Small sailboat solar w/monitoring; no inverters/alternators; how think about in Victron ecosystem

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I need help understanding the Victron ecosystem and options. I would appreciate any advice, explanations, pointers to documents, or directions to pursue.

Thanks in advance.

I’m looking for a simple DC system for a small (20 ft) sailboat on a mooring with Wi-Fi access to run a pump (maybe 2nd backup pump) with notifications. No inverters, no alternators.
I want notifications and don’t want only Bluetooth manual connections. With a Victron Battery Smart LiFEPO4 battery and a 55W non-Victron solar panel, how should I think about BMS/MPPT/Smart Shunt/Battery Protect(??), and Cerbo GX connections in this simple use case?

Details:

I wanted to go higher than the initial recommendation from a local marine electrical professional, so I am considering Victron. I want to be bulletproof with monitoring because I have had boats sink because of failed battery/pump systems. (I had Battery issues, but also once a stuck-off float switch, so monitoring the battery SOC would not have helped!)

• Boat is on a mooring without convenient access to shore power
• in New Hampshire during summer so not too cold or too warm
• Have new 55W solar panel (fits well in space to be permanently mounted) (21V Voc, 3A isc)

Could add another manually-placed panel when boat is not in use if that turns out not to generate enough power

Considering Victron

• Lithium Battery Smart 12V, 50Ah or 100Ah
o LiFePO4 for long life, lower weight (could take ashore now and then if solar can’t keep up)
• DC loads
o Main bilge pump (boat is not self-bailing, so rainwater will accumulate in modest amounts, even if covered). Currently a Rule model 25SA, 12V/1.6A; min 10.5v; runs every 2.5 mins to check for water, supposedly using “.2A” per day (unclear if that means .2Ah or is even accurate)
o Secondary pump mounted higher (possibility just a float switch as a “should never turn on” alarm) [not yet specked or installed]
o Navigation lights (rarely used)
o Currently, a switch goes to Torqeedo electric engine battery charger. This is not essential. I can periodically take that battery ashore to charge. The Torqeedo battery is 915Wh, 29.6V, 31Ah. The engine will be used sparingly (on and off the mooring)
• Cerbo GX for all the monitoring features. Mooring should have good Wi-Fi.

I am confused about the Victron ecosystem and wonder which combination of MPPT/BMS/smart shunt/battery protection is needed.

• Based on sizing the lowest end MPPT (75/10) and BMS (smallBMS) would be fine.
• But I am confused by which component does high voltage/temp charging shutdown or low voltage load shutdown and how needed those are
o MPPT 75/10 and smallBMS functionality on this seem to overlap. Might need to use the MPPT 75/10 Ve.Direct port for load shedding
• But stepping up to an MPPT 150/70 and VE.Bus BMS V2 to get VE.Can communication capability seems like a big step in cost and complexity
• I think a smart shunt is needed to monitor main pump power. But I would also like to monitor the main pump power and the secondary pump power (should never be on notification). Does that mean 2 smart shunts?

What am I missing? Or how should I think about the BMS/MPPT/Smart Shunt/Cerbo GX connections in this simple use case?

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For a small system like this the small BMS allow to charge (ATC) output would connect to the MPPT to stop that charging on high/low temperature and high cell voltage. You would then need to connect the allow to discharge (ATD) to a Battery Protect and feed the loads from the battery protect. The BMS would switch off the Battery Protect and the loads on low/high temperature and low cell voltage. You would need the MPPT for charging, a SmartShunt to monitor the battery and then one of the monitoring products (Cerbo S GX or Global Link) and depending on your choice a router. Note, on my 12V boat the Cerbo GX and router take a permanent 1A load, so 24Ah, you really need to consider this base load even before you get to pumps, I do not know the Global Link product but that may have a lower current draw than Cerbo + router. I have 680W of solar and that barely keeps up in UK winter.

Go to www.victronenergy.com click on the menu icon and choose products then a product and you will go to that product’s page where you can download datasheets, manuals and example system schematics. Put together a system and we can critique it. Do not forget wiring and fusing. Read Wiring Unlimited

We can help but we will not design your system for you.

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Interesting comment about your Cerbo GX draw 1A. I found this thread where most people reported actual measurements of about ~20w, sometimes less. What is your “router?” Are you not using wifi? I should be within easy wifi range and don’t know why I would need a router on the boat.

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I’m worried this is just too complicated.

Do I really need a battery protect? The MPPT 75/10 has a load shutoff, can’t I use that? My concern with that is that I think it would use the MPPT VE.direct port for the small BMS shutdown signal. So how would I connect to the Cerbo GX?

It doesn’t look like the smallBMS connects to the Cerbo GX. Is that right? Would one normally just connect the MPPT charger and a smart shunt to the Cerbo GX?

Thank you for your very helpful comments.

1 Like
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I have a SmartShunt measuring my DC loads and when the boat is unused it logs 12 to 12W which corresponds with the shunt on the battery. If there is wifi at your mooring and you do not want to connect when away from your mooring you do not need a router (mine is a mobile 4G LTE router, teltonika RUT X11). You could also use your phone as a mobile hotspot when away.

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The 75/10 MPPT does indeed have a load connection, also rated I believe at 10A and the could be used for some form of battery protection from discharge. The trouble is you want to run pumps off it and pumps have high start up currents. A pump rated at 3A could have an 18A start up current (typically 6 x rated current) and there are plenty of cases where the load out has problems or shuts off when running motors. You could try it and see if it works.

You are right the small BMS does not connect to the Cerbo, it just provides charge and discharge contacts so the charge contact goes to the remote on off on the MPPT. I am concerned that if the ATC turns off the MPPT charge I do not know if this also turns off the load, check the manual. If it does that would negate the use of the load port.

The VE Bus BMS communicates with the Cerbo GX and sends do not charge signal via the Cerbo GX to an MPPT. The VE Direct port on the MPPT can not be connected to other devices, just the Cerbo or other GX device.