Tuesday, February 2, 2016

Lithium Batteries

Our old AGM 4D batteries started dying this summer (August 2015). They symptom is that they would overheat. The Victron inverter system has a temperature sensor and it warned us of the pending disaster in time to disconnect the dying cell from the battery bank. After some investigation, we determined that a Lithium battery bank would be about 1/3 the weight of the AGM battery bank and that it would provide more usable capacity and last longer. AGMs are good for 100%-50% state of charge while LiFePO4 is good for 100%-20% state of charge. The AGMs can handle about 500 cycles while the LiFePO4 cells are supposedly good for 3000 cycles. So, while the Lithium bank is more (less than 3X the cost of Lifeline AGMs), they last much longer and provide more power while doing it with a lighter weight bank.
We checked out different types of Lithium batteries and selected LiFePO4 cells, which are much safer than so-called Lithium-Ion cells that you hear about with airplane and hoverboard fires. We acquired twelve 180AH Lithium cells from CALB, viaTroy Bethel, who was doing an order for several battery banks. He also did the initial top balancing and bottom balancing as well as the aluminum plates to hold the batteries. The cells are connected in a 3P4S arrangement, which means that three cells are paralleled to create a "super-cell". Do this four times to create four super-cells, then connect them in series using 2/0 cables that are the same length so that the wire resistance is the same. Our resulting battery bank is 3*180AH = 540AH at 12.8-13.2v. Most people report their LiFePO4 batteries running very flat voltages around 13.2v over a wide range of discharge capacities. These batteries can source a lot of current, around 10X their AH capacity (540AH * 10 = 5400A). But when consumed at a lower amperage, they can run a long time. LiFePO4 batteries can also be discharged to 20% of their capacity. Our system charges them to 14.2v (the CALB cells have a max voltage of 3.65v per cell, or 14.6v for the assembled house bank). We could have gotten by with a 400AH bank, but decided that having the extra capacity was worth the additional expense. We will have over 400AH of usable capacity. So we won't need to recharge every day if we don't want to. Speaking of charging, these batteries will take all the current we can generate, which means that we need to watch our alternators to make sure they don't overheat. So far the batteries have been down only about 130-140AH and one of our alternators will bring that back up over the course of a day's motoring (which we did yesterday to cover a lot of miles quickly). We would normally use the genset and Victron charger for significant charging at anchor.

Here's a photo comparison of the batteries.
Lithium Batteries vs Lead Acid 4D batteries
Wrap the wrench in tape to prevent accidental shorts
We had bought an inexpensive 12v 4D flooded lead acid battery to replace the dead AGM. But on our trip to Georgia, another AGM died, so we were down to 2 batteries. The Lithiums hadn't been installed yet. The last AGM died on the winter trip from Georgia to Florida, so we were down to the one flooded wet cell battery. That's when the Lithiums were finished and we were able to pick them up in central Flordia and get them to LUX at Titusville, FL.
It took over half the day to install them. They fit into the old slots where the AGM 4D batteries were installed. The Titusville marina took the old AGM cells. Here's what they look like installed. When working with Lithiums, we have to be careful - tools will vaporize if they bridge a battery's terminals. We used a box-end wrench wrapped in tape. We also placed some plastic sheets over the terminals while we worked on the connections. The photo below show plexiglass covers over the terminals.
LIthium Batteries Installed
HousePower BMS with Alarm
It is good to use a Battery Monitoring System (BMS) to monitor the individual cells to make sure they aren't out of balance. A couple of days later, we had an opportunity to mount it and get everything connected the way it should be.
Everything is now installed and working. It is nice to not worry too much about energy consumption while anchored out. Last night we left all the instruments on, some additional lights, and the VHF on while anchored on the Great Bahamas Bank. We wanted to be visible, monitor AIS, and to hear anyone hailing us on VHF. With everything running, we used 135AH, which one engine's alternator replaced when we were motor sailing today.

This morning (Feb 3), we used 145AH since we anchored last night and the battery voltage is 13.2v. We'll use about twice that for 24 hours. We plan on using the genset and Victron 150A charger to charge them later today.

We like our new batteries!


Gregg Billman said...

Terry. Is Troy Bethel located in the central Florida area?? Is he part of Bethel Marine in Melbourne?

Btw...we've been looking at upgrading to lithium, too. Would love to be able to run our air con without having to crank the genset at anchor (I installed a 4kw inverter for that eventual purpose).

Terry said...

No, Troy is in South Africa working on a boat build. We were fortunate to have caught him at a good time when he was building his own set of batteries and piggy-backed on it. I recommend going to one of the commercial companies (Victron, Genasun, Mastervolt, Relion) if you don't have the background to do the electrical engineering that's required. It's more expensive than building your own, but you get a supported product. Just Catamarans in Ft. Lauderdale is experienced in the installations.