Versatile Micropower Battery Protector

Protect your expensive batteries from discharge damage with this mini-sized electronic cutout switch. It uses virtually no power and can be built to suit a wide range of battery voltages.
Main Features

• Disconnects load at preset battery voltage
• Automatically reconnects load when battery recharged
• Ultra-low power consumption (<20ma)
• Miniature size
• 10A maximum rating
• Suitable for use with 4.8-12.5V batteries
• Transient voltage protection (optional)

Suitable for use in...

• Cars, boats & caravans
• Security systems
• Emergency lighting
• Small solar installations
• Camera battery packs
• Many other low-power applications

Picture of the project:

Back in May 2002, we (Silicon Chip) presented the "Battery Guardian", a project designed specifically for protecting 12V car batteries from over-discharge. This unit has proven to be very popular and is still available from kit suppliers. This new design does not supersede the Battery Guardian – at least not when it comes to 12V car batteries. Instead, it’s a more flexible alternative that can be used with a wide range of battery voltages.

Parts layout:

In this new "Micropower Battery Protector", we’ve dispensed with the low-battery warning circuitry and the relatively cheap N-channel MOSFET used in the Battery Guardian in favour of a physically smaller module that steals much less battery power. It costs a little more but can switch lower voltages, allowing it to be used with 6V & 12V lead-acid batteries and 4-cell to 10-cell NiCd and NiMH battery packs.

PCB layout:

Most battery-powered equipment provides no mechanism for disconnecting the batteries when they’re exhausted. Even when the voltage drops too low for normal operation, battery drain usually continues until all available energy is expended. This is particularly true of equipment designed to be powered from alkaline or carbon cells but retro-fitted with rechargeables.
Circuit diagram:

Another example is emergency lighting and security equipment designed to be float-charged from the mains. In an extended blackout period, the batteries can be completely drained and may not recover when the mains power is finally restored.

Source:   http://www.ecircuitslab.com/2011/06/versatile-micropower-battery-protector.html

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Lead Acid Battery Protector

The circuit described here can be used to  ensure  that  a  12 V  sealed  lead  acid  (SLA)  gel battery isn’t discharged too deeply. The  principal part of the circuit is a bistable relay,  which is driven by the output of an op amp.

Lead Acid Battery Protector Circuit Diagram

The battery voltage is first reduced via D1, R1,  P1 and R2, and then continuously compared  with a reference voltage set up by diode D2.  When the battery discharges too much and  its terminal voltage drops below the level  set by P1, the output of the opamp becomes  High, which causes the relay to toggle. This  in turn isolates the load from the battery. The  battery can be reconnected via S1 once the  battery has been replaced or recharged.

The relay used in the prototype is a 5 V bistable type made by Omron (G6AK-234P-ST-US  5 VDC). The two windings of the relay each  have a resistance of 139 Ω (for the RAL-D 5  W-K made by Fujitsu this is 167 Ω). When the  battery voltage starts to become too low and  the relay is being reset the current consumption of the circuit is about 45 mA. Shortly  after the load has been disconnected, when the battery voltage rises above the reference  voltage again, the reset coil will no longer be  powered and the current consumption drops  back to about 2.5 mA.

The range of P1 has intentionally been kept  small. With a reference voltage of 5.6 V (D2)  and a voltage drop of 0.64 V across D1, the circuit reacts within a voltage span of 11.5 V and  11.8 V. This range is obviously dependent on the zener diode used and the tolerance.

For a greater span you can use a larger value  for P1 without any problems. With the potentiometer at its mid setting the circuit switches  at about 11.6 V.

source : http://www.ecircuitslab.com/2012/05/lead-acid-battery-protector.html

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Power Resumption Alarm and Low Voltage Protector

The circuit described here protects your electrical appliances like AC motors from damage due to low voltage at power-on. It remains standby without giving power to the load after power resumes. The load can be switched on only manually. This prevents damage to the device if it is on when power resumes.

unregulated power supply is derived from a 12V-0-12V, 300mA step-down transformer and rectifying diodes D2 and D3. The rectified DC is made ripple-free using capacitor C3. An audio/video indicator (piezobuzzer and LED3) is provided along with the power supply for power resumption.

When power is switched on, capacitor C4 charges through the piezobuzzer and LED3, making both of them active. The piezobuzzer beeps and LED3 glows for a few seconds. When capacitor C4 is fully charged, the cathode of the LED becomes high inhibiting further flow of current through the buzzer.

When the power is off, capacitor C4 discharges through resistor R9.

The circuit uses IC CA3140 (IC1) as a voltage comparator to detect voltage changes in the unregulated power supply due to AC mains. Mains voltage changes in the primary as also the secondary winding of the transformer, which is sensed by IC1 to energise/de-energise the relay. Zener diode ZD1 provides a reference voltage of 3V to make transistor T1 conduct. Preset VR1 adjusts the breakdown point of ZD1.

Fig. 1: Power supply circuit with resume indicator

When the voltage level is normal, zener diode ZD1 breaks down and transistor T1 is forward-biased. Capacitor C1 provides time delay of a few seconds to avoid any fluctuation affecting the device during power-on. When transistor T1 conducts, the inverting input (pin 2) of IC1 goes low. However, IC1 does not give a high output as its power supply depends on the conduction of SCR1 (BT169). So manual operation is necessary to energise the relay.

When push-to-on swish S1 is pressed, SCR1 fires to provide voltage to IC1 at its pin 7. As the voltage level at the non-inverting input (pin 3) of IC1 is half of the supply voltage, its output becomes high and the relay (RL1) energises. LED2 glows to indicate the high output of IC1 and activation of relay.

When the line voltage goes below 180V, the secondary voltage of the transformer also drops, say, below 12 volts, ZD1 cease to conduct and the collector of T1 becomes high. This high voltage at the inverting input (pin 2) of IC1 makes its output low. The relay de-energises to stop power to the device.

Fig. 2:  Low-voltage Protector Circuit Diagram

Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Use a 12V PCB-mounted relay. Provide holes for LEDs and switch S1 on the front side of the case. Connect AC power voltage to the motor (load) through the common and normally-open (N/O) contacts of the relay. After assembly and checking the circuit, switch on the circuit and wait for a few minutes. LED1 will gradually become bright due to the charging of capacitor C1. Press S1 to energise the relay. Adjust VR1 so as to make LED1 fully on. This will allow easy latching of the relay.

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Versatile Micropower Battery Protector

Protect your expensive batteries from discharge damage with this mini-sized electronic cutout switch. It uses virtually no power and can be built to suit a wide range of battery voltages.

Main Features

• Disconnects load at preset battery voltage
• Automatically reconnects load when battery recharged
• Ultra-low power consumption (<20ma)
• Miniature size
• 10A maximum rating
• Suitable for use with 4.8-12.5V batteries
• Transient voltage protection (optional)

Suitable for use in...

• Cars, boats & caravans
• Security systems
• Emergency lighting
• Small solar installations
• Camera battery packs
• Many other low-power applications

Picture of the project:

Back in May 2002, we (Silicon Chip) presented the "Battery Guardian", a project designed specifically for protecting 12V car batteries from over-discharge. This unit has proven to be very popular and is still available from kit suppliers. This new design does not supersede the Battery Guardian – at least not when it comes to 12V car batteries. Instead, it’s a more flexible alternative that can be used with a wide range of battery voltages.

Parts layout:

In this new "Micropower Battery Protector", we’ve dispensed with the low-battery warning circuitry and the relatively cheap N-channel MOSFET used in the Battery Guardian in favour of a physically smaller module that steals much less battery power. It costs a little more but can switch lower voltages, allowing it to be used with 6V & 12V lead-acid batteries and 4-cell to 10-cell NiCd and NiMH battery packs.

PCB layout:

Most battery-powered equipment provides no mechanism for disconnecting the batteries when they’re exhausted. Even when the voltage drops too low for normal operation, battery drain usually continues until all available energy is expended. This is particularly true of equipment designed to be powered from alkaline or carbon cells but retro-fitted with rechargeables.

Circuit diagram:

Another example is emergency lighting and security equipment designed to be float-charged from the mains. In an extended blackout period, the batteries can be completely drained and may not recover when the mains power is finally restored.

Source: Silicon Chip 27 July 2004

Read More..