Alternator charging LFP + Lead acid – smart bms 12-200

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silverfish asked Dec 30, '23

Alternator charging LFP + Lead acid – smart bms 12-200

How does it work?

On the smart bms 12-200 manual, the system examples show a standard alternator (no special regulator mentionned) connected to the starter battery (lead acid) and (in parallel) to the “alternator port” of the smart bms.

As mentioned elsewhere the smart bms as no charging profile nor tension elevator, so my question is:

The standard alternator regulator should give between 13.5V and 14.5V which is OK for the starter battery, but how it is possible to charge also the lithium battery with a steady 14.2V during absorption and 13.5V for floating?

How the standard regulator is supposed to respond to lead-acid battery AND LFP at the same time?

Should we use some sort of advanced regulator (ws500,..) or insert a DC/DC charger between the starter battery and the alternator port of the BMS?

BMS alternator lead-acid smart lithium

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Answer 1 · 2023-12-30T19:28:18Z

pwfarnell answered · Dec 30, 2023 at 07:28 PM

The alternator should be one that has a charge voltage of 14.2V or higher, the system will not work with a Smart alternator in modern vehicles.

If you read the manual it describes how it works. To paraphrase, the BMS allows the lithium battery to be charged from the alternator at a current no greater than the current set by the fuse until the lithium battery reaches 14.2V at which time it stops charging from the alternator. When the battery voltage falls by 0.5V it restarts charging. The BMS does have some basic charge control.

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