Lipo LVC/LVA for radios

[BrianG]

I'm currently using 4 Turnigy LSD cells in my Spektrum radio and they work really well, but I'd really like to use lipos. A regulator is needed between the lipo and radio to give a solid 6v, but the radio's voltage display does not show the state of the actual lipo. So there has to be something that monitors the cells. A regular LVC circuit does not actually cut power, it just outputs a signal to the ESC that forces it to go to neutral, so that won't work. Seeing as how I like to tinker, I came up with a fairly simple LVC/LVA circuit to safely allow me to use lipos. It's basically just a couple of comparators.

The circuit inserts between the lipo and BEC and has two stages: When the cells get to ~3.5v/cell, it lights a warning LED telling the user voltage is getting low. Once the cells get to ~3.3v/cell, it shuts off power. The circuit is designed to completely cut power to itself and the radio to prevent parasitic drain once it shuts down (actually there still is some drain due to transistor leakage current, but it's in the low micro-amp range). However, this design requires the use of two extra momentary switches; one to turn on the radio and one to shut it off (the off button simply tricks the circuit into thinking the lipo is low and initiates the shutdown mode). The radio's stock on/off switch is no longer needed since the on/off function is done elsewhere.

The circuit works but I only made it for my particular use. If there is any interest, I can work on "mini-fying" it and can post the schematic.