Low Voltage Disconnects

Discharging lead acid batteries heavily is not at all good for them - particularly if they are then left for a long time before being recharged fully. Batteries treated in this way lose capacity, and will have a significantly shorter lifespan.

Low voltage disconnects prevent batteries being heavily discharged by the simple method of switching off any loads attached to them when they detect that the battery voltage is getting dangerously low. They are usually configured to switch loads back on when the battery has recharged. For example, the low voltage disconnect terminals on the SunSaver controllers (pictured) are configured to disconnect at 11.5 volts, and reconnect at 12.6 volts.

Low voltage disconnects (or LVDs) are common in solar charge regulators. Most high end controllers, such as the Tristar and ProStar models, have them as standard, while they are available as an optional extra on the Sunsaver 10 and 20A controllers.

They are most useful on systems that are left unattended - remote power systems that might be running automated scientific equipment for example. On systems on narrowboats and caravans they are less important, as usually there is someone keeping an eye on the battery voltage anyway. Even if the battery is getting low, you might not want your lights to all suddenly switch off!

Other charge regulator articles:

• Maximum Power Point Tracking
• Introduction to charge controllers for solar panels and wind turbines