Drop in lithium batteries

[a64pilot]

No, the charger only has the battery bank as a load, you disconnect it now, every time you turn it off with the CB to disconnect shorepower. That cause no surges or any other harm to anything on the boat.

The battery bank carries all the loads, the charger carries only the battery bank.

[tanglewood]

Originally Posted by Paul L

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?

OK, point taken. But it begs the question of what charge programming is required. Just changing voltages, and is that really sufficient when LFP doesn't really want an absorb cycle? And they don't want float at elevated voltages? And what about constant voltage chargers on many engine alternators?

[a64pilot]

From a charging standpoint an LFP bank only needs one set voltage, no bulk, absorption or float.
You or a BMS can connect charge at XX SOC and disconnect it at XX SOC, that is all there is from a charging standpoint.
Of course you want for safety the BMS to monitor pack temp and voltages and if temp goes above or below set points to disconnect, the potential for thermal runaway exists in any battery chemistry, just very low probability I guess in lead.

[a64pilot]

You float a lead bank for one reason so that house loads don’t discharge the bank, an LFP bank is charged, and charge disconnected, and discharged, charge connected and charged, even if your on shore power.

Or more logically the LFP bank is disconnected at a partial charge state (its bad to store fully charged, 50% is sort of the accepted storage SOC) and you run directly off of your charger or a small lead bank when on shore power.

[tanglewood]

Originally Posted by a64pilot

From a charging standpoint an LFP bank only needs one set voltage, no bulk, absorption or float.
You or a BMS can connect charge at XX SOC and disconnect it at XX SOC, that is all there is from a charging standpoint.
Of course you want for safety the BMS to monitor pack temp and voltages and if temp goes above or below set points to disconnect, the potential for thermal runaway exists in any battery chemistry, just very low probability I guess in lead.

How would this BMS connect and disconnect the chargers? This is where I think it stops being "drop-in"

[tanglewood]

Originally Posted by a64pilot

You float a lead bank for one reason so that house loads don’t discharge the bank, an LFP bank is charged, and charge disconnected, and discharged, charge connected and charged, even if your on shore power.

Well, you float a LA battery to counteract self-discharge, and it has the side effect that the chargers will carry loads up to their capacity.


For LFP, I agree that one way to manage them is to charge, disconnect the charger, drain them down, reconnect the charger and recharge, disconnect and discharge, etc. But I don't think it's very desirable since it gratuitously cycles the batteries.

Originally Posted by a64pilot

Or more logically the LFP bank is disconnected at a partial charge state (its bad to store fully charged, 50% is sort of the accepted storage SOC) and you run directly off of your charger or a small lead bank when on shore power.

Yes, that can be done, but is even less drop-in than before. It assumes the charger(s) can operate as power supplies without an attached battery. Some can, but other can't. And it requires various forms of battery switching for the LFP bank and the LA bank.



In general, we seem to be having two different conversations here. One is about different strategies and circuit designs to manage an LFP-based power system, and the other is about the viability of an LFP drop-ion replacement for a LA battery.

[Paul L]

Originally Posted by tanglewood

OK, point taken. But it begs the question of what charge programming is required. Just changing voltages, and is that really sufficient when LFP doesn't really want an absorb cycle? And they don't want float at elevated voltages? And what about constant voltage chargers on many engine alternators?

Clearly a lithium bank takes a more complicated set of regulation. That doesn't mean for a product to be called a drop in it needs to be only hook up wires and go away. As I pointed out all baterries require competent setup, whether they are marketed as drop in or not.
For most common battery technologies what is best practice or at least practical requirements, is both understood and easily practiced. For LFP banks there are endless threads of folks pontificating on why their approach is the clearly the correct interpretation of the gospel, so defining and creating a drop is tougher.

[a64pilot]

Originally Posted by tanglewood

How would this BMS connect and disconnect the chargers? This is where I think it stops being "drop-in"

A relay in the BMS.
You need one anyway for safety, or how else would you disconnect charging in the event of a high temp condition?
I believe it’s common to have two relays, one on the charge side of the bank and one on the output side.

However to me this is ALL theory, I don’t have an LFP bank and have installed none.
I’m just throwing things against the wall and seeing what sticks is all.
If I haven’t been wrong already, I will be.

I’m not arguing, don’t take it that way please, I’m throwing out a theory to have it shot down is all.

It’s just I see discrepancies is all, I believe a true drop in can be built, it may require a separate “box” if you will and that may make more sense than individual batteries each having their own set of relays etc.

[a64pilot]

OK, I guess I missed explaining something, a drop in would have two sets of posts, one input, the other set output.
Only way I could see being able to separate them, cause you would have to. You have to be able to connect and disconnect charge and load independent of each other

[Dockhead]

Originally Posted by a64pilot

OK, I guess I missed explaining something, a drop in would have two sets of posts, one input, the other set output.
Only way I could see being able to separate them, cause you would have to. You have to be able to connect and disconnect charge and load independent of each other

But that would require major rewiring of the boat, to separate charge from load buses.


You cannot achieve the ability to connect and disconnect charge and load independently, in anything like a drop-in solution.

[arsenelupiga]

Originally Posted by Dockhead

But that would require major rewiring of the boat, to separate charge from load buses.


You cannot achieve the ability to connect and disconnect charge and load independently, in anything like a drop-in solution.

you can always go manual route. It is safer, cheaper and more reliable.

[john61ct]

OK.

The marketing premise of "drop-in" is bogus for our use case. Can say "no such thing" if you like.

But it is possible to put in infrastructure to compensate for most of their failings, if you did want to use them.

No longer a drop-in installation.

But the term is still useful to describe the battery type.

Personally I don't see a reason to use them at all, go with quality prismatic

[Maine Sail]

Originally Posted by a64pilot

No, the charger only has the battery bank as a load, you disconnect it now, every time you turn it off with the CB to disconnect shorepower. That cause no surges or any other harm to anything on the boat.

The battery bank carries all the loads, the charger carries only the battery bank.

A drop in battery has but two external terminals Batt + and Batt -.

A sealed internal BMS battery or "drop-in" runs the risk of disconnecting the charger or inverter/charger on the DC load side not the AC/input side. A well engineered BMS, featuring an external communication port, would be able to disconnect loads or charge sources correctly by shutting down the input side. A sealed BMS drop-in battery can't do this and an owner may have no idea the battery is about to self disconnect because it is not always about voltage levels..

If a charger was pumping away at full output when this happened, and remained connected to the load bus, and suddenly looses the battery load, there will be a voltage transient on the load bus as the voltage regulator simply can't react fast enough. This all happens in fractions of a second. The voltage transient can be damaging to equipment if there is no means to divert that load to another source that can clamp/absorb the transient.

Internal BMS systems can shut off for many reasons:

High Voltage
Low Voltage
High temp of any one of the end boards
Low temp
Current Limits Exceeded - Over taxing the BMS's internal switch

You can create external alarms for "general" high or low voltage (but not at the cell level) but for the others, you really have little to no control over it.

[a64pilot]

Originally Posted by Maine Sail

A drop in battery has but two external terminals Batt + and Batt -.

A sealed internal BMS battery or "drop-in" runs the risk of disconnecting the charger or inverter/charger on the DC load side not the AC/input side. A well engineered BMS, featuring an external communication port, would be able to disconnect loads or charge sources correctly by shutting down the input side. A sealed BMS drop-in battery can't do this and an owner may have no idea the battery is about to self disconnect because it is not always about voltage levels..

If a charger was pumping away at full output when this happened, and remained connected to the load bus, and suddenly looses the battery load, there will be a voltage transient on the load bus as the voltage regulator simply can't react fast enough. This all happens in fractions of a second. The voltage transient can be damaging to equipment if there is no means to divert that load to another source that can clamp/absorb the transient.

Internal BMS systems can shut off for many reasons:

High Voltage
Low Voltage
High temp of any one of the end boards
Low temp
Current Limits Exceeded - Over taxing the BMS's internal switch

You can create external alarms for "general" high or low voltage (but not at the cell level) but for the others, you really have little to no control over it.

This is theoretical, not what is currently available.

The contention is that a successful drop in cannot be built, I disagree, I say one can be built, compared to the processing and hardware required for common rail for example, its an easy problem to solve.

Not that one has been built, but that it is a possibility, and I believe that if the market is there, someone will eventually do it.
The market is what I have no idea about, but my belief is it exists, but I’m also not going to be the one to develop one
It exists I believe in the billions of lead acid batteries out there. I put a drop in LFP battery in my Husqvarna TE-450 years ago and likely saved more weight with with it than the titanium exhaust system did, for less money.

I understand that apparently there is no successful drop ins currently available, and they existing ones are best avoided.

I coined the phrase “Science Experiment” as far as Lithium is concerned, and from the little reading that I have done, with no experience, it would seem to be beyond the abilities and desire of the majority of people I meet cruising.
From what little reading I have done, there is more “management”required of a Lithium bank than there is for any other system on a normal boat, and likely more than the entire rest of the boat.
The fact that there are not a lot of burned boats speaks to the inherit safety, cause you know there have been some mistakes.

It’s just from a curiously look from someone who has been contemplating an LFP bank, that it is not ever going to be mainstream, not unless or until there is a form of drop in replacement system that is available.

[a64pilot]

Originally Posted by Dockhead

But that would require major rewiring of the boat, to separate charge from load buses.

No, it wouldn’t.
It would only require that all loads be connected to the load post, and all charging be connected to the charging post.
If you have one large bus, you would need to have two busses. Most don’t, most connect directly to the battery post, stacking wires

With the possible exception of the alternator, I bet your charging sources all have their own cables that connect to the battery now, don’t they?
However some people like me have connected the alternator output to the big main power wire on the starter, those that have would have to run a separate alternator charging wire, but that not a major rewire.