I have a current seup with a single 2s lipo, it does what I want it to do, but I was wondering if you can run a single 3s lipo with the speed control. I know you can run 2 2s lipos.

Yes, a 2S is the minimum.

I just want to know if one 3s lipo will work.

Yes, you can run 2s, 3s or 4s packs on this speedo

people say a lot about bec what is that?

BEC = battery eliminator circuit. In the esc, theres a device called the BEC that takes full battery voltage and steps it down for the rx, servos and the brain board (in the esc) to use - usually 6v and maybe as much as 5amps.

There is heat associated with stepping the voltage down the way its usually done, the bigger the voltage step down, the more the heat. Usually the BEC is the limitiing factor driving an esc cell limits.

ou could run 4S and 5S with the old Mamba esc (rated to 3S) if you'd disable the esc's BEC and use an external BEC.

does anyone know if the low voltage cutoff will work with a single battery? I was told it would only work with a 4s.