Merged LiFeYPO4 1000Ah Winston prismatic cells and all electric galley...

[BrissyBrew]

Just found I can program a victron multiplus so AC-2output can be turned off on based on battery voltage, so could turn on heater at 100% SOC and off at 90% SOC. Avoids keeping the battery at 100% SOC too.

[CatNewBee]

I would use the BMV. it counts the Amp's and is more accurate than the inverter logic based on voltage.

[BrissyBrew]

Originally Posted by CatNewBee

I would use the BMV. it counts the Amp's and is more accurate than the inverter logic based on voltage.

Agree BMV would be better, but I am using a Zeva BMS to monitor SOC (and cell voltage of each cell) no BMV. No BMV in my system. Lithium pack using voltage for SOC estimation I could be able to get it pretty close dialling in the voltage. Not as precise for sure. If I had the colour controller I could do a custom assistant that would only turn the relay on when the solar charger is running at x amps of charge. But running at 90-100% SOC is not bad keeps the battery down a little less than 90% SOC unless the hot water is already hot (heat exchanger in a bus).

[dooleedooroo]

CatNewBee,
I see you use victron quatrro for your setup. What is the difference between quatro vs multiplus? Is there any benefit using quatrro over multiplus?

[john61ct]

Originally Posted by BrissyBrew

I am using a Zeva BMS to monitor SOC (and cell voltage of each cell) no BMV. No BMV in my system. Lithium pack using voltage for SOC estimation I could be able to get it pretty close dialling in the voltage. Not as precise for sure.

Except for when nearing the voltage shoulders at top 90%+ and bottom 10% SoCs, voltage will be **100% useless**, especially under even light activity but even when "at rest" even with a very precise voltmeter.

In the 15-85% range with LFP, the only way to know your SoC with any useful accuracy is with an Ah accumulator.

Your BMS' SoC estimate from coulomb counting may well be just as or more accurate than using an "outside" BM.

But if it isn't you're pretty much flying blind.

[CatNewBee]

Originally Posted by dooleedooroo

CatNewBee,
I see you use victron quatrro for your setup. What is the difference between quatro vs multiplus? Is there any benefit using quatrro over multiplus?

The Quattro stands for the 4 AC interfaces on the internal transfer switch. You have 2 inputs and 2 outputs, the inputs can be land-line and generator with priority switch, the outputs are one switched between the inputs and the inverter in power assist mode and one pass-through inputs to the output without the inverter for loads that should not drain the battery. Also the Quattro can be grid coupled and be configured to feed excess energy to the grid, if you have such a contract. You can parallel multiple quattros for more power or configure them to phase shift / 3 phase output with 3 of them, one for each phase.

The multiplus has more limitations, but is also a nice product if you not need the transfer switch on the inputs. I do use it with different configs for either limiting marina shore loads and juice up by the battery, team up 2 inverters for more power or limit / juice up the generator output if needed. I use the Quattro transfer switch instead of the original switchboard for automatically selecting the sources and parameters.

[nebster]

Originally Posted by john61ct

Except for when nearing the voltage shoulders at top 90%+ and bottom 10% SoCs, voltage will be **100% useless**, especially under even light activity but even when "at rest" even with a very precise voltmeter.

In the 15-85% range with LFP, the only way to know your SoC with any useful accuracy is with an Ah accumulator.

Absolutely incorrect.

If you walk into my real home, which is powered by a real LFP battery, and look at my real monitor on the wall, and you tell me these three things:

1) the pack voltage (which is measured at the bus bar)

2) the current being sourced by the pack (measured at a shunt)

3) that the current has been approximately the same for a minimum of thirty seconds (so that the voltage hysteresis has had a chance to dissipate)

...then I can tell you the SOC within 2-3% after looking at a graph. Moreover, I can usually tell you the SOC within 5-10% just off the top of my head, without even consulting any reference data. Both of those accuracies are more than enough for day-to-day living.

[nebster]

Originally Posted by CatNewBee

The multiplus has more limitations, but is also a nice product if you not need the transfer switch on the inputs. I do use it with different configs for either limiting marina shore loads and juice up by the battery, team up 2 inverters for more power or limit / juice up the generator output if needed. I use the Quattro transfer switch instead of the original switchboard for automatically selecting the sources and parameters.

Also, the Quattro line goes much larger than MultiPlus.

[john61ct]

Originally Posted by nebster

If you walk into my real home, which is powered by a real LFP battery, and look at my real monitor on the wall, and you tell me these three things:

1) the pack voltage (which is measured at the bus bar)

2) the current being sourced by the pack (measured at a shunt)

3) that the current has been approximately the same for a minimum of thirty seconds (so that the voltage hysteresis has had a chance to dissipate)

First off, voltage sag may well be consistent under various c-rate loads, but the sag from loads (or boost from charging) does not "dissipate" until the bank is at rest. With many setups loads and charge inputs are constantly varying anyway.

I'm not saying **you** can't guesstimate your SoC in your unique context, when you are so intimately familiar and usage patterns have become stable over time, most owners who pay attention to such details can become "pretty intuitive" about their gear's current condition.

Even our measuring instruments would need to be very precise and the (hard copy) chart would need to be three-dimensional and continuously variable to give you that level of accuracy.

In any case the person I was correcting was not talking about cross referencing against current amps flow rates in and out, but just using voltage.

What equipment do you use to determine that your accuracy is that close to objectively accurate SoC? Are you building your chart by doing hundreds of load tests?

[john61ct]

my point is that it is impossible to know how close a %age accurate your "educated guessing" is, unless you have instruments you trust more than that to compare to

[CatNewBee]

SOH is not important any way, it is useless information. What counts is, having power to do things without thinking too much about SOC and SOH. Just having sufficient at any time. And if not, add more capacity.

[nebster]

Originally Posted by john61ct

First off, voltage sag may well be consistent under various c-rate loads, but the sag from loads (or boost from charging) does not "dissipate" until the bank is at rest.

And I'm telling you, it's trivial to use load-compensated SOC curves to make the calculation.

With many setups loads and charge inputs are constantly varying anyway.

Which is why I stipulated requirement number 3, a stable load for a few moments. In a real system -- which you do not possess -- the loads do remain stable enough for voltage hysteresis to dissipate.

I'm not saying **you** can't guesstimate your SoC in your unique context, when you are so intimately familiar and usage patterns have become stable over time, most owners who pay attention to such details can become "pretty intuitive" about their gear's current condition.

I can walk up to any LFP setup with the above three conditions and tell you the SOC very accurately. I need about three digits of voltage precision after the decimal point, the reading must be accurate (at the terminals, no line losses), and the load must be reasonably stable and between 0.05 and 0.2C.

Under those conditions, anyone can learn to estimate SOC within 10%, and probably better.

Even our measuring instruments would need to be very precise and the (hard copy) chart would need to be three-dimensional and continuously variable to give you that level of accuracy.

Real life, John, is quite different than your make-believe world.

In any case the person I was correcting was not talking about cross referencing against current amps flow rates in and out, but just using voltage.

It's impossible for you to correct someone when what you write is objectively incorrect.

What equipment do you use to determine that your accuracy is that close to objectively accurate SoC? Are you building your chart by doing hundreds of load tests?

(It's ironic that you are asking these questions.)

I cross-reference with a coulomb counter that is totalizing against a bank of known total capacity.

But, another way to reality-check the measurements is to look at discharge curves for numerous LFP cells. They are remarkably similar, such that any well-plotted one is suitable as a "characteristic curve" for use in estimating any other battery's state.

Moreso in the linear regime, between the knees, from 10 to 90% SOC, where you so boldly claim that it is "impossible" to determine SOC and that the voltage is "useless." Quite the opposite: the mV/%SOC slope is very stable in this range, at constant current.

It is this stability, plus proper measurements and some common sense, that allows for Pretty Darn Good estimating by hand.

[nebster]

Originally Posted by CatNewBee

SOH is not important any way, it is useless information.

We are talking about SOC in these most recent posts.

Bank capacity ("SOH") is also useful, over a long time horizon. If my $25,000 battery pack is starting to deteriorate faster than others, I want to know about it early and figure out why. For large installations, it's data worth having.

What counts is, having power to do things without thinking too much about SOC and SOH. Just having sufficient at any time.

I always have sufficient power, since I have a large tank of diesel nearby.

But even with a huge battery, I find SOC important. I want to minimize diesel consumption (recharge off shore power where possible) and also minimize noise and disruption (by scheduling generator runs for the best times, avoiding social settings, quiet hours, etc.).

And if not, add more capacity.

Not always an option, e.g., if the battery has already been designed to consume all of the available space!

[john61ct]

OK nebster, "uncle", with your setup I guess you can get close, 10% would be pretty good.

But that is unusual, and regular users would both be hard-pressed to do the same, and still need a coulomb counter to dial things in for **their** setup.

Obviously loads and inputs must be converted to C-rates in order to begin transferring thos correspondence charts to different Ah capacity banks.

[CatNewBee]

... You know what, every evening, when the admiral makes a great dinner on the induction hob, every morning when having a espresso or a lungo or a cappuccino made of fresh grinded coffee beans along with fresh bread out of the convection oven, every time, when there is almost unlimited hot and cold fresh water for a shower and ice cubes for the sun downers you have a big grin in your face and think about how lucky you are and that you made the right decision about your power set up. It was worth every penny.

We love cruising on LFP and solar.

Fair winds from Italy, tomorrow we will sail to Greece...