I've read that it's not good to vape a cartomizer dry, but how do you know when to stop?
I vaped that carto for a day and a half but when I put maybe 6 or 8 drops in, a whole bunch came out of the bottom. So maybe I did it too soon?
Just a thought as I have had this happen to me...I had a coffee cart that I thought was close to burnt but decided to top it off and keep vaping it...halfway through the cart I noticed it tasted "funny" so I spun out the juice and took the cart apart only to find the poly was burnt to hell and back....just for fun i lit the poly on fire to see how it burned and after seeing and smelling that I never let my carts get anywhere near dry as I'm sure a burnt cart will produce vapor if covered up with a strong enough flavor but at the same time your vaping burnt poly fill...yuck
Yes....you can absolutely wait longer. The Juice will always settle on the bottom so it's perfectly natural for the top of the polyfill material to appear dry after only a minute of vaping. Cartomizers on average hold 25 drops or 1 ml, if you are taking 2-3 draws within 5 minutes or so you will typically need to top off after 2-2.5 hours. This can a very little bit depending on what type of Cartomizer and if you are using a higher voltage device like a passthrough. Even the difference is only 30 minutes and topping off is simply freshening the Cartomizer to prevent it from being burnt.
I would say that you should experiment a little even at the risk of burning up a Cartomizer. Then you'll know what is right for your vaping style. Here is some info that might be helpful with a detailed cut away of Cartomizer for you to see how they work.
YouTube - Vapor4life Tips, Tricks & Fixes for Cartomizers (burnt cartomizers....inner workings of a cartomizer...2:13 mark)
Hope that helps.....