Hey everyone, I have a question about LiFePo4 batteries and using them in my project. Is it actually safe to let the battery discharge until the built-in BMS (Battery Management System) kicks in and shuts it down? I have a no-name cheap LiFePo4 battery in mind and I'm wondering if the cut-off voltage is set at a safe level for the longevity of the battery, especially if this happens repeatedly. Would it be better to get an additional circuitry like a Victron Smart Battery Protect to set a higher disconnect voltage, or is relying on the BMS sufficient?
5 Answers
Consider the BMS more of a last-resort safety net. Instead of relying on it, I'd program your inverter to discharge just above the BMS's cut-off. This helps to protect your battery for regular use.
If you want your battery to last, avoid discharging it too deeply regularly. LiFePo4 can handle discharges down to 5-20% without major issues, but continuously draining it could damage it over time. Aim to keep it above that, or be prepared to replace it sooner than you’d like.
The absolute bottom for LiFePo4 cells is around 2.5V. Going below that can harm the cells. Even at 2.9V, you only get minimal capacity. I usually program my systems to warn at 3V and cut off at 2.8V. Remember, if your cells are balanced on top, they might not be on the bottom, so having a buffer helps prevent unexpected shut-offs.
Good point! The user should definitely check how many cells they have and what 0% actually means.
You’ve hit on a key point! The general consensus is to avoid regularly discharging your battery until the BMS cuts off. BMSs aren't meant for frequent deep discharges under load, as they can stress the cells. A cut-off is a safety feature primarily, so it's wise to keep your discharges above the recommended levels.
Yeah, totally makes sense! I was leaning towards getting that extra shut-off unit for more control.
Instead of buying a smart protect device, I’d recommend investing in another battery to increase your capacity and reduce the chances of discharging too low often. Plus, if you have an inverter, make sure it has a low voltage cut-off to shut down loads before you get too close to battery limits.
So basically, BMS is for emergency protection rather than long-term care?