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


Joerg Esdorn
 

I have 3x Mastervolt MLI Ultra 5500 batteries on my boat, new this year.  I’m starting to think about what to do with the batteries over the winter when I will not be on the boat.  When I had my gel batteries, I would turn off all loads and put the charger on or leave the solar charger on.  Following some of the discussion about charging LiFePO4 batteries on this forum, I‘m gathering that some people think it‘s not a good idea to leave these batteries on a charger all winter long.  However, the MV manual says just that:

„If the battery will not be used for a period exceeding 3 months, we advise the following:
• If external AC power is available switch off all loads and switch on the charger. Apply a float voltage as specified in the following table.
Model Float voltage setting
12V 13.5V 24V 27.0V
• If no external AC power is available:
- Charge the battery to > 80% of its capacity before storage.
- Set the safety relay knob to “LOCK OFF”, see page 11.
- Make sure MasterBus powering is not set to "Always on" (see Configuration tab in
MasterAdjust).
In this setup the batteries can be kept at least 6 months without maintenance. However, it is highly recommended to charge the battery to > 80% of its capacity every 100 days.“

I hate to second guess MV but I wonder if this group includes any engineers with the relevant specialist knowledge who can explain/critique this advice?  

I have considered just disconnecting them but with the boat in the water over the winter, I don‘t want to be without the bilge pump being operative.  

Thanks in advance!

Joerg Esdorn
A55 #53 Kincsem
Currently in La Rochelle



Dean Gillies
 

Hi Jeorg,
With your existing system, it looks like you only have two options. Either leave powered on float or disconnect completely and have someone attend the boat every 3 months and top them up.

The reason they only last 6 months is that they contain internally embedded electronics which consume some small amount of power. All LFP batteries with internal BMS will have this same problem.  The cells themselves last much longer (years) without needing topped up, but any batteries with internal BMS will always drain down slowly.

As to which option is preferable, my personal choice would be to have them topped up periodically. LFP do not like to be floated at high states of charge for long periods as it does negatively impact their life.

In my system I have 115Ah of Lead Acid in parallel with my LFP cells, so my wintering strategy involves dropping the LFP cells to about 60% SOC and disconnecting them completely from the system and the (external) BMS.  Unfortunately this is not possible if you have batteries with an internal BMS. 

Sorry, not much help!

Dean
SV Stella
A54-154

 


Scott SV Tengah
 

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


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


Joerg Esdorn
 

Thanks so much!  There are some excellent ideas here.  My thinking now - based on everyone's thoughts - is to do the following:

1.  Before I leave, charge the batteries to 80% and plug into shore power.  I will leave the batteries on so the bilge pump can run.
2.  Set the MV charger on shore power to a low bulk and absorption voltage - like 27V.  I can do this easily using the Masteradjust software which controls all settings for the Masterbus. I will experiment first what state of charge this will result in.  Should be close to 80%?
3.  Get a mobile hotspot that runs of 230V in the boat.  
3.  Have my laptop running both Masteradjust and Teamviewer connected to the hotspot.  The laptop is running off a 230V outlet.

Viola, with this setup I should be able to monitor the batteries and control the charger from my home in SFO while the boat is in La Rochelle!  So I will be able to charge to 100% every three months by changing the setting for the 60A charger.  I will also run a dehumidifier over the 230V outlets in the boat - Scott, presumably you didn't have shore power which is why you ran the dehumidifier over the inverter?  I had a dehumidifier running during the entire 18 months of Covid layup and it made a huge difference.  If there's something wrong with the 230V, I will know because I can't connect to the laptop.  Lastly, I will have a Netatmo security camera and a WIFI enabled water alarm in the engine room connected to the hotspot.  That way I will get emails if something moves inside the boat (and will be able to see video of the event) or the water goes above the alarm level in the engine room.   My boat watcher will not have to deal with the batteries  at all if all goes accordance with the plan!

Joerg Esdorn
A55 Kincsem
Currently in Ile d'Yeu, France


Scott SV Tengah
 

Joerg,

I would be surprised if the MV software doesn't allow you to stop charging at a certain SOC vs having to guess with voltage. I can implement that on my less well integrated Victron system. Again, ask Garulfo as I believe they said it was simple to do so.

With respect to ideal SOC for storage, Victron delivers their batteries around 50% SOC, so that might suggest something. There's literature out there on how to prolong lithium batteries, but it's generally for more sensitive / explosive cobalt based batteries, but the consensus is 50-60%, matching Victron's SOC at delivery.

And correct, I don't leave the boat on shore power, even when it's available. The solar is far more than enough during storage periods and I don't risk bad wiring at the marina eating up my zincs and then my through hulls. Note that I don't have an isolation transformer or even a galvanic isolator. Was considering installing it but I find we're rarely at marinas and even if we're at one and aboard, I often don't bother plugging in.

What I like about setting the inverter to run above 60% is that my solar is more than enough to put in more power than the dehumidifier can draw. That, in effect, causes the battery to fill to 100% every few days, at minimum, but even if it's taken to 100% by the time the sun sets, the dehumidifier will draw down the batteries overnight so they don't sit at full for very long. And even if it's drawn down to 60%, there's plenty of capacity remaining to run the bilge pump for a long time before the sun rises again.


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


Sv Garulfo
 


Hi all,

With MV you can define events that are based on the SOC, at either predefined levels (60%, 80%, etc) or a user defined level called “battery full”, and can be used to trigger actions on other components on the network, for instance switching on/off the inverter, switching charging elements to float   (or off), etc. 

Hope that’ll help

Thomas 
GARULFO
A54-122
Tahiti 


On 17 Sep 2021, at 10:11, Scott SV Tengah <Scott.nguyen@...> wrote:

Joerg,

I would be surprised if the MV software doesn't allow you to stop charging at a certain SOC vs having to guess with voltage. I can implement that on my less well integrated Victron system. Again, ask Garulfo as I believe they said it was simple to do so.

With respect to ideal SOC for storage, Victron delivers their batteries around 50% SOC, so that might suggest something. There's literature out there on how to prolong lithium batteries, but it's generally for more sensitive / explosive cobalt based batteries, but the consensus is 50-60%, matching Victron's SOC at delivery.

And correct, I don't leave the boat on shore power, even when it's available. The solar is far more than enough during storage periods and I don't risk bad wiring at the marina eating up my zincs and then my through hulls. Note that I don't have an isolation transformer or even a galvanic isolator. Was considering installing it but I find we're rarely at marinas and even if we're at one and aboard, I often don't bother plugging in.

What I like about setting the inverter to run above 60% is that my solar is more than enough to put in more power than the dehumidifier can draw. That, in effect, causes the battery to fill to 100% every few days, at minimum, but even if it's taken to 100% by the time the sun sets, the dehumidifier will draw down the batteries overnight so they don't sit at full for very long. And even if it's drawn down to 60%, there's plenty of capacity remaining to run the bilge pump for a long time before the sun rises again.


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