Can a Car Alternator Charge a LiFePO4 Battery?

I often get asked: How to charge LiFePO4 from an alternator?

Your car alternator is made to charge lead acid, not lithium. But there is a device we can use to make it happen.

This device is called a DC-to-DC charger.

Now, why do we need a DC-to-DC charger that can limit the current?

Lithium (LiFePO4) batteries have very low internal resistance. An alternator wants to deliver as much current as possible.

With a lead-acid battery, this will be okay because the internal resistance is higher than that of a lithium battery.

If you charge a lithium battery with a car alternator, the alternator will start to burn out or catch fire.

Victron made a video about this:

However, this experiment is partly failed because:

1. They used a small 60A car alternator while a normal alternator in a van would be close to 200A.
2. Secondly, there is no ventilation over the alternator. In a normal setting this would have been the case.
3. And thirdly, the wires that are being used are too big for the current they carry, which makes the resistance in the system even lower.

Some people have argued that a DC to DC charger is not necessary and you can adjust the length of the wire to increase the resistance in the circuit so there are no high currents going around.

However, if you are not experienced in electrical systems, I don’t advice you to do so.

Conclusion

When you want to use an alternator to charge a lithium battery you need a controller in between. This controller is a DC to DC converter.

Curious about what kind of DC-to-DC converter I recommend? Read my article about the best DC to DC battery chargers.

FAQ

Do you need a special alternator for lithium batteries?

You don’t need a special converter to charge a lithium battery. The only component you need is a DC-to-DC charger.

Can I charge a lithium battery with a car charger?

Yes, this is the standard charger for lead-acid batteries. But you need a DC-to-DC charger in between the alternator and the battery to regulate the charging current.

Do you need an isolated or non-isolated charger?

I have written a comparison between these two. Read the article here.