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Old 15-01-2025, 11:03   #16
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Re: Electrical system review: switch to Lithium

Some quick comments/questions:
  • You may have omitted them for clarity but the outputs of the DC/DC chargers should be fused,
  • May want a switch to be able isolate the start battery from engine when working around the engine,
  • Do you wish to allow for starting the engine from the house bank, or operation of house loads from the start battery in an emergency?
  • I may be misreading your diagram but it seems both your 30A (engine on), and 50A DC/DC chargers drive the same house positive buss.
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Old 15-01-2025, 15:04   #17
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Re: Electrical system review: switch to Lithium

I am more the theoretical / analytical type, and less the experienced one, but here's my comments :

AC charger 12V 50A 1+1 : LeadAcid and Lithium requires different charge algorithms and the voltage and the currents during charging are different. Are you sure this unit can handle two different charge algorithms at the same time ? (I suspect that it can not). In my boat I'm keeping the current lead acid charger for charging lead acids, and I've bought two new 60A Lithium chargers for charging the lithium banks (enables quicker charge time from a genny for instance). (They do take up some space though). On the other hand simply removing the red out to the lithium side will solve it (you loose some efficiency, but doesn't matter on shore power).

DC-DC charger 30A, on unconditionally (Thruster bank charger). In my boat it starts charging when the voltage is above a set level, which is only reached when the engine (generator) is running or when on shore power (from the AC powered charger). Maybe it can be configured ?.

I asume the Bow Thruster Lead Acid is an AGM (bigger is better).

The battery charged by the Alternator must be Lead Acid. BMS's can disconect the Lithum internally if the charge voltage is too high, and if all of them does that and your Alternator is still running, and there's no other consumers to consume the current it's generating, then you may get a voltage spike who may (will) fry all of your 12volt electronics. There are ways around that, but it's easier to simply keep it Lead Acid there.

Switch between starter and start battery tends to cause resistance and start problems at some future point in time in my experience, so if you want that, go for a high quality high amp switch (the best you can find). (That's not in your drawing).

Do'no why the switch between AC charger output and start battery is there ? (sees no need for it).

Lithium charger on when engine is one ?,... why not as well when AC charger charging ?,....... probably triggered by voltage level in any case, so is o.k. as is from what the drawing shows.

You have drawn 125A fuses, so then "all" of your cables should be capable of handling 125A without getting too warm (something drawing exact 120 amps will never happen but), and a cable can handle some more than the rated amps without getting too warm. If you can manage your consumption with a smaller fuse, you can use cheaper cable and save some money. From Lead Acid to starter and to thruster use oversized cable (you don't want too much voltage drop there), and they're likely already there.

Smart Shunt : Is the software there (and in the app) designed for Lithium ?,... should be. .....

Someone already talked about keeping the black/red cables to/from the 4 lithium banks the same length which is recommended.

Just a philosphical comment (not from the real world) : You have a 125A fuse out from the lithium,..... lets now asume the MPPT (solar) charger short circuits due to internal fault (not likely with Victron though but), then you have aprox 12Volts and 125Amps = 1.5KW of heat which if on small spot can cause a fire. On the other hand, such a fault will 99.9% of the cases draw as much current as it can (and you have a supply of 4x125A), which will be more than enough to trip the 125A fuse, so you should be as safe as can be then :-).

Regarding fuses on the solar side my thoughts are that both the MPPT and the cables can handle the max current the solars can produce, but does no harm. The risk is more from the 125A side, but fail to see a very likely case for that to happen (the one above is not likely at all).

2KW inverter : 12V*125A is max 1.5KW ...... and all electronics loose some of that in heat, so more likely max 1.3KW for your consumers. But a 2KW inverter is likely more efficient at a 1KW consumption than a smaller one, so just keep it :-). ... If the inverter AC output is connected to AC distribution then it will bite it's own tail, so you need to be able to turn off the battery charger maybe ;-). ........

That's all I could think of at the moment. But keep in mind that I lack the practical experience, though I do know how to use Ohms law which is what it's really all about.

With the best of intentions.
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Old 15-01-2025, 17:55   #18
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Re: Electrical system review: switch to Lithium

I know it's a pain to draw these diagrams, but it is worth the time/effort when in the future you need to consult the plan for fault finding. Keep at it.

The biggest issue I see is lack of circuit protection. Both lead acid batteries, MPPT, DC-DC, bow thruster, inverter, charger, "power consumers", etc all need either fuses or breakers.

I'd suggest looking at the Victron system diagrams and copying wherever they show fuse/breakers.

https://www.victronenergy.com/upload...-Tr-Smarts.pdf
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