A J4 variac is an electronics term. This term refers to the variable amount of wattage in the electric field.
In the electronics field, a J4 variac is a type of electric energy transfer. It involves the variance of the electric energy.
A variac is a transformer device that controls the output of AC line voltage to an electrical or electronic device. The variac is available in different sizes to suit ones needs.
The J4 first appears in the 1949-1950 gun Digest
These devices could, in theory, be interchangeable. Variac is a (typically single coiled) variable transformer, whereas rheostat is a variable resistor. Although they may look just the same, they differ in one aspect - wire resistance. It should be as low as possible for variac, but it can differ on rheostats. So-you can use wire rheostat as a low efficiency variac and you can use wire variac as ridiculously huge rheostat, resistive range of which serves no practical purpose.
alter. curent
single phase variac can give 0-270 voltage in ac forms. So it is used to know the voltage in any circuit.
A variac a variable auto-transformer, allowing the output voltage to be adjusted from zero up to a maximum voltage, which might be 20% greater than the supply voltage.
By using a Variac Transformer
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The phantom loading is that no external load is connected in actual sense and the current and pressure coils are connected seperatly so that it will consume only less power. In this connection the voltage across pressure coil will be supply voltage even if the variac is in minimum position. CONNECTION Connect a single phase supply through a single phase variac. Connect the currect coil of wattmeter M and energy meter c1 and an ammeter in series to phase terminal of singlephase variac. The pressure coil of both wattmeter and energymeter should be shorted and connected to phase of supply (not to the variac). The terminal V of wattmeter and p2, c2 of energy meter should be connected to neutral terminal of variac. PROCEDURE Keeping the variac in minimum position and switch on supply. Adjust the variac to get different reading in ammeter and note the time for 5 Revolution of energy meter disc and obtain the wattmeter reading. FORMULAE %error = (R.E - A.E)*100/A.E , WHERE, R.E is the recorded energy = n/N (n=5 & N=energymeter const.) A.E is the actual energy A.E= (wattmeter reading*time)/(3600*1000) while plotting a error graph it will be having a zig-zag shape. Normally the error can be upto 10%
Obviously that you work it out for yourself... The idea is to make your brain hurt.
The phantom loading is that no external load is connected in actual sense and the current and pressure coils are connected seperatly so that it will consume only less power. In this connection the voltage across pressure coil will be supply voltage even if the variac is in minimum position. CONNECTION Connect a single phase supply through a single phase variac. Connect the currect coil of wattmeter M and energy meter c1 and an ammeter in series to phase terminal of singlephase variac. The pressure coil of both wattmeter and energymeter should be shorted and connected to phase of supply (not to the variac). The terminal V of wattmeter and p2, c2 of energy meter should be connected to neutral terminal of variac. PROCEDURE Keeping the variac in minimum position and switch on supply. Adjust the variac to get different reading in ammeter and note the time for 5 Revolution of energy meter disc and obtain the wattmeter reading. FORMULAE %error = (R.E - A.E)*100/A.E , WHERE, R.E is the recorded energy = n/N (n=5 & N=energymeter const.) A.E is the actual energy A.E= (wattmeter reading*time)/(3600*1000) while plotting a error graph it will be having a zig-zag shape. Normally the error can be upto 10%. Winston Netto SSET-SCMS Engineering college.