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Re: Air Blast?
Subject:
Re: Air Blast?
Date:
Thu, 20 Mar 1997 07:13:19 -1200
From:
Ken Smith <ksmith-at-ihug.co.nz>
To:
Tesla List <tesla-at-pupman-dot-com>
>I was thinking of attaching a 950cfm blower to the assembly to cool the
>electrodes and heatsinks. this gets complicated if I try to incorporate
>a vacuum blower for the gaps, if I use compressed air it is a breeze.
>--
Just a though on air cooling / quenching - for what it is worth :
I have been playing around with my next Quick static gap design and I
decided to include some form of venting to exhaust all those nasty
smelly
fumes that come off the gaps to the outside world. My original plan was
a
blower (either an old vacuum cleaner or best to date is a 12 volt blower
unit designed for venting boat engine bays.)
Anyway it occurred to me that it would be nice to have all the airflow
going
down the slots where the sparks were for optimum cooling and some
quenching.
When you try to engineer this with vanes / pipes etc for blown air it
gets
very messy due to turbulence and general inefficiency.
However taking a leaf from older aircraft instruments - I decided to try
a
'suck' version. Absolute doddle. For my static which is in a 6"pipe it
looks like this :
Here comes one of Chips' famous ASCII drawings - or an attempt.
|
v lead in pipes
[------! !--------------------------------]
[______! !________________________________] - Plastic cap
| ! ! |
| ! ! |
| |
| | P | | | |
| | i | | | |
| | p | | | |
| | e | | | |
| |
| |----------------
| --------> Small
suction
| --------> Airflow
out
| |-----------------
[-----------------------------------------] - Plastic Cap
[_________________________________________]
Well that's the ASCII art for a moment. The trick was to use those
lead in
pipes. I used 3mm inside fairly rigid plastic pipe that I had left over
from some garden drip irrigation stand up sprays - but anything will do.
Drill through the top cap in appropriate positions to match up with the
spark faces and hot glue in a suitable length of pipe that termonates
(with
a nice straight face) about 10mm from the top of the pipe. Then connect
a
outlet pipe. I used a 75mm inset into the bottom of the main pipe
(because
I had one and it fits the diameter of the blower motor inlet).
The vacuum you are creating isn't that much and the odd leak won't
matter a
damn, but things work well because :
1. The air is going just where it is needed.
2. Incoming air has low turbulence
3. Good old P1V1T1 = P2V2T2 gives you an adiabatically cooled
airflow.
The big bonus for me is that I can have the blower well away from the
coil
and venting outside the garage and it hauls all those nasty ozone and
smells
away from the work area. Plus the sealed spark container cuts down on
noise
and stray UV. In all it seems a simple thing to make a big
improvement.
If you like the idea above - here is a small improvement to make it
automaticly switch on and off :
I am assuming you use a 12 volt blower (but this could be adapted)
required : 1 x smoke detector
1 x 12v 2amp relay
some bell wire.
Take the detector out of a smoke alarm (noting where it came from)
Extend the detector the length of your exhaust tube with the bell wire
and
secure it a little way up the outlet pipe so it is not in direct line of
sight of the sparks.
Take the input to the detector siren and use it to drive the relay that
powers the blower.
NB you have to get the detector electronics away from the coil and spark
gaps or it will fry the tranni(es). The detector sensor through is
pretty
tough and mine is surviving OK on the few runs that I have tried.
Although I
cannot guarantee (at the moment) the total bullet proof operation of
this idea.
For final neatness. wire the detector to the blower battery through a
100ohm
resistor. A small car battery or better a smaller motorcycle battery
will
power all this for ages without recharging and you can put in the corner
out
of the way and forget it.
The smoke detector is very sensitive to the fumes from a spark gap and
will
activate as soon as you fire up. It will also run for some time after
shut
down to clear all the crude and give some residual cooling also.
If you have one lying around, all the above comes as a specialised
package
as a fume sensor / blower activator from a power marine shop. However
they
are expensive. I took my circuit from something I used years ago to
provide
automatic bilging on my old Searay, but there I used the detector to
trigger
when it got wet. Wonderfully useful things smoke alarms. See my book
(to
be published in 2043 AD) "1001 useful things to do and make with a
pre-owned
smoke detector "
Hope this is useful.
Ken
Ken Smith
Weymouth
Auckland
http://homepages.ihug.co.nz/~ksmith
ksmith-at-ihug.co.nz