32 Volt System on a Motor Yacht

[Thom Price]

I'm in the process of buying a 53' Hatteras as my new home. We're planning on living aboard in a marina, and will probably not take it out more than a few times a year because the fuel consumption on this baby is ridiculous (twin Detroit Diesel V8s). These old Hatts have 32 volt systems on them where most other boats have 12 or 24. Not sure how they came up with that voltage, but evidently some golf carts use 8V batteries and this has 4 of them. There is also 110/220V onboard as well for outlets and appliances, but the 32V is for all of the lighting, starter motors, and any original equipment. There's also a step-down transformer for newer 12V equipment. It has an 8KW diesel generator and a 3.2KW inverter/charger for the shore power.
The boat currently has lead-acid batteries, naturally, but I am wanting to swap them out for lifepo4 when the time comes. Eventually, I'd like to add some solar panels as well, as the shore power is about $0.25/kWh and I'm estimating that we'll use around 1500 kWh/month, based on friends who liveaboard the same model boat. The big consumers are the heat pumps, water heater, microwave/convection oven, and the full-size fridge. I'll be swapping out all of the incandescent bulbs with LEDs.
My questions are:

• What cells should I use to build a 32V battery bank for marine use?
• What BMS should I get?
• What's the best enclosure for protecting the cells?
• What components would you suggest for a 4KW solar system?
• What am I not asking about that I should?

Thanks in advance for your recommendations. I'm looking forward to being a part of this forum and sharing my project as it progresses.
Stay healthy at home,
Thom

 

[dashdrum]

I wonder if you could go with a standard 24, 36, or 48 volt system, and step up/down to 32 for the legacy equipment. Over time, you could replace the 32 volt devices with 12v as part of normal upgrades.

Does this system include an inverter for the microwave, etc?

 

[Thom Price]

I wonder if you could go with a standard 24, 36, or 48 volt system, and step up/down to 32 for the legacy equipment. Over time, you could replace the 32 volt devices with 12v as part of normal upgrades.

Does this system include an inverter for the microwave, etc?

The thing is that the conductors are all sized for 32v, so just I could go with 48v devices, but not lower voltage without rewiring everything. For the lights, I'll have to put in special 32v LEDs made especially for old Hatts. There is an inverter for the 110/220v appliances.

 

[FilterGuy]

There is an inverter for the 110/220v appliances.

This may drive your choices. Do you know what types of battery chemistries (charge profiles) your inverter can accommodate?

 

[aybabtme]

I'd use a DC converter if you don't want to change all the wiring/legacy devices, and put a 12 or 24V LiFePO4 bank/system. It's really hard to find any marine hardware above 24V.

The water heater on my boat uses ~1500W when it turns on, it's probably common. With a 915W solar array, I get about 3.2kWh per day in the winter, on a sunny day, and 1.1kWh when it's raining. That's in the San Francisco Bay. My network (LTE and wifi), inverter base load, fridge and then the parasitic load from the large contactors protecting the LiFePO4 bank, all-together use about 100W continuously, so about 2.4kWh per day. That doesn't leave a ton of space for 1500W of hot water. I expect things to be better in the summer, but at least in the winter, I can't make hot water without running the diesel or connecting to shorepower.

Not sure if this is useful or not, my boat is a lot smaller than yours (38ft) but my solar system is pretty big, so it might be relevant? You can probably get a smaller base-load than me if you don't run a network (I run enterprise grade hardware), use solid-state contactors for the BMS (only works up to ~220A for the Victrons and they fail open...), and disconnect your inverter when not in use (I don't bother).

 

[Thom Price]

This may drive your choices. Do you know what types of battery chemistries (charge profiles) your inverter can accommodate?

I don't know. This is the inverter: https://www.solar-electric.com/outback-power-mobile-sinewave-inverter-vfx3232m.html
It seems like a pretty high quality unit, but I'm not finding info on chemistry.

 

[Thom Price]

I'd use a DC converter if you don't want to change all the wiring/legacy devices, and put a 12 or 24V LiFePO4 bank/system. It's really hard to find any marine hardware above 24V.

The water heater on my boat uses ~1500W when it turns on, it's probably common. With a 915W solar array, I get about 3.2kWh per day in the winter, on a sunny day, and 1.1kWh when it's raining. That's in the San Francisco Bay. My network (LTE and wifi), inverter base load, fridge and then the parasitic load from the large contactors protecting the LiFePO4 bank, all-together use about 100W continuously, so about 2.4kWh per day. That doesn't leave a ton of space for 1500W of hot water. I expect things to be better in the summer, but at least in the winter, I can't make hot water without running the diesel or connecting to shorepower.

Not sure if this is useful or not, my boat is a lot smaller than yours (38ft) but my solar system is pretty big, so it might be relevant? You can probably get a smaller base-load than me if you don't run a network (I run enterprise grade hardware), use solid-state contactors for the BMS (only works up to ~220A for the Victrons and they fail open...), and disconnect your inverter when not in use (I don't bother).

That's very useful. Thanks so much. I was worried about a 4KW system not being enough, but you're doing pretty well with less than 1KW. Maybe I could get by with 2KW. The boat has some good real estate for panels forward of the pilot house, but I'd rather have all of them up above the fly bridge if possible, to reduce shading.
We'll be in Baltimore, so our heating needs will be a little higher than for you, but we're practically the same latitude.
I'm going to do everything I can to reduce our base load. We may do most of our showering and laundry in the marina, but will need to see how that goes.
Honestly, I kind of like the 32V system because it doesn't need such large conductors. I wish that it were 30V or 33V, but I guess if I build a 33V battery, it should be okay. If I set the BMS to only charge to 90%, maybe that would be even better. Thoughts?
What do you think about community solar at a liveaboard marina? With all of those batteries around, I'd think that it could be an ideal situation, and might not even need to be grid tied, if done correctly.

 

[FilterGuy]

I don't know. This is the inverter: https://www.solar-electric.com/outback-power-mobile-sinewave-inverter-vfx3232m.html
It seems like a pretty high quality unit, but I'm not finding info on chemistry.

Whoops..... I had a brain fart. I was thinking Inverter/charger.... you just have an inverter.... it does not care as much about battery type.

The DC input on that inverter is 28 to 45.3 V. That's a pretty broad range of voltages. For LiFePO4 the sweet spot for that inverter appears to be 12 Cells
Edit: Corrected the math in the table.

# cells	@ 3.65V	@ 3.0 V
10	36.5	30
11	40.15	33
12	43.8	36
13	47.45	39
14	51.1	42

Do you know if the low cut-off on that inverter can be adjusted up to 36 or 37 V?

 

[dashdrum]

Back to your question about the battery. I'm no expert, so consult with those with actual knowledge, not me.

A LiFePo4 cell has a nominal voltage of 3.2V, so 10 would make a battery of 32V nominal, right? The upper voltage could be 36V, while the lower end could be 26V - quite a range. Could your equipment handle that? Perhaps by changing the charge voltage you could shrink that range a bit.

I wonder where a BMS for that arrangement could be had.

What do the experts say?

 

[FilterGuy]

In order to get a good handle on the needs, you should do an energy audit on the boat. This will give you a better idea of the energy hogs on the boat and tell you what your system size needs to be.

There is a link in my signature to a spreadsheet I use for energy audits.

 

[FilterGuy]

Whoops..... I had a brain fart. I was thinking Inverter/charger.... you just have an inverter.... it does not care as much about battery type.

The DC input on that inverter is 28 to 45.3 V. That's a pretty broad range of voltages. For LiFePO4 the sweet spot for that inverter appears to be 12 Cells
Edit: Corrected the math in the table.

# cells	@ 3.65V	@ 3.0 V
10	36.5	30
11	40.15	33
12	43.8	36
13	47.45	39
14	51.1	42

Do you know if the low cut-off on that inverter can be adjusted up to 36 or 37 V?

Note: Be sure to look at the voltage range of all of the loads on the boat. Even though the inverter could handle the voltage, you might have to cut back due to the limits of the other devices. Here is the table with some of the lower cell counts

# cells	@ 3.65V	@ 3.0 V
8	29.2	24
9	32.85	27
10	36.5	30
11	40.15	33
12	43.8	36
13	47.45	39
14	51.1	42

Depending on the voltage range of the various loads you may need to drop down to 10 or even 9 cells. (9 would be unfortunate because you would lose so much of the battery when the inverter cuts out at 28 volts.)

 

[aybabtme]

The existing 32V battery bank will also operate within a range of voltage: as such, it can probably be assumed that the 12S LFP setup should work fine, voltage-wise.

But I'd still go for a more standard voltage house bank. Smaller wires at 32V is cool but the small wires matter more with regard to heavy loads, and OP is going to have a hard time getting the heavy load items like windlass/bow thrusters/watermaker/AC/etc, in 32V. As such I'd really consider a 24V battery, or even 48V before 32V.

 

[FilterGuy]

The existing 32V battery bank will also operate within a range of voltage: as such, it can probably be assumed that the 12S LFP setup should work fine, voltage-wise.

But I'd still go for a more standard voltage house bank. Smaller wires at 32V is cool but the small wires matter more with regard to heavy loads, and OP is going to have a hard time getting the heavy load items like windlass/bow thrusters/watermaker/AC/etc, in 32V. As such I'd really consider a 24V battery, or even 48V before 32V.

All true, and if I was doing a design from scratch, I would do 24 or 48 V. However, like everything in life, there are trade-offs. Presumably the boat is already provisioned with all of the 32V appliances (and a 32V alternator). If he has to change them out, it could be prohibitively expensive.

I faced a kinda similar dilemma on my current build for a boat. The system is big enough that it really should be 24 volt. However the boat is currently all 24 volts. To re-do enough of the boat to make 24v work would be prohibitively expensive. What nails you is the high amp items (Like windlass and thrusters) that can't reasonably be operated off a buck converter. These pretty much have to be operated off the native voltage of the battery.

The good news is that while rare, 32 volt systems are around. You can usually get what you need for them. The bad news is everything is EXPEN$IVE.

 

[aybabtme]

I assume you mean that your current boat is all 12V? Same for me, and here's what I did:

- Keep 12V as is, keep only one battery from the legacy AGM house bank (for starting the diesel). I could probably change this to a much smaller one.
- Put a 24V to 12V battery charger (Victron Orion TR Smart)
- Make my LFP bank 24V.
- Use 24V for all heavy power draws (windlass, inverter).

The alternator is the original and feeds the 12V system. It's a bit redundant right now, since the B2B 24->12V charger keeps the start battery toped off all the time. I'll probably change the alternator for an externally regulated 24V Balmar or something. But doing so would be the first "change" to the original electrical system.

It works quite well and I didn't need to rewire anything. It helps that I installed all the heavy current items along with the 24V LFP.

But I agree there's lots of tradeoffs and there's many ways to cut it. I thought I'd bring up how I handled the legacy 12V system without requiring much change, while upgrading to a more appropriate voltage for my power needs.

 

[Thom Price]

Whoops..... I had a brain fart. I was thinking Inverter/charger.... you just have an inverter.... it does not care as much about battery type.

The DC input on that inverter is 28 to 45.3 V. That's a pretty broad range of voltages. For LiFePO4 the sweet spot for that inverter appears to be 12 Cells
Edit: Corrected the math in the table.

# cells	@ 3.65V	@ 3.0 V
10	36.5	30
11	40.15	33
12	43.8	36
13	47.45	39
14	51.1	42

Do you know if the low cut-off on that inverter can be adjusted up to 36 or 37 V?

I would assume that it cuts off around that voltage. I know that a 12V car battery is usually charged with around 14V. I don't have access to the boat yet, so I can't tell you what the normal operating voltages are precisely. I'm assuming that 32V is a nominal voltage, like 12V is for most low-voltage systems, but that is the minimum voltage that one would want to use, with normal operating voltages up to 115% of the nominal voltage. I was thinking of using 11 cells, and cutting them off when they get up to 37V, even if they could take a few more.
Any idea about which cells work best in a marine environment?

 

[Thom Price]

The existing 32V battery bank will also operate within a range of voltage: as such, it can probably be assumed that the 12S LFP setup should work fine, voltage-wise.

But I'd still go for a more standard voltage house bank. Smaller wires at 32V is cool but the small wires matter more with regard to heavy loads, and OP is going to have a hard time getting the heavy load items like windlass/bow thrusters/watermaker/AC/etc, in 32V. As such I'd really consider a 24V battery, or even 48V before 32V.

From what I've heard from other Hatteras owners, it isn't worth it to try to rewire the whole boat. Not only is it a huge expense in coper and new parts, but you pretty much have to dismantle the whole boat. It's one of those quirky things about owning an old Hatt, kind of like the Whitworth wrenches you need if you have an old MG. Also, the original wiring is known to be top quality. Messing with it would definitely not increase the value of the boat.
The alternators and starters are also 32V. Sometimes an OEM starter is hard to find and it gets replaced with a 24V starter, which will work for a while, but they can burn up fairly easily. I would consider replacing the alternators and starters with 24V and have dedicated batteries for them, but for the rest of the boat, I want to keep the 32V system.

 

[FilterGuy]

Any idea about which cells work best in a marine environment?

The two big issues with a marine environment is Corrosion and Vibration/movement. You can make any of the LiFePo4 cells work, but some of them are going to require a bit more care than others.

The best and perhaps most expensive are the Fortune cells. These a built with very heavy duty terminals and packaging. This means you can have solid connections and solid connections.

At the other end are the aluminum case cells. These can be made to work well, but you need to mount them very snugly in a box so they don't move and are well protected. The terminals on these tend to be small so they are not as mechanically robust. Consequently, you need to make sure the big battery cables don't put a lot of stress on them.

Between the Fortune cells and Aluminum cells are the various plastic case prismatic cells.

I would not even consider Cylindrical or pouch cells because they are so difficult to mount.

Note: Corrosion issues are about the same for all of them. The Fortune might have a slight advantage because of their big terminals, but on any of them if you make good connections to start with you will be fine (and if you don't have a good connection on any of them you will have issues).

If money isn't an issue, I would go with fortune. However, money often is an issue and I am in the midst of a battery build for a boat where I am using aluminum case cells. (I will be posting some picks in a week or two.... the Covid 19 mess has slowed things *way* down)

 

[Thom Price]

In order to get a good handle on the needs, you should do an energy audit on the boat. This will give you a better idea of the energy hogs on the boat and tell you what your system size needs to be.

There is a link in my signature to a spreadsheet I use for energy audits.

That is a great idea! If only I knew an energy auditor. Wait - I'm an energy auditor! Lol. My day job is with the US Department of Energy. I'll definitely be checking out every single appliance and using your spreadsheet. Thanks. My big concern is heating and cooling, which will change from day-to-day. I'm used to figuring all of that out for a house, so I'm curious to do it for a boat.

 

[FilterGuy]

BTW: Here is Will's review of the Fortune Cells

 

[FilterGuy]

BTW: A downside of the Fortune Cells is that they are bigger per Ahr than some of the others. I know space can be an issue on boats.