Lithium house and mini-lithium start

[LeighWebber]

I have a 32' sailboat where space is at a premium. I currently have two 150 AH Group 31 AGM batteries that are just about kaput. These are selectable with the usual A/B/Both switch. My goal is to create a larger LifePo4 house bank with two Group31 LifePo4 batteries in parallel and a separate tiny LifePo4 starter battery. The two Group 31s will replace the existing AGM batteries and will therefore fit where the existing batteries sit. The starter battery has to be super-tiny so I can tuck it in some available space in the cabin (not the engine compartment), about 2' from the starter. I already have an emergency starter power pack (like the ones you use to jump start a car). It starts my Beta 30 just fine. I keep it topped up on the boat, just in case.

Here's my reasoning. I want the biggest LifePo4 house bank I can get, as well as a separate starter battery in case I run my house bank completely down. I also don't want "dual use" batteries that support starting currents as well as deep discharge.

My proposed configuration is below (cable runs are simplified).

The starter battery has 450 CCA (the recommended CCA for a Beta 30). The APM-12 is there in case the house bank BMSs slam the batteries off. The DC-DC charger will handle topping up the starter battery.

I realize this is sort of backwards -- the DC-DC charger would normally be connected to the starter battery and would charge the house bank when the engine is running. But that would limit the house bank charging current to a measley 20 amps (I already own the Renogy 20-amp unit). Even with the biggest DC-DC charger it would limit charging current to 60 amps. The house bank could easily use the full output of the alternator, which means I could get them to 100% SOC with only a couple of hours of engine time.

The DC-DC charger supports LifePo4 charging. The Balmar regulator is super-tunable to match the desired charging profile of the house bank.

OK -- what do you think?

[hlev00]

Not backwards at all. In a retrofit it is often easier to leave the alternator charging the start, then DC-DC over to house. Also the start is usually left as lead-acid. That is why you see it so much. It is far more efficient to put all your charging sources onto the house bank.

Have you found a small LFP battery that can handle the starting requirements? I would be surprised to see a 30Ah LFP battery will handle the starting current required. I suggest staying with an appropriately sized AGM starting battery. Also in many forums with experienced marine electricians, Renogy gets some bad press. Not so much their panels, but their other gear. I would go for the extra cost and reputation of Victron for my DC-DC.

Don't forget fuses. At least MRBF on each battery on a T-Class if a single one for the bank.

Harry

[CaptainRivet]

What alternator do you exactly have, is it already externally regulated by the Balmar? V-Belt or serpentine belt?
The only Lifepo4 starting your engine would be a 12V 40AH Winston battery. Google and see if the measurements fit where you need it to be.
Forget 2x100AH and get a 200AH with single cells inside and a 200A BMS so that can start your engine as well. No you don‘t need redundancy here as lifepo4 is much more reliable then lead and if one battery has a problem then in 99.99% the other too.

[more]

Originally Posted by CaptainRivet

The only Lifepo4 starting your engine would be a 12V 40AH Winston battery.

noth thru but winston is best. today have 10 000 different brand for car start battery. 1 in usa like this cheap and 450cc

https://www.mightymaxbattery.com/sho...fepo4-battery/
3kg

winston WB-LP12V40AH is not easy to find in usa. for 1 battery. in EU is out of stock

[CaptainRivet]

Originally Posted by more

noth thru but winston is best. today have 10 000 different brand for car start battery. 1 in usa like this cheap and 450cc

https://www.mightymaxbattery.com/sho...fepo4-battery/
3kg

winston WB-LP12V40AH is not easy to find in usa. for 1 battery. in EU is out of stock

I only believe that this is a real Lifepo4 when you cut that open...that form factor you can only get with Li-ion delivering 300A.
Yes there are man car starting batteries claiming to be lifepo4...most are li-ion or derivates. And the ones that are really lifepo4 are bigger or last not even a year. Racing for 30years and tried a lot of them.
Good quality real Lifepo4 for cars and boats that really work are:
https://cs-batteries.de/20Ah-128V-60...ti-Dynamic-BMS.
But they cost more then you just put a battery from 4x280AH EVE+BMS together and just start from house.
I would still put my bet on the Winston 40 or 50AH...cheap for what they can do and their quality. Instead of the complete battery just buy 4 cells 40AH or 50AH.

[LeighWebber]

Thanks for the suggestions. The alternator is the 120 amp supplied by Beta. It's internally regulated, but Beta also supplies a device that attaches to the regulator and enables external regulation. Beta specifically recommends the Balmar regulator mentioned in my initial post. The engine already has a multi-groove serpentine belt and no change will be required to mount the 120. I should have mentioned that I currently have the stock 75 amp Beta alternator.

As for a single 200 AH instead of two 100s, my main constraint is the size of the battery compartments I currently have. They are both sized for Group 31 batteries - none of the larger form factors would work. I want 200 AH total capacity, and I think 2 x 100 Group 31s may be the only practical way to get there.

I need to research the start battery a bit more. a 40 AH unit will easily fit under one of the quarter berths. With my emergency start power pack, plus the ability to use house as a last resort, I'm not too worried about failure of the proposed LifePo4 mini.

[hlev00]

Good point by CaptainRivet on the question of the alternator.

Be sure to install the alternator temp sensor. Very important to start off with conservative parameters until you understand the capability of the alternator. Also, I agree that a serpentine belt kit is well worth it.

Also you might want to clarify in the diagram
1) that the alternator B+ does not pass through the MC618. The MC618 controls the alternator and B+ will go to the battery. Negs all go to common neg bus / stud. I sometimes leave the neg out of the drawing for simplification unless it is especially relevant, like a switched neg.
2) Ignition controlling the DC-DC charging is probably a good idea if you are going to use LFP for start. You don't want the DC-DC to keep charging it to 100% all the time or you will wear out the LFP.

Review your cable sizes and main fuses. Upgrades to LFP often require bigger cable sizes and fuse types to account for the much higher current capabilities of LFP.

If you don't have solar you might want it later so consider where you will connect it in the future. Definitely onto the house bank but will you have a place to bring the MPPT battery side onto the stud/bus bar?

Looking good though. Appears to be nice and simple.

[wholybee]

Originally Posted by CaptainRivet

I only believe that this is a real Lifepo4 when you cut that open...that form factor you can only get with Li-ion delivering 300A.
Yes there are man car starting batteries claiming to be lifepo4...most are li-ion or derivates. And the ones that are really lifepo4 are bigger or last not even a year. Racing for 30years and tried a lot of them.
Good quality real Lifepo4 for cars and boats that really work are:
https://cs-batteries.de/20Ah-128V-60...ti-Dynamic-BMS.
But they cost more then you just put a battery from 4x280AH EVE+BMS together and just start from house.
I would still put my bet on the Winston 40 or 50AH...cheap for what they can do and their quality. Instead of the complete battery just buy 4 cells 40AH or 50AH.

CCA is different that Continuous Amps. A battery rated for 0.2C could easily deliver 2C for long enough to rate a high CCA rating without damage. If most/all LFPs couldn't deliver that high current, we wouldn't need fuses with high AIC.

If you buy just some cells, then you also need a BMS. 1000CCA rated FET BMS's are available.

Personally, I would look at FLA for a start battery still, until you decide to only have one large and very reliable bank. Every other consideration aside, just comparing LFP to FLA, FLA is still a better start battery. The start battery is held at 100%, and even starting the engine doesn't appreciably discharge it. So that will shorten the life of the LFP.

[CaptainRivet]

Originally Posted by wholybee

CCA is different that Continuous Amps. A battery rated for 0.2C could easily deliver 2C for long enough to rate a high CCA rating without damage. If most/all LFPs couldn't deliver that high current, we wouldn't need fuses with high AIC.

If you buy just some cells, then you also need a BMS. 1000CCA rated FET BMS's are available.

Personally, I would look at FLA for a start battery still, until you decide to only have one large and very reliable bank. Every other consideration aside, just comparing LFP to FLA, FLA is still a better start battery. The start battery is held at 100%, and even starting the engine doesn't appreciably discharge it. So that will shorten the life of the LFP.

I am fully aware what CCA are and that Winston as only safe lifepo4 derviant is able to do 10C peak which is roughly CCA.
Winston sells since over 10years sealed 40-120AH 12V batteries without a BMS (and only rated 6C to make sure they stay in balance) as these cells are so stable in 12V/4S that no BMS is needed, installed dozen of them in cars and they run till today without any problem, also the ones that >10years old. These are not allowed to put in series, they are for peak current applications like starter battery and on purpose without BMS to always run. Beside LTOs the best starter battery available.
FLA is not the better start battery compared to a Winston and you can simply cut it of at 13.4V and charge it only to 80%….but not needed, they work with an AGM regulator if alternator is temp protected. That’s again armchair versus reality. That Winston 40AH costs around 250Euro and lasts longer then 10years, cheaper then any lead starter.

You can simply get good quality grade A cell (real grade a) like Winston or Calb in 1p4S, active balancer and use a BMV712 with a disconnect relay as low and high voltage cutoff, done is your LFP starter bat with no BMS issues. MOSFET BMS are the worst choice for starter bats…

[JBP]

You can get group 31 LFP with 140 or 150Ah now. Eco-worthy is decent brand.

The Epoch group 24 supports CCA of 400A for 10 seconds. Others are starting to also.

[CaptainRivet]

Originally Posted by wholybee

CCA is different that Continuous Amps. A battery rated for 0.2C could easily deliver 2C for long enough to rate a high CCA rating without damage. If most/all LFPs couldn't deliver that high current, we wouldn't need fuses with high AIC.

If you buy just some cells, then you also need a BMS. 1000CCA rated FET BMS's are available.

Personally, I would look at FLA for a start battery still, until you decide to only have one large and very reliable bank. Every other consideration aside, just comparing LFP to FLA, FLA is still a better start battery. The start battery is held at 100%, and even starting the engine doesn't appreciably discharge it. So that will shorten the life of the LFP.

Why do you need to Held a starter battery at 100%??
Simple answer because lead need to be kept at 100% otherwise they die fast and not really have all the CCA available at lower SOC.
Completely different with lithium…charge them to 70% and they can start the engine more times then an equivalent lead does. A lithium can deliver its full peak current independent from the SOC and has due to low internal resistance and no Peukert effect a much better power delivery which reduces wear on the starter.
Another fact a start of a 10-75hp engine takes less then 1AH put of the battery, so a LFP with small AH rating is more then sufficient if peak current fits.

[LeighWebber]

hlev00 -- Tx for your comments. I may not have mentioned, but the diagram was just to show the major components. Before I proceed I will create an actual wiring diagram with all the other bits and pieces (A/B/Both switch, fuses, etc.). I'll post it here for comments.

[LeighWebber]

wholybee -- good point about the start battery. I'll see if I can find one that is small enough to fit where I need to put it. I need to stick to the Beta specs for CCA, but I'll do some digging. My existing DC-DC charger would be perfectly happy charging an FLA.

[CaptainRivet]

Originally Posted by LeighWebber

wholybee -- good point about the start battery. I'll see if I can find one that is small enough to fit where I need to put it. I need to stick to the Beta specs for CCA, but I'll do some digging. My existing DC-DC charger would be perfectly happy charging an FLA.

Put a clamp meter and actually measure how much you need. A starter requiring 450CCA is in the 100A range. A lithium starting that would need 200-250A peak current, not 400...

CCA is always overspeced for cold weather and a saging lead going down to 9-10v means current goes massivle up to deliver the watts the starter need while the lithium stays at 12.8V and just delivers.

The 40AH winston can do 250A peak 30sec and 400A for 10 sec constant=straight and starts the 7L V8 of a buddy since 11 years and still going strong...7l V8 has a 850CCA requirement for this starter and a lead with 850CCA is hardly starting it in cold weather of switzerland, winston 40Ah without a sign of stress.
Same my Audi R8 5.2l V10...40AH winston 8 years old now, original a 110AH AGM starter that dies all 4 years as Audi has a lot constant current requirement the AGM cannot handle long.

[hlev00]

Originally Posted by CaptainRivet

Put a clamp meter and actually measure how much you need. A starter requiring 450CCA is in the 100A range. A lithium starting that would need 200-250A peak current, not 400...

.

Yes but you need a higher end clamp on DMM like from Fluke to measure the initial inrush current. A basic DMM from Harbor Freight, as example, won’t give you that.

For the OP here is an excellent article.

https://marinehowto.com/drop-in-life...ated-consumer/

The better LFP manufacturers are rapidly improving over the issues described but do your research. Of course if you are building your own battery that is a different kettle of fish. Scroll down or search for “DC Motor In-rush” to see the inrush issue. The author isn’t using a DMM but the better Fluke models can do this.