Alternator charging for lithium batteries

[Benny17441]

From our RV friends I found this article.

CHARGING DIY CAMPER BATTERIES WITH A B2B (BATTERY TO BATTERY) CHARGER
A battery to battery charger takes the voltage and amperage that is being put out by the vehicle alternator and regulates the amperage down to a modest pre-set level and boosts the voltage as necessary to fully charge any batteries.
This decrease in amperage lowers the strain of your alternator greatly and also gives us a solid number from which to work with when being able to accurately determine how many amps the charger will operate at.
The boost in voltage is INCREDIBLY important for being able to charge higher voltage lithium batteries from alternator that can’t quite put out that much voltage. If the power from the alternator is hitting the DC-DC Charger at 13.8V and the Batteries need to be charged at 14.6V, the DC-DC Charger will boost the 13.8V from the alternator to the 14.6V the batteries require. On DC-DC Chargers, this voltage is also programmable so it will work for Lithium, AGM, Carbon Foam, Salt Water, or whatever other battery type you throw at it.

I have never used this but might be worth for some to explore. From what I gather you could charge your AGM or Lithium batteries from the engine alternator using a regular battery (starting battery) as a pass thru to a converter which would boost the voltage. I heard about it from an RVer using the tow vehicle alternator to charge his lithium house bank when on the road.

 

[dlochner]

Voltage is one part of the charging equation, the other is current. Will the alternator produce enough current to properly charge the batteries? Will the motor be run long enough to enjoy any benefits if the charge current is low?

Firefly carbon foam batteries want to be charged at .4 C, or 40% of the battery's capacity, at 116 ah capacity, the alternator needs to produce 46 amps at 14.4 v to properly charge the battery. Some batteries are less sensitive to lower charge rates so this solution might work for them. It will also work for systems that have mixed chemistry, say a FLA start battery and an AGM house bank where the charging profiles are different.

 

[Maine Sail]

DC to DC charigng us useful for more than just charging LFP batteries.

The article below delves pretty deeply into DC to DC chargers and the article features the Sterling Power Pro Batt Ultra DC to DC battery to battery (B2B) chargers . Currently the only two DC to DC chargers we use or install are the Victron Orion TR Smart or the Sterling Power Pro Batt Ultra series.

https://marinehowto.com/understanding-the-sterling-power-pro-batt-ultra-battery-to-battery-charger/

 

[Benny17441]

Seem to be more effective for Gel or AGM batteries. I had no idea this B2B converters were on the market. I just threw it out there to see if it had possibilities. Thanks Maine for the article.

 

[Maine Sail]

Seem to be more effective for Gel or AGM batteries. I had no idea this B2B converters were on the market. I just threw it out there to see if it had possibilities. Thanks Maine for the article.

Or for trying to charge LiFePO4 batteries with the stock alternator when you want to take the inexpensive-way out rather than using a proper externally regulated alternator. A B2B charger is less expensive than an external regulator, performance alternator and LiFePO4 batteries that are actually designed for the marine market with a BMS that can safely shut down an alternator..