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

[nebster]

Originally Posted by john61ct

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

There's nothing special about my setup. In fact, I just helped a family member work on some tuning of his 12V/4s LFP setup in his RV. Within a few hours, we had a reliable voltage reading (at the terminals) and a current flow (via my clamp DC ammeter), and we were estimating SOC like champs. Well within a 10% margin of error, and again likely closer to within 3-5%.

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.

They would not be hard-pressed, they would simply need to look at the data and take a few basic measurements. I see no reason that it has to be unusual, either, but I don't doubt that it is unusual for people not to try it. Which is one of the reasons I'm bothering to write about it, in hopes that it encourages others to not be afraid to just dive in and go do it. It's super easy, and it provides for confidence-building when learning how to work with this new chemistry. (Well, it certainly did for me.)

Since a current measurement requires either a semi-expensive meter or a semi-expensive shunt, the latter of which usually comes part and parcel with a counter, and because continuous state estimation is quite useful all on its own... in most cases everyone will be smart to acquire a counter anyway. But strictly speaking, it is not "needed" at all.

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

Yes, current needs to be normalized over capacity, and voltage needs to be scaled to 1s values.

[tanglewood]

Originally Posted by nebster

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.

I completely agree.


People keep saying you can't tell SOC from voltage on LFP. In reality, it's EASIER to tell SOC from voltage with LFP than with LA.


People say the voltage variation is too small between full and empty. Exactly the opposite is true. There is actually MORE voltage swing in LFP than in LA across the SOC range.


People say that loads will distort the voltage making is unusable for SOC. This is much LESS of an issue with LFP since it holds voltage much better across load ranges. And the load issue is really only material for large loads. I don't know about you guys, but my load lever actually varies very little, and is very small as a %C. In these low ranges, the impact on voltage is completely negligible. For the duration of a large load - say when my air compressor is running or the car lift is raising a car - the voltage will sag, but recovery is almost immediate once the load stops.


This crap about having to let batteries rest for hours or even days is utter BS too. It's just not the way things actually work. The very worst case I've ever seen is the time for voltage to drop back to "normal" after a charge, say from an inverter/charger running off a generator. Then maybe you need to wait for a minute or two. But never much more.

[CatNewBee]

Originally Posted by tanglewood

I completely agree.


People keep saying you can't tell SOC from voltage on LFP. In reality, it's EASIER to tell SOC from voltage with LFP than with LA.


People say the voltage variation is too small between full and empty. Exactly the opposite is true. There is actually MORE voltage swing in LFP than in LA across the SOC range.


People say that loads will distort the voltage making is unusable for SOC. This is much LESS of an issue with LFP since it holds voltage much better across load ranges. And the load issue is really only material for large loads. I don't know about you guys, but my load lever actually varies very little, and is very small as a %C. In these low ranges, the impact on voltage is completely negligible. For the duration of a large load - say when my air compressor is running or the car lift is raising a car - the voltage will sag, but recovery is almost immediate once the load stops.


This crap about having to let batteries rest for hours or even days is utter BS too. It's just not the way things actually work. The very worst case I've ever seen is the time for voltage to drop back to "normal" after a charge, say from an inverter/charger running off a generator. Then maybe you need to wait for a minute or two. But never much more.

.. The voltage depends on the cell temp too. I agree, 3.65V per cell is a good indicator for a full charge.

[tanglewood]

Originally Posted by CatNewBee

.. The voltage depends on the cell temp too. I agree, 3.65V per cell is a good indicator for a full charge.

Yes, cell temp too. Good point. But for many of us operating at .5C or less, even that doesn't vary much. It's all quite different from a car or a hand power tool that's operating at C or multiples thereof. Then heating, voltage sag, internal resistance, etc. all becomes important. But I think for most of us in daily operation it's all in the noise.

[CatNewBee]

True, just use the power with a big grin when somebody tries to teach you about longevity and SOC...

Batteries are consumable items. They are there to do a job and not to be pampered.

[dooleedooroo]

I am trying to copy CNB setup for Lithium Housebank, but one thing I would like to change is using alternator for charging Lithium. But at the same time I do not want to change the alternator. ALso I want to keep the current start and house gel battery. So I think I can connect my house gel battery to lithium through Battery to Battery charger and control the charger to be on only when the engine is running. House gel battery will be disconnected from existing dc circuit but only connected to B2B charger to charge the lithium.
Anybody see any problem with this setup? Any recommendation for DC/DC charger for this application? Or any other recommendations?

[CatNewBee]

You can do that, no problem. Just chose one, that does not overwhelm the alternator in regards of Amp's. I have connected the alternators directly via a solenoid to the LFP bank, with cut off based on SOC. The alternators contribute about 40A each, but I use to sail, not to motor, so charging contribution of the alternators is neglectable. When I really need to charge, the generator is the fastest way with about 300A. Otherwise solar is the main charge source and usually sufficient.

[CatNewBee]

Short update...

We are now since 8 weeks full time cruisers, most of the time sailing. The electric system works great, after leaving Slovenia we never run the generator again for heating. All energy we needed for water making, warm water, cooking an laundry was powered by solar and LFP.

We hit only 3 times the 100% mark, mainly because we start to make water and heat it around noon so the energy goes straight from solar to the water maker. We use for the 2 of us around 120..160l fresh water per day, more when the washing machine is running.

I am really happy with the set up. When having guests on board, the water usage doubles and we have to be more careful with the energy, then we do not heat up the boiler too high. Cooking and baking was never a problem, nor making ice or ice cubes for the sun downers. We produce and use about 7kWh per day, autopilot, all electronics on and no engines most of the time.

[jmh2002]

^^^ Fantastic

[hzcruiser]

Originally Posted by CatNewBee

Short update...

Good on you! Seems like all the planning is paying off now.

[john61ct]

Originally Posted by dooleedooroo

I am trying to copy CNB setup for Lithium Housebank, but one thing I would like to change is using alternator for charging Lithium. But at the same time I do not want to change the alternator. ALso I want to keep the current start and house gel battery. So I think I can connect my house gel battery to lithium through Battery to Battery charger and control the charger to be on only when the engine is running. House gel battery will be disconnected from existing dc circuit but only connected to B2B charger to charge the lithium.

Anybody see any problem with this setup? Any recommendation for DC/DC charger for this application? Or any other recommendations?

Sterling BB series has the ability to control current demand (de-rating amps) as well as allowing a customized voltage setpoint, and can be controlled by IGN switch.

[Q Xopa]

Originally Posted by john61ct

Sterling BB series has the ability to control current demand (de-rating amps) as well as allowing a customized voltage setpoint, and can be controlled by IGN switch.

An Amperage limitation is not a design selling point.
Its like saying 'X' motor is terrific because it can 'only' output 40 HP.
Limitations exist to keep a lid on the price point. Im pretty sure most people would opt for a more capacity for less $.

But I guess it takes all kinds and others are happy with less.

Inovative thinking I guess?

[john61ct]

Originally Posted by Q Xopa

An Amperage limitation is not a design selling point.
Its like saying 'X' motor is terrific because it can 'only' output 40 HP.
Limitations exist to keep a lid on the price point. Im pretty sure most people would opt for a more capacity for less $.

Sorry, you keep repeating that wrong statement every time the issue arises, but no matter how many times you do, it never becomes any less incorrect.

There are **many** use cases where current limiting is not just valuable but absolutely required, often to protect the power source, often to protect the battery being charged, and sometimes both!

There may be alternative ways to accomplish that goal, so it is true you may not need to necessarily look for that feature in a DC-DC charger.

But for those that do know they need a good one, current limiting is indeed very often the reason why!

Constant current limiting is also a "very" important selling feature in **all kinds** of charge sources and DCDC converters, one of the main selling points rightly justifying higher prices when it is available.

It is such an important feature of Balmar's MC-614 for example, they tout both its "Small Engine mode" and the "Belt Manager" feature, separate multiple implementations of the same general idea in one product!

And for exactly the same reason that feature is valuable in a DCDC charger.

Another example - cheap Mean Well knockoffs rarely are constant-current capable, which is a major reason MW is preferred. Even within their dozens of different lines, some units have that feature, others don't

e.g. SP-200-24 has constant current limiting, while SP-240-24, does not, just has hiccup style OCP.

I really am tired of y'alls unceasing sniping

but setting that aside, at least do not spread such blatant misinformation while doing so!

I have tried to enlighten you on this specific topic on **at least** five separate occasions, are you just willfully refusing to at least go out and pursue a little verification?

It is very easy to put a stock alt/VR to work charging a high-CAR LFP bank, and with simple tools verify its inability to keep charging at the proper V setpoint as amps demanded by the bank surpasses its continuous output capacity.

You might even see the diodes get fried if it doesn't have good OCP.

[Q Xopa]

Hmmm, I'm not sure your last post is in the forum spirit of 'be nice'?

[Q Xopa]

Originally Posted by john61ct

Sorry, you keep repeating that wrong statement every time the issue arises, but no matter how many times you do, it never becomes any less incorrect.

There are **many** use cases where current limiting is not just valuable but absolutely required, often to protect the power source, often to protect the battery being charged, and sometimes both!

There may be alternative ways to accomplish that goal, so it is true you may not need to necessarily look for that feature in a DC-DC charger.

But for those that do know they need a good one, current limiting is indeed very often the reason why!

Constant current limiting is also a "very" important selling feature in **all kinds** of charge sources and DCDC converters, one of the main selling points rightly justifying higher prices when it is available.

It is such an important feature of Balmar's MC-614 for example, they tout both its "Small Engine mode" and the "Belt Manager" feature, separate multiple implementations of the same general idea in one product!

And for exactly the same reason that feature is valuable in a DCDC charger.

Another example - cheap Mean Well knockoffs rarely are constant-current capable, which is a major reason MW is preferred. Even within their dozens of different lines, some units have that feature, others don't

e.g. SP-200-24 has constant current limiting, while SP-240-24, does not, just has hiccup style OCP.

I really am tired of y'alls unceasing sniping

but setting that aside, at least do not spread such blatant misinformation while doing so!

I have tried to enlighten you on this specific topic on **at least** five separate occasions, are you just willfully refusing to at least go out and pursue a little verification?

It is very easy to put a stock alt/VR to work charging a high-CAR LFP bank, and with simple tools verify its inability to keep charging at the proper V setpoint as amps demanded by the bank surpasses its continuous output capacity.

You might even see the diodes get fried if it doesn't have good OCP.

John, I guess some name calling is ok as nobody has said otherwise to your last post?
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Sorry I also must have missed the memo saying you are the adjudicator of what is right and what is wrong. Like my ‘wrong statement’.
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You are exactly correct on many of the examples you cite.*
Belt manager etc. Im not disputing that. However that’s a different device for a different use case and a little off the B2B topic.
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However, no need to get so emotional resorting to a tirade of name calling like 'willful' and'unceasing sniping' etc.
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I think it is fair that if you are categorically stating something I don’t agree with I can question that. You obviously don’t.
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Or if you are making definite advice we can question how you have derived that definitive conclusion. You often ask others for details yet when you are asked you consider it a personal or business invasion. That’s an interesting business that is off bounds to ask about. Most try to promote as much as possible.
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'Blatant misinformation'. Hmmm. Ok you obviously see this differently to me, that's fine. I can live with that. But just because you say it is 'misinformation' doesn’t make it so.*
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Just like you asserting your opinions many times does not them make it right either.
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Yes I agree that you'vetried to enlighten me '5' times*( thanks for keeping count). Hmm'refusing to pursue a little verification'. Sounds a little condescending don’t you think?
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Like you I spend a fair amount of time trying to learn about this stuff.
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You seem to have a deep need to be right and not challenged.*
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Personally I am often wrong and. I welcome an opposing view and learn a lot from them. I can live with that.
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I’m not sure that your post is in the spirit of the forum 'be nice' rules. In fact cyber bully comes to mind.
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Unlike you I wouldn’t presume to ‘educate’ you as it’s obvious you are way smarter and more experienced than me. Its also obvious you have your position that I could not imagine you changing. That’s all fine.*
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What I don’t want is for your opinion to become unchallenged and be mistaken for gospel for unsuspecting people trying to learn.
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It also doesn’t mean I have to agree you are correct. I think I’m entitled to disagree and offer an alternate view so the other readers can make their own minds up.*
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You proclaiming something is correct is how you roll. I don’t agree that you have the right to judge who is right or wrong any more than I do. I try and offer my point of view instead of telling people it is fact and they should agree with me.
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At least that is my understanding of how a forum should operate.
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I can see you like the B2Bs. That’s fine so do I, in fact I actually own one.
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I’m simply saying that’s not the intended use for a B2B. Yes sure you can use it that way as you are suggesting. But I am simply saying if you want to regulate an Alternator most people simply do it with, as you cite a VR, 614 etc.
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I’m sure there are cases that upgrade to LFPs and don’t upgrade the Alternator and VR. But most that spend the money for the LFP want to get max utilization from them for their hard earned money with trying for more charging than 60A.
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Do you think if Sterling comes out with a 120A B2B for the same price as the 60A people will buy the 60 or the 120A?
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Just my guess but I reckon most would go the 120A. But that’s just my speculation and certainly not worth getting so emotional and resorting to name calling about.