what happen if we cross the limit of meta tag characters.

Yes. I am not so sure you'd be penalized as much as the search engines will just discount the meta tags entirely.

surely, you'll be penalized, I also read some article that some site are using invisible text to form their keywords, it is being detected by google, so don't overly put keywords on your meta tags. try to check submitexpress.com they have a meta tag analyzer

hope this helps

trial n error friend... thats the key.."-)

- 5 keywords and/or 5 keyphrases per page (keep them relevant ie: abbreviations, synonymous keyphrases etc.) for Meta Keywords

- 2 short complete captivating informative sentences for Meta Description

- short, accurate, not overly repetitive yet compelling Title

- don't forget to disable the DMOZ description qualifier <meta name=”ROBOTS” content=”NOODP”> (if you don't want your web page's description in the SERPs appear ridiculous and outdated)

- concentrate on quality words and phrases in all your optimizable HEAD tags and try to always have your focus on the Internet visitor's experience and perceptions rather than the search engine's.

I think Google or other search engines would only replace the excessive character with "..." in SERP pages and might be also in the database. :)

have a nice day,

I think you probably violate the ethical search engine optimization guidelines. In that case, may be google won't probably display all the information you put in your meta description when it indexed your website.