This ESR Meter is perfect for any electronics repair technicians, engineers or hobbyist. This handy ESR meter measures electrolytic capacitor equivalent series resistance (ESR) in the circuit. ESR is a very important characteristic of capacitors greater than 1 microfarad. This meter makes measurements which are often impossible to check with standard digital capacitance meters. This ESR meter is based around ICL7107, 4049, NE555 and TLC274 operational amplifier and can measure resistance from 0.01 Ohm up to 19.99 Ohm. ESR value is displayed in Ohm on four digit LED display . The power consumption is only 8mA using 12V battery. ESR Meter offers very simple design and is easy to assemble.
With the presented device can measure the equivalent series resistance of electrolytic capacitors and accumulators. The unit is original legally from the ELVjournal, Issue 4 / 2002, but - as the 18V battery charger - partially rebuilt, it has in this release, a Seven-segment LED display and is hospitalized by a network device 9 to 12 volts, whereby the auto power-off circuit of the original device is eliminated.
Each capacitor has three basic parasitic components: a series inductance Ls, due to the connecting wires, a parallel resistance Rp due to leakage currents, and a series resistance Rs
The lower the replacement series resistance (ESR Data Sheet, equivalent series resistance) is the better of the capacitor. The ESR increases with age and with high temperatures and a high ESR can lead to failures of the device (keyword: switching power supplies!).
With the presented device, the ESR of a capacitor approximately determined and so the condition can be determined. Also, batteries can be measured and assessed in this way, and moreover it is also still use a ohm meter in the range 0 to 20 ohms. It measures - in contrast to conventional ohmmeter - an AC voltage with a frequency of 60 kHz, so the (ideal) capacitor acts almost as a short circuit and only the ESR is measured.
Here there is the circuit diagram of the ESR meter (PDF file).
Top left of the diagram of the power supply is shown. The unit requires a DC voltage in the range of about 9 to 12 volts, which is used once directly and is additionally stabilized with IC1 to 5V. The diode D1 serves as a reverse polarity, C1 to C4 stabilize the voltages.
Including the oscillator part is visible, which is a type of IC NE555 established. (In the original circuit, a power-saving ICM7555 was used, but this here, thanks to power supply is not necessary.) At the output, pin 3, a square wave kHz with a frequency of about 60, about the two low passes R2/C7 and R3/C8 is sent and then roughly sinusoidal shape. T1 through the driver transistor is DC-coupled, where the measured input to the capacitor to be measured is connected. The voltage drop across the capacitor is removed, the OP-chain IC3A increased to C and the same direction as IC3D.
Subsequently, this ICL7107 voltage to the input of IC4, a display driver of the type given. This is wired up by default to data and includes all necessary components, the A / D converter to the display driver. The result is then added directly to four seven-segment displays (models with a common anode).
Reconstruction and reconciliation
When reproduction is for the high frequencies on a clean trace leadership ensured. The measuring cables should be connected securely or tightly seated in their sockets, as well as the wires should be kept close together (ideally every 10cm with tape and tie or the like).
The adjustment is relatively simple. After switching on the device, the test leads are held together. The trimmer R21 is now set so that the display reads zero. Then, a resistance 10 to 18 ohms, the value of her should be known as accurately as possible, connected and calibrated the display with R25 to that value.
Thus, the adjustment is already finished. Now a word about the measurement practice. Capacitors with low-capacity naturally have a higher ESR than larger capacity. However, if a value of 10 ohms measured, the capacitor can be safely classified as unusable. In the range below a value of 30μF can sometimes occur at the 3-5 ohm, which is not necessarily bad. Capacitors of 100uF, however, should be well below 2 ohms. Here is a little experience is needed with the values.
Incidentally, capacitors due to the low measuring voltage directly measured in the circuit and need not be previously developed.
The picture shows my finished device, installed in a pretty case of Bopla. In addition to the on / off switch, the two sockets to which the capacitor is connected. At the front jacks for power supply. At the entrance is just a capacitor with 47uF / 10V, which here because of the high value to no longer be considered fresh.
My own ESR meter is built on a strip-board (see photos above). Due to various demand is now created for a layout that can be downloaded here. In the replicas (see below), there are photos of some boards based on these devices.
Note: The layout is the one with the copper surface, the solder side.