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


Joerg Esdorn
 

Thanks very much everyone.  Based on Thomas’ suggestion, I‘ve now programmed an event for my 60A charger which switches it to float at 80% state of charge.  The voltage of the batteries at 80% with the charger off and minimal load (2A) is a little less than 26.8V.  So this may be the way to go - but I have an email into MV support to confirm.  Their advice quoted above strictly speaking only applies if all loads are off which won‘t be the case for me since the bilge pump and galvanic insulator will be on although the loads are minimal for a 600Ah battery bank.   It may also not be necessary to have this event if the charger never goes back to bulk with such a small load.  

Scott, given that MV recommends to charge the batteries to more than 80% at least every 3 month, I suspect that it‘s not good for them to be kept at 50% as you suggest.   

Joerg


Rudolf Waldispuehl
 

Hi Joerg

 

Hope you are doing well and all is fine on Kincsem. Where are you now?

 

Sorry to step in so late but I just finished my strategy with moving to LFP. I was also concerned about to lay-off the boat for a longer period.

My strategy is to keep 2x100AH of Lead Acid In the system and charge them by Solar (or Shore) when away from Boat. Therefore the Bilge pump and another small consumer can be active during absence. AND I have a Backup for the Starter- Batterie as well, which is always on and charged.

 

Your LFP can be switched off (no longer on the 24V bus) and the internal BMS is automatically switching off after 24h without any activity.

Mastervolt told me today that in this scenario I can keep the batteries for more than 6mt. untouched because there is no internal currency drain.

They said that it could go even up to one year or more, ….  but it depending of the SOC at the time of lay-off. Hope it’s not just Marketing 😉

BTW:

The Hybrid idea is not mine, I got from Dean (SV Stella) who just finished to build a Hybrid System with Lead Acid and LFP for similar reason and more….

I always had the idea to combine the 2 technology, but Dean gave me the confidents that it works.

 

Best regards

Ruedi

SY WASABI

A54#55

 

=======================

 

Thanks very much everyone.  Based on Thomas’ suggestion, I‘ve now programmed an event for my 60A charger which switches it to float at 80% state of charge.  The voltage of the batteries at 80% with the charger off and minimal load (2A) is a little less than 26.8V.  So this may be the way to go - but I have an email into MV support to confirm.  Their advice quoted above strictly speaking only applies if all loads are off which won‘t be the case for me since the bilge pump and galvanic insulator will be on although the loads are minimal for a 600Ah battery bank.   It may also not be necessary to have this event if the charger never goes back to bulk with such a small load.  

Scott, given that MV recommends to charge the batteries to more than 80% at least every 3 month, I suspect that it‘s not good for them to be kept at 50% as you suggest.   

Joerg


Scott SV Tengah
 

Joerg,

My understanding of the ideal SOC for storage is based on two things:

(1) I read the objective, peer reviewed research literature which all seem to point towards longer life at around 40-60% SOC for long term storage (hey, passages can be long and boring!)
(2) My conversation with a senior Victron tech to clarify whether they suggest the same.

What was explained to me "off the record" is that the research literature is correct that 40-60% maximizes lifepo4 life. But a manufacturer's primary goal is to minimize customer complaints and concerns and a secondary goal is to maximize longevity. And he jokingly said "and if batteries last forever, we'd go out of business".

Charging to 80% is the foolproof way to go, for sure as it reduces the likelihood of low voltage battery death in the off chance that the charger/power source is cut off. The cost of this is reduced longevity.

I opted to follow the objective research. Time will tell whether that research is correct.


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


Matt & Michelle Day, SM#208 SV Talia
 

For what it is worth....

Michelle and I just received our shipment of Victron 200Ah LiFePO4 batteries.  I measured all six of our batteries as received, and they are at an identical 48.2% SOC.  I purchased the batteries from PKYS (shipped direct from Victron).  Peter Kennedy (great technical guy to work with) ensured I purchased a small Victron battery charger to fully charge each battery individually prior to install.

To Scott's point, Victron is not going to have inventory age and expire in storage as an ongoing money making enterprise, and the SOC matches what all those boring peer reviewed studies say.  Just another data point worth considering.

If anyone is considering doing a LiFePO4 conversion, I would strongly recommend you read Scott's write-up, Bill Kinney's post, and then the peer reviewed papers.  The lithium conversion world is the wild west right now, with multiple companies selling silly "drop-in" full conversion batteries.  You are ultimately changing the power distribution architecture of your boat which has significant life safety risk.  Finding the right experienced technical resources has been challenging for us.  One can easily see why insurance companies are nervous, and I suspect redneck engineered conversions will be a fun new topic of new used boat sales in the near future.   

Matt & Michelle Day
SM#209
SV Talia
Hampton, VA


Dean Gillies
 

Hi Matt,
Out of interest, may I ask how you determined the initial SOC when you received the batteries?  Did you estimate SOC from a voltage measurement, or does the 'small Victron charger' you mention provide data to indicate how much capacity needed to be added to attain a full charge, or maybe the Victron BMS provides that data? (ie you added 52% by charging therefore they must have been at 48% when you started)
Best regards
Dean
SV Stella
Amel 54-154



Matt & Michelle Day, SM#208 SV Talia
 

Dean,
I have the benefit of the batteries being new, having the equipment in the box for battery monitoring and still being a land lubber with too much electrical test equipment on a work bench.  First I determined initial battery voltage of course...simple enough.  However, this does not tell you much because Li batteries do not act like the lead acid batteries we are used to dealing with and relating V to SOC is not linear.  But, I have the Smartshunt, charger and CERBO.  I took my cute little charger and charged the batteries to max capacity based on the Victron datasheet, driving through the SmartShunt, a datalogger and Scopemeter.  I then discharged the battery to the original shipped-to voltage using a bench inverter/charger + space heater + Smartshunt + datalogger + Scopemeter.  With the cycle and the data supplied from the Victron datasheet, the CERBO calculated the SOC with the Victron algorithm.  I could also manually calculate total battery capacity from the discharge/charge cycle data and extrapolate the data to verify battery capacity matched the 200Ah promised for the premium paid to Victron (my real motivation).  I could not bring myself to discharge the batteries beyond the storage voltage given the capital I have tied up in the batteries.  So I settled on the calcs for satisfying my curiosity.  I then repeated the charge/discharge cycle with the other 5 batteries. 

I want/need to pull the batteries back down to the storage SOC, as I will not be installing the batteries for a few months yet.  

Matt


Joerg Esdorn
 

I have discussed the issue with a senior technician at MV support.  His explanation for the recommendation to keep the batteries at 100% with a float voltage of 27.0V was that their batteries are different in design from other manufacturers' batteries.  They are made for being kept at full charge over long periods.  I further asked him if I wanted to keep them at a lower SOC, how to achieve that.  His response was to change the float voltage to 26.5 from 27.0V rather than program an event that turns the charger off at 80% SOC.  The event will result in a lot of switching which would be avoided with the adjustment of the float voltage.   I've tried to do this and the SOC essentially goes to about 78% with the charger connected.  So presumably you could set the float voltage to even less than 26.5V and end up with a SOC lower than 78%.  

I would be very interested in seeing the research paper(s) showing what the best SOC for long term storage is.  I am very hesitant setting the SOC for the winter at lower than 80% because of the risk that something will go wrong with the charger and the battery will go to the 20% cutoff point.   I also wonder whether it's worth avoiding charging the batteries to 100%.  I bought these batteries among other things to have much more capacity available than before.  I really don't want to restrict the range of SOC I can use to get some uncertain benefit on longevity.  MV says the batteries are good for 2000 cycles.  My Easyview monitor tells me I've used up 23 of those over the last 3 months on the boat.   At that rate, I will kick the bucket before the batteries!  

Joerg Esdorn
A55 Kincsem
Currently cruising Brittany

 


Scott SV Tengah
 

Joerg,

Avoiding charging the batteries to 100% during normal use is a completely different conversation than whether to leave batteries at high SOC or 50% SOC during wintering/long term storage. I know that Victron and likely Mastervolt do NOT charge to 100% even during normal use. It's obvious if you look at the absorption voltages preset by Victron lithium charging profiles and then compare it to what is considered 100% charged. I surmise that it's the same with Mastervolt, so the respective battery monitors are telling you it's 100% when it's really in the low-mid 90% SOC. They do this because the additional capacity going between 90%-100% SOC is more than offset by the faster deterioration of the batteries. 

Regarding Mastervolt batteries "being different in design from other manufacturers batteries", I am a bit skeptical considering actual product teardowns indicate that they use Winston prismatic cells, just like Victron and just like the guy who spent a fraction of what we spent for our batteries. A not-so-hidden secret of these expensive batteries is that they use the same Chinese cells that others get at a 75% discount to build their own homebrew lifepo4 batteries. Of course, the internal connections, BMS system, warranty and hence safety and reliability are theoretically better and the system is more integrated, which is why I paid a premium for my Victrons. But I'd be very skeptical when the guy selling you the batteries at a huge profit tries to tell you that theirs is different somehow. I am under no illusion that the battery cells in my Victrons or your MV are made of unobtanium or handbuilt by an MIT engineer - they are Chinese Winston prismatic cells that are subject to the same limitations.

Trying to achieve a desired SOC by specifying voltage is difficult for reasons mentioned earlier. By setting a lower float voltage, I believe that all you're doing is setting the lower limit of voltage that the batteries will go to while connected to the charger. The absorption voltage/duration is really what determines the high SOC limit. Give it a try and set your float voltage to 24v and see if it still charges to 78%.

Let me try to dig up those papers for you. Here are the results of a simplified test that is much less dry.


To be fair, he's comparing 50% vs. 100% SOC but it's probably safe to assume that the damage associated with high SOC storage is not a step function. 

At the end of the day, it's our individual boats, so we must do what we think is best. I find these engineering guys sometimes cross the border into marketing, so I always trust, but verify through objective means.

On Mon, Oct 4, 2021 at 7:16 PM Joerg Esdorn via groups.io <jhe1313=yahoo.com@groups.io> wrote:
I have discussed the issue with a senior technician at MV support.  His explanation for the recommendation to keep the batteries at 100% with a float voltage of 27.0V was that their batteries are different in design from other manufacturers' batteries.  They are made for being kept at full charge over long periods.  I further asked him if I wanted to keep them at a lower SOC, how to achieve that.  His response was to change the float voltage to 26.5 from 27.0V rather than program an event that turns the charger off at 80% SOC.  The event will result in a lot of switching which would be avoided with the adjustment of the float voltage.   I've tried to do this and the SOC essentially goes to about 78% with the charger connected.  So presumably you could set the float voltage to even less than 26.5V and end up with a SOC lower than 78%.  

I would be very interested in seeing the research paper(s) showing what the best SOC for long term storage is.  I am very hesitant setting the SOC for the winter at lower than 80% because of the risk that something will go wrong with the charger and the battery will go to the 20% cutoff point.   I also wonder whether it's worth avoiding charging the batteries to 100%.  I bought these batteries among other things to have much more capacity available than before.  I really don't want to restrict the range of SOC I can use to get some uncertain benefit on longevity.  MV says the batteries are good for 2000 cycles.  My Easyview monitor tells me I've used up 23 of those over the last 3 months on the boat.   At that rate, I will kick the bucket before the batteries!  

Joerg Esdorn
A55 Kincsem
Currently cruising Brittany

 


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


Joerg Esdorn
 

Thanks very much, Scott.  You certainly are putting a lot of effort into your posts!  I am sceptical as well of the MV support guys’ claim that his batteries are différent but MV’s advice to keep the batteries at 100% is out there right in their manual.  Why would they recommend something that is proven to be detrimental to the batteries?  

Thanks also for sending the article.  Having been an engineer in my first life and having done university level research work myself, I’m highly sceptical of the results of the simplified test for a number of reasons.  First, there is no indication that the researcher has any qualifications whatsoever - on his linked in page he’s described as a sales manager.  So I’m not sure of his motivations for writing the article.  Second, there is just ONE test run with ONE set of discharge and charge parameters.  These small differences he’s measured are they repeatable or could they be the result of variations between the cells, for example.  Also, a serious researcher would always run various parameters to see whether there are relationships between the outcome and your parameters.    For example, I charge my batteries at less than 25% of capacity because that’s all my chargers can do and at the the very end of the charging process my chargers would go into float, so the charge goes down to a few amps.  His test was at a charge rate of 50% of capacity - until full? If so, wow!  He’s also discharging the cells to 2.0V - my batteries would never go down so low because of the BMS.  Even more importantly, the cells he’s tested - are they what I and you have?  He used 1.5Ah capacity cells - that’s pretty small.  What is the testing setup he’s used?  Testing such minuscule voltage differences must require some expensive equipment, right?  

So I have a lot of questions and see this «test » more as the typical pseudo science that unfortunately pervades social media.  I’m curious to see whether there is any serious research out there.  Thanks again for your and everyone else’s thoughts! 

Joerg Esdorn
A55 #53 Kincsem
Currently cruising Brittany