I was curious if there was any benefit, audible, or not, in using capacitors with voltage ratings way higher than they need to be? I am rebuilding this DAC from about 1990 that has some bad capacitors. Most of the power supply capacitors look to be within reason but throughout the audio circuitry the capacitors they used are way overkill. Maybe it’s what they had wanted to use them I don’t know.
These large 16v filters are seeing about 8.25 volts each, so 16v is what I would use.
These blue filters are rated at 25v and they have 21v across each of them. Again, good rating and I might even go to 35v.
This single 35v cap has 21.5v, good!
Now this row of caps are 16v rated and they are only filtering the +/- 5v rails coming off of the regulators. So they each have about 4.9-5.1 volts across each of them. I’d be comfortable going to 10v rated caps, even if the regulator was to dead short the cap would only see about 8v as the regulators are regulating 8v to 5v. Though I have the value in 16v so I’ll use 16 v
Now here is the puzzling part. The board is absolutely riddled with 47uF 63v caps.
I measured across each one and the most I saw was 15v and that was across four of them. The rest had 5v or lower on them. By using 63v caps weee they thinking they’d get better performance? I have wayyyy more 47uF 16v, 25v, and 35v rated than I do have 63v. I just don’t see a need to go that high and can’t figure out why Mach 1 Acoustics went that high.
Thoughts?
Dan
These large 16v filters are seeing about 8.25 volts each, so 16v is what I would use.
These blue filters are rated at 25v and they have 21v across each of them. Again, good rating and I might even go to 35v.
This single 35v cap has 21.5v, good!
Now this row of caps are 16v rated and they are only filtering the +/- 5v rails coming off of the regulators. So they each have about 4.9-5.1 volts across each of them. I’d be comfortable going to 10v rated caps, even if the regulator was to dead short the cap would only see about 8v as the regulators are regulating 8v to 5v. Though I have the value in 16v so I’ll use 16 v
Now here is the puzzling part. The board is absolutely riddled with 47uF 63v caps.
I measured across each one and the most I saw was 15v and that was across four of them. The rest had 5v or lower on them. By using 63v caps weee they thinking they’d get better performance? I have wayyyy more 47uF 16v, 25v, and 35v rated than I do have 63v. I just don’t see a need to go that high and can’t figure out why Mach 1 Acoustics went that high.
Thoughts?
Dan
One thing is you generally cannot get the silver mica (brown case) caps in a low voltage. 300V may be as low as you will get.
Sometimes caps are overspec'd for their ripple current handling and not just voltage, generally ripple current handling goes up as voltage of cap goes up. Not sure if that's the case with the 47/63's you show but that's probably more of a manufacturer got a run out special / new old stock / needed a couple but cheaper to buy in bulk
Oh yes, absolutely, I’ve used 500 silver mica in circuits were the highest rail voltage is a + a -30 V , I have never found them nearly that low. I’m specifically talking about the electrolytic only in this case, though.
Dan
That’s kind of what I was thinking. They picked up 10,000 of these 47 µF caps and use them in units that see 50 V and units like this they only see 15 V. Use them if you got them.
Dan
It stopped working, and I found that I had lost some power supply, voltages, due to a capacitor, failing. I replaced it, and then I measured the voltages on the other cap, I figured that I might as well just do them all for longevity. The capacitors in the power supply didn’t look nearly as good as far as ESR and leakage goes, so I may just do all the power supply capacitors, and then leave all the 47s. But at the same time, I’m thinking it would be nice just to do them all and then not have to think about it for another 30 to 40 years.
Also, all of the 47 µF caps are Nichicon VX series, which aren’t anything special. I looked at the data sheet and the capacitors I would replace them with our rated better as far as ripple and ESR., etc so why not make it better if I’m already tearing it apart is my thought. I doubt these 35 year-old capacitors are performing at their peak.
Dan
With an electrolytic cap, it's best to use such a cap at near to its voltage rating. Reason is to be sure that the cap stays formed and that the dielectric maintains its thickness. That, and you pay more for a cap with a higher voltage rating. Why pay for what you won't use?
One thing you'll sometimes see in a design is BOM optimization, where fewer distinct part ratings are used in order to get bulk savings in procurement and in pick-and-place machine setup. Commoning the caps by value (rounding up voltage and or capacitance) is one way to reduce the BOM size. Buying separate 4u7/10V and 4u7/25V for instance can be expensive than all 25V parts.
And specific to electrolytics higher voltage parts usually have lower leakage current, which might be a factor (replace an expensive 10V low leakage cap with a cheap standard 50V part for instance).
And specific to electrolytics higher voltage parts usually have lower leakage current, which might be a factor (replace an expensive 10V low leakage cap with a cheap standard 50V part for instance).
Maybe they just bought a huge quantity (to minimize cost) of caps to be used for different circuits and voltages.
(Ok, mark was quicker!)
The larger the can the lower the ESR (usually). Most often ESR halfs when going from 5mm to 6.3mm or from 6.3mm to 8mm. And those 5mm cans can have several Ohms of impedance, which might be inconvenient depending on your application. For the VX series the first 8mm can with 47uF is at 63V.
Also the temperature and frequency characteristics of the capacitance and ESR can be quite different depending on voltage rating. Vishay often has some informative plots the end of their datasheets. The capacitance frequency dependence can be quite dramatic. Here's the 148 RUS as an example:
Also the temperature and frequency characteristics of the capacitance and ESR can be quite different depending on voltage rating. Vishay often has some informative plots the end of their datasheets. The capacitance frequency dependence can be quite dramatic. Here's the 148 RUS as an example:
Yes, lower leakage current is a fact, if we use an electrolytic cap with higher voltage rating. Also lifetime will be longer. For reliability reason, I do not use those caps near to their rated DC voltage.
I have heard that as well. Nothing you can do about 1 uF caps as I haven’t seen them lower than 50v, but yeah, I want to use as close as possible.
What is the consensus? What would you all do? Used capacitors closer to the voltage. The cap is seeing (The cap staying electrically formed is a concern)?
Or go with the original 63 V value to potentially get better ripple. I am thinking that since I’m putting a better quality capacitor in there, I’ll be ahead of the game anyway with ripple. I figure all of the capacitors that see 5 V or less would get a 16 V cap and then the ones that see 15 V on them would get a 25 or 35V cap
Dan
Sometimes in industry, you just pick a part from the 'approved parts list' that's immediately available and/or already has a CAD symbol and outline.
That goes in your 'A model' prototype and there is never an imperative to spend many man-hours getting it changed unless it becomes a mass-market low margin design. Once a design is approved and EMC qualified etc, you have to save an awful lot of '5 cents cheaper per capacitor' to pay for a re-spin and an outing to the test house.
Also in military design, it was common to de-rate things to score better in the 'mil reliability' process, whether it had any basis in reality or not.
Whether the caps you buy today are more reliable if used near their rated volts, I don't know, but I would not assume it to be the case just because it may have been true in the past.
That goes in your 'A model' prototype and there is never an imperative to spend many man-hours getting it changed unless it becomes a mass-market low margin design. Once a design is approved and EMC qualified etc, you have to save an awful lot of '5 cents cheaper per capacitor' to pay for a re-spin and an outing to the test house.
Also in military design, it was common to de-rate things to score better in the 'mil reliability' process, whether it had any basis in reality or not.
Whether the caps you buy today are more reliable if used near their rated volts, I don't know, but I would not assume it to be the case just because it may have been true in the past.
In my experience of electros in the input circuits and feedback circuits of amplifiers, there's quite often a tiny voltage across them, but I've not noticed any issue with longevity.
But perhaps < 1V the forming is less important?
When recapping and modding an old Sony, the only caps that were leaking were the ones drive close to their marked voltage, but they were 1977 Nichicons, so perhaps modern caps are different.
Personally I used caps a decent amount above the voltage if possible, but if quantity buying helps the price I'll just upgrade everything to a higher voltage 😀
Perhaps if the forming is at risk, the forming isn't really an issue ? Does it change the capacitance, or just the leakage current?
BSST,
I am like you. If you are already in there, it won't hurt anything to replace all the caps with a NEW better quality cap. Just because, I would go with the same voltages as what was 'engineered' to be there in the first place. As the voltage goes up, so does the price, so my thinking is that the people who designed this unit had a reason to the parts that they did. Safer to stick with that thinking.
I did see something that I have a question about. Those heat sinks on some of the IC's. I suppose that they are running them that hard? Hmmm. Just wondering.
I am like you. If you are already in there, it won't hurt anything to replace all the caps with a NEW better quality cap. Just because, I would go with the same voltages as what was 'engineered' to be there in the first place. As the voltage goes up, so does the price, so my thinking is that the people who designed this unit had a reason to the parts that they did. Safer to stick with that thinking.
I did see something that I have a question about. Those heat sinks on some of the IC's. I suppose that they are running them that hard? Hmmm. Just wondering.