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Peer Review Schematic for Alternator Charging of Lithium Battery

February 11, 2019, 08:15:06 am

Please peer review the following schematic with constructive comments. See photos: After six months of pondering, below is my proposed solution for charging a big 400AH lithium engine battery using the alternator:

1. Dedicated alternator battery; a small lead AGM battery, 35AH. Weight 23 pounds.
This was chosen since the stock alternator was designed to charge lead batteries and there are no fully-engineered, low-cost lithium compliant regulators. Plus, lead batteries can charge in colder or hotter temperatures than lithium and can take more charging abuse, which alternators are famous for.
2. Diode isolator, similar to the stock isolator. The Schottky diodes reduce voltage loss to about .4 volts.

Here are the pros and cons:

PROS
1. Worry-free charging of lithium engine battery using stock Foretravel alternator.
2. Uses BMS (Battery Management System), the iCharger 4010.
3. Multiple charging sources: alternator, shore or solar power.
4. Battery minder ensures full charge of lead AGM alternator battery.
5. Simple operation. No computers.
6. Low-cost. About $100.
7. Maintenance-free AGM and Lithium batteries.
8. Gained about 250Amp-Hours of usable capacity and house battery back up capacity.
9. Battery minder keeps small lead battery at 100% charge, which limits inrush current after engine is started. The large alternator could easily dump a lot of current into the small 35AH lead battery, causing damage.

CONS
1. Manual intervention before and after charge.
2. Complication of additional circuitry, lead AGM battery and related parts.

So, I would appreciate constructive comments.

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Re: Peer Review Schematic for Alternator Charging of Lithium Battery

Reply #1 – February 11, 2019, 08:45:56 am

No electrical guru here to say if it will work or not but the 2 red tops and a battery minder with the desulfnating feature work for
my traveling style,have updated alternator to the Delco 28s and updated isolator,no solar.

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Re: Peer Review Schematic for Alternator Charging of Lithium Battery

Reply #2 – March 17, 2019, 05:34:11 pm

See the photos. Here is the final schematic and photos of my lithium engine battery charging system. It was changed from a DC to an AC-based charging system because of a grounding issue with the iCharger 4010. The salient features are:

PROS
- Long-life, estimate about 10 years. Lithium engine battery with BMS (Battery Management System), an intelligent charging, balancing and storage. The lithium batteries are inside the coach and are protected from extreme hot and cold temperatures.
- Backup 120VAC source powered by a sine wave inverter, powered by the alternator.
- Charge in freezing temperatures. The small, light-weight lead battery (23lb) matches alternator voltages.
- Charge engine battery from five sources: shore power, the rig's inverter/house battery power, generator, solar power or alternator.
- Enhanced boondocking: Engine battery can be used to run key house systems like: the furnace, propane fridge, hot water heater, etc... while boondocking with low solar charging capability. Engine's alternator can be used as a second generator to produce 12VDC and 120VAC power.
- Maintenance-free. Automatic AGM battery maintainer. Easy lithium battery storage, charging and balancing.
- Low-cost compared to 400AH worth of Battle Born batteries ($3,800 vs $1300). Saved $2,500.

CONS
- Complexity. Added three switching power converters: inverter, power supply and charger
- Manual intervention required: When the rig is started, the inverter and the charger can be started if needed,
    a 30 second operation. For short trips, this is not required, but the engine battery will eventually need to be charged.

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