Thouhts on High&Safe Service Battery Voltage, Advantages

[SOLAR SUPPORT]

Thouhts on High&Safe Service Battery Voltage, Advantages

If your boat has sufficient solar energy capacity to meet the daily energy needs, charging the LFP service batteries using this source will reduce your installation costs. There's a lot you can do with an isolated LFP bank that's not directly connected to the alternator. You can benefit from alternator charging when necessary with a DCDC booster that you can activate only on very cloudy or shortening days. It is also possible to use an inverter as an alternative solution to benefit from the alternator charging at the highest capacity when necessary.

Service Battery Isolation:

When you have a battery bank isolated from a 12 volt system, it is possible to increase the operating voltage of the service batteries. 24V or the more advantageous 48V options can be considered. The advantages to be gained from the highest safe service battery bank voltage will increase in direct proportion to the rising voltage:

-Independently operating AC-DC charger and Solar Charge Controller sizes and unit power costs are reduced,
-You will have an adequate installation that works with thinner cross-section power transmission cables, smaller fuses and smaller circuit breakers,
-The size and unit power cost of the Inverter using high DC input voltage decreases,
-Use of devices working with AC~110V-220V increases with low-cost and more powerful Inverter,
-It is possible to operate all existing small-medium power 12V devices with a DCDC step-down device of sufficient capacity connected to high voltage LFP batteries,
-You can use high power and very cheap solutions with 48VDC input developed for Off-grid solutions on the boat. In this way, you can have a solar energy charge controller, AC-DC charger, and smart inverter that are compatible with the LFP battery and work integrated with each other, all at the same time and very cheaply.
-You can use your generator at its full capacity to charge service batteries when necessary.

The gains mentioned above may be more or less advantageous depending on boat sizes and your personal usage style. You must isolate the 12 volt alternator and 12 volt engine starter on the boat and all other 12 volt powered devices requiring high power from the service battery. For high-power 12Volt devices, a separate electrical installation powered by LTO-AGM batteries with alternator charging support and isolated from LFP service batteries or receiving charging support from the LFP battery bank can be used.

When it comes to electrical equipment designed from scratch for the boat, having all high power electric devices and battery banks with the same voltage provides the most ideal and economical solution. If we accept the safe maximum upper voltage limit as 48 volts; The ideal situation is for the alternator, starter motor, windlass motor and all other devices that works with high power to use the same voltage. Manufacturers of these devices have recently started offering options that work with 48 volts.

[Kettlewell]

It's really only an advantage if you run a lot of stuff off the inverter and never leave civilization. If your boat is 90% 12-volt instruments and modest loads you will save yourself a ton of hassle and money keeping everything 12 volt. Cruising boats must be able to be repaired anywhere in the world with whatever stuff you can find ashore. Replacing a 48-volt piece of equipment in the middle of nowhere will not be easy.

[SOLAR SUPPORT]

Originally Posted by Kettlewell

It's really only an advantage if you run a lot of stuff off the inverter and never leave civilization. If your boat is 90% 12-volt instruments and modest loads you will save yourself a ton of hassle and money keeping everything 12 volt. Cruising boats must be able to be repaired anywhere in the world with whatever stuff you can find ashore. Replacing a 48-volt piece of equipment in the middle of nowhere will not be easy.

There are ideas such as changing the lifestyle at sea, for example using an electric stove instead of kitchen gas, and reducing dependence on marinas by producing fresh water. Increasing solar energy capacities along with powerful and efficient lithium batteries have increased the easily usable energy potential on the boat.

New solar panels produce 90~100% more energy per unit area compared to 15-20 years ago. I replaced the solar panels, which I started using 18 years ago, with new ones while replacing the LA service batteries with LFP batteries. Energy storage capacity increased by 100% and solar power increased by 90%. With this energy increase, the first thing that comes to mind is to reduce kitchen gas consumption. As the boat grows, the potential for additional usable energy also increases. If you have a big inverter then you have lots of tools that can be used to increase the comfort in your boat. With these opportunities, the dependence on civilization does not increase.

Increasing the voltage of the second service battery bank is a good option for those who are looking for a more efficient and economical use of the excess energy potential of the devices previously running on 12V on the boat. Existing 12 volt devices do not need to be changed. There may be a separate LFP battery bank feeding existing 12V devices and a second LFP bank operating at higher voltage, feeding the larger inverter. Energy transfer can be made between battery banks using DCDC devices. On a newly manufactured boat, we see an increase in the number of options such as alternators, starter motors, winches, windlasses, etc., which are newly produced and operate with high DC voltage and produce and consume high power. You may be right about the malfunction. It may not be possible to prevent malfunctions with good design, quality materials and workmanship, but you can reduce the possibilities.

[mako]

"On a newly manufactured boat, we see an increase in the number of options such as alternators, starter motors, winches, windlasses, etc., which are newly produced and operate with high DC voltage and produce and consume high power."

I haven't seen a 48V starter motor for any common diesel. Do you have an example, or would you consider it practical to rewind the motor from a 24V variant?

[SOLAR SUPPORT]

Originally Posted by mako

"On a newly manufactured boat, we see an increase in the number of options such as alternators, starter motors, winches, windlasses, etc., which are newly produced and operate with high DC voltage and produce and consume high power."

I haven't seen a 48V starter motor for any common diesel. Do you have an example, or would you consider it practical to rewind the motor from a 24V variant?

There are hybrid engines that work with a newly designed 48 volt starter-alternator. These are very new technologies. Maybe they can be used on boats in the future. Why did you consider rewinding the existing starter? You don't need to change anything running on 12V. The main purpose is to benefit from a powerful, economical inverter working with a high voltage LFP bank. Many people do not want to use gas on the boat. You can use an electric stove working with 110-220 volts instead. or a 110-220V water maker, air-conditioner etc.

[Mal Reynolds]

Originally Posted by Kettlewell

It's really only an advantage if you run a lot of stuff off the inverter and never leave civilization. If your boat is 90% 12-volt instruments and modest loads you will save yourself a ton of hassle and money keeping everything 12 volt. Cruising boats must be able to be repaired anywhere in the world with whatever stuff you can find ashore. Replacing a 48-volt piece of equipment in the middle of nowhere will not be easy.

Everything on my boat is 12v, including the big windlass. 48v pumps & electronics do not exist yet.

However my new main battery bank will be 48v while I'm keeping everything else at 12v. 48/12 DC-DC converters with 95% efficiency will provide charging to a lead acid service battery at 12v. The service battery will really just stay in float and will absorb induction spikes. This way I get the charge efficiency advantages discussed with none of the pain of switching appliances.

Over time, pumps, lighting and other appliances will likely become available at 48v and I have room for spares. So I can do a conversion later if it makes sense.

[I am looking into 48v motors for the windlass though.]

[CaptainRivet]

Originally Posted by SOLAR SUPPORT

There are hybrid engines that work with a newly designed 48 volt starter-alternator. These are very new technologies. Maybe they can be used on boats in the future. Why did you consider rewinding the existing starter? You don't need to change anything running on 12V. The main purpose is to benefit from a powerful, economical inverter working with a high voltage LFP bank. Many people do not want to use gas on the boat. You can use an electric stove working with 110-220 volts instead. or a 110-220V water maker, air-conditioner etc.

The average cable length from service to inverter is 1,5m so if 24V or 48V the savings for cable, fuse and switch is below 100Euro.
With 200A current you can drive a 5kw inverter in 24V and even 2 in parallel is twice that in parallel directly of the main battery fuse. No cruising boat below 65ft needs more then 10kw inverter power, so no problem.
All is available in 24V around the world, so 24V is the best compromise with pure combustion propulsion as 99% of cruising boats still are.
So an all 24V boat is the best, yes if on a green field make sure as much as equipment is dual voltage 24/48V like MPPT and get 2x1p8S cell batteries so you can reconfigure for 48V easily if that standard pushes through which is not below 10years and with EV crises and potential fail of this whole industry the 48V Standard will take much longer.

The only real huge benefit over 24V is a 48V alternator which costs a liver.
And you will always have dual voltage banks as no leisure combustion marine engine runs on 48V and a lot equipment is still 12V only or very hard and expensive to source in 24V.
But yes you can build a 12V and 48V dual voltage system with the 12V being hybrid starter and service. for emergency starter you can tap into a 1p16S bank on the 4th cell but that requires a DIY or server rack battery with access to the cells.
Adding a seperate starter especially the beloved lead/AGM ones additionally is a noGo and would make the system overly complex.
Also doing triple voltage 12/24/48 is total nonsense as it adds a lot complexity and reduces redundancies we all need. Yes it looks favorably in first place to have eg 24V power winches instead 12V but having for that extra circuits, DC2DC converters, switchboard… is not advantageous at all.

[CaptainRivet]

The average cable length from service to inverter is 1,5m so if 24V or 48V the savings for cable, fuse and switch is below 100Euro.
With 200A current you can drive a 5kw inverter in 24V and even 2 in parallel is twice that in parallel directly of the main battery fuse. No cruising boat below 65ft needs more then 10kw inverter power, so no problem.
All is available in 24V around the world, so 24V is the best compromise with pure combustion propulsion as 99% of cruising boats still are.
So an all 24V boat is the best, yes if on a green field make sure as much as equipment is dual voltage 24/48V like MPPT and get 2x1p8S cell batteries so you can reconfigure for 48V easily if that standard pushes through which is not below 10years and with EV crises and potential fail of this whole industry the 48V Standard will take much longer.

The only real huge benefit over 24V is a 48V alternator which costs a liver.
And you will always have dual voltage banks as no leisure combustion marine engine runs on 48V and a lot equipment is still 12V only or very hard and expensive to source in 24V.
But yes you can build a 12V and 48V dual voltage system with the 12V being hybrid starter and service. for emergency starter you can tap into a 1p16S bank on the 4th cell but that requires a DIY or server rack battery with access to the cells.
Adding a seperate starter especially the beloved lead/AGM ones additionally is a noGo and would make the system overly complex.
Also doing triple voltage 12/24/48 is total nonsense as it adds a lot complexity and reduces redundancies we all need. Yes it looks favorably in first place to have eg 24V power winches instead 12V but having for that extra circuits, DC2DC converters, switchboard… is not advantageous at all.

And also most of us have no green field even the once that buy new boat as even with semi customs you have given electrical pack and that’s only 24V when not a hybrid or e-propulsion one. So that’s hypothetical for most of us.
Most will have 12V and what they do depends on age and conditions of the big power honks like starter, alternator, windlass and power whinches. Plus what your existing electrical equipment allows eg you have 3 Victron MPPTs and they can do dual voltage 12 and 24V so 48V means buying new MPPTs.
On my boat for example all the power honks where new or freshly overhauled when I bought it, so it would have made 0 sense to switch them to 24V. So a 12V system is mandatory, I could just add a 2nd one in 24V for running the inverters. As I need 6kw for the full electric galley that’s limit for 12V system, inverter within 1,5m of bank no issue just run double 70sqmm.
Yes making then bank and 12V main busbar and fuses for 6kw inverter=500A continuous was costly but I have the advantage of a lot redundancy and a quite simple system. And I designed it that way that I can easily switch to 24V house (by reconfiguring the cells of the bank and all new equipment incl BMS is dual voltage 12/24V) and 12V starter/house/booster bank if inverter growth further…which will happen soon as I have 2x Studer XTM 24/3500 inverter/charger and a Bauer electric dive compressor (which is the reason I need more inverter power, well 18kw peak for 5min capacity will do it once and for all) lying at my parents. And the 630A system design will garuntee a safe and sturdy operations with minimal losses on 24V.

But yes adding 24V with a hybrid starter/booster/service 12V bank would have been the way now I would go if I would start now doing it again and design&install system that if a power honk needs repair or overhaul it’s replaced in 24V(that I done already).
But if I only need 3-4max kw inverter power like most still do, staying 12V is still the way to go.

[CaptainRivet]

Originally Posted by Mal Reynolds

Everything on my boat is 12v, including the big windlass. 48v pumps & electronics do not exist yet.

However my new main battery bank will be 48v while I'm keeping everything else at 12v. 48/12 DC-DC converters with 95% efficiency will provide charging to a lead acid service battery at 12v. The service battery will really just stay in float and will absorb induction spikes. This way I get the charge efficiency advantages discussed with none of the pain of switching appliances.

Over time, pumps, lighting and other appliances will likely become available at 48v and I have room for spares. So I can do a conversion later if it makes sense.

[I am looking into 48v motors for the windlass though.]

Go 48V service with all 12V boat requires a dual voltage bank design (and not 48V service with 12V starter as you plan) and using LFP or LTO as 12V hybrid starter/service/boost because
A) running all the 12V power honks still of a lead is just nonsense
B) 12V lead starter adds enourmous complexity with no redundancies of 2 chemistries in combination with dual voltage then
C) all new charging equipment as 99 % cannot do triple 12/24/48V
D) in combo with c) charging a 12V lead and then converting that into 48V is also nonsense as extremely inefficient and adding a single point of failure…if the lead is dead your whole charging regime is dead.
E) adding a 3rd lead starter makes it even more complex and is not necessary due to redundancies of a 12V service/starter and a 48V bank where you tap into cell 4 for an emergency start from the 48V service. But that requires DIY or rack batteries where you can access the cells.

[rslifkin]

I'm not sure that lead is actually a poor choice for a 12V load buffer battery. Lead acid batteries like being kept 100% full and in float indefinitely, so that's pretty much the best use case for one. And depending on the loads and size of the DC-DC converters, it won't get drawn down much, so it doesn't need to be a particularly large battery, meaning weight isn't really an issue.

[CaptainRivet]

Originally Posted by rslifkin

I'm not sure that lead is actually a poor choice for a 12V load buffer battery. Lead acid batteries like being kept 100% full and in float indefinitely, so that's pretty much the best use case for one. And depending on the loads and size of the DC-DC converters, it won't get drawn down much, so it doesn't need to be a particularly large battery, meaning weight isn't really an issue.

Lead thinking again…you don‘t and won‘t keep a LFP service/starter/boost battery at 100% SOC. It’s used permanently so charged and discharged. and for use of a pure buffer you simply keep LFP at 85%SOC with a DC2DC converter with an adjustable voltage set to this voltage area plus this converter isolates galvanically the 12V from the 24V circuits.

Because of that a LTO as buffer is the perfect choice here as you can float it for 30years, it doesn‘t care. It doesn‘t care in which SOC you keep it or charge or discharge it, it has no measurable self discharge=no float needed but you can compared to LFP. and you can use lead equipment to charge it, only exception the alternator must have an (mostly internal) temp protection but can have a lead regulator. And obviously you can also charge it with LFP Profil or even parallel it to LFP, you only get 85% capacity but nothing happens as you never have to charge it full and a active balancer can balance an LTO at any SOC compared to a LFP only in the upper knee.

[rslifkin]

Originally Posted by CaptainRivet

Lead thinking again…you don‘t and won‘t keep a LFP service/starter/boost battery at 100% SOC. It’s used permanently so charged and discharged. and for use of a pure buffer you simply keep LFP at 85%SOC with a DC2DC converter with an adjustable voltage set to this voltage area plus this converter isolates galvanically the 12V from the 24V circuits.

Because of that a LTO as buffer is the perfect choice here as you can float it for 30years, it doesn‘t care. It doesn‘t care in which SOC you keep it or charge or discharge it, it has no measurable self discharge=no float needed but you can compared to LFP. and you can use lead equipment to charge it, only exception the alternator must have an (mostly internal) temp protection but can have a lead regulator. And obviously you can also charge it with LFP Profil or even parallel it to LFP, you only get 85% capacity but nothing happens as you never have to charge it full and a active balancer can balance an LTO at any SOC compared to a LFP only in the upper knee.

That setup will work fine as well. But the point is, if the DC-DC converter is big enough that the buffer battery isn't getting meaningfully cycled, there are multiple battery types that will work appropriately. It's basically the easiest application for just about any battery.

[CaptainRivet]

Originally Posted by rslifkin

That setup will work fine as well. But the point is, if the DC-DC converter is big enough that the buffer battery isn't getting meaningfully cycled, there are multiple battery types that will work appropriately. It's basically the easiest application for just about any battery.

1)Where is a buffer battery normally located?
At the Navstation because there is your sensitive electronics and your switchboard. And that excludes every chemistry that can gas means all lead batteries except gel.
2) you also need only an even small capacity LFP or LTO which makes the price difference negligible but LFP lifespan is 5 times longer minimum (so effectivly cheaper) and is much safer

In this dual voltage setup 12 and 48V the 12V battery is no pure buffer, it’s a 12V hybrid bank in LFP with at least 200-300AH (capable to handle surge loads of the 12V power honks, the capacity is only needed to cover the high peak loads but a good backup) or Winston LFP/LTO (that can be smaller like 40AH as they do 6C/20C) that powers starter and all other 12V loads like power whinch, windlass but also nav electronics, lights, fridges. And it’s only charged by 12V alternator and via DC2DC converter from 48V service that get charged via solar and shorepower charger (with eg mobile Honda gen too). As emergency starter backup taped into cell 4 of the 48V house, no need for a dedicated starter. Makes absolut 0 sense to use any kind of lead here.
For redundancy reason you can configure this 12V hybrid house from eg 2 parallel 40 or 50AH Winston cells in 1p4S with each BMV712 that handles LCV and HVC and an active balancer, no need for a BMS. Each of them can handle the surges of your starter, together they are not so stressed. If you have a big 4 or 6 cylinder diesel the 90 or 100AH Winston cells would be your prefect choice here. Winston because they are extremely robust and can do 6C peak, no other lifepo4 can do that.
Perfect setup.