LFP - Decline in charge acceptance rate with battery age

[sailorboy1]

Well my cheap batteries will accept all my alternator or charger can put it them till the batteries are in the 90s percent soc. What good would faster acceptance be.

I was just wondering as the cost thread I read seemed low because I didn’t cost of more charge capacity figured in.

[a64pilot]

I think they are talking instead of throwing 90 amps into a bank for three hours, throwing 300 in one hour.
While it takes me up to six or seven hours to fully recharge my AGM bank that has had 150 AH removed from it, they could literally do it in a half hour with LFP.

Of course I rely primarily on Solar to do it, so it’s doesn’t make much difference to me, however if I don’t have panels and was recharging by generator only, well then LFP can drastically reduce generator running time.
Solar and lead complement each other rather well

[a64pilot]

Originally Posted by sailorboy1

I was just wondering as the cost thread I read seemed low because I didn’t cost of more charge capacity figured in.

Your correct. It has a lot to do with some of the greatest proponents of the systems, have none of their own, and love to speak of non existent super big DC generators that will do the job.
They love to say instead of buying a $10,000 AC genset, I can roll my own DC generator for $2,000 or less.
Yeah I didn’t pay anything close to $10K for my genset either, and the little single cylinder Kubota is pretty much busting a gut to make 200 amps, wanting more is going to require more HP.

Now I am not at all trying to be nasty, it’s just often when you start planning on systems and start using optimistic numbers stacked on top of other optimism, your results just aren’t realistic.

In the Aviation world we call these “paper airplanes” cause they work on paper, but not in the air.

[tanglewood]

Originally Posted by john61ct

You are likely looking at the limitations of a given BMS, link to the products.

The cells themselves can go much higher than catnewbee's numbers.

Those are likely just his own, or a conservative POV.

In reality very few setups as House banks can even get close to 1C anyway, which is why I reckon this "problem" is a non-issue IRL.

I'm looking at the CALB and Winston cell specs and manuals. So the numbers before a BMS is involved. And Victron's LFP batteries used CALB cells, and specify the same allowed charge rates. So the original seems to consistently be the battery cell manufacturers.

[a64pilot]

You can charge a Lithium bank too hard, they can take huge charge amps, but they can be pushed too hard and thermal runaway.
Any airplane hobby guy has seen that, usually takes more than one charge cycle though.

However it’s unlikely a cruising boat is going to have that big a charge source, most I’d think can only manage 200 or so amps, and most I’d think would have about a 400 AH bank.

[tanglewood]

Originally Posted by a64pilot

You can charge a Lithium bank too hard, they can take huge charge amps, but they can be pushed too hard and thermal runaway.
Any airplane hobby guy has seen that, usually takes more than one charge cycle though.

However it’s unlikely a cruising boat is going to have that big a charge source, most I’d think can only manage 200 or so amps, and most I’d think would have about a 400 AH bank.

Got it. Still trying to learn more about the OPs assertion that acceptance rate drops as the batteries age. At what charge rates is the drop seen, and by how much. If this is a demonstrable phenomenon in the cell manufacturer's specified charging range, then it's something I want to take into consideration. If it's a phenomenon for charge rates that would be considered abusive, i.e. rates above the cell specs, then I really don't care about it when designing systems since I intend to operate within the cell specs.


For what it's worth, two of the systems I'm working on will have charge capacities of 1000A @24V if everything is cranking. More common will be 400A. But they will be into a 720ah bank in one case, and a 1440ah bank in the other.

[a64pilot]

1,000 amps at 24v is a 24 KW generator at 100% efficiency, so realistically a 30 KW generator?
Only 30 KW generators I have experience with were huge, towed behind 2 1/2 ton military trucks.

You putting that in a boat? Have you calculated the cabling necessary to carry 24KW at 24 volts? Is this some kind of DC generator?

You putting this in a Boat?

[a64pilot]

If you accept that you ought to recharge having used 50% of the banks capacity, if you could charge at .5 C you’ll only be recharging for 30 min?
Is that correct? Why would you want to spend $$ and weight to charge faster?

[CatNewBee]

Originally Posted by sailorboy1

So are people installing these super batteries really also installing a 1C charging source to support them? Or is it a 'they charge real fast", but they are still only using the stock 90-100 alternator and battery charger they had before?

Nope, this is in most cases not economical / feasible.

In a 1000Ah house bank (and there are bigger installations with 1400Ah and more out there), it would be a 1000A charger source. simply not available ore more expensive than the battery.

You charge them with all you have, but are still far away from what is possible.

The maximum I can throw at my LFP would be :

180A (220A nominal) from the Victron Quattro 5kW
60A (2 x 40A Crystec, that also charge the start batteries)
(when the 7kW Onan is running or sufficient shore power available.)

100A from Solar MPPT (usually it delivers 80A, 100A is an exception on a very short time during the day)

2 x 40A from the alternators.

Is a total of 420A charging maximum or 0.4C

Even if I could double everything, I would never reach 1C at any time.

A small 400Ah battery however would do the trick with 1C charging, but is not enough for my power demands and safe capacity during bad weather.

During normal operation the battery is charged by solar while the on-board devices consume power, so effectively my vessel takes between 20A (refrigeration) and 30A (refrigeration and navigation, autopilot), and charging current effectively is between 0 and 70A, what translates to 0 to 0.07C

BTW, same for discharge. Maximum possible load is around 500A or 0.5C, very safe for 1000Ah cells, normally we use 20-30A permanent and spikes up to 250A during cooking. The battery delivers from full to empty 15kWh (measured).

[CatNewBee]

Originally Posted by a64pilot

If you accept that you ought to recharge having used 50% of the banks capacity, if you could charge at .5 C you’ll only be recharging for 30 min?
Is that correct? Why would you want to spend $$ and weight to charge faster?

No, you would charge 1h. If your bank is 50% SOC and you charge with 0.5C you will need 2 hours to charge from 0% to 100% or 1h from 50% to 100%. And no, even then I would not buy a 500A charger for my 12V/1000Ah bank, because it would mean 7.5kW reliable charge source - or at least a 10kVA generator to deliver that amount of energy. Btw same figures for a 24V/500Ah bank - charger 250A - generator 10kVA.

[sailorboy1]

Originally Posted by CatNewBee

BTW, same for discharge. Maximum possible load is around 500A or 0.5C, very safe for 1000Ah cells, normally we use 20-30A permanent and spikes up to 250A during cooking.

See that's an extra on a "benefit" of no usr to me. The most I ever see is -160 amps running the microwave a few minutes and my T105 440AH handles that.

This fast charging thing looks to me to be another rabbit hole because most boat don't have more than 100 amp charging source.

[CatNewBee]

Originally Posted by sailorboy1

See that's an extra on a "benefit" of no usr to me. The most I ever see is -160 amps running the microwave a few minutes and my T105 440AH handles that.

This fast charging thing looks to me to be another rabbit hole because most boat don't have more than 100 amp charging source.

Well not really, FLA 440Ah will never use the 100A until SOC 100% full, because the acceptance of FLA especially above 80% decline significantly. Same size LFP will charge several hours faster - and deliver more usable Ah without desroying the battery (deeper discharge). It will also deliver always above 12V no matter at what SOC, while a FLA would have a significant voltage drop below 50% SOC and high load - like your Microwave or windlass / winches etc.

But you have to experience it in real life, otherwise it is like telling a blind man about colors. He will not get the point, because they do not sound different to him.

[tanglewood]

Originally Posted by a64pilot

1,000 amps at 24v is a 24 KW generator at 100% efficiency, so realistically a 30 KW generator?
Only 30 KW generators I have experience with were huge, towed behind 2 1/2 ton military trucks.

You putting that in a boat? Have you calculated the cabling necessary to carry 24KW at 24 volts? Is this some kind of DC generator?

You putting this in a Boat?

Yes, all on a boat, but a very different boat than most here.

[tanglewood]

Originally Posted by a64pilot

You can charge a Lithium bank too hard, they can take huge charge amps, but they can be pushed too hard and thermal runaway.
Any airplane hobby guy has seen that, usually takes more than one charge cycle though.

However it’s unlikely a cruising boat is going to have that big a charge source, most I’d think can only manage 200 or so amps, and most I’d think would have about a 400 AH bank.

Faster charging of LFP doesn't come from adding bigger chargers - you can do that with any type of battery. The faster charging comes from elimination of the 2-3hr absorb charge required by LA, and instead continuing to charge at max rate right up until they are full. So that last 10-20% charge that takes 2-3hrs with LA only takes 5-10 min with LFP. That's the benefit regardless of your charge capacity.

[Albro359]

Sounds like BS to me.....100A from solar...seriously ???