Solar Panel Charge Controller / Low Voltage Disconnect Circuit (SPC1)

This circuit has been updated, see the new SPC3 design. An SPC3 circuit board and parts kit is available.

This design appeared as a pair of articles in Home Power Magazine.

The charge controller is used to connect a solar panel to a 12 volt lead acid battery, it regulates the charging of the battery and allows the battery to be charged up to a preset voltage. This prevents the battery from over-charging and boiling off electrolyte. The low voltage disconnect is used to connect a load to the same 12 volt lead acid battery, the LVD acts as a smart switch, it auto disconnects the load if the battery voltage falls below a set point. When used together, these circuits keep the battery operating within normal voltage limits which greatly extends the life of the battery.

Charge Controller / Low Voltage Disconnect circuit in GIF format (17kb)

Charge Controller / Low Voltage Disconnect circuit in PostScript format (30kb)

Charge Controller article

Low Voltage Disconnect article

Circuit Board Assembly Instructions and Parts List

Circuit Alignment Instructions

This circuit is no longer offered as a kit, thanks to the many customers who bought this version.

Solar Circuit Board Kits For Sale

The SPC3 charge controller/low voltage disconnect kit is an equivalent, but improved version of this circuit, it is available from CirKits.
The SPC3 is much easier to align, it has a single adjustment for the charge controller section, compared to the three found on the SPC1.

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