LFP FLA hybrid

[Dockhead]

Originally Posted by john61ct

A fully setpoint adjustable B2B DCDC charger will convert any primary source feeding your FLA bank to exactly what you want your LFP bank to receive.

If anyone knows one besides Sterling's let me know.

Much better solution than doubling up on separate mains / solar / alt+VR setups.

I know this is an old post in the thread, but the issues raised are worth thinking about again.


The Sterling B2B chargers are brill and I would for sure use one for any charging source which can't be doubled -- like an alternator, for example, if you already have two.


But I don't think I would want to share a mains charger between two banks using this. Much simpler to add a second mains charger, which will have additional benefits like redundancy, and in this case also efficiency, since there is only one charger processing the current. Also good way to increase the total charging capacity for loading up your generator.


The Sterling B2B chargers are anyway limited to 30amps (24v to 24v).

[evm1024]

Originally Posted by Dockhead

OK, but I don't think that connecting a starting battery into the system is actually a hybrid bank along the lines that the OP and others have been discussing it.


Do you use the starting battery to provide backup power to any systems (which ones?). Or just as a "dump load"?

Not hybrid in the sense used in this thread (which is why I listened more than talked).

And I should say that backup is not the same as failsafe (as in never fail).


Briefly my own power strategy is to size the house bank for 3 or 4 day no charge operation (LiFePO4 in this case). And to have AGM start and windless batteries.

There are 2 implications from having LiFePO4 and LA together, firstly the differing charge requirements and 2nd the need to protect LiFePO4 from over and under discharge.

For me a simple BMS does the protection function. Loud alarms are the primary means of protecting the bank from when I screw up and do not pay attention to it. At the moment I do not have a disconnect set up to automatically drop the bank. I'll likely add one in when we are ready for long term cruising but also install a bypass switch that will be parallel to the disconnect switch.

In any case the Housepower cell boards low voltage disconnect signal is temp compensated and is: 2.5 vpc at 0 degree C, 2.75 vpc at 25C and 2.9 at 40C (a more typical engine room temp). The BMS does LVC at 2.9 volts (11.6). Which is quite low for a LiFePO4 bank.

On to charging. There are 3 charging sources. The first is the inverter/charger for when you have shore power.

Next there is a Honda to the inverter/charger or a genset ( I do not have a genset).

Next there is the main engine and the 200 amp alt run at 135 amps.

Next there is Solar. Currently I have just a small panel but expect to put in 900 watts of solar.

All of the above sources are set up to charge the LiFePO4 bank and then stop charging it.

The AGM batteries are charged by either shore/generator power through dedicated 10 amp chargers (xantrex turecharge 2). In my case anytime I have 120 volts the AGM batteries are being charged by these small 3 stage chargers. If I am running the main engine then I can enable the inverter/charger to get 120 to charge the AGM. Not really efficient of course - but the engine is running (is the watermaker the reason?).

The AGM are also hooked up to victron mppt 75/15 solar controllers which are (or rather will be) from the 900 watt solar array. That is why I was doing some research on driving 2 (or more ) solar controllers from a single panel set. This will recharge the AGM and bring them to 100% over some time.

It occurs to me that someone with a 24 volt house bank could use the Mppt 75/15 to charge a 12 volts start battery. (rather than a B2B)

Moving on - What is important to me is to identify mode of operation.

Passage making is one where there are significant loads. In that case the LiFePO4 house bank capacity is such as to allow for 2, perhaps 3 days of no charge operation.

Solar in my case (and running the gen for those without solar) is sized to take care of the daily usage. LiFePO4 really shines here in the form of near 100% CEF and full voltage at almost any SOC. The backup is the genset (or honda), or the main engine alt.

At anchor is like passage making but the loads are lower (no AP, radar etc). The house bank should cover 3-4 days no charge operation.

Of course there is the docked with shore power mode but with an inverter./charger power is not an issue.

In all of the above modes of operation someone is there to respond to alarms . And to fall back on an alternate charging source if needed.

Off boat modes are the more interesting. And have some choices.

The primary load is likely to be the fridge. The LiFePO4 bank should handle that load for (what?) a week or more. So the question you have to ask yourself is how long will you be willing to let the boat go on its own? This is likely where I would turn the disconnect bypass off and let the BMS save my LiFePO4 batteries at the expense of the food in the fridge. Solar charging (if you have it) could extend the time quite a while if not forever. I would want someone looking into the boat in that case.

In the case of a long time away from the boat. The fridge is shut off and the largest load (might) be the anchor light. In that case the LiFePO4 bank is (discharged to) 50% SOC and disconnected and thus isolated from charge or discharge.

The start battery is switched to the main load bus and powers the anchor light and any other things that need power. Bilge pumps for example. Solar continues to charge the start and windlass batteries. The boat is put to sleep.

Perfect? Hardly....

[tanglewood]

I don’t know if this is a hybrid or a non-hybrid, but you asked about backup to LFP, so here goes.

The boat I’m building will have both LFP and LA, but they will never be connected except in an emergency.

There are two LA start banks, and each engine has a 1-2-off switch to select which bank to use to start. This provides redundancy for all engines.

The house bank is LFP only, with BMS that controls chargers in case they get carried away, though with chargers programmed correctly it should be a rare occurrence. High voltage, low voltage, and high temp will generate alarms in addition to shutting down chargers. Measure of last resort is a contractor to completely disconnect the batteries.

As a backup to the LFP bank, it will be possible to switch in either of the start banks, leaving the LFP isolated. Battery capacity will be severely limited, but the boat can keep running.

[john61ct]

Just get a PM on this, prefer to address here.

The FLA - LFP hybrid idea has only one goal that I consider makes sense, or at least any other benefits are side effects.

That is combatting the PSOC issue, handling lead's long tail problem off-grid.

Using ICE power for that IMO is just a non starter.

So as an alternative or supplement to solar.

This means energy flowing **from** LFP **to** lead, when there is no primary charge source active.

Going the other way in that context makes **no** sense.

This above proposal is outlandish, very much denigrated over the years by Maine Sail and others, and currently being discussed only as a thought experiment.

If someone with the right knowledge and tools wants to give it a try, that would be great, but it would be experimental, not suggested for a production setup to be relied upon.

_____
Now, put an active primary charge source in the picture, and you have the traditional "charge multiple banks at the same time" scenario.

The power is not going from battery to battery, even though that's what Charles calls his DC-DC BB line of chargers.

They are only required because of the very different voltage setpoints of the two chemistries.

This is a bog standard scenario, nothing speculative about it, and can be relied upon in a production install.

[john61ct]

Originally Posted by CatNewBee

It is not a good idea to just keep FLA on float all the time.

Sure it is, no problem at all.

Just need a good charge regulator, and to keep water topped up.

Done every day in millions of setups, no idea where you get that notion, totally false.

Now if you were talking long term unattended **storage**, I would suggest complete isolation, and an overnight charge every few weeks, but that's a different story.

[john61ct]

Originally Posted by tanglewood

I don’t know if this is a hybrid or a non-hybrid, but you asked about backup to LFP, so here goes.

The boat I’m building will have both LFP and LA, but they will never be connected except in an emergency.

There are two LA start banks, and each engine has a 1-2-off switch to select which bank to use to start. This provides redundancy for all engines.

The house bank is LFP only, with BMS that controls chargers in case they get carried away, though with chargers programmed correctly it should be a rare occurrence. High voltage, low voltage, and high temp will generate alarms in addition to shutting down chargers. Measure of last resort is a contractor to completely disconnect the batteries.

As a backup to the LFP bank, it will be possible to switch in either of the start banks, leaving the LFP isolated. Battery capacity will be severely limited, but the boat can keep running.

Yes, fine scenario, not to me a Hybrid setup.

Means to me ongoing energy flow between the two banks, as with the lead long tail charge from LFP as outlined above.

Not just a disconnected Reserve bank.

Of course a Hybrid system can also provide a Reserve as a side benefit if the LFP is large enough.

[tanglewood]

Originally Posted by john61ct

Just get a PM on this, prefer to address here.

The FLA - LFP hybrid idea has only one goal that I consider makes sense, or at least any other benefits are side effects.

That is combatting the PSOC issue, handling lead's long tail problem off-grid.

Using ICE power for that IMO is just a non starter.

So as an alternative or supplement to solar.

This means energy flowing **from** LFP **to** lead, when there is no primary charge source active.

Going the other way in that context makes **no** sense.

This above proposal is outlandish, very much denigrated over the years by Maine Sail and others, and currently being discussed only as a thought experiment.

If someone with the right knowledge and tools wants to give it a try, that would be great, but it would be experimental, not suggested for a production setup to be relied upon.

_____
Now, put an active primary charge source in the picture, and you have the traditional "charge multiple banks at the same time" scenario.

The power is not going from battery to battery, even though that's what Charles calls his DC-DC BB line of chargers.

They are only required because of the very different voltage setpoints of the two chemistries.

This is a bog standard scenario, nothing speculative about it, and can be relied upon in a production install.

What “above proposal” are you referring to? Several have been discussed.

[john61ct]

Originally Posted by Dockhead

The Sterling B2B chargers are brill and I would for sure use one for any charging source which can't be doubled -- like an alternator, for example, if you already have two.

But I don't think I would want to share a mains charger between two banks using this. Much simpler to add a second mains charger

Yes but only for redundancy. Obviously with a very large LFP bank, stacking them is sub-optimal, we all wish he'd ship the bigger ones soon.

But high amps is only needed if charge time is limited, as in from an AC genset not routinely run for other purposes.

For marina shore power there's no rush, so if you have a B2B, there is no need for a second mains charger.

But minor point, your boat your choice.

For simplicity, portability, integration with "BMS stuff",

I like to think of the BB as "the only source to touch the LFP bank".

[john61ct]

Originally Posted by Delfin

the size of the LFP bank to do what was expected of it in the envisioned hybrid configuration was a great deal larger than folks were suggesting.

For the long tail functionality, a 60-100AH LFP bank would be plenty to service even a very large FLA one.

The key variable is what SoC do you want to stop running your ICE charging. On say an 800AH bank you may need to go to 90%, where a 400AH bank you could stop sooner at 80%.

Either way you are saving many ICE runtime hours per year, the bigger the LFP bank the more you save.

[john61ct]

Originally Posted by rom

batt is LFP, you just need to make sure every now and then it is properly sitting at 50% SOC.

Note that the rule is

Don't store LFP at high SoC.

Usually spec'd as

Don't store **higher than** 50-60%.

In fact lower is just fine.

You just want to be **100% sure** that self-discharge does not drop voltage much below 12V, because dead flat is instant scrap time.

But just like 'don't go below 50%' with lead banks, there is nothing magic about that number, 20% is just fine, actually better for long storage, as long as there is no risk of letting it get down to 0%.

Note a packaged system often does not isolate from the cells, so its electronics will drop SoC much faster one that does, maybe in some cases 60% is safer.

[john61ct]

CNB, you make a lot of exaggeratedly negative comments about lead / FLA.

Not going to argue them here, if you want to, start a new thread.

Just wanted to post a heads up for relative noobs to take them with a grain of salt.

With other members prejudiced in the other direction, too much against LFP, I guess things b balance out 8-)

[evm1024]

Originally Posted by john61ct

SNIP

You just want to be **100% sure** that self-discharge does not drop voltage much below 12V, because dead flat is instant scrap time.

SNIP

I have no doubt that the above quote is true. To what extent is the question.

How low for how long for what capacity loss. Does anyone have a paper they can point me to?

I think next time my local surplus place has A123 18650 sized LiFePO4 cslls in stock (for $3 or so each!) I might pick up a few and try to answer some of those questions.

The 18650 is not a large prismatic cell of course but still something could be learned for a few dollars and a bunch of time.

[john61ct]

The closer to dead flat the less likely to get any usable life.

All depends on your standards. Industry standard EoL is 80% SoH, aka residual capacity. I don't like to push past 70% myself, but then I shoot for No Surprises.

Many owners limp along until unexpected failure comes or is imminent.

Starting with second-batts is IMO a science experiment.

But those can be interesting!

[evm1024]

Originally Posted by john61ct

The closer to dead flat the less likely to get any usable life.

All depends on your standards. Industry standard EoL is 80% SoH, aka residual capacity. I don't like to push past 70% myself, but then I shoot for No Surprises.

Many owners limp along until unexpected failure comes or is imminent.

Starting with second-batts is IMO a science experiment.

But those can be interesting!

Science experiment sounds good to me (I am a research engineer after all).

I went ahead and ordered up some 18650 1100 mAh cells to destroy. It will be a week or so till they get here.

I'll document the experiment in another thread.... Till then back to our regularly scheduled program.

[tanglewood]

Google LFP papers. There are dozens and dozens doing all sorts of tests and comparisons over year or more time periods. Lots of really good info, including the details of what happens when SOC is allowed to drop too low. I can’t remember the details, but I believe it is pretty sudden and complete death. Same on over charging. It’s not like LA where you can get away with one brief mishap and still have a usable bank. It’s death, not injury.