[SI-LIST] Re: Fw: Re: Re: Reset problem with power supply

Olaney.

I have an old Grebe Synchrophase Model MU-1 1927 Synchrophase Radio that I 
would like to restore.  Can you restore old radio's too? 
 I am willing to pay a good price to get it rebuilt. 

How about it? 

Richard Jungert


> To: olaney@xxxxxxxx
> CC: si-list@xxxxxxxxxxxxx
> Date: Sun, 7 Dec 2008 19:21:00 -0800
> Subject: [SI-LIST] Fw: Re: Re: Reset problem with power supply
> From: olaney@xxxxxxxx
> 
> On all the military design projects I've worked on recently, you could
> not use an aluminum electrolytic cap without a long and painful
> justification process.  You could get a yes if there was no other way to
> get there, but basically electrolytics were verboten.  Allowable
> temperature range was an issue even if the cap was all but hermetic
> against  leakage.  Electrolytic caps use wet chemistry and if they freeze
> it causes damage.  Also note that electrolytic voltage ratings don't
> derate well.  If you operate a 50 volt rated electrolytic cap at 25
> volts, over time it will become a 25 volt capacitor.  It's inherent in
> the chemistry between the aluminum and electrolyte, which is not stable
> like a polymer dielectric.  You could put the worn cap on a current
> limited supply and build it back up to 50 volts, but the general advice
> for electrolytic caps is to choose one rated not much higher than the
> working voltage of the circuit, e.g. 6.3V rated caps for 5V applications.
>  This raises another issue: the chemistry that maintains the dielectric
> barrier on the surface of the aluminum is an active process.  As is
> typical of many chemical processes, the tiny amount of leakage current
> that results is noisy.  This doesn't matter for bypassing, but for low
> level coupling I go for tantalum caps, film or ceramic if I can get away
> with the cost and size.
>  
> I know this discussion makes aluminum electrolytics seem like an
> invention of the devil, but it is a very successful technology where the
> limitations are not constraining. 
>  
> Miltary equipment is designed for long service life and can be quite old
> before it is discarded, sooner only if replacement parts cannnot be had
> or new technology offers advantages that cannot be ignored.  Other than
> that, the stuff keeps going.  The B-52 is one of the few planes in our
> active defense inventory that is older than the pilots flying them, but
> the cockpit electronics get refreshed somewhere in the 10 to 20 year
> range.
>  
> Orin Laney
>  
> On Sun, 07 Dec 2008 02:19:34 -0800 Hal Murray <hmurray@xxxxxxxxxxxxxxx>
> writes:
> > 
> > weirsi@xxxxxxxxxx said:
> > > Electrolytic caps come along with some engineering requirements.  
> > The
> > > first is long term product life:  electrolytics have a typical 
> > shelf
> > > life of 5-10 years for cheap to very high quality.  This is a 
> > function
> > >  primarily of the seals.  However it is not that unusual to find a 
> > box
> > >  with large body computer grade electrolytics going for more than 
> > 20
> > > years.  The big issues: are  initial conditioning, adequate
> > > temperature,  voltage derating, and absolutely : NO EXPOSURE TO
> > > HALOGENS.  A 10 year  life is readily attainable, and with a lot 
> > of
> > > derating 20 years can be  had in large body parts.  Miniatures are
> > > really constrained to about 10  years no matter what is done.
> > > Consumer products contain only miniatures  these days, and are so
> > > fiercely price sensitive that no one pays for the  kind of 
> > derating
> > > needed to see long service lives.  As a result, the  electrolytics
> > > rank #1 to #2 for failure rates in consumer electronics  ahead or
> > > behind of the power semiconductors.
> > 
> > Thanks.
> > 
> > I assume the halogens mostly come from cleaning.  Has that been 
> > solved by the 
> > save-the-ozone efforts?  Do assembly houses know about that?  Is it 
> > in the 
> > data sheets?
> > 
> > I don't remember hearing it before, but I could easily have not paid 
> > 
> > attention.  I just scanned one handy data sheet.  I didn't see 
> > anything about 
> > cleaning.  It's probably buried off in an app note or such.
> > 
> > I did see that they are only rated for 2000 hours.  I hadn't paid 
> > much 
> > attention to that before.  That's under 3 months at 24/7.  Ouch.  
> > Thanks for 
> > the heads up.  I'll have to find the temperature re-rating specs.  
> > Sigh.
> > 
> > 
> > What do military or other high reliability folks do?
> > 
> > I expect a lot of military gear is still in service after 10 years.  
> > (B-52s 
> > are still flying.)  Does the electronics turn over fast enough to 
> > avoid this 
> > problem?
> > 
> > 
> > 
> > 
> > -- 
> > These are my opinions, not necessarily my employer's.  I hate spam.
> > 
> > 
> > 
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