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Can Lithium batteries support an AGM installation for Solar Powered Catamaran

A

althemusicwizard

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Joined
Jun 10, 2021
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I'm like Martin Luther King.......'I have a dream'.

Only by this time next week, hopefully I'll be the owner of a 40foot mulithull catamaran. The cat has been partially completed, about 70% and I'll be hopefully finishing it. The build has been based around a twin outboard setup, with twin petrol fuel tanks of 250L each and 60HP engines. I want to go electric because of fuel costs and maintenance. My build will incorporate a solar canopy about 7.5kW-10kW in size. The ELCO outboard motors I'm considering are the equivalent of 50HP petrol ones. The blurb on their site recommends eight, 12V Victron 230Ah connected in series to provide the 96V DC needed for the motors. Since 96V is into the realms of 'bespoke' territory as far as solar inverters is concerned, I wondered whether I could support the Victron 96V battery bank with a 48V LiFePO4 battery bank.
I've yet to speak to ELCO but wondered if this was anywhere need feasible. I've attached an initial sketch diagram, omitting fuses and switches for aid of clarity.
The equipment I'm considering is this:

www.elcomotoryachts.com

EP-50 Electric Outboard - Elco Motor Yachts

Comparable HP:50HP Voltage:96 Volts Suggested Battery Package Options: Deep Cycle AGM - Victron - 12V / 220ah (8 pack) Lithium Iron Phosphate - 96V / 200ah (4 pack minimum) Congratulations on getting one step closer to purchasing your award-winning Elco Electric Outboard. Select the options and...
www.elcomotoryachts.com www.elcomotoryachts.com

climbingvan.co.uk

Victron Super Cycle 230Ah AGM Leisure Battery - 12V

The Victron Super Cycle 230Ah AGM 12V Leisure Battery can achieve an impressive 300 cycles at 100% DoD. The Victron Super Cycle is a deep cycle AGM battery.
climbingvan.co.uk climbingvan.co.uk

www.gobelpower.com

Choose Your Battery Gobel Power GP-SR1-PC200 Standard 51.2V 280Ah 15kWh LiFePO4 Server Rack Battery

Gobel Power GP-SR1-PC200 Server Rack LiFePO4 Lithium Battery Application Scenarios * Home energy storage * FTTB, FTTH, RRU, BBU and other small mobile communication fields * Suitable for communication base stations, central computer rooms and other communication energy storage scenarios...
www.gobelpower.com www.gobelpower.com

12V solar panels charging kits for caravans, motorhomes, boats, yachts, marine

12V solar panel solar charging kits for motorhome caravan boat campervan yacht marine off-grid
www.photonicuniverse.com

Canadian Solar Panel 550W | Canadian Solar Panel | HDM SOLAR

The Canadian Solar 550W Mono-Crystaline Panel is a high-performing large-scale solar panel with up to 550w of power. It is suited to commercial and utility-level solar farms, featuring comprehensive LeTID and LID mitigation technology, to ensure up to 50% less degradation than other panels.
www.hdmsolar.co.uk www.hdmsolar.co.uk

Any advice gratefully received.
 

Attachments

Thanks for your thoughts. I may have this wrong, but why do you think the busbar will be at 96V? I've kind of taken what I've learned from installing my home solar system and come up with this. In my 48V home system, I have 28, 12V batteries connected in series / parallel. They are connected in fours in series to make a 48V group, and these seven groups are connected to busbars coming from the 48V inverters. If you put a multimeter across the series batteries, you can 'create a 12V supply (one battery) or a 24V supply (two batteries) or a 36V supply (three batteries) depending where you connect your leads. I'm not sure if my diagram this would lead to imbalanced charging in the AGM batteries though. I've tried to indicate on the diagram that connections would be separate leads from the motors to the AGM bank, and from the AGM bank to the 48V busbar. The leads to the motors would be at 96V. The leads to the busbar will only be a group of 4 AGM batteries which should be at 48V nominal if I have this figured out right. I realise too that the charging rate or graph for lithiums are different than AGM, but in this example I would only be concerned at charging the lithiums correctly as the Iconica inverters let you define charging voltage and cutoff, though no special lithium setting. As the world of electric boating seems to be at a very experimental stage at the moment in so far as range, sea state, usage is concerned, only real-life application would I think inform you of what to truly expect from a given setup on a given boat.
 
I have trouble following your diagram but If you have 2 wires on opposite ends of a group of cells going to the same bus bar, you have created a dead short. poof! I think I see 4 such connections on your diagram.
 
I've just found a similar thread to this and a poster called 'pollenface' suggested a similar solution as to the one I've posted here. I've redone the schematic to show switches that could switch the AGM bank between being a 48V bank and a 96V bank. The AGM bank couldn't be charged as well as running, however maybe the solution is to have one AGM bank supplying both motors and the other one being recharged or some combination of this idea depending on the C rate of the AGM bank. Thanks for spotting the 'shorts' guys. Here's the new schematic.
 

Attachments

Carry out some more research.
You don't need both types of battery.
Solar controllers for 96 volt batteries are available.
Run the motors direct from a 96 volt lithium battery bank, use Winston Cells.
Do you really need 50 HP motors, research actual need for your vessel and proposed operation.
I think you are based In the UK, where will the vessel be used?
 
Last edited:
Thanks for those replies guys. I'm finding 96V stuff in the UK is non-existent. I've installed a 48V home system using solar inverters and it's been extremely successful. I do have a lead-acid bank. The need for 50HP motors is because the cat is 40ft, with a 20ft beam. It will weigh in around 4-5tonnes (depending on batteries, panels and motors......that lot alone could be 1.5tonnes). I'd like to be able to cruise at 6-8knots. The use of AGM batteries is really as a buffer between the 48V LiFePO4 bank. All the companies have battery solutions but they're probably at least twice the price of sourcing a solution myself.
 
Sorry I should have added, this is a power catamaran. There are no sails. Propulsion is solely via engine and in this case, the design was for two, 60HP outboard engines minimum, although if money was no object you could install a couple of 300HP outboards presuming you could afford the fuel.
 
althemusicwizard said:
Thanks for the link, but I think they're only good to 600W. Each motor at maximum might draw 21kW if the batteries allow it.
Click to expand...
That isn't for the motor. Just showing there is products on the market that can handle converting that 96V down to 12V for running other devices that normally would require 12V. I don't know off-hand a solar charge controller that can connect to 96V battery bank but I'm sure there is some.
 
Q-Dog said:
AGM is heavier then LiFePO4. Why not use all lithium?
Click to expand...
The problem is being able to create a 96V supply for the motors from a 48V supply. AFAIK you can't just hook up two 48V lithium packs like the Gobel I listed in series. Fine for parallel and a bigger bank, but not for series. 48V stuff is abundant and relatively cheap these days.
 
rhino said:
That isn't for the motor. Just showing there is products on the market that can handle converting that 96V down to 12V for running other devices that normally would require 12V. I don't know off-hand a solar charge controller that can connect to 96V battery bank but I'm sure there is some.
Click to expand...
Oh sorry....I won't have a problem getting a 12V or 24V supply from the 48V bank for running 'boaty' stuff, nor for 230V AC which will come straight from the inverters, it's the 96V DC supply to the inverters that I'm having difficulty with.
 
Q-Dog said:
You need to be thinking like an EV, not like a house. EV folks build high voltage packs all the time.
Click to expand...
It's not the problem of building a 96V pack (though finding a BMS that is tried and tested may be) it's then charging that from the 48V (or the 230V AC) that will be coming from the panels / inverters / 48V LiFePO4 bank.
 
althemusicwizard said:
I've just found a similar thread to this and a poster called 'pollenface' suggested a similar solution as to the one I've posted here. I've redone the schematic to show switches that could switch the AGM bank between being a 48V bank and a 96V bank. The AGM bank couldn't be charged as well as running, however maybe the solution is to have one AGM bank supplying both motors and the other one being recharged or some combination of this idea depending on the C rate of the AGM bank. Thanks for spotting the 'shorts' guys. Here's the new schematic.
Click to expand...

I think that shows 48V lithium bank and two 96V AGM banks, each consisting of two 48V AGM banks with switch between them.
The lithium bank can switch to parallel with each 48V AGM bank.

When switch in middle separates 96V bank into two 48V banks, I don't think any current can flow to motor.

I think lithium bank is supposed to be able to charge or share current with 48V AGM banks. But can't charge effectively, need it to be higher voltage but regulated current (or voltage.)

Assuming 48V lithium banks are not designed for series use, I think a high current reverse-polarity diode across them (like bypass diode of PV panel) would protect them. That would let you make 96V lithium.

Some form of isolated DC/DC charger could charge multiple 48V AGM banks from 48V lithium bank. An off the shelf method would be inverter fed from lithium, feeding Chargeverter. Inefficiencies of double conversion, but at least it is off the shelf.
 
For anyone who's looked into this problem before (solar boat), I compiled what video history I could find of 'Solarwave 42'. This was the boat that Heike and Micheal Kohler designed and built and now they run Silent Yachts.


In one shot, it shows the nav station and about ten battery bank switches with some of the batteries underneath:

https://flic.kr/p/2pf78HC

They are similar to this product:

https://www.bluesea.com/support/articles/681/Switching_Solutions_for_Multiple_Battery_Banks

I wonder if that is how they solved the problem back then?
 
Hedges said:
I think that shows 48V lithium bank and two 96V AGM banks, each consisting of two 48V AGM banks with switch between them.
The lithium bank can switch to parallel with each 48V AGM bank.

When switch in middle separates 96V bank into two 48V banks, I don't think any current can flow to motor.

I think lithium bank is supposed to be able to charge or share current with 48V AGM banks. But can't charge effectively, need it to be higher voltage but regulated current (or voltage.)

Assuming 48V lithium banks are not designed for series use, I think a high current reverse-polarity diode across them (like bypass diode of PV panel) would protect them. That would let you make 96V lithium.

Some form of isolated DC/DC charger could charge multiple 48V AGM banks from 48V lithium bank. An off the shelf method would be inverter fed from lithium, feeding Chargeverter. Inefficiencies of double conversion, but at least it is off the shelf.
Click to expand...
Thanks for those replies. I'd have to look into diodes etc. as it's above my pay-grade :).......but the combination of separate AGM banks and separate solar inverter for the AGM bank so I could hit it hard when needed, might be a solution.
 
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