How to charge lifepo4 batteries

If you’re looking to prolong your battery life while still maintaining its performance, knowing the best ways to charge a LiFePO4 battery will be helpful.

Several lithium battery chemistries are on the market, but the LiFePO4 is undoubtedly the best, particularly for applications requiring a large battery bank.

Due to its highly stable chemistry, LiFePO4 (Lithium Iron Phosphate) batteries provide a much safer option than other lithium technologies, which can lead to a fire if mishandled.

The LiFePO4 batteries are much more resistant and can withstand electrical and thermal abusive conditions. This means they can stand the test of time, performing many cycles without compromising performance.

Despite being more expensive than their lithium or lead-acid counterparts, LiFePO4 batteries are an excellent long-term investment if — and that’s a critical condition — they are adequately maintained.

This article will provide the four best ways to charge a LiFePO4 battery. This will assist those of you aiming to get the most out of your battery system and make it a worthwhile investment.

Do LiFePO4 Batteries Need A Special Charger?

This is a ubiquitous question when switching to Lithium Iron Phosphate batteries.

The short answer is no — a special charger is not a requirement. What is required, though, is that the charger supplies the battery with the appropriate charging specifications.

But what does that mean? What are the charging specifications of a LiFePO4 battery?

To answer these questions, let’s first revisit a few relevant concepts:

Charging

Charging a battery means applying an external voltage to force the flow of electrons (current) from the cathode to the anode. While discharging, the electrons flow in the opposite direction.

Voltage

Voltage is a force that makes electric charges move. In other words, voltage is the pressure at which the current moves through an electrical system.

Batteries are an assembly of several cells. The number of cells in a battery will determine its nominal voltage.

Lithium Iron Phosphate cells have a nominal voltage of 3.2V, so placing four cells in series provides a nominal voltage of 12.8V. Lead-acid battery cells have a 2V output, so six cells in sequence result in a 12V nominal voltage.

This nominal voltage compatibility makes the LiFePO4 a viable alternative to lead-acid batteries.

For the current to flow to the battery – and effectively charge it – the external voltage should be slightly higher than the open-circuit battery voltage.

But if the applied voltage is too high or too low, the battery won’t charge because the BMS protection will kick in. Or, in a worst-case scenario, the battery will die.

So, to properly charge a LiFePO4 battery, respect the voltage specifications provided by the battery manufacturer.

Below is a table showing the usually recommended charging parameters of a LiFePObattery:

System VoltageCharging Parameters
12V14V – 14.6V
24V28V – 28.6V
36V42V – 42.8V
48V56V – 57.8V

This table shows you can charge your 12V LiFePO4 battery with any charging equipment if the charging voltage is within the 14V to 14.6V range.

But of course, just because you can doesn’t mean you should. So here we present the four best ways to charge your LiFePO4.

3 Best Ways To Charge A LiFePO Battery

1. Using A Lead-Acid Battery Charger    

So you’re considering switching your lead-acid deep cycle batteries to brand new LiFePO4 batteries (smart move) and wondering if you’ll need a new charger?

The good news — not necessarily! Most lead-acid battery chargers will do the job just fine.

If the charging settings are within the acceptable parameters for LiFePO4 batteries, they can be used with lead-acid battery chargers.

Because lead-acid batteries (AGM and Gel) and LiFePO4 have similar nominal voltages, AGM and Gel charging algorithms typically meet the LiFePO4 charging voltage requirements.

An essential difference between these batteries is that LiFePO4 batteries don’t rapidly lose charge when disconnected, unlike lead-acid batteries. This means that float charging is not necessary.

In addition, LiFePO4 batteries don’t need equalization or temperature compensation. So turning off these features is also necessary.

So, when using a lead-acid battery charger to charge a LiFePO4 battery, the float charge option should be switched off. If that’s not possible, the float stage voltage should be set low enough so it can never be reached. Setting the floating voltage under 13.6V is good enough.

If these required adjustments cannot be made to the lead-acid battery charger, then buying an appropriate LiFePO4 battery charger (or a smart charger) is highly recommended.

2. Using Solar Panels    

Using a solar energy system to charge LiFePO4 batteries is possible and highly encouraged.

That’s because the energy being stored is not just taken from another energy source (like shore power); solar panels generate it.

A simple scheme of the charging process in LiFePO4 cells.

Whether in a home, a boat, or an RV, a solar energy system looks pretty much the same (as shown in the scheme above):

1. Solar panels convert energy from sunlight into electrical energy.

2. Charge controller: regulates the power output of the solar panels according to the battery’s charging requirements, avoiding battery overcharge.

3. Battery: stores the energy provided by the solar panels as chemical energy.

4. Inverter: converts direct current (produced by solar panels) into alternating current (which the appliances can use).

Once again, correctly sizing the components is critical to maintaining the system running appropriately.

So, a charge controller that can efficiently charge the LiFePO4 battery – respecting its charging requirements – is crucial to ensure the battery functions well and for a long time.

3. Using An Alternator (And A DC-DC Charger)    

And last but not least, another great way to charge a LiFePO4 battery is using an alternator. This is an excellent solution for RVs and boats with a battery storage setup.

What Is An Alternator?

An alternator is simply a generator that converts mechanical energy into electrical energy. It generates alternating current (hence the name), which the rectifier attached to the alternator then converts into direct current.

This device is essential to every combustion engine vehicle’s electrical system. It charges the starter battery, which is used to start the vehicle’s engine.

With a few adjustments, you can use this electrical system to charge your battery bank (in this case, LiFePO4 batteries) while driving your vehicle.A system scheme in which an alternator is used to charge a battery bank.
Source: custommarineproducts.com

The above image shows a DC/DC charger as a necessary system part.

Because LiFePO4 batteries have a low internal resistance when not fully charged, they can draw any current from the alternator, which can overheat the alternator and damage the battery.

A DC/DC charger limits the current drawn from the alternator, avoiding the overheating issue. It also regulates the output voltage to the required charging voltage of the LiFePO4 battery, protecting it from overcharging.

What Happens Inside A LiFePOBattery When It Is Charged?

Before we can successfully answer this question, here are a few essential things to know:

Lithium Iron Phosphate cells are made of four main components:

  • Cathode: LiFePO4
  • Anode: Graphite (which stores lithium by intercalation)
  • Electrolyte: Lithium Salts in organic solvent
  • Separator: Polyethylene microporous membrane

Below is an illustration that helps to understand the charging process:

A simple scheme of the charging process in LiFePO4 cells.
Source: “Adaptive state of charge estimation for battery packs” – Saeed Sepasi

So when a LiFePO4 is charged, external power forces the electrons to flow to the negative electrode. This result is lithium ions flow from the cathode to the anode.

When discharging, the opposite happens. Lithium ions move from the anode to the cathode, while electrons flow to the positive electrode through the load.

Once fully charged, the lithium ions in the battery are located mainly in the graphite, so there aren’t many electrons left to move from the cathode to the anode.

At this point, the application of external power should stop. Battery Management Systems detect when the battery is fully charged and cease the charging process, avoiding overcharging.

What Is The Safest Way To Charge A LiFePOBattery?

Unlike other lithium battery chemistries, LiFePO4 is very safe due to its superior thermal and chemical stability.

That’s because LiFePO4 is naturally a stable compound. The P – O bond (in the PO43- species) is quite strong, so the oxygen atoms aren’t released so quickly when the battery is abused (overcharged or short-circuited).

As a result, lithium iron phosphate cells are much harder to ignite. This critical feature makes them far superior to other Lithium battery chemistries.

Even though LiFePO4 batteries are a relatively safe technology, it’s extremely important to respect the charging parameters discussed in this article in order to avoid safety risks.

The safest way to charge these batteries would be respecting the exact specifications of the storm in terms of voltage, optimal charging temperature, use of appropriate wires, etc., whether you use a LiFePO4 charger, a solar system, or any other way.

Tip: Always check your battery’s manual to see what the manufacturer recommends regarding charging.

Final Thoughts

LiFePO4 batteries offer a great battery storage solution and can be used for various applications. Their thermal and chemical stability makes them very safe compared to other battery chemistries, but this comes at a very high price.

What makes this investment worthwhile is the promise of a very long battery life, with little maintenance and high performance. Manufacturers claim these batteries can perform thousands of cycles lasting 8 to 10 years if the recommended charging instructions are meticulously followed.

So, now that you know the best ways to charge LiFePO4 batteries, which method will you use to set yours?

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