Replacing a capacitor with one with lower ESR

Lestraveled

Joined May 19, 2014
1,946
MrAl
I did read post #12. I should have added the statement in my last post that there are instances where a cap with a higher ESR is desirable.
 

recklessrog

Joined May 23, 2013
985
It seems to come down to the fact that there are no "perfect" capacitors, or resistors, or inductors etc. as in practice they will exhibit some of the characteristics of the others, I.e, one type of construction of a capacitor may give it a higher level of inductance/series resistance than one of a different construction. This is why when we design a circuit, we select a component which most fits the requirement, ie. it is fairly obvious that it would not be generally acceptable to couple two R.f stages working at more than a few tens of Khz with an electrolytic!
Some regulators do indeed exhibit strange performance when used with some types of capacitors and the maker specifies a certain type should be used.
In my humble opinion this has more to do with shortcomings in the design/construction of the regulator that then needs a higher E.S.R capacitor to ensure the device operates correctly. All design is ultimately a compromise between theoretical perfection and practical real world working.
If the end result is that the design is "fit for purpose" within the original design premise, then it is a successful design. if not, then it's back to the drawing board!
 
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ian field

Joined Oct 27, 2012
6,536
That is my wondering - which are those cases
Mostly in pulse or signal shaping type circuits or allowing a certain amount of degenerative feedback on the emitter resistor of a common emitter stage. Once or twice I've seen a resistor in series with a low value electrolytic in the nfb network to stabilise a TL431 programmable zener in SMPSUs.

In almost every other application of electrolytics, lower ESR is better. If the capacitor has to handle ripple current, the repeated charging and discharging produces dissipation in the ESR, that heats the capacitor and eventually dries out the electrolyte. SMPSUs and PWM motor controls generally operate about 15kHz or mors, even if the ripple current is small - there's a lot of it in a second.
 

dannyf

Joined Sep 13, 2015
2,197
When you think about ESR, don't think about it from a low ESR perspective: how low of an ESR do I need in a circuit?

Instead, think about it from a high ESR perspective: how high of an ESR I can go before I encounter a problem? Once you have a sense about that, any capacitor that fits the bill there will be good for the job.
 
Thank you Lastraveled
I will stick to Nichicon then, because they are at moderate price and got positive feedback here :)
But what about the bad batch of counterfeit caps that got into the computer motherboard and video card industry back in 2006-2008?
Check every cap even within the same brand before installing.. argh. It's another thing to make it fit. I ordered replacements for my retail shelf space to augment the already 1500 cap types in stock. Stubborn people don't know how to run a set of leads and move the larger cap elsewhere .
 
When you think about ESR, don't think about it from a low ESR perspective: how low of an ESR do I need in a circuit?

Instead, think about it from a high ESR perspective: how high of an ESR I can go before I encounter a problem? Once you have a sense about that, any capacitor that fits the bill there will be good for the job.

Is there a scale to which you can compare the ESR of given capacitors of the same construction type? without testing them before installing them in circuit?
I have had people ask me for lower ESR caps both polar and non polar electrolytic while building amps and speaker crossover circuits. I know there is a huge ESR difference from say tantalum to ceramic to electrolytic. But how to compare within the same type? How come the industry doesn't rate them except for "low esr" and just normal? That's sort of vague. How low is low? Do we know? Is there a metric?
Given that you replaced one cap with another of the same type and several in the same spot in the circuit. Ergo, they would be operating at the same frequency.

Of course I see this as a passive aggressive attempt to market parts which might have cheaper manufacturing methods and seldom used standards or unknown properties. I got the gist from the hobbyist asking me he didn't know and by the time I got to the first few formulas explaining ESR, he flipped out in resignation.
I know a bit much on how ceramic chip caps are made as I did the manufacturing station rotation for each step at Kyocera, and made my own caps for Tesla coils, but this guy had a point, there is no easy comparison datapoint for same types of class of caps.
 
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