Today we completed a three way battery charger time controller for use in a motor home. This motor home has been fitted with three 12V batteries which are periodically independently used and charged (via a mains powered battery charger).

In order to keep all three batteries well charged when at home or on a mains hook-up at a camp site, we made an automatic controller. This connects each of the batteries in turn to the charger, with the user able to programme in the charging duration required for each battery – e.g. 3 hours, or 5 hours etc.

To make this controller more flexible we also added in a manual override enabling the user to manually select a battery to leave connected to the charger until they cancel the override – useful if one particular battery needs a lot of charging immediately.

We fitted one red LED per battery to give a visual indication of which battery is currently being charged, and the green LED lights up when manual mode has been selected.

The low current 12V outputs from our controller/timer go to the coils of three 25A automotive relays which switch the positive output from the mains powered charger to the appropriate battery.