I was building some boards for someone, with the parts supplied from the well known very large US supplier. The caps were brand name electrolytics in the 47-200 uF range, 10-50 V. Being the anal person I tend to be, I quickly checked a few on the bridge and did a double take. These brand new caps had dissipation factors as bad as 1.0 at 1kHz. When I'm servicing old equipment I get nervous when I see anything up over.5 or so for small caps. 1.0 would head straight to the trash. Not that they won't work, especially at 60Hz, but I've never purchased new brand name parts that were this bad. Do you really want a cap with a -53 degrees phase shift? It barely deserves to be called a capacitor. I'm not naming any names until I check out the data sheets for the specific parts, but I'll continue my suspicious ways and test every cap I'm about to install. One more time, just for the record, get a cap meter that reads DF, or use a high frequency esr meter. The simple DVM cap meters can't see this stuff.
CH
CH
A brand new 470u 250V Fuhjyyu recently went into the 70 vdc bias supply of a project amp. It showed visible end bulging within a month. They're still around.
if you use the keyword "bad caps" by google, you get many informations e. g. this
bad caps - Google Search
have a look also about
http://www.diyaudio.com/forums/parts/151392-best-electrolytic-capacitors.html
bad caps - Google Search
have a look also about
http://www.diyaudio.com/forums/parts/151392-best-electrolytic-capacitors.html
I've bought bad caps before...
from an electronics supplier in Atlanta. They were wide open. They looked like old stock which is why I checked them. I went to the owner and he said that I could bring them back for exchange. But all he had was more of the same. He supplies to Georgia Tech also. Unbelievable!
from an electronics supplier in Atlanta. They were wide open. They looked like old stock which is why I checked them. I went to the owner and he said that I could bring them back for exchange. But all he had was more of the same. He supplies to Georgia Tech also. Unbelievable!
Well, here's what I think. Low voltage electrolytics are inherently not very good at anything above line frequency. Some are probably worse than others (like these), but all should be avoided. It's said that you shouldn't run an electrolytic way under its rated voltage, but all my experience says it's an old wives tale. Any slight loss of performance over the years by using say a 63V cap in a 5V circuit, is negligible compared to the overall poor performance of a 10V (or lower) cap to begin with. I've also seen a much higher failure rate over the years with low voltage caps. When I rebuild test equipment, it's always the LV caps that go first. The case size of caps keeps getting smaller and that's not a good thing either.
The cap in question was a Panasonic 220uF, 10V part, EEU-EB1A221S (Digikey P13456-ND). At 120 Hz it looked ok, 211.6 uF with D=0.178 (series measurement) At 1kHz it was 197.0 uF with D=1.19 (series measurement). That's equivalent to a parallel combination of 1.64 ohms and 81.5 uF, giving a total Z of 1.2 ohms. Yes, it'll work, but don't expect great HF noise filtering.
Just for comparison, a NOS Rubycon YXF out of my junk box, also 220uF but 35V and a slightly larger case size, measured 196.6uF with D=0.194 (1kHz series measurement). That's equivalent to a parallel combination of 4.33 ohms and 189 uF, giving a total Z of 825 milliohms. Remember, these are AC model equivalents- I'm not suggesting a short circuit!
Note that soaking the 10V cap at 10V didn't improve things any, in fact it got slightly worse.
Ignoring all the numbers, if you can use a 25V or greater electrolytic, do so, even in a low or no voltage circuit.
Ok, these are garden variety caps. You want something really good? How about an Illinois KXM series, 220uf/35V? 1kHz is 202.1 uF with D=0.079 (1kHz series measurement). That's equivalent to a parallel combination of 10 ohms and 201 uF, giving a total Z of 789 milliohms. That's pretty much the Z of the reactance alone. More importantly, it maintains good performance at much higher frequencies, and is a perfect part for switching supplies because it won't overheat and fail. For a 60 Hz supply, I'd still use the Rubycon.
CH
The cap in question was a Panasonic 220uF, 10V part, EEU-EB1A221S (Digikey P13456-ND). At 120 Hz it looked ok, 211.6 uF with D=0.178 (series measurement) At 1kHz it was 197.0 uF with D=1.19 (series measurement). That's equivalent to a parallel combination of 1.64 ohms and 81.5 uF, giving a total Z of 1.2 ohms. Yes, it'll work, but don't expect great HF noise filtering.
Just for comparison, a NOS Rubycon YXF out of my junk box, also 220uF but 35V and a slightly larger case size, measured 196.6uF with D=0.194 (1kHz series measurement). That's equivalent to a parallel combination of 4.33 ohms and 189 uF, giving a total Z of 825 milliohms. Remember, these are AC model equivalents- I'm not suggesting a short circuit!
Note that soaking the 10V cap at 10V didn't improve things any, in fact it got slightly worse.
Ignoring all the numbers, if you can use a 25V or greater electrolytic, do so, even in a low or no voltage circuit.
Ok, these are garden variety caps. You want something really good? How about an Illinois KXM series, 220uf/35V? 1kHz is 202.1 uF with D=0.079 (1kHz series measurement). That's equivalent to a parallel combination of 10 ohms and 201 uF, giving a total Z of 789 milliohms. That's pretty much the Z of the reactance alone. More importantly, it maintains good performance at much higher frequencies, and is a perfect part for switching supplies because it won't overheat and fail. For a 60 Hz supply, I'd still use the Rubycon.
CH
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Would this be the same for PS caps .... say 35 v rails would be better off with 100V PS caps ...
FWIW , i do remember being told this years ago about electrolytic or caps in general to use voltage ratings @ least double what is needed ..
Once you get up to 25-35V I don't think it matters much. The really low voltage parts just seem to be iffy on their losses. For safety factor I try to estimate what the worst case high line voltage might be, and how high the supply might go under that condition and with no load on it. Then I add maybe 10-20%. Caps already have a surge rating that's usually higher than the continuous rating, and I think doubling the voltage might increase the size and cost excessively for what's gained. A typical audio supply running at 40VDC with 50VDC caps seems about right to me, though I've no doubt someone can make a case for 75 or 100V caps. I'm just not that paranoid, and you should always design with the assumption that the caps could fail at some point- choose fuses and such accordingly.
CH
CH
Hi Conrad,
thanks a lot for your numbers, that's great and rare information!
I'm really surprised the Panasonic EB perform so poorly. While I have never used the EB, I use massively the NHG for small current applications and TS-UP or TSHA for the cans. To rebuild SMPS I use FC or FM and honestly I never had a single problem (overheating, failure...) with any of the Panasonic parts.
Thanks also for mentioning good ones!
Now another difficulty 😉 is to get high quality axial caps, I have a signal generator here that's full of it. Nearly no choice in parts available for axials.
Have fun, Hannes
thanks a lot for your numbers, that's great and rare information!
I'm really surprised the Panasonic EB perform so poorly. While I have never used the EB, I use massively the NHG for small current applications and TS-UP or TSHA for the cans. To rebuild SMPS I use FC or FM and honestly I never had a single problem (overheating, failure...) with any of the Panasonic parts.
Thanks also for mentioning good ones!
Now another difficulty 😉 is to get high quality axial caps, I have a signal generator here that's full of it. Nearly no choice in parts available for axials.
Have fun, Hannes
in that case, I think my ESR meter (100kHz test freq) should show common problems easily?
Yes, those caps should look terrible on a high frequency esr meter! IMO, if one doesn't have a bridge that gives DF, an esr meter is almost essential to troubleshooting. Just knowing a capacitance value isn't enough.
For axial lead caps, I've found a huge number on the surplus market in years past. In a pinch, I've certainly soldered a wire to one lead and folded it back over to make a radial fit where an axial went, but I'm never happy about it.
CH
For axial lead caps, I've found a huge number on the surplus market in years past. In a pinch, I've certainly soldered a wire to one lead and folded it back over to make a radial fit where an axial went, but I'm never happy about it.
CH
Thanks for documenting something that I've noticed and whined about but never took data. With the proliferation of poor quality components these days you begin to understand why people say they can hear the difference between passive components.
I assume this performance didn't match the datasheet? Was this ancient stock?
I assume this performance didn't match the datasheet? Was this ancient stock?
The low cost general purpose electrolytics are only intended to be used in high impedance circuits, mainly for AC coupling and the like...
For example, the datasheets of the low voltage, low value, miniature Panasonics specify max. 120Hz ripple currents around 30mA and 120Hz dissipation factors of 0.35, so high dissipation factors at 1Khz are nothing surprising.
These capacitors are not intended to work with substantial 1Khz AC voltage across them. On the other hand, high dissipation factor prevents resonances when capacitors are paralleled with PCB track and wiring inductances inbetween.
Other capacitor series (bigger) are intended for low losses.
For example, the datasheets of the low voltage, low value, miniature Panasonics specify max. 120Hz ripple currents around 30mA and 120Hz dissipation factors of 0.35, so high dissipation factors at 1Khz are nothing surprising.
These capacitors are not intended to work with substantial 1Khz AC voltage across them. On the other hand, high dissipation factor prevents resonances when capacitors are paralleled with PCB track and wiring inductances inbetween.
Other capacitor series (bigger) are intended for low losses.
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Eva's right in that the parts are only specified at 120Hz, and they meet the spec. As to what they're intended for is anybody's guess, but the sharp rise in DF with frequency, compared to slightly higher voltage rated parts would be unexpected unless one had done the measurements- there's nothing to suggest it in the data sheet, so let the buyer beware. If one's goal is to shunt some HF noise in a lower impedance circuit, a typical use, these wouldn't be my first choice. I'm not sure I could get very excited about using them for coupling either, though I've seen dozens of similar parts in consumer electronics.
Best,
Conrad
Best,
Conrad
exactly. Any application where you're looking for more than 30dB attenuation at normal impedance levels will be a problem with these caps.
buyer beware!
buyer beware!
Beware also of those minature surface mount (with a black plastic bases) aluminium electro's. Many aren't even adequate for basic audio.
I use the miniature surface mount caps in the stuff that I'm currently doing and there are several series to choose, like in thru-hole capacitors.
The low ESR heavy duty series are ok for low power SMPS output filtering and for supply rail decoupling (like panasonic FC and FP).
But for example, what capacitor would you use in a limiter/VCA circuit to hold the amount of gain reduction as a voltage? A general purpose one would be ok. Electrolytic capacitors are used for many things.
When ESR is not specified, capacitors are not usually intended to handle any substantial AC current.
The low ESR heavy duty series are ok for low power SMPS output filtering and for supply rail decoupling (like panasonic FC and FP).
But for example, what capacitor would you use in a limiter/VCA circuit to hold the amount of gain reduction as a voltage? A general purpose one would be ok. Electrolytic capacitors are used for many things.
When ESR is not specified, capacitors are not usually intended to handle any substantial AC current.
Well in all but the most non demanding applications for AGC circuits you generally require low esr/esl capacitors throughout the chain as it is important to attenuate the AC component of the rectified signal. This is especially so in low THD oscillator control loops and RF circuits.
There are high performance minature SMD AL electros, but some of the cheaper ones are amongst the worst electro's I've ever measured - not even good enough for LF supply rail decoupling for an LM386.
There are high performance minature SMD AL electros, but some of the cheaper ones are amongst the worst electro's I've ever measured - not even good enough for LF supply rail decoupling for an LM386.
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