Lithium Iron Phosphate Battery vs lead acid

[steveeasy]

Currently my boat has 1 single house battery and 1 engine start battery. both are 75 Amp lead acid. These sit in the original battery box and I dont want to build new battery boxes. Ive been thinking I could fit larger, 100 amp hr Lithium Iron batteries in the same space. increasing battery storage capacity. ie 2 house batteries, and fit a small lead acid engine start battery somewhere else.
I wondered if anyone can offer any advice on this and should I change the 1,2 B switch at the same time. Perhaps I should start from scratch and if so any suggestions appreciated. was going to fit a victron battery monitor and have a 50 watt solar panel with a Renogy 10 watt controller.

Steveeasy

 

[Tranona]

Not so straight forward as you will probably need to change your charging from the alternator with an external regulator or more commonly use a B2B 30A charger from the engine start battery. Yes, dump the 1,2,B and fit individual breakers. Unless you have heavy consumption or want to spend long periods away from charging or using the engine (for which you need more solar) then you may find lA simpler and less costly overall. That is the route I went with 2*95Ah AGMs and an Odyssey high power start battery because that all fitted neatly in the existing battery box. Managed by a BEP switch cluster with a VSR individual isolators and a parallel switch for emergency start. Photos taken before all wiring completed

 

[B27]

The other thing is, most Lifepo4 batteries are not rated to start an engine, unless you have a very big bank of them.
Personally I feel having a back-up for the start battery is pretty important, although you could get around that by buying new ones every few years.

 

[Neeves]

The other thing is, most Lifepo4 batteries are not rated to start an engine, unless you have a very big bank of them.
Personally I feel having a back-up for the start battery is pretty important, although you could get around that by buying new ones every few years.

Just buy a motor vehicle emergency jump start, as back up to the engine start. Relatively cheap, small and many of them will pump up your dinghy and provide emergency lighting.

Jonathan

 

[thinwater]

Currently my boat has 1 single house battery and 1 engine start battery. both are 75 Amp lead acid. These sit in the original battery box and I dont want to build new battery boxes. Ive been thinking I could fit larger, 100 amp hr Lithium Iron batteries in the same space. increasing battery storage capacity. ie 2 house batteries, and fit a small lead acid engine start battery somewhere else.
I wondered if anyone can offer any advice on this and should I change the 1,2 B switch at the same time. Perhaps I should start from scratch and if so any suggestions appreciated. was going to fit a victron battery monitor and have a 50 watt solar panel with a Renogy 10 watt controller.

Steveeasy

First, to be pendantic, correct nomenclature will help. Your batteries are 75 Ah and 100 Ah, not amps. This is actually a big deal, because batteries do have cranking current amp ratings, but you are talking about energy capacity, which is amps x hours = Ah [amp-hours].

Yes, you will be redesigning the charging system, but you didn't share a lot of information on that.

 

[steveeasy]

First, to be pendantic, correct nomenclature will help. Your batteries are 75 Ah and 100 Ah, not amps. This is actually a big deal, because batteries do have cranking current amp ratings, but you are talking about energy capacity, which is amps x hours = Ah [amp-hours].

Yes, you will be redesigning the charging system, but you didn't share a lot of information on that.

.Great thanks. Not provided much info as quite frankly I’ve no idea yet what I’m going to do.

Think I’ll get a book, may well be easier. Which ever battery type I install I want to upgrade the switch to charge both batteries. I want to install fuses and id like to have bilge pump/ diesel heater and solar cabling not just bolted to batteries. Like to use busbars. Simple improvements to make things safer. A good battery monitor so I know what is going on.
Thanks
Steveeasy

 

[Sea Change]

LiFePO4 offers many, many benefits:
- almost 100% useable capacity, vs ~50% for lead acid
- smaller/lighter
- much faster charging rates
- almost no voltage drop under load
- thousands of cycles lifespan vs low hundreds
- considerably lower cost than lead acid over the lifespan of the battery

Sounds too good to be true? Well there's a bit of a catch. Your boat will likely need a number of other systems changed/upgraded. For a small boat with low power needs, it might not be worth it.

Without going in to full detail, the simplest way of upgrading a smaller boat would involve a DC-DC charger, suitable fuses, and if necessary new lithium-compatible solar and shore power chargers. These upgrades are likely to cost over £200 which isn't a big deal for a large boat but might make the upgrade less attractive on a smaller boat.

Happy to explain why these upgrades are needed, and suggest alternatives, but it can get pretty long winded.

 

[B27]

You also have to question the benefits of storing lots of Ah when you've only got a 50W panel to recharge it.

there are some alternatives, like getting a small lifepo4 battery which could be taken home to charge.
Something like a 30Ah would run a fridge for more than a day, or a heater for a few evenings.
These things keep coming down in price.

 

[steveeasy]

LiFePO4 offers many, many benefits:
- almost 100% useable capacity, vs ~50% for lead acid
- smaller/lighter
- much faster charging rates
- almost no voltage drop under load
- thousands of cycles lifespan vs low hundreds
- considerably lower cost than lead acid over the lifespan of the battery

Sounds too good to be true? Well there's a bit of a catch. Your boat will likely need a number of other systems changed/upgraded. For a small boat with low power needs, it might not be worth it.

Without going in to full detail, the simplest way of upgrading a smaller boat would involve a DC-DC charger, suitable fuses, and if necessary new lithium-compatible solar and shore power chargers. These upgrades are likely to cost over £200 which isn't a big deal for a large boat but might make the upgrade less attractive on a smaller boat.

Happy to explain why these upgrades are needed, and suggest alternatives, but it can get pretty long winded.

Thanks for the information. I use a tiller pilot. A couple of iPads. A diesel heater.
It seams if I fit 2 lead acid 75 ah batteries I’ll have about 30 ah available. If I fitted a lithium 100 ah battery I’d have 70-80 ah available. So it seams potentially worthwhile. As I understand it I need to install a DC to DC unit. Id like to sort the wiring with relevant fuses.
I wonder if my Renogy wanderer 10 will charge lithium batteries.

I don’t want a big solar panel. Just one to maintain battery while away. Could add a portable one but wonder if my consumption warrants it.

I’ll see how much a battery is. 2 lead acid 75 ah batteries are £160.

Steveeasy

 

[Tranona]

If you don't have a fridge, your demands are modest. with my Bavaria my typical daily consumption when cruising was 80Ah of which 30+ was the fridge. Engine run for an hour a day would put back in about 20amps so net consumption 60Ah. So your 150 (75 usable) would be more than adequate for a couple of nights away.

Most new boats of your size come with about 200Ah as standard as they all have fridges. Choose the full nav packages and heater they go up about 50% in capacity - the Bavaria had 3*95Ah AGMs. The key to making these conventional systems work is to start with a full charge. Easy if you have shorepower, but more challenging if you are on a swinging mooring. Lithium helps because of the high usable capacity for size and the high charge acceptance rates but you really need more solar to take advantage of the latter if you do not have access to shorepower (or motor a lot!).

If i were doing my boat now rather than 3 years ago I would probably go lithium as the cost has come down and I would not have needed the expensive start battery to fit the space. Overall the cost (including all the switches, cabling, bus bars, fuses etc would be much the same as my conventional set up (+/- £1k)

 

[PaulRainbow]

Thanks for the information. I use a tiller pilot. A couple of iPads. A diesel heater.
It seams if I fit 2 lead acid 75 ah batteries I’ll have about 30 ah available. If I fitted a lithium 100 ah battery I’d have 70-80 ah available.

2x75ah batteries gives you a usable 75ah. A 100ah LifeP04 gives you about 80ah.

So it seams potentially worthwhile. As I understand it I need to install a DC to DC unit. Id like to sort the wiring with relevant fuses.
I wonder if my Renogy wanderer 10 will charge lithium batteries.

I don’t want a big solar panel. Just one to maintain battery while away. Could add a portable one but wonder if my consumption warrants it.

I’ll see how much a battery is. 2 lead acid 75 ah batteries are £160.

Steveeasy

For you, given what you have said, Lithium isn't worth it. You''need a DC-DC charger, possible a new mains charger, possibly a new solar controller and you don't have enough solar to benefit from the faster charging of Lithium.

I would do the other improvements you have mentioned and fit two of the biggest lead acid batteries that you can squeeze in to the space.

 

[Sea Change]

I'm a big fan of lithium but I agree for such small power needs it would be hard to justify the cost and effort involved to upgrade.

At the risk of complicating things, there is a third way... a hybrid system where lithium sits in parallel with lead acid. I don't know very much about it myself, but somebody else on the forum has gone this route.

 

[thinwater]

Currently my boat has 1 single house battery and 1 engine start battery. both are 75 Amp lead acid. These sit in the original battery box and I dont want to build new battery boxes. Ive been thinking I could fit larger, 100 amp hr Lithium Iron batteries in the same space. increasing battery storage capacity. ie 2 house batteries, and fit a small lead acid engine start battery somewhere else.
I wondered if anyone can offer any advice on this and should I change the 1,2 B switch at the same time. Perhaps I should start from scratch and if so any suggestions appreciated. was going to fit a victron battery monitor and have a 50 watt solar panel with a Renogy 10 watt controller.

Steveeasy

It looks like the the solar charger you have is suitable for LI. I have the same one, controlling 50W on the F-24 trimaran I day sail, which is enough to maintain the battery without plugging in, plus the very, very rare overnight. For you, I would at least double the solar.
https://www.renogy.com/wanderer-10a-pwm-charge-controller-with-bt1/

You did not mention engine charging. That will have to be regulated. In my case, On my F-24 I don't have engine charging, so one less thing. I wouldn't run it enough to help if I did.

I may switch to Li on the next go, simply because it may become the cheaper choice. At the same time I will actually downsize, saving perhaps 40 pounds (the F-24 is a very light boat). But that is not your goal.

No, do not install lead and LiFePO4 in parallel, This is a really bad idea because their charging curves are far too different. You can have both, but they must be separated by a DC/DC charger. Long explanation.

 

[steveeasy]

2x75ah batteries gives you a usable 75ah. A 100ah LifeP04 gives you about 80ah.

For you, given what you have said, Lithium isn't worth it. You''need a DC-DC charger, possible a new mains charger, possibly a new solar controller and you don't have enough solar to benefit from the faster charging of Lithium.

I would do the other improvements you have mentioned and fit two of the biggest lead acid batteries that you can squeeze in to the space.

At the risk of asking too many questions, could you explain what a fully charged lead battery should read?and accordingly what would be the minimum level to discharge a battery ?

Also can I charge 2 12 v batteries from my Renogy 10 watt solar charger ?. If so Ill can install easily 2 x 75/85 ah batteries but if not I’ll fit a larger 150 ah battery.
Thanks
Steveeasy

 

[Sea Change]

No, do not install lead and LiFePO4 in parallel, This is a really bad idea because their charging curves are far too different. You can have both, but they must be separated by a DC/DC charger. Long explanation.

It sounds like a bad idea, but it can actually work pretty well. I've not tried it myself, but it appears to be quite common in the narrowboat scene.

What seems to happen is that the lithium wants to sit at a higher voltage, so it will naturally try to charge the lead acid. But the high internal resistance and low charge acceptance of the lead acid means that this charging current will remain manageable, and slow to a trickle as the lead acid reaches full.

If the lithium goes offline (BMS shutdown) the lead acid is still there to absorb charging currents, and to provide power to essential systems. If this happened because of low voltage, the lead acid will charge first before the lithium kicks in again.

It does seem to work surprisingly well, but again I don't have direct experience.

 

[Tranona]

At the risk of asking too many questions, could you explain what a fully charged lead battery should read?and accordingly what would be the minimum level to discharge a battery ?

Also can I charge 2 12 v batteries from my Renogy 10 watt solar charger ?. If so Ill can install easily 2 x 75/85 ah batteries but if not I’ll fit a larger 150 ah battery.
Thanks
Steveeasy

SOC chart here octopusasia.com/battery-soc-to-voltage-chart/ Australian but their batteries are the same as ours! General view is that LA should not be regularly discharged below 50%, that is a resting voltage of around 12v. Of course you can go lower but this shortens the life of the battery.

It is unclear from what you say how your current batteries are wired. From what I can see you have the classic 2 equal batteries, one nominally for engine start so controlled by position 1 and the other house controlled by position 2. There are different ways of using this system, perhaps most common using 1 at start, then when the engine is not being used switched to 2 for house loads, and possibly both if the engine battery goes flat or you need greater capacity for house. The last obviously means you run the risk of running both down and not being able to start the engine.

It is sensible therefore to split them into 2 independent banks so the engine start is never used for house, but of course this means having only limited house capacity. This was OK in the dim and distant (when your boat was built) and electrically powered kit was limited (no heater/fridge, autopilot, nav gear etc). So the norm now is to at least have a house bank that is a minimum size equal to your current (150Ah) in either one battery or 2 in parallel and a dedicated smaller (50-60Ah) start individually switched and charged from the alternator via a charge splitter such as a VSR. A means of linking the house to the engine in an emergency is also useful. A simple way of arranging the switching is in post#2, but there are other ways.

To do this on your boat you need to find a place close to your existing batteries if possible to fit a new start battery. The cheapest way of doing this is to use a simple car battery for starting a small Diesel car which are usually around 50Ah and a high CCA to give the oomph to start your engine. This will be charged up quickly after the engine starts so generally needs no additional charging source. The little battery I used is only 28Ah but is small and can be mounted in any orientation. It is commonly used on small racing cars. Downside is 3-4 times the price of a normal car battery, but a potential life of 15-20 years. I have one in my Morgan and it lasted 19 years.

In addition to charge from the alternator you can add other sources such as a mains charger from shorepower (I have a 15A one) normally just to the house, but you can have up to 3 outputs if you need to. Your little solar can be used but with such low output really only sensible to use it for one bank which is normally the house.

In principle there is nothing difficult in installing such a system, but the challenge is finding a sensible place for all the bits , bus bars and fuses plus making up all the cables. Paul has a good circuit diagram that will help you. I followed this broadly except for using the BEP cluster and a NASA monitor rather than a Victron. In my layout looking aft as in the photo of the engine box, all the bus bars and switching (plus the shorepower consumer unit) are on the right and the house DC switch panel is on the left. Details in the 2 photos here.

Hope this helps

 

[steveeasy]

SOC chart here octopusasia.com/battery-soc-to-voltage-chart/ Australian but their batteries are the same as ours! General view is that LA should not be regularly discharged below 50%, that is a resting voltage of around 12v. Of course you can go lower but this shortens the life of the battery.

It is unclear from what you say how your current batteries are wired. From what I can see you have the classic 2 equal batteries, one nominally for engine start so controlled by position 1 and the other house controlled by position 2. There are different ways of using this system, perhaps most common using 1 at start, then when the engine is not being used switched to 2 for house loads, and possibly both if the engine battery goes flat or you need greater capacity for house. The last obviously means you run the risk of running both down and not being able to start the engine.

It is sensible therefore to split them into 2 independent banks so the engine start is never used for house, but of course this means having only limited house capacity. This was OK in the dim and distant (when your boat was built) and electrically powered kit was limited (no heater/fridge, autopilot, nav gear etc). So the norm now is to at least have a house bank that is a minimum size equal to your current (150Ah) in either one battery or 2 in parallel and a dedicated smaller (50-60Ah) start individually switched and charged from the alternator via a charge splitter such as a VSR. A means of linking the house to the engine in an emergency is also useful. A simple way of arranging the switching is in post#2, but there are other ways.

To do this on your boat you need to find a place close to your existing batteries if possible to fit a new start battery. The cheapest way of doing this is to use a simple car battery for starting a small Diesel car which are usually around 50Ah and a high CCA to give the oomph to start your engine. This will be charged up quickly after the engine starts so generally needs no additional charging source. The little battery I used is only 28Ah but is small and can be mounted in any orientation. It is commonly used on small racing cars. Downside is 3-4 times the price of a normal car battery, but a potential life of 15-20 years. I have one in my Morgan and it lasted 19 years.

In addition to charge from the alternator you can add other sources such as a mains charger from shorepower (I have a 15A one) normally just to the house, but you can have up to 3 outputs if you need to. Your little solar can be used but with such low output really only sensible to use it for one bank which is normally the house.

In principle there is nothing difficult in installing such a system, but the challenge is finding a sensible place for all the bits , bus bars and fuses plus making up all the cables. Paul has a good circuit diagram that will help you. I followed this broadly except for using the BEP cluster and a NASA monitor rather than a Victron. In my layout looking aft as in the photo of the engine box, all the bus bars and switching (plus the shorepower consumer unit) are on the right and the house DC switch panel is on the left. Details in the 2 photos here.

Hope this helps

Yes all very helpful indeed. Yes I have the very classic set up of 2 batteries 1 house, 1 engine. This space I intend to use for either 1 large house battery or 2 smaller house batteries. I’ve plenty of space for an additional engine battery.
Think I’ll have to get Nigel kalders book on boat electrics.

Steveeasy

 

[PaulRainbow]

It sounds like a bad idea, but it can actually work pretty well. I've not tried it myself, but it appears to be quite common in the narrowboat scene.

What seems to happen is that the lithium wants to sit at a higher voltage, so it will naturally try to charge the lead acid. But the high interest resistance and low charge acceptance of the lead acid means that this charging current will remain manageable, and slow to a trickle as the lead acid reaches full.

If the lithium goes offline (BMS shutdown) the lead acid is still there to absorb charging currents, and to provide power to essential systems. If this happened because of low voltage, the lead acid will charge first before the lithium kicks in again.

It does seem to work surprisingly well, but again I don't have direct experience.

I have some real World figures that suggest it works really well, will post them when i have time. The figures are not what one might expect.

 

[PaulRainbow]

At the risk of asking too many questions, could you explain what a fully charged lead battery should read?and accordingly what would be the minimum level to discharge a battery ?

Fully charged, rested (no charging or loads) about 12.8v. Discharge no lower than 50%

Also can I charge 2 12 v batteries from my Renogy 10 watt solar charger ?. If so Ill can install easily 2 x 75/85 ah batteries but if not I’ll fit a larger 150 ah battery.
Thanks
Steveeasy

2x75ah or 1x150ah doesn't make any real difference. More solar would be good.

 

[steveeasy]

Fully charged, rested (no charging or loads) about 12.8v. Discharge no lower than 50%

Hi Paul,
No lower than 50%. Approximately how many volts would the battery be at then ?

Steveeasy

Edit.
Tranona provided me with that useful attachment and if Ive read it right, then approx 12.1 Volts. Blimey, my diesel heater can use that up very quickly. probably as my existing house battery has been discharged too many times. If I fit a good battery monitor and fit 2 new house batteries, ill have a much better idea of how much I am consuming.
Steveeasy