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LiFpO4 when you don't live-aboard


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What's the deal with Marine Lithium LiFpO4 when you don't liveaboard?  I know that you need a really good BMS.
But what about when you are off the boat for extended periods....do you just switch off your solar so that the batteries don't overcharge - because that, from my very basic knowledge is one of the main "weakness" (that may not be the best word) of Marine Lithium on a boat, is that you do not ever want to overcharge.

 

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29 minutes ago, Zozza said:

What's the deal with Marine Lithium LiFpO4 when you don't liveaboard?  I know that you need a really good BMS.
But what about when you are off the boat for extended periods....do you just switch off your solar so that the batteries don't overcharge - because that, from my very basic knowledge is one of the main "weakness" (that may not be the best word) of Marine Lithium on a boat, is that you do not ever want to overcharge.

 

Or leave enough loads running overnight, like the fridge and freezer. 

It's not a weakness of lfp it's a weakness of the charging solution.

Most solar chargers will start again each morning, If your lfp has no loads this will eventually lead to over charging.

If you have no permanent house loads then disable charging. 

On CD we disable all charging including the alternator and shorepower.  We can do about 6 winter races before the charging gets enabled again.  We have a composting toilet that's continually running a fan but the draw is incidental and is far from enough to avoid solar overcharge. 

It's just a different mindset, when we step on the boat, we ask, do we have enough Wh for today's activity. If the answer is yes we go racing/cruising and worry about it next time.  If no, we enable charging and motor out of the marina, 30 minutes later the battery has enough charge for the day and we hoist the sails. 

NB if you are leaving the boat for a months and months then you might need to consider a more detailed shutdown procedure because the BMS is a sacrificial load and will eventually drop the LFP to low levels before shutting down. 

 

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40 minutes ago, CarpeDiem said:

Or leave enough loads running overnight, like the fridge and freezer. 

It's not a weakness of lfp it's a weakness of the charging solution.

Most solar chargers will start again each morning, If your lfp has no loads this will eventually lead to over charging.

If you have no permanent house loads then disable charging. 

On CD we disable all charging including the alternator and shorepower.  We can do about 6 winter races before the charging gets enabled again.  We have a composting toilet that's continually running a fan but the draw is incidental and is far from enough to avoid solar overcharge. 

It's just a different mindset, when we step on the boat, we ask, do we have enough Wh for today's activity. If the answer is yes we go racing/cruising and worry about it next time.  If no, we enable charging and motor out of the marina, 30 minutes later the battery has enough charge for the day and we hoist the sails. 

NB if you are leaving the boat for a months and months then you might need to consider a more detailed shutdown procedure because the BMS is a sacrificial load and will eventually drop the LFP to low levels before shutting down. 

 

What loo do you have ?  I’m relieved we aren’t the only freaks out there with a composter 😂

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21 hours ago, Ex Machina said:

Same ,  very happy with it .

Well joining the Fred Drift in my own Fred..... I have pre-ordered one of these.  Was under $400 .  Won't be shipped to me till end of August, and then won't be put to serious use until its used in anger post my yacht rebuild / refit -- but I will try to remember to make comments on the robustness of it once it has been delivered.

https://www.joolca.co.nz/products/gottago

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Screenshot 2024-06-14 at 7.05.48 AM.png

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Second CD's & Machina's  MO.

Fridge is always on. Beer is always cold. Solar disconnected for type of sailing I'm currently doing.

I have been absent for 3 weeks and its usually around 30%soc when i return. Never low voltage disconnect but have run it down to check operation. Usually do 80/30 state of charge, with a 95%+ balance charge before multi day sail. Usually just changing anchorages is enough to stay in that 80/30 zone as charging at a steady 80A with the alternator brings it up quickly. Should have done it sooner.

Drift---LTO's on hold as a bit skeptical how windlass and starter motor will handle 15V+ and no sag. I believe 14.2V  is less than 80% for LTO so have a DC DC booster.

Whats the maintenance schedule with the OGO?

Ummm, what do the girls say? Hate putting stuff back in that I've taken out!

 

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32 minutes ago, Guest said:

 

Drift---LTO's on hold as a bit skeptical how windlass and starter motor will handle 15V+ and no sag. I believe 14.2V  is less than 80% for LTO so have a DC DC booster.

Assuming YINGLONG then 80% is approximately 2.6v

You could consider a 5 cell pack.

 

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We have the Victron GX system that talks to the solar and BMS of our batteries. When I leave the boat, I set the max charge voltage to 13.4v which seems to keep the batteries at about 70%ish. With this system, you can remotely log in and change the settings, so a few days before we go away, I let it charge back to full to be balanced and ready to go when we get on the boat. 

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Question,

I thought one of the benefits of LiFePo was that you could use the full battery capacity, as in 100%. That is a clear advantage over the lead acid variants where you generally can't go below 50% DoD as it greatly reduces cycle life - as in you can if you need to, but you don't design your system to so that you get good cycle life.

If you keep your LiFePo between 80% and 30%, you are only using 50% of the capacity.

Noting I would probably do the same if I had a LiFePo, but what is the main reason for doing that?

Is it just being conservative? (which is a good thing), better cycle life?, simpler management, in that you aren't banging into the BMS hard stops all the time / relying on the BMS?

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The TAO BMS units that I use have simple Mode controls, Keep full, Normal (20% to 80%)  Storage (40%-60%). Just select what you want on the menu, and the BMS controls all charge and discharge sources as needed.  Keeping LiFePo4 full will reduce it's ultimate cycle life... but it's not a safety issue or anything.. 

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1 hour ago, K4309 said:

Question,

I thought one of the benefits of LiFePo was that you could use the full battery capacity, as in 100%. That is a clear advantage over the lead acid variants where you generally can't go below 50% DoD as it greatly reduces cycle life - as in you can if you need to, but you don't design your system to so that you get good cycle life.

If you keep your LiFePo between 80% and 30%, you are only using 50% of the capacity.

Noting I would probably do the same if I had a LiFePo, but what is the main reason for doing that?

Is it just being conservative? (which is a good thing), better cycle life?, simpler management, in that you aren't banging into the BMS hard stops all the time / relying on the BMS?

Yep you can use the full capacity.  Yes it will reduce the lifetime.

I smash ours, I charge it at double the recommended rate, but below the maximum, I take it to within an hour of being completely flat and shutting down.  I charge it to whatever and then start discharging it again... and sometimes I leave it fully charged for a whole week... 

Following my current usage profile, of racing weekly and getting away for a couple of weekends a month, I will get, conservatively, 15 years out of the battery.

I would like to get fewer years out of it - as that would mean I'd be out sailing more :-)

If I spent the effort trying to do the 30%-80%, I reckon I could extend the lifetime of the battery beyond my remaining sailing years.

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Geez.......I gotta toughen up!

7 hours ago, CarpeDiem said:

Assuming YINGLONG then 80% is approximately 2.6v

You could consider a 5 cell pack.

 

Hmmm, could get overcharged with 14.2V  with no dc-dc. 6 seems safer. Discharge curve is steeper than LiFe. Also cable run to windlass will alleviate bit of high V on 6 pack.

Not so with starter though. Yanmar will get a fright!

BTW  CD, what %C tail current do you call 100%soc?

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1 hour ago, Island Time said:

The TAO BMS units that I use have simple Mode controls, Keep full, Normal (20% to 80%)  Storage (40%-60%). Just select what you want on the menu, and the BMS controls all charge and discharge sources as needed.  Keeping LiFePo4 full will reduce it's ultimate cycle life... but it's not a safety issue or anything.. 

This is clearly an entirely different mindset to using the lead acid variants and wanting to keep them as topped up as possible at all times.

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22 minutes ago, Guest said:

Geez.......I gotta toughen up!

Hmmm, could get overcharged with 14.2V  with no dc-dc. 6 seems safer. Discharge curve is steeper than LiFe. Also cable run to windlass will alleviate bit of high V on 6 pack.

Not so with starter though. Yanmar will get a fright!

You will still need dc/dc...

But 5S at 80% SoC is ~13.2v which is a bit less obnoxious than 14.8v

Of course you lose Wh's

29 minutes ago, Guest said:

BTW  CD, what %C tail current do you call 100%soc?

Is this a trick question...? 

Cause tail current termination depends on voltage 😉😉

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42 minutes ago, Guest said:

Not so with starter though. Yanmar will get a fright!

Nope.  It will start quicker, and given the duty cycle of a starter, 15% higher supply voltage is a "meh".

 

I used to do 6v to 12v conversions on VW beetles. StArter was one of the things we left stock standard.  Man, they cranked and fired inside one revolution!!!

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17 minutes ago, CarpeDiem said:

 

Is this a trick question...? 

Cause tail current termination depends on voltage 😉😉

Ok, re phrase. What %C tail current do you call 100%soc at what target voltage.

Guessing that it will be high TV  for LiFe and errr, 2%C seeing as you like smashing.

I do TV= 14.6V  and 0.1%C  for top balance and sync.  (0.5A) 6monthly or less.

Normally 14.2V and 2%.

 

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28 minutes ago, aardvarkash10 said:

Nope.  It will start quicker, and given the duty cycle of a starter, 15% higher supply voltage is a "meh".

 

I used to do 6v to 12v conversions on VW beetles. StArter was one of the things we left stock standard.  Man, they cranked and fired inside one revolution!!!

Still be a "meh" at 25% aye? 100% would be "nah, not going there". Not for non terrestrial vehicle anyway.

Electronics of the Balmar mc618 I better check on tho as its powered from ignition.

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20 minutes ago, Guest said:

Ok, re phrase. What %C tail current do you call 100%soc at what target voltage.

Guessing that it will be high TV  for LiFe and errr, 2%C seeing as you like smashing.

I do TV= 14.6V  and 0.1%C  for top balance and sync.  (0.5A) 6monthly or less.

Normally 14.2V and 2%.

 

Firstly the smashing is during the CC phase (typically called bulk). I charge at 0.9C the recommended is 0.5C the manufacturer max is 1C.

Termination current occurs in the CV phase (typically called absorb).

Termination current is a function of the manufacturers max voltage and term current. 

So if the manufacturer states 3.65v @ 0.05C (which mine does) 

Then we have:

I_term=(V_absorb-3.37)/0.28 * 0.05

0.28 comes from 3.65 - 3.37 (3.37v is the voltage at which no charging is occurring). 

I have found that v_absorb of 3.5v/cell is perfect to provide a good time for balancing and deal with any cells that have been at low charge. 

So I charge at 14v with a tail termination of 0.023C, which for my moderate setup I call 3Amps 

A long winded response to a short question 🤣

What cells are you using that are rated for 0.01C at 3.65v that's out there 😊

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