Bringing up a old Powersupply

From: Dwight Elvey <elvey_at_hal.com>
Date: Fri Apr 23 11:06:28 1999

Chuck McManis <cmcmanis_at_mcmanis.com> wrote:
> At 10:09 PM 4/22/99 -0800, Zane H. Healy wrote:
> > Is this a good idea? [slow power up]
>
> I'm on the fence about it. On the one hand you will find out if you've got
> a short fairly harmlessly, on the other hand its going to have to withstand
> power eventually.
>
> > If so, how slowly is a good idea?
>

Hi
 There are a couple of issues here. When electrolitics
aren't used for a long period of time,they need to be
reformed. This is an electro-chemical action. The way
to do that is to bring the voltage up slowly.
 Now for the bad part. First many pieces of solid
state electronics will draw higher current until the
voltage properly biases things off. This is normally
not a problem since the power supply usually comes up fast.
 Even worse, if the supply is a switcher and not a linear
supply, bringing the AC voltage up slowly will most likely
blow the supply. Many older switchers don't have brown
out protection. Because of the way they work, the
run the switching part hard enough to get the full
output voltage and current. If the input voltage is
low, the input switcher will draw more current until it
meets the power requirements of the output. Since
the input switching transistor(s) main limit is how
much current goes through them, they will often blow
out.
 If you fear the electrolitics are vary old, disconnect
one lead and form them from a bench supply and a current
limiting resistor.
Dwight
Received on Fri Apr 23 1999 - 11:06:28 BST