Can I run single coova chilli and radius server externally for different access points?

Currently coova chilli and radius server are running in AP only. But problem is that if I switch from one access point to another then it again comes with splash page for authentication however I was already authenticated on previous AP. So can I use my common chilli server and common radius server externally for these AP's. So that once authenticated then again I will not be asked for authentication while switching my connection with different AP. Please suggest me solution for this.

Yes that can be done. When a wireless client moves, the chilli operative on the new AP makes a RADIUS request including the client's MAC. The central server should recognize that MAC as already authenticated.

Thanks for your reply. How it can be done, do i have to modify the chilli code? Please elaborate it and also if i change connection from one AP to another then will my session break or it will remain same for accounting purpose?

Yes, you need to modify chillis pars. Session will break, but you could take care of the accounting effects on the RADIUS.
However, all this is not specific to openwrt, and better to be asked in chilli forum, radius etc.
Especially, as it looks like a commercial entity you are asking for/from. In which case you can send me a PM for commercial support.
As an alternative, you might read the chilli code.