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HVACR214 – Electrical for Oil

Transformers

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The transformer

• The transformer is a non-mechanical electrical device.

• Transformers are both a load and a source.– The primary side of the transformer uses

electrical current.– The secondary side of the transformer

produces electrical current.

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The Transformer

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The Transformer

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The transformer primary

• Is the side of the transformer that voltage and current is applied to.

• This is a set of windings wrapped around an iron core.

• These windings produce a magnetic field.

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The transformer secondary

• This is the side of the transformer which produces electrical current.

• These windings are also wrapped around a magnetic core.

• The secondary side is electrically isolated from the primary, it is its own circuit.

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Windings

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Types of transformers

• A step down transformer reduces voltage from the primary to the secondary.

• A step up transformer increases the voltage from the primary to the secondary.

• The ratio of windings between primary and secondary determines how much the voltage is changed.

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Winding Ratio

• Keeping it real simple, if the primary side has 10 windings and the secondary side has 1 winding, this is a ration of 10:1.

• In this case if the transformer is supplied with 120v it will deliver 12 volts on the secondary side.

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Transformer ratings

• Transformers are rated by voltage on the primary side and volt amps on the secondary side.

• Most primary voltages in the HVAC industry are 120, 208/230, 240, 480.

• Secondary side of the transformer in the HVAC industry is 24 volts. In reality this can range from 24 to 28 volts.

• To establish the VA rating:Secondary volts X Secondary Amps = VA

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Troubleshooting Transformers

• First, check for source on the primary side. • If you have voltage, check for voltage on the

secondary side.• If no voltage check for a fuse or breaker and reset. • If still no voltage on the secondary, it is a bad

transformer. Replace it!