Practical Questions about LiFePo4 Power Systems

[travellerw]

Originally Posted by john61ct

Yes those Nordkyn resources are very widely cited.

"House charger" meaning from shore AC while at a slip?

And BP meaning cell-level active balancing? protection?

Yes.. a "House Charger" means a AC-DC charger. Either run from slip power or from onboard generator (in our case, the latter as we haven't been to a slip in over 24 months). In my case its has a "dumb" setting that allows it to output 13.8V@65A until I turn it off (no stages). It can also be operated as a "power supply" without a battery bank hooked up (and will be if we ever go to a marina).

BP = Battery Protection. Our battery protection does cell voltage, pack voltage and temperature. No active balancing. Disconnection is done through 2 Blueseas latching relays (one on the positive, one on the negative).

[travellerw]

Originally Posted by john61ct

Not even LVDs at the bank level?

No HVD for charging in case the sources' regulation fails?

Such devices are not expensive.

Sigh.. You are so bleeping frusterating. My post was pretty clear. Also.. PLEASE PLEASE stop posting multiple posts, it makes threads hard to read and difficult to repsond too. Its not hard to think of ALL your questions and type them in a single post. I'm sure you even have time to do it between you IT tasks at work.

Yes a basic BP has HVD and LVD which is triggered from either cell voltage, pack volgate or temperature..

I also very much disagree with your "alternator is key to the system". Most likely due to the fact that I have actually lived aboard and maintained our diesel engines. %95 of cruising is living on our anchor. I would rather run my $650 Honda 2000 and put amps back in my pack through the house charger, than my $15,000 diesel. Not only am I not putting hours on my diesel, but the Honda is MUCH cheaper to maintain. I now run small, easily replaceable $100 alternators on my motors to charge the starting batteries only.

Its pretty much a moot point on our boat as our solar arrays provide %99 of our power.

[CharlieJ]

My design philosophy has been:
> Don't float. (This was not my position in my first design.)
> Terminate charging about 5% before the charging knee.
> Terminate discharging about 5% before the discharge knee.
> For house banks, don't top balance on a regular basis. Check the balance periodically and balance as required.
> Charging. Use charging sources that are feature rich so that their native charging algorithms control the process. The BMS is the next layer of protection; much like a lifeguard. If a charging source allows the pack or cell voltage to approach the charging knee, the operator is notified and if the fault doesn't clear, the charging source is turned off and, if need be, the charging contactor is opened.
> Discharging. I am not quite as worried about this end of the cycle as most boaters understand that they need to keep tabs on the battery monitor. At any rate, I use an inverter/charger (generally the largest load) with the capability of turning it off if its native algorithm limits are violated. Again, the BMS is the next layer of protection and, if the inverter/charge doesn't turn off then an alarm is sounded and so on.

In all cases there is an override that allows the operator to make the conscious decision that, based on operational considerations, it is better to leave the bank on line and suffer the consequences when the vessel is safe and stable.

[john61ct]

Originally Posted by travellerw

BP = Battery Protection. Our battery protection does cell voltage, pack voltage and temperature. No active balancing. Disconnection is done through 2 Blueseas latching relays (one on the positive, one on the negative).

Then that is BMS functionality.

Just not using "a BMS" in the packaged commercial sense, more DIY.

[john61ct]

Sorry to those I annoy.

Not trying to claim one right way, your rig your choice, not necessarily addressing any individual even if your statement triggered mine.

Feel free to just ignore.

[Dockhead]

Originally Posted by john61ct

The fact that, given enough amps input, any LFP bank can go from completely depleted, user-defined 0% back to completely Full in under 60 minutes of charging.

To me makes the alternator a key player in system design. Even sitting on the hook for weeks, just run your already-installed propulsion engine for an hour, a few times per week, and you've got all the power you need.

Solar becomes irrelevant, unless **you want** to never burn dino juice.

And no dedicated genny needed at all.

Indeed, that's the whole appeal of LiFePo, to me at least.


Thinking about building a new boat, I thought a giant alternator (like one of these beasts: https://www.ecotechalternators.com/p...or-j180-mount/) would be really all you would need, with a lithium bank able to soak up the whole output and not needing any finish charge.

[missourisailor]

I think that most of the "BMS" confusion rises from different folks using the same three letters for two different acronyms.


1) BMS => Battery Management System.

Meaning that it has the capability to equalize (balance) individual cells.


2) BMS => Battery Monitoring System.
No equalization function. Only basic voltage, temp etc..


Method 2 is what travellerw is talking about.
Also, FWIW, what Mainesail and most early adapters advocates.
Myself included.



We need to find a different acronym for one of them!

[john61ct]

I see my post #25 above as including everything a BMS should do, and only use it to mean management.

Whether from a single-vendor packaged system, DIY, or a combination, I see the term as functionality more than physical.

And cell-level balancing the least significant aspect.

BM means a bank monitor, usually coulomb-counting, as in 712-BMV

[missourisailor]

Originally Posted by john61ct

I see my post #25 above as including everything a BMS should do, and only use it to mean management.

Whether from a single-vendor packaged system, DIY, or a combination, I see the term as functionality more than physical.

And cell-level balancing the least significant aspect.

BM means a bank monitor, usually coulomb-counting, as in 712-BMV

Yeah, I read it and have different thoughts and experiences.


Cell level monitoring is needed. A cell will go high or low, long before the bank does.



LVD is not needed. And this is for safety reasons. If the bank is going low, then that means that there is something else going on. Like no charge source. Meaning some emergency, is most likely happening. To hell with the bank when life or limb is at risk.
However, on the system's that I have built, there still is a electro/mechanical cutout device in the LVD place. It is there to manually remove the load buss if the need arises.



High current protection is done with fuses and C/B's. No way in hell do I want the BMS opening the circut when I draw 175+ amps using the windless.


This is just what I have learned from the systems I've designed, built and used.
Your experiences may be different.

[Singularity]

Originally Posted by Dockhead

I understanding from reading about BMS systems, that the BMS needs a way to disconnect the charging source in case of overvoltage.
That will fry the diodes of an alternator, if it happens.

So, I don't know where we are with this, but I'm planning to put put in 24v lead acid battery in parallel with the LFP (I've got 16 100ah Calb and a Magnum MSH4024M).

Per Nordkyn:
The simplest way of resolving all the challenges mentioned at the beginning of this article is running the lithium bank in parallel with some standard lead-acid capacity.

This mandates an independent BMS for the LFP bank, best I can tell. But again the 24v lead battery should keep vital electronics online. (should it merit a special circuit?)

FWIW SV Delos guys just put in LFP. Clip here shows them using their lead starter battery as a buffer. They also show their conversion from propane to induction cooking.

If bandwith limited, should start at 10 minute mark:

https://www.youtube.com/watch?v=GvDC...utu.be&t=10m0s

[john61ct]

Again, LVD is functionality, not a specific type of device.

Many many people operate avoiding the voltage shoulders, without any "live" per-cell anything,

so just a difference of opinion there.

IMO you definitely need per-cell if going above 13.9V or below 11.9V, even if just monitoring / alarms for imbalances.

And yes over-current protection can be CP.

[john61ct]

Originally Posted by Singularity

lead acid battery in parallel with the LFP

As long as you realize they don't (shouldn't) get the same charge profiles.

I suppose the LFP could just be isolated off the charge buss at 27.6V/3.45Vpc, as the CC/Bulk stage is climbing, then leave the lead going until endAmps.

With cheap sacrificial lead gets simpler.

Personally I'd put the alt on the lead, then use a DCDC charger for the LFP to ensure accuracy.

[Dockhead]

Originally Posted by john61ct

As long as you realize they don't (shouldn't) get the same charge profiles.

I suppose the LFP could just be isolated off the charge buss at 27.6V/3.45Vpc, as the CC/Bulk stage is climbing, then leave the lead going until endAmps.

With cheap sacrificial lead gets simpler.

Personally I'd put the alt on the lead, then use a DCDC charger for the LFP to ensure accuracy.

Yes, it's complicated, and messy.


The only way to make this even semi-elegant on my boat, apart from ripping out the entire electrical system and doing it over (yeah, right), would be to go back to the original configuration with two banks, one for house loads, the other for windlass, winches, thruster, and separate them, as they were originally. Install the lithium in place of the house bank, install a separate mains charger on the lead bank.


So far so good, but that leaves how to connect the alternator. I don't know how to do this. Perhaps use a diode splitter (there is a good one already on the boat, a Driftgate, part of the original build) and instead of regulating the alternator, use an alternator-to-battery charger on both sides.



I don't think I could just connect the alternator to the lead -- then it would need to be regulated for the lead bank. I have a heavy duty school bus alternator, and one of the main advantages of lithium is being able to pump the whole output of the alternator into the lithium. I don't see how I could do that passing the current through the lead first.


This is far more complex than what I originally had in mind and I'm not sure it's worth it.



Instead of putting the lithium in place of the house bank, maybe it would make more sense to put it in the other position, and interconnect the two banks with a battery-to-battery charger. That way the house loads would be run from the lithium bank until that was switched off for whatever reason (either manually or in an undervoltage situation), then the lead would take over automatically and instantly -- making a highly reliable power supply, a definite plus. Also the lead would practically extend the usable battery capacity, and maybe I wouldn't need as much lithium.



This would have some pretty big advantages, but would be getting borderline ridiculous, what concerns complexity.

[john61ct]

An alternator setup to output high amps, precise voltage, proper staged profile is a lot of very expensive work

not saying not worth it, but

If you have inexpensive lead on board, then whatever existing alternator setup can be leveraged for the LFP

with a DCDC charger, e.g. Sterling BB series.

And once you have that, it can become the **only** charge source that touches the LFP.

No need for special fancy mains charger, even solar controller can route through the DCDC.

Since your well-coddled LFP bank will last longer than your boat, or when you move into an off-grid home or buy an RV

you are never upgrading any charge sources anywhere, just use whatever's there.

In effect you get all the benefits of "drop-in" without their limitations.

Not a panacea for all use cases maybe, but one idea worth considering.

[john61ct]

The alternator-to-battery unit is like an expensive VR, like an alt component only good for alt charging.

The B2B version becomes the bank's front-end for any source, no mods to other existing charge infrastructure required.

Charles said a 180A even a 240A version "coming soon" have not heard back.