LiFePo4 Power -- Controlling Alternator and Inverter/Charger

[Delfin]

Originally Posted by mikedefieslife

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?

The voltage curve is so flat, that probably wouldn't work real well. At 13.2/26.4 volts resting current, the bank could be anywhere from 30% to 80% SoC.

[mikedefieslife]

Originally Posted by Delfin

The voltage curve is so flat, that probably wouldn't work real well. At 13.2/26.4 volts resting current, the bank could be anywhere from 30% to 80% SoC.

True. That is one of the benefits of LFP. It was my understanding that most people float at 13.2v

[john61ct]

As stated, Maine Sail and others have made the case that floating even at lower voltage may impact longevity and advise to try to avoid that.

This does require greater design complexity in control systems for those who want everything to be automated.

Personally I think a 13.3-13.4V float is an acceptable compromise, if maximising longevity is not of the utmost priority and the other longevity factors are well satisfied.

With precisely accurate charge sources, adjusting from a float of from say 13.32V up to 13.36V, when load currents are lower than input amps, it should be possible to target a desired SoC within 10-20%; great precision is not required.

But ultimately for now I favor the simplest setups, where the attentive human makes decisions, so long as the monitoring is detailed and effective failsafe protections in place to prevent outright damage. In which case a single voltage is fine, no need for it to vary between Absorb and Float, to the point a plain DC converter or other straight power supply is fine, no "intelligent" staged charger is required at all. Having a Reserve lead bank in the mix seems to be a good idea for several reasons.

A fully programmable central controller to take care of everything is entirely feasible at low cost and high reliability for a DIY hacker/programmer willing to put in the effort. The rest of us just need to wait, I am confident FOSS / Open Hardware packaged solutions will emerge in coming years, perhaps if Al Thomason's Wakespeed / APS project is successful that could be his next project.

Yes, for those with convenient high-amp ICE sources on demand, bank sizes can be kept small, under a few days' consumption. They can also keep solar to a low-windage minimum or dispense with it completely out of aesthetic preference.

[mikedefieslife]

Originally Posted by john61ct

As stated, Maine Sail and others have made the case that floating even at lower voltage may impact longevity and advise to try to avoid that.

Longevity and maximising it always needs to be qualified.

Personally I thing it's a waste of time going to some lengths people do to get 9 years from FLA bank rather than 7 years.

Similarly if the LFP banks will only last 1800 cycles rather than 2000 cycles I don't think that is a problem.

[john61ct]

My thinking is 3-5000 is easy, assuming top quality to start with.

Getting to where the banks can be passed down to the grandkids is what I strive for beyond that.

[CatNewBee]

Floating LFP is a non issue, you only have to configure it to the right Voltage, then there will be no charge current and charging will start only, when the battery has lost some Ah to the loads and the voltage drops way below the float voltage, otherwise all current from the charger goes straight to the loads.

It a little religious believing and not based on facts, that float is dangerous to LFP longetivity when daily using the battery.

It is a completly different beast, when leaving the battery in storage connected to a solar charger, it will charge the battery to absorption, then turn off to float, but it will do it every single day, the battery will stay all the time at 100SOC this can well affect longetivity, but it is not the float setting what kills cycles then.

[john61ct]

There is no proof that even lowered voltage Float with no current flow is not to some extent harmful to longevity.

But truly, having the battery isolated from any charge source can be said with certainty to do no harm.

I'm willing to say that belief in either reco is taking it on Faith at this point.

And also concede the overall impact on lifecycles is below the threshold that most owners would concern themselves about, as discussed above.

But for those of us willing to do what it takes to truly maximize longevity, it is an important issue that needs resolving.

And for ordinary users, having a connection to any Float will result in the LFP bank spending a higher proportion of its lifespan at an SoC closer to 100%.

That is in fact very widely acknowledged as being a significant longevity-reducing factor.

[tanglewood]

The whole float issue is based on people not really understanding MaineSail’s statements about the hazards of floating. There is a thread here somewhere in this topic, and I think he concurred that as long as you stop charging the battery, I.e. there is no charge current flowing, then it’s fine.

The confusion is over what people mean by “float”. Some mean “float” to be a continued, low current charge. That is bad for LFP. Others mean “float” to be a reduced voltage charge set point. With a correctly selected float voltage, a charger will carry loads, but not continue to charge the batteries. That is good for LFP.

[tanglewood]

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"?

Yes, that’s correct

Originally Posted by Dockhead

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?

I can’t speak for Delfin, but I believe this is correct.

Originally Posted by Dockhead

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?

I don’t even think that’s necessary. If you connect to mains, the multi will charge to full, then switch to float. The batteries will carry loads and drift down in SOC until it matches the float voltage, then mains/charger will carry loads and batteries will hold at the float SOC.

Then when you get underway, your Balmar will start a full charge cycle and top off the batteries, provided you have enough time motoring.

The only down side is that the top 20% of SOC might not always be available, but that’s the price to maintain the batteries long term at a lower SOC

Originally Posted by Dockhead

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?

Ideally your Balmar can do the top off charge for you with no manual intervention required.

Originally Posted by Dockhead

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

Correct, and one of the compelling reasons to utilize the float capability is chargers.

Originally Posted by Dockhead

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.

I’m not 100% sure, but I don’t think you can invoke float from the CCGX. In fact, I don’t believe you can do any configuration of the Multi other than adjusting the mains power limit.

Originally Posted by Dockhead

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.

Although there is nothing wrong with controlling all this from the BMS, and I actually think that’s where all this will end up in a number of years, I don’t think it’s required if you have reasonably programmable chargers.

[s/v Jedi]

Has anyone here considered separate load- and charge busses instead of a single positive busbar? I am considering multiple smaller LFP 12V units (180-200Ah) each able to connect to charge bus, load bus or both. This allows a lot of flexibility, just like bringing power modules online in Star Trek
Seriously, you could switch 80% charged modules offline as spares or connect one module to the charge bus while the others are only connected to the load bus so that you can do an easy full charge on a module to keep it healthy, etc.

For charging sources, you could even make it possible to connect them to either bus... for example one solar charge controller is used for fully charging a module while the restof the batteries and charge sources are all on the other bus. Would be more like A and B busses in that case.

Wonder what your thoughts are and if this has been considered by you

[john61ct]

Originally Posted by s/v Jedi

Has anyone here considered separate load- and charge busses instead of a single positive busbar?

That is a very common design, and IMO the only way to go.

It does preclude getting PowerAssist style advantages from the use of Combi inverter-chargers, the two functions need to be implemented with separate kit. . .

[john61ct]

Originally Posted by mikedefieslife

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?

Of course, you can do anything you like.

Float is **always** a lower voltage than that used for the two charging stages. Its purpose is usually both to compensate for self-discharge, and to carry concurrent loads.

If your bank tests at say 3.34Vpc **resting** after surface charge removed, then a Float voltage (much) lower than that will result in maintaining a SoC correspondingly below 100%.

But there is no hard data showing there is no resulting "damage" (stress reducing some life cycles off the back end) on the bank by doing so.

So, for those striving to absolutely maximize lifetime, it is better to design the overall system so that the LFP bank is only brought up to high SoC just before loads will require that,

keeping the bank at low "storage "SoC isolated from charge inputs otherwise,

implemented as simply as possible, with redundancy in protection / control systems so as not to threaten reliability, increase the risk of damaging events.

Or babysit our banks manually, as many do, foregoing the standard packaged "BMS" for a minimalist DIY setup.

Again, I concede all such options are considered "dangerous", impractical or just not worth the trouble by most normal LFP owners and prospects.

[john61ct]

Originally Posted by tanglewood

The whole float issue is based on people not really understanding MaineSail’s statements about the hazards of floating.

Those statements are clear, and have remained in his LFP article at http://marinehowto.com despite edits over the years, and the transition from the old site.

> There is a thread here somewhere in this topic, and I think he concurred that as long as you stop charging the battery, I.e. there is no charge current flowing, then it’s fine.

I've been following many forums paying close attention to MS's posts specifically, and do not recall ever seeing such a statement. If it does exist I'd really appreciate a link from anyone.

Here is one to the contrary from not too long ago about his ongoing Float testing, did not keep the link:

" last batch had some major variations in capacity changes between cells, all lost capacity, some quite badly
..
some cell makers claim their cells can be floated without diminishing capacity. Those claims are not what I have seen so far, and this is why I am repeating the test."

_____
Again, just because I keep harping on this particular care factor in maximising longevity, does not imply I think it is a significant factor relative to the more mainstream-accepted factors.

And I keep needing to qualify, those not seeking max longevity, happy with just a few thousand cycles, most of these "finer points" can be completely ignored.

[CatNewBee]

Originally Posted by s/v Jedi

Has anyone here considered separate load- and charge busses instead of a single positive busbar? I am considering multiple smaller LFP 12V units (180-200Ah) each able to connect to charge bus, load bus or both. This allows a lot of flexibility, just like bringing power modules online in Star Trek
Seriously, you could switch 80% charged modules offline as spares or connect one module to the charge bus while the others are only connected to the load bus so that you can do an easy full charge on a module to keep it healthy, etc.

For charging sources, you could even make it possible to connect them to either bus... for example one solar charge controller is used for fully charging a module while the restof the batteries and charge sources are all on the other bus. Would be more like A and B busses in that case.

Wonder what your thoughts are and if this has been considered by you

Bad idea.
And this is why.

A full module has a higher cell voltage than a empty module.
Having modules connected to the load bus, lets say at 50%SOC, getting one module out for charging will deplete the remaining modules even faster, with high loads like inverter, and turned off modules, the remaining will be punished even more, the voltage drop is higher and very likely you will trigger low voltage protection, that can lead to a cascaded shutdown, like the blackout in London recently.

Then the full module connects to this mess with a voltage difference above 1V and very low inner resistance causing high cross module currents due to equalization, this will charge the empty modules on the load bus and somewhat drain the charged module, also stress for unnecessary cycles. You can prevent cross currents by using diodes to connect to the bus bars, but then there will be power loss by heat in high current applications, also the load will be inequally distributed, resulting the drain of the fresh cell first with much higher current due to the higher module voltage.

You can mitigate this by usung b2b charger per module and limit or control the currents but is it really worth it?

To answer your question,
Yes, I have a separate charge bus, load bus and inverter charger bus, that is a mix of both, but separately controlled by the BMS. I use a single 4S 1000Ah LiFeYPO4 battery, so no mess with cross currents. The battery is connected in normal conditions to all three busses, allowing direct supply from charge sources to loads - another advantage of this dessign. Busses are only separated and disconnected in case of an unusual cell voltage ot cell temperature to protect the battery.
Another advantage of having the busses combined in normal operation is, all charge sources contribute directly to the energy balance and feeding the loads before current is flowing into the battery, what leads to less and shallower cycles, resulting in a longer life.

[Flod]

My system have proved to work really well this summer given my use case. I have been out 45 days with only 4 days with shore power. 150w of solar and standard hitachi 80A Alternator as the main charge sources. We normally spent 1-3 days in the same spot and then motored/sailed to the next. My BMS LVC never kicked in. The HVC did kick in a lot but mostly I used my manual switch (which overide the BMS HVC). Especially when motoring for longer periods I just shut the charge relay off after like 2 hrs. Worked very well and the battery is now like the water tanks. I fill them up to a level which is correct given the plans for the coming days. My 123bms HVC is a little low since it cuts the charge relay when all cells are over 3.40. I think this might be a little low but as said I can overide this with my manual switch. Now the boat is in the dock and the bank is at 44% and I plan to keep it that way so the manual charge switch is off Long text but I think my combination of Sterling Pro alt C, 123BMS, 123 dual relay and manual overide switch is a good and practical solution that have proved to work. No floating. Just charge and then stop.