Battery Monitor Alarm

If all you are looking for is a low battery voltage alarm indication then it is simple to create a circuit from one Op-Amp and a few other components driving a relay. Cost in the order of a couple of $ at most.

Bernie,

If it is intended for the alarm to go to a DCS, a PLC, or any other system that has analog input cards, you might try this method: A typical AI is actually a 1 - 5 VDC input with a 250 Ohm range resistor to convert 4 - 20 mA to the correct voltage. Assuming your battery voltage is a nominal 24 VDC, connect the negative of the battery to the neutral of the AI. Connect the positive via a 1 K Ohm series resistor to the positive of the AI.. This creates a 250 / ( 1000+250) voltage divider. Your 24 VDC will appear as 4.8 volts at your DCS input. The point should be scaled at 5 to 25 VDC. You can configure your alarms at any value you like. All it costs is one resistor plus an AI point.

Walter.