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

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