Last Updated: 09/21/2022
The electrical systems and issues on our previous boat, a 1980's CSY monohull, were quite different than those on our 2004 St. Francis Catamaran. For all the great stuff I did over the years on the CSY electrical system, go to this link: CSY Electrical Systems.
When we purchased our St. Francis 44 catamaran 7 years ago, the house bank consisted of six 6-volt Sonnenschein Solar Block 200 batteries, for a rated total of 600 Ahrs at 12 volts. They are very high quality German Gel batteries. In early 2020, locked down by COVID in the Philippines, and with our Gel battery bank then 13 years old, we decided it was a good opportunity to install new lithium technology. The Gels might have lasted several more years according to Gel literature and because of the quality charging equipment we had, but given our location in SE Asia, and the time we had available, this was a good opportunity to upgrade.
Our installation is optimized for a catamaran cruising full time overseas. We have little tolerance for jury rigs, marginally safe practices and unnecessarily high cost equipment. We believe that if installing lithium on a cruising boat, it is worthwhile to develop the skills to install and make repairs ourselves with adequate spares and proper tools onboard.
Had we not had the time to study the technology, place the orders, and make the necessary electrical system changes, we would not have taken this on. It is not a project for those not willing to spend time learning how to do the installation properly.
Basics: LiFePO4 (LFP) batteries suitable for cruising boats consist of an appropriate number of individual prismatic 3.2 volt cells that operate safely within a narrow voltage range. Straying beyond this range can cause permanent cell damage.
For a Best Practices LFP battery system, a boat�s electrical system should have separate charging and load busses wired to a single house bank through appropriate shunts and fuses. Each of the charging sources (solar, alternator, shore, etc.) should have a relay that allows a battery management system (BMS), monitoring individual cells, to shut it down, not just disconnect it from the battery. This should happen automatically if there is a problem beyond what the charging device does with its own onboard charge termination.
In normal operation, the charging sources, reading total battery voltage, will control the charging and charge termination using mainly the bulk phase with no or only minimal absorption. The BMS will act as a backup to terminate the charge (HVD) if a single cell�s voltage gets too high and the charging source fails to terminate the charge in time. There should also be a relay or relays on the load buss for the BMS to disconnect loads (LVD) if the battery or cell reaches too low a state of charge.
Basic LiFePO4 battery wiring diagram with BMS and separate charging and load busses. Fuses, shunts, relays, etc not shown.After significant research and living with the new technology now for over two years, below find our thoughts on how to choose equipment and complete a DIY LiFePO4 lithium cell installation on a cruising sailboat.
First here are some cautions:
Replacing our LA Gels with blue LiFePO4 lithium prismatic cells. Only one of 8 LFP cells is shown.
Lead Acid (LA) vs Lithium (LFP) Differences: Because of the vast differences between these two types of batteries, great care must be taken to not make a mistake during planning and installation. A number of different lithium ion type cells are available now, but LifePO4 is the choice for cruiser batteries. It has significant advantages over the others, including being reasonably safe and stable in a marine environment. Even some of the electric vehicle companies are now changing to LFP.
Below are some differences between LFP and LA technologies:
Our older Xantrex Link 2000 LA battery monitor that displays only total battery parameters.
Do It Yourself (DIY) LifePO4 Cells: After a great deal of research, we settled on prismatic-style aluminum-cased individual LifePO4 cells, purchased directly from RJ Lithium in China. There are a number of other Chinese cell companies we could have bought from, but other cruising friends locally had researched this and were buying from RJ. Their reputation was good, they offered documented Grade-A cells, the sales representatives were responsive, the website was informative, and they offered a 5 year warranty.
All eight of our cells with taped terminals and typical Grade-A labels, just out of the shipping boxes
Four of our prismatic cells with Grade A
testing stickers intact , showing, among other things,
, showing, among other things,
We purchased eight 3.2 volt 271 amp hour (Ah) LFP cells, for about $150 each plus about $35 shipping each for a total house bank capacity of 542 Ah. (Note that the shipping cost was extremely high at the time, due to the peculiarities of shipping into the Philippines via Hong Kong).
Of that 542 Ah, more than 450 Ah are useable, so we increased our capacity by about 50% over our Gel bank's useful capacity. And we were able to remove 390 lbs of Gels and replace with only 100 lbs of lithium cells.
Later we discovered that we could have bought similar well-regarded EVE or Lishen cells for $100 USD each and modest shipping cost, sourced locally in the Philippines, but without the longer warranty. So our cost for the RJ cells was about $1500 US including shipping. Lishen or EVE cells would have been around $900 including shipping. The LFP cell market is constantly changing, and competition is fierce, so this pricing from China is now likely different. On the forums we often see these Grade A cells being shipped to the US and Europe at very reasonable prices. A cruising friend in our marina in the Philippines in early 2022 purchased 240 Ah Grade A EVE cells with a 2 year warranty and minimal shipping for about $100 US each.
Drop-In LifePO4 Batteries: We do not recommend installing what is commonly referred to as 'drop in lithium batteries' on a serious cruising boat. They are better suited to coastal power boats and outboards for the following reasons:
If you can't take the time to do a proper DIY installation yourself, or with help from a knowledgeable friend who will teach you the system, we recommend buying quality Gel batteries to install into your existing LA electrical system.
Four 3.2v LFP cells with MOSFET BMS, wired in series inside a 12v pre-assembled/drop in battery case. (source: RJ Energy)
Charging and Discharging: The LFP cell charging curve is very flat in the middle between 3.20-3.4 volts per cell (vpc). Then it goes nearly vertical (the knee) as the cell approaches full state of charge (SOC) at about 3.45 vpc and above. Because charging through the upper knee takes only a couple of minutes it represents very few Ahrs and may not be really necessary. Likewise, as the battery is discharging, the voltage stays very flat until dropping off rapidly below about 3.15 vpc as the battery reaches 10 percent SOC. The relatively high stable voltage and flat discharge curve are a big help when using high amp draw equipment like an inverter or windlass.
LFP Charge and Discharge Curve comparison
Cell Matching and Balance: Factory matching of cell capacity and internal resistance are important for being able to maintain cell voltage balance. But it is a labor-intensive, and therefore expensive, process, so few companies selling cells at competitive pricing are able to do a perfect job.
Several companies, like Winston and a few others, do better matching work, but this is reflected in their significantly higher pricing. This is where a good balancer in the BMS (at lease 200 milliamps) or a separately purchased quality balancer earns its keep.
If the cells are not perfectly matched in capacity and internal resistance, when charging, one cell can get to 3.65 vpc well before the others. This is an over voltage situation that can destroy that cell before the total battery voltage reaches an alarm condition. Likewise, when discharging, if one cell is slightly more depleted than the others, its voltage can drop rapidly to below 2.5 vpc, a destructive under voltage situation, again while the overall battery voltage is still at a safe level. A quality BMS that can monitor cell voltages can control these situations through external relays and prevent cell damage.
Also, cells that are not well matched for internal resistance will have
slightly different charge curves that might cause an automatic balancer to
balance the wrong cells during charging. Our cells are not perfectly
matched, so their charge curves intertwine voltage levels as they are being
charged. Sometimes the low voltage cell at the start of charging becomes the
high voltage cell at charge termination. A good cell balancer can handle
this and keep cell balance levels within a reasonable delta.
Cell Grading: Well-regarded lithium factories produce thousands of individual cells a week. During initial testing, those that match advertised specifications are graded as A cells. Those that do not become grade B cells and could have a range of problems. Both are sold on the open market. Grade A cells are usually a bit more expensive, have QR and testing stickers intact and usually have warranties of a year or more. Grade B cells are often sold to off-grid applications that use hundreds of cells so that they can afford to have a few that have problems. Serious cruisers would do well to always buy Grade A cells as it helps ensure full usable bank capacity and makes balancing much easier.
Even after being assured we had Grade A cells, and doing exhaustive testing upon receipt, we ended up with one bad cell that would excessively self-discharge compared to the others. It lost a half millivolt (mv) at rest on a daily basis, which resulted in it quickly falling behind the others at charge termination. This is one symptom of a grade B cell.
After much testing and consultation with RJ to discover the source (checking contact integrity, remeasuring internal resistance and swapping cells around, etc), we determined it to be an internal problem. To their credit, RJ replaced the cell under warranty with us only paying the $20 US shipping cost. Meanwhile, we purchased two similar Grade B Lishen cells from an online source in Manila. They performed well, but we eventually went back to using all RJ cells in our house bank. The Lishen cells have been kept as spares. As we all know, cruisers can never have too many spares.
Configuration: Banks of lithium cells are typically connected in sets of four 3.2 volt cells in series for a nominal 12 volt battery system. If you have a 24 volt electrical system, connect 8 cells in series. For more capacity than 4 or 8 single cells will allow, first connect cells in equal parallel sets, then connect those sets in series. The parallel sets can be comprised of various capacity cells, but the series sets must all be of equal total capacity and voltage.
We originally planned to configure our 8 cells into two 4-cell "batteries", with a 1-2-Both selector switch so we could switch between batteries if we ran into a problem with one battery. However, once we started wiring up the two Electrodacus BMS's, we found that trying to control the separate loads, charging sources, 2 busses, and multiple external relays with two BMS's became too difficult. Some internal relay BMSs are able to do this, but with somewhat degraded reliability and battery balance problems. We also realized that if we ever ran into an extremely rare sudden cell problem, rearranging the cells with our spares to make repairs was a pretty simple temporary solution.
So we ended up with 4 sets of 2 cells in parallel to make 4 "supercells", then those 4 cells in series for a 542 Ah at 13.2v bank. This also had the advantage of requiring only one BMS instead of two. Since we had ordered two BMSs we now had a spare. And as all cruisers know, you can never have too many spares.
Whether our configuration is called 2P4S or 4S2P configuration depends on who you ask. It is written both ways all over lithium literature and the internet. So be mindful of this when asking questions on lithium forums. Sometimes it is preferable to better describe your configuration rather than using one of the above abbreviations.
Our 8 LifePO4 cells in their compression box in a
2P4S configuration. Two of the four threaded compression rods are visible in
place. Flexible connecting straps are made of multiple layers copper
carefully cleaned and firmly fastened to the terminals.
Cell Compression: Most literature and experts on LFP cells recommend using a 'compression box' to house the cells. This is more of a 'limitation box' that prevents the cells from chafing against each other and shorting, terminals being damaged by connector tension as a result of expansion during charging, and sliding around as a bank in rough weather. According to EVE Energy, one of the largest lithium cell manufacturers in China, their aluminum case cells require compression in order to reach their full service life. Many others agree.
So we built a compression box to store the cells using epoxy-coated 3/4-inch marine plywood and 3/8-inch Stainless Steel threaded rod. Between the cells we used 1 mm soft placemat material to prevent the cell sides from shorting together and provide somewhat of a cushion. The box has a polycarbonate cover and is strongly secured under our main cabin settee in the middle of the boat. It is only about 3 feet from the BMS, busses, regulators, relays and other major wiring. The addition of calibrated springs on the threaded rod would allow us to control the amount of compression, but we think that is overkill. With more effort/expense, the compression box could also be made of fiberglass, aluminum or steel.
Front of our battery box, with cover on and secured
under the settee seat. Four threaded compression rods are visible in place.
Red large cable is positive and brown negative.
Battery Management System (BMS): A good BMS is a critical component of a LifePO4 system. Unlike most lead acid battery monitors that display overall battery voltages, a good BMS should monitor individual cell voltages. So a BMS can watch the voltage and state of charge of each cell, and make appropriate decisions regarding when to disconnect charge sources in case of an over voltage event (HVD) or disconnect loads in case of an under voltage event (LVD) in order to prevent cell damage.
There are two types of BMSs. One uses small internal MOSFET relays to turn on and off charging and loads when required. The other type of BMS can control much larger external relays. Since loads like inverters and windlasses and charging sources like alternators and generators might involve relatively high currents, cruising boat systems are better done with a BMS that uses high capacity external relays.
An important BMS feature is its ability to display externally what it is doing and important battery details such as voltage, current and SOC. Options include hard wiring to a display device such as a computer, wireless Wi-Fi, and wireless Bluetooth using an application. We are using Wi-Fi so that we can see what is happening with our system when on or off the boat.
Also, a good BMS will have some sort of cell balancing capability. 200 milliamps are usually sufficient to keep most reasonably matched and balanced marine house banks in line. Although most BMSs use some form of low current passive balancing, and that is usually sufficient over time, larger active balancers are available. They work with large cell deltas more quickly, removing excess amp hours from high voltage cells and placing it in lower cells.
BMSs range in price from cheap/dumb $15 USD small open boards with no user interface, to high-quality programmable BMSs that will integrate seamlessly with existing proprietary equipment like smart Victron components, for about $600 USD. High price doesn�t always give you equipment with features you may need, but better quality BMSs are usually priced over $100 US. Before purchasing a BMS you should look at the several internet sources for comparing BMSs, including user forums and YouTube videos. Just remember serious cruisers cannot afford unreliable gear, so paying for reasonable quality and reliability is worthwhile, but no need to go overboard for capabilities you don�t need.
We chose a very smart programmable BMS, an Electrodacus SBMS0, made in Canada by a small well-regarded company. This one is targeted at the DIY Solar community and can control multiple external relays with many adjustable parameters. It has an included detailed monitor screen, a 200 milliamp balancer, excellent HVD/LVD protection capability, and an optional Wi-Fi interface. Just about every parameter for charging, discharging, balancing and HVD/LVD control is adjustable by the user. The HVD/LVD controls have 6 ways to set the control function. It has a very sophisticated logging capability. Finally, the developer and others provides significant help to users as needed via a forum and several beginners� guides.
Our Electrodacus SBMS0 and its main monitoring screen, one of about two dozen screens available for monitoring and parameter adjustment. This screen shows, among other things, cell and total voltages, charging and load amps, maximum cell delta and SOC.
The Electrodacus SBMS0 also has some built-in historical logging, and with the addition of the optional Wi-Fi module, can provide a wireless MQTT feed to integrate into any Internet-of-Things (IOT) system. The MQTT capability allowed us to build a custom monitoring and logging screen (below), running on our Nav Station Computer. With internet access, and a bit of free software, we can monitor our electrical system from anywhere in the world.
What our current monitoring screen looks like (click on the picture for an enlarged copy):
Our Battery Management monitoring screen,
using the MQTT feed
We are pleased with our choice of BMS, but it has involved a steep learning curve. (LifePO4 in general is a big learning curve!) Considerable help is available from the detailed User Manual, an even more helpful user-built Beginner's Guide, two forums with experienced users and the developer, Dacian, answering questions. Dacian will even diagnose problems and fix them if necessary, sometimes at no charge, if you send the unit to him in Canada.
Wiring & Fuses: It is important to use proper wire sizes, quality terminals, and make good connections, because proper monitoring and balancing involve millivolts and milliamps (thousanths of volts and amps). Any weak connection will affect readings and function.
The display and balancing wires are typically 20 gauge or smaller, so you might need better crimping and stripping tools. For example, the ElectroDacus system uses twisted solid Cat 5 or 6 24 gauge wires for connections to the SBMS0. Common stripping tools won't strip those small wires. (See our tool recommendations below).
Fusing and circuit breakers must be of quality construction and function as advertised. These relatively small batteries can produce huge amounts of amps if shorted. Although fires are rare with LiFePO4 technology, a shorted cell can melt tools instantly and cause sparking that can ruin your day and your boat. Proper installation will also prevent disapproval of an insurance claim should something go wrong. It is worth checking your insurance information to see if there are any specific clauses about LFP batteries.
Relays & Shunts: When using a BMS capable of controlling external relays, care must be taken regarding which relays to use for which circuits. And quality shunts must be used in order to display accurate current flow and State of Charge (SOC). Below is a list of those we used:
Initial Testing and Balancing: Not everyone will have the time or want to do the initial testing that we did. We had purchased the cells with an electrical engineer friend--a total of 24 prismatic 271 Ah cells. Our friend had the proper large load and bench power supply equipment available, and we wanted to fully test that the capacity of the cells we received matched the manufacturer specs. This may be the only way to discover early on a cell lacking capacity or with a high internal resistance.
We started by charging all cells up individually to 3.6 volts per cell (vpc). Then we discharged them individually to 2.8 vpc and graphed the resulting discharge curve and capacity. Finally, we made a graph of the charge curves taking them back up to 3.6 vpc. (see graphs earlier)
After removing the charge, each cell fell back to a rest voltage of about 3.35 vpc. All capacities were within a few amp hours just below 271, since we did not fully charge or discharge them. The charge and discharge curves were similar, but not exactly the same. Internal resistance for all cells was measured to be .076 ohm at 3.0 vpc.
Top Balancing: Later we did what is referred to in the literature as a 'top balance'. That is taking all cells in parallel to some voltage above 3.5 vpc--in our case to 3.62 vpc--and letting them absorb to about 5 amp or less tail current. This should get them all balanced to within a few millivolts of each other at charge termination.
Although we did this a second time to less than 1 amp tail current, we did not find it to be very effective at getting the cells closer than about 100 mv apart at charge termination of 3.45 vpc. It probably would have been better to take them only to our charge termination voltage and let them absorb there to an absolute minimum tail current. There are a number of opinions on the internet as to exactly how best to do this.
We found the most effective balancing technique to be using our bench power supply and adjustable load equipment to manually get the cell voltages closer at charge termination. This consists of attaching the equipment to individual or a group of cells to raise or lower their voltage by adding or subtracting milliamps over time.
Regardless of how the cell voltages look at rest, they will always have a much higher delta when the voltage reaches the knee. After a week or so of adding and subtracting mA, cell voltage deltas can be reduced to an acceptable 10-20 mV.
Then the small passive automatic balancer in the SBMS0 can be used to keep them in balance, despite our not-well-matched cells.
The balancing mechanism on our BMS uses resistors that are latched in during charging, when the cell voltage delta goes above the minimum balancing setpoint, to suppress charging the highest cell(s). So the lowest cells receive full charge current, while the highest cell(s) receive less.
Our cells are now resting with a 7 mV delta and 20-30 mV delta at charge termination. These figures are entirely adequate for cell balance.
Tools and Equipment: We purchased the following equipment to help us better do the installation:
Lithium Safety and The Insurance Issue
And a couple of thoughts on insurance coverage:
Have fun learning about this new technology, but remember that not everything you read is true, and the experts don't all agree. The forums, especially, are full of inaccurate opinions. So study carefully, and subscribe as we did, to the preponderance of evidence from the trusted sources below.
A good way to start, as a minimum, is to watch some of Will Prouse's YouTube videos, then graduate to some of those from Andy's Off Grid Garage, and finally read the detailed articles at MarineHowTo, NordkynDesign, and FilterGuy's Summary of BMS Functions. Once finished you will be ready to start your LFP project. Links to these resources are below.
Will Prowse's DIY Lithium and Solar on YouTube [link]
Andy's Off Grid Garage [link]
Bussed_As NZ's DIY Lithium and Solar on YouTube [link]
LifePO4 on a Boat
NordkynDesign.com's Lithium Pages
FilterGuy's excellent summary of BMS features is provided in this document on DIY Solar. All beginners should read and understand this before purchasing a BMS.
More DIY Solar Forum "Beginner's Resources" [link]
Electrodacus Google Group (not boat-specific)
We have consolidated all of our current knowledge and experience (with contributions from others) for the ElectroDacus SBMS0 BMS on a separate ElectroDacus page. However, we continue to follow many of the links above, especially the forums, for new ideas and updates to the technology and equipment.
This is a big subject and it is always interesting to see how others are set up also. Much of how you set up the boat depends on how you plan to use it. If you are dockside most of the time you will want a different system than if you are cruising and away from docks. We are currently cruising, often away from docks and also away from good (expensive) repair facilities.
It has taken me several years to get my new catamaran set up the way I wanted it... with all charging systems wired to the House bank and a trickle charge arrangement for the Start battery. On the catamaran it is a little more complicated because we now have 2 engines and 2 alternators to worry about.
My system keeps the House and Start batteries physically isolated from each other in the normal use/charging situation. It allows multi step charging for the house bank and trickle charging for the start battery.
First, connect all your charging sources (alternator, 120v charger, solar, etc) on one "charge bus" and connect that directly to the house bank.
Run your charging sense and temperature wires to the house bank.
Connect your starting battery direct to the starter. Then connect the house bank to terminal 1 of the battery selector switch and the start battery to terminal 2.
Next connect all your loads to
the common terminal of your battery selector switch. Add cutout switches
and/or fuses as desired in the battery cables within 18" of the batteries, if
you want to comply with ABYC specs.
See Trickle Charging the Start Battery,
for details, below.
Also, keep your house batteries away from heat while charging, as it is a killer. If in the engine room, for example, with temps over 115 degrees F you will lose 75% of your cycle life! And if you are using Lead Acid technology for your house bank, don't forget to equalize!
At the 1998 SSCA Gam the Four Winds/Everfair owner, Bill Owra, gave what I thought was a very well thought out and much better wiring diagram for a house bank and a starting battery setup. It featured, among other things, hands off trickle charging of the start battery off the house bank, an anti theft switch in the starter/starter battery cable, using the battery selector switch to normally control only battery loads, rather than charging and loading, emergency cross connect for starting and house loads, and routing all charging source cables directly to the house bank so there's no possibility of an alternator or other disconnect problem while charging. It was the best layout I've seen and I've looked at many in the past 20 years of boat ownership.
I thought that the best feature was the automatic trickle charging of the starting battery from the house bank through a short 12 gauge wire with a diode (one way current flow) and thermal circuit breaker.
The idea is that when the house bank is being charged from any charging source the diode will keep the voltage to the starting battery about 1/2 volt below the house bank voltage, and the thermal circuit breaker will break the charging circuit off if the charging amperage get too high.
The starting battery can take up to about 15 amps if it needs it but with this system it normally just takes small float current. I've never seen more than about 2 amps going into my starting battery from the house bank.
This circuit provides a reasonable float charge to keep the starting battery always at 100 percent, just like in your car. A true starting battery with thin, large surface area plates and a high CCA/MCA rating is great for starting your engine and will last as long as your house bank if kept this way.
And it's all automatic with no risk of inadvertently disconnecting the house bank from its alternator charging source. I also keep a couple of spare diodes and thermal circuit breakers aboard just in case.
I used this electrical layout on our CSY, and have just (2018) installed it on our new catamaran. Here are the components required:
And links to online sources:
And a picture of ours, installed. I just mounted it on a piece of scrap aluminum, near the battery box:
evolution of our solar system on Soggy Paws the CSY, see this page.
When we bought the catamaran, I sold off the old system that came with the boat and installed 4 new 200 watt 36v panels, and a new Morningstar MPPT solar regulator. Though we really liked the Outback MPPT regulator that we had on the CSY, the Morningstar offered a way to monitor the system via computer connection.
Though the catamaran mounting doesn't allow rotation of the panels fore and aft, as we had on the CSY, we made up for it by adding another 200 watts of solar capacity.
As with the CSY system, on a good solar day, we are cranking out the amps, and our batteries are fully charged at mid-day on a sunny day, even if we're wantonly charging computers and stuff. With the excess watts, we can handle several days worth of overcast days before we have to think about charging with other means. Also, in the wintertime, when the solar days are much shorter and the sun angle is not directly overhead even at midday, we have enough power to run the boat at anchor without running any other charging system.
I have taken apart and rebuilt my own alternators ever since
I paid about $100 for a rebuild down in the islands that did not work. The
problem was that the shop installed 30a diodes in my 150a alternator that
needed 50a diodes. Back then I was still trusting third world mechanics with
some of the work on my boat. They are real simple to take apart, test and
replace parts. See
Nigel Calder's Mechanical and Electrical Manual. You certainly don't
need to send them anywhere for repair if you have basic tools, electrical
skills and first time instructions. If you have one of the older Delco,
Balmar or Powerlines, it is fairly simple.
Here is a bit of
interesting info on lightning, its cause, prevention and cure from a
discussion on an SSCA forum:
So reducing the "electrical" apparent height of your boat is good. This can
be done with static dissipators such as the Forespar Lightning Master.
(Which is a copy of the static wick principle used on airplanes and
airliners). The sharp small "spikes" of the device "bleeds" off ions as they
build up and electrically reduces your mast height to equal that of the
ocean. However, to do this it must have a "significant" and good ground to
the ocean. That translates to 4 square feet of flat plate copper in contact
with the ocean and 2/0 welding cable between the mast and the plates
submerged in the ocean. A static dissipator will not dissipate if it is not
connected with the ocean.
Here's what he says (comparing a 12'
strip to a 1 sf plate):
A grounding plate, if used instead, should be solid, rather than the
sintered bronze type often used as radio grounds. The sponge-like structure
of the sintered bronze plates may, in the event of a strike, allow the
instant formation of steam, which could blow the plate apart, resulting in
possible severe damage to the surrounding hull".
If you Google boat lightning
grounds/protection you will find much more info on this, including this
useful tidbit on Kasten's site: