HVAC Training Board:
How To Troubleshoot A Transformer (How To Check A HVAC Step Down Transformer) How a Transformer Works: Michael Faraday, the 19th century British physicist, made transformers possible when he discovered the phenomenon of magnetic induction. To make a long story short, a transformer uses induction to alter the voltage in an AC circuit, and it can either raise it (step it up) or lower it (step it down). An HVAC transformer is a step-down transformer that uses — as all transformers do — a pair of conducting coils wrapped around a metal core.
The primary coil receives the incoming signal, and as electricity passes through it, it induces a magnetic field in the core. That field energizes the secondary, or output, core, which in turn induces an electromotive force in the output coil. The EMF is directly proportional to the number of windings in the coil, so if the coils have different numbers of windings, the voltage in each circuit will be different. This only works with AC current because the electricity has to be in flux to induce a magnetic field.
The Control Circuit Is Isolated: The electric signal from the transformer is used by the system to open and close a series of relays and contacts that control the various system functions. The way it operates a particular component, such as the blower motor, is something like this: The neutral leg of the 24-volt circuit that originates at the transformer is connected to one terminal of a control relay that consists of a coil and a dry -contact switch. The hot leg is fed through the thermostat before connecting to the other relay terminal. When the thermostat switch closes and allows power to flow, it energizes the coil in the relay, which generates a magnetic field that closes the switch. The blower, which is powered by an independent 120- or 240-volt circuit, comes on.
Signs of a Bad Transformer: As a passive electrical device, it's rare for a transformer to malfunction, and a certain amount of humming is normal. A transformer can malfunction, however, if there is a power surge large enough to damage the coils or wire contacts. When the transformer is damaged, the circuit breaker controlling the system will usually trip to prevent damage to any of the sensitive electronic components of the control system. The breaker can trip for a number of other reasons, and it usually takes an HVAC professional to trace the cause to a bad transformer.
HVAC Training Board:
How To Troubleshoot A Transformer (How To Check A HVAC Step Down Transformer) How a Transformer Works: Michael Faraday, the 19th century British physicist, made transformers possible when he discovered the phenomenon of magnetic induction. To make a long story short, a transformer uses induction to alter the voltage in an AC circuit, and it can either raise it (step it up) or lower it (step it down). An HVAC transformer is a step-down transformer that uses — as all transformers do — a pair of conducting coils wrapped around a metal core.
The primary coil receives the incoming signal, and as electricity passes through it, it induces a magnetic field in the core. That field energizes the secondary, or output, core, which in turn induces an electromotive force in the output coil. The EMF is directly proportional to the number of windings in the coil, so if the coils have different numbers of windings, the voltage in each circuit will be different. This only works with AC current because the electricity has to be in flux to induce a magnetic field.
The Control Circuit Is Isolated: The electric signal from the transformer is used by the system to open and close a series of relays and contacts that control the various system functions. The way it operates a particular component, such as the blower motor, is something like this: The neutral leg of the 24-volt circuit that originates at the transformer is connected to one terminal of a control relay that consists of a coil and a dry -contact switch. The hot leg is fed through the thermostat before connecting to the other relay terminal. When the thermostat switch closes and allows power to flow, it energizes the coil in the relay, which generates a magnetic field that closes the switch. The blower, which is powered by an independent 120- or 240-volt circuit, comes on.
Signs of a Bad Transformer: As a passive electrical device, it's rare for a transformer to malfunction, and a certain amount of humming is normal. A transformer can malfunction, however, if there is a power surge large enough to damage the coils or wire contacts. When the transformer is damaged, the circuit breaker controlling the system will usually trip to prevent damage to any of the sensitive electronic components of the control system. The breaker can trip for a number of other reasons, and it usually takes an HVAC professional to trace the cause to a bad transformer.
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