Before you shout “oh no not again”, I have done some searching and reading (including https://www.canalworld.net/forums/index.php?/topic/127535-iwaca-guidance-note-on-lithium-battery-installation/), but I haven’t found the article that would make it clear to me what is needed in our case.

The engine has two alternators, the small one (50A) charging the lead-acid starter battery and the bigger one (150A) charging 3 x 110Ah LA leisure batteries. I was thinking in terms of replacing the very tired leisure batteries with a single LiFePO4 (e.g. a 300Ah Fogstar?) but what other kit is required?

We’re also considering adding solar panels so would that alter which extra item(s) to go for?

If we went ahead, we would have the installation done professionally (and I guess that could double the price) but at the moment I’m just trying to understand what the parts might cost so I can present a reasonable case to the other owners of the boat.

To charge the Fogstar batt from the 150A alternator, keep one Lead acid leisure battery to act as a buffer. You could use one of the new Victron 70A Orion XS battery to battery chargers to engine charge the Lithium batt. This keeps the charge current within 50% of the rated alternator current and should keep it safe from overheating.

If you use Victron mppt solar controllers too, then getting a Cerbro unit networked to talk to everything means that the Cerbro can cut charge before the Fogstar BMS will, meaning there isn't a potential single point of failure, leading to overcharging. Install the Li batt somewhere that is not the cabin. There are add ons to the Cerbro software that will let it talk to the Fogstar battery. However, whoever you chose to do the installation will likely have their own ideas on kit to use. Run their proposal past the forum for a sanity check. Not all professional boat sparkies are au fait with Li batts yet.

Arguably the simplest way would be to connect the large domestic alternator to the start battery and leave the smaller one as a tensioner for the drive belt for the water pump.

Fit the LFP battery and connect the two battery negative (unless the B2B you have uses a negative battery interconnect as well as a positive).

Connect the positive from the stat battery to the B2B and then the positive (out) of the B2B to the LFP positive.

Set the B2B so the alternator is not charging the LFP (via the B2B) at full output, at a guess maybe 60% of the alternator's rated out put, but others can give advice based on experience. This is to stop the alternator burning out.

NOTE: Battery to Battery chargers (B2B) go by different names from different suppliers, but Victron are arguably the most integrated and best. Victron also integrates with their battery monitors etc.

Any other charge source like solar or mains charging also charges the start battery.

This method is NOT considered mixing different battery technologies because the B2B sits between them.

You could leave the smaller alternator connected to the start battery as well, but one member reported this did not provide the added charge he thought it should, so for simplicity I would simply disconnect it.

58 minutes ago, Tony Brooks said:

Arguably the simplest way would be to connect the large domestic alternator to the start battery and leave the smaller one as a tensioner for the drive belt for the water pump.

Fit the LFP battery and connect the two battery negative (unless the B2B you have uses a negative battery interconnect as well as a positive).

Connect the positive from the stat battery to the B2B and then the positive (out) of the B2B to the LFP positive.

Set the B2B so the alternator is not charging the LFP (via the B2B) at full output, at a guess maybe 60% of the alternator's rated out put, but others can give advice based on experience. This is to stop the alternator burning out.

NOTE: Battery to Battery chargers (B2B) go by different names from different suppliers, but Victron are arguably the most integrated and best. Victron also integrates with their battery monitors etc.

Any other charge source like solar or mains charging also charges the start battery.

This method is NOT considered mixing different battery technologies because the B2B sits between them.

You could leave the smaller alternator connected to the start battery as well, but one member reported this did not provide the added charge he thought it should, so for simplicity I would simply disconnect it.

That is the simplest solution. The maximum current for the Victron Orion XS 12/12/70 is 70A which should be fine for the 150A alternator, even when charging the start battery as well, and will stop it overheating when charging for long periods at 70A.

If you want more charging current than this to cut engine running time then you'll have to go to a more complex and much more expensive solution like an externally controlled alternator with temperature sensing and 2 parallel Orion DC-DC, but this will end up costing well into four figures.

Thank you for the prompt replies as always. Am I right in deducing from what's been said that one can't just plonk the Orion between the 150A alternator and the lithium battery?

Be aware that some boat insurers are specifying that Lithium batteries may not be charged at night or when the boat is unattended. The solar turns itself off at night, so you don't need to worry about that side of things. But you need to switch off the Orion when you leave the boat. This is fine as the Li batteries should not be left on charge, and will happily look after themselves for 3 months at a time. And if you connect the solar to the LA start battery it will be kept topped up when the boat is unattended.

27 minutes ago, PineappleGuy said:

Thank you for the prompt replies as always. Am I right in deducing from what's been said that one can't just plonk the Orion between the 150A alternator and the lithium battery?

There are some things called alternator to battery chargers that can do this but I have no experience of them, Victron do not make one and all my experience is with Victron kit. The Victron Orion units are battery to battery (B2B) chargers so you need to keep a lead acid on the alternator output. Reports from people who have tried to use one direct from an alternator report large voltage and current cycles as the alternator regulator has nothing to dampen / buffer the system and the B2B starts cycling aswell.

The only way to reliably charge direct from an alternator to a lithium battery is using an external alternator controller such as a Wakespeed WS500 or Arco Zeus, quite involved and expensive. However, with batteries such as Fogstar with a built in BMS, if the BMS shuts off charge a voltage spike can occur (load dump), doing this is best with a battery system that communicates to the alternator controller to shut the alternator down several seconds before the BMS isolates the battery. Things become expensive with that type of battery, such as the Victron NG batteries and Voctron Lynx NG BMS.

Going with the above post from @Jen-in-Wellies consider getting a battery with CAN Bus communication, a Victron Cerbo GX and Victron Orion B2B charger and Victron SmartSolar and you will be getting towards a system per the guidance note. The battery tells the Cerbo what charge voltage and current is required and set up correctly, the Cerbo controls the chargers to match what the battery calls for.

55 minutes ago, PineappleGuy said:

Thank you for the prompt replies as always. Am I right in deducing from what's been said that one can't just plonk the Orion between the 150A alternator and the lithium battery?

Apart from overheating another problem with using "standard" alternators is that if/when the inbuilt battery BMS stops further charging it is the equivalent of disconnecting the battery while the engine is running. If you do that the alternator will try to produce a voltage surge that can wreck its electronics or even boat equipment. The more often it happens the more likely you are to suffer damage. By charging the start battery "first" there will always be a battery in circuit with the alternator so if the BMS stops charging there will still be a load (start battery) on the alternator.

I do not know, but strongly suspect, that the Orion will not provide a sufficient load on the alternator when the BMS disconnects, so I would not risk it. If I am right you will be risking the alternator and Orion.

Happy to be corrected if I am wrong.

I've now found the Victron community website where very similar questions to mine have been posted resulting in very similar answers to those given here so that's reassuring I suppose, although I have to say I'm disappointed that the Orion can't handle the alternator directly.

Another option I was considering was to potentially gain some useful extra capacity by going for AGM leisure batteries instead of lead-acid, particularly as they don't seem to be that much more expensive these days. However, I get the impression that even that is risky and would not be recommended as a drop-in replacement - is that so?

AGM batteries ARE lead acid.

Just a different way of containing the electrolyte AIUI.

People report they are more resistant to sulphation though, even though this seems improbable.

Just to go against the grain here, if like me you're a fair weather boater and your solar panels give you plenty of charge in summer, then you could keep the installation really simple and just remove the domestic alternator fan belt. That's assuming the engine water pump pulley is on the start alternator side. If you do that then your Fogstar lithium battery becomes a drop in replacement for your old LA batteries and you don't need any other equipment.

I did install a Victron Orion 50A B2B when I put in my 2 x 280A Fogstars, but it's basically a botch and if I was doing it again I probably wouldn't bother. For me it was a load of faff and expense for marginal benefit. In your case it turns your big 150A alternator into <50A alternator so you have to decide whether it's worth it. If you want to do it properly you'll have to buy an expensive Wakespeed alternator controller.

8 hours ago, PineappleGuy said:

Another option I was considering was to potentially gain some useful extra capacity by going for AGM leisure batteries instead of lead-acid, particularly as they don't seem to be that much more expensive these days. However, I get the impression that even that is risky and would not be recommended as a drop-in replacement - is that so?

AGM batteries of the same physical size and terminal type/layout are a direct drop-in replacement for flooded call lead acid batteries. As Mike says, they ARE lead acid batteries, but I will add that they are far more difficult for a boater to diagnose early signs of failure.

Like Mike, I can't see why they resist sulphation any better than flooded cell batteries, but they normally have a longer/larger cyclic life. This means that ignoring sulphation for a moment and as long as you have a satisfactory recharging regime they will last longer than typical flat plate flooded cell batteries.

Now sulphation. This is caused by leaving the batteries in a partially charged state so solar helps a lot, especially on holiday boats. There is/was one vendor who stated their AGMs needed a higher charging voltage than many alternators of the time could produce and recommended the use of an alternator to battery charger, but they got very threatening when I tried to question them on this - chemistry suggests otherwise. I feel it was because their AGM batteries would not gas at a slightly higher charging voltage and thus help with effective charging to reduce sulphation. There have also been an AGM chemistry/design the needed a lower than normal charging voltage, but I have not seen anything about them for years.

If you have effective battery monitoring equipment, know its limitations, how to set it up and use it, and ensure the batteries spend more time fully charged than discharged then AGMs should give you a slightly longer life, but that is more difficult on a live-aboard boat.

Take care, do not be seduced by marketing claims, the battery market seems full of them.

1 hour ago, blackrose said:

Just to go against the grain here, if like me you're a fair weather boater and your solar panels give you plenty of charge in summer, then you could keep the installation really simple and just remove the domestic alternator fan belt. That's assuming the engine water pump pulley is on the start alternator side. If you do that then your Fogstar lithium battery becomes a drop in replacement for your old LA batteries and you don't need any other equipment.

So how do you limit the current so the alternator does not burn out? LFP batteries will take the alternator's maximum output for the whole time between starting and the BMS stopping charging when the battery is fully charged.

How do you stop the BMS open circuiting the alternator when it decides the batteries are charged? When that happens alternators do get destroyed, not every time, but there is always that risk.

I suppose one could mitigate the first case by using a long charging cable, but that is really a bodge.

Edited October 3Oct 3 by Tony Brooks

1 hour ago, Tony Brooks said:

I suppose one could mitigate the first case by using a long charging cable, but that is really a bodge.

This works if you design it right and put a LA battery in parallel to protect the alternator from a disconnect, but relies on the battery BMS to to disconnect the LFP in the event of a LFP cell over or under voltage 'event'.

But yes its better to spend £thousands on doing it correctly in order for the installation to be idiot-proof.

1 hour ago, Tony Brooks said:

How do you stop the BMS open circuiting the alternator when it decides the batteries are charged? When that happens alternators do get destroyed, not every time, but there is always that risk.

Why would the alternator self destruct when there is no belt driving it so it's producing nothing?

1 hour ago, Tony Brooks said:

So how do you limit the current so the alternator does not burn out?

By as Mike said removing the belt so the alternator does nothing.

Edited October 3Oct 3 by GUMPY

1 hour ago, blackrose said:

That's assuming the engine water pump pulley is on the start alternator side. If you do that then your Fogstar lithium battery becomes a drop in replacement for your old LA batteries and you don't need any other equipment.

I now understand that you are advocating totally relying upon solar to provide sufficient charge rather than having the alternator available for if or when it may be required. That certainly simplifies things as long as the solar controller has a suitable charging profile of LFPs or a custom one that can be set. However, this rather goes against the often stated advice on here for heating and charging systems that one should have redundancy, so if one fails there is an alternative.

Just relying upon solar on a summer holiday boat may not be viable if the user has high electrical demands, and we don't know what the OP's demands are.

In the current uncertainty regarding the installation of lithium based battery's, it might be better to wait until the requirements are known.

Fitting solar panels is not a difficult job,nor is fitting one of the simpler battery monitors, which must be fully understood to get the best from the  information.

If the LA batteries are sized well to the boats electrical use, with solar panels fitted, then many years use can be expected. I've just had to replace 13 year old semi traction batteries, that had solar panel charging fitted for their last 8 years. (before the panels were fitted, the boat sat on shore line, with a timer connected to the charger, 2 days per week on charge, 5 days off charge, the batteries had a bit of natural cycling, seemed to keep them happy.)

Bod.

43 minutes ago, Tony Brooks said:

I now understand that you are advocating totally relying upon solar to provide sufficient charge rather than having the alternator available for if or when it may be required. That certainly simplifies things as long as the solar controller has a suitable charging profile of LFPs or a custom one that can be set. However, this rather goes against the often stated advice on here for heating and charging systems that one should have redundancy, so if one fails there is an alternative.

Just relying upon solar on a summer holiday boat may not be viable if the user has high electrical demands, and we don't know what the OP's demands are.

Especially in a traditional British summer, which we are less likely to see now, when someone's fortnight on the boat has nothing but continuous rain. Imagine if your booked time on the boat coincides with Wimbledon, or a test match series!

If you:

i) are prepared to pay for a professional installation

ii) want a slightly different take on your requirements

iii) are in the Midlands (or are prepared to cruise there)

have a chat with Kevin Mascall on 07929 140069.

5 hours ago, Tony Brooks said:

So how do you limit the current so the alternator does not burn out? LFP batteries will take the alternator's maximum output for the whole time between starting and the BMS stopping charging when the battery is fully charged.

I don't think the alternator will be generating much current if it isn't spinning!

3 hours ago, Tony Brooks said:

I now understand that you are advocating totally relying upon solar to provide sufficient charge rather than having the alternator available for if or when it may be required. That certainly simplifies things as long as the solar controller has a suitable charging profile of LFPs or a custom one that can be set. However, this rather goes against the often stated advice on here for heating and charging systems that one should have redundancy, so if one fails there is an alternative.

Just relying upon solar on a summer holiday boat may not be viable if the user has high electrical demands, and we don't know what the OP's demands are.

Well I have 910w of panels and totally rely on solar for generating power in summer. I never run the generator after the around the end of March. As a liveaboard my electrical demands are pretty high - at least compared to some. I run a 1600w washing machine a couple of times a week; work from home so the laptop and 22" monitor is on all day; heat the calorifier using the 1kW immersion when the sun is out; sometimes use the microwave, watch lots of TV, plus all the other 12v stuff.

I was just presenting the OP with another option, it's up to them to decide if it's suitable.

Thanks @Up-Side-Down, as it happens, the boat was taken to meet Kevin on the Ashby Canal last year so he's on our radar.

Thank you everyone for all the input, very illuminating as usual. I must say, having only last year acquired a new engine (Shire 35) with two alternators, I’d be reluctant to recommend effectively moth-balling one of them!

Taking into consideration that our bank account is still as depleted as a Leicestershire reservoir, I think my advice to the group this time will be to stick with conventional batteries with a slight preference for AGM.

Regarding battery usage, the main issue we have is that people often spend a few days on the boat canalside without going anywhere. The inverter doesn’t get hammered but I reckon the fridge consumes 50Ah in a day in the summers that we have nowadays, so users are urged to run the engine for an hour. Hopefully with new batteries that strategy will suffice as, I guess, would 300W of solar panels (we don’t have much usable roof space).

3 hours ago, Jen-in-Wellies said:

Especially in a traditional British summer, which we are less likely to see now, when someone's fortnight on the boat has nothing but continuous rain. Imagine if your booked time on the boat coincides with Wimbledon, or a test match series!

Well I've been totally relying on solar for the last 4 summers, even before I fitted the lithium batteries. I don't know if they've been typical summers or not, but I never run the engine or generator in summer to generate electricity. I haven't done much cruising so it's all been down to the panels.

Please don't take this the wrong way, but I can't help thinking that some here can't have very efficient panels or haven't matched their MPPT with their panels and aren't getting as much power from their solar systems as perhaps they could be? Even in winter I'm only starting the generator a couple of times a week for a few hours and that's mainly to run the washing machine. Hot water comes from a daily hour or two of Websato use. I sometimes angle the panels on sunny winter days and can easily generate 30-40A.

28 minutes ago, blackrose said:

I don't think the alternator will be generating much current if it isn't spinning!

Well I have 910w of panels and totally rely on solar for generating power in summer. I never run the generator after the around the end of March. As a liveaboard my electrical demands are pretty high - at least compared to some. I run a 1600w washing machine a couple of times a week; work from home so the laptop and 22" monitor is on all day; heat the calorifier using the 1kW immersion when the sun is out; sometimes use the microwave, watch lots of TV, plus all the other 12v stuff.

I was just presenting the OP with another option, it's up to them to decide if it's suitable.

having properly understood what you were proposing, I agree, it is well worth considering.

I think it would have been clearer if you had said "and just rely upon solar"

31 minutes ago, blackrose said:

Well I've been totally relying on solar for the last 4 summers, even before I fitted the lithium batteries. I don't know if they've been typical summers or not, but I never run the engine or generator in summer to generate electricity. I haven't done much cruising so it's all been down to the panels.

Please don't take this the wrong way, but I can't help thinking that some here can't have very efficient panels or haven't matched their MPPT with their panels and aren't getting as much power from their solar systems as perhaps they could be? Even in winter I'm only starting the generator a couple of times a week for a few hours and that's mainly to run the washing machine. Hot water comes from a daily hour or two of Websato use. I sometimes angle the panels on sunny winter days and can easily generate 30-40A.

That's my experience of summer and winter off grid power too. Summer, the B2Bs might as well not be installed, as they are not needed. I have them disabled by switches across the hi-lo terminals. January, I am fine with an average of one hour a day of engine running, which might be three hours every three days, or any combination and might be cruising, or not.

However, in summer, a rainy day is like a good winter day. A run of several of them, traditional Wimbledon fortnight weather, could leave the Li batt very depleted and no alternative chsrging option.

44 minutes ago, PineappleGuy said:

Thanks @Up-Side-Down, as it happens, the boat was taken to meet Kevin on the Ashby Canal last year so he's on our radar.

Thank you everyone for all the input, very illuminating as usual. I must say, having only last year acquired a new engine (Shire 35) with two alternators, I’d be reluctant to recommend effectively moth-balling one of them!

Taking into consideration that our bank account is still as depleted as a Leicestershire reservoir, I think my advice to the group this time will be to stick with conventional batteries with a slight preference for AGM.

Regarding battery usage, the main issue we have is that people often spend a few days on the boat canalside without going anywhere. The inverter doesn’t get hammered but I reckon the fridge consumes 50Ah in a day in the summers that we have nowadays, so users are urged to run the engine for an hour. Hopefully with new batteries that strategy will suffice as, I guess, would 300W of solar panels (we don’t have much usable roof space).

300W of solar isn't much, even in the middle of summer that'll only give you about 1kWh/day on average (less at this time of year), and the fridge alone would consume more than half of that -- or most/all of it at this time of year. Especially if money is tight, more solar (plus an MPPT controller) is likely to be your best bet, before looking at expensive things like B2B chargers and LFP batteries -- panels are dirt cheap nowadays. What's filling up your roof, is there any way you can you make more space for panels?

1 hour ago, PineappleGuy said:

Regarding battery usage, the main issue we have is that people often spend a few days on the boat canalside without going anywhere. The inverter doesn’t get hammered but I reckon the fridge consumes 50Ah in a day in the summers that we have nowadays, so users are urged to run the engine for an hour.

This certainly sounds to me like a recipe for quickly wrecking any new LA battery bank you might fit.

Now we know this I'm inclined to say fit a chunky LFP with a buffer LA and a B2B to protect the alternator.