Electronics Forum / Basics / January 2007

This is where I get confused.
I actually purchased a negative ion generator "air purifier" on ebay, just
to see what makes it tick and was surprised at it's configuration.

This particular design is one of those common tower form factor ones you see
for sale at radio shack for around $200 with a dust collecting "plate"
inside which can be removed for cleaning purposes. You can see a similar
item here:

http://cgi.ebay.ca/NEW-IONIC-AIR-PURIFIER-IONIZER-OZONE-TOWER_W0QQitemZ200073342
623QQihZ010QQcategoryZ14949QQrdZ1QQcmdZViewItem

The high voltage unit is in the base, the metal collection cannister is in
the center, (I assume positively charged or grounded?) and running parallel
to the collector plate are 4 thin bare steel wires around it's perimeter,
which I  assume are  responsible for  emitting the negative ions. (I could
be way off on my assumptions, which is why I'm posting here!)

The flip up top which opens to allow removal of the cleaning plate also
contains a round black fan (visible in the auction picture) which blows the
air out an exit port in the front of the flip up lid. (the air is pulled out
of the unit by the fan) I don't think there are any needles even in this
design.

Everything about this design goes against everything I've been told is the
right way to design an ion generator, or a dust collector.
This negative ion generator not only has something obstructing it's exit
like a plastic grill, but also a powered fan!

This makes me wonder if the "no moving parts" style negative ion generator
dust collectors are more efficient at emitting negative ions but poorer at
collecting  dust, or are the models with fans more efficient air cleaners as
they move more air across the plate, and are less efficient negative ion
generators (less negative ion output into the surrounding air) because of
the fan?
Or are the ones with fans just plain more efficient in all aspects as the
fan and other obstructions the negative ions come into contact with on the
way out of the unit have no effect on them and the fan improves it's
performance?

I guess this is a more specific example of the concept I'm trying to
understand.
Once I understand the true proven design rules, then I can design my own
more efficient purifiers.
Thanks!

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These things seem to be a cross between an ion generator and an
electrostatic air cleaner. I'm not sure they do either well. The
electrostatic air cleaners rely on the furnace fan to move the air. The ion
generators don't normally use a fan AFAIK. Hope it helps.

FWIW, if I wanted to fool around with a home design I recall articles on
building both in back copies of Pop Electronics and / or Radio Electronics.
Both are defunct, but bigger libraries have back copies for reference.

Dear Technician:

...

Positively charged plate.

Both, probably.

No, you have guessed correctly.  The radius of the charged surface
affects the local potential for a given charge.  The wires are a small
radius, which yields a high local charge.

Needles are not required.

Turn it off and put in the garage.  It collects lots of dust.  ;>)

If a patent relies on the charged air flow to move air, and you make
one that has a powered air mover, you are not violating the patent.

Neither and both, to some extent.  Ionizing air makes ozone and other
oxidants.

Plastics can be statically conductive, depending on what they are
"alloyed" with, and can be the positive plate.

Good:
1) don't use ion anything,
2) don't use UV of longer wavelength than 254 nm,
3) HEPA filter the air,
4) carbon filter for chemical activity, probably bathed by UV,
5) keep humidity at some settable value.

Using ozone to occasionally chemically clean stuff is excellent.  
Chronic exposure by design is a lawsuit just waiting to happen.

David A. Smith