MP20 - Optional Battery Charger
This is a special but simple power supply, used
to keep a 12 volt 7 Amp Hour Gel-Cell charged.
Any size battery, less than 20 AH could be used.
You could also add a line filter on the input side
of the power transformer. The Recifiers are not
critical; Any of the 5400 series are fine here.
Maximum current draw from the PS could be over
one amp for a short time with a dead battery, so
use a heat sink on the LM317. The 5 ohm resistor
used here has a 10 watt rating. You could use
two 10 ohm power resistors in parallel.
When using a battery, as in the schematic, adjust
the 1K trim-pot for 14.5 volts on the output of
the LM317. After the voltage drop across D3, the
voltage on a fully charged battery is about 13.9V
You can keep the PS on all the time to keep the
battery fully charged
