Capacitors

© Brooke Clarke 2010

These were purchased at test subjects for the ESR Micro combined Effective Series Resistance and Capacitance meter.  I was going to put this data on that page but way too large so is here as a seperate page.

The first choice was to get leaded parts to allow insertion in the ESR MIcro and the SR715.  Parts that are a few cents were ordered on tape at 100 each so in some photos you will see the tape.  The photos have been scaled so they are all 200 pixels wide, so the scale factor varies a lot, i.e. they are NOT shown in relative size.

The photos will help ID different types of caps.  More photos on the Capacitor Failure paragraph on the Hints & Tips web page.
Wiki page Capacitor plague about the bad electrolytic caps (Wiki) made around 1999 but still being used up to about 2007 and failing in 2010.

These are related to using the ESR-Cap meter.

Heathkit GC-1000 Most Accurate Clock

This had nearly all the electrolytic caps bad.  It's now working great on the built-in whip antenna. 

Oven Controller

See Hints and Tips: Cold Oven Robertshaw Controller in GE Electric Oven
Two caps in the analog temperature control circuitry, both marked 4.7 uF 35 V, tested C: 000 ESR: ---.  The interesting thing is that the replacement caps, rated 4.7 uF 25 V, are larger.

I didn't determine the working voltage of the 4-bit micro controller but expect it runs on 5 volts.  The LM324 op amp might be running as high as 32 V, but I very much doubt it, +/- 15 would be the max expected, so getting 25 V replacement caps seems to be conservative.

The bad C1 and C17 caps were punched into a copy of the board photograph to keep track of them and then bare wires were soldered on to allow them to fit in the SR LCR meter or HP LCR fixture.  You can see that the new caps are much bigger. Cap WVDC dia mm height mm pitch mm Old 4.7 35 4 6 1.5 New 4.7 25 5 11 2 The height needs to be short in order to allow for the relay board that's mounted directly above this board (see the Hints and Tips web page).  The replacement parts were installed laying on their sides out of general principles.   But it turned out it was required for vertical clearnace. The volume of an electrylytic capacitor depends on both the capacitance and on the working voltage and since the new part has a lower working voltage there's a huge difference in volume.

The SR 715 (1 kHz & 1V drive) shows the bad caps as about 20 nF (0.02 uF) not the 4.7 uF they should be and with a series resistance of about 40 k Ohms.  This is consistant with the electrolyte evaporating.  Note that total hours of use this oven has seen is probably under 10 so the problem was not heat.  But the controler board (clock) is powered 24/7/365 minus the occasional power failure.

Tested in # order using all the testers, then the next #.  A Lazy Susan helped.

Note 1 The Fluke 87 has trouble measuring the capactiance of parts in the pf range because it's difficult to get a repeatable delta to zero the meter.  A plug in axial capacitor fixture might solve that problem.
Note 2 the Stanford Research 715 is fixtured for axial lead parts only, SMT and supercaps do not fit.
Note 3 Multi Layer Ceramic Caps (MLCC) have frequency dependent capacitance and series resistance on the SR 715.
Note 4 FRS is Fair Radio Sales

ESR-Cap meter -
EVB ESR Meter - Modified for testing Batteries

Fluke 87V DMM -has Capactiance test capability
HP 4260A Universal Bridge
HP 4328A Milliohmmeter
HP 4332 LCR Meter
Marconi TF-2700 Universal Bridge
Stanford Research 715 LCR Meter
ZM-11/U Capactance-Inductance-Resistance Bridge
Test Equipment