The biggest test of our new outboard motor is getting Morty to shore multiple times a day in a timely fashion. It is plain to say that Morty approves of this motor.
Not only does it get us to shore quickly, it does so silently.
New Electric Motor Testing to Come
With all this battery building, we now have plenty of power on hand and I got tired of always needing to tinker with our gas outboard to keep it running. We decided to build some additional batteries (more info on that process later) and power our dinghy with an electric outboard!
After looking around online, I came across this company that seems to have embraced the electric outboard concept and separated themselves from the limitations of “electric trolling motors”. Electric trolling motors (like the image on the left) have a long motor tube ending in a rather small propeller. They are for fishing and will not move any boat quickly because the propeller they have is not designed to move at more than a few knots. If you go too fast, you are no longer trolling and people who fish would not be pleased! Crazy sailboat people with dinghies do want to go fast, and electric trolling motors left us sailors a bit disappointed in the speed department.
Aquos said: “Let’s make it happen” and built a powerful trolling motor with a massive propeller that can push a dinghy at speeds comparable to a gas outboard!
I bought a 24v 110lbs thrust motor from Aquos and built a 24v LiFePO4 battery for it and gave it a quick test in a pond near my parents house (hardly the conditions we will encounter while cruising), but it was a success and fun! The dinghy moved at the same speeds we got out of our Honda 2.3 and Suzuki 2.5, but with none of the noise that goes with a gas outboard.
We are heading back to the boat next week and will give it a try in salt water (fingers crossed) and let you know how it holds up to real world cruising duty usage.
Which Sextant can you Trust?
GPS is a wonderful technology. It allows you to glance at your display and see exactly where you are! Chart plotters are even better, granting you the ability to see not only your coordinates, but your live position on a digital chart. Snaking your way through coral reefs at night becomes easy as driving down a country road, just follow the map and keep your digital representation on the map in the middle of your digital representation of a road and hope that there is no new debris in the way that you could bump into.
So we all agree relying too heavily on GPS is a bad thing and that it doesn’t replace proper seamanship and navigation?
If a nuclear bomb detonates in space at the start of World War III or if lightning strikes your mast (both equally probable events), the GPS as well as all your electronic navigational equipment will be toast! This is where backups come into play.
The most reliable and time tested backup is the classic sextant. You see them in movies where they try to make the captain look extra “shippy” by having him look out into the distance and say “Aye, we be nearin’ the coast”. The sextants they show in movies are in fact movie props, but they look like the bronze masterpieces created by expert craftsmen.
For the price of a small boat, you can have a piece of navigational history! You will have an expensive antique that has stood the test of time and is incredibly heavy to hold while you try to sight the sun to find your position.
For that price, you could buy yourself a fancy Raymarine chartplotter and be able to snake your way through narrow waterways on the giant display screen!
What about those significantly less expensive plastic sextants? Are they any good? What are the problems with them? Why are they so much cheaper than the bronze models?
In 2020, we crossed the Atlantic from Cape Verde to Suriname (East to West crossing) using a plastic sextant as our guide. We turned off the GPS and primarily used noon sights to find our way across the ocean.
The plastic sextant did the trick! It accurately records the height of the sun in the sky and is easy to hold while you are doing a reading thanks to its lightweight plastic design.
As for concerns that the plastic sextants are “cheap”: They are a delicate measuring device that needs to be cared for. If you feel that a $2000 bronze sextant needs to live in its case, safely stowed inside the boat, why shouldn’t you do the same thing for your $300 plastic sextant?
We keep our sextant in a specially made box, safely stowed in the cabin away from strong sunlight. If I left it out on the deck, the heat from the sun could distort the arc of the sextant and ruin it; but why would you do that? Take care of your sextant and treat it as a priceless piece of equipment while you are sailing because regardless of the price, all sextants are irreplaceable out at sea.
Some people feel that you get what you pay for and if you paid more, it’s naturally better! Bronze is an expensive metal to make things out of compared to plastic, which is why the bronze units are so much more expensive! A solid gold sextant would be the most expensive option of all, but being made of gold would not make it any better than a bronze or plastic unit. The second part of the cost is the act of making the unit calibrated. Regardless of the material, calibrating the unit is an exacting task which takes money to do, and the result is a precise measuring device made out of different materials. The major cost difference is in the material that the measurements are produced on.
For a reliable backup to navigational electronics, we trust our plastic sextant! It does the job, is light weight, and won’t corrode in the marine environment. If it does die a watery or heat related death, it can also be replaced at an affordable rate compared to a more expensive unit.
Building a Bridge
This has nothing to do with Karma or friendships or anything like that. This is about building a battery!
In the battery being built above, the cells are not aligned in neat and even patterns. This is due to space limitations and just makes things complicated. With a little thought, major problems can be avoided, and the implementation takes a small amount of effort.
In this example, I’m building a 16s16p battery. That’s fancy talk for a 48v battery made up of a ton of tiny battery cells. Each cell is 3.2v, and when I link 16 of them up in series, I end up with 51.2v (which ironically is considered a 48v battery). Each cell is only 6ah, so if I just linked 16 of them up in series I would have a 48v battery that holds 6amps; not very useful to power the electric motor in our sailboat along with all of our house loads. To beef up the amp capacity a bit, we simply add more cells in parallel, 15 more to be precise! This gives us a battery that will hold 16x6=96 amp hours and is made up of 16 cell groups in series.
The final result is 16 series and 16 parallel, or also called a 16s16p battery.
That’s cool and all, but why do the cells need to be in strange interlocking patterns? Space. Being how these are batteries for a boat, space is never existent and we will need to cram these batteries into wherever we can fit them. We didn’t have the space to fit 16 cells in a row, so we arranged them into an arrangement that is 10 cells wide. This means that each parallel group is 10 cells in a row with another 6 cells crammed around next to them in the next row. The next row can fit 4 more cells of the next group, the following row is 10 of the same, and then 2 more cells spilling over into the next row. This pattern will continue all the way down the line until you finally get to the last cell group where the pattern just ends.
Why does this matter?
You need to know how much power you plan on pulling from your battery at any point in time and then build the battery to handle this load. In our case, the battery will need to supply 400 amps to power our electric motor when it runs at full speed. Building one battery that can yield 400 amps is pretty ridiculous so we did the logical thing of building 5 batteries that combined will yield 400 amps. Each battery only needs to do 1/5th of the work and therefore each battery will only need to yield 80 amps.
80 amps is our magical number and those pretty Ni strips we have linking the cells together can only flow 5 amps.
These 4 cells here at the end can become quite the problem! 4 cells can theoretically flow out 4/10ths of the power from the battery. That’s 32 amps that will come rushing out of those cells at full speed from the motor. If we simply connected the cells together with those strips of Ni, power would flow through the area and it would look like everything is fine.
Then when we give the engine a good bit of throttle to move us in a hurry, our battery would break! The little Ni strip that connects those last 4 cells to the rest of the battery can only flow 5 amps. When you start pushing 32 amps through it, that Ni strip will heat up and magically transform itself from a conductor into a fuse. When it gets hot enough, hopefully it will melt and sever the connection. If it remains connected and heated, it can cause the Li cells it is running over to ignite into a flame which will burn with all the fury of Hell, even submerged underwater!
The solution is very simple: Build a bridge.
The last cell will flow out the least amount of power, but the cell leading to it will flow the amount of power that it needs plus the amount of power of the cell downstream from it. The next cell over will have the same conundrum.
By stacking the Ni strips, the amp capacity of the connections increases by 5 amps at each stack. This stacking is called a “bridge” as it bridges a pass that would otherwise serve as an electrical bottleneck. This bridge stacks up to look like the silhouette of an arch bridge which will then flow the power across the gap.
It is important to remember that the bridge needs to extend out the other side in the same manner, otherwise the bottleneck simply gets transferred.
If you notice, I didn’t build the bridge up to 35 amps, but instead stopped at 20. This is because the 80 amps that will flow out of the side of the battery are being directed out through the strips that run off to the sides.
Since we need to flow 80 amps and each strip carries 5 amps, we would need 16 strips to be safe. By doubling the strips, we create a flow of 10 amps out certain cells while single strips only flow 5 amps. This area beyond the bridge only has single strips, meaning that only 20 amps will leave the battery in this area and therefore 20 amps needs to flow by the bridge.
When you build your battery, trace out how the electrons will flow along and trace out their path from the positive pole to the negative pole. If you find an area where a bottleneck exists, simply add more strips to increase the ampacity of that portion. When you build a bridge, also look at the areas that feed the bridge and extend the additional strips into those areas as well to account for the added flow of electrons in these narrow areas.
How do you connect a BMS?
You are saving money by building your own Lithium battery bank, excellent! We built a massive 19.2kW` battery bank for $5,000 which would have cost us $18,000 if we bought Battle Born Batteries!
Battle Born Batteries, the gold standard for marine lithium batteries cost around $950 for a 12 volt 100 amp hour battery. This battery will provide 1,200 Watts of power to your application at a price tag of $950, or $1.26 per Watt.
The battery bank we built consists of five 48 volt 96 amp hour batteries, providing us a grand total of 23,040 Watts of power. Each battery contains 4,608 Watts and cost approximately $1000 to make, but contains 4x the power of a Battle Born; and for roughly the same price!
A 48v battery is created by linking 4 12v batteries in series, meaning that each 100ah 48v Battle Born setup would cost a grand total of $3,800!
Needless to say, it’s significantly cheaper to build your own battery than to buy one that is ready made.
Wonderful! You assemble all the cells and the battery is done being built. Then you open up the BMS (Battery Management System) and pull it out of the package. Suddenly the easy assembly turns into a spider web of wires that need to go somewhere and if you get it wrong the BMS will fry! What do you do?!
It’s not really that complicated. The BMS has a lead that runs to each positive cell of the battery and an extra wire (the black one) that leads to the Negative terminal of the battery.
Ok, but what if you are building a high voltage battery with a ton of leads, now you have two black wires! Which one is the negative wire?
Easy, all BMS start with the large plug that has a bunch of wires where the black one on the far left is the Negative and the red one on the right is the positive, unless the BMS needs a supplemental plug to fit all the battery balancing leads, in which case, the smaller plug will be the supplemental and therefore the black wire will be a regular lead instead of the negative.
The Negative wire I have been referring to is called the “Most Negative” wire. The last positive balance lead, which is red on the opposite side of the plugs is called the “Most Positive” wire. With that knowledge alone, you can look at any BMS with any plug configuration and sort out which wire is the most negative, and by default, which wire is the most positive.
The concept is simple: The black wire attaches to the Most Negative terminal, and each wire that follows in sequential order attaches to the next positive cell.
See the Black Wire on the far left of the battery? That is the negative terminal of the battery and the black wire connects to that point. The next wire in the BMS balance lead is a white wire which connects to the same cell groups positive side, which is the other side of that same row of cells. This is the only part of the battery where you will have BMS leads going to both the negative and positive points of the same cell. All the other leads will connect to the positive points of the cell groups.
The next wire on the plug, moving left to right will connect to the next positive point of the battery from left to right.
The reason behind this is simple, the BMS needs to know the voltage of each cell group. To do this, the BMS needs to read the voltage of each cell group, but it uses the most negative as the Negative point in the circuit. If you get the order of the positive wires wrong, you will make the BMS think that one of the cell groups is incredibly high in voltage, as the voltage should increase by 3.xx volts per cell group as they add up in series.
Assuming that each cell is charged to 3.5v, the first positive lead connected to the first row of cells will tell the BMS that their voltage is 3.5, the second will tell the BMS 7.0v and the BMS will calculate that it is 3.5v. If you accidentally connected the second wire to the 3rd group of cells, you would tell the BMS that the “second” group is reading 10.5v, and the BMS would calculate the voltage to be 10.5-3.5= 7.0v in the second string. The BMS shuts down the battery pack if the voltages exceed the safe parameters, which are normally set to have a voltage minimum of 2.5v and a voltage maximum of 3.6v. If you tell the BMS that one of the cells is at 7.0v, it will shut down the whole pack and sadly it might also fry the BMS! Be very careful while you are connecting the balance leads that way the wires don’t get crossed and you don’t fry this expensive piece of equipment.
Once the balance leads are all connected, its just a matter of tiding up the wires so that this spider web of wire can be tamed by the power of zip ties!
After all the leads are tamed, I like to wrap the whole area over with 2 inch wide Kapton tape which holds them all close to the pack and reduces the risk of the wires getting hooked up on something and pulled free.
While the balance leads are the main concern for people who are thinking about building their lithium battery and worry about the BMS, there is one additional component that needs to be connected. The BMS monitors and controls the battery pack by checking its voltage, but it also will shut the pack down if it begins to over heat! Thermal runaway is a huge concern for boaters who are contemplating converting their batteries to Lithium.
The prospect of fitting a huge fire hazard that will continue to burn even underwater is a tough pill to swallow! The BMS has a temperature probe which must be attached (with Kapton tape) to the side of a cell. The BMS will also monitor the temperature of the cell it is attached to and if that cell begins to heat up, it will shut the pack down long before the battery can ignite into an inextinguishable flame.
I like the BMS from Overkill Solar, as it allows you to log into the BMS through a BlueTooth module and set the parameters of the battery manually. I have mine set very conservatively!
Before any parameters get too far out of whack, the BMS shuts down the battery pack and prevents it from getting into dangerous levels.
The BMS also works to balance out the cells in the pack so that if one of the cells is significantly higher voltage, it will balance the voltages and bring it down to safe levels while so that the rest of the cells can continue to charge as a whole.
We have used this BMS for a few months now and motored on the ICW with it powering our electric motor without issue. The solar panels charge up the batteries and this cuts them off when they get full as well as cuts the packs offline when they run empty during long motoring adventures up the ICW.
The best part so far about the lithium batteries for electric propulsion is the fact that you will have full power all the way down to 0% charge when the BMS takes the pack offline. With AGM batteries, the voltage gets low as the charge runs out and the motor just doesn’t have the same oomph that it had when the batteries were fully charged. These lithium batteries let you have full thrust at any state of charge, all the way from 100% down to 0%. The only problem with this wonderful feature is you have to keep an eye on the battery charge level, as you will be motoring along for hours and think everything is fine because the boat isn’t slowing down until the motor just cuts off because the BMS had to disconnect the pack due to one of the cells running out of power. It really is awesome!
If you are contemplating Lithium batteries and considering making them yourself, the BMS shouldn’t be a huge concern. It is just a box with a bunch of wires that need to be connected in a specific order. We managed to make our own batteries in two weeks inside our salon with very simple tools. This saved us thousands of dollars and has afforded us the ability to motor farther and faster on our electric motor.
