Using a Variac to revive power supplies
dkelvey at hotmail.com
Fri Dec 24 13:07:25 CST 2010
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.
> 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.
> 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
> 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,
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