Is there a reason not to put a beefy cap on the output of a homemade power supply?

Question

I'm a beginner in electronics, and in the process of completing a homemade power supply would love to get some advice.

The power supply itself is fairly straightforward - I'm using a laptop power supply with an output of about 20V and it powers my circuit which consists of:

2 fixed at 3.3V and 5.0V
2 adjustable with voltage and current limit
and another 5.0V to power an arduino nano
4 INA219 breakouts to measure each channel voltage and current
an arduino nano to collect the data
and an LCD to display voltages, currents, current limits, etc.

It all works, however, when I attach my homemade (arduino based) oscilloscope to the outputs, I'm noticing some ripple on the 3.3V and 5V channels, adding a 100uF cap improved it but didn't get rid of it, so I upped it to 1000uF which got the job done, (or at least within +-0.03V which is the margin of error of my crappy home-made oscilloscope).

So, the question is - is there any reason not to put a 1000uF cap at the outputs of these channels?

I don't have a schematic because the circuit was simple enough, so I didn't make one before implementing it.

To simplify my question further, imagine just a DC power source and a step-down switching voltage regulator, would there be any reason not to put a 1000uF capacitor on the output of the regulator?

EDIT: Added line breaks, I couldn't figure out how to do it last night. Sorry for the mess.

Good for including full information about your question. But PLEASE learn to format it so that we can read it. Few people an read that much detail in such a huge "wall of text"! — Richard Crowley, Apr 03 '16 at 03:56
There can be downsides - see http://electronics.stackexchange.com/questions/224421/is-there-any-downside-to-using-a-larger-than-needed-smoothing-capacitor for pros and cons. — Peter Smith, Apr 03 '16 at 13:58

score 3 · Accepted Answer · edited Jun 11 '20 at 15:10

The main reasons against are

inrush current

During startup, the capacitor effectively looks like a short to the power supply, so it will need to limit the current here.
"higher-than" requirements

The +5V rail might need to be kept above the +3.3V rail all the time, even during startup and shutdown. If you add large output capacitors and the +5V rail drops faster during shutdown, then the +3.3V capacitors need to be discharged into the +5V rail to protect any dual-supply ICs. If you have a large capacitor, this needs to be a fairly beefy diode.

score 0 · Answer 2 · answered Apr 03 '16 at 02:53

0

If your DC/DC converters are current-limited, then inrush current isn't an issue.

Be sure they are stable with a large capacitor.

answered Apr 03 '16 at 02:53

jp314

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Is there a reason not to put a beefy cap on the output of a homemade power supply?

2 Answers2