Drop in lithium batteries

[john61ct]

Originally Posted by Delfin

I think you are confusing Constant Current voltage settings with Constant Voltage settings. As CMS notes, when pressed for clarity, manufacturers make it clear that high CV absorption charging is harmful.

First off "harmful" is one thing, "not optimal for longevity" when seeking to get to say 10000 cycles when the vendor specs only 2000. My POV is the latter.

I only want to Absorb to endAmps when I need a precise calibration. For daily cycling, no, just hit a voltage setpoint and stop, zero Absorb time.

There is **no** good reason to push past the voltage shoulders.

Now, what that Voltage setpoint will be is pretty arbitrary, and a lot depends on amps rate of charge.

A high current rate can go to a higher voltage, and be at a lower SoC, compared to the lower setpoint needed in a solar-only context, ending at a higher SoC.

So yes, **if** shortest time to re-charge is important to you (it is not even on my radar) then at a high current rate 3.50Vpc as you spec (28V for I assume 8S) is fine. But why wait for amps to fall? What does that accomplish?

> if you simply charge the bank until it reaches 3.45v, it may be anywhere from 40% to 80% filled.

No, using a good AH meter every bank I've seen "just stop at V setpoint" vs endAmps is only adding another 2-4% SoC at most. And already over 100% as per the rated 20hr AH capacity.

> I think if you look at a SoC vs Voltage chart, you will see that higher voltages are still in the "flat part" of the curve.

Well I would hope so. My approach is to not get near those shoulders.

But basically with any given bank and a given charge source, calibrate based on whatever you like. Start on the low side, and when you get to a profile that ends up at **resting** 13.6V (3.4vpc), that is 100% Full.

> All you do by pumping more current at an Li bank after it is full is generate heat.

Preaching to the choir there. I think you and I are using "Full" very differently though.

I completely ignore any "capacity" beyond **my definition** of Full as above. For every quality-maker cell I've seen that will be over the 20-hour AH rating anyway.

> bad for an Li bank to sit fully charged for more than a few minutes?

Again, not saying "harmful", just not conducive to optimizing lifespan. The lower your definition of Fully Charged is, the more minutes will be fine.

> If there is one thing everyone seems to agree on, and that is that any absorption phase is pointless with Li batts, and is generally where any to them damage is generally done.

As I stated I do not do any Absorption in daily use. You were the one advocating for that, so now I am confused. You do realize that continuing CV charging for even a minute or two is Absorb stage right?

_____
Storage SoC: The goal is as low as possible. To the extent you see zero self-discharge over the between inspection timespan at that temperature, then lower the better.

Adding charge is only to counter that, so again if no need, don't do it.

Sorry have not saved the dozens of posts that state "the lower the better" but they are from those I trust and more recent that just "stay below 50-60%".

The DoD vs cycles issue:

storage and testing is a completely different scenario from usage cycling. Those DoD vs cycles charts are **average** DoD while cycling.

Storing at a low SoC even if for six months or more, is a **single cycle** out of thousands, so does not impact that factor at all.

I'm expecting way over 5000 anyway (hoping 10000+) even cycling deep when needed. In most contexts I end up staying pretty shallow anyway, but I'm not worrying about cycling DoD, since at least for mostly-solar contexts I've sized for worst case scenarios anyway.

[tanglewood]

Getting back to drop-ins, I can see how a battery can monitor adn protect itself against over/under temp, and over/under charge. But when any of those conditions occur, all it can do is disconnect, and that's really anti-social behavior for a boat.


Drop-in also implies no changes to the charging and load systems, so it's easy to see how at least over charge could easily occur on a regular basis.


All the professionally designed systems have communications between the batteries, the loads, and the chargers. This provides a way to shut down chargers when the batteries are full and never to an over-charge situation that will require a disconnect. That requires a BMS that talks, and chargers that respond. And the BMS indicates when the battery is getting low and loads need to be shed, once again with a goal of NOT disconnecting the battery.


But the idea of a drop-in replacement is so compelling that I think a lot of people will believe it because they really want to believe it, and people are very susceptible to believing what they want to be true.

[Delfin]

Originally Posted by tanglewood

Getting back to drop-ins, I can see how a battery can monitor adn protect itself against over/under temp, and over/under charge. But when any of those conditions occur, all it can do is disconnect, and that's really anti-social behavior for a boat.


Drop-in also implies no changes to the charging and load systems, so it's easy to see how at least over charge could easily occur on a regular basis.


All the professionally designed systems have communications between the batteries, the loads, and the chargers. This provides a way to shut down chargers when the batteries are full and never to an over-charge situation that will require a disconnect. That requires a BMS that talks, and chargers that respond. And the BMS indicates when the battery is getting low and loads need to be shed, once again with a goal of NOT disconnecting the battery.


But the idea of a drop-in replacement is so compelling that I think a lot of people will believe it because they really want to believe it, and people are very susceptible to believing what they want to be true.

Just one person's experience, but if drop-in means not changing equipment, then the Lithionics I installed were drop in because I changed nothing. If drop-in means not changing how you manage your house bank compared to LA, then I guess what I installed isn't.

The Lithionics BMS can turn off the alternator when a HV situation occurs, but I never let that happen. Instead, I just flip over to the lead acid starter bank when the Lithiums are full (CAR < 3% or so). That is a change in my behavior, since I didn't have to do that with my prior AGMs, but since I have, so far at least, been able to pay sufficient attention to my surroundings never to sink a boat after 50,000 miles I think I can manage that task as just part of running the boat. As a safety backup, the Balmar is programmed for minimal absorption time and open circuit voltage float, but I haven't had to rely on that so far.

[john61ct]

A packaged system with BMS that communicates with other devices and you could physically access the component cells without destroying the system is NOT a drop-in, that is clear.

The in-between case, all sealed up can't get to the 4 cells, but some comms, is the one with no category name so far,

I propose "hybrid drop-in", other suggestions welcome.

[alctel]

Yeah I think people are talking about several different things here, as 'dropin' means different things to different people.

The Victron stuff seems to be ok (if expensive) as it's basically the standard 'BMS with relays' setup just wrapped up in a package for ease of use, but I'm not sure about what the battle born stuff is about and would be very sceptical of it.

[john61ct]

And there are dozens of less-known straight from China ones.

Battle Born are actually the best-known, lots of fans in the US automotive / RV sector.

Put the G-31 into an ArkPak 730 or alternatively a Firefly

and you have a decent portable powerpak where you can replace the batt as needed, unlike Yeti etc.

But I agree needs careful design to adapt to a large-bank House bank use case, and IMO prismatics are better value.

[a64pilot]

Originally Posted by tanglewood

Getting back to drop-ins, I can see how a battery can monitor adn protect itself against over/under temp, and over/under charge. But when any of those conditions occur, all it can do is disconnect, and that's really anti-social behavior for a boat.


Drop-in also implies no changes to the charging and load systems, so it's easy to see how at least over charge could easily occur on a regular basis.

All you guys are failing to understand that instead of disconnecting the bank, all that is needed is to disconnect the charge source, it’s not going to hurt anything at all for the charger to sit there, turned on and connected to nothing.

Level 2 if you will of battery protection is to disconnect the bank, that ought to occur at a higher voltage / temp setting than disconnecting the charger, but isn’t a bad idea safety wise.

Like I said, many leave their laptop connected to the charger all the time. The laptop BMS does not communicate with the charger and turn it on and off, it simply connects or disconnects it.
KISS.

[john61ct]

Where you open the circuit of course is a fundamental piece of the system design.

Sometimes you want to disconnect the charge source, stop it producing output.

In which case, should cut upstream power **to** the charge source.

Isolate panels from the SC.

Mains from the shore power charger.

Shut off the generator.

Sometimes you just want to isolate the LFP bank from the charge source, but want it to continue feeding the load devices.

A load dump (e.g. lead bank) is then required to prevent transient spikes / surges, not just to protect alternators.

All depends on the situation, no one design is correct for all.

[a64pilot]

No, I don’t believe simply cutting the connection to a charger will hurt it, if it did then we all would have fried a many an automobile charger, case nearly everyone simply disconnects them.
Alternator is the exception.

What your suggesting is a BMS controlling a “smart charger” and is likely a more elegant solution, however that means of course replacing every charger you have, if such chargers even exist.

Really irrelevant, someone will build true drop ins or they won’t.
I believe it’s inevitable, too many devices out there to market to, new vehicles whether they be motorcycles to cars, snowmobiles etc could be made with smart chargers, but retrofitting isn’t likely, and that is where the drop in market will be.
Currently no market, cause lead is so cheap, and actually there has been LFP drop ins for motorcycles for years, based off of A123 cells.

[tanglewood]

Originally Posted by a64pilot

All you guys are failing to understand that instead of disconnecting the bank, all that is needed is to disconnect the charge source, it’s not going to hurt anything at all for the charger to sit there, turned on and connected to nothing.

Level 2 if you will of battery protection is to disconnect the bank, that ought to occur at a higher voltage / temp setting than disconnecting the charger, but isn’t a bad idea safety wise.

Like I said, many leave their laptop connected to the charger all the time. The laptop BMS does not communicate with the charger and turn it on and off, it simply connects or disconnects it.
KISS.

I get that stopping the chargers is the desired thing to do, but that seems directly in conflict with the notions of a "drop-in" battery. Maybe it's just me, but "drop-in" means disconnect the battery cables from the old battery and remove it, then drop in the new battery and reattach the cables. Then go sailing. No rewiring, no changes to charger settings, no splitting of load and charge buses, and no "disable" signal wires to control chargers.

[john61ct]

None of this has to do with drop-ins themselves, but the infrastructure to enable making them work better for our purposes.

Maybe "meta-BMS" is a good term?

Originally Posted by a64pilot

No, I don’t believe simply cutting the connection to a charger will hurt it, if it did then we all would have fried a many an automobile charger, case nearly everyone simply disconnects them.

I did not only mention damaging the charge source.

When sensitive loads are active on the circuit load dump can spikes / surges can do damage, sometimes over time.

And I was not discussing any particular solution type, can be done with generic sensors & relays.

Right now a DIY domain, but open-hardware + FOSS project will mature I am sure, perhaps evolve into reliable and supported commercial products one day.

[john61ct]

Originally Posted by tanglewood

I get that stopping the chargers is the desired thing to do, but that seems directly in conflict with the notions of a "drop-in" battery. Maybe it's just me, but "drop-in" means disconnect the battery cables from the old battery and remove it, then drop in the new battery and reattach the cables. Then go sailing. No rewiring, no changes to charger settings, no splitting of load and charge buses, and no "disable" signal wires to control chargers.

Yes that is the sales pitch.

But if you want to buy into it, Rich was right

Originally Posted by SV THIRD DAY

No such thing as drop in LiFePO4 batteries.... and a company that claims that there is I wouldn't put much credibility in .....

[Paul L]

Originally Posted by tanglewood

.... Maybe it's just me, but "drop-in" means disconnect the battery cables from the old battery and remove it, then drop in the new battery and reattach the cables. Then go sailing. No rewiring, no changes to charger settings, no splitting of load and charge buses, and no "disable" signal wires to control chargers.

That's kind of an extreme take on drop in. Under your definition then almost any battery change is not a drop in. If you switch to AGM, Gel, even different brand of deep cycle FLA you need to adjust regulators and charge profiles to correctly manage the new batts. Why should a drop in Lithium setup be held to a higher standard?

[john61ct]

Most of the people these are marketed to are not aware of such distinctions.

[tanglewood]

Originally Posted by a64pilot

Like I said, many leave their laptop connected to the charger all the time. The laptop BMS does not communicate with the charger and turn it on and off, it simply connects or disconnects it.
KISS.

True, but that's because it can control the charge circuit in the laptop. With a true drop-in battery on a boat, it's not possible to disconnect the charger without also disconnecting the loads. You can only do that if you re-wire the boat to separate loads and chargers, and connect each individually to the battery. Or you can control an external relay to disconnect the chargers, or turn the chargers off through some control signal. Then it's no longer drop-in.