Lifepo4 cutoff discharge???

[klabeaume]

So I bought 2 8400mah 4s lifepo4 batteries for a RC power wheel project. My charger handles life batteries so I am not worried about that, but how do I monitor when to stop driving/discharging? My rx8 esc only has lipo cutoffs. I've been searching the web for a while and I am finding that voltage isn't a reliable way to monitor these batteries. Looking for some advice. Thanks

 

[Solitaire]

You can get a LiPo alarm. Since LiFE batteries have lower nominal voltage, the LiPo alarm should give you a bit more insurance.

Alternately, my MT-4 radio has a voltage alarm built into it for the receiver voltage. Perhaps your Tx has the same option.

 

[Olle P]

2V/cell is the damage level. ~2.5V/cell is the recommended cut-off for a 1C discharge rate.
If you set LVC on the ESC to level "3" it will cut at 9.6V (2.4V/cell) which is perfect!

 

[klabeaume]

Everything I've read says not to rely on voltage for discharge. I may need a mah tester to only run the battery down 70%.

 

[Olle P]

Everything I've read says not to rely on voltage for discharge. ...

Rely with regards to what?
* If you continuously measure the voltage on each cell individually you can rely 100% on it to cut the current before running dry.
* If only monitoring the pack voltage you can be sure to prevent damage unless one cell is considerably less capacity than the rest.
* The voltage at rest of each cell can be relied upon to reflect its current charge level (not to be confused with capacity).
* You can not rely on the LVC to make sure you drain the battery to at least 70% or whatever desired level.

I may need a mah tester to only run the battery down 70%.

Why such a limit? The important part is to not have any cell reach 2.0V before re-charging. The 9.6V cut-off will easily do that!