Li-Po Cutoff Voltage

[Hell-e-Guy]

Hi,
I am building a few external cutoff units for some old ESC's that Don't support Li-Po cutoff.
What is the recommended cutoff voltage for a 3s pack?
I will be sampling the voltage right from the ESC's battery connector...
Is 8V OK ? taking into account the voltage drop on the wires, connectors and internal resistance...
Should a more conservative voltage be taken, closer to the recommended 9V?

Thanks !

[coro]

It depends... but using 3.3V / cell (9.9V) can save the pack in case of blocked prop or gear.
Look at discharge graphs and consider diference in life of pack.

[Dan Baldwin]

The voltage that has been used as a standard for LVC voltage for some time is 3 volts/cell, so for a 3 cell pack you would use 9 volts. The actual best voltage to use would depend on the circumstances. I have some older 10C rated lipos being used at about 8C that give me 10 minute flights with the LVC set to 2.8 volts/cell, but I would get less than 5 minutes if I were to set the LVC to 3 volts/cell. The packs always come up to about 3.7 volts/cell shortly after the flight, and they have been performing well for almost two years. If, on the other hand, you are running a very light load on the pack, you would need to use a higher cut off voltage.

some of the newer lipo's have such low internal resistance, that if you used 3 volts/cell, and flew to LVC, you would have over discharged the pack. For those packs, 3.2 volts/cell or higher would be better.

I don't think that there is one correct LVC voltage for all situations, but the best bet is probably to land well before your LVC starts to cut out; basically just use it as a safety.

Dan

[Hell-e-Guy]

Thanks Dan,
I'll be using the LVC with some old Li-Po's 10c and even 8c.
I will start with 3V/cell and work my way down if needed after a couple of flights.