# [amsat-bb] Re: solder heat switch

i8cvs domenico.i8cvs at tin.it
Sat Apr 2 16:36:47 PDT 2011

```----- Original Message -----
From: "Dave Guimont" <dguimon1 at san.rr.com>
To: <domenico.i8cvs at tin.it>
Cc: <amsat-bb at amsat.org>
Sent: Saturday, April 02, 2011 10:51 PM
Subject: solder heat switch

> Hi Dom,
>
> I was pondering the temp reduction for the tip after we had our
> discussion the other day...
>
> The current is fully off for half of the cycle and reduced by some
> percentage on the other half, but I can't remember the procedure  to
> determine it....The figure .7 sticks in my mind...
>
> That percentage would probably be close to the idling tip
> temperature, influenced by radiation and some other factors of course...
>
> These kind of things (queries) pop in, but the answerers don't pop in
> as easily any more!!
>
> Ready for a math lesson, tnx!!

>
>             73, Dave, WB6LLO
>            dguimon1 at san.rr.com
>
>                Disagree: I learn....
>
>                Pulling for P3E...

Hi Dave, WB6LLO

The figure .7 sticks in your mind to remember the meaning of the
term rms or Root Mean Squared voltage as explained in the
following web page.

http://www.practicalphysics.org/go/Guidance_107.html

Supposing that your soldering iron is supplied by 220 Vac rms with
a single diode in series the current is fully off for half of the cycle so
that the output voltage of a half wave rectifier applied to the resistor
of your iron tip can be calculated with the following  two equations.

Vpeak            220 x 1.41
Vdc =    -----------  =  ---------------- = 99 V dc
3.14                  3.14

and

Vpeak            220 x 1.41
Vrms = -----------  = ----------------- = 155 Vrms
2                        2

and this is why your soldering iron is not so hot as without the diode
in series of it.

The same circuit with a diode in series to a AC motor and a heating
resistor is used into any two speed blower to dry  hair.

See also please the following web page.

http://en.wikipedia.org/wiki/Rectifier

Best 73" de

i8CVS Domenico

```

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