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< ### Regulation All Transformer windings have an internal resistance due to the length of the copper wire making up that winding. From "Ohms Law" we know that when a current is passed through a resistance, there will be a potential difference or "Voltage Drop" across that resistance. This is calculated as V = I.R. , where V=Voltage Drop , I=Current , R=Resistance. Applying this logic to the secondary winding of a transformer, we can see that when no current is flowing in the winding, there will be no voltage drop across the winding. In other words, if we measure the No-Load output voltage of a secondary winding, we will be measuring the actual induced voltage (induced EMF). However, once we connect a load across this winding, current will flow, and there will be a voltage drop across the winding. Hence, the voltage measured "On-Load" will be smaller than the voltage measure at "No-Load". This voltage difference is known as "Regulation" and is normally expressed as a percentage of the full-load voltage. Example: Secondary winding designed to provide 10 Volts when delivering its rated current. If we assume a no-load voltage of 11 Volts, we can then calculate : Regulation = (11 - 10) / 10 = 1 / 10 = 0.1 = 10% *NB* Some transformer manufacturers will divide by the higher figure (No-Load voltage) instead of dividing by the smaller figure. This gives a false lower regulation value. Typical regulation figures for transformers from 15VA to 5000VA are shown below. Click here for 'Custom Deisgned' page Click here for 'Applications' page Click Here to email an inquiry