[Premium-Rx] Cubic R 2411/R 3030 blows caps

[Gary Geissinger]

Al,

Mark brings up a really good point.  Without inrush limiting I've seen
some tantalum capacitors instantly go bad.

Also, tantalum capacitors aren't all equal.  Wet slug vs dry slug makes
a big difference.

Finally aluminum electrolytics may need a monolythic ceramic in parallel
to give the performance of a good tantalum capacitor.  In my designs
when possible I'm trying to phase out tantalum capacitors (and I can't
use electolytics anyway) by using "stacked monolythic ceramic
capacitors." Unfortunately they aren't perfect either (I guess nothing
is.)

Regards,

Gary WA0SPM

Gary A. Geissinger
Chief Electrical Engineer
DigitalGlobe Inc.
1601 Dry Creek Drive
Suite 260
Longmont, CO 80503
ggeissinger at digitalglobe.com
see www.digitalglobe.com
"An imaging and information company."


-----Original Message-----
From: premium-rx-bounces at mailman.qth.net
[mailto:premium-rx-bounces at mailman.qth.net] On Behalf Of Mark Donaldson
Sent: Tuesday, September 18, 2007 9:50 AM
To: Royce, Alan (Space Technology); premium-rx at mailman.qth.net
Subject: Re: [Premium-Rx] Cubic R 2411/R 3030 blows caps

Try replacing them with electrolytics, Tantalums have this wierd
property where for a brief instant upon application of voltage they will
present a very low impedance, so low in fact that they can weld
themselves short circuit if there is not sufficient current limiting on
the supply line, electrolytics do not exhibit this characteristic. Once
these tantalums weld themselves into a short circuit they sit there on
the PCB board and procede to burn a hole through it if there is nothing
to limit current. I have worked at two companies so far that have
eliminated tantalums from their products for this reason. Unfortunately
electrolytics are limited on their low end operating temperature range
due to electrolyte freezing thus the reason tantalums are used.

Mark Donaldson WA1QHQ

--- "Royce, Alan (Space Technology)"
<alan.royce at ngc.com> wrote:

> Hi,
> Got a R 2411 that blows the 35 volt 10u tantalums when you power it 
> up.
>  Caps/tantrums, are located at the input to the plus and minus to the 
> 16 volt line to each of the modules on the left side radio.
> I have looked at the 16 volt lines and can not see any spikes on them.
> I have al ready replaced at least 10 tantalums, even now replacing the

> ones that I replaced before.
> Any one have a clue to what is going on??
> Thanks
> Al
> _______________________________________________
> Premium-Rx Mailing List
> To Post: premium-rx at mailman.qth.net
> For Info:
> http://mailman.qth.net/mailman/listinfo/premium-rx
> Visit the Website: http://www.premium-rx.org Email Help: 
> paul at premium-rx.org
> 
> 



       
________________________________________________________________________
____________
Building a website is a piece of cake. Yahoo! Small Business gives you
all the tools to get online.
http://smallbusiness.yahoo.com/webhosting
_______________________________________________
Premium-Rx Mailing List
To Post: premium-rx at mailman.qth.net
For Info: http://mailman.qth.net/mailman/listinfo/premium-rx
Visit the Website: http://www.premium-rx.org Email Help:
paul at premium-rx.org