An Affordable Lithium Boat Battery

[migs]

'large DC inductive loads through your [lithium] cells'

In fact, inductive loads actually reduce current build up compared to resistive. Capacitive loads are responsible for inrush currents. Motors sometimes have additional start up currents until their back emf reduces their current to a normal running value.

The static and dynamic loads on our lithium battery (as designed) are well within the cell manufacturer's rating. We have also measured the actual system to confirm our design calculations

 

[Kelpie]

Interesting article, thanks for sharing.
It's good to see somebody taking the simple approach. So many lithium projects become overtaken by geeky add-ons.

I spent about the same as you on my cells, and like you this was cheaper than the equivalent good quality lead acid which was the alternative.

I didn't, however, attempt to make my own BMS. I was originally going to use a basic BMS plus a relay to handle bigger loads. But in practice I found that I could get a 120A BMS for about £60 and this was enough for my needs. I later upgraded to a 200A version when it became available, and have kept the original as a spare.

Interesting thoughts about fuses. I really struggled to get a definitive answer. I am also using an ANL but will shortly be upgrading to class T. I'm going to add a second battery so it seems a good time to make that change.

It was very hard to get a good answer on the short circuit current of LFP cells, and the numbers I found were conflicting. I think in practise the short circuit would go through a certain length of cabling, or a faulty component like an inverter, which would greatly reduce the current.

 

[B27]

'large DC inductive loads through your [lithium] cells'

In fact, inductive loads actually reduce current build up compared to resistive. Capacitive loads are responsible for inrush currents. Motors sometimes have additional start up currents until their back emf reduces their current to a normal running value.

The static and dynamic loads on our lithium battery (as designed) are well within the cell manufacturer's rating. We have also measured the actual system to confirm our design calculations

It's not really that motor loads are inductive, the problem is that a motor looks a lot like a short circuit until it starts turning.
Inrush currents for DC motors are often four or five times the max load running current and for your thruster that is a very big number.

The effect of inductance in a motor comes into play when you switch it off.

This is quite basic circuit understanding for someone experimenting with kW systems.

 

[noelex]

Great article. It sound like a perfect system for your boat and many others.

One concern is while the discharge current for your batteries is 2C, which is 560A, this is limited to a maximum of 30 seconds. The continuous discharge current is 1C, which is 280A.

While bow thrusters are not commonly used for more than 30 seconds this is occasionally needed and this is a restriction you should be aware of especially if you factor in the effects of the higher inrush current placing further demands on the battery bank.

 

[migs]

Our cell specification is 2C (560A) for 1minute, but in practice we never use the thruster for more than a few one second bursts. 10s would be sufficient to rotate the boat through 180 degrees! Maybe our thruster is particularly effective - its a powerful twin blade model, and we've seen other boats where the thruster just seems to make a noise rather than push. In fact we need to watch out when standing on our bow when the thruster is used as you can be knocked over. See attached photo; note the depth of forefoot under water, the thruster is also positioned close to the stem - perhaps that helps with thrust? And as mentioned in the article Lithium does give that extra puissance.

To keep in practice, we do try to maneuver without using the thruster; however, it's saved our bacon on more than one occasion.

 

[noelex]

Our cell specification is 2C (560A) for 1minute.

This is the link listing 2C for a maximum of 30 seconds is below:

https://www.battery-germany.de/wp-c...80K-280Ah-Product-Specification-Version-B.pdf

Obviously the specifications for your cells are different but it is something anyone planning to copy your system should check.

 

[migs]

If we were starting again, we might be tempted to use expensive Winston cells as they have a 3C continuous rating! If you look at Winston teardowns compared to aluminium cased cell teardowns this is most likely because Winston's have multiple parallel internal elements, whereas the aluminum case cells only have two.

In summary: aluminium cells are smaller, lighter, have a more modern design and are very much cheaper; Winston cells have tougher cases, more robust terminals and a better discharge rate. (The jury is still out on Winston cells' low temperature charging capability - many consider this to be marketing puff...)

 

[Kelpie]

If all you want to do is draw more current, you're probably better off just buying more aluminium prismatic cells. And then you get more storage too.

Of course the better build quality of Winstons might appeal. It really depends on your budget and what you're trying to achieve.

 

[geem]

If all you want to do is draw more current, you're probably better off just buying more aluminium prismatic cells. And then you get more storage too.

Of course the better build quality of Winstons might appeal. It really depends on your budget and what you're trying to achieve.

If you are using conventional off the shelf BMS then building a pair of 4 cell 12v batteries will half the amps draw through the BMS and you get redundancy in case of BMS failure on one battery.
I will build a second, 8 cell 24v battery when I get back up to Antigua in October.

 

[Neeves]

Thanks for this, I've saved migs' article for future reference as we've just fitted a fridge, so our current 112AH of LA batteries may well prove inadequate, and LFP does seem to be the future, albeit an expensive one.


I'm curious abut what's available as building my own is way above my capacity as an electronics engineer - I can solder, scruffily, and I know what a transistor is, but that's about it!

With a twin engined cat, 200W of solar and modest domestic needs - the new fridge is probably the biggest eater of electrons, though we do have a windlass. At present, we have a pair of batteries that start the port engine and cover domestic supply and a single battery that only starts the starboard engine. If I went down the LFP route, would it be OK to use a single battery to start both engines, charged by one alternator, and the other to charge the LFP system? It's a standard Beta alternator of unexceptional performance so, presumably, I'd need some clever electronics to control it, or a small LA battery and a B to B charger.

I'm some way off doing all this, especially having spent far too much money on rectifying "deferred maintenance" by the previous owner, but I like to let plans develop slowly and build up knowledge well in advance, so all suggestions gratefully received.

Thanks in advance. Off to the boat now, so won't be able to reply for a few days

Our system is lead - but planning for Lithium. We are in no hurry for Lithium but when the lead goes down we intend to replace - and we want to be ready - at our leisure.

In answer to one of your questions:

We have one engine start battery 60a/hr. We have 2 x 20hp MD2020. We start one engine leave to run, in neutral, for a few minutes (check water flow by simply looking over the side). We then start the second engine. Both engines and the house bank 400a/hr are charged from the standard Volvo alternators (but I believe the alternators were modified by the electrician). We have never had any problems. Josepheline is now over 20 years old we have replaced, pre Lithium, the house and engine start once. The big draw for us would be the windlass, if you are retrieving 80m of chain and releasing a well set anchor, it takes some time, and we would always run the engines, largely in neutral (we put in gear, 'pushing' the yacht toward where the anchor is on the bottom - then put back into neutral), when we retrieve. Another big draw for us, apart from the AP, would be radar which we would have active (Simrad, Broadband) at night and in 'inclement' weather.

Suggesting that a Fridge draws 24a/day and that daily consumption is 24a/day does not make much sense to me - or it suggests rejection of every other domestic needs, laptop, phone, lights, deep freeze, bread maker, drill, freshwater pump, juicer, water maker, windlass, electric winch - its 2023 - and one we don't have - a camper washing machine. If this seems excessive - we try to survive without recourse to a marina nor supermarket for upto 3 months - and 2 hot showers per day is standard and non negotiable and we need the freezer to store the tuna, crayfish and lamb chops/roast (not forgetting chilling the white wine )

Jonathan

 

[migs]

'domestic needs, laptop, phone, lights, deep freeze, bread maker, drill, freshwater pump, juicer, water maker, windlass, electric winch'

From the article:

'Much of the information published about lithium upgrades seemed to focus on complex, expensive systems for blue water boats (with electric galleys, water makers, freezers, washing machines etc.), and there appeared to be very little advice for more modest boats like ours.'

If you are concerned that other people's decisions don't coincide with yours, don't fret - instead let's celebrate the differences...

 

[Tranona]

Suggesting that a Fridge draws 24a/day and that daily consumption is 24a/day does not make much sense to me - or it suggests rejection of every other domestic needs, laptop, phone, lights, deep freeze, bread maker, drill, freshwater pump, juicer, water maker, windlass, electric winch - its 2023 - and one we don't have - a camper washing machine. If this seems excessive - we try to survive without recourse to a marina nor supermarket for upto 3 months - and 2 hot showers per day is standard and non negotiable and we need the freezer to store the tuna, crayfish and lamb chops/roast (not forgetting chilling the white wine )

Jonathan

This is not typical of the way that we use our electrical systems - and even if we were like you it is clear from what you say it can be done with LA if you have the means to recharge at a rate that balances your usage.

The OP to my mind has shown 2 things. First there is not a direct lithium replacement for LA - at least not at a level that makes sense economically unless you DIY. Second the only real advantage is the reduction is size and weight for a given usable capacity.

Lithium only makes sense if you revise the systems on your boat to take advantage of the properties of the batteries, such as electric cooking, or adding more power consuming items and have a boat that will accommodate the extra solar required to provide the energy that you use.

 

[migs]

Actually, the main reason we went for lithium was because we were annoyed that our AGMs died after only five years (they were Lead Crystal AGMs, but that's another story). Replacement batteries that were actually cheaper for the same energy storage - and ones that will last for many many years was a compelling argument.

There is nothing stopping an enterprising firm developing and selling a system similar to ours at an affordable price; however, I guess the market is quite small, and it's already owned by a certain 'blue box' manufacturer.

 

[B27]

The OP is only concerned with providing about 24Ah per day, mostly to a fridge.
That is not outside the range of 'normal' for a UK weekend/holiday boat.
In fact it's very close to my own situation.
I serve that need with a well-used 110Ah leisure battery which came with my boat, and a £40 solar panel.
Fridge, instruments, autopilot, LED cabin lights, charging phones and tablets.

I don't have a bow thruster or a windlass or electric winches.
Mostly only use the autopilot when we're motoring.

The only advantage of lithium in serving these kind of needs would seem to be that Li batteries will take fast charging, you could for instance shove 60A into the battery for half an hour a day, which might be ideal for those days when you motor out of harbour, put the main up and then turn off the motor until it's time to anchor. When solar isn't delivering, you need too many engine hours to properly charge a Lead-acid battery.

I do have a diesel hot air heater, I can imagine that will make some demands on the system if we get more late-season sailing this year. So far it's not been used heavily on consecutive days, so the solar has been able to catch up over the next day or two. I'm considering adding a couple of small solar panels.

 

[geem]

For most people sailing in the UK, lithium is no benefit. The benefits come when you change the way you use your boat. For us here in the Caribbean or those in the Med in summer, not having to cook on gas is a benefit. When the cabin is over 30degC, adding more heat and humidity to the boat through gas cooking is not great. Induction cooking is so much cooler. Not having to the get the batteries fully charged every day is also a bonus.
If you want to make full use of lithium you need to know that you can recharge what you are using. Thr obvious choice is solar but what do you do when there is no sun for a couple of days? We have a diesel generator. With a couple of consecutive wet days, we run the generator to make water and hot water plus we run the battery charger. We supplement the induction cooking with gas cooking if the boat isn't too hot.
I think to make the full use of the lithium, you really need a reasonable size boat to give you space for solar, otherwise, its not so easy replenishing the amps in you battery.
If you want to build a simple 280Ah domestic battery, you can do it yourself with off the shelf items but it won't be cheap. For many people, a couple of Trojan 105RE deep cycle lead batteries would be a better choice with a life expectancy of over 8 years very realistic. There would be no rewiring of the boat electrics and nsurance concerns.
You only have yo go on some of the lithium forums online to realise that most people are totally clueless about electrics. Don't build a lithium battery unless you have a reasonable knowledge of the subject. Don't install drop in lithium batteries if you have no understanding of the subject.

 

[Neeves]

One constant thought at the back of my mind (not relevant for us, yet, as our current battery bank, management and charging are all adequate) :

is that the alternatives to lead are still under constant development and what is ideal (accepting there are already different ideal option - dependent on usage) now might be replaced by something better in a very short time. Replacement might not even be lithium, nor batteries.

Geem points out the disadvantage of using Lithium with built in management - surely this will change - with no disrespect.... if Geem can develop a better system - so can others .... and make it commercially successful and sensible. But is Lithium, as we know it today, going to be the optimum answer? With the speed with which lithium has caught our attention - find me a supportive thread from 5 years ago - have we reached optimum technical solutions?

I'm immensely grateful that Geem and migs have taken the plunge but as our current battery bank and engine start battery are adequate we are also not going to make the investment - despite the advantages of Lithium. Our usage is not that different to Geem's and if we had to replace the battery bank - we would follow his lead - but its an expensive upgrade - that might be overtaken within 5 (?) years.

Different battery technology, different electronics, different fuel

Now I'm off to investigate induction hobs (as our knowledge base is built on gas)

Jonathan

 

[migs]

We use our boat all year round, and when you are at Newtown Creek in January (with ice on the decks and no sun) you need plenty of battery capacity. Our Wallas diesel heater is very efficient and uses only 0.1l/h of diesel and 1.5A of electricity; it is also virtually silent both inside and out. When you're the only boat about (just you, the geese and perfect peace), the last thing you want to do is fire up your engine or a generator. Some of our best times on the boat have been in the middle of Winter...

Incidentally, to get the same capacity as our 240Ah useable Lithium with Trojan 105s, it looks like you it would cost about £800 (4 batteries) from Tanya i.e. twice the price of our battery.

 

[geem]

If we were starting again, we might be tempted to use expensive Winston cells as they have a 3C continuous rating! If you look at Winston teardowns compared to aluminium cased cell teardowns this is most likely because Winston's have multiple parallel internal elements, whereas the aluminum case cells only have two.

In summary: aluminium cells are smaller, lighter, have a more modern design and are very much cheaper; Winston cells have tougher cases, more robust terminals and a better discharge rate. (The jury is still out on Winston cells' low temperature charging capability - many consider this to be marketing puff...)

Surely if you were to install Winston cells with 3C rating it would be a total waste of time with your set up. You aren't doing anything with your lithium that others aren't doing with lead. Normal EVE, CATL, CALB cells are robust and cost effective without going to Winston cells. I don't know of any major battery manufacturer thst is using .Winston cells any more? I think even Victron have moved on. Winston cells are high end. Perfect for traction projects with their 3C rating. I do know of some massive motor yachts using them but they have a serious budget.
The company I am consulting for have a liquid cooled prototype using Winston cells but we are testing it to exceed 3C, charge and discharge. It's a specialist product

 

[migs]

It never ceases to surprise us how much people get quite so worked up about this type of thing (anchors anybody?). For example, the 'Lithium Batteries On A Boat' Facebook group are staunch supporters of Winston; most of them think that aluminium cells are the work of the devil. Let's just let people do what they want, it's their life...

 

[Kelpie]

We use our boat all year round, and when you are at Newtown Creek in January (with ice on the decks and no sun) you need plenty of battery capacity. Our Wallas diesel heater is very efficient and uses only 0.1l/h of diesel and 1.5A of electricity; it is also virtually silent both inside and out. When you're the only boat about (just you, the geese and perfect peace), the last thing you want to do is fire up your engine or a generator. Some of our best times on the boat have been in the middle of Winter...

Incidentally, to get the same capacity as our 240Ah useable Lithium with Trojan 105s, it looks like you it would cost about £800 (4 batteries) from Tanya i.e. twice the price of our battery.

You're almost making me homesick
I was in the same position as you, I couldn't afford to put in Trojan 105 batteries, it would have cost me £790 delivered to address. My cells and BMS were £407. It's a big saving, for batteries that should have a far longer lifespan, without monthly maintenance, etc. A no brainer really.

Can we put to bed the idea that lithium is the expensive option?