Posted by LJD on October 07, 2012 at 15:30:15 from (75.213.81.16):
While we're sort of on the topic of RVs, DC to AC, AD to DC, etc. - I've got a comment and a question to anyone that knows.
The general topic is the difficulty of making microwave ovens work properly when run off an inverter. One problem is the Root-Mean-Square thing (RMS voltage). It is used to give voltage "equivalents" so a person can figure what will run what off an inverter. For example - a cheap modified wave inverter will often only read 95 volts at the AC output with a common voltmeter, but will read 120 volts AC when checked with an RMS capable voltmeter. RMS voltage works OK with resistance-element heat makers, e.g. toaster, electric ovens, etc. It does not work however with microwave ovens.
So, to make a long-story shorter. Most microwaves will barely work off a mod-wave inverter when that inverter has 14 volts at the DC input. That cannot happen when only running off batteries. Thus the reason why the microwaves in RVs often work MUCH better if you start the engine (or genny) and make battery voltage rise from 12.7 volts to 14 something volts. With a fully charged battery bank - at 12.7 (or around) volts - a microwave is lucky to work at 1/2 its rated output, if that. And often, battery voltage with such a draw will drop to 11.5 or 12 volts which can render the microwave near useless.
Now -about conventional microwaves. None have variable power. The way they work is - at full current draw but slamming "on" and "off" like machine guns. That's why a small 700 watt microwave often draws 14 amps of AC current in repeated surges. That "700 watts" only refers to cooking power - not AC power draw.
Now - Panasonic has a new tech microwave called the "Inverter Microwave." Note the word "inverter" here has nothing to do with the inverter we use to make AC power from a DC source. This new microwave actually has steady linear power that can be trimmed down at a lower power setting. I'm not sure how it all actually works but I just ordered one. I'm anxious to see how it performs.
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