Does impedance or ripple current matter when selecting caps?

dukesilverfan

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More specifically, do these matter when picking caps for general arcade hardware; I know it can matter in certain electronics applications.

I typically by cap kits from an arcade parts seller, or bulk caps from Digikey/Mouser. I never look much past buying Nichicon, 105C, and then matching compacitance and matching/exceeding voltage. Sometimes I'll look or specific physical sizes when I know the area is tight on the PCB.

Is there ever a reason to look at impedance or ripple current as well?
 
Assuming you mean "big" capacitors, specifically electrolytic types in power supplies (and monitors).

Yes. Ripple current and ESR matter in a lot of ways. Always look at both. For new caps, ripple current rating is more important than ESR.
The manufacturer considers the ESR when they specify the ripple current limit.

Impedance is related to frequency and ESR and some other stuff and.....it's complicated.
I'm not sure how Digikey defines it for instance. And I ignore that column for that reason!

And sometime the ESR is "wrong" too. Or under-defined.

Always look at the device's data sheet! That is all that you can depend on.

The power dissipated by a capacitor is roughly ESR * Iripple(rms)^2. The capacitor's internal temperature rises based on this power dissipation. And temperature kills.

A basic rule is to figure out how much ripple current your circuit will have and multiply that by a fudge factor for safety margin. Then select a capacitor with a rated ripple current larger than that value. I like to go about 30% above my measured/computed worst case needs for a first pass choice.

But as always....it really depends on the situation.
 
What would you consider the threshold of needing to take ESR into consideration? HV applications? Or another case of it really depends on the situation? I feel for game pcbs, I tend to use a combination of what I have in stock, and what fits, while meeting the primary values.
 
ESR is case by case. And lower is not always better!
You always need to consider it.
But yes, unfortunately....it depends on the application.
 
ESR is case by case. And lower is not always better!
You always need to consider it.
But yes, unfortunately....it depends on the application.
As cwilkson has stated, there is no easy answer.

Each capacitor is different. Some need low ESR and high impedance, others don't.

Buy what you need. Look up the original data sheets when you can.

Years ago (I was Rapid Response Manager at LaSalle), we got a report of bad AC ripple in some of our power supplies. The instrument techs had just replaced the capacitors.

They got the rating correct. But not the ESR.

I found some at a local electronics store (Mainline in Plainfield, now long gone) and they installed them and the AC Ripple met standards.

So it IS important in some cases. The key is figuring out which case, which goes to the requirement to review the data sheet and see what it calls for.
 
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