I hope someone can answer a few question about my visa.

I have a ED visa that i have to extend at the end of the month, ( last extention for the ED visa) but the day before my visa runs out, am i going back to my home country for a 3 week period. I will buy a Non-im re-entry permit before i leave. But do i have to renew my visa before leaving? or can i do it when i back? Because if i do before leaving, i will use 3 weeks of my visa while i not stay here. I know when i get back, i will only get 14 days at the airport, before i have to go back to immigration.

If i example get a new Visa in my home country, Non-O. Can i enter Thailand on my ED visa, or is it impossible?

It is not clear if you have a visa for entry or an extension of stay from Immigration but a re-entry permit only allows the current permitted to stay date - it does not add anything to your permitted to stay at all. So if extension you renew - obtain re-entry permit and return using that for the same renewal period. You lose any time outside of Thailand.

As for having two visas for entry that is not allowed and if Consulate see they will not issue a new visa unless the previous has been void.

The OP states the visa will run out the day before he leaves, so if an extension from Immigration it runs out, and he is on one days overstay. If this is so then OP the re-entry permit does not help you.

Thanks for the replay.

so i will do as i did before, i will buy a re-entry permit and extend my current ED visa. Then i will applay for a new Non-o Visa in my country. If i by some reason not get my Non-o, i can still enter on my ED visa.

The correct sequence is

1. Get new extension of stay.

2. Get re-entry permit.