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Old 27th January 2012, 04:25 PM   #1
VMUNIX is offline VMUNIX  Argentina
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Default Vintage electrolytic capacitors

Ok people, I'm starting this thread because I didn't find old posts about this.

Bought a stock of old electrolytic capacitos, even knowing that these degrade or gone dry with time, expecting that at least some of them still work, because i think they look cool, specially those TESLA with the screw on the base. The problem is as you would imagine they are built in a country that no longer exist as such (Czechoslovakia) and others made in England which still exists, though my guess is these are at least 35 to 40 years old.

Tried a few 16mF + 16mF tesla brand with 100V DC and they get warm, possibly behaving more like a resistor than a capacitor.
I have a good analog multimeter and a digital multimeter that measures capacitance up to 22mF. Still I don't know a proper way to determine if a cap is good or not to be installed.
Ideas?
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Old 27th January 2012, 04:52 PM   #2
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by VMUNIX View Post
Ok people, I'm starting this thread because I didn't find old posts about this.

Ideas?
Pics are related.



dirt.
Here are my thoughts,

The reason noboby has probably asked is...old caps can contain dangerous chemicals (PCB)...The warm caps you refer to could heat up and explode covering you with hot electrolyte..

I have seen people opening caps and using the can with new caps inside...This is dangerous you are exposing yourself to unknown chemicals..

You could try reforming them...however I would not do this..
You could put them on a variable DC supply with a current limit and run them up slowly watch the heat and current...any leakage is a sign that they are damaged or faulty..don't put them on a bench and just look at them...I would put them behind a screen or use enclosure..

This is not a good Idea...life of the caps is going to be unknown..so cut a hole in the chassis for an old component that is not available?

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M. Gregg
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Last edited by M Gregg; 27th January 2012 at 04:55 PM.
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Old 27th January 2012, 05:12 PM   #3
VMUNIX is offline VMUNIX  Argentina
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Gregg, thank you for your reply, I was considering opening them up, specially the Tesla ones for the reasons I stated, they look neat screwed in the chassis along with the valves but now that you mention that is dangerous I think is a stupid idea. Also just checked them with my analog multimeter and most of them discharge completely after less than a minute, as opposed to my brand new capacitors of similar rating that retain the charge for several minutes. So I think I will toss them away.
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Old 27th January 2012, 05:17 PM   #4
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by VMUNIX View Post
Gregg, thank you for your reply, I was considering opening them up, specially the Tesla ones for the reasons I stated, they look neat screwed in the chassis along with the valves but now that you mention that is dangerous I think is a stupid idea. Also just checked them with my analog multimeter and most of them discharge completely after less than a minute, as opposed to my brand new capacitors of similar rating that retain the charge for several minutes. So I think I will toss them away.
Some of the chemicals can be very dangerous..(PCB is an example)
I understand why you want to do this, however I am concerned for your safety.

Remember you may need special disposal...some countries can fine you if you just throw them away..

Regards
M. Gregg
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Old 27th January 2012, 05:20 PM   #5
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I'm not aware that electrolytic caps ever used PCBs, only oil filled HV and motor caps. Still, worth checking. If you power these up with a DC supply and a large value resistor, they should (maybe) improve. If the leakage doesn't drop to normal levels after a day or so, they're probably junk. Though I still need to update it with several people's good suggestions, you might enjoy the capacitor article on my web site (click my name).
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Old 27th January 2012, 05:31 PM   #6
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It all depends at which level you are trying to restore something.

At level 1 (The Ultimate level) only original components will do the job.

At level 2 (Looks the same) then you can disassemble cans and put different bits inside.

At level 3 (It works) you can just substitute.

Which level are you trying to achieve ?
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Old 27th January 2012, 05:37 PM   #7
VMUNIX is offline VMUNIX  Argentina
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Originally Posted by KatieandDad View Post
It all depends at which level you are trying to restore something.

At level 1 (The Ultimate level) only original components will do the job.

At level 2 (Looks the same) then you can disassemble cans and put different bits inside.

At level 3 (It works) you can just substitute.

Which level are you trying to achieve ?
To make them look old equipment, for instance I'm going to use Rimlock base valves (41,42 types), a modern capacitor simply won't look nice, I suppose I'll hide it beneath the chassis.
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Old 27th January 2012, 05:38 PM   #8
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Opening anything up with chemicals inside it will always be hazardous.

I've never known a capacitor to be deadly though, so as long as you dont eat or breathe the contents you should be fairly safe.

It's not going to explode as you open it up.

Be careful with Cadmium though. It's not a common component but was used by the Americans a lot. It is toxic when it is oxidised ( identified as a white dust).

Cadmium though is still OK if you work in a well ventilated area and DO NOT ingest the stuff. (WASH EVERYTHING THOROUGHLY)

Last edited by KatieandDad; 27th January 2012 at 05:42 PM.
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Old 27th January 2012, 06:07 PM   #9
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I'm not aware that electrolytic caps ever used PCBs, only oil filled HV and motor caps.
They did not. PCB's were used in oil caps to improve the dielectric. PCB's were not used in electrolytics.

Electrolytics did contain some strong alkalai's that eat components and PC board traces if they leak. They can violently explode if overheated. I know this from experience. The old ones did not have vents to prevent explosions.

Old electrolytics can and do dry out. They can become leaky with age. This is why they get hot. DO NOT use one in a circuit if it gets hot. It can EXPLODE. A cap that gets warm can sometimes be cured by "re-forming". Connect it to a variable DC power supply that has a current meter capable of reading 1 to 10 mA. Slowly turn up the voltage until the capacitor draws a small current (1 or 2 mA) or the rated voltage is reached. Let the cap sit at this voltage while watching the current meter. It should go down with time. If it does, turn the voltage up some more. Repeat this process until the rated voltage is reached and the capacitor draws less than 1 mA. If the cap increases current with time, or doesn't decrease, don't use it. It will explode.
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Old 27th January 2012, 06:41 PM   #10
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This whole business about exposure to toxic materials is somewhat over-exaggerated when compared to the other trash around in society....UK immigrants tipping sump oil down drains.. smelly cars, smoking fags...energy saving lamps with mercury in the trash... plus all the batteries....Cadmium based plating is universally used on most hardware washers, bolts etc; one can find plenty of toxins in ones living room.. one doesn't have to look hard either, asthmatic formaldehyde is everywhere in furniture and buildings so no point getting scaremongered about the gylcerine alkali in standard electrolytics....good ones should have a rubber bung to release pressure, if wrinkled and like a boil,a sure sign of end of life..others have a deliberate triangulation indented in the can usually at the opposite end..to the same effect....
High voltage is our forum business and even more dangerous...and some of us work at quite high potential with plenty of Joules and have a beer at the same time......put it all in perspective. One is not going to get any work done if one is obsessive & petrified about hazards.Electronics is a dirty profession, no escape from it......rare metals used in mobile phones and beryllium oxide used in RF semi's are by far the worst toxic offenders...and yet widespread and easily obtained.
Electrolytics caps have the lowest life expectancy of all the components, life halves for every 10C temp rise....so I trash any electrolytic over a yr old unless I've known it's history...the WEEE local directives deals with their disposal if required. SOme are organic and can be simply binned.
I can assure you in the 1950-60's it was not unusual to come across power tubes with radioactive cathodes used in TV line output stages and in transmitter tank/outputs circuits in radio and diathermy equipment. The natural gamma radiation from the rock in my vicinity is quite high, 20-40 counts per minute on a GM counter (some locations in the world way worse and people live quite normally without any side effects)... What can I do about it ? Nothing.. Carry on as usual. Life is too short anyway.

richy

Last edited by richwalters; 27th January 2012 at 06:54 PM. Reason: spelling
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