Problems with mb_convert_encoding

I have some problems with PHP mb_detect_encoding function. I can not convert it to ISO-8859-1. Any help?

The code:

$str = "åäö";
$encoding = mb_detect_encoding($str);
echo $encoding;

$encoding = mb_detect_encoding(mb_convert_encoding($str, "ISO-8859-1"));
echo $encoding;

Conclusion:

Utf-8

Utf-8

Updated solution:

I updated mb_detect_order to an array ('UTF-8', 'ISO-8859-1') and it worked.