question

easyrunaway avatar image
easyrunaway asked

Alternator to Buck Boost to Lithium built-in BMS, marine application.

I am planning a new system on my boat powered by twin outboards, ideally my 2 aux batteries will be fed separately by the aux/isolator circuit from the stator in each outboard. This is not via the engine cables to my starting battery, that is a separate system that I want to keep separate. The stator maintains 14.4 volts output but adjusts current based on various factors, it also prioritizes the starter battery from what I understand. My thought is to go isolator circuit to fuse to buck boost in, to buck boost out to fuse to lithium battery with built in BMS. The battery specs give me what I need to program on the buck boost. My question is can I go direct from the stator with this, it appears to be how it's designed but all diagrams show a battery in parallel which I won't and don't have/want. Is there any other precautions I need other than appropriately sized fuses for the correct wire size.

buckboost
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

1 Answer
pwfarnell avatar image
pwfarnell answered ·

The battery between the alternator and the DC-DC converter (buck boost) acts as a buffer. The buffer battery is typically there to protect the alternator and other components in the system if the BMS stopped charging the lithium battery whilst at high charge current, a so called "load dump". An alternator running at high current will produce a large voltage spike that can damage equipment and the alternator if the load is suddenly disconnected. The buffer battery absorbs this and moderates the voltage spike. Secondly, the buffer battery also provides smoothing to the alternator voltage regulation, without it alternator voltage can cycle especially if the load also has a control circuit and the two controllers fight each other. There have been many posts on here of people using DC-DC converters direct on alternators that cause voltage cycling if they do not have a battery on the alternator.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Related Resources

Additional resources still need to be added for this topic