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Old 29-04-2022, 05:07   #31
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Re: Proper shore power "float" voltage for live aboard?

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Originally Posted by jordanbigel View Post
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.

Donít you have a BMS that can stop various devices from charging when the SOC and/or voltage reach a certain level (assuming you have lithium batteries)? Via relays the BMS should be able to cut off the charge for the Multiplus and the VE MPPT controllers - they all have remote on/off terminals.
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Old 29-04-2022, 05:13   #32
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Re: Proper shore power "float" voltage for live aboard?

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Originally Posted by Ballsnall View Post
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?

#1 will kill the lithium batteries quickly
#2 use SOC rather than voltage. A maximum of 80% and a low limit of 20% would provide a large charge cycle without going into the knees
#3 the benefits of lithium would be lost, if the boat is being used and normal consumers are present
#4 what a PITA to do it manually. Let the BMS do the work with the shore power charger

#2 is the winner of the boat is being used.

If the boat is in storage and not being used then #2 or #3 would be the way to go.
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Old 29-04-2022, 07:04   #33
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Re: Proper shore power "float" voltage for live aboard?

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Originally Posted by fxykty View Post
Donít you have a BMS that can stop various devices from charging when the SOC and/or voltage reach a certain level (assuming you have lithium batteries)? Via relays the BMS should be able to cut off the charge for the Multiplus and the VE MPPT controllers - they all have remote on/off terminals.
I have heard some BMSs can be programmed to act as the charge controller, instructing the charger (and/or alternator) when to charge and when to stop. But the BestGo batteries do not have that capability.

The BestGo BMS does provide signal relays which will send warning signals before the batteries shut down, and these signals ARE wired to the Multiplus and to a relay connected to my (Balmar) voltage regulator.

But, this is not intended to control charging, it is an emergency backup to allow time to shut things down gracefully before the battery des an auto-shutdown. (The BestGo batteries also provide signals requesting cooling and/or heating as required by the batteries, but so far I do not plan to use these although I have been investigating Peltier coolers since my cruising plans are mostly tropical).

With these batteries the charge controlling has to be done by the charging source, in this case the Multiplus/BMV700. Using the Multiplus assistants, I believe I can program it to begin and end changing based on SOC provided by the BMV7xx.
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Old 29-04-2022, 08:29   #34
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Re: Proper shore power "float" voltage for live aboard?

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Originally Posted by fxykty View Post
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.


Lithium s have a cycle lifetime. Short cycling , consumes those cycles
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Old 29-04-2022, 09:37   #35
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Re: Proper shore power "float" voltage for live aboard?

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Originally Posted by HeywoodJ View Post
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).
I am interested in what Heywood has to say, because his organization and their manufacturers have some serious skin in the game. His bank is something like 10,000 boat banks of 800 amp hours at 12.5 volts, and is an investment of over $50 million.

Heywood, I would like to know more about your system. If you charge to 100% SOC during the day and discharge to 5% every night, it seems both your nightly load and your solar capacity are bigger than your bank capacity. Are you simply tied to the grid to provide peaking capacity, or do you have a load that you can shift to some other power source when the bank is depleted? How long has the bank been in operation? Is the warranty to provide replacement cells or is it a pro rata rebate?
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Old 29-04-2022, 13:51   #36
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Re: Proper shore power "float" voltage for live aboard?

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Originally Posted by goboatingnow View Post
Lithium s have a cycle lifetime. Short cycling , consumes those cycles

????

Taking a battery from 100% to 0% and back is one cycle. Taking a battery from 60% to 40% and back is 0.2 of a cycle.

If we define short cycling as charging and consuming a battery within a relatively narrow SOC range, the question is whether this is a bad from a capacity point of view. I havenít seen anything about that and am really curious.

This has relevance for live aboards who are in marinas and have constant shore power, or on the hook with lots of solar and sunny weather. Is it better to cycle the bank in a narrow range, so 40-60%, or larger range 20-80%?

On passage it becomes a different problem, as you want to avoid overnight usage (in the absence of hydro generators and/or wind generators) dropping the SOC too much. We generally have a 60-90% profile then (which still can yield cycling between 30-70% if charge is cut off during the day and the next day is cloudy).
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Old 29-04-2022, 17:23   #37
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Re: Proper shore power "float" voltage for live aboard?

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...Heywood, I would like to know more about your system. If you charge to 100% SOC during the day and discharge to 5% every night, it seems both your nightly load and your solar capacity are bigger than your bank capacity. Are you simply tied to the grid to provide peaking capacity, or do you have a load that you can shift to some other power source when the bank is depleted? How long has the bank been in operation? Is the warranty to provide replacement cells or is it a pro rata rebate?
The systems I'm managing are entirely different from boat systems, but at the same time they are constructed of the same basic cells. One of these days I'm going to have see if I can't get a few cells to fall off a truck and into the boat

We have two general use cases, the first is generation shifting for grid-connected PV systems. We charge from PV, generally in the morning when electricity value is low, then PV goes to the grid when batteries are full and electricity value is average, and then discharge in the evening when electricity value is high. These systems fall into very specific rate programs, and the length of the peak payment is usually 2 or 4 hours depending on what program. So the batteries are sized to equal the maximum PV output for that length of time. There's some special cases where our professional "guessers" (they're about as accurate as old school weather forecasters) ask me to hold charge because they're predicting a scarcity event and prices will go way up, but normally its a daily cycle with most of the night spent at very low SOC.

Our other use case is with PV and battery behind-the-meter at some big electrical consumer. In that use case we're attempting to hold their grid import level to reduce demand charges. Those batteries see a lot more partial charge/discharge cycles as we try to load follow the facility. Not enough years of data yet to know how much difference that will make in capacity longevity/degradation.

Our oldest systems are at about two years (we have a few older, but they are not LFP, that was a big shift in the industry about three years ago), so still early days, with another 100MWh going online this year. The warranty provides replacement cells or additional cells, and labor to install them, if we fall below the guarantee level, although we have already been approached on at least one claim with a request for a buyout rather than replacement. There are some pretty strict monitoring requirements to maintain the warranty, one of them that I don't know the reasoning behind, and that could be tough on a boat, is relative humidity below 65%.

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Originally Posted by fxykty View Post
...Taking a battery from 100% to 0% and back is one cycle. Taking a battery from 60% to 40% and back is 0.2 of a cycle...

This has relevance for live aboards who are in marinas and have constant shore power, or on the hook with lots of solar and sunny weather. Is it better to cycle the bank in a narrow range, so 40-60%, or larger range 20-80%?...
This an interesting question. All I can contribute is that for the capacity warranty I am discussing, the actual measured value is total annual energy throughput (in MWh). This is then divided by the guaranteed capacity for the current year to get an equivalent number of 100% cycles, and that is the number that is then used in the calculations. In that regard, 10-10% discharges are exactly the same as 1-100% discharge. Don't know if that's reality, but that is how the batteries are sold to us.

One other fascinating piece of this is that batteries at zero cycles/year are guaranteed for 90% capacity at 12 years when stored at 5% rSOC and 84% when stored at 100 rSOC. The manufacturers puts most of the degradation in the calendar and in the storage SOC rather than in the cycle count.
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Old 30-04-2022, 07:47   #38
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Re: Proper shore power "float" voltage for live aboard?

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Originally Posted by HeywoodJ View Post
The systems I'm managing are entirely different from boat systems, but at the same time they are constructed of the same basic cells. One of these days I'm going to have see if I can't get a few cells to fall off a truck and into the boat

We have two general use cases, the first is generation shifting for grid-connected PV systems. We charge from PV, generally in the morning when electricity value is low, then PV goes to the grid when batteries are full and electricity value is average, and then discharge in the evening when electricity value is high. These systems fall into very specific rate programs, and the length of the peak payment is usually 2 or 4 hours depending on what program. So the batteries are sized to equal the maximum PV output for that length of time. There's some special cases where our professional "guessers" (they're about as accurate as old school weather forecasters) ask me to hold charge because they're predicting a scarcity event and prices will go way up, but normally its a daily cycle with most of the night spent at very low SOC.

Our other use case is with PV and battery behind-the-meter at some big electrical consumer. In that use case we're attempting to hold their grid import level to reduce demand charges. Those batteries see a lot more partial charge/discharge cycles as we try to load follow the facility. Not enough years of data yet to know how much difference that will make in capacity longevity/degradation.

Our oldest systems are at about two years (we have a few older, but they are not LFP, that was a big shift in the industry about three years ago), so still early days, with another 100MWh going online this year. The warranty provides replacement cells or additional cells, and labor to install them, if we fall below the guarantee level, although we have already been approached on at least one claim with a request for a buyout rather than replacement. There are some pretty strict monitoring requirements to maintain the warranty, one of them that I don't know the reasoning behind, and that could be tough on a boat, is relative humidity below 65%.



This an interesting question. All I can contribute is that for the capacity warranty I am discussing, the actual measured value is total annual energy throughput (in MWh). This is then divided by the guaranteed capacity for the current year to get an equivalent number of 100% cycles, and that is the number that is then used in the calculations. In that regard, 10-10% discharges are exactly the same as 1-100% discharge. Don't know if that's reality, but that is how the batteries are sold to us.

One other fascinating piece of this is that batteries at zero cycles/year are guaranteed for 90% capacity at 12 years when stored at 5% rSOC and 84% when stored at 100 rSOC. The manufacturers puts most of the degradation in the calendar and in the storage SOC rather than in the cycle count.
All good stuff. It sounds like discharge rates can get up near 0.5C on your banks if you want to maximize profits. The good news is that we should be able to get 12 years out of our banks, regardless of full or short cycles.

On another note, the local 300 Mwhr bank is having its problems. Do you know if they are using Life technology?

https://www.pv-magazine.com/2022/02/...is-down-again/
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Old 30-04-2022, 08:33   #39
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Re: Proper shore power "float" voltage for live aboard?

Moss Landing uses LG TR1300 battery racks, assembled from LG JH4 NMC cells (3.67V nominal, 72.5Ah). The fires in Arizona, Moss Landing, and Victoria have all been NMC/NCA.

One of our biggest challenges (and judging by the insurance thread running here on CF it is the same for boaters) is explaining the differences in battery chemistry to those who issue permits. "Lithium" all gets lumped together in a single bucket, and yet the different chemistries behave differently and need different protection features.
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Old 08-05-2022, 22:35   #40
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Re: Proper shore power "float" voltage for live aboard?

Just an interesting tidbit.


I've just brought my LiFePO4 system fully online, and the behaviour is interesting.


After doing the initial bulk charging up to 14.5V, my REC BMS has directed the system to hold the battery bank at 13.9V. After the initial charge, it didn't take long for the battery to relax down to that 13.9V.
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