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Starter Lead Acid House Lithium (Battery Query)

4K views 41 replies 7 participants last post by  colemj 
#1 ·
Hi All,

Quick question. Does anyone here have information about using two types of batteries, one for start (Lead Acid) and another (2) for House (Lithium) Do I need two chargers? What about the 1 | 2 | Combine switch is this still usable? I like the idea of the CCA of a lead acid for the starter battery as we have an ancient bukh dv24 diesel that takes a bit of kicking to get going. I am afraid it would harm the lithium bank if I went fully lithium. Any suggestions will be greatly appreciated.
 
#3 ·
We have been using LFP house with LA start for over 3yrs. We chose the simple path of putting a Blue Seas ACR between the house and start and just combining the batteries. The ACR will leave the batteries combined full-time until the LFP voltage drops below 12.7V - at which time the ACR disconnects the house and start.

In this manner, the start battery will always be held at float voltage (13.3V) when a charge source is not present, and will charge up to the LFP maximum voltage of 13.8V when a charge source is present. If the LFP house bank gets below the LA fully charged voltage of 12.7V, then the ACR disconnects the start from the house and leaves the start isolated at full charge.

Any downside to this method is that the start battery is "technically" not getting its proper bulk/absorption charge profile. However, the start battery is never discharged more than a few Ah's during starting, and that is immediately recovered, so it never experiences discharge cycling.

I suppose one could argue that keeping a LA battery on float almost continually, and only occasionally charging it to slightly less than designed bulk voltages, will shorten its life through sulphation.

This may be the case, but our start batteries have been working like new for over 3yrs, and they are just $50 Walmart car batteries. So if they only last 6yrs instead of 7yrs, they are cheap and easy to replace, and we aren't concerned about the slight lifetime hit.

Your other option is to use an expensive DC-DC charger to provide the "proper" charge profile, or to use a second alternator dedicated to the start battery.
Mark
 
#6 · (Edited)
Also, the lithium bank will outperform any LA battery for providing high current for long time. Your old Bukh would love it.

Mark
We really do need more information such as the brand, model and type of LFP batteries you are considering. Marine specific LFP batteries can easily start engines in which case you could keep the lead acid as a reserve or for starting and charge it with a DC to DC battery to battery charger such as a Sterling Power BB1230 from the LFP bank where all charging would be routed to. Many in drop-in LFP batteries can't handle high cranking or other high load current, due to the mosfet based BMS switches current limitations so you would not want to crank the engine with this type of LFP battery.

The cranking limitation is not a limitation of the cells inside but rather the sealed internal BMS design that uses FET based switches. Most of these BMS's/switches can trip on over-current and a high BMS temp (over-heating caused by drawing or charging with too much current.)

In early September a transient customer who had a yard in RI install a bank of drop-in batteries lost all electrical power while docking and nearly took out a 7 figure boat in 20 knots of wind. No one had bothered to look at the BMS current handling capability of the drop-in LFP bank. When he hit his bow thruster it worked for a few seconds, then poof, no 12V power. When he finally got tied up, the batteries eventually re-set, but his alternator was toast...

Marine specific or DIY LFP banks, that use actual contactors, such as Mastervolt or the Lithionics OPE-Li3 system can handle starting, windlass, thruster larger inverter etc.. loads with ease. The new Lithionics drop-in model 12V125A-G31-5CND-LRB can also handle cranking..

One drawback to an ACR is that it is bleeding LFP energy to float the LA battery. If you have excess energy not a big deal but if you don't then every little bit helps.

We also do not yet know where the forthcoming ABYC standard will land on paralleling Lead and LFP, so a DC to DC charger is not necessarily a bad idea, if your vessel is insured and you may need a compliant LFP system.
 
#8 ·
By the time regular ACRs isolate, the LFP bank would be dead flat, not a great scenario.

What you need is adjustable setpoints.

Have a look at the Magnum Smart Battery Combiner.

Adjustable setpoints, I believe "connect" as high as 13.8V, and LVC at 13.5V would work well to prevent Starter from drawing LFP House down when a charge source is not active.

25A limit so not to be used for jumpstarting, and as usual best for all significant charge sources to be routed direct to House, so the combiner is just used for maintaining Starter.
 
#16 ·
By the time regular ACRs isolate, the LFP bank would be dead flat, not a great scenario.
This is not true. The Blue Seas ACR combines the banks at 13.1V and disconnects the banks whenever any battery reaches 12.7V.

The LFP bank is not dead flat at 12.7V - it is ~20% SOC, which is where most want a disconnect to occur. On the way down to 12.7V, the start battery is not drawing any significant current from the LFP because it is fully charged already.

Even at 12.8V with the banks still connected, the ACR will disconnect them when starting the engine because the engine battery will drop below 12.7V, so the LFP isn't even being drawn upon for this.

Mark
 
#10 ·
Many boaters today, and many who don't know a lot about LFP, are looking at buying "drop-in" LFP batteries. These batteries have often have, especially when choosing based on price, low current handling FET based BMS switches that are not intended nor designed to handle high current such as starting loads.

We have a reader of MarineHowTo.com who bought himself a "Sweet 300Ah LiFePO4 battery". Problem is he had no idea what he was doing and his 300Ah LiFePO4 battery has a max charge rate of just 50A. He blew up a couple of alternators and had numerous BMS disconnects before he emailed us. His entire system had to be reconfigured around his dainty little BMS and in the end he was charging slower than flooded lead acid batteries...
 
#25 ·
Just curious...

My situation is

Optima Blue Top - Start 55ah
2 8D AGM - House 490 sh

ALL charging is to the house bank...
Start is on an Echo charge from the house bank

I am not aware of "charge profile issues" with the Echo charge. My start is always topped up and of course only used or a few seconds to start.... then it sits being trickle charged by the Echo Charge.

My BlueSeas batt switch DOES let me combine banks... I never do.

Would an Echo charge work for the OP?
 
#27 ·
Would an Echo charge work for the OP?
It will, but in the same way, and no different from, a simple combiner.

The Echo charger is a voltage follower that switches on/off at 13V, and bleeds a portion of charge to the start bank. I don't believe it can boost voltage, so the start battery will still only see the lower voltage the house bank is being charged to (I could be wrong on this point).

With LFP, when charge source is removed, the echo charge will stay connected and charging until the LFP voltage falls to 12.9V - which is similar to the ACR's 12.7V disconnect.

The LFP will cause it to behave differently than it does with your LA.

Mark
 
#31 · (Edited)
If you go back and parse it carefully, don't think I could be more clear.

Do an actual CC load discharge test - precisely timed rather than using a coulomb counter

between 13V and whatever your definition of zero SoC, where you set **your** LVC while regularly cycling

and tell me what % of total Ah you get.

If it's more than 5-10% you are really reducing the lifespan of your bank, by a **lot**.

Of course that is under gentle House loads, 0.1-2C rates.

If you're feeding a windlass, thrusters etc then your LVC may need to be tweaked a bit lower, but really IMO you need a bigger bank, and/or a more powerful energy source supporting such high discharges.

In any case the topic was allowing Starter to pull House down, and that's at a **very** low rate, thus 3.25Vpc represents a **much** lower SoC%.

I can't imagine anyone designing or choosing a combiner / isolator circuit for that purpose would intentionally program 13V as the open / isolation setpoint.

Can you, really?
 
#32 ·
If you go back and parse it carefully, don't think I could be more clear.

Do an actual CC load discharge test - precisely timed rather than using a coulomb counter
Have you actually ever done this? If so please tell us the discharge rate and DoD you had when the battery crossed the 12.75V ACR disconnect level.

between 13V and whatever your definition of zero SoC, where you set **your** LVC while regularly cycling

and tell me what % of total Ah you get.
How about you tell us???? You type in absolutes so you clearly must know the answer..?

If it's more than 5-10% you are really reducing the lifespan of your bank, by a **lot**.
Define "a **lot**" and the actual physical experience, with real cells, you have that backs this statement up?

In any case the topic was allowing Starter to pull House down, and that's at a **very** low rate, thus 3.25Vpc represents a **much** lower SoC%.
How much lower John? Lower than what? Clearly you must have the answers to this? Can you share with us a discharge graph you made with your equipment, on your cells, to make such a statement?

I can't imagine anyone designing or choosing a combiner / isolator circuit for that purpose would intentionally program 13V as the open / isolation setpoint.

Can you, really?
Really? Once again...

What practical experience do you have with LiFePO4 cells?
What cells do you actually own? Brand, model and capacity?
What boat do you own or is it an RV?
What charging & discharging equipment do you own?
How many cycles on your bank do you have?
What BMS are you using?

You post frequently in absolutes, as an expert, but then you post stuff like this........
 
#33 ·
Are you now saying that you think it **is** a good idea to use a Xantrex / Heart Echo Charge as the (only) device combining / isolating an LFP House bank to a lead Starter?

Obviously each case is different, and in fact I can think of a hybrid Main/Reserve design where the EC would be a perfect fit.

But not here, IMO from what the OP has laid out so far anyway.

If anything I've stated is actually wrong, please as always, I'd be grateful if you let me know, never stop being open to learning.
 
#36 ·
Are you now saying that you think it **is** a good idea to use a Xantrex / Heart Echo Charge as the (only) device combining / isolating an LFP House bank to a lead Starter?
The Echo charge was not brought up by the OP, nor by anyone answering the OP with suggestions. It was only brought up by someone who has one correctly operating on their AGM batteries - in which he asked if it would work similarly for a mixed LFP/LA bank. It was a valid quest for knowledge, not a proposal for the OP. I answered that in the negative, as did you, so that door is closed.

You have now chosen to focus on this echo charge angle as a diversion simply because you have been caught out (once again) saying things that are not true, about things you have no experience with (prove me wrong by posting your equipment and experience). Nobody else is discussing this, and any questions toward you are not about the echo charge.

The OP has a legitimate question about an issue many of us have had to deal with. In real life, using real equipment. There isn't any clear-cut definitive answer - only relative solutions with trade-offs. He deserves better than your absolutist, internet learned, theoretical, pedantic pontification.

He at least deserves truth and facts.

Mark
 
#38 · (Edited)
The likelier solutions are

an adjustable DCDC charger, my reco Sterling, but Kisae may work

or the manual switch idea

or letting the Starter(s) have their own separate charge source.

Those are afaict the only options that work well, and the reasons I gave above - which were disputed - are perfectly factual and true.
 
#40 ·
the reasons I gave above - which were disputed - are perfectly factual and true.
They are not. I would be happy to be shown to be wrong when you present your experimental data showing otherwise.

Maybe you could just start by telling us what specific LFP batteries and experimental equipment you own, as well as how you have applied them.

Mark
 
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