如何更改使用多个构造函数？

I am making a script and am currently working on the database class. I am currently building the Banning class with two child classes BanSingleIp and BanIpRange.

I am puzzled at the moment because I can't seem to think of another way of passing $_POST variables into the classes without using __construct().

This is my Banning class:

/**
* BANNING CLASS EXTENDS DATABASE CLASS
*/

class Banning extends Database {

}

class BanSingleIp extends Banning {
    // Variables for single IP Ban
    protected $_S_user_ip;
    protected $_S_ban_length;
    protected $_S_ban_reason;
    protected $_S_ban_start;
    protected $_S_ban_end;

    /**
    * Constructor, assign variables to their values
    */
    private function __construct() {
        $this->_S_user_ip    = ''; // TODO: Replace with $_POST['S_user_ip'];
        $this->_S_ban_length = ''; // TODO: Replace with $_POST['S_ban_length'];
        $this->_S_ban_reason = ''; // TODO: Replace with $_POST['S_ban_reason'];
        $this->_S_ban_start  = time();
        $this->_S_ban_end    = $this->_S_ban_start + $this->_S_ban_length;
      }
}

class BanIpRange extends Banning {
    protected $_R_user_ip_lowest;
    protected $_R_user_ip_highest;
    protected $_R_ban_length;
    protected $_R_ban_reason;
    protected $_R_ban_start;
    protected $_R_ban_end;

    /**
    * Constructor, assign variables to their values
    */
    private function __construct() {
         // Variables for IP Range Ban
        $this->_R_user_ip_lowest  = ''; // TODO: Replace with $_POST['R_ip_lowest'];
        $this->_R_user_ip_highest = ''; // TODO: Replace with $_POST['R_ip_highest'];
        $this->_R_ban_length      = ''; // TODO: Replace with $_POST['R_ban_length'];
        $this->_R_ban_reason      = ''; // TODO: Replace with $_POST['R_ban_reason];
        $this->_R_ban_start       = time();
        $this->_R_ban_end         = $this->_R_ban_start + $this->_R_ban_length;
    }
}
?>

Because I have two separate banning inserts, a single IP and an IP range I created two child classes with new constructors, however PHP won't allow this. Is there any other way I can do what I am trying to do without the constructors? (I haven't created the $_POST variables yet so that is why they are commented).