What is ESR METER ? Written by Jestine Yong
All capacitors have a certain amount of resistance to passage of AC current. ESR (Equivalent Series Resistance) is sum of all internal resistances of a capacitor measured in Ohms. An ideal capacitor has ZERO ohms ESR. From diagram below you can see a resistor in series with a “PERFECT CAPACITOR”. The value of resistor is called ESR. Electrolytic Capacitors have a tendency to increase its ESR overtime due to drying or corrosion. High ESR is a frequent problem in today’s electronic circuit. Even a 1 or 2 ohms rise in ESR can cause complicated problems. Under normal conditions ESR has a very low value, which stays that way for many years unless rubber seal is defective, in which case electrolyte’s water component gradually dries out and ESR creeps up with time. The increase in ESR increases both voltage drops within capacitor and heat, produced in capacitors due to resistive heating. If you don’t check for ESR, you may be in for a “TOUGH DOG” repair. High ESR is first sign of a capacitor failure. High ESR will cause complete circuit failure, over heating of capacitor, loading of circuit, overstressing of other circuit components and other undesirable effects. Why should I use an ESR?Because measuring an electrolytic capacitor with an analog or digital capacitance meter can MISLEAD a technician into believing that a defective capacitor is good. This can waste your precious time and you are unable to repair equipment. Which means you can’t charge your customer! If you don’t test for ESR on capacitor, you will always miss bad capacitor. Normally, these bad capacitors have high ESR reading which your normal multimeter or digital capacitance meter can’t measure. Only by using ESR meter, you will be able to measure ESR on capacitor and you will not be fooled by capacitors with bad ESR. ESR meter can even work IN-CIRCUIT, which means you don’t have to solder out capacitor in order to measure it using normal capacitor tester, which would not be accurate anyway. Do you know that ESR meters can perform other wonders besides checking ESR of a capacitor? Some digital ESR meter have features of checking:
| | What is a Fuse ? And how to test it.Written by Jestine Yong
A fuse is a very thin wire, which either melts or vaporizes when too much current flows through it. The thin wire may be made of aluminum, tin-coated copper or nickel. The resulting open in circuit stops current flow. In electronic equipment, most fuses are cylindrical glass or ceramic type with a metal cap at each end! The current rating also can be seen in one of two metal end caps. There are two popular physical sizes: 1 – ¼ X ¼ - inch and 5X20mm. The 1 – ¼ X ¼ - inch size is used in many automobiles. You’ll find both sizes in many electronic equipment, but smaller 5 X 20mm has become more common. Fuses are available with current ratings from 1/500 Ampere to hundreds of amperes. Purpose of Fuses The purpose of a fuse is to open an electronic circuit when current flow exceeds a certain amount, determined by rating of fuse. Opening a circuit under high current conditions can save electronic components from damaged and prevents overheating, which could cause a fire. Types of Fuses There is two basic types of fuses: fast acting and slow blow. The fast acting type will open very quickly when their particular current rating is exceeded. This is important for analog meter movements, which can quickly be destroyed when too much current flows through them, for even a very small amount of time. Slow blow fuse have a coiled construction inside. They are designed to open only on a continued overload, such as a short circuit. The purpose of coiled construction is to prevent fuse from blowing on just a temporary current surge. Do not use a slow blow fuse in place of a fast acting fuse. It may not open fast enough to prevent components damage under a high current condition. It’s not harmful to replace a slow blow fuse with a fast-acting fuse, but it will probably open up unnecessarily every now and then when equipment is first switch on. A blown fuse can tell you something about your service problem. Often glass case of fuse appears clear, and you can still see broken pieces of fuse element. This means you have kind of problem that causes a slow, gradual overload on power supply. Some fuses even die of old age. But if inside of glass fuse is discolored, and there is no trace of fuse element (the center connector), you know that center connector was destroyed quickly and violently, using a lot of heat. The fault was a short circuit or other problem that caused a lot of current to flow very quickly.
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