Adding a power station to dual battery LiFePo boat system

DIY
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1

Why?
In New Zealand a 240V system on a boat has to be certified by an electrical inspector which complicates things because this inspection will also include the 12V system and can lead to expensive alterations which are not always practical on our boat. This could easily add another $5000 which is uneconomical. A way around that is to use only pre-wired 240V components which can be tested and tagged individually. A power pack like an EcoFlow would work well for the 240V equipment we use occasionally.

I am thinking of upgrading the old lead acid house battery bank to LiFePo which will power everything navigation/safety related plus the fridge. After that I want to add a 240V system which consists of a EcoFlow (4000W) for induction cooking, the odd power tool and maybe a hot shower and heater.

So basically:
Charging LiFePo house battery with DC-DC charger while engine is running.
Charging LiFePo house battery with solar panels while the sun is shining.
Charging LiFePo house battery with small pre-wired portable charger from shore power from time to time.

I want to charge the power station whenever there is left over power from the engine or the solar panels.
It would be useful to have an option to top up the house battery if the engine is off at night.
I would like always priority to the house battery.

Can I charge the EcoFlow e.g. from a DC-DC charger from the house battery? If I switch the DC-DC charger to on at e.g. 95% state of charge and off again once it falls below 90% of the house battery this would mean that all the power for the EcoFlow will be always routed through the house battery. Is this a concern for the longevity of the house battery?
Would it be better instead to have the solar panels connected to an MPPT for charging the house battery and then when 95% state of charge is achieved swich the solar panels directly to the EcoFlow inbuild MPPT? This way the current would stop running through the house battery but there is a risk for the integrity of the vital navigation system?

I am also not sure how to achieve good visibility of this system using a Cerbo GX.

2

Lithium batteries are more likely to fail from calendar aging than from cycling. However, if you’d like to use them in your setup, it is feasible. Considering your system, it appears you have a 60V and 150V MPPT on the EcoFlow. You can integrate a 1000W boost DC-DC converter, which is relatively affordable. A 48V model should work fine for this purpose.

To control charging, you can use a relay to start charging the EcoFlow when the battery SOC reaches 95%. Keep in mind that DC-DC converters often experience a large inrush current at startup, which could stress the relay. To address this:

  1. Durable Relay: Use a relay capable of handling the inrush current.
  2. Precharge Circuit: Set up a precharge relay using a resistor to limit the inrush current. This can be managed by the Cerbo GX for precise control.
  3. Output Switching: Alternatively, switch the output of the DC-DC converter and leave the input side charged continuously.

One potential downside to leaving the DC-DC converter on all the time is its standby power draw, which can be significant—possibly in the range of 20-30W (a fraction of an amp). Be sure to account for this in your energy budget to avoid unnecessary losses.

3

Thanks for this very helpful answer!
I will probably charge the EcoFlow with the 800W EcoFlow alternator charger directly off the house battery system. Thanks alerting me of potential inrush current problems which I haven’t considered :-).

4

The high-wattage DC-DC converters have very large caps that will arc most switches and relays.