Trickle Charger 12 volt or 6 volt

Here is a simple cheap easy to build trickle charger for a 12 volt lead acid battery from my salvage basket of parts. Keep your cars battery charged and ready to go if the car is not used regularly.

I actually built 2 , 1 for a lead acid car battery and 1 for a gel cell battery. The car trickle charger uses a 500 mA transformer (see below where I used a 2 amp transformer - working) , you could use a 1 amp transformer but that is the maximum I would go to as all the parts are rated at 1 amp , and the gel cell trickle charger uses a 300 mA transformer. To regulate the voltage I have used a 15 volt voltage regulator and a couple of diodes , with a bypass switch on the diodes for a high / low voltage output. A LED indicates the charger is on. As a after thought I should have added a fuse to the output.

Some  knowledge of electronics and soldering is required , but really , its not that difficult.

List of parts:
1 x transformer 18 volts
1 x bridge rectifier 1 amp
1 x capacitor 35v 330uF
1 x 15v voltage regulator 1 amp
3 x small diodes
1 x LED
1 x resistor
1 x on /off switch
1 x potting box
wires and clips

Schematic diagram for lead acid battery trickle charger

Trickle Charger 12 volt or 6 volt

Trickle Charger 12 volt or 6 volt

Trickle Charger 12 volt or 6 volt

Trickle Charger 12 volt or 6 volt

Trickle Charger 12 volt or 6 volt

Here is another lead acid battery charger.
I had to build urgently for a car that does not get driven regularly , so the battery discharges over time.
Some info on lead acid batteries: if the battery discharges down to a level below 12.5 volts sulfation starts to occur inside the battery , this causes the battery to loose its amperage capacity and will eventually cause the battery to fail and not start the engine , also if a battery discharges to below 60 percent of its capacity the life of the battery is shortened by +- 25 percent. Therefor a trickle charger should be connected to the battery to maintain the voltage above13.5 volts but not more than 15 volts.

With this trickle charger I used a 2 amp transformer with a 4 amp bridge rectifier. May not be the most elegant build but it works. As the voltage regulator is only rated a 1 amp I used a large heat sync as the regulator gets quite hot when connected to a "flat" battery. While running some testing on this build I noticed the regulator and transformer would get quite hot when bringing up the voltage ( starting voltage +- 12 volts) , but would cool down when the voltage  reached 14 volts or more. This lead me to investigate the charging amperage , what I found was the amperage would be high ( +- 1.7 amp)  but would drop to 0.1 amp when the voltage reached 14 volts. This happens because a discharged battery has a high internal resistance causing the circuit to work 'harder' ,  IE ,  input more amperage to bring the voltage up , but once the battery had 'charged' up and reached 14 volts the internal resistance is much lower  so current (amps) can flow much easier through the battery , so the circuit works less harder and the components operate at a lower temperature. I still plan to add a circuit to turn on a LED  when 14 volts + is reached.

Trickle Charger 12 volt

Trickle Charger 12 volt

Trickle Charger 12 volt

Trickle Charger 12 volt

Trickle Charger 12 volt

Trickle Charger 12 volt

Trickle Charger 12 volt