The article talks about a 12V backup supply with battery charger circuit which is often executed as an uninterruptible emergency heating system for incubator chambers.
The concept is meant to make sure an continuous method of getting warmth to an incubator chamber no matter the existence or lack of the mains grid voltage through a battery backup system.
Talking about the above design of the offered emergency incubator lamp with charger circuit, we are able to notice an easy layout comprise of a transistorized voltage regulator phase created by a Darlington paired 2N3055/TIP41 BJTs and an opamp based battery over voltage, lower voltage cut off level.
The mentioned 30V input DC is resulting from the stated 30V 25amp transformer after properly correcting it via a bridge rectifier and a filter capacitor (3300uF).
The provided input is done by the Darlington BJT phase and an approximately 14V is accomplished across the emitter of the 2N3005 transistor at a specific current level based on the 1k resistor at the base of the TIP41 transistor. This resistor might be improved or reduced for correspondingly improving or reducing the emitter current of the 2N3055.
The above controlled output is employed to power the incubator heater lamp as well as to charge the connected 12V 60AH battery.
So long as the battery voltage is below the optimal full charge level, the red LED at pin6 of the opamp 741 stays lighted and the green LED continues turned OFF.
The above circumstance maintains the BC547 and the linked relay toggled OFF, that permits the DC voltage from the 2N3055 emitter to cross to the battery via the N/C contact of the relay and via the specific 6amp diode attached at the N/C of the relay.
As soon as the battery is fully charged, the red LED switches OFF, the green LED is switched on, so does the BC547 transistor and the relay.
The relay contact currently changes from its N/C to N/O, cutting off the charging supply to the battery, and stopping any chance of over charging for the battery.
The above activity also allows the battery voltage to reach the heater lamp via the N/O contact and the series diode at the N/O contact.
In spite of this the described situation has an issue.....here the changeover action from mains to battery could be inhibited at any time the battery might be in the charging mode.
Simply because in the course of the charging stage the battery voltage could be somewhere within the full charge and low charge value, sustaining the relay contacts towards the N/C position which often would certainly reduce the battery voltage from achieving the heater lamp.
To be able to correct the above problem a BC557 can be viewed launched, that will make certain that every time mains goes wrong and the relay is at the N/C, it's compelled to revert to the N/O position and hold this until the battery level drops below the fixed risky low voltage level.