Buck & Boost Autotransformers - Short 126

HVAC School - For Techs, By Techs

In today’s short podcast, Bryan discusses buck-boost (auto) transformers and what they do.

Autotransformers are not automatic; the “auto” prefix comes from the fact that autotransformers only have one inductive winding. That winding is shared by the primary and the secondary, so it is not an isolation-type transformer. These transformers run current through the same winding used for induction.

Buck-boost transformers rise or decrease voltage. When the transformer “bucks,” it decreases voltage from primary to secondary, and a “boost” increases the voltage from primary to secondary. In other words, a “boost” is a step up, and a “buck” is a step down on a small scale.

You can only wire these transformers if you use the manufacturer literature. There are many types of autotransformers, and you need to know the exact setup for your transformer’s specific design. Generic diagrams will usually not suffice.

When sizing a buck-boost transformer, you must keep your start load in mind as well. As technicians, we might not be able to handle the specifics of sizing based on the start load, but it’s still something to keep in mind.

The “buck” configuration of the buck-boost transformer is especially helpful in markets where the utility company tends to produce overvoltage. Our specific setup uses the Micron J750A1EB1A02, which you can learn more about on YouTube HERE. The “boost” configuration helps when a motor doesn’t get enough voltage from the utility source.

Before you buck or boost the voltage, remember to account for both sides of the equation; if the utility changes the voltage, you still want to be within range.

Bryan also covers:

• Ratings
• Current and capacity changes based on voltage
• Inverter-driven technology
• Voltage monitors (ICM493)

You can learn more about the 2022 HVACR Training Symposium HERE.

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