Re: ATM Re: [VacuumX] 24" vacuum chamber is getting closer :)

["James Lerch" <jlerch1@tampabay.rr.com>]

----- Original Message ----- 
From: "Dominic-Luc Webb" <dlwebb@canit.se>
>
> > 120vac -> Dimmer -> Transformer -> Filaments
>
>
> Are your filaments parallel or serial, BTW?

Both actually :)  Here goes some ascii art

   AC Input
         |
      /---\
    /         \
  F1        F4
   |             |
  F2        F5
   |             |
  F3        F6
    \           /
      \ ___/
          |
        Ground

If the ascii art is unreadable, I have six filaments separated into two parallel
circuits, each circuit having 3 filaments in it.


> If it works what the heck. By my learnings and schoolings you
> never ever use a light dimmer to control induction loads. There
> are other circuits for that.

Your education is indeed correct, as I had the same understanding.  Here a
responce that put my concerns to rest:

< **Begin Quote from Dick Pierce on rec.audio.tech**>

A transformer presents essentially the same impedance
characteristics as its load, the magnitude of which is changed
by the square of the turns ratio. If the secondary load is
largely resistive, like a filament, then the impedance seen on
the primary is resistive.

Transformer primaries present inductive loads only if 1) the
secondary is inductive or 2) there is NO secondary load, in
which case you simply see the residual leakage inductance.

Thus, in your case, the dimmer would be seeing an inductive load
only if the secondary load were inductive. And with a big honker
filament glowing bright yellow, it sure ain't inductive!

-- 
|            Dick Pierce            |
|   Professional Audio Development  |
|   1-781/826-4953  Voice and FAX   |
|       DPierce@world.std.com       |

<** end quote **>

>I suspect it would be good to
> have some way to uncouple the transformer from the dimmer.
> Alternatively, perhaps there is some other kind of load (i.e.,
> non-inductive) that could replace the transformer (light bulb)?

Have to be one heck of a big light bulb :)

>
> > Actually, I can reliable control the temperature from very dull red to white
hot
> > and any where in between.
>
> That is great! It says much about your dimmer. If you were operating
> outside its operational window you would notice. You would for
> instance notice filament at room temp and then suddenly, with only a
> slight turn of the dimmer, too hot, lacking control over the full range.
> I worry the humming of your transformer (hysteresis?) might be also
> causing your filaments to rattle.

Doesn't seem to be a problem while in use....

>
> > I just got your other email, have you done any experiments yet?
>
> Not yet. I just know the vacuum works and I am now trying to reason
> my way into getting the filaments going (sanely). Getting close and
> getting exciting!

Just wait till you finally make shiny glass! :)  JUST WATCH OUT FOR DRIPS OF
MOLTEN ALUMINIUM!!!!!

James