How to charge lithium battery with alternator
Lithium batteries have emerged as a popular choice for their high energy density and long lifespan. However, it can be challenging to charge them when you’re away from traditional power sources. Fortunately, a very clever way to circumvent this issue exists that involves an alternator.
Unlike a lead-acid battery the internal resistance and corresponding voltage of a lithium battery does not rise until it is nearly 95% fully charged. This can cause alternators to run longer at full output which can cause alternator burnout. The length of a time a lithium battery can draw a constant current at or above the alternators max output can exceed the design parameters of the alternator. This can cause the alternator to over heat and burn-out. Alternators are internally cooled by a fan on its rotor. Lithium batteries will draw a high charge current at all times meaning alternators are prone to burn-out at low RPM when charging lithium batteries at high currents.
To protect your LiFePO4 battery and alternator please be sure to use a compatible high-quality alternator or install a voltage regulator. Please contact Aimeno technical support if you need assistance.
Charging Lithium Batteries With an Alternator
Can you charge a lithium battery with an alternator?
Yes, you can charge your lithium battery with an alternator. There are three ways you can connect an alternator to your lithium battery:
Parallel connection.
DC-DC charger.
External voltage regulator.
Regardless of the method you choose, it’s important that you exercise caution.
Unlike traditional lead-acid batteries, lithium batteries require a specific charging profile, so you must use a battery charger that matches up well with lithium batteries.
Additionally, you must ensure that the charging voltage and current are within the battery manufacturer’s recommended range and monitor the battery’s temperature during charging.
Three different ways to connect your alternator to your lithium battery
1. Parallel connection
In this setup, you connect the alternator straight to the starter battery and then place the lithium battery in parallel with the starter battery, like so:
This setup is easy to install, and you don’t need any special equipment.
However, the major downside is that this configuration will negatively impact your battery’s life and your alternator. Additionally, the charging speed won’t be optimal because the voltage provided by the alternator will be used to charge both batteries (starter battery and solar battery).Moreover, it’ll charge both batteries with the same voltage (single-stage charging) — this is far from ideal, especially when charging different battery chemistries.
2. Using a DC-DC charger
You can connect your alternator to your starter battery and then link your starter battery to your lithium battery via a DC-to-DC charger. A simple wiring scheme for this configuration is shown below:
This setup beats the first one. Why? Because the DC-DC limits the amount of current going into your lithium battery. This way, it doesn’t damage your alternator by constantly drawing a large amount of current — it only draws a safe amount of amperage.You can also adjust the DC-DC charger to provide the correct lithium battery charging algorithm.
The problem with this setup is that it draws current from the starter battery, which can considerably slow the charging process of the lithium battery.
3. Using an external voltage regulator
With this configuration, you use an external voltage regulator to connect the alternator to the lithium battery. Then, you use a DC-to-DC charger to connect the lithium battery to the starter battery, as shown in the image below:
This configuration offers many advantages:
It optimizes the alternator, allowing fast charging for your lithium battery bank and starter battery.
It provides the correct charging profile, as required by the lithium batteries.The DC-DC charger also ensures the starter battery is charged correctly with the proper charging settings.
Drawbacks
However, significant drawbacks of this configuration include high additional costs (especially with the external regulator), a relatively large system (with two extra devices), and increased installation complexity.Therefore, considering efficiency and costs, the most recommended configuration would be number 2 — connecting your alternator to your starter battery and then linking your starter battery to your lithium battery via a DC-DC charger.