[Boatanchors] ESR Measurements: How Bad Is Bad ??

[Garey Barrell]

Dave -

Wow!   Are you sure they weren't shorted!??  :-)   That's the only way I 
can think of for a dried out cap to read low ESR.  In fact I think they 
recommend using the ESR meter in parallel with an ohmmeter to catch 
shorted caps for just that reason.

That's the only "misleading" readings I've gotten, where a cap is 
shorted and reads nice and low.  The meter uses a roughly 100 kHz pulse, 
and the only caps I've seen read higher are very low voltage units where 
there was enough inductance to "lose" the pulse.  Caps less than 10 uF 
tend to have higher ESRs than larger ones, but still less than 10-15 
ohms.  It should work fine on anything over 1 uFd.

It's the second piece of test equipment I grab with a "new" piece of 
gear.  Right after I check to see what some numbskull might have stuck 
in the fuse-holder instead of the correct fuse!  I've found everything 
from the right fuse to one wrapped in aluminum foil to a piece of # 6 
copper wire cut to length!

I guess it's like any other piece of test equipment, if the results 
don't look "right", retest using another method.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>



Dave Harmon wrote:
> Interesting....I have one of those Dick Smith meters too and in the course
> of using it I was scratching my head when 47 year old electrolytics I
> removed from several Collins 516F-2's were testing good on the meter but the
> pop-tops were blown open and they stunk indicating that the electrolyte had
> left town years before....mebby decades.
> I replaced the caps anyway of course but perhaps this meter would be best
> used on smaller caps like what would be used on today's electronics instead
> of boatanchors.
>
> Regards
>
> Dave Harmon
> CCA 97-535
> Midwestern Collins
> K6XYZ[at]sbcglobal[dot]net
> Sperry, Ok.
>
> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net
> [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Garey Barrell
> Sent: Wednesday, December 03, 2008 9:05 PM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] ESR Measurements: How Bad Is Bad ??
>
> Dick -
>
> Generally speaking, bad is  _BAD_  , i.e., either a cap will read 
> fractional ohms for most caps, certainly less than 2-3 ohms.    Bad caps 
> will read hundreds of ohms or more depending upon the rest of the 
> circuit.  I don't think I've ever seen one over 3-4 ohms that wasn't BAD.
>
> 73, Garey - K4OAH
> Glen Allen, VA
>
> Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
> <www.k4oah.com>
>
>
>
> Richard W. Solomon wrote:
>   
>> I have one of the Dick Smith ESR meters. Nice device, but I
>> wish I could find more info on analyzing the test results.
>>
>> For example, I test a 470 mfd @ 50 vdc cap. The meter reads
>> 0.15, the chart on the meter says 0.09. How bad is bad ??
>>
>>
>> Thanks for any tips,
>>
>> 73, Dick, W1KSZ
>>   
>>