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A while back I posted that I was considering adding LiFePO4 batteries to my boat. At the time, I was afraid of going down a rabbit hole making this change. The research turned out to be not so bad, but I'm planning a very simple system.
My current setup is 2 large lead acid deep cycle, Trojan T1275, which are a nominal 120 amp hours each. Realistically, this gives my about half that in usable energy. These function as my start and house batteries, with each on a 1-2-B-O switch. I know, deep cycles aren't good start batteries, but the A4 is so easy to start that I do it anyway.
My electricity needs are simple. I have no refrigeration. My power users are instruments, chartplotter, AIS, VHF, running and cabin lights (all LED), and autopilot (below deck linear drive- my largest single user, at about 3 amps/hr average) for a total which I round up to 5 amps/hr.for planning purposes. No real big surge users like thruster, electric winches, windlass, etc.
My dislike of the current system came about 10 years ago when I started doing long distance singlehanded racing. The races are about 300 miles. I can do about 24 hours on my current batteries, then the annoyance begins. I have to run the engine to charge about every 4-6 hours for 1-1.5 hours and my batteries never get to a healthy state of charge, with diminishing returns at each charge. The races typically last 60-72 hours, so battery maintenance becomes a real drag. And of course, running deep cycle batteries down so low and never getting them charged fully kills their longevity. I may get 3 good years out of a battery that is now over $300.
Other charging sources- solar, wind, etc, are not an option on my small boat (C&C30-1), and certainly not while racing.
I did my research on what to buy and how to wire the system. I got a fantastic deal on 3 Kilovault 100 amp hr batteries at $250 each. I suspect it was a pricing error, but they shipped the batteries without comment. Just after I bought them the price promptly doubled. These are reputed to be a really high quality, best buy battery.
A no brainer at that price, as they're usually 500-600 each. Im not going to worry about charging the Li batteries from the alternator. I'll get rid of one of the lead acid batteries and wire the 3 Lithiums in parallel to the empty battery switch position, or alternatively, which I think I like better, to another 1-2 switch interrupting the feed to the house panel. That separates the alternator/ starter cable from the Lithiums altogether and I think makes the system more foolproof (after the 2nd day of these races I need all the mental help I can get).
Ability to charge from the alternator would require a DC-DC charger and more complex wiring, and I may want to do this some day but it's not necessary now for my purposes. I am installing a Victron 30 amp charger for shore power charging. I should have 300 amp hours from the Lithiums and a backup of 50-60 amp hours from my remaining deep cycle lead battery, which I can charge from the alternator if I need to. This should be more than enough power to last the race without recharging. And even if I run them down to 100% discharge the life of the batteries should be much, much longer than lead acid (estimate 2000 cycles of 100% discharge). All this and I'm losing weight. The 3 lithiums weigh a total of 75 pounds, as opposed to about 100 pounds per each lead battery.
I'll be using large cables both for safety and to reduce voltage drop. Probably 8 gauge from the charger with 2-3 foot run, and 6 gauge to the panel feed for max of 12 feet of run. Fusing at 40 amps from the charger, and 30 amps to the panel. Battery interconnects of 2-0 with battery terminal fusing at 150-200 amps on each battery.
I'm not an electrician, but this plan seems reasonable to me. If anyone has any suggestions or comments, let me know.
My current setup is 2 large lead acid deep cycle, Trojan T1275, which are a nominal 120 amp hours each. Realistically, this gives my about half that in usable energy. These function as my start and house batteries, with each on a 1-2-B-O switch. I know, deep cycles aren't good start batteries, but the A4 is so easy to start that I do it anyway.
My electricity needs are simple. I have no refrigeration. My power users are instruments, chartplotter, AIS, VHF, running and cabin lights (all LED), and autopilot (below deck linear drive- my largest single user, at about 3 amps/hr average) for a total which I round up to 5 amps/hr.for planning purposes. No real big surge users like thruster, electric winches, windlass, etc.
My dislike of the current system came about 10 years ago when I started doing long distance singlehanded racing. The races are about 300 miles. I can do about 24 hours on my current batteries, then the annoyance begins. I have to run the engine to charge about every 4-6 hours for 1-1.5 hours and my batteries never get to a healthy state of charge, with diminishing returns at each charge. The races typically last 60-72 hours, so battery maintenance becomes a real drag. And of course, running deep cycle batteries down so low and never getting them charged fully kills their longevity. I may get 3 good years out of a battery that is now over $300.
Other charging sources- solar, wind, etc, are not an option on my small boat (C&C30-1), and certainly not while racing.
I did my research on what to buy and how to wire the system. I got a fantastic deal on 3 Kilovault 100 amp hr batteries at $250 each. I suspect it was a pricing error, but they shipped the batteries without comment. Just after I bought them the price promptly doubled. These are reputed to be a really high quality, best buy battery.
A no brainer at that price, as they're usually 500-600 each. Im not going to worry about charging the Li batteries from the alternator. I'll get rid of one of the lead acid batteries and wire the 3 Lithiums in parallel to the empty battery switch position, or alternatively, which I think I like better, to another 1-2 switch interrupting the feed to the house panel. That separates the alternator/ starter cable from the Lithiums altogether and I think makes the system more foolproof (after the 2nd day of these races I need all the mental help I can get).
Ability to charge from the alternator would require a DC-DC charger and more complex wiring, and I may want to do this some day but it's not necessary now for my purposes. I am installing a Victron 30 amp charger for shore power charging. I should have 300 amp hours from the Lithiums and a backup of 50-60 amp hours from my remaining deep cycle lead battery, which I can charge from the alternator if I need to. This should be more than enough power to last the race without recharging. And even if I run them down to 100% discharge the life of the batteries should be much, much longer than lead acid (estimate 2000 cycles of 100% discharge). All this and I'm losing weight. The 3 lithiums weigh a total of 75 pounds, as opposed to about 100 pounds per each lead battery.
I'll be using large cables both for safety and to reduce voltage drop. Probably 8 gauge from the charger with 2-3 foot run, and 6 gauge to the panel feed for max of 12 feet of run. Fusing at 40 amps from the charger, and 30 amps to the panel. Battery interconnects of 2-0 with battery terminal fusing at 150-200 amps on each battery.
I'm not an electrician, but this plan seems reasonable to me. If anyone has any suggestions or comments, let me know.
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