I need to replace some capacitors in a boat anchor receiver. These caps
are across the power supply rails on a logic circuit board. They are
marked "227 +10K". My interpretation of that is 220 MF. at 10 VDC with a
10% tolerance. Does my interpretation sound correct?

Any suggestions for a replacement? If I use tantalums will I be doing this
again in 20 years?

Thanks,
--
HZ

Hank Zoeller wrote:
I need to replace some capacitors in a boat anchor receiver. These caps
are across the power supply rails on a logic circuit board. They are
marked "227 +10K". My interpretation of that is 220 MF. at 10 VDC with
a 10% tolerance. Does my interpretation sound correct?

Any suggestions for a replacement? If I use tantalums will I be doing
this again in 20 years?

Thanks,

That looks right. Unless I was willing to do some analysis I'd replace
them with tantalums that have the same general look, and expect to
replace them again down the road. The only real alternative that would
approach the size are niobium or other rare-earth caps which have aging
and performance characteristics that are substantially the same as
tantalums, or some of the newer aluminum electrolytic caps which will
tend to have a shorter life (although with less dramatic failure modes).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Hank Zoeller wrote:
I need to replace some capacitors in a boat anchor receiver. These
caps are across the power supply rails on a logic circuit board. They
are marked "227 +10K". My interpretation of that is 220 MF. at 10 VDC
with a 10% tolerance. Does my interpretation sound correct?

Any suggestions for a replacement? If I use tantalums will I be doing
this again in 20 years?

Thanks,

Tantalums are quite reliable if you choose them correctly.

The usual causes of short life are the magnitude of applied voltage, and
charge/discharge current. As a rule of thumb, pick a capacitor that has a
voltage rating that is a minimum of 2 times the maximum voltage the capacitor
will ever see, and you should be ok.

High charge and discharge currents can sometimes be solved by using a series
resistor between the source that you are filtering, and the capacitor that
is doing the filtering.

Applying reverse polarity will cause an extremely short life.

-Chuck

Tim Wescott wrote:
That looks right. Unless I was willing to do some analysis I'd replace
them with tantalums that have the same general look, and expect to
replace them again down the road.

That is useful information, Tim, thank you!

--
HZ

Chuck Harris wrote:
The usual causes of short life

Thank you, Chuck. The existing tantalums in the receiver lived for about
25 years so I guess that's not considered "short life". The one that
failed did so in a rather startling way. Scared the bejeezus out of me
when it exploded and let loose a bunch of smoke.

I guess if I get 25 years out of it's replacement I'll be happy..
--
HZ