Small marine system

DIY
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1

I need some help understanding the Victron ecosystem/options. Any advice, explanations, pointers to docs, or directions to pursue would be very appreciated.

I’m looking for a simple DC system for a small (20 ft) sailboat on a mooring in New Hampshire with Wi-Fi access to run a pump with notifications. No inverters, no alternators. The pump will be needed for rain.

I want monitoring/notifications because I have had bad experiences with pump/battery failures.

Thinking of a LiFEPO4 battery, MPPT 75/15, fixed 55W solar panel (for physical size reasons), smart shunt for SOC, and a Cerbo-GX. If the 55W panel isn’t enough, I could add another panel and wire it in series (the MPPT could handle V/A easily, and I could manually position a second one when leaving the boat) and/or occasionally charge on shore (especially if a Lithium lower-weight battery).

See the attached diagram for what I am thinking about.

  1. Am I missing anything? Is the MPPT choice reasonable, or is another model better?

  2. Do you have any LiFEPO4 model/brand recommendations? Victron seems very expensive with limited availability. Thinking of internal BMS for one less competent. 50Ah or 100Ah.

  3. Optionally, I might use a second smart shunt in DC monitor mode to alert on any usage of a higher second pump, which should never activate absent a failure of the primary pump. Is there an easier way of getting such an alert? A smart shunt seems like overkill.

  4. I am unclear about the importance of the MPPT load shutoff, given the presence of a BMS on the battery. Also, whether or not to wire the Cerbo-GX after the MPPT load or directly to the battery (after the SOC smart shunt)

Thank you for any advice.

diagram.pdf (1.4 MB)

2

In Reverse order:
4) The MPPT load output is best used for power to the pump (if the current rating is good) This can be programed to shut off befor the battery BMS shuts down. The Cerbo should be wired to the battery shunt (load terminal) via fuse not the load output of the MPPT, you then get monitoring at low battery voltage, and can see that remotely.
3) you can use a higher level sensor wired to a digital input of the cerbo to monitor for pump failure. You can then use that to switch a second pump, via a cerbo relay. This also allows you to switch the pump on/off remotely.(also answers Q1)).
2) No comment on battery, but you don’t need to stick to Victron. A possible advantage of Victron battery could be that the BMS talks directly to the Cerbo, eliminating the need for a shunt.
The use of a second shunt in your diagram is not necessary. The MPPT has load voltage & Current monitoring.

  1. you can also wire a second Cerbo relay across the float sensor for the first pump to give you a manual override on the float switch.