• The Transformer is simple solid state device. It converts high voltage-low current to low voltage-high current for the spot welding process. They come in hundereds of shapes and sizes and the internal windings can be very different even if the KVA ratings are the same. Remember, the KVA rating is only a thermal rating. The number of windings, size of the internal copper, water flow rate required, and primary voltage can all be different and give a different amperage output (Welding Current) with the same KVA rating.



• Formulas for transformers should be calculated according to the following: See the Formula Details
below if interested. How many amps do you need to make the weld? How big is the throat of the machine? What is the primary voltage for the machine? How many welds per minute will you be making? What duty cycle do you intend to weld at? How long is your weld time? In addition, the mechanical connection of the TX to the machine, transgun, welder, rocker arm, spot welder etc. can be very different. If you need a replacement, what does the secondary connection look like? What materials are you welding? Basically this type of engineering work is complex and difficult.

Transformers are a turns ratio between a large number of primary windings and a smaller number of secondary windings which convert high voltage-low amperage into low voltage-high amperage. Often the secondary number of turns is only one. Transformers normally have steel in them to help couple the power from the primary to the secondary. The size of the resistance welding secondary copper must be large enough to carry the amps needed to make a spot weld. Most spot welds are made with 5,000 to 20,000 amps and this is why the spot welder secondary copper is so large and water coolng so important. In addition, they are designed for 50 hertz or 60 hertz for A/C transformers and normally 1000 hertz for MFDC or inverter technology.

Often transformers come with a Tap Switch. The tap switch is a simple device that changes the number of primary windings. It has been heard that in the old days a different tap was used for different thicknesses. Now the current is mostly controled with the % Heat setting of the controller/timer. There are many machines that don't have a tap switch. Normally the current change with the tap switch is not very much. This again is a function of the transformer and who made it and how it was made.

When operating, Transformers should have a slight hum that is to the frequesncy of the A/C power going through them.

• Duty Cycle(D.C.)
• [(N x t)/(60 x f)] x 100
• N=Production Rate in welds per minute
• t=Weld Time in cycles
• f=Frequency in Hz
• D.C. can also be related to kVA demand: kVA 50%=(kVA dem) x (D.C./50)^(1/2)
• Turns Ratio
• (V_primary) / (V_secondary)=(T_primary) / (T_secondary)
• V_primary=Primary Voltage
• V_secondary=Secondary Voltage
• T_primary=Primary Turns
• T_secondary=Secondary Turns
• kVA input=kVA output
• V_primary x I_primary=V_secondary x I_secondary
• I_primary=Primary Current(Amperes)
• I_secondary=Secondary Current(Amperes)
• Ampere Turn_primary=Ampere Turn_secondary
• I_primary x T_primary=I_secondary x T_secondary
• Ohm's Law
• For direct-current(dc) circuits the formula is:I = E / R
• I=Current(Ameperes)
• E=Potential(Volts)
• R=Resistance(Ohms)
• For alternating-current(ac) circuits the formula is: I = E / Z
• Z=Impedance(Ohms)
• Joule's Law
• Q=I^2Rt
• Q=Heat Energy in Watt-seconds or Joules
• I=Current(Amperes)
• R=Resistance(Ohms)
• t=Time(seconds)
• Throat