Re: What to do with LiFePO4 batteries when the boat is layed up?


Dan Carlson
 

On BeBe I have a Victron Venus GX which acts as a hub between all ov my Victron devices. It can also monitor and control other devices through CAN Bus connections. But with respect to this thread, it connects to Victron's web server via WiFi.  

You can potentially connect it directly to a marina wifi or via your ships network. In my case we purchased a stand alone wifi hotspot called SkyRoam, from Solaris. It works globally (130+ countries) via cellular networks (I don't know if it is sold everywhere).  They have very flexible data packages. The data is not necessarily cheap but we loaded up 5 gig before we left for the summer and have barely used 100 meg while away.

Once connected I can see the Victron GX (see attached screenshot) from anywhere on my phone app, AND I can also turn my Victron MultiPlus charger/inverter on and off remotely.  I have a trickle charger on my Inverter circuit that is connected to my starter battery, a month ago I turned on the inverter and monitored the current flow as the I topped off the start battery for a few hours)

I maintain my LiFePo house bank via solar, but have set the float back to about 26.6v (less than 70% SOC).

The screen shot taken earlier this am shows my over night voltage and some charge starting to come in from the solar. 
I can drill in and see consumption, solar generation and trends over time.  

It gives me great peace of mind to be able to click on an app and see a few critical things going on the boat while away.

Daniel and Lori Carlson on sv BeBe, sm #387





On Wed, Sep 15, 2021, 7:08 AM Scott SV Tengah <Scott.nguyen@...> wrote:
We left the boat for 4 months earlier this year and while I have a Victron based system, I think you can achieve the same on MV:

I left one fridge on (brushless pump, so pump life is less of a concern) to circulate freshwater in the tanks and had my battery monitor (BMV-712) open the bi-stable programmable relay when the battery went above 70% and close again when it went below 60%. This signal fed into the remote on/off input on my Quattro inverter and acted to turn on the inverter above 70% and turn off the inverter below 60%.

I had a 220v dehumidifier (around 200w) plugged in. 

Per my boat watcher, it worked perfectly. Our boat was drier than any other he had seen and the battery stayed in a range to maximize longevity.With my 960w solar, this keeps the battery cycling between roughly 55% and 100%. At that depth of discharge, the batteries would outlive me! Bonus is that the boat is completely dry inside, too. 

I am almost certain you can do something similar with MV. Sv Garulfo has a full MV lithium setup and borrowed my dehumidifier when they left for a brief period so they can probably explain how they did it.

Also, MV's solution doesn't seem terrible as long as the charger goes into float at a low enough SOC. If bulk/absorption ends at say 27.4v and that is the equivalent of around 65% SOC and then it holds at 27v float, then you aren't holding your battery at high SOC, so it should be ok. The flat voltage discharge curve that makes lithium so great also makes it hard to estimate SOC from voltage.  But I'm sure MV's battery monitor can talk to the chargers to tell them to shutoff charging at a user-specified SOC level?

--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com

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