Do I just need a DC-DC charger to charge lithium?

[Rockinar]

I have a small sailboat. Just a single lead acid starter battery and a single lead acid house battery. I was looking to replace the lead acid house battery with a lithium.

To charge the lithium, do I just a need a DC-DC charger between the starter and lithium? Or is it more complicated than that? Boat is kept in a marina on shore power.

[mbartosch]

If you have frequent access to shore power there is no need for replacing a lead acid battery with a LiFePO4 bank, IMO. LiFePO4 really shines if you need to catch every Joule of energy your scarce charging sources deliver.

That said the same question has been posed and answered a significant number of times on this forum. May I suggest to do some reading and research in existing threads?

[tkeithlu]

A lithium system will save you weight, if you need that, or supply more power and slower self-discharge than a lead acid system. Demanding to charge, expensive as hell, but wonderful in place. A mixed system part Lithium and part lead-acid just sounds like a monumental PITA. Two systems, different charging, not easy to parallel, and so forth. I think that leads to two questions that lie before your original post. First, as mbartosch says, do the advantages of Lithium outweigh the disadvantages in your situation? And, second, if so why not completely convert to Lithium?

[mbartosch]

Originally Posted by tkeithlu

A lithium system will save you weight, if you need that, or supply more power and slower self-discharge than a lead acid system. Demanding to charge, expensive as hell, but wonderful in place. A mixed system part Lithium and part lead-acid just sounds like a monumental PITA. Two systems, different charging, not easy to parallel, and so forth. I think that leads to two questions that lie before your original post. First, as mbartosch says, do the advantages of Lithium outweigh the disadvantages in your situation? And, second, if so why not completely convert to Lithium?

From first hand experience I can confirm that LiFePO4 house and lead acid starter is a good solution. Lead acid has its advantages for starting the diesel engine: only very little energy is needed to start the engine, the battery is immediately recharged to full afterwards. This is the perfect use case for lead acid batteries.
LiFePO4 as starter batt is not optimal in my opinion. Best for longevity is to keep it between 40 and 70 % SoC which becomes difficult over time if you are doing coulomb counting. Which effectively means you will have charge the battery fully every once in a while and discharge to 50 % soon after.
That's not convenient for a starter batt.

If I were to get rid of my lead acid starter batt I'd either completely ditch it and only use the house bank (which will be able to deliver enough current to the starter even if at 0 % nominal SoC/2.8 V cell voltage).
Or the other option would be to to do it right and replace the lead acid starter battery with a small LTO battery. The perfect starter battery, but probably overkill.

[Stewie12]

I would not use the house battery as a starter battery. The two must be kept separate so that if the house if flat you can still start the engine and re charge both.

[Hermia II]

If you have one lead and one LiFePo4 you can use a Mastervolt Charge Mate Pro 40 to limit the output from your alternator which is very good. If you don't, you need an alternator with a 200Amp charge for a 100Ah LiFePo4 battery, or you will broil your alternator.

[kirklkjb]

It's never quite that simple. You'll need to think about building two isolated systems. 1) your lead acid starter battery and 2) your Lion house battery.

If you keep your shore charger it will need to be moved to the lead acid system.
Then you need to make sure your DC-DC charger does not overload your lead acid systems (Shore charger, alternator, cabling etc.).

Make a drawing and work through the details.

There are all in one charger/inverters that make this easier and more fool proof.

[BAD ORCA]

At the risk of straying off topic you might want to consider/looking into a Firefly Battery. I recently added one to my small sailboat and the performance has been exceptional.

They would need their own voltage, different from a lead acid so a B to B charger could be used between the two batteries. It would be the closest performance wise to a lithium that would be as close to a drop in replacement as you could get without any major modifications.

[NPCampbell]

Originally Posted by Rockinar

I have a small sailboat. Just a single lead acid starter battery and a single lead acid house battery. I was looking to replace the lead acid house battery with a lithium.

To charge the lithium, do I just a need a DC-DC charger between the starter and lithium? Or is it more complicated than that? Boat is kept in a marina on shore power.

A DC to DC charger or maybe a BIM should work.

You typically need 3 alternator protections (I am assuming you meant alternator and not starter):

1. overload - The DC to DC charger can protect against the huge charging current that a lithium battery can draw
2. load dump - If the lithium battery's BMS disconnects, the lead acid starter battery will present enough load to prevent a regulator burnout.
3. overheating at low speeds - This is a "maybe" depending on the current rating of the DC to DC charger. At low speeds, the alternators mechanical fan may not provide enough cooling to cover the heat generated from a decent load.

[Pete7]

Can you confirm why you want a Lithium (LFP) rather than simply fit another flooded lead acid (FLA) battery?

We have just installed a hybrid house bank consisting of one LFP and one FLA. They play nicely together so far. We use the LFP for high current loads like the kettle, toaster and shortly induction hob, oh and the wifey wants a hair dryer.

You can't run these main voltage items off a small house bank likely to be found on a smaller yacht until recently when LFP started to become mainstream.

However, you need to be sure that you need LFP before starting down this route as set up costs are high. Also there is some reading to be done because abuse a FLA battery and they can normally be recovered if you are quick. Not so with LFP over charge or completely discharge and it could end in tears.

Be interested in why.

Pete

[kirklkjb]

No endorsement and I have not used this device but it may fit the bill. Precision Circuits Lithium Battery Isolation Manager (Li-BIM). It's a high current continuous connection so your alternator will need to be able to support it.

[kirklkjb]

Here is a nice description with recommendations from Battleborn. https://battlebornbatteries.com/batt...ium-lead-acid/

[kenbo]

Originally Posted by kirklkjb

No endorsement and I have not used this device but it may fit the bill. Precision Circuits Lithium Battery Isolation Manager (Li-BIM). It's a high current continuous connection so your alternator will need to be able to support it.

I see no value in that product. It is essentially a diode splitter that will not charge either bank more than 80%. How they measure that is by voltage which has many serious pitfalls.

[kirklkjb]

It is recommended by the battleborn folks. Caveat Emptor.

[kenbo]

Originally Posted by kirklkjb

It is recommended by the battleborn folks. Caveat Emptor.

That does not make it a good product. I would guess that Battleborn sees this product as easy to install and should protect their battery. But it does nothing to fully charge a lead acid start battery which is the best way to kill a lead acid and does nothing to protect a small case alternator from overheating.