Preventing lead acid batteries from being deeply discharged is absolutely key in terms of ensuring battery longevity. We sell a selection of user programmable low voltage disconnect circuits for 12V battery systems.
A low voltage battery disconnect (LVD) is a circuit which will automatically turn off the load connected to a battery if the battery voltage falls to low. Preventing lead acid batteries from being deeply discharged is absolutely key in terms of ensuring battery longevity.
If we break the name Lead Acid battery we will get Lead, Acid, and Battery. Lead is a chemical element (symbol is Pb and the atomic number is 82). It is a soft and malleable element. We know what Acid is; it can donate a proton or accept an electron pair when it is reacting.
Putting together a low voltage disconnect circuit is not as simple as it may initially appear. If you were to simply use a relay to disconnect the battery from the load whenever the battery voltage falls below 11.5V say, then immediately after the load is shut off, the battery voltage will jump up again re-connecting the battery to the load!
In addition to taking care of hysteresis, a good low voltage battery disconnect will also include a timer. When a pump or motor is first switched on for example, the battery voltage will dip down (due to the high current required to start the pump/motor from stationary) for less than a second.
For 12V lead acid batteries we have found that the value of y should be at least 0.5V, and ideally 1.0V for greater system stability. Good quality power inverters are always fitted with LVD capability – typically turning off the inverter when battery voltage falls to 11.5V and back on when it reaches 12.5-12.7V.