Last Updated: 04/27/2021
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.
About a year ago we embarked on replacing our 13 year old Gel batteries with lithium LiFePO4 cells. We quickly learned that:
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. However, we do believe in developing the skills to make repairs ourselves with adequate spares and proper tools. Below find our thoughts on how to complete a DIY installation after significant research, money expended and living with the new technology for about 6 months.
When we purchased our St. Francis 44 catamaran 6 years ago, the house bank consisted six 6-volt Sonneschein Solar Block 200 batteries, for a total of 600Ah. They are very high quality German Gel batteries. In early 2020, locked down by COVID, and with our gel battery bank now 13 years old, we decided it was a good opportunity to upgrade to new Lithium technology. The Gels might have lasted several more years according to Gel literature, but given our location in SE Asia, and the time we had available, this was a good opportunity to upgrade. Had we not had the years’ time to study the technology and make the many 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.
Lead Acid (LA) vs Lithium Differences: Because of the vast differences between these two types of batteries, great care must be taken to not make a mistake during installation. A number of different lithium type cells are available now, but LiFePO4 is the best choice for cruiser batteries.
LifePO4 Cells: After a great deal of research, we settled on prismatic style aluminum cased 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 friends locally had researched this and were buying from RJ. Their reputation was good, the sales representatives were responsive, the website was informative, and they offered a 5 year warranty.
We purchased eight 3.2 volt 271 Ah LifePO4 cells, for about $150 each plus about $35 shipping each for a total house bank capacity of 540 Ah. (Note that the shipping cost was excessively high due to the peculiarities of shipping into the Philippines).
Of that 540 Ah, about 450 Ah are useable, so we increased our capacity by about 50% over our Gel battery 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 about $100 each and modest shipping cost, sourced locally here in the Philippines, but without the longer warranty.
Drop-In LifePO4 Batteries: We do not recommend installing what is commonly referred to as ‘drop in lithium batteries’ on a cruising boat. They are better suited to coastal power boats and outboards since the cells and most of the electrical components are secured inside the battery box and are inaccessible if there is a problem. Also, typically the BMSs provided use small internal relay components that must control the high currents usually found on cruising boats. They are also frightfully expensive compared to a DIY installation using individual cells. And you will still need to do most of the electrical work as with a DIY system. If you can’t take the time to do a proper DIY installation yourself, we recommend buying quality Gel batteries to install into your existing electrical system.
Cell Matching and Balance: Factory matching of cell capacity and internal resistance is important to being able to maintain cell voltage balance. The charging curve is very flat in the middle between 3.20-3.4v per cell, and then goes nearly vertical (the knee) as the cell approaches full SOC at about 3.45v per cell and above. Likewise, as the battery is discharging, the voltage stays very flat until dropping off rapidly below about 3.15vpc as the battery reaches 10-15% state of charge.
Charge Curve for 4 Cells in Parallel
This curve reflects
one cell being discharged from "full" at 35 amps continuously.
If the cells are not perfectly matched in capacity and internal resistance, when charging one cell can get to 3.65v per cell well before the others, and end up in an overvoltage situation that will 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 2.5v, again while the overall battery voltage is still at a safe level.
Also, cells that are not well matched will have slightly different charge
curves that might cause an automatic balancer to balance the wrong cells
Configuration: We originally planned to configure the cells into 2 4-cell "batteries", with a 1-2-Both selector switch so we could switch between batteries if we ran into a problem with one cell. However, once we started wiring up the BMS, we found that trying to control the separate Loads and Charging busses with two BMS's got way too complicated. We also found that rearranging the cells from an 8-cell bank to a 4-cell bank, if we ran into a cell problem, to be pretty simple.
So we ended up with 4 sets of 2 cells in parallel to make 4 "supercells", then those 4 cells in series for a 540Ah at 13.2v bank. This also had the advantage of requiring only one BMS instead of two. Whether this is called 2P4S or 4S2P configuration depends on who you ask. It is written both ways all over lithium literature and the internet.
Compression box: Most literature and experts on LiFePO4 recommend using a ‘compression box’ to house the cells. Really this should be more of a Limitation box that prevents the cells from chafing against each other, terminals being damaged by connector tension as a result of expansion during charging, and sliding around as a bank in rough weather. Also, 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 cycle life. So we built a compression box to store the cells using epoxy coated ¾” marine plywood and 3/8” SS threaded rod. Between the cells we used 1mm Formica to prevent the sides shorting together. The box is strongly secured, has a Lexan cover, and is mounted under our main cabin settee only about 3 feet from the BMS and busses.
The LifePO4 cells in the compression box
Battery Box, Closed and Secured
Battery Management System: A good BMS is a critical component of a LifePO4 system. Unlike most lead acid battery charge sources that monitor overall battery voltages, a good BMS can 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, the other 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 external relays.
BMSs range in price from inexpensive/dumb $15 USD small open boards with no user interface, to high-quality programmable BMSs that will integrate seamlessly with existing smart Victron equipment for about $600 USD.
We chose a very smart programmable BMS made in Canada with a Wi-Fi interface called an Electrodacus SBMS0, for about $120 USD. This one is targeted at the DIY Solar community and can control multiple external relays with many adjustable parameters. It has a detailed monitor, a small balancer and excellent HVD/LVD protection capability.
The Electrodacus SBMS0 also has some built-in historical logging, and with the addition of an optional wifi module, can provide a wireless MQTT feed to integrate into any Internet-of-Things (IOT) system.
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!)
Wiring & Fuses: It is important to use proper wire sizes and fusing in a lithium battery project because these 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.
Also, 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 5/6 24 gauge wires for connections to the SBMS0. Our tool recommendations are below.
Relays & Shunts: When using a BMS capable of controlling external relays, care must be taken regarding which relays to use for which circuits. And shunts must be used in order to display current 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 24 271 Ah cells. Our friend had the proper 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.
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 charge curve and capacity. Finally, we made a graph of the charge curves taking them back up to 3.6 vpc. (see graphs at the beginning of this writeup)
After removing the charge, each cell fell back to a rest voltage of about 3.35 vpc. All capacities were within 260-270 Ah, since we did not fully charge or discharge them. The charge and discharge curves were similar, but not exactly the same. Internal resistance 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 exactly 3.62 vpc and letting them absorb to about 5 amp tail current. This should get them all balanced to within a few millivolts (mv) of each other at charge termination. Although we did this a second time, 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.
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. This consists of attaching the equipment to individual or a group of cells to raise or lower their voltage by adding or subtracting milliamps (mA).
Regardless of how the cell voltages look at rest, they will always have a much higher delta near charge termination, especially if well up the charge knee. After a week or so of adding and subtracting mA, cell voltage deltas can be reduced to 10-20 mV.
Then the small passive automatic balancer in the SBMS0 can be used to keep them in balance, if only allowed to balance above about 3.4 vpc. This is because at lower voltages, the cell voltages sometimes reverse which is high and which is low.
The balancing mechanism on our BMS uses resistors that are latched in during charging, when the cell voltage delta goes above 20mV, to suppress charging the highest cell(s).
Our cells are now resting and charging with a 7 mV delta and 20-25 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:
• Long Wei PS1310F DC bench power supply.
We have consolidated our knowledge and experience (with contributions from others) for the Electrodacus SBMS0 BMS on a separate Electrodacus page.
An excellent summary of BMS features is provided in this document on DIY Solar:
For those contemplating a LifePO4 upgrade on their boats, here are the resources we found best to educate yourself before you get started.
LifePO4 on a Boat
NordkynDesign.com's Lithium Pages
Will Prowse's DIY Lithium and Solar on YouTube [link]
Bussed_As NZ's DIY Lithium and Solar on YouTube [link]
DIY Solar Forum "Beginner's Resources"
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: