Make your PC Power supply last- 73's de Edd

[bushtech]

This post by 73's de Edd deserves better publicity:

ASIDE . . . .Hear one and all . . . . .
On my computer power supplies, an initial task is to take the secondary filters and use two capacitors instead of the single ones. This done by stacking the second one vertically above the initial one with an insulative bakelite disc placed atop the primary cap and insulative polyolefin sleeving insulating for routing the side wires down to the bottom one . . .with microdots of E2000 adhesive assisting in wire dress and hold down.

A final test is logging in all of the filters AC ripple readings to reference against for future analysis.
UBER reliability experienced . . . . . the oldest case is a computer that is having 8 years of use and only a 2 and 5% ripple increase on the 3.3 and 5 supplies . Lo o o o o o ng way to go on that !

Thassssssit . . . .
73's de Edd

St Edd

Here is a photo of (I hope) a typical power supply. Please can you point out the cap that needs a mate

 

[bushtech]

I am only on page 30 of Mr Horowitz's "Art of Electronics". so identifying a secondary filter = not possible

 

[bushtech]

After some investigative reading up (have never looked at a SMPS) am I correct in saying that the 2 caps to be doubled up are the 2 little black ones next to the smaller coiled copper whatchamacallit
in the photo below

 

[davenn]

After some investigative reading up (have never looked at a SMPS) am I correct in saying that the 2 caps to be doubled up are the 2 little black ones next to the smaller coiled copper whatchamacallit
in the photo below

OK, lets start at the start

.... does this PSU have a specific fault ?

.... those 6 electro caps that I can see, don't appear to be bulging ( obvious sign of failure). Tho they may have started to dry out and are loosing some of their capacitance value
and causing loss of smoothing, removing and testing would prove that

On my computer power supplies, an initial task is to take the secondary filters and use two capacitors instead of the single ones. This done by stacking the second one vertically above the initial one with an insulative bakelite disc placed atop the primary cap and insulative polyolefin sleeving insulating for routing the side wires down to the bottom one . . .with microdots of E2000 adhesive assisting in wire dress and hold down

.... This comment from Edd, I cannot agree with. I would NEVER leave faulty caps in circuit, just a recipe for future failure ....

.... I can see 4 small caps in the central section as well as the 2 large ones on the HV primary side ( the 2 large ones are probably rated somewhere between 350V and 450V
some times fail ... but failures are more common for the output caps

small caps like those in the middle section and output section are dirt cheap ... if you have any doubts ... REPLACE THEM ALL

use 105 deg C same capacitance and same or higher voltage ( remember physical sizes if considering higher voltage ones


Dave

 

[bushtech]

Thanks Dave, some very good advice.
I haven't got a problem with a power supply. I am looking for confirmation on where the 2 caps (secondary filter caps) are. Edd is not suggesting putting an extra cap on a dodgy cap, he is suggesting putting a second cap on a good cap to increase the reliability of a power supply

 

[davenn]

Edd is not suggesting putting an extra cap on a dodgy cap, he is suggesting putting a second cap on a good cap to increase the reliability of a power supply

yeah rereading that post of his several times, it seems that yes you are right
Still, I see it as a strange thing to do

I am looking for confirmation on where the 2 caps (secondary filter caps) are

ALL those caps in that final stage are secondary side of the switching transformer and are all caps for each of the different voltage rails outputs

 

[HellasTechn]

ALL those caps in that final stage are secondary side of the switching transformer and are all caps for each of the different voltage rails outputs

some of them in parallel to each other to increase capacitance. The higher the current rating for the rail, the higher capacitance needed.

 

[davenn]

The higher the current rating for the rail, the higher capacitance needed.

whilst that is true

some of them in parallel to each other to increase capacitance

in the case of this, and most, PSU, is isn't

count up the number of rails in the usual PC PSU .... +5, -5, +12, -12, 3.3 and maybe others ( there's 5 rails for a start)

it would be VERY un usual to find more than 1 cap per rail

if they needed more caps, the norm would just be to use a bigger cap

 

[bushtech]

I hope 73's de Edd cruises by this thread sometime. I'd like to know why he uses bakelite discs for insulation and if I can use a rubber disc cut from an old bicycle tube.

 

[davenn]

I'd like to know why he uses bakelite discs for insulation and if I can use a rubber disc cut from an old bicycle tube

more resilient ... the rubber will perish with heat and age, would be my guess