LFP FLA hybrid

[ramblinrod]

Originally Posted by evm1024

Oh and by the way. Perhaps you could address the point of my post i.e. Mailesails reasons for not consulting remotely rather than offering up the voltage sag strawman.

I'm sorry, responding to this nonsense is just not worthy of my time.

[ramblinrod]

Originally Posted by Delfin

With LFP, when the voltage drops below 13 v with a .1C discharge rate, you are approaching the lower knee. Why on earth would you want to hear motors slowing down, exposing PCBs to damage, as the indicator that you need to recharge?

Are you saying that voltage sag is a virtue?

I meant exactly what I clearly posted.

[evm1024]

Originally Posted by ramblinrod

Knock off the insults. You are the one in error here.

I may be in error or I may not be. Please do take the time to refute my assertions.

In regards to insults, none have been given, at least not by me.

I am here on this thread to learn something and to share what I know. When I post I expect that people who disagree with me to use logic, reason and facts to show me my error.

So how did I get here?

Dockhead said

Originally Posted by dockhead

Exactly. If the fear is that a LVC event may occur because of operating heavy loads when the bank is at a low SOC -- lithium has almost no voltage sag and won't trigger a LVC unless the battery is really empty.

As MaineSail said -- we have to forget what we know about lead batteries.

It is clear that we are talking about a voltage sag induced by heavy loads which is common in FLA and not likely in LiFePO4. Also, Mainesail is quoted.

To which you reply:

Originally Posted by ramblinrod

Well there is certainly "disconnect" somewhere, because Mainsail won't even consult remote customers on LFP anymore because too many were zapping their electronics and trashing their LFP banks.

IN that post you imply that Mainesail does not support LiFePO4 and implied that it was because of too many were zapping their electronics. Which again supposes a voltage sag causing a bank disconnect.

I responded in the next post refuting your assertions by quoting mainesail and stating that LiFePO4 does not sag (and thus no disconnect) and thus no zapping....

Originally Posted by evm1024

I no longer do any long distance consulting or design work for LFP batteries or systems. If the boat is not readily accessible here in Maine, Casco Bay to be specific, I can no longer do LFP consults. Why? Far too many owners insisting on cutting corners and multiple situations where end user implementation was not done to the design or design criteria have forced my hand. If you happen to glean something from this article, that’s great, but please don’t email me with further consulting questions on LFP.

So the disconnect is in understanding why mainesail does not do long distance consulting.

The disconnect is when someone uses what they know about FLA to make choices with LiFePO4. Simple things like assuming that the LiFePO4 voltage will sag at low SOC (what is low SOC? 20%?).

Further, you state in a later post that the fans etc slow down due to a voltage sag. It appears that you are still stuck in the FLA mindset.

Originally Posted by ramblinrod

Not having some voltage sag and things slow down to warn diminishing capacity, probably makes an under load cut-off event more inevitable.

Then you assert that you were not speaking about a voltage sag.

Originally Posted by ramblinrod

But nobody assumed voltage sag from LFP.

Which for the life of me is puzzling. You say that the bank will be disconnected but a BMS uses voltage to trigger a disconnect (that is all they typically measure). How do we get a disconnect if we do not have low voltage? How do we have low voltage if not a sag?

We know that LiFePO4 holds it voltage quite constant until the bank is nearly depleted. So if not a sag then you are suggesting that the boater just ignore the alarms and run the bank to zero. Which of course is just a false narrative. A strawman if you will.

Given the unrealistic nature of your assertions so far I counter stating that:

Originally Posted by evm1024

Nobody assumed it. You postulated it.

regarding voltage sag and suggested that you are still thinking in terms of FLA and need to up knowledge base.

Originally Posted by evm1024

You really should take some time to come up to speed with current technology. A number of your assertions assume that LiFePO4 will act like FLA. This leads to errors in logic and assumptions that are false.

I also request that you address my counter to your assertion regarding mainesails reason for not consulting remotely.

Originally Posted by evm1024

Oh and by the way. Perhaps you could address the point of my post i.e. Mailesails reasons for not consulting remotely rather than offering up the voltage sag strawman

I suppose that my claiming that you are using strawman arguments could be insulting. I don't see it that way but to each their own.

At this point you do not use logic, reason or facts to counter my assertions but:

Originally Posted by ramblinrod

False.

No where, did I assume or postulate, there was any FLA like sag associated with LFP.
Knock off the insults.
You are the one in error here.

And further:

Originally Posted by ramblinrod

I'm sorry, responding to this nonsense is just not worthy of my time.

I actually try not to post nonsense. I am mildly insulted that you would consider my post nonsense.

In any case you made assertions, I countered them with logic, reason and facts. You can show me to be wrong with logic, reason and facts or not....

[Stu Jackson]

Originally Posted by ramblinrod

I'm sorry, responding to this nonsense is just not worthy of my time.

Then perhaps you could refrain from misquoting Maine Sail. This is at least the second thread in which you have done so. And have had to be corrected. Please.

[Delfin]

Originally Posted by ramblinrod

I'm sorry, responding to this nonsense is just not worthy of my time.

Nor apparently is learning anything about marine electronics.

[CatNewBee]

You have on any power source a voltage drop when you put heavy loads on, even on shore power.

But this is a no-brainer for someone with electricity knowledge, because any real world power source has a inner resistance.

Anyway, a good bms measures not only voltage and temperature, but also current and resistance of the cells by differential measurements of the cell voltage and the current. Knowing the inner resistance at the current SOC you can calculate the cell voltage as if there is no load and correct the cut-off voltage for under voltage protection under load.

We are talking about some 10..100mV on at 0.5...1C load. It is more difficult if you have a pulsing load like a PWM regulator or Inverter running, because the voltage measurement on the bms is done by A/D converter that has also a sampling rate, that can create interferences if there are similar frequences / multiple freq. between both devices. Some adjustments on the software usualy can easy fix those issues.

So the cut off is done really at that point on the cell voltage as if the battery is not undr load and not earlier because of the voltage drop caused by the load.

[Qayaq]

Ha. See this has turned into a lot of irreverent BS. Shame.
In my original post and drawing the idea was to keep the FLAs fully charged which they like, and to cycle the LFPs which they like. Then in the event of an occasional LVC on the LFP there is a fully charged FLA as back up.
Surprised no one caught onto that.

[CatNewBee]

Originally Posted by Qayaq

Ha. See this has turned into a lot of irreverent BS. Shame.
In my original post and drawing the idea was to keep the FLAs fully charged which they like, and to cycle the LFPs which they like. Then in the event of an occasional LVC on the LFP there is a fully charged FLA as back up.
Surprised no one caught onto that.

LVC is at 2.9V cell voltage, that translates to 11.6V battery voltage. , what is a empty FLA below 50% SOC.

If you run them in parallel, they will drain in parallel, if you run them separately, you will have to handle switching under load between them with all possible issues of cross-currents, cut-offs, sparks, voltage spikes, reverse-currents, drops outs etc. because of voltage differences, inductive loads and different inner resistances. So you need some powerfull smart switch to do a soft transition to protect your electronics. There are such pre-charge devices, that can do the trick. Checkout REC ABMS website, they are selling one along their BMS to do a soft start when switching on.

[Qayaq]

Oh dear,
You didn't look at the drawing or read the post I guess

[CatNewBee]

Originally Posted by Qayaq

Oh dear,
You didn't look at the drawing or read the post I guess

It is a long tread, and various options were discussed.

The diode separation thing is in fact running them in parallel, by preventing cross-currents - so they will be discharged together before LVC occurs.

you have to disconnect the lfp to charge the fla by a b2b charger to full, doable, but the whole thing gets more complex. Also separation diodes for high currents are both - expensive and hardly available on the consumer market.

[Qayaq]

Yep as I thought you missed the whole point of the post.
It might require a B2B.
Diode packs are cheap and old technology and just might lower the normal FLA max charging voltage to an acceptable max charging voltage for LFP.

No charging specifics required just stuff as much charge into the LFP as you can until it hits HVC. Voltage drop required before HVC re contacts.

Just a seed of a plan but I think it has promise

[Dockhead]

Originally Posted by Qayaq

Ha. See this has turned into a lot of irreverent BS. Shame.
In my original post and drawing the idea was to keep the FLAs fully charged which they like, and to cycle the LFPs which they like. Then in the event of an occasional LVC on the LFP there is a fully charged FLA as back up.
Surprised no one caught onto that.

If you think no one "caught onto that", then you didn't read the thread. A lot of people have had the same idea, and there are other threads on it. I am considering such an arrangement on my own boat and redirected a discussion about it in another thread, into this one. On pages 2 and 3 of the thread, you'll see an intelligent debate on the pros and cons of a hybrid system vs. simply two independent lithium banks, before the thread got disrupted.


I'm kind of on the fence myself. And I think the biggest argument AGAINST a hybrid system is not actually complexity, but the fact that once you've engineered a good lithium system and understand how to operate it, there's not much to be gained anymore by retaining an antique battery technology which costs MORE per quantum of energy stored and cycled.



If it were actually cheaper to store energy in a lead bank, then the synergy between lead and lithium would be more useful, but by my calculations it's not.




On the other hand, if you don't need to cycle the whole capacity every time, but need part of your capacity only occasionally, then that could look different. So for my particular case -- if I had say 260 amp/hours (@24v) of lithium in my technical bank, and kept 420 amp hours of lead in my house bank, I could supply the whole boat with power most of the time off the lithium which will be feeding the house bank via a B2B charger. Only occasionally would I need to dip into the lead bank for another 200 amp/hours (or whatever) of capacity; mostly it would be sitting there fully charged, and the lead bank would last forever since it would immediately get a perfect finishing charge after every use.


On the other hand, I'd have similar usable capacity out of two lithium banks of 200 amp/hours each and the cost would not be dramatically different, and I wouldn't be operating two different types of batteries, and I could cycle both of them to my heart's content without faffing with "finishing charges" or such other quaint 19th century procedures.


So it's not an obvious decision, with quite good arguments on both sides.

[Qayaq]

Originally Posted by Dockhead

If you think no one "caught onto that", then you didn't read the thread. A lot of people have had the same idea, and there are other threads on it. I am considering such an arrangement on my own boat and redirected a discussion about it in another thread, into this one. On pages 2 and 3 of the thread, you'll see an intelligent debate on the pros and cons of a hybrid system vs. simply two independent lithium banks, before the thread got disrupted.


I'm kind of on the fence myself. And I think the biggest argument AGAINST a hybrid system is not actually complexity, but the fact that once you've engineered a good lithium system and understand how to operate it, there's not much to be gained anymore by retaining an antique battery technology which costs MORE per quantum of energy stored and cycled.



If it were actually cheaper to store energy in a lead bank, then the synergy between lead and lithium would be more useful, but by my calculations it's not.




On the other hand, if you don't need to cycle the whole capacity every time, but need part of your capacity only occasionally, then that could look different. So for my particular case -- if I had say 260 amp/hours (@24v) of lithium in my technical bank, and kept 420 amp hours of lead in my house bank, I could supply the whole boat with power most of the time off the lithium which will be feeding the house bank via a B2B charger. Only occasionally would I need to dip into the lead bank for another 200 amp/hours (or whatever) of capacity; mostly it would be sitting there fully charged, and the lead bank would last forever since it would immediately get a perfect finishing charge after every use.


On the other hand, I'd have similar usable capacity out of two lithium banks of 200 amp/hours each and the cost would not be dramatically different, and I wouldn't be operating two different types of batteries, and I could cycle both of them to my heart's content without faffing with "finishing charges" or such other quaint 19th century procedures.


So it's not an obvious decision, with quite good arguments on both sides.

Hi Dock head,
You make some very good points, my boats smaller than yours but I see we are thinking similar thoughts.

One of my issues with LFP, its like my battery drill, loads of power and running just fine, but then it hits LVC and its all over, time to swop out the battery, or loose the use of the drill and re charge, that's not handy if its your Nav systems, Nav lights or bilge pumps or anything that's imperative to keep running.

FLA, not so much of an issue, just run them flatter and somehow get some more charge in.

It seems people are thinking of charging the FLA via a B2B from the LFP.

That's not so much my thoughts.

My thoughts are.

Keep my FLA system just as it is including it's charging system. But not the output.

What drains my batteries is the Fridge, Radar and Autopilot.
I split my output so my FLA doesn't have to deal with that drain.

FLA output gets the high amps low drain items, such as windlass, freshwater pump etc, high amp but not constant & therefore low drain.

I put in a separate bank of LFP, enough to cope with 1 to 2 days of no sun.

The FLA bank should always remain Full, it has no drain, just high load every now and again.

The LFP gets drained a lot, its got a constant load on it, it'll probably hit LVC on occasions and that's when the FLA gets that load switched back to it.

Using an old style cheap splitter diode pack on the original charge bus, use just one diode to feed LFP, it Should drop 1 Volt from FLA suitable to suitable for LFP max volts.
My hope is it would feed constant current to the LFP and when the LFP hits max volts use an HVC to kill that charge line.You could fool charging systems to do this by running their volt sense wire to LFP POS on the LFP side of the diode.

When an LVC event occurs, Alternators etc will be protected because they are also feeding the FLA
Under normal use FLA is fully charged allowing the LFP under normal circumstances to take all the charge it can get.
To prevent the FLA back charging into the LFP , say at night when sailing and no charge source available the LFPs should be draining and heading towards LVC the HVC would need to sense no charge source and stay open circuit.
When LVC is hit it simply switches all of the switchboard back to original FLA which should be full and now act as the back up system. And you wouldn't need a big switch for this as its a low amp load.

Going to be ordering some LFPs soon, so hope I'm not totally barking up the wrong tree.

Cheers for you input Dockhead

[john61ct]

The system description needs greater clarity, with numeric range examples.

A high current **load** has to mean high drain, can't have one without the other.

[Dockhead]

Originally Posted by Qayaq

Yep as I thought you missed the whole point of the post.
It might require a B2B.
Diode packs are cheap and old technology and just might lower the normal FLA max charging voltage to an acceptable max charging voltage for LFP.

No charging specifics required just stuff as much charge into the LFP as you can until it hits HVC. Voltage drop required before HVC re contacts.

Just a seed of a plan but I think it has promise

Well, you should read back through this and other threads on the subject. We have gone into all of these issues, and there are some very knowledgeable people providing very useful information.



It is strongly not recommended to use HVC to regulate charging, in any case.


In my opinion, it is not possible to charge and discharge lead and lithium connected together, whatever diodes or other devices you have between them, and get a reasonable charging regime which suits both of them. Their needs are just totally different, and not only what regards voltage.


I think a hybrid bank will need to have entirely separated charging systems. It's dead simple to have separate AC chargers, so that part of it is no challenge, but what you do with the alternator is a puzzle.


If you put the alternator on the lead bank, then you solve the issue of protecting the alternator from a HVC event, and you can charge the lithium with a B2B charger. So you regulate the alternator to give the lead what it wants and both banks get an ideal charging regime. That might be a good way to do it if you have your loads connected to the lithium bank. But then you have the issue of what to do if the loads get disconnected by a LVC event.


My own case is unusual in that my boat is already configured with two banks, with technical loads connected to one (thruster, windlass, winches) and house loads to the other. If I go with a hybrid system, I would put the lithium in the technical load box, regulate the alternator for lithium, and connect it to the lithium bank, and charge the house bank with a B2B charger. That solves the problem of how to keep essential equipment working through a LVC event, but it leaves the issue of what to do to protect the alternator from a HVC event, but this can be done with other devices, such as the Sterling Alternator Lineariser.