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PE1BIV > TECH 07.09.05 17:17l 39 Lines 1828 Bytes #-6967 (0) @ WW
BID : 5147PE1BIV
Read: GUEST DL1LCA OE7FMI
Subj: Re: Power inverter waveform
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Sent: 050907/1328z @:PE1BIV.PI8DAZ.#TWE.NLD.EU JNOS #:1960 $:5147pe1biv
Hi Dick and all,
> From: <g4bbh@hb9ak.che.eu>
> I have a 300W 12V to 230V power inverter which has what is described as
> a 'modified sine' wave output. Is this synonymous with 'square wave'?
> If it is really square wave what can I do do protect switch mode power
> supplies as loads. Will a large pi-network filter help? Any ideas
> what 'modified sine' actually means and what I can do to improve it.
The older inverters probably indeed give a pulse of 5ms positive and 5ms
negative, together with two periodes of 0 for 5ms is full 50Hz cycle.
A more modern one will have steps of maybe 2.5ms with the voltage increasing
and decreasing, so you might call that a modified sine wave. The more
expensive inverters even have more steps, so they produce an output that
even more resembles a sine wave.
But, if you are using a switch-mode power supply which is fed by an
inverter, I would not worry at all.
In a switcher, in general the incoming AC is rectified and buffered and this
rectified power is then switched to feed a transformer (higher to even
higher frequency) which output is rectified again. In general the main
output is used for a feedback to regulate the switching proces.
So, basically your switching power supply doesn't care less what form of AC
is being supplied, as long as the effective average voltage is what the
switcher is designed to work with
My first UPS indeed was the type with 5ms positive, 5 ms off, 5ms negative
and again 5ms off. Only using a true RMS volt mter you will see the voltage
you would expect.
To be honest, I have not even looked at the wave form coming from the
inverter in the car, nor have I looked what the currently used APC UPS'es
have as output waveform. I think they were specified as modified sinewave.
But, it's good enough for the computers to run on.
Angela
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