[Lowfer] Operating from 12VDC battery full time.

[Bob Roehrig]

On Sun, 24 Feb 2002, Les Rayburn wrote:

> Is there a way to filter the charger's input so that I don't pick up more
> noise from it? Someone mentioned putting  a choke on the charger but
> no details.

The Heath charger I mentioned uses a pair of SCR's in full wave for
rectifiers. The current is controlled by the pulse width applied to the
SCR gates. These pulses were getting into the transmit audio of the
repeater. The filter I devised was built from taking an old large filter
choke, removing the winding entirely and replacing it with maybe 20 turns
of #14 enameled wire. This was followed by a 5000uf filter cap.

The simplest charger for the type of battery you have is a standard full
wave rectifier off a center tapped transformer. You might want to put a
couple of small caps across the diodes (.01 or so). and follow with a
fairly large filter cap. This should eliminate noise, at least from the
charger itself. You want to limit the charge current - the simplest way is
to use a Variac ahead of the charger and adjust it for about 13.8V output.
If the charge current is excessive, add a low value/high wattage resistor
in the output (maybe an ohm or two). As a last resort, as someone else
mentioned, maybe you want to switch off the charger when you are trying to
receive.



                    73        Bob Roehrig        K9EUI
                    Aurora University Telecom/IS dept.
                    630-844-4898   broehrig@aurora.edu