From: John Tserkezis 
Reply-To: Fidonet AVtech Echo 

Bob Lawrence wrote:

> JT> BTW, you get a little better performance if you leave out that
> JT> limiting resistor- giving you a low impedance output to the
> JT> surrounding air

>  The capacitor is what gives the low impedance, and anything over
> 1000pF is plenty.

  Yeah, but that's before the output limiting resistor.  Why muck around?  Just 
put a tesla coil behind it, and let the five foot spark burn the dust to a 
crisp. :-)

>  Resistors connected to the mains are supposed to be "safety"
> resistors defined in AS 3250 able to withstand 150% nominal voltage
> and 10KV from 1000pF without changing value more than 50% (from
> memory). In practice, any spiral-cut 1/2W resistor will pass.

  Till it gets past the warranty period.  We were taught to check the charge on 
power supply bleeders even if they looked good. Many used to go open and you'de 
never know till you touched it.

>  According to the bullshit, they have to be *negative* ions (derived
> from a negative high-voltage, not TV sets and monitors). No one has
> ever proved that positive ions have a deleterious effect on hay fever
> or asthma, or that negative ions fix it... or even that a little 5KV
> spike has any affect on the charge in the air. If they were *serious*
> about causing corona, they'd use a high-voltage pulse rather than
> filtered 50Hz.

  Use a tesla coil and be done with it.

>  I used to design vacuum cleaners. Pye was big is vacuum cleaners.

  No Bob, you're going senile, you used to design television sets. :-)

>  How did we move from engineering to PR?

  When you implied that vacuums were better for dust allergies.

>  Yair... so vacuum once a week and get some benefit.

  You don't know what dust allergies are like, do you?

> JT> You just have to remember to clean it out every so often.... A
> JT> "vacuum cleaner' by it's very own purpose uses high air flow,
> JT> defeating the purpose.

>  So, use a bigger motor. Back in the 70s, a 600W motor was *big*. Now
> the entry level is 1600w!

  Actually no, it's better to use a low power unit for better fine dist 
collection.  When I used to be a field techo, I carried a vacuum to suck up 
toner from laser printers.  We were all given low power units because the 
photocopier guys (who used them more than us) found the high power units used 
to suck too much toner through the bag, into the motor and seriously reduce the 
motor life.

> JT> Even if they do use a venturi (or whatever) effect to confine
> JT> particles to a containment area. Works great for bits of paper
> JT> in the demonstration, but pointless for stuff that you actually
> JT> WANT to suck up. 

>  Yes. We used to weigh the bag tested against an unmodified machine
> on the same carpet. The head makes the biggest difference, and the
> really hard part is to get it to work right to the edge.

  They never do, that's why they give you that small nozzle thingy.

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Fido: 3:712/610  BBS/FAX: +61-2-9716-8310  Internet: jt{at}techniciansyndrome.org

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