Re: [pvusers] The Exeltech Pure Sine waveform is really good

[Michael Welch <michael.welch@homepower.com>]

Scott Willing wrote at 07:10 PM 07/19/2002 -0500:
  
>Oops, another quick question gig,
>
>What kind of acoustic noise do they make? Right off the unit, I mean - 
>hmm, buzz, sizzle? Silence plus fan noise?

There's been a recent discussion among RE installers about this very issue. The consensus is that high quality electronic appliances have not had a problem.

However, lower quality ones have. Here is a a recent post from an Exeltech technician on this very issue:

>Greetings Wrenches:
>
>I've been nudged out of lurk mode to reply to the recent series of interference-related postings.
>
>Rather than turn this into a complex dissertation on EMI (electro-magnetic interference) and RFI (radio frequency interference) .. I'll do my best to cover the specifics in a summary form, beginning with Interference 101.
>
>One of many sources of electronic interference occurs when electricity is turned on or off very rapidly.  To achieve the inverter efficiencies we all desire, some of the circuits spend their time either full on, or full off, with as little time as possible spent in the middle.  It's the transitional region between those two states that represents one of the larger causes of loss in the circuits.  Thus, in switching rapidly between on and off, we create unwanted interference in the process, which must then be reduced to FCC mandated levels if we are to attain specific certifications on the equipment.
>
>Interference escapes from the equipment in two ways - conducted (where power leads act as "pipes" between the inverter and other electronic equipment) and radiated, where the unit and connecting wires act as antennas.  Interference also encompasses frequencies from very low (low audio range to a few hundred kilohertz) to very high - well into the television frequencies and beyond.
>
>Solutions differ greatly for interference types and frequency ranges.  Conducted interference filters may not do well on radiated signals.  Filters for low-frequency interference are generally ineffective for high frequencies, and so forth.  Subsequently, combinations of filters must be utilized.  To further aggravate the situation, filters for the DC side must deal with very high currents while posing minimal voltage drop.  This requires very large conductors, which in turn make for some very unwieldy inductors (coils).
>
>That having been said .. it's a given that no two situations are identical.  Solutions aren't either.
>
>
>In summary:
>
>Keep all DC leads as short and heavy as possible.
>
>Twisting DC leads together helps on some forms of interference, but not all,  It won't hurt to try, but don't expect miracles.  Tighter twists work better than loose ones, but use care not to damage insulation.
>
>RF (radio frequency) filtering of the AC output leads directly at the inverter AC output may be helpful in some cases.  There are countless sources listed on the Internet.  I found over 25,000 using "RFI" and "filter" as search words.
>
>TV reception in remote areas with a regular (non-satellite) TV antenna MAY be helped in some instances by the use of an antenna-mounted signal amplifier; the use of coaxial cable for a feed line (though it loses more signal than quality twin-lead); locating the inverter and TV antenna as far from each other as possible; separation of AC and antenna leads (don't run the antenna lead alongside the extension cord feeding the TV); use of better quality power strips that have self-contained RF filtering; and keeping in mind that some receivers (TV, AM/FM, or otherwise) are more susceptible to interference than others.
>
>And finally .. keep in mind that no electronic power device is interference free.  Even with filtering, some junk still gets out.  If you or your customer are in a very marginal signal level area, all the filtering you can install may not be enough. Remember, the interference must be reduced below certain levels to attain certification - not eliminated.
>
>One big secret to all this is to keep the receiving antennas as far as possible from the interference source.
>
>This is a synopsis.  I have a much more detailed reply I'll be happy to send to you if you contact me offline.
>
>Regards to all from Fort Worth...
>
>Dan Lepinski
>Sr. Engineer
>Exeltech

  
Michael Welch
  
------------------------
"In a nation of sheep, one brave man forms a majority."
			Edward Abbey
        
Michael Welch, michael.welch@homepower.com
     Home Power magazine
     www.homepower.com
     To reach me: 707-822-7884
     To reach Home Power: 800-707-6585


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