Filling PSU pcb empty spaces for caps and coils?

[Calchaqui]

Hi guys, I know that adding caps in lesser mobos PCB could be a disaster (lower speed, inestability), meaning coz affected timings.
But in PSU is another story? can i fill the space of caps and coils? I have an "idea" of the values from a more "full" PCB. Same with the little vertical coils? or I'm gonna blew it?

[ben7]

Re: Filling PSU pcb empty spaces for caps and coils?

I doubt anything will blow. You might have some problems with the feedback circuit and sub switching frequency oscillations/noise.

[Calchaqui]

Re: Filling PSU pcb empty spaces for caps and coils?

I doubt anything will blow. You might have some problems with the feedback circuit and sub switching frequency oscillations/noise.

I dont realy understand that, I did mean adding caps and coils to the secondary part's pcb , could it bring me feedback circuit and sub switching frequency oscillations/noise like you said? thnx

[momaka]

Re: Filling PSU pcb empty spaces for caps and coils?

Hi guys, I know that adding caps in lesser mobos PCB could be a disaster (lower speed, inestability), meaning coz affected timings.

Not really. I've done this many times and never had instability issues.

But in PSU is another story? can i fill the space of caps and coils? I have an "idea" of the values from a more "full" PCB. Same with the little vertical coils?

Yes, you can fill in the missing coils and caps. If it's a cheap PSU, this will greatly reduce the output noise and ripple, which is a good thing.

You might have some problems with the feedback circuit and sub switching frequency oscillations/noise.

I've only seen this happen to Sirtec -built PSUs - particularly trying to improve the caps on the 12V rail is what does it. Never had problems with any other PSUs, though. Older Bestec power supplies seem to take anything - even motherboard grade capacitors such as Nichicon HN and HZ.

[Wester547]

Re: Filling PSU pcb empty spaces for caps and coils?

I've only seen this happen to Sirtec -built PSUs - particularly trying to improve the caps on the 12V rail is what does it. Never had problems with any other PSUs, though. Older Bestec power supplies seem to take anything - even motherboard grade capacitors such as Nichicon HN and HZ.

Maybe that's why Bestec use general purpose capacitors with no ESR rating in the datasheet and no particular ESR rating, since anything seems to go in those output circuits they seem to always use GP capacitors on almost every rail (except +5VSB) so as to save money. Those old Sirtec PSUs usually have a general purpose 1000uF, 16V capacitor and a PI filter coil to form the PI filter. That would probably be okay to power hard drives, optical drives, floppy drives, and DC fans, but it wouldn't work well for anything +12V heavy and those PSUs usually came from +5V heavy systems anyway.

I do recommend adding PI filter coils in cheap gutless PSUs if there's room for it. It will greatly improve upon ripple suppression. as stated before me. If you want to add capacitors in gutless wonders, it shouldn't be a problem either. It's only that the output of certain PSUs (or most older ones) have PI filters that are tuned to a certain frequency or feedback loop so deviating from that too much can wreak havoc upon regulation.