Charging Drop in Lithium, with Diagrams

[SVQuestOfPaget]

Hello folks - I'm in the midst of restoring a 39ft Frers sloop, and that includes removing the old complicated Ample Power Next Step regulator and solenoid, and completely revising and simplifying the wiring.

I know the words "simplify" and "lithium installation" don't go in the same sentence... I'm not looking to engineer the perfect DIY lithium battery and BMS, but instead use off-the-shelf parts combined with what I already have. I'm hoping that this post and subsequent discussion might help others who want to jump in, but don't want to drastically redo what they already have.

Like the rest of you, I've spent far too many hours (as the admiral will attest) reading through this and other forums, and I've sketched a couple of wiring diagrams, attached below. I'm asking from fellow members to look over these, and please tell me if you see any glaring mistakes, especially in the neg/grounds. I think I've got the positives all wired correctly, but am not certain on grounding with the B2B charger. Please note, these don't include all of the small wires and fuses, just the general overview.

Both systems use my existing 120amp alternator and Balmar 614 Regulator, as well as existing On/Off switches. For the moment I don't want a way to parallel the two switches (though I have a 1/2/B/O switch that I can drop in as well). For reference, this is on a Yanmar 3gm30, which is a bit undersized for the boat's displacement. I don't want to go anywhere near rated capacity of the alternator for better longevity, and less stress on the engine.

System 1: Charged directly to Lithium bank, with Sterling Alternator Protect, and low amp B2B charger to AGM starter battery. The 614 will be adjusted for Lithium settings and belt load manager will reduce overall output to 60-80amps, depending where I end up tweaking things. I know the ideal setup might be a Victron or Lithionics system where the regulator is shut down prior to HVD. The Alternator Protect on the other hand is a lot less expensive, but what happens to the alternator and regulator after HVD occurs - do they charge past the lithium bank directly to the B2B and AGM?

System 2: Charge to AGM starter battery then high amp B2B charger to Lithium bank. The regulator is adjusted for AGM settings, then the B2B charges at Lithium profiles. This would negate the HVD/Alternator issue, but would take longer to charge the Lithium bank.

The overall cost of the two systems is about the same. The cost of two 100ah batteries - the most I can fit without major boat surgery, and the additional cost of the high amp B2B in system two roughly equaling that of the Sterling alternator protect and low amp B2B of the first system.

Thank you very much in advance for your thoughts! Trying to learn more and get to the point where I can move forward on this. Fire away !

[rma]

Your second system is the way to go, even at the cost of some reduced charging capability. The danger of an HVD event leading to unregulated voltage from the alternator into the rest of the system is too great to justify some marginal increase in charging ability.

You should really be thinking about a dual DC bus topology and batteries and BMS that are designed with this in mind. The batteries need to "tell" (via the BMS) the chargers to disconnect or the loads to disconnect in order to protect the batteries. These disconnects need to be automated. That is, you cannot rely on some alarm or battery monitor to tell YOU to take action. See my wiring diagram attached. It utilizes a dual DC bus topology and alternator charging via a Victron B2B. Feel free to message me with more questions.

[MerMike]

You can parallel multiple Orion DC-DC chargers if you need to send more amps to the LiFePO4 banks.

[T1 Terry]

The first diagram would have created a return loop from the DC to DC to the positive bus bar and back to the alternator and the input side of the DC to DC .... unless the alternator voltage was higher than the DC to DC output voltage, then the DC to DC would have simply shut down because it couldn't control the output voltage, and how was the start battery being recharged?

On the second diagram, you need a method for the BMS to shut down the DC to DC when the battery is fully charged. Just using the loads to absorb the DC to DC output when the battery BMS opens will result in voltage spikes that could damage sensitive equipment as well as possibly letting the smoke out of the DC to DC charger.

T1 Terry