[RE-wrenches] Exeltech

Dan exeltech at yahoo.com
Thu Jul 18 12:58:42 PDT 2002


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


__________________________________________________
Do You Yahoo!?
Yahoo! Autos - Get free new car price quotes
http://autos.yahoo.com

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

==^================================================================
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9
Or send an email to: RE-wrenches-unsubscribe at topica.com

T O P I C A -- Register now to manage your mail!
http://www.topica.com/partner/tag02/register
==^================================================================





More information about the RE-wrenches mailing list