From: Patrick Jankowiak (recycler@swbell.net)
Date: Mon Jan 10 2005 - 17:20:05 PST
(note, view with fixed-width font such as 'courier new')
Most modern inverters have a "modified sinewave" waveform like
this, about 150V peak voltage. good for many modern appliances,
but noisy since it is made of square waves, but work reasonably
well with transformers:
_ _
_| |_ _| |_ _
|_| |_|
Older inverters have a square wave like this, about 120V peak
voltage (and with a square wave then 120V RMS also), and can be
very noisy as well as not playing nice with transformers (core
losses and heating) and also not providing the high peak voltage
required by some power supplies. These are good for lights,
electric razors, some appliances, etc:
__ __ __
| | | | |
|__| |__| |__
The best inverters have a sinewave (drawn sideways) with 120V RMS
and 168V peak. Appliances can't tell the diference between those
and the wall outlet. Quiet also:
(
)
(
)
In the first 2 cases, a noise supresor or 2-3 stage L-C filter as
suggested will help. be sure to ground it to the inverter and
ground the inverter case with heavy wire to minimize inductance
so that the current from the bypassed noise can easily go to
ground. Noise spikes however are sometimes generated by a
transformer connected to the unit in cases 1 or 2 regardless of
such a filter, as the fast rise and fall times causes back EMF in
the transformer resulting in a spike at each point where the
wave's instantaneous voltage changes abruptly. A capacitor (0.05
to 1.0 uF rated 3-5 times the transformer's secondary voltage for
safety) connected across each of the transformer secondaries can
help. Old ham radio books have articles on how to deal with this
kind of interference.
--- Patrick
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