LifePO4 BMS selection

[geem]

You never have to think about it with lead because you don't tend to run huge inverters off them.

Since you are at 24v your have already halved the problem. All of the main options have already been discussed so not much to add there.

It really depends how much money you have and how idiot proof you want to make the system.
I have gone ultra cheap: a 4S pack with a 120A JBD BMS. Everything currently runs through that, and I just take care not to load it too much. So I don't hoover and cook at the same time.

I do have a plan to install a relay which will activate the remote on/off switch on my inverter, and that will mean it can bypass the BMS. But I haven't got around to setting that up yet, and tbh drawing 250A from a set of 270Ah cells doesn't really sit well with me.
So I think I will build a second pack, with another 120A BMS, and that will solve a lot of problems at the same time.

FWIW I've been living aboard full time with this system for over six months now, and I'm very happy with it. I had to switch back to gas cooking for a day, because we had two days of almost no sun. But given I spent about £1k in total I'm not complaining.

When you say cooking, what does that mean for you? Microwave? Electric oven? Induction hob? How much solar do you have? How much power do you take out and put back from your lithium bank daily?
We don't intend to cook with electric extensively so we will always have gas but we will be able to use the electric kettle and induction hob. The windlass load (1700w) will come from the lithium bank. If we lose the diesel genset for and reason, the lithium will run the 2000w load via the inverter but only for 15mins per day.
I plan to install a bus 155amp @24v alternator I have at some point. I may run a pair of Victron b2b chargers to limit to 60amp charging if that's possible or go external reg

 

[Kelpie]

We have a small two burner induction hob (2x800- it doesn't sound much but it works. Induction is very efficient)
We also use a Remoska tabletop oven, about 500w. Does decent pizzas and will do a roast chicken with ease. Struggles a bit with chips.
We also use a toaster, a 1000w wet and dry hoover (no more cordless rubbish for us!) and a laser printer.
We haven't added a microwave, might do if we feel the need. We just use a stove top kettle, we carry one anyway for those days when use gas, so why carry two of them.

Total solar is about 1200w, of which 920w is feeding the lithium. We do not have alternator charging for the lithium .

I don't have any way of keeping track of my exact numbers but I think we're making 100Ah+ most days. I just check the SOC in the morning and evening and if we're taking out more than we are putting back in, we make a few changes- cereal instead of toast, pressure cooker risotto instead of a three course cooked dinner. If things get really low we switch back to gas, but that's a surprising rare occurrence.

The fridge and freezer also run off the lithium, but their consumption is so low compared to cooking that it's virtually in the noise.

Why do you want to run your windlass from the lithium? We don't have one yet, but when I do install it I plan to run it from its own SLA. I'm not asking it to cycle deeply, it will usually be used with the engine is running, and it needs short bursts of high current. Seems a better fit for lead acid than lithium, to me.

 

[geem]

We have a small two burner induction hob (2x800- it doesn't sound much but it works. Induction is very efficient)
We also use a Remoska tabletop oven, about 500w. Does decent pizzas and will do a roast chicken with ease. Struggles a bit with chips.
We also use a toaster, a 1000w wet and dry hoover (no more cordless rubbish for us!) and a laser printer.
We haven't added a microwave, might do if we feel the need. We just use a stove top kettle, we carry one anyway for those days when use gas, so why carry two of them.

Total solar is about 1200w, of which 920w is feeding the lithium. We do not have alternator charging for the lithium .

I don't have any way of keeping track of my exact numbers but I think we're making 100Ah+ most days. I just check the SOC in the morning and evening and if we're taking out more than we are putting back in, we make a few changes- cereal instead of toast, pressure cooker risotto instead of a three course cooked dinner. If things get really low we switch back to gas, but that's a surprising rare occurrence.

The fridge and freezer also run off the lithium, but their consumption is so low compared to cooking that it's virtually in the noise.

Why do you want to run your windlass from the lithium? We don't have one yet, but when I do install it I plan to run it from its own SLA. I'm not asking it to cycle deeply, it will usually be used with the engine is running, and it needs short bursts of high current. Seems a better fit for lead acid than lithium, to me.

My bank will likely be 280ah at 24v. It should easily run the windlass for a few minutes. The bank needs to run the 2kw load of the inverter so their is no problem. In reality, when the engine is on, there will be charge from b2bs or alternator. If you lost your engine and needed to leave an anchorage under sail, you would need to be able to lift the anchor. It seems best to me to do this with the lithium that is charged by the sun.
We have no intention of removing the gas cooker. My wife is a great cook and we cook a lot. Not having a three ring cooker or good oven would not be acceptable to her.
You do highlight the problem of cooking by electric. You have to put back what you take out. Here in the Caribbean, cooking gas is cheap.

 

[Poey50]

I have our windlass wired to the LFP mainly because I like to have a dedicated engine battery. I do of course usually have the engine running when weighing anchor but on the few occasions I haven't (a small adjustment to length of warp for example) I've appreciated the higher residual voltage of LFP over lead acid.

 

[Kelpie]

We have no intention of removing the gas cooker. My wife is a great cook and we cook a lot. Not having a three ring cooker or good oven would not be acceptable to her.
You do highlight the problem of cooking by electric. You have to put back what you take out. Here in the Caribbean, cooking gas is cheap.

Yes don't plan to remove the gas either. We've never had more than a two burner, so adding the induction gives us four. And we can use an extension cord and cook on deck if the cabin is getting too hot.
The gas oven still gets a wee bit of use e.g. for keeping things warm, because the Remoska takes a long time to heat up. But to put it in perspective, we only just finished the gas bottle we were using when we left Scotland in August.
We average maybe twice a month eating out, so this basic galley we have put together gets a lot of use.

My reasons for wanting to cook electrically are not really about cost. I like self sufficiency. I also like flexibility. And I wanted to add lithium anyway, along with some electrification for use in marinas, so the only expense which can be levelled solely at the electric cooking project is the size of the inverter.

 

[geem]

Yes don't plan to remove the gas either. We've never had more than a two burner, so adding the induction gives us four. And we can use an extension cord and cook on deck if the cabin is getting too hot.
The gas oven still gets a wee bit of use e.g. for keeping things warm, because the Remoska takes a long time to heat up. But to put it in perspective, we only just finished the gas bottle we were using when we left Scotland in August.
We average maybe twice a month eating out, so this basic galley we have put together gets a lot of use.

My reasons for wanting to cook electrically are not really about cost. I like self sufficiency. I also like flexibility. And I wanted to add lithium anyway, along with some electrification for use in marinas, so the only expense which can be levelled solely at the electric cooking project is the size of the inverter.

For us the 3kw inverter is sized off the need to run the AC watermaker should the diesel generator fail. Our back up to the gas cooking is an induction hob that can run from the generator. Having said that, we have never had a problem with getting gas as we carry 4 cylinders. A British cylinder, an American cylinder and 2 camping gas cylinders. We can fill the British and America cylinders from each other with a custom pipe connection.