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From: (no name) (no email)
Date: Thu Dec 02 2004 - 01:10:11 EST
Quoting "Jason Pringle (Accenture)" <>:
> take a look at the two articles on Ample Power's website regarding inverters
and microwave ovens (http://www.amplepower.com/pwrnews/index.html).
> Apparantly microwave ovens don't like modified sine-wave AC, and are
> very sensitive to the DC input voltages
REPLY
I had not seen these article for quite a while. Nor did I see any updates of
more recent tests.
Further to the findings of the Ample Power tests I would like to add some info.
The loss in AC power is also a function of power factor of the inverter.
Until we started marketing the Prosin epure sinewave inverter the most common
inverter was the Heart model. Lab tests demonstrated a market difference
between equal power Hear and Prosine models. The reason being the Prosine model
has a power factor of 1.0 wheras the Hear tmodel variss from 0.9 down to 0.5
depending on several operating parameter.
This is not intended to knock any one brand or promote another.
However the technical differences in design between the line frequency swith
mode of th eHEart and the high frequency switch mod of the Prosine does make a
huge difference. In additon the Heart MSW model is very sensitive to DC voltage
inputs whereas the Prosine suffers less degradation in output waveform quality
or power level.
I suspect the tests were done with a view to demonstrating the superiority of
the Prevailer brand of battery. The Prevasiler battery are sealed whereas the
other deep cycle battery the article refers to is a flooded wet cell.
Since the time of the Ample Power tests several manufacturers hav ecome out
with AGM batteries which exhibit even better characteristics than what is
described in the test.
For example while doing the USCG contract I tested som eMeridian batteries
agains some Lifeline gel batteries. to my surprise the Meridian batteries
proved able to hold up the terminal voltage much longer than the Lifeline brand.
Only towards the very end of the test cycle did the voltage nosedive.
The test was terminated at the point when the inverter shut off due to a low
voltage condition set at 10.5V for a 12V battery.
So what does that have to do with microwave ovens?
Several points. MSw waveforsm contain more harmonics than a pure sinewave.
Thsi results in eddy currents being set up in the microwave transformer.
You can hear the difference because the transformer rattles or hums louder with
MSw than with pure sinewaves.
Secondlym the transformer heatts up more internally with MSW than with puresine
waves. This heat means higher wire resistance in the transformer windings and
thus greate losses and less efficiency. Thsi also contributes to less
microwave output for heatign your food.
And of course the power factor issue as described in the test article.
So the bottom line is MSW inverters reduce the service life of you microwave
oven (and many of your other inductive load appliances) while also resulting in
longer cooking time and shorter battery run time for the same Amp hour capacity.
We demonstrated a 20% gain in run time for pure sinewave compared to the Heart
MSW or even the Prowatt MSW inverter of the same output rating.
After the merger of Statpower, Trace and Heart into Xantrex there was a lot of
friendly rivalry and product comparison done amongst the technical staff.
Since we all now worked for the same company there was no longer a reason for
witholding information and the comparisons were valid.
I will be the rfirst on eto admit that if you only look at th efirst three or
four years of using an appliance you will not notice the deterioation due to
MSW. However you will immediately notice the difference in run time on fully
charged batteries when comparing MSW and pure sinewave inverters.
So if overall system efficiency is a concern for you then you should seriously
consider going sine wave instead of buying the lower priced MSW inverters.
And that goes for al the brands. The efficiency difference is a result of
physics laws not marketing hype.
Cheers
Arild
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