Avoid the discharge of the car battery when not used using a simple relay and interruptor

Relay connection scheme

An old Fiat Bravo was draining battery when not used for a couple of days, and the battery had to be recharged every time: The electronics had an excess of consumption, far surpassed the admissible 0.3 Amps.

After reviewing the possible cause (alternator regulator in poor condition, or something that was connected) by removing fuses and checking consumption every time, I did not found the source of the problem, so we decided to place a switch controlling a relay to disconnect the battery when the car was not in use.

Thus the battery, although the car is not used for 1 full year, only 30-40% is discharged (typical self-discharge at 1 year for batteries Pb / Calcium). Furthermore we lengthen the life of the Central Computer by completely disconnecting it. 

I also take the opportunity to see how these relays are for my next project, which would be programmatically control the battery charging to save fuel by turning off the alternator.

NOTE : Keep in mind that if the battery gets disconnected, you lose the date and time of the control panel (if any).

Using a relay just have to carry three thin wires into the cabin to turn the switch and voltage indicator, because power is handled as close to the battery as possible.

Turn off RadioCD in a Xsara Picasso car: Connection to the burner

We dropped the front screws and side to find the lighter wiring

RadioCD included by factory in the Citroen Xsara Picasso does not disconnected immediately after removing the key, so remains on a couple of minutes after the unit is disconnected.

In this case it is advisable to connect the red wire RadioCD "ON" (not the one going to the battery, but the activator) to positive cable of the burner, and then this hassle is avoided.