In article , "Frank
Dresser" writes:

Here's the results, checked on a Heathkit IT-28:

Interesting. With very few and small exceptions, every cap measured LESS than
marked. And we thought lytics were being made with very high positive
tolerances, up to 100% or double the value.

I guess you get (almost) what you pay for, no mas! --Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.

"Mike Knudsen" wrote in message
...


Interesting. With very few and small exceptions, every cap measured LESS
than
marked. And we thought lytics were being made with very high positive
tolerances, up to 100% or double the value.

I guess you get (almost) what you pay for, no mas! --Mike K.


I can't be sure the checker isn't just reading low. I do get repeatable and
sensible readings from it.

I also don't know if the caps I checked just by chance happened to be
generally bunched around common values, or if they are actually made with
more precision than they are rated for. It's a small sample.

But modern (maybe even 50 years ago) manufacturing ought to be able to make
a reasonably precise product as long as they are able to stick with a
process that is known to work. I have to figure that the capacitor
manufacturers know what they are doing, they regularly check samples of
their product and can make running changes to hit their target specs with
almost every lot.

Just as speculation, let's say cap manufacturers have learned to make
electrolytic capacitors with good precision at little extra cost. And let's
imagine that setting the target capacitance to 5% - 10% low reduces the cost
of the "active ingredients" by 5% -10%. Well, that would be a nice reward
for knowing how to do the job!

Frank Dresser

In article , "Frank
Dresser" writes:

Just as speculation, let's say cap manufacturers have learned to make
electrolytic capacitors with good precision at little extra cost. And let's
imagine that setting the target capacitance to 5% - 10% low reduces the cost
of the "active ingredients" by 5% -10%. Well, that would be a nice reward
for knowing how to do the job!

This makes very good sense.
I suspect that back in the old days, manufacturers would throw in up to 100%
extra foil plates area just to make sure they at least met the rated
capacitance. So you would get caps well over the ratings.

But yes, once they got the process down really tight, why toss in extra
material. In fact, shaving it on the low side is just what the front-office
bean coutners probably tell them to do nowadays! --Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.

"Mike Knudsen" wrote in message
...

This makes very good sense.
I suspect that back in the old days, manufacturers would
throw in up to 100%
extra foil plates area just to make sure they at least met
the rated
capacitance. So you would get caps well over the ratings.

But yes, once they got the process down really tight, why
toss in extra
material. In fact, shaving it on the low side is just
what the front-office
bean coutners probably tell them to do nowadays! --Mike
K.

Oscar loves trash, but hates Spam! Delete him to reply to
me.

I don't think I've ever seen an electrolytic capacitor read
more than 20% high, and even that range is very rare. Even
on the few low ESR survivors from the late 40's - early
50's. I'm not using a lab quality bridge, or checking large
numbers of electrolytic capacitors, so I can't come to
really firm conclusions. But I'm thinking the manufacturing
process was reasonably precise by 1950.

I don't know if the comparision holds, but carbon
composition resistors were getting more precise all through
that era, as well. The 5%ers were pretty common around
1970. I have to wonder how much expense was added to the
more precise resistors just for keeping extra inventory.
There's about twice as many values for 10%ers as 20%ers.
Double it again for the 5%ers. Assuming the cap makers
could reliably come with 5% electrolytics, would there be
any value to stocking 4 times as many values? I can't think
of any. They are used almost entirely for power supply
filtering, or audio coupling. So maybe they kept the old
20% spec on 5% tolerence caps only to keep inventory simple.

Frank Dresser

"Mike Knudsen" wrote in message
...

This makes very good sense.
I suspect that back in the old days, manufacturers would
throw in up to 100%
extra foil plates area just to make sure they at least met
the rated
capacitance. So you would get caps well over the ratings.

But yes, once they got the process down really tight, why
toss in extra
material. In fact, shaving it on the low side is just
what the front-office
bean coutners probably tell them to do nowadays! --Mike
K.

Oscar loves trash, but hates Spam! Delete him to reply to
me.

I don't think I've ever seen an electrolytic capacitor read
more than 20% high, and even that range is very rare. Even
on the few low ESR survivors from the late 40's - early
50's. I'm not using a lab quality bridge, or checking large
numbers of electrolytic capacitors, so I can't come to
really firm conclusions. But I'm thinking the manufacturing
process was reasonably precise by 1950.

I don't know if the comparision holds, but carbon
composition resistors were getting more precise all through
that era, as well. The 5%ers were pretty common around
1970. I have to wonder how much expense was added to the
more precise resistors just for keeping extra inventory.
There's about twice as many values for 10%ers as 20%ers.
Double it again for the 5%ers. Assuming the cap makers
could reliably come with 5% electrolytics, would there be
any value to stocking 4 times as many values? I can't think
of any. They are used almost entirely for power supply
filtering, or audio coupling. So maybe they kept the old
20% spec on 5% tolerence caps only to keep inventory simple.

Frank Dresser

The capacitance and voltage rating of an electrolytic capacitor is
set by the thickness of an aluminum oxide layer deposited on the
metal foil "plates" of the capacitor. Of course, the bulk amount of
square inches of aluminum plate material also determines the range
of capacitance that is possible with varying thicknesses of oxide.

The electrolyte serves the purpose of making an intimate electrical
connection to the plate. The problem is the electrolyte shows some
tendancy to dissolve the oxide layer. When this happens, the
capacitor's value increases, and its safe voltage rating decreases.
This is why a long disused electrolytic capacitor tends to blow up
when it is abruptly put back into service.

Electrolytic capacitors are self adjusting for working voltage (to
some degree). If they are operated for a long time at 50% of their
rating, the oxide reduces in thickness, and they become higher
capacitance, and lower working voltage. If you try to increase their
operating voltage, they will draw too much current. They will either
adapt to the new higher voltage, or they will blow up from the heat.

The tolerance has nothing to do with manufacturing capabilities, or
price, and everything to do with the highly variable nature of the
oxide layer.

-Chuck, WA3UQV




Mike Knudsen wrote:
In article , "Frank
Dresser" writes:


Just as speculation, let's say cap manufacturers have learned to make
electrolytic capacitors with good precision at little extra cost. And let's
imagine that setting the target capacitance to 5% - 10% low reduces the cost
of the "active ingredients" by 5% -10%. Well, that would be a nice reward
for knowing how to do the job!


This makes very good sense.
I suspect that back in the old days, manufacturers would throw in up to 100%
extra foil plates area just to make sure they at least met the rated
capacitance. So you would get caps well over the ratings.

But yes, once they got the process down really tight, why toss in extra
material. In fact, shaving it on the low side is just what the front-office
bean coutners probably tell them to do nowadays! --Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.

Chuck Harris wrote:

Electrolytic capacitors are self adjusting for working voltage (to
some degree). If they are operated for a long time at 50% of their
rating, the oxide reduces in thickness, and they become higher
capacitance, and lower working voltage. If you try to increase their
operating voltage, they will draw too much current. They will either
adapt to the new higher voltage, or they will blow up from the heat.

Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

-Bill

--exray-- wrote:
Chuck Harris wrote:


Electrolytic capacitors are self adjusting for working voltage (to
some degree). If they are operated for a long time at 50% of their
rating, the oxide reduces in thickness, and they become higher
capacitance, and lower working voltage. If you try to increase their
operating voltage, they will draw too much current. They will either
adapt to the new higher voltage, or they will blow up from the heat.


Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

It is all about the electrolyte. The older electrolytes tended to eat
the oxide layer pretty quickly. The manufacturers rated them for a
1 to 2 year shelf life... longer if they were in continuous use.

There have been alot of improvements in the electrolytes, and now the
caps last virtually forever. But the oxide thickness still determines
the tolerance, and as such it still changes with temperature, age and
voltage. Just not as much as it used to.

-Chuck

-Bill

Hi,

Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

I'd make that "1950."

There have been alot of improvements in the electrolytes, and now the
caps last virtually forever. But the oxide thickness still determines
the tolerance, and as such it still changes with temperature, age and
voltage. Just not as much as it used to.

Funny, I've measured a dozen caps before and after reforming, new
old stock from 1946 to 1997. Other than the 1946 one, which dropped
from 17 to 12.1 µF, all the others *increased* their capacitance. That
includes ones from 1947, 1962, and 1967.

73, Alan

Hi,

Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

I'd make that "1950."

There have been alot of improvements in the electrolytes, and now the
caps last virtually forever. But the oxide thickness still determines
the tolerance, and as such it still changes with temperature, age and
voltage. Just not as much as it used to.

Funny, I've measured a dozen caps before and after reforming, new
old stock from 1946 to 1997. Other than the 1946 one, which dropped
from 17 to 12.1 µF, all the others *increased* their capacitance. That
includes ones from 1947, 1962, and 1967.

73, Alan