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44 year old electrolytic capacitor as good as new
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VK3DRB:
My plug pack for my 1976 scientific calculator died. I have used that calculator and the original plug pack for 44 years. I opened it up and the transformer had gone open. It did not upset me - these linear plug pack power supplies waste power and are much less efficient than a modern SMPS, so I changed it to a 5V SMPS regulated output plug pack and transplanted the DC connector.

Out of curiosity, I tested the 1000uF filtering capacitor which was "Bellcon" brand. I could not believe that after 44 years, the cap measured 1269 uF.

It was definitely not made in China, because back then China exported nothing. I suspect the capacitor may have been made in Taiwan. I could find nothing on Bellcon brand, except a few rash statements on blogs by people saying Bellcon are rubbish, without any backup evidence.

I have seen many crappy electrolytic capacitors in my day - especially in cheapo radios where they are used for DC blocking in audio output stages and in TV sets.

But this capacitor was impressive. The body was in perfect condition. Why didn't the electrolyte dry up at least a bit in all those years?





Ranayna:
Aren't those generally -20/+80% Tolerance? ;)
So it could have lost capacity after all.

But to be real, in addition to that there are likely many more contributing factors explaining the remaining capacity. Two come to mind: It is a well made part in general. The cap has probably been made before the drive to extreme penny-pinching. And also severe de-rating. Caps last a log longer if kept cool.
There are likely many more reasons for the apparently good condition.

And, as far as I understand it, capacity is not everything in a capacitor. It could be deteriorated in other ways that a low voltage/power DMM test cannot detect.
floobydust:
That Bellcon looks like from Japan? A high percentage I encounter are dried out and low capacity.
I think it's due to the rubber bung shrinking and turning rock hard. You can poke it and see.
Must have been in high humidity or hand soldered.
Bud:
I replaced a few of these in my Commodore 64 made in 1984. They seemed to measure OK except for one which experienced high ripple current in the power supply. I did not know how much longer they would last so replaced them anyway.
VK3DRB:
I lived in Wangaratta for 13 years without air conditioning. We had many days over 100 degrees F. Hottest day was 116 deg F (46.7 deg C). That calculator did not have a comfortable life.

The output voltage on the linear supply would have been about 5V or so when the calculator was off and maybe 3V or so when it was on (stamped on the plug pack was" 3V 200mA"), so at least they used a cap rated at least double the DC working voltage. The cap was not mounted on a PCB, but soldered between the common anodes of two discrete diodes joined in mid air and the centre tap on the transformer as a full wave rectifier. The rubber grommet seal is sill soft and there is no discolouration on it.

One failure mode of RB type electrolytic caps when mounted flush to a PCB is thermal expansion and contraction that eventually causes them to open circuit. Another is dried up electrolyte. Another was using underrated capacitors to save pennies. This cap suffered from none of this.

This Bellcom, whoever they were, obviously made a good quality capacitor. Maybe they were Japanese. I would like to meet the engineer who designed and made this cap, but they are probably long retired or dead. But the cap lives on. I will put it in my spares box along with the two diodes.

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