My doctor said I need Lithium

[msmith10]

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.

[Al Schober]

To start your A4, you need a Gp 24 lead acid battery. Getting one rated for starting should not be hard. Simple on/off switch.
Rest of stuff is house loads, separate battery bank. Separate on/off switch. I never found a reason to not use lead acid chemistry. Of course, deep cycle. Would be curious to know your reason for selecting some Li chemistry? Do not use batteries that you can't get up and out of the boat. I found Gp 31s to be too heavy for me to move around.
I found 2 of Gp 27 to be adequate for a house bank. No electric refrigeration.
Charging was from engine alternator. 60 amp unit went directly to the house bank. When the house bank came up to about 12.7 volts, a VSR closed and sent charge current to the start battery.
Mixed feeling about battery monitors. Had one for a few years, got leery of it.

[joe_db]

Originally Posted by Al Schober

To start your A4, you need a Gp 24 lead acid battery. Getting one rated for starting should not be hard. Simple on/off switch.
Rest of stuff is house loads, separate battery bank. Separate on/off switch. I never found a reason to not use lead acid chemistry. Of course, deep cycle. Would be curious to know your reason for selecting some Li chemistry? Do not use batteries that you can't get up and out of the boat. I found Gp 31s to be too heavy for me to move around.
I found 2 of Gp 27 to be adequate for a house bank. No electric refrigeration.
Charging was from engine alternator. 60 amp unit went directly to the house bank. When the house bank came up to about 12.7 volts, a VSR closed and sent charge current to the start battery.
Mixed feeling about battery monitors. Had one for a few years, got leery of it.

Most battery monitors eventually drift off from reality and need to be reset to full when the batteries actually are full every so often.

[msmith10]

Originally Posted by Al Schober

To start your A4, you need a Gp 24 lead acid battery. Getting one rated for starting should not be hard. Simple on/off switch.
Rest of stuff is house loads, separate battery bank. Separate on/off switch. I never found a reason to not use lead acid chemistry. Of course, deep cycle. Would be curious to know your reason for selecting some Li chemistry? Do not use batteries that you can't get up and out of the boat. I found Gp 31s to be too heavy for me to move around.
I found 2 of Gp 27 to be adequate for a house bank. No electric refrigeration.
Charging was from engine alternator. 60 amp unit went directly to the house bank. When the house bank came up to about 12.7 volts, a VSR closed and sent charge current to the start battery.
Mixed feeling about battery monitors. Had one for a few years, got leery of it.

I thought I explained my rationale for going to Lithium, but here are the bullet points (granted my case is a little unusual):
1. weight: I get 3 times the available energy for less than 1/2 the same weight
2. cost: break even out of the gate. At the end of 10 years, the estimated life of the lithiums, I will have spent about 1/3 as much. The price of lead batteries is going up, lithiums down.
3. convenience: I can meet all my energy needs without recharging the batteries, which was a real nuisance with my old setup. When I have to recharge, the charging cycle is much faster than with lead, and unlike lead, you can charge/stop charging at any point in the charge cycle without significant impact on battery life.
4. Lithiums maintain constant voltage until the end of their charge. Start at 12.8 volts and stay there for a full 300 amp hours.

Yes, you need a lead acid battery for starting and for charging lithiums thru an alternator, but other than that, the only lead I want on my boat is in the keel.