LiFePo4 Power -- Controlling Alternator and Inverter/Charger

[tanglewood]

Originally Posted by Dockhead

The main thing is you will need a manual control to allow you to charge full if you are going to need all the capacity, or charge to 70% or whatever and stop, if you are not going to need all the capacity and don't want the battery sitting fully charged.


Is this possible with available charging control gear? For me, that is the very question.

You understand all this quite well, in fact much better than most people, including your understanding of floating LFP.


Most chargers can be programmed to run through a charge cycle suitable for LFP, then kick down to a float voltage programmed to stop charging, but carry loads. It's a perfectly acceptable, if not desirable way to manage power, and seems to be exactly what you are looking for.



In most cases I don't think you need to force the charger(s) to float, as most can be programmed to do so on their own. However in practice thare are a number of things to watch out for.


- Some chargers want to be in absorb for longer than you might otherwise select for LFP. You Multiplus is a good example, with a minimum absorb time of 1hr. It does also have the ability to force a switch to float provided you have something to control it. If your BMS has a suitable output, that's a viable path. Otherwise you will have to live with the 1hr absorb, which is probably just fine.


- Most LS chargers want to periodically switch back to bulk/absorb and run through a new full charge cycle. This is undesirable with LFP. Ideally the charger would float forever, but most don't. Some restart when voltage drops below a certain level. This may work really well with LFP since it's better at holding voltage. But you will just have to look at the threshold vs you desired float voltage to see what it might do. Other chargers restart a full charge cycle once a day, or once a week, or based on some other timer. Stretch this out as long as possible, if you can. If you can't get around it, lower your float point a bit so the batteries can fall a bit further before they get a full recharge.


- Some chargers like the Balmar restart the full charge cycle when they see a certain current load level. I think this is quite undesirable, so set the threshold as high as possible (ffl parameter for Balmar).


I think the bottom line is that you need to evaluate each charger to see how it will behave when running for an extended time. This can be an inverter/charger on mains, an alternator on an extended motoring run, and solar when it can readily reach full battery charge.

[a64pilot]

Now I’ve not read many or most of the 41,000 Lithium threads, but from being around one or two of the other larger Lithium batteries there are some commonalities among them.
A BMS is always used, this BMS monitors cells individually and charges by cell or at least by paralleling cells, once a bank is near full it will begin to balance cells by disconnecting each cell as it becomes full, and full is never really full, they always stop well shy of full voltage.
A good BMS will control the current in charging and limit it on discharge as well as of course have high and low voltage limits and temp monitoring .

I can’t imagine why with boats that people aren’t balancing and or using as sophisticated a BMS as even people who put motors on bicycles are.
https://www.electricbike.com/bmss-what-do-they-do/

It’s why I’m waiting, I believe it will mature and there will one day be a true drop in replacement, yes it will require all charge sources to be programmable, and alternator cut off is easy, not at all hard to do.

I assume that the market just doesn’t exist, but I’m surprised no one is selling “kits” or you go to them and they install systems.

I’d expect the real market is the million dollar Cats that want to run air conditioning off of batteries.

You don’t need or want to be able to manually override the BMS and overcharge the bank, just size the bank correctly and live within its capacity, just like we do now.

[DeepFrz]

Dockhead, you might be interested in this video, or not. He talks a bit about BMS.

https://www.youtube.com/watch?v=gOqQp2Xjr6U

[Delfin]

Originally Posted by tanglewood

You understand all this quite well, in fact much better than most people, including your understanding of floating LFP.


Most chargers can be programmed to run through a charge cycle suitable for LFP, then kick down to a float voltage programmed to stop charging, but carry loads. It's a perfectly acceptable, if not desirable way to manage power, and seems to be exactly what you are looking for.



In most cases I don't think you need to force the charger(s) to float, as most can be programmed to do so on their own. However in practice thare are a number of things to watch out for.


- Some chargers want to be in absorb for longer than you might otherwise select for LFP. You Multiplus is a good example, with a minimum absorb time of 1hr. It does also have the ability to force a switch to float provided you have something to control it. If your BMS has a suitable output, that's a viable path. Otherwise you will have to live with the 1hr absorb, which is probably just fine.


- Most LS chargers want to periodically switch back to bulk/absorb and run through a new full charge cycle. This is undesirable with LFP. Ideally the charger would float forever, but most don't. Some restart when voltage drops below a certain level. This may work really well with LFP since it's better at holding voltage. But you will just have to look at the threshold vs you desired float voltage to see what it might do. Other chargers restart a full charge cycle once a day, or once a week, or based on some other timer. Stretch this out as long as possible, if you can. If you can't get around it, lower your float point a bit so the batteries can fall a bit further before they get a full recharge.


- Some chargers like the Balmar restart the full charge cycle when they see a certain current load level. I think this is quite undesirable, so set the threshold as high as possible (ffl parameter for Balmar).


I think the bottom line is that you need to evaluate each charger to see how it will behave when running for an extended time. This can be an inverter/charger on mains, an alternator on an extended motoring run, and solar when it can readily reach full battery charge.

FWIW, Lithionics recommends floating at 13.4/26.8 vdc, with loads less than 2% of capacity during float.

[john61ct]

If you are going to float LFP, 13.40V after going to Full will allow loads to pull SoC down back below 85% - a good thing.

If it's getting late in the day and you want to stay higher, 13.60V or even 13.65V will keep above 90% as long as loads are light.

Of course when loads are higher current rates than what the charge source is putting out, go back up to Absorb if you want SoC high by evening.

Ideally an intelligent microcontroller could automate these "judgment calls", but for most that would run counter to failsafe reliability as a much higher priority.

Going to a higher capacity bank allows for greater flexibility and less stress staying up at near-Full SoCs too many hours a day.

[tanglewood]

Originally Posted by Delfin

FWIW, Lithionics recommends floating at 13.4/26.8 vdc, with loads less than 2% of capacity during float.

That seems to be a commonly selected float voltage (Lithionics, Victron, MG, etc.), and is what I'm using as well.



The load limit is interesting, though. I haven't seen that before, and wonder what's behind the recommendation.

[Dockhead]

OK, so I guess then to summarize:


Do we all agree that floating at 13.4/26.8 will support loads without changing the state of charge of the batteries. So no need to "isolate the batteries from the charging source"?


If that is the case, then setting a regulator like Balmar or a charger like Victron Multiplus with the appropriate float voltage, can automatically charge a LiFePo4 bank to whatever state of charge we consider "full" using whatever program, by sensing voltage and charging current? Are we happy that these charging programs? This is what you are using, right Delfin?


So if that's all true, then ALL we need is a MANUAL control to kick either device into float, whenever we do not desire a "full" charge on the battery, such as when we are on shore power and plan to be docked for a while, right?


In that case then we can just switch over from float to charge when we're a few hours from casting off, and charge up the batts so that we leave the dock with a full charge, but weren't shortening their lives by holding them at full unnecessarily when shore power was abundant. Right?


And we retain full use of Power Boost even when we are sitting intentionally on partial charge.


If all this is true, then this looks like a perfectly satisfactory way to manage these batteries, and all we need is the actual control.



I can force my Multiplus to float with a certain manipulation of the standard controller; perhaps it is easier with the Color Controller GX.


What about the Balmar MC 612, or is there another regulator which lets you manually force the alternator into float? Perhaps that is less important since we don't use the alternator at the dock.


I was thinking that alternator regulator and Multiplus need some signal from the BMS to know when to go into float, but maybe they are capable of figuring that out for themselves? Views? I have read the Batrium manuals and didn't see where this very sophisticated BMS gives such a signal.

[Dockhead]

Originally Posted by john61ct

If you are going to float LFP, 13.40V after going to Full will allow loads to pull SoC down back below 85% - a good thing.

If it's getting late in the day and you want to stay higher, 13.60V or even 13.65V will keep above 90% as long as loads are light.

Of course when loads are higher current rates than what the charge source is putting out, go back up to Absorb if you want SoC high by evening.

Ideally an intelligent microcontroller could automate these "judgment calls", but for most that would run counter to failsafe reliability as a much higher priority.

Going to a higher capacity bank allows for greater flexibility and less stress staying up at near-Full SoCs too many hours a day.

One judgement call which I would certainly like to automate somehow if possible is maintaining a given SOC in "float". I don't know why that would compromise reliability.



But otherwise I think none of it is a big deal -- I think lithium will be much much lower stress than lead because it's just not that big a deal. If you find yourself low on power just fire up the generator and POUR power into the bank and shut off whenever you want without worrying about finishing charges or any of the rest of that crap.



So with that in mind, and coming full circle, I guess it's perhaps not even a big deal if the SOC drifts down during float because some occasional bigger loads pull it down. So many of the lead problems are absent from lithium that it's hard to change the mentality, isn't it? I'm not sure an extra large bank is needed -- it's just such a not big deal to get power into the batteries, who cares? I'm thinking 300 amp/hours @24v is going to be just fine on my boat -- with 140 amps of charging capacity, always on tap because there is not tapering off of the charge, and with a 100 amp alternator (which I will probably derate to 80 or 90 amps), there is just so much power available so fast, that you just won't worry any more if the batteries start to get low. So even this mentality and the idea of really big banks may need to be shedded.


The basic purpose of the battery bank is to allow blissful silent life running off batteries. A giant bank is not necessary if huge amounts of power can be put into your bank in short periods of time. So what if you run the generator a little even twice a day?


Where a large bank would really be nice however would be bringing a nice big load of shore power with you when you leave the dock, or harvesting a bunch of nearly free power from your main engine after you've been motoring. Of course more is better. But that's not a big enough deal, it seems to me, to be worth spending huge amounts of money on a giant lithium bank. The great purpose of lithium bank is already served even with a relatively small one. It's hard to wrap your brain around it after a lifetime of cruising with Dr. Frankenstein Victorian lead technology.

[Skip JayR]

Just like to share an article I just read about latest research of Lithium-Ion batteries and alternative materials, e.g. Sodium. Sounds promising for me.

https://oilprice.com/Energy/Energy-G...Batteries.html

[Q Xopa]

Originally Posted by Dockhead

OK, so I guess then to summarize:


Do we all agree that floating at 13.4/26.8 will support loads without changing the state of charge of the batteries. So no need to "isolate the batteries from the charging source"?


If that is the case, then setting a regulator like Balmar or a charger like Victron Multiplus with the appropriate float voltage, can automatically charge a LiFePo4 bank to whatever state of charge we consider "full" using whatever program, by sensing voltage and charging current? Are we happy that these charging programs? This is what you are using, right Delfin?


So if that's all true, then ALL we need is a MANUAL control to kick either device into float, whenever we do not desire a "full" charge on the battery, such as when we are on shore power and plan to be docked for a while, right?


In that case then we can just switch over from float to charge when we're a few hours from casting off, and charge up the batts so that we leave the dock with a full charge, but weren't shortening their lives by holding them at full unnecessarily when shore power was abundant. Right?


And we retain full use of Power Boost even when we are sitting intentionally on partial charge.


If all this is true, then this looks like a perfectly satisfactory way to manage these batteries, and all we need is the actual control.



I can force my Multiplus to float with a certain manipulation of the standard controller; perhaps it is easier with the Color Controller GX.


What about the Balmar MC 612, or is there another regulator which lets you manually force the alternator into float? Perhaps that is less important since we don't use the alternator at the dock.


I was thinking that alternator regulator and Multiplus need some signal from the BMS to know when to go into float, but maybe they are capable of figuring that out for themselves? Views? I have read the Batrium manuals and didn't see where this very sophisticated BMS gives such a signal.

Yes I believe you are correct with what you are saying regarding 'Float' and Charge settings.

However re Isloating the Charge sources from your LFP bank is still usually done, generally by a BMS at a Voltage higher than the Absorb or Float levels.

But it is not a normal situation. Its is only when one of the charge sources fails to stop charging at our set voltage. Its only there to stop cooking cells if a charger fails to the high side.

I hadn't considered it before but it sounds correct what you are saying about effecting Assist mode.

If you had those sorts of loads demands pulling your house LFP bank down, you would soon be back below HVC voltage levels and connected again in short order.

[Dockhead]

Originally Posted by Q Xopa

Yes I believe you are correct with what you are saying regarding 'Float' and Charge settings.

However re Isloating the Charge sources from your LFP bank is still usually done, generally by a BMS at a Voltage higher than the Absorb or Float levels.

But it is not a normal situation. Its is only when one of the charge sources fails to stop charging at our set voltage. Its only there to stop cooking cells if a charger fails to the high side.

I hadn't considered it before but it sounds correct what you are saying about effecting Assist mode.

If you had those sorts of loads demands pulling your house LFP bank down, you would soon be back below HVC voltage levels and connected again in short order.

Yes, I'm not discussing the High Voltage Cutoff at all. That is a different, emergency function which ideally will NEVER be triggered. This is just to save the battery in case of a failure of the other control systems. The charging sources should stop charging when the battery is "full", that is 90% or whatever we have planned on as "full".


What you say about Power Boost however seems right and seems to screw up my idea. That will be enough of a load that the charger will kick back into charging mode every time it's used. Damn.



So my idea won't work unless we have some way to force float which will persistently force float mode. I don't know if the Victron can be set for that at all.


Anybody have any other ideas?

[Kenomac]

It appears that you’ve opted for the design by committee method.

[Viking Sailor]

DH,


If you connect the output of a charger to the input of an inverter while charging the battery you have implemented power boost. Just like floating the battery while using the inverter to supply AC current.

[Delfin]

Originally Posted by Dockhead

OK, so I guess then to summarize:


Do we all agree that floating at 13.4/26.8 will support loads without changing the state of charge of the batteries. So no need to "isolate the batteries from the charging source"?


If that is the case, then setting a regulator like Balmar or a charger like Victron Multiplus with the appropriate float voltage, can automatically charge a LiFePo4 bank to whatever state of charge we consider "full" using whatever program, by sensing voltage and charging current? Are we happy that these charging programs? This is what you are using, right Delfin?


So if that's all true, then ALL we need is a MANUAL control to kick either device into float, whenever we do not desire a "full" charge on the battery, such as when we are on shore power and plan to be docked for a while, right?


In that case then we can just switch over from float to charge when we're a few hours from casting off, and charge up the batts so that we leave the dock with a full charge, but weren't shortening their lives by holding them at full unnecessarily when shore power was abundant. Right?


And we retain full use of Power Boost even when we are sitting intentionally on partial charge.


If all this is true, then this looks like a perfectly satisfactory way to manage these batteries, and all we need is the actual control.



I can force my Multiplus to float with a certain manipulation of the standard controller; perhaps it is easier with the Color Controller GX.


What about the Balmar MC 612, or is there another regulator which lets you manually force the alternator into float? Perhaps that is less important since we don't use the alternator at the dock.


I was thinking that alternator regulator and Multiplus need some signal from the BMS to know when to go into float, but maybe they are capable of figuring that out for themselves? Views? I have read the Batrium manuals and didn't see where this very sophisticated BMS gives such a signal.

No, that isn't my use case. I do have the Balmar 624 set to float at 26.8 v, but that is only if I forget to take the LFP bank off line after it is "full". If you have both house and starter banks, then you don't need to worry about whether floating is good or bad for the longevity and performance of the LFP bank. While I can't see an electrical reason why it should be bad, people I respect with a great deal more experience I have, like Mainesail, recommend against it, or so I recall.

With a LA starter battery plus the LFP bank there are only three situations I deal with.

1. I'm underway and charging the LFP bank. When it is full based on charge acceptance rate and voltage I flip a switch on the ACR and turn off the BMS of the LFP bank. Now charge current flows to the LA bank. No float required for the LFP bank, and the LA bank can go to float whenever the parameters of the 624 are met.
2. I'm at the dock on shore power. The LFP bank is isolated because the BMS is depowered and the charge current from shore power is going to the LA bank. Again, no float required for the LFP.
3. I'm without shore power, as in at anchor or a dock without it. House loads are supplied by the LFP bank, and when it needs charging I fire up the genset for a couple of hours. When full, I shut down the genset.

It is all very, very simple and I do think that there has been a tendency with this new technology to make it more complicated than it needs to be.

If I had solar, it wouldn't supply enough to power our energy hungry cruising, but might be nice to have as an additional source of energy. Since it wouldn't keep up with our consumption, I also wouldn't have to worry about floating the LFP but could extend the time between genset recharges.

If you go the forced float route, and I don't know why anyone would if you already have two banks, the Balmar is not your huckleberry, at least not out of the box. Too fiddly to change the charge parameters and I think that is what you would have to do to accomplish that objective when you wanted to maintain a partial SoC in the bank.

Regarding sizing I've found that 2X daily consumption seems to work well. I charge every day or day and a half, and that is with two freezers and a refer running. We use the genset time to cool the boat if needed with a/c, do laundry, make water, etc., so it is a necessary event regardless of what type of batteries we have. Having LFP just means that battery charging happens in the minimum amount of time, and that is a real blessing.

[mikedefieslife]

Originally Posted by john61ct

If you accept the premise that your LFP bank should not be floated

there is no need to complicate things by varying voltage levels.

It is just a question of isolating the bank from charge sources when it gets to your desired "working Full" definition whatever that is.

Then bringing the LFP bank online to the loads buss when charging source input current is lower than what loads require.

None of this implies a "float voltage" different from the charging setpoint.

Can't you just set float to a point lower than the battery resting voltage at say 30-50% then there is no need to disconnect?