And with the scope you load it to at least 50% of power rating.
That is steady state 50 not a peak or switch on surge...

Many power supplies are designed to be run under load, like the real
world. Some blow up if not loaded. Those are typically the high
current supplies. High voltage supplies are internally loaded.

Martin

On 7/10/2015 3:33 PM, Baron wrote:
robobass prodded the keyboard with:

I know this is a metalworking site, but there is quite a bit of
expertise on subjects like this here.

I just bought a 200/300Watt 230v inverter. I attached it to a car
battery on the bench (nothing else attached) and plugged in a few
lamps. The output measured 330v with loads of 50 and 150 watts. The
lights did seem brighter, but not excessively so. The voltmeter is a
cheapie, but seems generally accurate. I know that these devices
produce a modified sinewave, and I should expect a different
reading, but I thought the reading should be lower if anything. Is
this inverter a dud, or do I just not know how to measure?

Thanks

The issue is the waveform of the output from the inverter. The meter
is measuring the peak voltage rather than the average over a complete
cycle. You really need to use an oscilloscope to see and measure the
individual points of the modified sinewave form.