UC384x critical cap

[eccerr0r]

Well I had repaired an old Antec SP350 that had a blown (IIRC) Fuhjyyu 47uF 25V capacitor for the critical cap with an Elna 47uF 25V 85°C general purpose capacitor. It works but I can bet this will fail someday...

However I still do not have any 47uF 25V 105°C low ESR caps on hand.

What I'm wondering... I have a small pile 100uF 50V 105°C PM capacitors... Tempted to swap that 47uF with the 100uF which should be a quality capacitor and won't die prematurely...

But it's double the capacitance!

I wonder what would happen if I do the swap, the PSU probably would take longer to start up, but would it do anything ... and whether I should use two 100uF capacitors in series to more closely match the original? This unfortunately is tricky as each 100uF is already like double the size of the original 47uF.

[stj]

Re: UC384x critical cap

100uf will work, but the startup will be delayed a bit while the cap charges

[eccerr0r]

Re: UC384x critical cap

wondering if the slowdown would affect power good and other powerup sequencing... anyone tried?

oh it's a Nichicon PM cap... 5000 hour, probably due to its larger than average size for a 100μF cap...

[stj]

Re: UC384x critical cap

unlikely, i suspect this is the standby supply,
PG is related to the main supply

[eccerr0r]

Re: UC384x critical cap

Actually I think this PSU uses the UC384x as the main supply much like the SP300 (the SP400 seems to use a TL494).

[sam_sam_sam]

Re: UC384x critical cap

I once did some testing on a switching power supply that had issues with supplying enough current so tried to changed the capacitor by the switching power supply regulator and either it would not power on or it did a lot wining noise so you might be able to go up a little bit higher in UF value but it might not be to double it like you are thinking about

[eccerr0r]

Re: UC384x critical cap

FSCK. Nope, was wrong, the 47uF capacitor was not the critical cap for the UC384x, it's for the 2T standby PSU... So agreed I don't think I can much with the value that much, ugh.... need to locate specific values...

[CapLeaker]

Re: UC384x critical cap

I did that before in one case, because of the same reason not caving the right cap on hand. So instead of 25V 47uF I put 50V 100uF. All that happened was the power supply took now a quarter to a half of a second more to turn on. Funny thing is I did forget this until I read this thread. Guess what: That thingy I fixed still works like that. 8 years no issues.