LFP FLA hybrid

[john61ct]

Originally Posted by tanglewood

if I could only figure out where I found that paper

More trustworthy to just test yourself, measure with your specific gear.

A cheap infrared temp gun lets you stand back a bit.

[tanglewood]

Originally Posted by Dockhead

By the way, does anyone know whether you can still switch on and off, individual Victron Multipluses, individually, when they are ganged together?


If I did do dual lithium, I would add not an additional charger only, but an additional charger/inverter, provided I could choose "either" as well as both, depending on the SOC of the individual banks.


Also, to gang them together, do they need to be identical models?

I think the answer is No.


I haven't tried it myself, but have asked Victron exactly this question in the context of Quatros. I was hoping to run two in parallel, hoping a survivor would keep running if the other failed. Or at least have a 50/50 chance is the slave failed. I.e. have double capacity and also redundancy.



No cigar. When their outputs are paralleled, they have to be configured as such, and if both units are not present an healthy, it all shuts down. So switching between one unit, the other unit, or both requires config modification.


Now if the outputs are NOT connected, i.e. they each power independent and separate AC load busses, then they can be run completely independently.

[john61ct]

Originally Posted by Delfin

Not so sure about #1 above. My experience is that there is no tail at all for LFP

No doubt, he misunderstood, that #1 statement is 100% wrong.

In fact I use no Absorb at all, hit the Full voltage and stop, best for longevity and easy to implement.

But when I do allow Absorb time for calibration purposes

until trailing amps drop to .03C

it is rarely more than a few minutes.

[Delfin]

Originally Posted by rgleason

Thanks John,


That is just as bad as FLA!!!
Do they get there any faster?
Say for a 90ah battery using a 120ah Alternator with belt management output easily 80ah recharging 60ah to 100%SOC?
Do we still have all the same problems determining when the batterys are full?
IE Measure trailing amps with a clampon meter still?

It seems like Victron Datasheet says:
"A LFP battery does not need to be fully charged. Service life even slightly improves in case of partial charge instead of a full charge. This is a major advantage of LFP compared to lead-acid."

They don't mention the need to get to 100%SOC.

2-3 hours of ICE is not really the idea I had in mind, perhaps 2 hrs, but not 3....

They don't need to be recharged to 100%, ever. If you want them to be 100%, then you need to charge to 14.6 volts and at that point the BMS will start to shunt current from cells reaching that voltage. But, if you never charge north of 14.2 volts, you'll be at 95 - 98% SoC and balanced cells will tend to stay in balance for a very long time, or so I believe is the case.

[tanglewood]

Originally Posted by john61ct

More trustworthy to just test yourself, measure with your specific gear.

A cheap infrared temp gun lets you stand back a bit.

I don't really agree. No harm in trying it yourself, but the paper did a thorough job with a sampling of cells, and exploring paralleling at various different SOC levels. Then recorded and graphed the asymptotic current flow, and time to come into balance. It was a much more thorough job than most of us would do, and with more sophisticated equipment. And why reinvent the wheel.

[john61ct]

Originally Posted by Delfin

They don't need to be recharged to 100%, ever. If you want them to be 100%, then you need to charge to 14.6 volts and at that point the BMS will start to shunt current from cells reaching that voltage. But, if you never charge north of 14.2 volts, you'll be at 95 - 98% SoC and balanced cells will tend to stay in balance for a very long time, or so I believe is the case.

You define your own version of 100%.

14.anything is too high.

Mine is 13.8V.

Still over the rated AH capacity at that much safer definition.

[john61ct]

Originally Posted by tanglewood

I don't really agree. No harm in trying it yourself, but the paper did a thorough job with a sampling of cells, and exploring paralleling at various different SOC levels. Then recorded and graphed the asymptotic current flow, and time to come into balance. It was a much more thorough job than most of us would do, and with more sophisticated equipment. And why reinvent the wheel.

Because it is unlikely they used the same cells.

And lots of "research" is corrupted by vendor money.

But yes, worth posting a link if not too much trouble.

[Delfin]

Originally Posted by tanglewood

Just read CALB and/or Winston's cell spec sheets. Also the more packaged offerings from Victron, Mastervolt, Lithionics, Relion, etc., some of which I know are built around those cells, and others I expect are too.

On my 300 Ah Lithionics packages, the recommended max discharge rate is 1.3 C continuous and the recommended max charge rate is 1 C continuous. They don't manufacture their own cells, and the specs on those are higher, as you say. However, I think Lithionics throttles those recommendations in part because they warranty 2,000 cycles at 100% DoD if the charge/discharge parameters meet their recommendations. In turn, I throttle back Lithionics recommendations to .33 C charge rate and use a more conservative charge voltage than they say is fine.

[john61ct]

Originally Posted by ramblinrod

Danger Will Robinson....

If you connect high current charging sources to a Lithium bank directly, when you hit HVD it can induce equipment damaging transients through all devices connected (think nav electronics and refrigerant compressor modules).

Additionally, when LFP HVD activates your alternator could be facing "open circuit" and take out the rectifier diodes.

High currents are not the problem.

Only voltage is, HVD should never activate unless charge source is broken.

And everyone knows you need a Starter or sacrificial cheap lead batt in the alt charging circuit.

Or just use a B2B charger.

I find it very irritating you have instantly switched from LFP naysayer to an "expert advisor" on the subject.

[Dockhead]

Originally Posted by ramblinrod

Danger Will Robinson....

If you connect high current charging sources to a Lithium bank directly, when you hit HVD it can induce equipment damaging transients through all devices connected (think nav electronics and refrigerant compressor modules).

Additionally, when LFP HVD activates your alternator could be facing "open circuit" and take out the rectifier diodes.

Yes, we are all well aware of these issues, which is one of the main design challenges of any lithium power system.


It's easy to solve with a hybrid bank if you connect the loads and the main charging sources to the lead bank. But that's not the only way to solve it, by any means.


Here is one way to deal with the alternator:


https://sterling-power.com/products/...-70f-ald-17500

[john61ct]

Originally Posted by Delfin

On my 300 Ah Lithionics packages, the recommended max discharge rate is 1.3 C continuous and the recommended max charge rate is 1 C continuous. They don't manufacture their own cells, and the specs on those are higher, as you say. However, I think Lithionics throttles those recommendations in part because they warranty 2,000 cycles at 100% DoD if the charge/discharge parameters meet their recommendations. In turn, I throttle back Lithionics recommendations to .33 C charge rate and use a more conservative charge voltage than they say is fine.

More likely accommodating the higher rates requires their spending lots more on their included proprietary BMS.

You get a lot more longevity lowering their voltage recommendations than worrying about current rates.

[Dockhead]

Originally Posted by tanglewood

I think the answer is No.


I haven't tried it myself, but have asked Victron exactly this question in the context of Quatros. I was hoping to run two in parallel, hoping a survivor would keep running if the other failed. Or at least have a 50/50 chance is the slave failed. I.e. have double capacity and also redundancy.



No cigar. When their outputs are paralleled, they have to be configured as such, and if both units are not present an healthy, it all shuts down. So switching between one unit, the other unit, or both requires config modification.


Now if the outputs are NOT connected, i.e. they each power independent and separate AC load busses, then they can be run completely independently.

Too bad!!


That would have been a significant reason to go to dual lithium versus hybrid, for my case.


Thanks for the information

[Delfin]

Originally Posted by john61ct

You define your own version of 100%.

No John, that is not correct. It may be correct with LA, but not with LFP. When the acceptance rate of an LFP battery drops to near zero, it is full, regardless of the voltage you are charging the battery at. Do you have an actual LFP bank that you use?

Originally Posted by john61ct

14.anything is too high.

That is an opinion not shared by any manufacturer. Yes, I know you believe that those manufacturers are scheming to have their customers be disappointed with longevity so they will, what, buy more of the product that disappoints them? In any case, as Maine Sail has pointed out, 14.2 volts for 5 minutes has a very different effect on an LFP battery than 14.2 volts for 4 hours. The reason is simply because the impedance is so low on an LFP battery that after it reaches saturation, all additional current is just going to go to producing heat and blowing Li ions away.

Originally Posted by john61ct

Mine is 13.8V.

Still over the rated AH capacity at that much safer definition.

Very sensible and conservative approach. However, if you want to maximize the number of cycles you get, try not discharging them to the 10 - 20% you have recommended as a great storage SoC. That will have more of an effect on longevity than not charging to 28 volts for 90 seconds.

[Dockhead]

Originally Posted by john61ct

High currents are not the problem.

Only voltage is, HVD should never activate unless charge source is broken.

And everyone knows you need a Starter or sacrificial cheap lead batt in the alt charging circuit.

Or just use a B2B charger.. .

Of course. Lithium 101.




In my particular case, using a starter battery as "sacrificial lead" is not an option, because my starter batteries (two of them, on two separate systems) are 12v and house and technical systems are 24v.


So lithium will require more engineering on my system -- probably Charles' ingenious device linked to above, plus perhaps something else for flyback currents on the main loads bus, maybe just a grounded diode would do it.


Or in my case, if I do hybrid instead of dual lithium, then the only loads directly connected to lithium will be winches, windlass and thruster -- beefy devices which probably don't care two spits about those kind of spikes. So protecting the alternator might be enough. But this aspect of the design will require a real EE to look at it I think.

[Dockhead]

Originally Posted by Delfin

No John, that is not correct. It may be correct with LA, but not with LFP. When the acceptance rate of an LFP battery drops to near zero, it is full, regardless of the voltage you are charging the battery at. Do you have an actual LFP bank that you use?

That is an opinion not shared by any manufacturer. Yes, I know you believe that those manufacturers are scheming to have their customers be disappointed with longevity so they will, what, buy more of the product that disappoints them? In any case, as Maine Sail has pointed out, 14.2 volts for 5 minutes has a very different effect on an LFP battery than 14.2 volts for 4 hours. The reason is simply because the impedance is so low on an LFP battery that after it reaches saturation, all additional current is just going to go to producing heat and blowing Li ions away.

Very sensible and conservative approach. However, if you want to maximize the number of cycles you get, try not discharging them to the 10 - 20% you have recommended as a great storage SoC. That will have more of an effect on longevity than not charging to 28 volts for 90 seconds.

Thanks to both of you for all this great information. It's cool to see all the sheer brainpower which has been invested into this technology by users.


Lithium is surely not yet ready for accountants or for weekend boaters who are not smart or knowledgeable enough to dive deeply into the technology -- as I think everyone agrees. But that doesn't mean that there aren't people smart enough to reach an adequate understanding!