capacitors ESR from the 1970's

[algorithm]

Lately I have found myself without the datasheet for most "obsolete" capacitors.
Making it tough to know what the ? impedance is, or test frequency.

For instance, earlier, I tested 2 mystery purple caps, both 16v 100uf.
On 1, I got 0.90, the other 0.66
Since there is no data about these caps, I am unsure.
I have a suspicion that is pretty high for 16v, but maybe low esr was like that back then?
Thanks everyone

[mzzj]

Lately I have found myself without the datasheet for most "obsolete" capacitors.
Making it tough to know what the ? impedance is, or test frequency.

For instance, earlier, I tested 2 mystery purple caps, both 16v 100uf.
On 1, I got 0.90, the other 0.66
Since there is no data about these caps, I am unsure.
I have a suspicion that is pretty high for 16v, but maybe low esr was like that back then?
Thanks everyone

Sounds normal for me even for today's caps.
http://preher-tv.blogspot.fi/2011/03/typical-electrolytic-capacitor-esr.html

[David Hess]

Back then fewer capacitors were specified with ESR and ripple current ratings but despite that, many like the Sprague 30D series would qualify as low ESR and high ripple current now.

[Joule Thief]

+ 1 on the seems normal opinion.

Most 70's equipment I repair gets a full recap of all electrolytics. Too often, leaving the original caps in a piece of gear that has been idle for the last 20 years of its 40 year life only leads to the gear coming back for repair after a year of active use.

I would only test, compare and retain small electrolytics if there was an interest in maintaining some degree of "originality".

Also note there is a 40% difference in ESR between similar? capacitors. To me, that is suspicious on its own.

[SeanB]

I recapped a Panasonic quad control centre to use it as an audio control for PC speakers. Most of the small caps were replaced, and most were pretty much close to being resistors ESR wise. Only left the one in, as i was not going to dig through the wiring knitting on both sides of the board to get to it, and it was in a filter path for some effect I was never going to use in any case. Main power supply had a new cap of 2200uF instead of the 220uF it had, only change is now that it will still work for over 3 minutes after power off before it starts to distort. The capacitors I used were some very old 1960's vintage dry tantalum units I had lying around. A little hard to use as they have no polarity markings, just one lead is gold plated and the other is tinned, but they do work well.

[algorithm]

Ok, thanks everyone.

I am constantly confused about ESR readings... Is that chart for that meter the same for all other ESR meters? or roughly?
I find myself thinking higher voltage caps have high ESR, but I think that is the way it should be?
I also find it confusing how it shows up like 0.00 everytime on my meter. I never see 0.0 readings.
the chart linked earlier says 0.9?for 16v 100µf, for another rating, it lists 0.25?...

+ 1 on the seems normal opinion.

Most 70's equipment I repair gets a full recap of all electrolytics. Too often, leaving the original caps in a piece of gear that has been idle for the last 20 years of its 40 year life only leads to the gear coming back for repair after a year of active use.

I would only test, compare and retain small electrolytics if there was an interest in maintaining some degree of "originality".

Also note there is a 40% difference in ESR. To me, that is a suspicious on its own.

Thank you, exactly what I thought. Just the discrepancy between the 2 made me wonder, considering they are the same..
This thing has a lot of caps besides the 2 in question.
The thing is an analog synthesizer if anyone wondered.
Although, sometimes I wonder if a total recap is the way.
Then people say that there is no way all the caps are bad, etc...
I suppose full recap is the right thing to do. Preventing any future repair over the caps (hopefully).

Thanks again everyone!

[Joule Thief]

I should have been more specific with my recapping comment.

I would suspect / replace all power supply or power rail electrolytics and tantalums.

I would not arbitrarily replace any poly, ceramic or mica caps until performance issues proved otherwise.

With the wild sounds produced by a synthesizer, bad caps could provide you with a new funk sound never heard before. 

[Joule Thief]

I also find it confusing how it shows up like 0.00 everytime on my meter. I never see 0.0 readings.

Could you explain this in more detail?

What type of meter are you using? Does it self zero or do you need to manually zero the readout?

[David Hess]

I find myself thinking higher voltage caps have high ESR, but I think that is the way it should be?

ESR usually goes down up to 100 volts or so and then jumps up at about 160 volts because the electrolyte is different.  For a given ESR, higher voltage capacitors have a higher ripple current rating because they have a larger surface area to dissipate heat.

[algorithm]

Could you explain this in more detail?

What type of meter are you using? Does it self zero or do you need to manually zero the readout?

Yeah, actually the acceptable amount of extra volts from the transformer on some of my synths does give it more "UMPH" to its sound, especially low end. It definitely brought some ideas of improving or altering the sound by component value. Hopefully someday I will be able to know how to do such things.

Yeah, my meter is a cheap chinese ESR meter, although, it seems accurate/correct. It is manually zeroing.
What I mean is the digits never show on the screen like "0.9" with my meter.
It would say 0.90 or 0.09, etc.
when I see 0.9 on the chart, as well as 0.25, Im not sure if 0.9 means 0.09 or 0.99...

[algorithm]

ESR usually goes down up to 100 volts or so and then jumps up at about 160 volts because the electrolyte is different.  For a given ESR, higher voltage capacitors have a higher ripple current rating because they have a larger surface area to dissipate heat.

Great stuff, thanks for the details.

[deth502]

Yeah, my meter is a cheap chinese ESR meter, although, it seems accurate/correct. It is manually zeroing.
What I mean is the digits never show on the screen like "0.9" with my meter.
It would say 0.90 or 0.09, etc.
when I see 0.9 on the chart, as well as 0.25, Im not sure if 0.9 means 0.09 or 0.99...

read your units, very important. ie, you cant compere amps to milliamps without conversion. that said assuming the units are the same, 0.9 means 0.9. if they meant 0.09, then they would have said 0.09 and not 0.9. if your meter reads to another decimal point, then 0.9 means anywhere from 0.86 to 0.94, which rounds to 0.9. if a higher precision than that was required, then they would spec it as 0.90 and not 0.9

[algorithm]

Thanks again every1. I finally managed to get a capacitance meter, when I tested these 2 identical purple 16v10uf caps, 1 was 12.90uf, the second 1 was 13.20uf or so. Someone tried to tell me that was in tolerance, & I dont think so. I mean, 12.90 is 0.90 past that 20% mark, right?
Thanks for any advice.

[wraper]

Thanks again every1. I finally managed to get a capacitance meter, when I tested these 2 identical purple 16v10uf caps, 1 was 12.90uf, the second 1 was 13.20uf or so. Someone tried to tell me that was in tolerance, & I dont think so. I mean, 12.90 is 0.90 past that 20% mark, right?
Thanks for any advice.

With no or small voltage applied, oxide layer (insulator) becomes thinner with time so capacitance increases. If you reform them by applying close to rated voltage for some time, capacitance will decrease as oxide layer restores.

[mariush]

Thanks again every1. I finally managed to get a capacitance meter, when I tested these 2 identical purple 16v10uf caps, 1 was 12.90uf, the second 1 was 13.20uf or so. Someone tried to tell me that was in tolerance, & I dont think so. I mean, 12.90 is 0.90 past that 20% mark, right?
Thanks for any advice.

The capacitor itself could be +/- 20%, but based on new capacitors I buy, at least the ones from reputable brands (nichicon, rubycon, panasonic etc) they're all around +/- 5% ... 

Then, your multimeter also has a particular accuracy, usually a few percent + a few counts. I mean, if the multimeter specification is +/- 5% + 3 count  and you measure a perfect 1000uF capacitor, the multimeter could show 950-1050 + 3 uF on the display, depending on how well the multimeter is actually calibrated... and from the multimeter's point of view, he did it right. The multimeter isn't perfect.
With smaller capacitors, the leads and terminals can have some residual capacitance, the multimeter itself can have a few tens of picoFarads of capacitance... that's when you use the REL button on the meter, to remove that temporarly.

[algorithm]

My meter seems pretty accurate, but these are small... Testing a 6800uf cap was spot on perfectly.
& It was in REL^ mode.
The meter is +(3.0%+5) on accuracy.

EDIT:
Hmm.. So when would it be clear that a cap was bad by capacitance reading?
If its lower? Or beyond the 3.0%+5?

I really wish these caps were what was wrong, because I have tried replacing everything else I could think of...
The weird thing is the one with a 13.20uf reading looks bulged on its top on 1 side...
Could get this thing get wacky if some heat got thrown in the mix?
I have heard of/seen some tantalums short after they got power for a few minutes.
Thanks for all the great advice and info. This community is beyond great.

[David Hess]

I use an impedance bridge so I get capacitance and dissipation at a test frequency of 1000 Hz instead of ESR.  In the worn out capacitors that I find, usually the dissipation has risen by several times even if the capacitance has not fallen. 

In one case however I ran across a Sprague 30D series which tested good in all respects but was in fact bad having poor high frequency response.  I suspect a network analyser or maybe a tester which operates at higher frequencies would have revealed it.  The reason I knew it was bad was that replacing it fixed the problem and putting it back restored the problem.

[KB8CWB]

Ok, thanks everyone.

I am constantly confused about ESR readings... Is that chart for that meter the same for all other ESR meters? or roughly?
I find myself thinking higher voltage caps have high ESR, but I think that is the way it should be?
I also find it confusing how it shows up like 0.00 everytime on my meter. I never see 0.0 readings.
the chart linked earlier says 0.9?for 16v 100µf, for another rating, it lists 0.25?...

+ 1 on the seems normal opinion.

Most 70's equipment I repair gets a full recap of all electrolytics. Too often, leaving the original caps in a piece of gear that has been idle for the last 20 years of its 40 year life only leads to the gear coming back for repair after a year of active use.

I would only test, compare and retain small electrolytics if there was an interest in maintaining some degree of "originality".

Also note there is a 40% difference in ESR. To me, that is a suspicious on its own.

Thank you, exactly what I thought. Just the discrepancy between the 2 made me wonder, considering they are the same..
This thing has a lot of caps besides the 2 in question.
The thing is an analog synthesizer if anyone wondered.
Although, sometimes I wonder if a total recap is the way.
Then people say that there is no way all the caps are bad, etc...
I suppose full recap is the right thing to do. Preventing any future repair over the caps (hopefully).

Thanks again everyone!

I second this opinion on totally re-capping the electrolytics in something from the 70s.  I would probably push that up well into the 80s as well.  Depending upon low or high voltage electrolytics, I will use either an ESR meter or my trusty Sprague bridge/leakage tester on the newer stuff.  If I find more then a few are out of spec or failed, I will just re-cap the thing.  My thoughts on this are two-fold.  One, especially if it is something I am restoring for my own use I would much rather to not have to go back in for quite some time after going over it.  Two, caps typically are what take out probably 90+% of components causing collateral damage.  And that collateral damage maybe some part that was made from unobtanium or is very expensive like a power transformer.   

And that isn't even mentioning the capacitor scandal (stolen electrolyte formula) that cause premature failure of all manners of electronics from Chinese sourced caps.  That one I am sure most remember.  If I see CHEAP capacitors in a product (Chinese unbranded crap), they end up in my garbage can.  HP and others had some serious issues with electrolytics failing using these caps.  I can't count the number of failed PS in computers and other equipment from that time period that have come across my bench...   

[PedroDaGr8]

Also, they are =/-20% typically at 120Hz. Deviate from this much and that value can change pretty dramatically and unpredicatably. many multimeters are typically a few Hz or less so don't be suprised for the value to read pretty far off.

[algorithm]

Yeah... When I first attempted to repair PSU's, I would replace every electrolytic capacitor. Nearly every time being successful. The PSU's I were working on had a wide variety of caps.

Although I never seem to do that anymore... 1 reason is I have trouble affording capacitors, while other people could use those caps in 1 sitting without a 2nd thought. Everything I buy I have to justify, it is hard to live comfortably without enough money.

I also always wonder about quality, because I know tesla made things that never failed. That makes me question rather or not a capacitor needs replacement. I know I have worked on really old things that had original capacitors and they still worked a treat, and they were twice my age. (laughs)

Also, they are =/-20% typically at 120Hz. Deviate from this much and that value can change pretty dramatically and unpredicatably. many multimeters are typically a few Hz or less so don't be suprised for the value to read pretty far off.

So I really needed an LCR meter or signal generator?