Drop in Lithium Batteries - the basics?

[dgadee]

Reading Kelpie's and other's posts and current prices it looks as though my next batteries might be Lithium.

I know nothing about them except that you can go beyond 50% charge.

Can you charge directly from the alternator?
Can you lay them on their side?
How heavy are they in comparison to lead acid?

Apart from 2 x 200ah, what would I need for a basic replacement system?

 

[Kelpie]

So the basic differences are:

- lithium doesn't really care about state of charge. It's not a good idea to leave them at 100% for extended periods, nor is it a good idea to regularly use the last 10% or so. If you plan to use the 20-100% region then they will last for thousands of cycles and perhaps decades, unless they are subject to extreme temperatures or discharge currents etc. The upside of this is that you don't want to 'float' them like with lead acid. So a different charging profile is required.

- they have a very flat voltage curve. It's almost impossible to tell how full they are just by voltage. So you probably want to fit a battery monitor- although if the battery has Bluetooth, you can access it's BMS directly and that will tell you.

- ah yes, the BMS. This is a small circuit board which monitors what's going on. Generally drop-in batteries have this built in, and all you see on the outside is two terminals, like any other battery. It will either be pre-set or adjustable (via Bluetooth). It is there to step in to prevent over or under discharge, or to shut things off in extreme temperatures. Lithium is very robust if kept within its happy range of parameters. You could argue that all batteries should have a BMS, our lead acids would probably last a few more years if they did! On cheap batteries, the parameters are set very wide so that you can get maximum performance. Which is the opposite of getting maximum lifespan. The main consideration of having a BMS is that the battery is able to disconnect itself, possibly without warning, and you have to bear that in mind. It's unlikely, it's not routine, but it's possible.

- lithium has very low resistance. This means it will suck up a charging current about as fast as you can throw amps at it. This is excellent news for solar charging, but makes things more complicated for your alternator, which is unlikely to last long if you don't do something to restrict the current. The other downside of low resistance is that lithium can generate welding-level currents in a dead short. With a drop-in battery a dead short isn't really possible (unlike a lead acid of course!) everything will at least have to go through the internal BMS first. But just to be on the safe side, you want to use the right type of fuse- class T is best, MRBF are next best, ANL may be adequate on a small system.

So bearing in mind these factors, how do you add a lithium battery?
1- make sure all charging sources are set to the right profile. If you have a basic PWM solar charger, you may need to replace it with an MPPT
2- consider what happens if the battery goes offline. Will you lose crucial systems? Will your alternator be damaged by no longer having anywhere to dump it's current?
3- how are you going to prevent your alternator from overheating whilst charging the lithium?

That's about as much as I can boil it down without oversimplification.

There are various solutions. On my boat, I went for an extremely simple option. I left anything important (autopilot etc) running off lead acid. And I only charged the lithium from solar. It's certainly not everybody's answer, but it kept my costs very low and achieved what I wanted.

I later added a crossover to allow me to power essential systems from either the lithium or the lead, but not both at the same time. Still no engine charging. When swapping between systems, I have to shut everything down for a couple of seconds. It's no big deal.

More recently, I did finally add a little 18A DC-DC charger. This is in many ways the simplest way of allowing engine charging whilst protecting your alternator from over current or sudden disconnects. The alternative involves fitting a bigger alternator and suitable regulator. It depends on how much you are going to rely on engine charging I didn't really want to start swapping out pulleys and fitting serpentine belts etc.

Another option, which I've not tried, is to fit lithium in parallel with a lead acid battery. I'm not aware that anybody in the forum has tried this but it is quite a tempting idea.

 

[Kelpie]

Cn you charge directly from the alternator?
Can you lay them on their side?
How heavy are they in comparison to lead acid?

Apart from 2 x 200ah, what would I need for a basic replacement system?

Just realised that I didn't exactly answer these questions. So:
1- no, unless your alternator already has protection built in. It will overheat.
2- yes, but it's better not to
3- you only need half as many Ah so less than half the weight
4- hopefully answered this in my first post. Assuming normal UK weekend cruiser type boat use, you want a DC-DC charger comfortably smaller than your alternator's maximum continuous output. You likely want to get rid of your 1-2-both switch and separate your start and domestic batteries (or you'll unwittingly create a hybrid system). And you'll almost certainly want to look at your general wiring and fusing and make a few upgrades there.

 

[dgadee]

Many thanks. I may have a year left before replacement so time to think.

 

[mattonthesea]

What Kelpie said.

If you go web searching look at the dates; some sites are a bit dated. My favourite utube channel is Off-grid Garage. It's not marine focused but he is very entertaining as he explores what happens when you try different things! Recommended to me by someone in this parish.

 

[dgadee]

Would both batteries be liable to stop powering at the same time ("off line")?

 

[Kelpie]

Would both batteries be liable to stop powering at the same time ("off line")?

It depends why they're going offline. If it's a high or low voltage disconnect, chances are one battery will reach that before the other, I think. But you won't know if one has gone offline without checking. And the other may not be far behind.
If it's an over-current disconnect (this is the only type I've experienced in practice) then I'd expect both batteries would shut off together- if the current is too much when shared, it's obviously going to be too much for one battery on its own.

 

[Neeves]

What Kelpie said.

If you go web searching look at the dates; some sites are a bit dated. My favourite utube channel is Off-grid Garage. It's not marine focused but he is very entertaining as he explores what happens when you try different things! Recommended to me by someone in this parish.

Lithium seems very much to be an evolving technology and we should expect 'improvements' - the biggest changes are on the horizon, for example replacement of Lithium - maybe. I have found the Lithium threads here on YBW of immense value - but they will become worthless if suddenly Sodium become flavour of the decade.

Jonathan

 

[lustyd]

Sodium is at least a decade away so suddenly just isn’t going to happen. Even then production would need to ramp up slowly before it’s affordable and even then it’ll likely be aimed at home power walls initially

 

[Poey50]

Would both batteries be liable to stop powering at the same time ("off line")?

This is the right question to ask for drop-ins. The ISO and ABYC require systems to have an advanced warning of disconnect at the helm. That's hard to achieve. It is sensible to have two batteries in parallel but as Kelpie says the loss of one will not be detectable. At minimum you need a good battery monitor and Bluetooth facility to read the cell voltages. You also need a backup plan to cover a complete disconnect.

 

[Kelpie]

You also need a backup plan to cover a complete disconnect.

My backup is a that there are two totally separate power supplies to the instruments. Each controlled by a simple keyed isolator. There is only one key, so you have to turn one supply off, remove the key, and then turn the other supply on. Without the use of a second key you cannot turn them both on together.

It takes a few seconds for the plotter to boot up again but it works well for me. Nav lights and autopilot will drop out for a couple of seconds as you make the switch.

 

[Poey50]

My backup is a that there are two totally separate power supplies to the instruments. Each controlled by a simple keyed isolator. There is only one key, so you have to turn one supply off, remove the key, and then turn the other supply on. Without the use of a second key you cannot turn them both on together.

It takes a few seconds for the plotter to boot up again but it works well for me. Nav lights and autopilot will drop out for a couple of seconds as you make the switch.

Sounds good.

 

[dgadee]

Kelpie, how would you set up a new Lithium system for us if you were "in charge". We are in Greece, and the Med for several more years.

250 watt solar with mttp by victron.
2 * 180 ah lead acid (+ starter)
Sterling ultra 60a charger - will charge Lithium (but we are usually anchored).
Yanmar 140a alternator.

We have a Honda 2kw which used to power the watermaker. Now we use a 2Kw inverter and run the engine. Was going to sell this. Might I need it?

We have an electric winch and windlass. May replace the hydrovane with a better electric autopilot than we currently have.

Only the fridge is power hungry. We cook with gas.

 

[Kelpie]

Firstly, establish how much power you actually need/consume on average.
Then choose your battery bank size based on that.
If you're getting on well with 360Ah lead acid, then you'll likely be fine with about 200Ah lithium.
Your MPPT is already lithium compatible, just a case of changing the settings.
You have a nice big alternator already, and I guess if your Med experience is anything like ours, you're going to be motoring a lot. So you probably want to go down a different route to me and take advantage of that, which I can't offer much advice on.

The main consideration is to separate your starter and house banks (unless you want to go hybrid, again I have no experience there). Do you have a 1-2-both switch at the moment?

 

[B27]

Kelpie, how would you set up a new Lithium system for us if you were "in charge". We are in Greece, and the Med for several more years.

250 watt solar with mttp by victron.
2 * 180 ah lead acid (+ starter)
Sterling ultra 60a charger - will charge Lithium (but we are usually anchored).
Yanmar 140a alternator.

We have a Honda 2kw which used to power the watermaker. Now we use a 2Kw inverter and run the engine. Was going to sell this. Might I need it?

We have an electric winch and windlass. May replace the hydrovane with a better electric autopilot than we currently have.

Only the fridge is power hungry. We cook with gas.

I think you may need to consider how your alternator charges a big lithium bank?
When you run the engine to drive the watermaker, what is the current from a) the alternator and b) the batteries? If all that charge will now come from the Lithium, how does that get replenished?

 

[dgadee]

Kelpie, No 1 2 switch. Starter battery charged from alternator then to VSR to house batteries. Solar direct to house from mttp.

I suppose I am wondering about what do do with the alternator output. We are moving back to the Ionian (too windy for the crew in the Aegean) so there will be quite a lot of electrons from the alternator.

B27, not really sure. The motor is 1hp (720 watts in theory) and quite efficient and usually we run for an hour, so the batteries aren't too discharged. If I keep charging the starter lead acid battery from the alternator can I use a battery to battery charger to the Lithium?

 

[B27]

...

B27, not really sure. The motor is 1hp (720 watts in theory) and quite efficient and usually we run for an hour, so the batteries aren't too discharged. If I keep charging the starter lead acid battery from the alternator can I use a battery to battery charger to the Lithium?

1hp motor might draw 800 + watts plus the inverter losses, could be nearly 100A.
OR it could be much less if the load on the motor is not 1HP.
If it's taking say 80A, the alternator will be doing most of the work.
If you don't get a big B2B charger, a lot of that current will come from the batteries, needing either more solar or more hours running the engine and the B2B.
Only you can know the use patterns and what level of 'service' from your system you're happy to live with.

 

[Kelpie]

So you've already got a separated system, that's good. Just make sure that it stays separated, e.g. does your shore power charger connect to the house battery only?

You'll probably want to upgrade your main fuse on the house bank- class T is the best although a lot of people use ANL or MRBF on small systems like you'd be installing.

You certainly can use a B2B to charge the lithium, and that would mean no changes to your alternator. But it's not the most efficient way of doing it. It seems a bit of a waste of your large alternator tbh.

 

[Poey50]

So you've already got a separated system, that's good. Just make sure that it stays separated, e.g. does your shore power charger connect to the house battery only?

You'll probably want to upgrade your main fuse on the house bank- class T is the best although a lot of people use ANL or MRBF on small systems like you'd be installing.

You certainly can use a B2B to charge the lithium, and that would mean no changes to your alternator. But it's not the most efficient way of doing it. It seems a bit of a waste of your large alternator tbh.

I don't recall the exact amperage interrupt figures but for small systems the MRBF fuses are significantly better than ANL or MEGA fuses but as you say, Class T is best. I wouldn't go lower than MRBF.

 

[dgadee]

You certainly can use a B2B to charge the lithium, and that would mean no changes to your alternator. But it's not the most efficient way of doing it. It seems a bit of a waste of your large alternator tbh.

What other options are there? I can't imagine what else.

I will look into fuses.