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Posted by David Nebenzahl on May 2, 2008, 12:21 am
On 5/1/2008 6:29 PM Don Klipstein spake thus:
> Nebenzahl wrote:
>
>>On 4/30/2008 7:57 PM Don Klipstein spake thus:
>>
>>> The usual low power factor CFLs will run a bit dim from the slightly
>>> lower peak voltage of the modified sine, and more so from the squarewave -
>>> maybe not work too well on a squarewave, with peak voltage of 120V.
>>> Modified sine has a peak voltage of 139 volts, while true sine has a peak
>>> voltage of 170 volts. This largely affects what the circuitry in a usual
>>> low power factor electronic ballasted CFL actually works with.
>>>
>>> The peak current through the rectifier and filter capacitor in a usual
>>> low power factor electronic ballast CFL wil be high, from the abrupt
>>> waveform edges from these inverters. I would ask for an engineer at the
>>> CFL manufacturer to find out if this is OK for the CFL - the filter
>>> capacitor or any RF filtering choke will get warmer than normal. Any RFI
>>> filtering choke may also buzz.
>>
>>Question (somewhat naive, perhaps, so please bear with me): couldn't a
>>guy turn square wave current into something closer to sine wave just by
>>using a bunch of big honking capacitors as a filter? I'm thinking across
>>the line, but then it occurs to me that if their impedance is too low,
>>too much current'll flow through them and they'll blow ...
>
> I've blown a modified sine inverter in the past with current spikes
> drawn by capacitors.
>
> There are LC filters, but those tend to be homebrew and experimental and
> things can go wrong. For example, you have to really know what you're
> doing to not have them resonate (whether at the fundamental frequency or a
> harmonic), or get close enough to resonating to deliver excessive voltage.
> I'm sure one not professionally made and rated for use with inverters
> would void warranties and safety ratings all over the place. And I don't
> know where to get any that are rated for this.
So are you saying that an LC filter (say, a pi configuration, two caps
and an inductor) *could* work, if one were to select the correct values
of L and C? I understand how one would want to avoid resonance (@60 &
120 Hz) here. Should be simple to do, one would think; not exactly
rocket science.
--
The best argument against democracy is a five-minute
conversation with the average voter.
- Attributed to Winston Churchill
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