What is ESR? ESR is the abbreviation for “Equivalent Series Resistance”, sometimes referred to as “Effective Series Resistance”. ESR is a DYNAMIC (AC) property of a capacitor and cannot be measured with a DC ohm meter. ESR can be considered to be the total series NON-REACTIVE AC resistance of a capacitor. ESR includes the DC resistance of the leads, DC resistance of the connections to the dielectric, capacitor plate resistance, and the IN-PHASE AC resistance of the dielectric material. The combination of components that make up ESR are symbolized by a resistor in series with a capacitor as shown. The series resistor in the symbolic representation of “ESR” does not exist as a physical entity. Direct measurements across the ESR resistor are not possible! The Capacitor Wizard® overcomes this limitation by measuring only the NON-REACTIVE AC resistance(ESR).

Why check ESR? An increase in ESR is the first indicator of a bad capacitor. As a capacitor fails its’ ESR increases until ESR reaches infinity, total failure. By measuring ESR one can locate failing capacitors before they quit completely. Often a capacitor will measure GOOD with a capacitance reading meter yet it will actually be BAD due to increased ESR! Todays' modern circuits are designed with low ESR parts. Checking ESR guarantees a reliable test of a capacitors health.

Why does my other capacitance meter read "GOOD" on known bad parts? Capacitance meters cannot read ESR. They only measure capacitance. Capacitance is important but it is not the only important capacitor property. ESR is probably more important. A BAD capacitor can have the correct capacitance and HIGH ESR. High ESR upsets time constants, causes part heating, inserts unwanted series resistance which impedes current flow. These undesirable circuit changes frequently cause failures, even when capacitance measures correctly. Without the ESR test you may accidentally declare a BAD capacitor GOOD. Your "known bad" parts are likely due to high ESR. Don't be fooled by a standard capacitance meter!! Use the Capacitor Wizard® In-Cicuit ESR Meter.

How does the Capacitor Wizard® ignore other in-circuit parts? There are four EXTERNAL parallel parts that could interfere with in-circuit ESR measurements: inductors, resistors, solid state junctions, capacitors. Parallel inductance: The test frequency is high enough ( 100khz ) to force expected inductive reactance (power transformers, coils) many orders of magnitude higher than the ESR scale. Parallel Resistors: Resistors found around capacitors 1uf and up will be large values compared to the Capacitor Wizard®'s low input impedance (2.5ohm). Parallel resistors have little effect on the reading and can be ignored. Solid State Junctions: The test voltage is less than 20 mv pp, too low to turn on any GOOD solid state devices. (You can use the Capacitor Wizard® to find leaky or shorted diodes, transistors IN-CIRCUIT!) Parallel Capacitors: Rarely will you encounter a circuit design using parallel capacitors. One leg of a parallel cap must be lifted. Both caps can then be individually tested.

What happens if I accidentally test a CHARGED CAP? Often no damage is done. Download Doug's Tech Notes: http://www.midwestdevices.com/_pdfs/Sbullit8.pdf for the easy repair instructions.

How do I know my Wizard is working? Measure some low value resistors (1ohm, 2ohm 3ohm etc). Verify agreement with the Capacitor Wizard®. If the Capacitor Wizard® closely agrees then it is working properly and in calibration.

Why must I discharge Capacitors? The input resistance of the Capacitor Wizard® is held very low by two one ohm resistors (R51 & R52) and the low probe lead resistance of 500 milliohm. This low impedance insures a proper ESR measurement discarding transients. If you attempt to test a charged cap these resistors will often just discharge the capacitor, no damage done. However if the unit under test is turned on or if the capacitor has a lot of stored energy you will damage one or both of these resistors. You may also damage (2) capacitors (C23, 33uf@25v & C8, .1uf@50v), (Q5) 2N3904, (Q6) 2N3906, (R53) 100ohm 1/8w, U1 - TLC2274 (or Raytheon RC3403) - Do not substitute a LM324, MC3403 or any other part for the TLC2274 as they don't have enough gain @100khz to zero the meter.