LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[daddle]

On the charging subject: for me anyone who discusses absorption, acceptance and float in relation to LFP disqualifies themselves. Those are LA concepts (poorly implemented by over zealous marketers) that do not apply in any way to LFP health.

LFP health is controlled by ideas like "charge processed", "state of charge" and such terms that do not equate well to the Neanderthal mindset of our favorite marine equipment manufacturers. They will be slow in coming up with good solutions. They probably do not even understand the problem. Most have never even been in a boat....

[goboatingnow]

Originally Posted by ebaugh

There are questions that need answering, but until the answers are known, I don't think it's that hard to program today's chargers to work. In the meantime, conservative values with only a slight reduction in capacity works around the issues.

Can you define "nominal cell value", used above? Is that 3.2V, the published nominal value, 3.4V the approximate full charge resting value, or something else?

Many Many pages back there is a link to a presentation by professor Dr. Jay Whitacre, explaining the chemistry in almost plain language. But what I got out of this...I think my own analogy though...is the charging/discharging process could be like a sand (electron) filled hourglass. Turn it one way to charge the other way to discharge, but always make sure there is some sand on both sides. Floating turns the hour glass on its side. Running out of sand on either side causes problems since there is no more sand to move. But theoretically, there is little "wear" caused by moving the sand until you run out.....

I think the floating issue is a need to discover the value that does not move sand either direction. So much research is done with the little 2Ah cells, but if you have 1200Ah, leave some sand to build a buffer. A few milliamperes takes a very long time to overcharge if you leave 100Ah on the top. And what is a micro cycle for a 1200AH cell? It would seem that capacity would have some impact, perhaps significant.

I promise to read anything you can provide links for....Bob

Bob , have a read through the whole Lithium section on Battery University website ( maintained via Cadex), in particular the charging section in realtion to Li. I post some links next week when Im back at work

While my professional designs are all involving LiCo and some LiMn I have some LiFe cells for experiments. All my designs are small capacity designs at the moment.

At a simplistic level , charging in Li is not chemical, more involving ion movement, hence charging ( ion movement) takes place once any electrical field is present. If the cell is already at full, this is not a good thing as plating occurs , which results in lost capacity, exposes the cell to voltage stress and subsequent charges risk overcharging the battery.

Ok in LiFe at least we have more cycle life to play with as opposed to the typical 500 full cycles in cheap LiCo. Also at least the thermal profile is safe (safer) .

The issue here for me and load sharing , is that in LiCo/Mn the reccomended approach now, is isolating the battery behind an "ideal diode" ( mosfet). Obviously this has limits for high capacity designs. But still the evidence is that this is the best way to load share and hence also charge. ( have a look at Microchip, Maxim and LTC application notes )

For high capacity LiFe, I think load sharing represents a lessor risk, possibly leading to capacity loss, but we simply don't have enough feedback to really know,

My personal professional opinion is that cells should be conservatively charged to about 80%, load sharing should occur at the cell nominal value, preferrably via diode isolation ( maybe we need a 200A ideal diode design here !). Since this is difficult with current marine chargers, in effect we need a PSU and charger combined.

So, that leaves us picking what voltage the charger should adopt under load sharing.

My great concern reading this thread , is users using conventional LA charging sequences (often with LA charging mentality) and either tweaking them or using them as is and thinking all is well. ( well for how long). AT best we could see much shorter then expected life times or unexpected loss of capacity or both.

I agree with the previous poster, talking about bulk, absorption, float is completely wrong with Li

I think we need to begin investing isolating the load sharing and charging as it applies to the marine environment.

Dave

[roetter]

Here are two typical cruising scenarios as we experience them. Let me know what we should consider doing.

1 at anchor or sailing - early morning. Batts are fairly empty from all the night usages. Generator is started to charge batteries, run water maker, water heater, laundry, etc. Charging should be stopped at about 80% full. At 700Ah that leaves 140 Ah to top off. Solar is taking over consumption load during the day and adding about 150Ah on a good day into the battery.
This cycle repeats every day. Good for the batts.
I don' see a problem here.

2 underway with no wind - running under engine all the time. 2-3 days would be the worst case scenario I can imagine.
Engine alternator delivers 80 A max for the next 72 hours.
If the batts are really low, would the alternator survive the high demand? Standard Hitachi on a Yanmar with internal regulator.
If the batts are full at start, the alternator can deliver at max 60A above usage (worst case scenario). For LA have measured 13.2V arriving at the terminals when pumping 20A. Is there a chance of over charging at that voltage. Should there be a disconnect switch installed nr the field. Maybe on a timer set to 3 hours, so the batts can drain somewhat before being subjected to additional charging.

Any other ideas?

[goboatingnow]

1 at anchor or sailing - early morning. Batts are fairly empty from all the night usages. Generator is started to charge batteries, run water maker, water heater, laundry, etc. Charging should be stopped at about 80% full. At 700Ah that leaves 140 Ah to top off. Solar is taking over consumption load during the day and adding about 150Ah on a good day into the battery.
This cycle repeats every day. Good for the batts.

No need to charge Li to 100% , in fact leaving them at 85-90% improves life and reduces voltage stress.

If the batts are really low, would the alternator survive the high demand? Standard Hitachi on a Yanmar with internal regulator.

probably not, they will derate or inadequately cooled run hot

If the batts are full at start, the alternator can deliver at max 60A above usage (worst case scenario). For LA have measured 13.2V arriving at the terminals when pumping 20A. Is there a chance of over charging at that voltage. Should there be a disconnect switch installed nr the field. Maybe on a timer set to 3 hours, so the batts can drain somewhat before being subjected to additional charging.

Li should not be charged when already full.


Dave

[hellosailor]

"For LA have measured 13.2V arriving at the terminals when pumping 20A."
While that might be working out nicely, 13.2v would indicate a fairly large voltage drop compared to the 14.4 a standard integral Hitachi puts out. Even at idle it should put out 13.8 as a minimum, so it might pay to look into where your voltage drop is coming from.

[ebaugh]

Originally Posted by roetter

Here are two typical cruising scenarios as we experience them. Let me know what we should consider doing.

1 at anchor or sailing - early morning. Batts are fairly empty from all the night usages. Generator is started to charge batteries, run water maker, water heater, laundry, etc. Charging should be stopped at about 80% full. At 700Ah that leaves 140 Ah to top off. Solar is taking over consumption load during the day and adding about 150Ah on a good day into the battery.
This cycle repeats every day. Good for the batts.
I don' see a problem here.

2 underway with no wind - running under engine all the time. 2-3 days would be the worst case scenario I can imagine.
Engine alternator delivers 80 A max for the next 72 hours.
If the batts are really low, would the alternator survive the high demand? Standard Hitachi on a Yanmar with internal regulator.
If the batts are full at start, the alternator can deliver at max 60A above usage (worst case scenario). For LA have measured 13.2V arriving at the terminals when pumping 20A. Is there a chance of over charging at that voltage. Should there be a disconnect switch installed nr the field. Maybe on a timer set to 3 hours, so the batts can drain somewhat before being subjected to additional charging.

Any other ideas?

I agree with Dave, on problem with 1, no worries.

Number 2 depends on if it continues to charge. You can experiment and see if it stops charging depending on your other loads underway. Otherwise, buy a controllable regulator, or replace the alternator. I have 2 of these:

http://www.prestolite.com/pgs_produc...uct=Alternator

They work, can have the output voltage adjusted on the pot in their internal regulator, and can be found for just over $200 in the US from distributors, looks like they are harder to find in Europe. There are a couple of variations of this with the same controller. They don't put out anywhere 90A with LFP connected and adjusted properly, but won't overrun either. Temps are fine so far, but might present a problem if the LFP was below 25% SOC, I have not tested that yet.

Disconnecting the field will work, but it's more manual than I'd like to see.

[diugo]

So are we basically giving up on all floating---even well below 3.38 volts per cell?

[Maine Sail]

Originally Posted by goboatingnow

I agree with the previous poster, talking about bulk, absorption, float is completely wrong with Li

I think we need to begin investing isolating the load sharing and charging as it applies to the marine environment.

Dave

Bulk is any time before you've reached a "limiting voltage" this applies to all CC/CV chargers. When charging a Li bank it is in BULK most of the time. Absorption is simply a voltage limit, call it CV if you like.

IMHO the question should be:

With a Li bank we are in bulk 99% of the time, on most boats with inadequate charging capacity. Once we get to "limiting voltage" how long do we stay there? Is this driven by time or current? After the limiting/absorption/CV stage voltage where do we go and how do we again re-trigger "charging"...

There is still bulk and absorption/CV what happens after that is the real question.

You can still easily program some better chargers & regulators for absorption and then a float at a voltage that is below the resting voltage of the bank. Programming float at below resting voltage simply turns off charging after your CV stage. I have done this with my Balmar regulator and so far it seems to be doing its job, other than losing the tach when the regulator cuts the field, because voltage is above the "float" level that I set it for.

I have found that when the charger/controller kicks back on, with a voltage drop to the "float level", the charger goes right back to absorption/CV because it can't bring up the voltage quickly enough due to the current the bank is willing to take (this depends upon where you set "float" on a "smart" product.. This seems to make a programmable charger/controller/regulator a CC/CV/OFF charger.

I asked a while back for input on this but got little. I have done my own experimenting and found this to work with the Balmar MC-614. I'm awaiting Rogue's new solar controller so I can test it... In the mean time I really need to send my Genasun controller back to Cambridge for custom
programming...

[ebaugh]

Originally Posted by diugo

So are we basically giving up on all floating---even well below 3.38 volts per cell?

I'm not convinced yet. What we need is controlled experimental data for LFP that indicates this behavior, and Im not sure it exists to support or deny the problem. I do still need to read a couple of things Dave mentioned in his last post.

Until I see proof otherwise, my gut feeling with a modern regulated shore power charger anything below 3.38 will not cause any issues. The battery sees essentially zero current flow, so I can't see where the battery can tell its even connected to a charger.

Ask me August next year...by then I will have 1 year of "float", probably at more like 3.33-3.35V with a capacity test before and after, but that adds little today...and even then a small difference could be related to cell aging and not float since there is no baseline.

[rainmaking]

Since it is hard to figure out what is going on with an alternator while under somewhat ambiguous loading and charging conditions, how about this as an experiment:
While underway on a long run, once the bank reaches a SoC that puts it near the regulated limit of the alternator (hopefully ~3.4V/cell), shut everything down--engines and loads--and check the resting voltage of the bank. Even better, the individual cells if you are all in series. Do this and then run another hour and do it again...see if the resting voltage is climbing.

If it isn't, you aren't bringing the cells above ~90% SoC or their 'knee'. This would be ideal. If they do continue to climb into their knee then you know more attention will need to be paid to controlling the alternators, like shutting off their fields.

[ebaugh]

Originally Posted by Maine Sail

I have found that when the charger/controller kicks back on, with a voltage drop to the "float level", the charger goes right back to absorption/CV because it can't bring up the voltage quickly enough due to the current the bank is willing to take (this depends upon where you set "float" on a "smart" product.. This seems to make a programmable charger/controller/regulator a CC/CV/OFF charger.

I asked a while back for input on this but got little. I have done my own experimenting and found this to work with the Balmar MC-614. I'm awaiting Rogue's new solar controller so I can test it... In the mean time I really need to send my Genasun controller back to Cambridge for custom
programming...

I don't have solar to play with...and my alternators are stupid...

But my Xantrex/Trace designed MSW inverter charger works like I want it to with the AGM settings, albeit a little higher voltages, it does CC to 14.4, CV at 14.4 for 60 mins, then CV forever at 13.4.

This translates to, measured at the battery vs the charger to CC 100A to about 13.9, then reducing current to about 14.2V, then off until 13.4, then CV at 13.4V. The cycle does not reset when 13.4 is reached. The charger just covers any DC loads present at the time.

I'm not sure why a good smart alternator regulator could not do the same? You could try setting absorption and float to the same value? Might sacrifice a little charge, but not much.

I do have the tach problem you described on my dual alternator system with a near full battery, but only on the weakest side. I've never been able to find the exact setting that keeps them both in very low output mode...but I can tell from the fly bridge when my wife heats a cup of coffee in the microwave since the tach comes back for a couple minutes. I have an engine monitoring system also connected in parallel using the same alternator tach senders, but it continues to work, so it must be a weaker, but not non existent signal. This behavior is not specific to LFP, it did the same thing with LA.

With solar, since the rates are slow, I think you will want a lower value to end "CC" bulk portion and no absorption CV, straight to float CV. I think I would use 13.8 and 13.4. Then ideally if the voltage fell to 13.2 or lower for 30 minutes, reset to 13.8 bulk mode and repeat.

[ebaugh]

Originally Posted by rainmaking

Since it is hard to figure out what is going on with an alternator while under somewhat ambiguous loading and charging conditions, how about this as an experiment:
While underway on a long run, once the bank reaches a SoC that puts it near the regulated limit of the alternator (hopefully ~3.4V/cell), shut everything down--engines and loads--and check the resting voltage of the bank. Even better, the individual cells if you are all in series. Do this and then run another hour and do it again...see if the resting voltage is climbing.

If it isn't, you aren't bringing the cells above ~90% SoC or their 'knee'. This would be ideal. If they do continue to climb into their knee then you know more attention will need to be paid to controlling the alternators, like shutting off their fields.

You can try this, but I would set a fixed timeframe, perhaps an hour to measure the resting voltage. Which maybe too long depending on where you are? Thats a compromise timeframe, Ive read it takes 24 hours or so to get a good read on resting voltage.

I think you also need an amp meter in the circuit to the battery to detect when charge goes to zero or near zero amps to know when to initiate the test. But overall, if you are still charging, the voltage will rise eventually. If not charging and the voltage is constant, I'd be very surprised to see a difference in rested voltage, especially after 24 hours in the test described. If there was a difference, it's going to take a very sensitive DVM to measure with any accuracy.

[daddle]

You don't want anything like a "float" charge if a requirement is long life. LFP will have a longer life if the average SOC is in the middle of the capacity range. That is what the research says. Against that, one wants to minimize the cycles, the in and out total.

The research advice is to not charge any more than is required to satisfy the next discharge cycle. While doing proper cruising probably charge all the way while one can. Then discharge as necessary. While languishing in purgatory, at the dock, turn down the charger to some middle C voltage. Use a shore charger that can run the small regular loads to minimize the demand on the battery.

How this is done in the yachting lifestyle is not obvious. Maybe better to just not worry about it. Even less than ideal lifetime is better than LA.

[rainmaking]

I would think a relative measurement would still tell you whether charging is occurring. Stopping in the middle of the ocean for an hour with no power may be inconvenient...��

[FlyingCloud1937]

While it might seem counter intuitive, I think the real answer is going to be going back to 2 banks with the old 1-2 all switch.

A charge bank and a discharge bank. Sized for the 24 hr load with some headroom. It's going to be more expensive having 2 banks, and more hands on management.

But it does solve the floating issue. It also offer some level of redundancy.

Lloyd