How to Build a Grid Transformer Fire Hazard Protector Circuit

The article describes a wise mains fire hazard protector circuit that are available for stopping mains grid transformers from over heating and resulting in sparks or perhaps burning due to a possible fire.
A transformer would certainly are likely to catch fire or result in sparks if the load associated with it surpasses its optimum bearable wattage rating.
In spite of this before the obstruction is prepared to start, the transformer would possibly first warm up to severe ranges leading to a possible fire or sparks across the winding.
The recommended transformer fire hazard protector circuit is built to monitor both of these difficulties, and switch off the system in the event these kinds of crucial problems can cross the danger threshold.
Let’s make sure to know how the circuit is meant to function for the avoiding a possible fire inside a transformer.
Making reference to the circuit diagram, we observe the configuration comprise of three phases, a heat sensor stage composed the BJT BC547 as the sensing element, a threshold detector stage made around the opamp IC 741 and a current sensing wired around Rx along with the associated bridge network making use of D7—D10.
Since mentioned above, a transformer would certainly get too hot before any kind of fire hazard, the heat sensor in the circuit is placed to deal with this problem before it gets too late.
Transistor T1 in addition to D5, R1, R2, VR1 and OP1 form the heat sensor stage, the circuit performing might be discovered in detaul Right here.
OP1 is a hand made opto coupler whereby two 5mm red LEDs are sealed together with a tiny LDR face to face inside a light proof enclosure, an illustration unit utilizing a single LED could be analyzed in this post.
For the current application two LEDs will have to be bounded with one LDR inside the opto module.
VR1 is placed in such a way that when the heat around BC547 is more than 90 degrees Celsius, the left hand side LED inside OP1 commences illuminating.
The above illumination of the left hand side LED inside the opto decreases the LDR resistance which in turn causes pin2 of the opamp to turn out to be simply more than its pin3 reference voltage.
The moment the above condition arises opamp output flips to a low logic from its initial high logic state, turning on the relay.
The relay associates that happen to be wired in series with the transformer mains input immediately switches OFF the transformer avoiding any more heating up of the system and a feasible fire hazard.
The right hand side LED inside the opto is placed for detecting an overload or an over current condition within the transformer.
In the event of an over load, the derived increased amp level encourages a potential rise across the sensing resistor Rx which often is translated into a DC for illuminating the right hand side LED of the opto.
Quite exactly the same this problem too lowers the LDR resistance producing a higher potential to build at pin2 of the opamp than its pin3 driving the relay to actuate and cut off the supply to the transformer resting all chances of a possible spark or burning inside the transformer.
Rx might be determined employing the following formula:
Rx = LED forward drop/maximum amp threshold = 1.2/Amp
Believe the maximum bearable amp that is certain to not surpass the output is 30amps, Rx could possibly be figured as:
Rx = 1.2/30 = 0.04 ohms
wattage of the resistor could well be 1.2 x 30 = 36 watts


Note: T1 needs to be located as close as possible to the transformer, while D5 needs to be stored exposed to ambient atmosphere, well removed from the transformer heat.
Parts List
R1 = 2k7,
R2, R5, R6 = 1K
R3 = 100K,
R4 = 1M
D1—D4, D6, D7—D10 = 1N4007,
D5 = 1N4148,
VR1 = 200 Ohms, 1Watt, Potentimeter
C1 = 1000uF/25V,
T1 = BC547,
T2 = 2N2907,
IC = 741,
OPTO = LED/LDR Combo (see text).
Relay = 12 V, SPDT. amp spec as per transformer rating