NEW INFO! Electrostatic Air Filter Using Neon Transformer?

[For The Popcorn]

We are building a filter for a 48" x 36" laser cutter to reduce objectionable fumes. Doing this with commercial HVAC duct parts is outrageously expensive, so we're using a less-rageous DIY approach using plywood and 2"x6" steel studs. The pictures show the pieces, which will be connected by a 20" cube of plywood and 2x2s at right angles. There's a 1" thick pre-filter and a 4" thick MIRV14 main filter. We have high hopes that this does the trick.

I'm thinking of a plan b, just in case this isn't enough. I have a 9KV solid state neon sign transformer. I'm thinking this transformer with a 10KV diode could form the basic of an electrostatic filter. The positive terminal would be connected to a sharpened rod in the rectangular duct section next to the round duct adapter. The negative terminal would be connected to the steel stud that forms the square duct section.

Do you think this might work? Can the negative side of the neon transformer be connected to earth ground?

 

[For The Popcorn]

Here's a picture of the nearly complete filter box. The doors for the two filter compartments aren't fitted yet.

 

[Diver300]

Commercial electrostatic filters sometimes use square-section electrodes that have been twisted. The corona discharge from the sharp corners forms a spiral, so that more of the air passes through parts of the discharge.

You probably want to have multiple discharge points one way or another to filter as much of the air as possible.

 

[For The Popcorn]

Let me expand on this a bit. I am disappointed to report that our initial testing was mostly a flop. Probably too much bypass between sections and the filter wasn't a high enough MIRV rating. But some information revealed, so we're marching onward.

Regarding electrostatic filtering, it's still something we're considering, with some added knowledge.

Honeywell "Electronic Air Cleaner" cells, aka electrostatic cells, are available used on ebay relatively cheaply. These consist of wires and charged plates, so there's nothing to wear out.

The power supplies are a different story. The power supplies are built into racks that the cartridges plug into. They supply something like 8KV and 6KV with connections to alternate plates. This should be within the range of neon sign transformers, and the max current is around 10mA as I recall.

I have not found any reference to anybody using a neon transformer in an application like this. An HV diode or bridge, perhaps a filter cap and some HV-rated resistors to make a suitable voltage divider. Sure seems like it should work. Arcing to generate ozone probably is not desired here, so the current draw would be insignificant.

Of course, everything would be interlocked, bleeder resistor across the filter cap, air flow switch to operate only when the blower is running.

Comments? Suggestions?

 

[rjenkinsgb]

You probably want to have multiple discharge points one way or another to filter as much of the air as possible.

A zigzag run of barbed wire / razor wire for the charged electrode, between two layers of wire mesh/chicken wire for ground??

That should give a large number of discharge "points" and the modules could be unplugged and blown or vacuumed out easily, if they were made fairly thin overall?