US Mac Book Pro, Living in Ireland (Same UK Plugs)

Hi, I bought my macbook pro in the US and I am now back in Ireland, my macbook just has the US power adaptor....in Ireland we use the same plugs (sockets) as those in the UK...

I have plugged my mac book into a US to UK plug adaptor and into the socket, the macbook charges for around ten minutes that stops (100% charge still not reached)....do I need a special convertor that will change the voltage to the correct setting? Anyone had/have the same problem..

Thanks in advance