FR2523694A1 - SECURITY DEVICE FOR RECURRENT BATTERY IGNITER - Google Patents

Abstract

In the safety device, an apparatus is provided for forming the ignition sparks which inhibits the formation of ignition sparks at the secondary side of a high-voltage transformer, when the charging rate of the capacitor falls to a value below a predetermined threshold.

Description

The invention relates to instantaneous gas appliances of the water heater or bath heater type and more specifically relates to a safety device for recurrent igniters with batteries.

It is known that in this type of apparatus, the ignition of the gas is generally ensured by a recurrent igniter with battery in which a capacitor is charged by means of a diode up to the ignition voltage of a spark gap. As soon as this ignition voltage is reached, the spark gap suddenly discharges the capacitor in the primary of a high-voltage transformer causing the appearance of a voltage across the secondary of this transformer and consequently of a spark at the spark plug located near the gas burner. The charging speed of the capacitor and of course the frequency of the sparks is determined by an oscillator as a function in particular of the battery voltage.

If for any reason the charging speed of the capacitor decreases and therefore the frequency of sparks, for example due to a drop in battery voltage or aging of the spark gap, there may be an excess of gas to the appliance at the time of ignition and therefore an explosive ignition.

This is very unpleasant and causes a feeling of discomfort for the users. In addition, it can cause vibration damage to the various mechanisms of the device.

The invention therefore provides a security device which makes it possible to avoid the abovementioned drawbacks.

According to the invention, the safety device comprises a means which prohibits the formation of sparks at the secondary of a high-voltage transformer if the charging speed of the capacitor drops below a threshold determines.

According to a particular characteristic of the invention, the means forming the safety device consists of an electronic circuit in the form of a dipole mounted in parallel with the capacitor.

Other characteristics and advantages of the invention will appear on reading the following description of an embodiment with reference to the single appended figure which represents the electrical diagram of a recurrent igniter comprising the safety device conforming to the invention. 'invention.

In the single figure, a voltage source has been shown
V consisting of a battery, which supplies the primary winding of a high-voltage transformer TR1. An oscillator 2 mounted in parallel with this primary winding, determines the frequency of sparks.

The secondary winding of the transformer TR1 is mounted in series with a diode CR1, a spark gap E as well as with the primary winding of a second high-voltage transformer TR2 whose secondary winding is connected to a spark plug 3 placed at near a gas burner 4.

In parallel with the secondary winding of the transformer TR1 and the primary winding of the second transformer TR2 are mounted on the one hand a capacitor C1 and on the other hand an electronic circuit designated as a whole by the reference 1 which constitutes the safety device prohibiting ignition when the spark frequency is below a certain threshold and which is presented as a dipole placed in parallel with the capacitor C1.

Circuit 1 includes a resistor R1 in series with a capacitor C2 and in parallel with these elements a triac or thyristor T1. The triac T1 trigger is connected with a diac D1 and with two diodes CR2, CR3.

We will now describe the operation of this device. In normal operation, the transformer
TRi raises the voltage V and charges the capacitor C1 via the diode CRI at a certain speed determined by the oscillator 2. As soon as the charge of the capacitor C1 reaches the ignition voltage of the spark gap E, this this suddenly discharges this capacitor in the primary of the transformer TR2 causing the appearance of a voltage across the secondary of this transformer and consequently a spark at the spark plug 3. After dissipation of the stored energy in capacitor C1, spark gap E is defused and capacitor C1 is recharged again by diode CR1.

During the same time, the capacitor C2 is charged via the diode CR1 and the resistor R1.

If the charge of the capacitor C1 is fast enough, the capacitor C2 will not have time to charge up to the starting value of the diac D1; it will therefore be discharged at the same time as the capacitor C1 in the primary winding of the high voltage transformer TR2 by the diode CR2. The discharge of the capacitor C1 in the primary of the transformer TR2 is an oscillating discharge and the capacitor C1 therefore loses all of its charge while the capacitor C2 recovers a negative charge thanks to the diodes CR2 and CR3.

If the voltage V of the battery drops, the charging speed of the capacitor C1 therefore decreases, which leads to a reduction in the frequency of sparks, there will come a time when the capacitor C2 will have reached the starting voltage of the diac DI first. . At this time, the capacitor
C2 partially discharges into the trigger of the triac T1 which, becoming a conductor, completely discharges the capacitors C1 and C2 via the diode CR2. As the primary winding of the transformer TR2 has not been used, no spark appears on the secondary of this transformer and therefore on the spark plug 3, which means that the battery must be changed.

The discharge of capacitors C1 and C2 is not or very little oscillating because there is no inductance or only parasitic inductances of the circuit. After dissipation of the energy stored in the capacitors C1 and C2, the charge resumes again but, the capacitor C2 is recharged from a zero and non-negative voltage.

As a result, it will reach the priming value of diac D1 even faster.

The time constant of the resistor R1 and of the capacitor C2, as well as the switching threshold of the diac D1 therefore determine the lower threshold of the spark frequency and the triac T1 has a large holding current to ensure the re-ignition of the system, otherwise, it would remain conductive thanks to the sole power supply of oscillator 2. In addition, the CR2 diode makes it possible to give hysteresis to the operation of the device.

It is obviously possible to replace the diac D1 by an indicator light which would indicate by flashing the need to change the battery. This indicator light must have electrical characteristics equivalent to those of a diac or a switching diode
This device, easily adaptable to recurrent battery ignitors, therefore makes it possible to prohibit ignition when the frequency of sparks drops below a certain threshold and indicates the moment when the battery must be replaced.

The description relates to a preferred embodiment of the invention, variants which can be envisaged without departing from the scope of this invention.

Claims (3)

Claims 10 / Safety device for recurrent igniter with battery  intended to supply ignition sparks in  gas appliances such as water heaters or bath heaters  and comprising for this purpose, a capacitor which de  load across the primary of a high transformer  voltage whose secondary is connected to a candle  ignition placed near a characteristic burner  se by the fact that it uses an additional means  to the recurrent igniter to prohibit the formation of  secondary transformer sparks  voltage (TR2) if the frequency of these drops to  below a determined threshold.  2 / safety device according to claim 1  characterized by the fact that the means consists  by an electronic circuit (1) having under  the shape of a dipole mounted in parallel with the  capacitor (C1).  3 / safety device according to claim 2  characterized by the fact that the electronic circuit  (1) comprises in series a capacitor (C2) and a  resistance (R1) and in parallel with these elements  a triac or thyristor (T1) whose trigger is  connected to a diac (D1) and to two diodes (CR2) and (CR3). 40 / safety device according to claim 3 charac  terrified by the fact that the time constant of the resis  tance (R1) and capacitor (C2) as well as the threshold  switching diac (D1) determine the threshold in  the frequency of sparks. 50 / Safety device according to claim 3 charac  terrified by the fact that the diac (D1) can be  replaced by an indicator light.