Nano Power Inverter - Roll Your Own Style

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Joined: 21/06/2018
Location: Australia
Posts: 951
Posted: 01:23pm 30 Mar 2023      

Roger thanks for the extra information you looked up and posted for me.

I found when working out the idling power of a transformer you need to measure the true power with an accurate energy meter. The unloaded transformer will have inductive reactance and even if the current is measured with an RMS meter because of the phase shift between the voltage and current it will not give the correct result.

The analogy is a bit easier to see if you put a capacitor say 10u across the mains and monitor the current, amps can be seen flowing but the true energy meter might show just a watt or so, when the sum of the current times voltage would be a much bigger number.

The transformer is a similar scenario but the phase shift is different by nearly 180 degrees.

However monitoring the primary or secondary current when the inverter is running will lead you a bit astray as it will show amps flowing but the battery will be supplying much less than that.  The battery volts and current supplied to the inverter can be simply multiplied to determine transformer idling current (dont forget to minus the solenoid/relay, DC fan and nano controller etc).   The load current on the secondary of the transformer must be measured after the filter capacitor for accurate results.

The inverter transformer circulating current is from the smoothing capacitor we place across the transformer secondary to integrate the HF Sine PWM back into a smooth sinewave. It causes more current to be flowing back and forth than what we actually feed it.
Edited 2023-03-30 23:24 by wiseguy