thanx Mike and Dave for you circuits,
DO NOT ATTEMPT TO BUILD THIS CIRCUIT
UNLESS YOU ARE QUALIFIED
OR EXPERIENCED WITH MAINS VOLTAGE.
THIS CIRCUIT INVOLVES SWITCHING
AN EARTH TO AN ELEMENT THAT CAN DRAW
10AMPS, THIS WILL KILL YOU.
YOU CAN BUY CONTROLLERS LIKE THESE
(COMMERCIAL) FROM ELECTRONIC
SUPPLY SHOPS, SO WHY RISK YOUR
now where was I, oh yeah
I ran with the I.C controlled (TDA1023) without
using a temp probe.
the specs on this (and application data) can be
you will need to download the above PDF file (page
14,15) to understand what I am
talking about below.
there were a few changes that I made for safety and
to compensate for the
240V 10Amp supply that we have.
they are as follows
RD 6.8Kohm 10W
RG 110ohm (100 and a
Triac was a BT-139-800
heater (load) is a 1380Watt element in theory
this circuit could handle 2.4KW
Ct 1uF 63V
Rntc I replaced this with a 22kohm resister
as I didn't require temp feedback
pin 5 of TDA1023 goes to earth to give you 400mV
I played around with resistors between pin 11 and
Rp (40kohm) and also between Rp and
Neutral (37kohm), this was only to trim the
potentiometer into the range that I wanted.
I also place a neon indicator across the load to
give me a visual on when power
was applied to the element
the Triac requires a fair amount of cooling, I used
a finned heatsink (100mm x 45mm x 45mm)
this keeps it reletively cool, I also used plastic
screws, heat compound and a mica washer to
electricly insulate the triac from the heatsink
the Resister RD dissipates approx 5W, so I advise
that you heat sink this as well, this item does
get to hot to touch if you don't, this is my next
Mount it all in a well ventilated preferrably
that is about all I have to say about
it worked really well on the first batch (25lt)
the neon indicator is a good idea and lets you know
everything is working ok.
for the future,
1. I'm going to have a water flow sensor that
will switch heater power off if water stops.
2. I'm going to have my laptop do all of temp
,water control and failure monitoring