Low ESR capacitors

[sys-eng]

What is the definition of a capacitor with low ESR?
Is there a standard are is it only meaningful within a specific brand?

I searched on the Internet for a while and did not find this info. When I built circuits in electronics lab in the 1970's, there was not the wide selection that we have today so ESR was not readily available.

[tom66]

Re: Low ESR capacitors

All capacitors have a usually undesired property known as "equivalent series resistance." This is in series with the ideal capacitor model. On a power supply it is important to have a low ESR because the capacitor is rapidly charged and discharged to maintain the output voltage, which causes a current to flow through the capacitor. Current with resistance creates a voltage drop (so the power supply voltage will not be high enough, causing a variety of problems) but it -also- creates heat inside the capacitor. Heat accelerates the degradation of the capacitor, leading to increased ESR, which leads to increased heat, which leads ... And this causes the cap to fail.

There are several good manufacturers of capacitors with good low ESR series. Recommended often here is Panasonic FC, FM or FR, from "not as good" to "best" - although FC will be fine in almost any situation. Some other good series are Chemicon KY, Rubycon ZL/ZLH/ZLG/ZLJ and Nichicon HD/HM/HN.

[sys-eng]

Re: Low ESR capacitors

Thanks tom66. Although I understand what ESR is, you gave a good explanation and it is important for others. The reason I asked is I noticed that some capacitors not labeled as ESR on the OEM website have lower ESR than other brand capacitors marketed as low-ESR capacitors. This led me to think that the term low-ESR is only relevant within a given brand.

I also noticed that a regular 10V capacitor often has a lower ESR than a 6V low-ESR capacitor. I looked at a 61-page resistor & capacitor catalog by NTE and the term "ESR" is not found anywhere in the catalog.

[momaka]

Re: Low ESR capacitors

Low ESR is a very loose term when it comes to different companies. The "low" ESR caps from one company may be something labeled as general purpose by another. Therefore, when replacing capacitors in equipment, it is best to look up the info (data sheet) of the original caps and then pick proper replacements with same or very similar specs (and by specs, I mean ESR and ripple current). Matching the capacitance is also important. As for voltage, it okay to go higher but *usually* not okay to go lower (if you want to go lower, you have to make sure that the peak voltage in the circuit you will be placing the cap will not exceed the capacitor's voltage rating at any given time).

I also noticed that a regular 10V capacitor often has a lower ESR than a 6V low-ESR capacitor.

That's because within each capacitor series of each brand, the ESR is directly proportional to the can size and *only* the can size. Given two capacitors of the same capacitor brand and series: whether you have a 6.3V 2200uF cap in a 10x20 can or a 10V 1500uF cap also in a 10x20 can, the ESR *should* always be the same (and I say *should* only because some cheap Chinese/Taiwanese caps do not always seem to follow this rule for some reason).

Also, if you open a data sheet for a capacitor series that does not contain any info about ESR, then assume the capacitor is for general purpose use only (i.e. not for switching or high-frequency applications).

[sys-eng]

Re: Low ESR capacitors

Thanks momaka. Your excellent explanation confirmed my suspicion about the term "Low ESR" not being a standard.

I was in engineering school and building audio amplifiers and power inverters around 1978. I know semiconductors have changed since then but our general rule was to use wet electrolytic capacitors twice the working voltage as this had the most influence on service life if the temperature was the same. The other part of that rule is to increase the capacitance about 20% because the rated capacitance is observed at the working voltage rating. In other words, a capacitor rated at 1000uf & 10V may have capacitance of 800uf @ 6V. The working voltage did not seem to affect the dry capacitors much at all.

[Brkn42lc7d]

Re: Low ESR capacitors

Hello tom66 I saw that you have fixed many tv's and I was wondering what capacitors ad what type to use to replace some bad caps on a 42lc7d LG LCD tv. I have 5 bad ones. I have (4) 10v 2200mf and one 35v 1500mf one. They are both samwha brand and rated for 115 degrees celcius. Any help would be greatly appreciated. Should I use a low-ear or what kind?

[PeteS in CA]

Re: Low ESR capacitors

Thanks momaka. Your excellent explanation confirmed my suspicion about the term "Low ESR" not being a standard.

I was in engineering school and building audio amplifiers and power inverters around 1978. I know semiconductors have changed since then but our general rule was to use wet electrolytic capacitors twice the working voltage as this had the most influence on service life if the temperature was the same. The other part of that rule is to increase the capacitance about 20% because the rated capacitance is observed at the working voltage rating. In other words, a capacitor rated at 1000uf & 10V may have capacitance of 800uf @ 6V. The working voltage did not seem to affect the dry capacitors much at all.

This post is not recent, a caveat should be posted. Some ceramic capacitors have a horrendous voltage coefficient. If operated near the rated voltage, a Z5U or Y5V 1000uF ceramic capacitor may only really be 200uF-300uF; if also operated near the cold or hot extreme of their rating the actual capacitance may be 100uF-200uF.