If you still do not have a multimeter or other test instrument on your bench and want to know if the "stock" of electrolytes taken from some disassembled appliance has any defective then this taster can be of great use. It efficiently tests electrolytic capacitors from 1 to 1000 uF giving an indication of both leakage and even giving an idea of the value of the component.
The device is extremely simple and can be permanently built and installed in a plastic box. The principle of operation is simple: a transistor is polarized by a resistor (R1) in order to drive the current that causes an LED to illuminate.
If we momentarily connect an electrolytic capacitor between the base and the emitter of this transistor, the capacitor absorbs the bias current when charging. This means that during its charging period of a few seconds the LED goes out.
Since the charge time is the greater the higher the capacitor, the longer capacitors will have more time until the LED lights up. We will have something ranging from 1 second for capacitors of 1 uF to more than 1 minute for 1 000 uF.
If, when the capacitor is switched on, the LED lights up, it is signaled that it is open, and if it does not light up, it is because it is short or with high leaks. Comparing with the known capacitor time, we can determine the value of a capacitor under test. In Figure 1 we have the complete tester diagram.
In figure 2 we have the assembly of the circuit based on a strip of insulated terminals.
The probes can be improvised with nails. The resistors are 1/8 W or larger and the LED can be any. The power can be supplied with batteries (6 V) or a 9 V battery. Observe the polarity of the batteries and the LED.
To use, simply push the test leads into the terminals of the capacitor under test, observing the polarity and observing the LED. To disconnect the device, simply remove the batteries from the cradle.
Material list
Q1- BC548 - general purpose NPN transistor
LED - Common LED of any color
B1- 6 V or 9 V - 4 batteries or battery
R1- 47k ohm x1 / 8W - resistor - yellow, violet, orange
R2 - 470 ohm x 1/8 W - resistor - yellow, violet, brown
Miscellaneous: terminal strip, battery holder, probes, wires, solder, etc.
