[Boatanchors] BBOD's are really reliable (sic)

[Philip Atchley]

Hi All,

In checking capacitors, there is one slight problem with Meters, whether 
they're digital or whatever.  They check the "value" or capacity just fine. 
Some even test ESR (useful if you're troubleshooting switching power 
supplies).  I have one of the "better" R/S do-all DVM's that "checks 
capacitors".  It is actually quite accurate (as checked against some 1% 
capacitors) and results are repeatable.

HOWEVER, these type of meters are TOTALLY USELESS in checking for the usual 
failures of BBODs or other capacitors in our beloved boatanchors.  The reason 
is quite simple.  The capacitors have excessive electrical leakage and the 
usual meter isn't sensitive enough to read this leakage resistance.  A meter 
operating at 9 VOLTS CANNOT simulate conditions of a capacitor that is 
operating with 400 or so Volts applied.  There ARE ways of checking them with 
the meter and an external power supply, but that has been covered elsewhere.

Most of the better resistance/capacitance bridges (Heathkit, Eico, Sprague 
etc) CAN check your capacitor at rated Voltage.  The Heathkit IT-28 I have is 
very good for this task.  IF YOU DON'T HAVE such a way to test your capacitors 
in a BA, then it definitely is to your advantage top do a wholesale 
replacement of said capacitors without even trying to measure them on your 
"DVM".  Even with the proper test gear I usually do a wholesale "shotgun" 
replacement of ALL paper and electrolytic capacitors, it saves destroying 
expensive or hard to find components later if one fails.

And, what to do with your "Capacitance Meter"?  Well, it's good for "matching 
capacitors" for value if you're making filters etc. Not a whole lot else.

73 de Phil,  KO6BB
991 Different NDB's heard to date.
SWL QSL GALLERY: http://photobucket.com/albums/y123/KO6BB/
THE BEACONEER'S LAIR:    http://www.geocities.com/ko6bb/
Merced, Central California, 37.3N  120.48W  CM97sh



> Re: your question (about some capacitor checking means/
> sources?)
>
> Jeff, Several years ago, I purchased a Wavetek "Meterman"
> Capacitance/Resistance checker, Model CR50, thru Grainger.
> True, the capacitance range is not too exceptional, but it's
> $69.95  was quite acceptable for my  requirements.
> It has performed exceptionally well on indicating capacitance
> readings being in accordance with component printed values, as
> well as showing poor performers.   (it also works well when one
> has the gumption to rig up a few sets of known capacitance
> "strings" -either series or paralleled- when the expected value
> of the capacitance to be measured exceeds (or is less than) the
> available ranges. Hi Hi)  In those instances though, the old
> pencil or the calculator has to be used to facilitate further
> calculations.