Limit Characters - This works

add_filter("the_content", "plugin_myContentFilter");

function plugin_myContentFilter($content) {
$post_type = get_post_type($post_id);
if ( $post_type == 'ideas')  {
// Take the existing content and return a subset of it
//return wp_trim_words( $content, 600, NULL );
return substr($content, 0, 3000);
} else {
  return $content;
}
}