The LM741 is an op-amp which has many uses in renewable energy applications. In a previousREUK.co.uk article* we looked at how this chip can be used to make a general voltage level indicator.
* Click here to read the introductory LM741 Op-Amp Voltage Indicator article.

In this article we will briefly look at how this circuit can be modified specifically for the 12 Volt lead acid batteries typically used in renewable energy projects for back-up power storage. An LED warning indicator will turn on when the battery (or battery bank) voltage falls below a certain (user selectable).

12 Volt Battery Monitor Circuit Plans

Pictured above is a circuit diagram for this 12 Volt battery monitor. The key components are the 100K variable resistor, the LM741 Op-Amp, and a 5.6 Volt Zener Diode.

The 100K variable resistor is adjusted* such that the LED indicator just turns on when the battery voltage (Vin) falls to the required level – e.g. 12.00 Volts indicates the battery is 75% discharged.
*Full details on setting up this type of voltage indicator are provided here (scroll down to Configuring the Voltage Indicator at the end of that article.

Purchasing the Components

Main components such as the LM741, and LED are listed for sale in the REUK Shop. The rest (and many other items) are available upon request – contact neil@reuk.co.uk for details.