One industrial precipitator uses a voltage of 70- 83KV at a frequency of 50 KHz.
TV flyback transformers produce 20-50 KV at 15 KHz (Wikipedia).
I'm a bit confused as to whether either of these are AC or DC.
Would it be possible to build a lab scale electrostatic precipitator using a flyback transformer from a junked TV?
[Edited on 21-6-2015 by Magpie]
If there's frequency involved it has to be AC.
But are you sure the eletrostatic precipitators operate at alternating current? it seems counterintuitive that having the polarity changing all the
time would help getting the particles settled.
I always thought these equipments operated like huge capacitors with air flowing between its plates, and due to the strong field between the plates
the particles would end up collected at one of them.Magpie - 20-6-2015 at 21:01
I agree that the precipitator must be DC. That's why I am confused. I guess I need to read more carefully about this.
The flyback is a rectified AC that produces a sawtooth waveform, I believe. So it would be a DC also, right? Sulaiman - 21-6-2015 at 02:00
Almost all of the 'flyback' or 'line output' transformers of CRT TVs and monitors in recent years have been of the 'split diode' type,
they have rectifiers/diodes as a part of the internal construction.
and give positive high voltage for the crt anode.
I doubt that you will find 50 kV rated lopt easily/cheaply,
but even 5 kV will ionise air to cause electrostatic precipitation.
The output is basically positive pulses, which will ionise air nicely
when wiring and electrodes (a row of sewing needles works well) are connected the added capacitance 'smooths' the output to be a more constant
voltage.
Try to add as little extra capacitance as possible for safety reasons.
(stored energy = 0.5 x capacitance x voltage-squared)
[Edited on 21-6-2015 by Sulaiman]Pumukli - 28-6-2015 at 12:47
Yeah, the precipitators use DC or at least pulsating DC.
One thing I wanted to mention is that long ago (well, not too long ago) it was "cool" to have a so-called ionizer in one's car, which got its power
from the cigar lighter. These gizmos ran at a few kV and they did precipitate a little dust besides their intended "negative ion output". They could
get very dirty in a smoker's car.
So it seems a few kV might suffice.
On the other hand beyond say 5 kV there is an increasing chance (and intensity) of corona discharge and O3 generation. It may be a real
problem or not, depending on the actual physical layout of the precipitator electrodes.aga - 28-6-2015 at 14:34
If you decide to strip an old tubed TV for the LOPT, steal the driver transistor(s) as well, as they are rated to handle the voltage/current.
The output is crude DC of around 20~25kv due to the integrated diode/capacitor doubler or tripler (as Sulaiman described).
The 15kHz simply refers to the frequency at which the transformer primary is being switched.
It generally isn't perfectly smoothed DC on the output, but pretty good for an experiment.
I agree that the precipitator must be DC. That's why I am confused. I guess I need to read more carefully about this.
The flyback is a rectified AC that produces a sawtooth waveform, I believe. So it would be a DC also, right?
You want to charge the capacitive structure with DC to collect dust and then cycle it every so often with AC to erase the charge on the collection
electrode. This allows the dust build up to be removed by falling off the collector (a good unit has a collection trap and a vibrator). With AC HV
applied the plate is vibrated to drop off the dust into whatever collection scheme is devised. Then it goes back to DC HV. In areas with oil or other
vapors which buildup on the plate it eventually must be cleaned with solvent spray since the film 'glues' the particles and they will not shake off. A
surplus cell or pager vibrator works great, is only a buck from Goldmine or similar surplus outlet. It must be insulated from the plate obviously.
Filter types require cleaning often. Better designs have solenoid controlled duct plate(s) with high speed fan and dust is (sucked) dropped into a
collector (now open while second plate blocks flow through) which is easy to remove and clean out. It has a filter to prevent dust from blowing back
out. Control circuitry after a set time of DC HV shut this off, activates solenoid/vibrator/AC HV at once for a set time. All you do is every so often
slide out the collector, clean it and slide it back in. For a home type air cleaner a filter on the output side is still desirable although you now
have two tasks every so often. Those built cheaply which just use a filter as the collector drop off in air flow volume too soon and do not work as
well. They run for a long time with greatly reduced efficiency due to slowly increasing blockage. aga - 29-6-2015 at 13:10
With DC plate systems it is common to simply switch polarities after a while to even out the wear on electrodes for example, or shift built-up
charges.
