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G8MNY > TECH 10.02.21 09:48l 57 Lines 2466 Bytes #999 (0) @ WW
BID : 22976_GB7CIP
Read: GUEST
Subj: Thermostatic Iron Repair
Path: IW8PGT<IZ3LSV<F1OYP<AB0AF<KF5JRV<N7HPX<GB7CIP
Sent: 210210/0746Z @:GB7CIP.#32.GBR.EURO #:22976 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Feb 21)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I pickup a "Weller" type iron by "AdcolA" that has electronic temperature
control, using a negative temperature thermistor with the element. This is
rather than "Magnetic Curie Point" temperature switch of Weller system, or a
thermocouple & sensitive op amp system!
In the handle was a 14 pin control chip which was dud & did not trigger the
triac. So I developed this much simpler 1 transistor circuit as a replacement.
24V oÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
AC 1K ³
2A _³_ ³
\_/ 12R The thermistor is about 50K cold
ÃÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ 48W cold & less than 1K hot. The 3K9
³ ³ ³ + 2K Element & 150R set lowest & highest temp
³ +³ NTC ÚÄ´ÃÄÄÄÂÄÄ´ ³ with my thermistor.
10V_³_=== Therm ³47u ³/ _³_ ³
'/_\ ³100u ÃÄÄÄÂÄÁÄÄÄÄ´ \_/=LED ³
³ ³ Temp ³ BC337³\e ³ ___³___
³ ³ ÚÄ>pot ³ ³ ³ _\/_/\_
³ ³ ³ 2K ³ ³ ³____/ ³3A
³ ³ ÀÄÄÄ´ 3K9 ³ ³Triac
³ ³ 150 ³ ³ ³
0V oÄÄÁÄÄÁÄÄÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÙ
iron earth
EÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
///
The traic is no longer phase fired, as I assume the original IC could do, but a
simple on off including an added status LED (used on some of their irons).
HOW IT WORKS
The 100uF is charged up via 1K & diode, when the zener conducts limiting the
voltage to 10V. The triac is turned on via the LED & 2K7, giving full power to
the heater element. When the thermistor is hot enough (lower resistance) to put
0.6V on the NPN base with the preset pot load, the NPN conducts, & bypasses the
current going through the LED & gate, turning the triac off. The 47uF slows the
action, so the triac gets a chance to conduct on both has cycles & even a few
on & off, as shown on the flashing LED.
The circuit needs scoping to check the triac is firing OK on both + & - half
cycles, if not, damage can be done to very small 24V AC transformers!
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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