Ripple Current and ESR

Started by Chris June 18, 2017
Hi all,

What's the deal with this? I read somewhere that a high ripple current 
figure for an electrolytic is a bonus; an expensive and sought-after 
characteristic. However, I'd always thought ripple was anathema to PSUs.
Can some expert kindly explain the relationship between ESR, ripple 
current, capacitor ageing and whatnot?

thanks.
On 2017-06-18, Chris <cbx@noreply.com> wrote:
> Hi all, > > What's the deal with this? I read somewhere that a high ripple current > figure for an electrolytic is a bonus; an expensive and sought-after > characteristic. However, I'd always thought ripple was anathema to PSUs. > Can some expert kindly explain the relationship between ESR, ripple > current, capacitor ageing and whatnot?
It means that it withstands a high ripple current. -- This email has not been checked by half-arsed antivirus software
On Sun, 18 Jun 2017 19:35:44 +0000, Jasen Betts wrote:

> On 2017-06-18, Chris <cbx@noreply.com> wrote: >> Hi all, >> >> What's the deal with this? I read somewhere that a high ripple current >> figure for an electrolytic is a bonus; an expensive and sought-after >> characteristic. However, I'd always thought ripple was anathema to >> PSUs. >> Can some expert kindly explain the relationship between ESR, ripple >> current, capacitor ageing and whatnot? > > It means that it withstands a high ripple current.
What's to "withstand"? Electroytics are designed to smooth that out, after all.
Chris wrote:

--------------

> > What's the deal with this? I read somewhere that a high ripple current > figure for an electrolytic is a bonus; an expensive and sought-after > characteristic. However, I'd always thought ripple was anathema to PSUs. > Can some expert kindly explain the relationship between ESR, ripple > current, capacitor ageing and whatnot? > >
** Ripple current is simply the RMS value of the current flowing into and out of a capacitor as it charges and discharges - something it must do in order to smooth rectified AC. The current's magnitude depends on the p-p ripple voltage and the value of the cap and is somewhat greater than the DC load current. Ripple current heats the cap according to "I squared R" where R is the actual ESR at the frequency and temperature of operation. So a low ESR cap has a higher ripple current rating. However, I have not come across a electro cap where operation at 100Hz and with the usual 10% to 15% ripple voltage exceeds its ripple current rating. When an electro cap is used on the OUTPUT of a SMPS the rating becomes more important as the ripple voltage at high frequencies can be small while the current is large. Luckily the ESR of a electro caps improves at high frequencies and also when the temperature rises. Electro cap life is normally a function of operating temperature, halving for each 10 degrees C rise above room temp. It is purely due to the liquid electrolyte escaping from the cap as vapour - a few molecules at a time. Manufacturers use about 3 time more electrolyte than needed inside electros so the cap will have a long life without change is ESR or capacitance until nearly all the electrolyte is gone. .... Phil
On Mon, 19 Jun 2017 07:14:31 +1000, Chris <cbx@noreply.com> wrote:

> On Sun, 18 Jun 2017 19:35:44 +0000, Jasen Betts wrote: > >> On 2017-06-18, Chris <cbx@noreply.com> wrote: >>> Hi all, >>> >>> What's the deal with this? I read somewhere that a high ripple current >>> figure for an electrolytic is a bonus; an expensive and sought-after >>> characteristic. However, I'd always thought ripple was anathema to >>> PSUs. >>> Can some expert kindly explain the relationship between ESR, ripple >>> current, capacitor ageing and whatnot? >> >> It means that it withstands a high ripple current. > > What's to "withstand"? Electroytics are designed to smooth that out, > after all. >
the capacitor is not perfect - it also has internal resistance (and inductance). As ripple current flows in and out of the capacitor it causes heat via the internal resistance. To much heat and the service life is short. Way too much heat and it vents messy crap all over the place. -- Using Opera's mail client: http://www.opera.com/mail/
On Sunday, June 18, 2017 at 10:24:06 AM UTC-4, Chris wrote:
> Hi all, > > What's the deal with this? I read somewhere that a high ripple current > figure for an electrolytic is a bonus; an expensive and sought-after > characteristic. However, I'd always thought ripple was anathema to PSUs. > Can some expert kindly explain the relationship between ESR, ripple > current, capacitor ageing and whatnot? > > thanks.
Very nice explanations!
>"Very nice explanations! "
Yeah Phil beat me to it and probably did a better job, except for explaining the actual power dissipation of the cap in question. Really, it is as simple as Ohm's law except you need an accurate RMS current factor. In service I found out a few things about the engineering of newer TVs, annd this also means computer main boards. They use banks of caps, mainly to get that ripple current handling capacity. I have serived so many TVs that were dead but the customer failed to mention that there was a dark part of the screen or some shit, or lines that I no longer replaced the banks of caps for testing. I found that just replacing one would do the trick and at least get it alive. It is amazing how these sets can suck the life out of three 3,300 uFs in a matter of years. I think part of it is the quality of the caps because in this respect, my sister has this monitor wound up needing something ay 35 volts but I only had 25 volters, so I put in a twenty year old 100/160 which of course worked. I expected to have to order the right cap soon but the thing worked for years. YEARS. But in servicing, if you are going to do it, look to see what caps are in banks. You might have a bank of five 1000s on one one, to get the thing alive you only need to replace (or just bridge) one. Once you confirm proper operation and the estimate is OKed then you go on and replace them all. I actually kept a bunch of caps at the bench for that purpose and never cut the leads down. With the long leads they "fit" where they never would, but they fit the circuit well enough to make it work. we tried to avoid doing a total repair in the estimate stage but that is almost impossible. Even in the old RPTVs they could have a screen burn and the customer could be a prick about it. The laws here are very servicer unfriendly. I am glad to be out of it, but do seek to do something. And if they had a dead set and a week later they have a screen problem, they think the whole thing is under warranty. Actually that is why every repair became $300 even when we only put in a three buck part, if that. I tried to reason with people and draw an analogy to cars. If I fix the transmisssion on our car is are the brakes under my warranty ? Hell no. Neither is the radio. People flat out argued against that. My pussy boss let them get away with alot of shit and he got scammed more than once. I once told him he could have made twice the money, ut for whatevber reason he did not have the fight. We lost a TV temporarily, the customer sued for $800 which is MAYBE what it would be worth working and in pristeen condition. We found the TV and he called the to let them know. they told him "OK we will drop the suit so you don't have to bother going to court" and then they showed up and won the default judgement. This is a country of fucking scam artists. the kid (younger) has a job at lube stop and there is this customer who wanted a fluid change in his power steering. The company recommended against it because there was a leak, telling him that it might make the leak worse. And it did. And they were topping him off for free for a long time. The general manager bitched and corporate said "The customer is always tight". Well I am here to tell you that is not true. If the customer was always right he would not need you to do WHAT HE CANNOT DO. But the kid says (and actually he is pretty sharp for his age) that many companies are so afraid of any bad publicity that they will just bend over and take the ass fucking from anyone. Well homey don't play dat. I had people try to run game on me at my shop and I ran them off with a shotgun. And we did fine. Always made money. If you're straight with me I am straight with you.
jurb...@gmail.com wrote:

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> > >"Very nice explanations! " > > Yeah Phil beat me to it and probably did a better job, except for > explaining the actual power dissipation of the cap in question. > Really, it is as simple as Ohm's law except you need an accurate > RMS current factor. >
** It is not simple to measure or calculate the ACTUAL dissipation - cos ESR varies from sample to sample plus with running temp and age of the cap. ..... Phil

"Chris" <cbx@noreply.com> wrote in message 
news:oi6qfn$gsh$31@dont-email.me...
> On Sun, 18 Jun 2017 19:35:44 +0000, Jasen Betts wrote: > >> On 2017-06-18, Chris <cbx@noreply.com> wrote: >>> Hi all, >>> >>> What's the deal with this? I read somewhere that a high ripple current >>> figure for an electrolytic is a bonus; an expensive and sought-after >>> characteristic. However, I'd always thought ripple was anathema to >>> PSUs. >>> Can some expert kindly explain the relationship between ESR, ripple >>> current, capacitor ageing and whatnot? >> >> It means that it withstands a high ripple current. > > What's to "withstand"? Electroytics are designed to smooth that out, > after all.
ESR is an apparent series resistance inside the capacitor. Ripple current is the capacitor charging and discharging from the rectifier pulses of current and the load current in between the rectifier current. The ripple current flows through the apparent series resistance and produces heat. heat accelerates the processes that cause ESR to increase. Low ESR is good, but its things like SMPSUs that need the more expensive parts. Very often you can improve matters by putting metalized foil or MLCC capacitors in parallel with electrolytics.
Ian Field wrote:

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> > > The ripple current flows through the apparent series resistance and produces > heat. heat accelerates the processes that cause ESR to increase. >
** Fraid it does the opposite. ESR is almost entirely due to the conductivity of the electrolyte and THAT improves as it get hotter. At max rated temp ( ie 85C or 105C ) the ESR falls by a factor of 4 or 5 compared to room temp.
> > Very often you can improve matters by putting metalized foil or MLCC > capacitors in parallel with electrolytics. >
** No you can't. .... Phil