Proper shore power "float" voltage for live aboard?

[fxykty]

Originally Posted by Ballsnall

Pretty much what you need to do. If you can keep the batteries at that 50 - 70% storage charge you should be fine long term. I just think it's so much simpler and safer to just use a FLA for the year or so knowing that the lithiums will have full life remaining once you start using them.

Better would be 30 - 50% for storage.

[sailcrazy]

following. We're still using LA batts; trying to learn about the Lithium batts benefits...and peculiarities.

[goboatingnow]

Originally Posted by fxykty

Better would be 30 - 50% for storage.

30% is too low because of parasitic action , 50-60 is best

[alctel]

I just let my pack cycle with solar as someone else said, and if it got low id just charge it up using shore power.

When i left the boat I disconnected the pack entirely

[fxykty]

Originally Posted by goboatingnow

30% is too low because of parasitic action , 50-60 is best

What do you mean “parasitic action”?

And as long as the BMS allows charging to take place once the batteries are at 30% what bad could happen?

But if you mean for isolated storage with no regular on board consumers then then charge to 50% and disconnect the lithium battery. Connect bilge pumps (and any other loads you want) to a lead acid (starter) battery and charge that via a trickle charger and/or solar panel. The second discharge rate of lithium is so slow that this setup would be just fine for years.

[HeywoodJ]

I recently fell into a job that has me managing about 100MWh of LFP, all constructed from 40Ah blue cells (from several manufacturers). The systems are built up of racks that are 360S8P and then the racks are paralleled. The battery manufacturers are providing a capacity warranty at 80% capacity after 12 years when operated under the following conditions:

HV Warning 3.6V
HVDC 3.7V
LV Warning 3.0V
LVDC 2.8V

Charge to 3.4V/cell.
Discharge to 3.1V/cell
Charge at 0-0.5C (all from solar, so variable charge rate)
Discharge at 0.5C

At these settings a cycle is defined as 0-100% SoC and 40Ah/cell (actually 128Wh/cell = 40Ah @ 3.2V). We have some pretty expensive metering to measure those values. Linear decline over 12 years to 32Ah (102.4Wh) if cycled once daily.

Critically for this discussion, those values and degradation rate are based on rSoC (resting state of charge) of 5%! If the rSoC is > 5% then capacity guarantee is reduced. rSoC is defined by measuring SoC every 15 minutes while the battery is not actively charging or discharging, and taking the average of those measurements. What this really means is we charge all day, discharge at sunset, and hold the batteries between 1-5% until the next morning to maximize capacity. The capacity loss at 50% rSoC (as compared to 5% rSoC) is about 4%, so not huge, but also not insignificant.

For long term storage (no active charge or discharge) we are required to hold the batteries at 30% SoC, the lower the better but with some consideration for self-discharge and BMS losses. Long term is defined as 3 months, at which time SoC needs to be checked and system charged back to that level to make up for any losses.

SoC during storage of 30% is for two reasons:
1). This is required for transport safety under UN DOT 38.3
2). this is the optimal SoC to prevent calendar degradation while still being far enough away from the "voltage cliff" so you don't have to worry about parasitic losses.

Those values don't answer the OP's question directly, they are offered as general guidance from the big battery manufacturers on best practices to use as a guideline in determining a float value.

[kupo2kupo]

Originally Posted by HeywoodJ

The capacity loss at 50% rSoC (as compared to 5% rSoC) is about 4%, so not huge, but also not insignificant.

HeywoodJ, thanks for this contribution. Obviously, that is not how we like to operate batteries on our boat, but this is interesting data!
For clarification: Are you saying the capacity loss at 50% rSOC would 4% per year, so 48% after 12 years? And the loss at <5% rSOC would be 20% after 12 years, that is 1.7% per year?

[HeywoodJ]

Originally Posted by kupo2kupo

HeywoodJ, thanks for this contribution. Obviously, that is not how we like to operate batteries on our boat, but this is interesting data!
For clarification: Are you saying the capacity loss at 50% rSOC would 4% per year, so 48% after 12 years? And the loss at <5% rSOC would be 20% after 12 years, that is 1.7% per year?

Reading back I see I was not at all clear, so apologies. Nothing so drastic, the capacity loss at 50% rSOC is about 24% over the 12-year period, as compared with 20% at 5% rSOC. It goes up by about the same amount from 50% rSOC to 100% rSOC, and is essentially linear. The overall message being the manufacturers are recommending that to maintain capacity we should use the lowest possible SOC when not in use, but the capacity hit is not unbearable (except to my financial folk, who have given me a 10% rSOC target because that capacity makes a difference).

[goboatingnow]

What’s the Lithium chemistry being used in those batteries, oh sorry I see they are LFP.

[goboatingnow]

Originally Posted by fxykty

What do you mean “parasitic action”?

And as long as the BMS allows charging to take place once the batteries are at 30% what bad could happen?

But if you mean for isolated storage with no regular on board consumers then then charge to 50% and disconnect the lithium battery. Connect bilge pumps (and any other loads you want) to a lead acid (starter) battery and charge that via a trickle charger and/or solar panel. The second discharge rate of lithium is so slow that this setup would be just fine for years.

Well , what I meant is a storage charge of 50-60 % as long as no consumers are active , disconnected batteries

If there is consumption , you need to watch out for short cycling , so better to initiate a standard 20-80 charge cycle.

[fxykty]

Originally Posted by goboatingnow

Well , what I meant is a storage charge of 50-60 % as long as no consumers are active , disconnected batteries

If there is consumption , you need to watch out for short cycling , so better to initiate a standard 20-80 charge cycle.

How is short cycling a problem? What exactly is short cycling?

This is an issue for live aboards that have a shore power connection. What is the optimum charge profile (when to turn on charging and when to stop charging)?

For storage without consumers lower than 50% is recommended. The lower the SOC the better apparently.

[Ballsnall]

The storage SOC % is just semantics, the ops problem is how best to run lithium's with shore power for an extended duration. How much of an issue is it and are we just being a little too anal?

4 options as I see it.
1. Let shore power maintain the batteries at 100%
2. Use a modified charge profile to a lower voltage.
3. Store the lithiums and use a sacrificial FLA.
4. Connect & disconnect shore power manually.

Any other options?

[jordanbigel]

Originally Posted by Ballsnall

The storage SOC % is just semantics, the ops problem is how best to run lithium's with shore power for an extended duration. How much of an issue is it and are we just being a little too anal?

4 options as I see it.
1. Let shore power maintain the batteries at 100%
2. Use a modified charge profile to a lower voltage.
3. Store the lithiums and use a sacrificial FLA.
4. Connect & disconnect shore power manually.

Any other options?

I've pretty much settled on 2 , if I understand you correctly - a modified charge profile which cycles a "normal" range, as if we were at anchor, say 20%/80%. I can program the Multiplus to do that and I won't have to manually shut it off and turn it back on, etc., etc (though I will do this the first week or two just to track usage and verify capacity, etc).

My original concern about cycling at the dock was that it would "waste" or burn through the limited number of cycles in the lifetime of the battery bank. But, I have now come to realize (via math) that it would be impossible for me to use up all the cycles before I plan to sell the boat, in 8-10 years.

Based on my estimates, with 960ah usable power, I should be able to go 3 days between charging this bank without trying to conserve power (I do not use electric cookers, strictly propane) so, I estimate we will use only about 120 cycles per year at the dock, fewer when really at anchor (because we will be more frugal with power).

The batteries are guaranteed for 3,000 cycles (by the US based vendor). SO, I figure 25 years based on 3,000 cycles and 120/year! Therefore, why bother messing around with hacks and tricks, I'm just going to treat the batteries like we are at anchor but without having to run the genset (and the hot water heater will run on shore power 24/7) - will be good to see how they perform under "normal" usage.

[Ballsnall]

Perfect solution if your shore power charger has that capability. Did you factor in your solar as well or is it all through the same charger?

[jordanbigel]

Originally Posted by Ballsnall

Perfect solution if your shore power charger has that capability. Did you factor in your solar as well or is it all through the same charger?

I am also replacing my PWM solar controller with a pair of Victron MPPT controllers (and replacing my 20 year old panels) which should work well in concert with the Multiplus. I also have a cutoff switch wired to the solar and usually leave it disconnected when at the dock.