When your Steem-Power gets high enough (I think it is 500), you'll have a voting slider that looks like this (every time that you try to upvote):

Voting at 100% about 11 times a day will pretty much deplete your voting power, after doing it for many days -- that's how I understand it, anyways. In other words, ten 100% votes per day is ideal.

You can check your voting power at the following site:

https://steemstats.com/#!/#%2F

The higher your voting power % is, the more rewards you provide with your upvote and the higher the percentage of curation rewards you can earn from that vote.

If you don't have a voting slider yet, all of your upvotes happen at 100%. If you overdo your upvotes, you'll deplete your voting power, but you can never reach 0%. You always have at least a small fraction of a percent of voting power.