The Dream - LiFePo4
We have lived aboard our yacht full-time for a few years now, and this is our third power storage system.
With a good understanding of our needs and desires, we were now coming to the point of being prepared to upgrade our battery system to LiFePo4, something that had been on our wishing list from the very early stages of ownership.
Back in 2017 when we moved onboard we felt this option was still too expensive, and we needed to get real-life experience living aboard to confirm or correct our power audit calculations.
From our perspective, before getting this high-performance battery system we needed to get a high-performance solar set-up that could power it.
Three years have passed since we upgraded our solar panels from flexible to rigid and we are quite satisfied with their performance.
From 2017 when we moved on board until mid-2022 when we returned to Lisbon, where our adventure had started we had been educating ourselves in 12v electrical systems and battery setups. We had been working together with a marine electrician specialising in LiFePo4 systems using Victron Energy hardware, and we felt we finally had a schematic design that was robust yet simple and should suit our needs. We were ready to proceed with this big upgrade.
The first step was to decide which batteries specifically we were going to use, with inbuilt BMS (battery management system) or with an external BMS.
Batteries with in-built BMS usually have lower maximum charge and discharge rates than the ones with external BMS, considering the loads we need and generate that could be an important factor to cause stress in the system. The other point is that most batteries with in-built BMS communicate via Bluetooth only and have limited options regarding integration with other requirements like alarms (the more recent ABYC (American Boat and Yacht Council) chapter on lithium batteries indicates that a sound alarm should be incorporated into a lithium system). We decided to go for the externally regulated batteries for the two reasons above.
With our space constraints, we decided on 3 Victron Energy Smart Lithium 12v/200Ah LiFePo4 batteries. A total of 600Ah capacity would give us up to 480Ah of usable power (allowing only 80% discharge) of usable capacity with a total weight of 60kg (our batteries model are 20kg each).
This is a huge improvement from the standard 40% usable capacity of traditional batteries and close to 50kg per 200Ah battery. To have a 480Ah usable bank on a standard battery bank we would need to install close to 1200Ah, and that would mean around 300kg of weight aboard or a bit more!
The new system was designed to incorporate the Victron Energy equipment we already had, with a few new equipment components to be added.
It was more about beefing up the connections, aiming for a higher standard of installation and safeguarding our system, with each battery and load individually fused neatly and easily. Previously we had used busbars and individual fuse holders resulting in a system full of connections and cables, slightly challenging to perceive with the naked eye.
With the new batteries being much smaller we recovered enough space in the battery box allowing us to use the Lynx distributor busbars that allow each positive terminal to be directly fused at the bar while at the same time keeping the corresponding negative terminal organised in the same slot but at a lower level.
Although the Lynx do take a much bigger footprint compared to normal busbars in the end it creates a much neater installation and a reduction of total cable lengths in some of the equipment.
Another thing the Lynx facilitated was that it was possible to install a master switch that allow us to isolate the batteries from the remaining system turning it all off except the bilge pumps. Something we had long desired, was to make life easier and safer when it came to the maintenance checkups for bolt tightening or installation of new or additional equipment.
We also took the opportunity to have new cables made to size with a 95sqm section for the connection between the batteries and the Lynx, ensuring reduced voltage drops.
The shore and solar power charges were already taken care of by the already installed 3kw Multiplus charger/inverter and 150/100 MPPT, the only things to be done still were programming both items for the correct charging profile for lithium and to connect these devices to the main BMS to ensure the loads are connected and disconnected as needed.
Due to the specific charging profile of the LiFePo4, we now had an issue we never had before which was how to deal with the charge coming from the alternator. Traditional batteries have less resistance when discharged than when getting closer to being full so the alternator works with that resistance and self-regulates (putting it in a very simplistic way the closer to full they get the less charge they accept), the problem is LiFePo4 doesn’t have this resistance, it accepts all charge available until it abruptly stops accepting it. Two things can happen with these batteries and traditional alternators that are not somehow protected or prepared for this, one is that the alternator will run at full speed for prolonged periods potentially overheating and burning out or it runs at full speed and all of a sudden the batteries no longer accept charge current and the alternator overloads and shorts circuits. There are several ways of dealing with this, from new-generation alternators that are bigger and temperature regulated to charge control equipment.
The Dream has a 110A traditional alternator, and replacing it with a new one was not on the table, with the assistance of our Victron designer we decided to go for a reasonable, simple and cost-effective way instead of the most commonly used solution where one or multiple DC to DC chargers are used depending on how much power is needed to get from the alternator. We found this typical option more costly and take more space, we also read several comments regarding the heat generated by these DC-to-DC chargers.
For the alternator charges, we opted to use a Smart BMS CL 12-100 (this allows a direct connection to an alternator) instead. We wired it to be a slave BMS controlled by the VE.Bus BMS (the main BMS in our system) and this way we can control the charge limit more freely by installing the appropriate fuse for our desired allowed power draw for the charging batteries and adjusting settings accordingly without having to buy more units or having to deal with radiant heat. This device will digitally allow 80% of the installed fuse capacity installed, ie. an 80amp fuse and setting will allow the device to demand up to 60A from the alternator which is 50% of the alternator output capacity and a safe load on it that won’t cause any damage even with prolonged use.
As for the starter battery, we kept our original Victron AGM Super Cycle 165Ah just like we had for the last 5 years. The starter battery is charged directly from the alternator through the original Cristec battery splitter and trickle-charged from the Multiplus charger/inverter.
Besides figuring out how to efficiently and safely deal with the alternator charges the other concern was dealing with the 12v house loads.
In this case, the concern was which device suited us best to control the loads considering we have an electric windlass (fused at 150A), an electric winch (fused at 100A), all house fridges and freezers, all lights and navigation equipment on one 12v circuit. The concern was that although the windlass and electric winch are never used at the same time any of these two high-power devices paired with the other 12v loads all at the same time could trigger the load's controller.
The two options on the table, the Cyrix-Li-Load 230A or the Smart Battery Protect 220A, seemed to be capable of doing the job perfectly the difference in capacity between the two seemed so small, but we learned (through our Victron adviser) that occasionally the Smart Battery Protect 220A would turn off due to the start peak power draw of pieces of equipment like windlass while the Cyrix-Li-Load seemed to be more tolerant to that very short peak. For this reason, we chose the Cyrix-Li-Load.
With all the components decided, purchased and delivered all that was missing was to proceed with the installation, programming and testing. The fact The Dream was on the hard for some unrelated work add life easier as there was no pressure getting things done fast we could take our time.
Changing to LiFePo4 was indeed a big upgrade to our lifestyle and allowed us to upgrade a few other things that had been on our mind like removing the LPG cooktop and installing an induction stove and convection oven. And install a new freezer.
All these upgrades change the overall power consumption, but that is something we will discuss in another post.
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