Ammeter heating up.........

If you really want to improve, there are shunt less ways to measure current. It involves measuring magnetic field around a current carrying conductor with a linear Hall circuit.

Here is an example:
http://www.panucatt.com/mobile/product.aspx?ProductCode=cs-100a&404;http://www.panucatt.com:80/Current_Sensor_for_Arduino_p/cs-100a.htm=