An Affordable Lithium Boat Battery

[migs]

A couple of years ago we looked into upgrading our failing AGM house batteries to lithium, but unfortunately the price of a commercial system was somewhat beyond our budget. Nevertheless, we wondered whether a diy approach would bring the cost down to an affordable level and started investigating. Published designs didn’t seem to meet our needs, but by taking a fresh approach and challenging some received wisdom we came up with our own design; an affordable solution that works well. We’ve been enjoying the benefits of Lithium for more than two years now, and our system has proved both reliable and effective. Here is the story; we hope it is of interest. bit.ly/43D3X1h

 

[fredrussell]

Link doesn’t work for me.

 

[migs]

Try this: bit.ly/43D3X1h

 

[RunAgroundHard]

Thanks for posting the link (works for me) and sharing your design and build notes. Appreciated.

 

[vas]

interesting, demanding 24Ah daily (except for windlass, et al which I guess are not daily) means you have a very relaxed charging/discharging regime for your system and it works for you.
Just to note that not everyone's able to have such low demand for such a large (relatively) bank, so imho balancing becomes necessary once you tend to demand more from the lifepo4 bank.

cheers

V.

 

[geem]

A couple of years ago we looked into upgrading our failing AGM house batteries to lithium, but unfortunately the price of a commercial system was somewhat beyond our budget. Nevertheless, we wondered whether a diy approach would bring the cost down to an affordable level and started investigating. Published designs didn’t seem to meet our needs, but by taking a fresh approach and challenging some received wisdom we came up with our own design; an affordable solution that works well. We’ve been enjoying the benefits of Lithium for more than two years now, and our system has proved both reliable and effective. Here is the story; we hope it is of interest. bit.ly/43D3X1h

BMS for lithium has moved on from when you built your battery. There are now good, cheap BMS available. I will be building my second lithium battery later this year. It will have its own BMS with 2A active balancing, class T fuse, Victron smart shunt and isolator just like the existing one. This will give me 100% redundancy and a lot more capacity.
You hardly use your battery. We take a huge capacity out of our battery by comparison. We also only charge to about 90% capacity but we still balance the cells for long life. This only happens every few days.
Everybody uses there systems a little bit differently. You system wouldn't work on our boat. Our battery is twice your capacity and we use a chunk of that capacity daily.
The lithium battery will die of old age before you can use the cycles they are designed to do. Use it or lose it. We work our lithium hard and if we had more charging capacity, we would work it even harder.

 

[migs]

'interesting, demanding 24Ah daily'

Thanks for your comments. As I mentioned in the piece, our energy usage is no doubt similar to typical UK boats i.e. a small fraction of that used by bluewater liveaboards. We spend about three months of the year onboard and our sailing area is the English Channel.

Our main load is really just the fridge (which is a standard Isotherm upright), but we ensure that its condensor air is drawn from the cool bilge and then immediately vented away. We are not agressive with the fridge's thermostat settings, and of course Northern Europe ambient temperatures are often fairly chilly. The fridge normally runs about a third of the time at less than 3A.

 

[migs]

'How do you top balance the cells in your battery?'

The cells were top balanced before being put into service, and haven't needed top balancing since.


'How are you monitoring the battery at cell level?'

Our BMS (see photo in our article) measures individual cell voltages; monitoring is by Bluetooth. Voltage resolution is <1mV with accuracy confirmed by our bench reference.


'There are now good, cheap BMS available'

Do they handle 270A continuous (without warming up) and survive 1k5A without damage, as ours does. (Our BMS was very inexpensive...)

 

[Neeves]

Very useful to have details of another Lithium build - they engender discussion. We don't have a lithium bank yet but are planning same.

Not entirely relevant to what you have achieved

I'm interested in how you manage to contain your daily usage of power to 24amp, if I've read that correctly. A marine fridge Waeco/Dometic of a size to be useful for more than weekend sailing will consume that and if you are making passages the power demands of a Autopilot will not be insignificant (plus the fridge, chartplotter etc).

On top of your daily requirement of 24 amp you will have need to factor in windlass, electric winches and your bow thruster - all of which need to be added on the same day you have already used some of that 24 amps

As with Geem, post immediately above, I wonder how you are measuring/monitoring the battery at cell level.

Jonathan

Sorry your reply, on the fridge, crossed with mine.

 

[sailaboutvic]

We build ours several years back 400 ah calbs bank,
we was very happy with them we ran a 3000w inverter then kettle , microwave,hot water heater just to mention a few .

 

[sailaboutvic]

Very useful to have details of another Lithium build - they engender discussion. We don't have a lithium bank yet but are planning same.

Not entirely relevant to what you have achieved

I'm interested in how you manage to contain your daily usage of power to 24amp, if I've read that correctly. A marine fridge Waeco/Dometic of a size to be useful for more than weekend sailing will consume that and if you are making passages the power demands of a Autopilot will not be insignificant (plus the fridge, chartplotter etc).

On top of your daily requirement of 24 amp you will have need to factor in windlass, electric winches and your bow thruster - all of which need to be added on the same day you have already used some of that 24 amps

As with Geem, post immediately above, I wonder how you are measuring/monitoring the battery at cell level.

Jonathan

Sorry your reply, on the fridge, crossed with mine.

Sadly. people forget all the extra stuff that needs batteries power when calculating the Amps needed.
we needed 750w of solar tokeep our batteries charged to keep all stuff running .
that was in the Med .

 

[geem]

We build ours several years back 400 ah calbs bank,
we was very happy with them we ran a 3000w inverter then kettle , microwave,hot water heater just to mention a few .

Yep, we do all that with a £100 BMS and 3000w inverter. Really loving the lithium. We pull about 90Ah at 24v (180Ah at 12v) from our battery per day.

 

[geem]

Sadly. people forget all the extra stuff that needs batteries power when calculating the Amps needed.
we needed 750w of solar tokeep our batteries charged to keep all stuff running .
that was in the Med .

We increased ours to 920w recently. Peak daily harvest has hit 4.4kw this week. A new record

 

[migs]

'if you are making passages the power demands of a Autopilot will not be insignificant (plus the fridge, chartplotter etc).'

From the article:

At anchor, our 120W solar panel provides sufficient energy to keep up with our daily energy consumption of ~24Ah (fridge, lighting, entertainment, electric toilet etc.); however, even with no sun at all, our240Ah LFP battery lasts for 10 days before needing a recharge. When sailing, daily energy consumption rises to about 80Ah, so we can sail for three days and nights (or longer given sun) before needing to run the engine.

The 24Ah daily consumption was measured over three months using our diy data logger


'you will have need to factor in windlass, electric winches and your bow thruster'

Whilst we are at anchor they're not in use. Incidentally, those items typically consume about 1Ah when used.

 

[sailaboutvic]

Yep, we do all that with a £100 BMS and 3000w inverter. Really loving the lithium. We pull about 90Ah at 24v (180Ah at 12v) from our battery per day.

I used the smart 123 BMS , it it’s expensive for what it is and it don’t balance as it should

 

[migs]

'A marine fridge Waeco/Dometic of a size to be useful for more than weekend sailing will consume that'

We just returned from seven weeks cruising in Normandy. The fresh food was wonderful...

 

[geem]

'How do you top balance the cells in your battery?'

The cells were top balanced before being put into service, and haven't needed top balancing since.


'How are you monitoring the battery at cell level?'

Our BMS (see photo in our article) measures individual cell voltages; monitoring is by Bluetooth. Voltage resolution is <1mV with accuracy confirmed by our bench reference.


'There are now good, cheap BMS available'

Do they handle 270A continuous (without warming up) and survive 1k5A without damage, as ours does. (Our BMS was very inexpensive...)

You are choosing to run large DC inductive loads through your cells. That's a decision you can make when selecting your BMS. Let your BMS operate a relay or run windlass and thruster from your engine start battery. We chose to run the windlass from the engine start battery as we have a pair of 100Ah 12v batteries being a 24v boat. In reality, the 1700w windlass motor pulls nothing like that when in use.
The relay in your system is another potential single point of failure. Its not wrong, its just different.
Most modern production boats run the windlass from the start battery so for many people installing lithium, this is something they don't need to change.

For me the biggest benefit of lithium is the ability to run life aboard differently. You can cook with an induction hob, run the immersion heater off the large inverter and for us, run the watermaker. These things are not easily achieve with lead unless you have a very large battery bank.
With your system, you don't take advantage of the benefits of Lithium. It looks like a wasted opportunity to me. You went to a lot of trouble to build your own system. All credit to you but you haven't moved on from thinking like a leadite

 

[Stemar]

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.

There are now good, cheap BMS available

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

 

[migs]

'run windlass and thruster from your engine start battery'

We prefer no electrical services connected to the start battery apart from the engine - for obvious reasons...


'you haven't moved on from thinking like a leadite'

I'll take that as a compliment; for a lot of UK boats lead acid batteries are a good choice. £400 all in for a complete system with all the benefits of Lithium is a compelling argument. For our type of UK boating, we are able to restock with provisions and water any time we chose; bluewater livaboards are in a different position, and I agree a different approach is needed.

The main point of publishing our piece is that it is possible to upgrade to Lithium at an affordable price for typical UK boats .

 

[sailaboutvic]

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

Re charging , I would leave your LA as starter batteries and to run windlass , then use a B2B off your LA to charge the lithium this will save you buying external reg or alternator, you can also then use the same shore charger to charge the lithium as well as any solar you have .