Re: Carbon Comp: Aging Causes Out Of Tol?


"Jim Adney" <jadney@xxxxxxxxxxx> wrote in message
news:8vvf819a1qo9d84a9c4kqggcjumo2pg0hc@xxxxxxxxxx
> On Sun, 15 May 2005 05:13:49 -0700 "Watson A.Name - \"Watt Sun, the
> Dark Remover\"" <NOSPAM@xxxxxxxxxxxxxx> wrote:
>
> >I have fifty 910 ohm 1/4W carbon composition resistors, still in the
> >paper tape, which is labeled:
> >
> >OHMITE
> >910 OHM
> >1/4 W 5%
> >RC07GF911J
> >OC9115
> >
> >Judging from the last line, they're 14 years old. They've never been
> >used, AKA New Old Stock. Every resistor measures greater than 5%,
some
> >are over 1k. Over 14 years, would drift from aging cause them to go
> >that far out of tolerance? I have carbon film resistore much older
than
> >these and they still measure within 5% tolerance, usually within 2%.
>
> If you could find an old Allen-Bradley catalog you'd be truly amazed
> at the amount of detail they lay out on the moisture sensitivity of
> these resistors.
>
> The gist of it is as follows:
>
> 1) Carbon composition resistors will absorb moisture out of the air
> and go up in resistance. If the resistance is important to the
> manufacturer, they much keep them in a special dry engvironment, just
> like flux coated welding rods.
>
> 2) If you have carbon composition resistors which have gotten damp,
> they can be dryed out by heating them to temps below 100C for several
> days. 2 Watters take longer than 1/4 Watters. Don't try to speed this
> up by using higher temps.
>
> 3) If you solder them when they are "damp" the change in resistance
> will be locked in, ie no longer reversible.

Thanks for the info. The four I put on the soldering iron were probably
overheated and won't be salvageable. The rest haven't been exposed to
water or high humidity, generally it's low humidity most of the time
here. So I don't see why they could've changed. I'm thinking that I
might be able to put them inside a ziplock bag with a dessicant and
leave them out in the sun for awhile, and it might help. Can't hurt
much since they're already nearly worthless.

> I did this test on a batch of 27k, 2W carbon comp resistors a number
> of years ago. They were all high, and most of them were out of
> tolerance, this was immediately as purchased from Newark. But they all
> came back into tolerance after heating in my home-made oven for about
> a week.

But at what temperature? I've got a bunch of old 1- and 2-watt
resistors and I don't think I'll ever use them because I'll never need a
(for example) 27k 2W resistor since it takes a couple hundred volts to
get up to 2W and I don't do tubes anymore.

> -


.

Relevant Pages

  • Re: Carbon Comp: Aging Causes Out Of Tol?
    ... >I have fifty 910 ohm 1/4W carbon composition resistors, ... >these and they still measure within 5% tolerance, ... Carbon composition resistors will absorb moisture out of the air ...
    (sci.electronics.components)
  • Carbon Comp: Aging Causes Out Of Tol?
    ... I have fifty 910 ohm 1/4W carbon composition resistors, ... these and they still measure within 5% tolerance, ...
    (sci.electronics.components)
  • Re: Replacement for Carbon Comp resistors
    ... Sources for higher wattage carbon composition resistors seem ... Can ceramic composition resistors, such as Ohmite's ... inductance, so you always have to ask. ... watt to 5 watt monsters, ...
    (rec.radio.amateur.homebrew)
  • Re: Replacement for Carbon Comp resistors
    ... Sources for higher wattage carbon composition resistors seem ... Can ceramic composition resistors, such as Ohmite's ... inductance, so you always have to ask. ... watt to 5 watt monsters, ...
    (rec.radio.amateur.homebrew)
  • Re: Replacement for Carbon Comp resistors
    ... Can ceramic composition resistors, such as Ohmite's ... inductance, so you always have to ask. ... Carbon composition resistors never were completely "non-inductive"... ... most makers of big power amplifiers have moved ...
    (rec.radio.amateur.homebrew)