How many words should I aim to learn per day?

I've been building a good habit of studying using flashcards through Renshuu's terms, but I've been wondering how many new words I should try to memorize per day.

The default setting is 12 per day, and I guess it's working fine, but when I try to translate a word from the top of my head sometimes it doesn't work out.

Also, the vectors I've got set up are Kanji to Kana, Japanese to Meaning and Meaning to Japanese, it that's relevant.

Edit: I also like writing the kanji as I go so I can memorize them better, mnemonics help from time to time

Edit 2: I actually got it wrong, the vectors I got are Kanji to Kana, Kana to Kanji, and Japanese to Meaning