Equivalent Series Resistance Meter (ESR Meter)

Project Description
This project was conceived as a way to enhance the collection of test equipment on my test bench. I buy a lot of older HP test gear off ebay as well as older radios. Most of this gear is 25-60 years old and needless to say, the condition of the electrolytic capacitors is somewhat suspect. I needed a way to quickly weed out bad caps with an in circuit tester.
At the present time, there are no plans to market circuit boards, kits, parts or complete units for sale.

What is ESR?
"ESR" stands for equivalent series resistance. ESR is one of the characteristics that defines the performance of an electrolytic capacitor. Low ESR is highly desirable in a capacitor as any ripple current through the capacitor causes the capacitor to heat up due to the resistive loses. This heating accelerates the demise of the capacitor by drying out the electrolyte at an ever increasing rate. Over the lifetime of a capacitor, it is not uncommon for the ESR to increase by a factor of 10 to 30 times or even go open circuit. Typical lifetime ratings for electrolytics are 2000-15000 hours and are very dependant on ambient operating temperature. As the ESR increases, the filtering operation of the capacitor becomes impaired and eventually the circuit fails to operate correctly.

Why are ESR Meters so Useful?
A typical capacitor checker measures the capacity (usually in micro farads) of the test capacitor. Some advanced units also test for leakage current. Most of these testers require that the capacitor be removed from the circuit. Unless the capacitor has totally failed, they will not detect a high ESR value. In a typical circuit, there may be 10's or 100's of capacitors. Having to remove each one for testing is very tedious and there is a great risk of damaging circuit boards. This tester uses a low voltage ( 250mv ) high frequency (150khz) A/C current to read the ESR of a capacitor in the circuit. The in circuit testing is possible because of the low voltage used for obtaining the measurement. The voltage is low enough that solid state devices in the surrounding circuitry are not activated and do not affect the low resistance reading we are attempting to obtain. A lot of capacitor checkers will be damaged if you happen to test a charged capacitor. This circuit is A/C coupled and will withstand up to 400vdc of charge on a capacitor (but watch your fingers!). The ESR checker will not detect shorted capacitors as they will read with a very low ESR value. If you are trouble shooting a circuit, you will have to use several instruments including your nose, voltmeter and oscilloscope to locate all the possible failure modes. My experience has found that the ESR meter catches about 95% of capacitor problems and potential problems.

 

Features

•     Tests electrolytic capacitors > 1uf in circuit.
•     Caps may be tested in circuit or by bridging them across the terminal posts or using test leads.
•     Polarity insensitive testing.
•     Tolerates charged capacitors up to 400vdc.
•     Low battery draw (approx 25ma) resulting in about 20 hours of battery time when using 4 cheap AA nicads.
•     Easy to read analog meter.
•     Measures ESR range from 0-75ohms with an expanded scale A/C ohmmeter.

Jadi pemahaman gampangnya :

• Semakin kecil ESR (hambatan / resistansi)sebuah elco, semakin baik kondisi elco tersebut.
• Semakin besar ESR (hambatan / resistansi)sebuah elco, semakin buruk kondisi elco tersebut.

 

Project Files

• Schematic Drawing - esrschematic.png(94.7K)
• Parts Layout - esrbuildit.png(13.4K)
• PCB bottom view - esrpcb.png(4.8K)
• PCB Xray View - esrxray.png(4.8K)
• Eagle PCB files - esrmeter-9mar05.tgz(173.2K)
• LTSpice/SWCadiii - Linear Technology Spice model esr.asc(5.8k)

Source: http://www.members.shaw.ca/swstuff/esrmeter.html