nayther wrote:
time2roll wrote:
nayther wrote:
I've got a Harbor Freight 400 watt now but its only putting out 102 volts with no load and 13v input, voltage drops off to below minimum with any load so assume it's a POS.
MSW always reads low unless you have a true RMS meter.
Standard peak to peak meter will read low due to the MSW form.
Guess I need to check my DVM, it's a Fluke so thought that would be best but maybe it's not, how would I know?
It depends on the model. Some Flukes are "true RMS" meters and will accurately read the RMS voltage of most any waveform (within their limits, of course; a high enough frequency wave, for instance, would probably give trouble).
Non-RMS meters are generally either peak responding or average responding. I think my Fluke 73 is average responding. Either one will not give accurate RMS readings, in general, for non-sinusoidal waveforms. It is possible in either case to specially make a non-sinusoidal waveform that reads correctly, but it's not the general case.
At least some MSW inverters are designed so that the peak-to-peak voltage is approximately the same as a sine wave. Usually, particularly for low-cost inverters, the peak-to-peak voltage is not very well regulated with load variations, even if the RMS voltage is somewhat better regulated. (They can regulate the RMS voltage by changing the duty cycle of the output waveform, while the peak-to-peak voltage is determined by the internal voltage booster that is more or less free-running.)
