How To Seek Out Happiness With LiFePO4 (Lithium-Ion) Batteries – Solacity Inc

Most common photo voltaic charge controllers have no trouble charging lithium-ion batteries. The Voltages wanted are very just like these used for AGM batteries (a type of sealed lead-acid battery). The BMS helps too, in ensuring the battery cells see the fitting Voltage, don’t get overcharged, or overly-discharged, it balances the cells, and ensures the cell temperature is within cause whereas they’re being charged.

The graph below exhibits a typical profile of a LiFePO4 battery getting charged. To make it easier to read the Voltages have been converted to what a 12 Volt LFP battery pack would see (4x the one-cell Voltage).

LiFePO4 Charge Voltage vs. SOC

Shown in the graph is a charge price of 0.5C, or half of the Ah capability, in other words for a 100Ah battery this can be a cost fee of 50 Amp. The cost Voltage (in red) will not likely change much for larger or decrease charge charges (in blue), LFP batteries have a very flat Voltage curve.

Lithium-ion batteries are charged in two phases: First the present is stored constant, or with solar PV that usually means that we try and send as much current into the batteries as out there from the solar. The Voltage will slowly rise during this time, until it reaches the ‘absorb’ Voltage, 14.6V within the graph above. Once absorb is reached the battery is about 90% full, and to fill it the rest of the way in which the Voltage is saved fixed while the present slowly tapers off. Once the current drops to around 5% – 10% of the Ah ranking of the battery it is at 100% State-Of-Charge.

In many ways a lithium-ion battery is easier to cost than a lead-acid battery: As lengthy because the charge Voltage is excessive enough to maneuver ions it expenses. Lithium-ion batteries do not care if they aren’t fully 100% charged, in reality they final longer if they don’t seem to be. There isn’t any sulphating, there isn’t any equalizing, the absorb time does probably not matter, you can’t really overcharge the battery, and the BMS takes care of holding things within cheap boundaries.

Charge Voltage Needed

So what Voltage is enough to get those ions moving? A bit of experimenting shows that 13.6 Volt (3.4V per cell) is the minimize-off level; under that very little occurs, whereas above that the battery will get at the very least 95% full given sufficient time. At 14.Zero Volt (3.5V per cell) the battery easily charges as much as 95+ % with a couple of hours absorb time and for all intents and functions there may be little difference in charging between 14.Zero or larger Voltages, things simply happen a little faster at 14.2 Volt and Lipo battery above.

Lithium-ion cell structure

Bulk/Absorb Voltage

To summarize this, a bulk/absorb setting between 14.2 and 14.6 Volt will work nice for LiFePO4! Lower is feasible too, all the way down to about 14.Zero Volt, with the assistance of some absorb time. Slightly increased Voltages are potential, the BMS for most batteries will permit around 14.8 – 15.Zero Volt before disconnecting the battery. There isn’t a benefit to the next Voltage although, and extra risk of getting lower of by the BMS, and probably injury.

Float Voltage

LFP batteries don’t have to be floated. Charge controllers have this as a result of lead-acid batteries have such a excessive fee of self-discharge that it is smart to keep trickling in additional cost to maintain them happy. For lithium-ion batteries it is not great if the battery continuously sits at a high State-Of-Charge, so if your cost controller cannot disable float, LiFePO4 battery just set it to a low sufficient Voltage that no precise charging will occur. Any Voltage of 13.6 Volt or much less will do.

Equalize Voltage

With charge Voltages over 14.6 Volt actively discouraged, it should be clear that no equalize must be finished to a lithium-ion battery! If equalize can’t be disabled, set it to 14.6V or much less, so it becomes just an everyday absorb charge cycle.

Absorb Time

There may be quite a bit to be mentioned for merely setting the absorb Voltage to 14.4V or 14.6V, and then simply stop charging as soon as the battery reaches that Voltage! In brief, zero (or a short) absorb time. At that point your battery will likely be round 90% full. LiFePO4 batteries will be happier in the long term when they don’t sit at 100% SOC for too long, so this follow will lengthen battery life. When you completely have to have 100% SOC in your battery then absorb will try this! Officially that is reached when the charge current drops to 5% – 10% of the Ah score of the battery, so 5 – 10 Amp for a 100Ah battery. If you cannot cease absorb based mostly on present, then set absorb time to about 2 hours and call it a day.

Temperature Compensation

LiFePO4 batteries don’t want temperature compensation! Please swap this off in your charge controller, or your charge Voltage will likely be wildly off when it is very warm or cold.

Make sure to test your charge controller Voltage settings in opposition to these truly measured with a great high quality digital multi-meter! Small modifications in Voltage can have an enormous impact when charging a lithium-ion battery! Change the cost settings accordingly!