybe not. You could ramp up the votlage across the smoothing
capacitors (straight after the transformer/rectifier), but don't you want
to limit the currnet (if they need reforming) or at least check the
leakage current. In which case you will ahve to disconenct one end of the
capacitor anyway.
Anyyhing downstream of the rgualtor can't really be reformed using a
variaco n the mains input either..
I'm currently rebuilding one of my PDP-8/E's
which has a linear PSU which I
believe is ok, but will it also work with later DEC switchmode PSUs?
I would never use a variac on an SMPSU. SMPSUs are one of the few things
that approciomate a constant _power_ load which emans they actually draw
more current as the input voltage decreases. It's possible to damage some
tupes of SMPUS by giving them too little input voltage.
-tony
24 Dec
24 Dec
3:41 a.m.
I know it's obvious but a Variac is AC out. It's capable of 2.2KVA! You
would be relying on the old PSU's transformer and rectifier circuits to
generate the reform voltage.
DC from a bench PSU across an isolated capacitor via a limiting resistor is
probably a better option.
As many switchmode PSU's are automatic dual voltage. Usually 110v to 240v
They might be OK to run from the Variac. Otherwise probably not.
Regards
?
Rod Smallwood
?
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Tobias Russell
Sent: 23 December 2010 14:12
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Using a Variac to revive power supplies
I've recently acquired a Variac (220V 10A) and was wondering what the
collectives views are on using them to revive long dormant power supplies.
Previously I have removed the electrolytics and reformed them with a bench
power supply setup, slowly ramping up the voltage (as per
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm). Am I right in
thinking I can use the Variac to effectively reform the capacitors in
circuit?
I'm currently rebuilding one of my PDP-8/E's which has a linear PSU which I
believe is ok, but will it also work with later DEC switchmode PSUs?
All the best,
Toby
2:07 p.m.
Hi
Still the light bulb in series is a good safety measure.
The main disadvantage of the variac method, even with the light bulb,
is that one can't monitor the leakage current of the capacitors.
Dwight
From: rodsmallwood at btconnect.com
To: cctech at classiccmp.org
Subject: RE: Using a Variac to revive power supplies
Date: Fri, 24 Dec 2010 08:41:09 +0000
I know it's obvious but a Variac is AC out. It's capable of 2.2KVA! You
would be relying on the old PSU's transformer and rectifier circuits to
generate the reform voltage.
DC from a bench PSU across an isolated capacitor via a limiting resistor is
probably a better option.
As many switchmode PSU's are automatic dual voltage. Usually 110v to 240v
They might be OK to run from the Variac. Otherwise probably not.
Regards
Rod Smallwood
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Tobias Russell
Sent: 23 December 2010 14:12
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Using a Variac to revive power supplies
I've recently acquired a Variac (220V 10A) and was wondering what the
collectives views are on using them to revive long dormant power supplies.
Previously I have removed the electrolytics and reformed them with a bench
power supply setup, slowly ramping up the voltage (as per
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm). Am I right in
thinking I can use the Variac to effectively reform the capacitors in
circuit?
I'm currently rebuilding one of my PDP-8/E's which has a linear PSU which I
believe is ok, but will it also work with later DEC switchmode PSUs?
All the best,
Toby
5:39 p.m.
I know it's obvious but a Variac is AC out.
It's capable of 2.2KVA! You
would be relying on the old PSU's transformer and rectifier circuits to
generate the reform voltage.
DC from a bench PSU across an isolated capacitor via a limiting resistor =
is
probably a better option.=20
I would agree. While I have a Variac and find it useful for testing PSUs
at high/low input voltage and things like that, I don't find it much use
for repairing linear or switch-mode PSUs.
As many switchmode PSU's are automatic dual voltage. Usually 110v to =
240v
They might be OK to run from the Variac. Otherwise probably not.=20
Not always!.
Older SMPUs geenrally had a manual voltage selecrtor switch. Often the
input circuit was configured as a bridge rectifier for 230V mains
charging a pair of smoothing capacitors in series (with suitable
bleeder/balanace resistors, which often also provided the startup
supply), and as a votlage doubler fro 115V mains. In either case you got
abot 350V DC across the capacitors.
A lot, if not all of the automatic voltage-seelcting supplies do much the
same thing with an automatic circuit in place of the selector swtich.
They will not nevessarily work correctly fore any input voltage from
(say) 100V to 260V. I was readign a specification for such a supply the
other day which speicifically stated that for input voltages in the range
140V to 190V (or something), the PSU would not operate, but it would not
be damaged. I beleive some PSUs are acutally damaged under such
conditions. Certainly in either case running it up on a vVriac will do
nothing useful.
-tony
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18 comments
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toby＠pdp11.co.uk