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G8MNY  > TECH     14.02.26 00:19l 51 Lines 2120 Bytes #6 (0) @ WW
BID : 52040_GB7CIP
Subj: Thermostatic Soldering Iron LED
Path: JH4XSY<N3HYM<K5DAT<GB7CIP
Sent: 260213/1518Z @:GB7CIP.#32.GBR.EURO #:52040 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                 (Updated Mar 11)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

This circuit is suitable "Magnetic Curie Point" temperature switch controlled
mains irons! The LED lights up when the Iron is plugged in & is drawing current
in its heat cycle it goes out when it is up to temperature. It also works on
some internally electronic controlled 24V irons too.

Also shown is a static earth, that keeps the stray tip voltage down to about
12V AC MAX, while still giving an "un earthed iron" for work on live circuits
(~100V) safely.

CIRCUIT
  Fuse   ON
Lトo-oトトトトo\oトトトトトトトトソ                        Temp
 250mA               )|| レトトトトトツトトトoトトトトトトトトトトo_oトトトトトトトトトトトトトトトトトソ
       LED           )||(     10k           Switch        Curie   ウ
     レトエ<テトソ     230V)||(24V レトエ               :...Magnet Iron   12R Element
     ウ     ウ         )||(    ウ10k                         Bit    48W
     テトエ>テトエ         )|| タトトト)トチトトトoトトトトトトトトトトトトトトトトトトトトトトトトトトトトトトル
Nトトトトエ     テトトトトトトトトル ウ      ウ-----------------------------iron earth
     タト33Rトル          ウ     1M          If 3 wire
Eトトツトトトトトトトトトトトトトトトトトトチトトトトトトル
   チ
The LED is connected to the mains neutral, but even so good insulation is
needed! The bypass diode connected the reverse way is a 1N4001 and stops mains
reverse voltage appearing across the LED. The value of 33R is selected so that
the LED is not lite with just the transformer magnetising current.

If the 50Hz flashing LED is anoying, blows up the LED, or is not bright enough
try this more complex circuit instead...

         LED
  レトエ<テツトエ<テトツエ<テトソ
  ウ    ウ100u+ウ    ウ      Here the 27R is selected for brightness & unlit LED
トトエ    テトトエテトエ    テトト    when the iron is not on. The 100uF protects the LED
  テエ>テト)トトトトトル    ウ      from some of spikes in mains power surges as well as
  ウ    タトトトトトトエ>テトエ      reducing the 100Hz LED flicker. Diodes are all 1N4001.
  タト27Rトトトトトトトトトトトル


Also see my Tech Bul on "Soldering Iron Economiser/Boost"


Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP


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