[HomeBrew] Inverters

[smattila at homemail.com.au]

It may be, that the fast switching in the inverter
produces very short high-voltage spikes or ringing.
Full low-pass filtering to 50 or 60 Hz would be the
best solution, but varistors (MOV) across the power output
line would prevent the peaks and protect your equipment.
Varistor (MOV) protection is good for all electronic
equipment when used with something else that grid mains
power. Varistor voltage should be ca. 30 % higher
than peak voltage (1.41 times nominal RMS voltage)
and varistors need to be for high power.

What is broken in your TV is the switching PSU IC,
maybe only the PSU input diodes. With older transformer
devices, square wave power can overheat and burn the
transformer. Basic square wave inverter gives out
much lower peak voltage than true sine wave and some
equipment do not work at all. Modified square wave
inverters produce about equal peak voltage and average
power in resistive load than mains sine voltage.
However, modified square wave inverters may produce
very strange waveforms and voltages if the load is
inductive like motors.

Sakari, VK2XIN

> Does anyone know how to smooth the stepped square wave coming out of these
> cheap inverters to something more like a sine wave?  Transformer?  LC
> network?

> It blew up my little color TV at my station. After that I put the scope on
> it and found it was a two step inverter.  It SAID is was good for TV,
> appliances, etc up to 1200 W.  Bull.

> TIA, de Jim KG0KP