i have a bone stock blitz. i need to know how much run time i can get on these packs.

5000 mah 3s 11.1v 30c lipo
4800 mah 2s 7.4v 20c lipo

i dont have a lipo cutoff so how do i go about determining approximate runtime so i dont destroy these cells?

What esc are you using ?

If it is a stock esc designed for nimh's only I doubt you will be able to run 3s lipo on it

You can buy a cheap lipo warning buzzer from ebay that will flash a light and make a noise if cells drop below 3.3v or so, they work fine

Cheers

BTW the esc is an old lrp ics digital speed control no motor limit 10 cell max but on a factory hpi motor. maybe 3s wont work too well on that motor... lol

If you don't use something like a Novak Smart Stop, easiest thing is to make a short timed run like you would be running - prob no more than 5 min. Then see what the charger puts back in. This lets you calculate a mah/min. Base your time estimates on 80% of the pack capacity - you don't want to use more than that since its basically the same as running the pack below the voltage cutoff.

so the idea on a 4800 would be not to have to put in more than 3840 mah into my pack?

Correct....otherwise you're basically overdischarging.

Go and get a used ESC from another racer that is Lipo capable. Why mess with the effort of Lipo cutoff. A low-level ESC with Lipo cutoff is cheap. Probably cheaper than the Lipo you are putting at risk.

^^^ There's a lot to be said for doing that too....