In this video, we're going to show a typical 40va residential or Light commercial. Transformer. Well, this is a very typical Transformer that residential and Light commercial technicians will see. There are many other types of Transformers that work on the same or similar principles.

The Transformer's job is to either step up a lower voltage to a higher voltage known as a Step up, Transformer or like this Step Down Transformer convert a higher voltage to a lower voltage for the control circuitry. Here you see that we have common 208 and 240 volt Taps on the primary of the Transformer. In this type of Transformer, the primary and secondary windings don't touch each other. Energy is transferred through an electromagnetic field known as induction.

Here we show high voltage power coming into the disconnect and then moving into the Transformer primary. The primary can also be thought of as the inlet of the Transformer. In this case, this is where the high voltage comes in. You'll notice we have it tapped on the 240 volt Tab and common because the power coming in is 240 volts.

Make sure to move the tab down to 208 where 208 volt power is present usually in three-phase buildings. Here you'll notice there are more wraps of wire on the primary than on the bottom, which is the secondary which heads to the 24 volt. Controls The ratio of wraps between the primary and secondary dictates whether a Transformer is a step up or Step Down Transformer. In this case, there are 10 times more wraps on the primary than on the secondary, which means that it steps down the voltage by a factor of 10.

you'll notice there are two distinct coils. They don't actually connect at all, but they wrap around an iron core which in this case are iron laminations. Here, we show this in a pictorial version. You'll get the higher voltage coming in through the top.

Alternating current is represented by the motion back and forth in the field generated. This field then induces inductively into the secondary, but now at a lower voltage. Now we're going to show how to check out the Transformer using an Ohmmeter. We set a multimeter to the Ohm scale and we can ohm out the primary.

You'll notice that the resistance is higher on the primary than on the secondary because of the increased number of wraps. You'll also notice that the resistance at the higher voltage rating on the primary is higher because there are more wraps versus the lower voltage at 208 it Taps into an area of the coil with further wraps by utilizing fewer wraps in order to keep the output voltage the same at a 208 volt input. If the primary were failed such as due to a power surge, this would read ol' or open. In rare cases that it's shorted between the primary and secondary, you would read a path between the terminals or Spades and the casing of the Transformer.

Now we're going to check the secondary and again, we show an OHM measurement meaning that it's not shorted and you can also check the secondary to the casing again. You do these tests with it de-energized and the primary and secondary disconnected. Here, we show the Transformer feeding into the circuit board. The high voltage feeds the fuse before it goes out to the control circuitry.

Many people diagnosed failed Transformers when in fact it's a blown fuse. Another way to test whether a Transformer is functional is just to measure the inputs and outputs via voltage while it's energized. This is why Transformers are actually quite easy to troubleshoot if you have voltage coming in and no voltage going out that indicates a failed. Transformer Just don't forget to watch for fuses or resettable low voltage.

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