Replacement caps on switcher, same or bigger okay?

Thread Starter

Hamlet

Joined Jun 10, 2015
308
I have a vanilla boost switcher from ebay, caps on input & output look bad. Input is 1000uf @ 63v, and output is two 470up @ 100v.

Can I use larger, say 2200uf at 100v on for each? I have box of low esr electros I'd like to use with that rating.
 

dl324

Joined Mar 30, 2015
10,734
It depends.

More isn't always better. Using more capacitance will increase surge current and discharge current at turn off. Higher capacitance and voltage specs usually means larger dimensions; packing components more tightly could affect heat dissipation.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
308
Am I to understand that switching frequencies/dynamics are not affected with input and output capacitance's on modern designs?
Because, oh boy, I can cram some cans into tight places if I'm not otherwise constrained, and a fan can take away the heat.
 

dendad

Joined Feb 20, 2016
3,519
Personally, I would just go with the same capacity rating, or close to it. using higher voltage caps will be ok as long as they are low ESR types.
There is probably no benefit found by using more capacitance if the supply was designed correctly in the first place.
 

MrAl

Joined Jun 17, 2014
7,590
Hello,

With an unknown circuit design it is impossible to know what type of cap to use. There are many possibilities that could cause problems.
For example, often high ESR is a problem because it allows too much ripple, but sometimes ESR that is too low also causes a problem with oscillations. Most of the time however low ESR is good and higher capacitance is ok.

With that said, it is wise to test any repair no matter what kind of caps you use unless they are exactly the same type and have the same manufacturer, which means the same model number. Even then it is a good idea to test before using because you never know if something else went wrong either before those caps went bad or during the repair.

I used slightly higher value caps on some repairs and they worked out well, but the difference was not as much as 4 to 1 as you are suggesting. That may work ok or it may not, it's too hard to judge without knowing everything about the circuit.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
308
Alright, I'll order similar replacements, but if I have time, I might try it both ways, to see what I can learn. Thanks everyone.
 

MrAl

Joined Jun 17, 2014
7,590
Alright, I'll order similar replacements, but if I have time, I might try it both ways, to see what I can learn. Thanks everyone.
Hi,

I remember one time on a purchased ready made buck type regulator board i tacked on a higher value output cap. It worked well. Bucks are not as picky as boost switchers though.
 

ian field

Joined Oct 27, 2012
6,539
I have a vanilla boost switcher from ebay, caps on input & output look bad. Input is 1000uf @ 63v, and output is two 470up @ 100v.

Can I use larger, say 2200uf at 100v on for each? I have box of low esr electros I'd like to use with that rating.
Depends what you're trying to accomplish. Beefing up the input caps is probably OK, but the output caps are actually part of a low pass filter.

As others have mentioned - bigger caps won't improve anything if they have poor ESR rating.
 
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