----- Original Message ----- From: "Dave Guimont" [email protected] To: [email protected] Cc: [email protected] 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
       [email protected]

           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