What size AC charger for 650 AH of LiFe batteries

[Maine Sail]

The 0.2c rule is for FLA and does not pertain to FLP.

I can only speak for what I did on my boat. When charging from shore power, I wanted to be able to recharge the fully depleted battery to full charge in about 10-hours so that I could go into a marina near 0% SOC in the evening and leave the next morning with 100%. I have 560Ah and I installed two Victron IP22 30A charger which met my design goal.

When charging from the engine, I wanted the least run time I could manage. I installed a 250A large frame Denso Hairpin alternator on my 23-hp Universal M25XP which is controlled by the Zeus regulator. I limit the max output to 190A to stay withing the limits of other items in my charging system. With output limiting to control the alternator temperature, this lets me do a 0% to 100% in less than 4-hours.

Actually, 98%+ of LFP bats have a recommended charge rate of .2C. This is not because the cells cant handle it, it's because most al drop-ins except a select few have passive balancing 30-50mA and you will have cut off issues when trying to charge faster..

 

[Maine Sail]

A lot of good replies, thanks so much! Yes, I'm sure I will go all LIFe eventually. But there are some more urgent system fixes needed for this new-to-me 1985 cruiser, like a mass of wires and fuel lines broken loose from rusted fittings flopping around in big tangle in bilge water! (The last owner was good about 'keep the boat from rotting' things like replacing hatches and portals and keeping the deck sealed, but the engine room is very neglected!). This project is just that 4 of 7 100 Ah LA batteries needed replacing and I was not going to buy more LA batteries! So four 165 Ah LiFe batteries with bluetooth are replacing them with minimal changes to charging system this year. The individual battery 'blueteeth' give me accurate SOS, down to the cell--I would not buy a LiFe battery without bluetooth at this point just for that feature alone, i.e. is there a bad cell, are the cells equalized, etc!

Yes, I'm pretty sold on the Victron at this point as I do like to program things to be optimal. But I also like to just relax when actually sailing. Right now, rather than one big Victron charger I can reprogram for different situations, I'm thinking about two of the 25 Ah Smart Blue ip67 chargers; one on all the time when on shore power set to voltages that gives me about 75% SOC and a second on a switch, set to give me 100% state of charge I can turn on before a trip. That also gives me redundancy in case one fails.

But that is a good point about using solar and wind power ahead of dock power. I used to teach an IOT architecture course, so I could create a little IOT box that reads my outlook calendar to find the next sail, looks at the weather forcast to see how much sun and wind I would get and then turns on the dock power chargers the night before my trip. The home solar power DIY community has a Rasberry Pi open source kit to build stuff like that.....But I'm not doing anything like that until my fuel lines and wires in the engine room are all secure and safe! And the soundpooofing that is flopping around. And the ... (Ok, a remote on/off over the Internet would be simpler!

Right now I also don't trust the charge point setting on the two Rutland 1200 MPPT controllers, so I turn off the wind and solar charging when I'm not on the boat. Keeps the wind generators safer in storms too. But that can change with some effort.

Victron chargers are the only chargers to have a built in storage voltage. The storage voltage kicks in after float. So, 14.0-14.2V absorption, 13.5V float and 13.2V storage.

 

[Hayden Watson]

Victron chargers are the only chargers to have a built in storage voltage. The storage voltage kicks in after float. So, 14.0-14.2V absorption, 13.5V float and 13.2V storage.

That was one of my considerations when I got my new chargers. I ended up with two IP22 30A chargers. They are set up with the VE Smart Net and synchronize to each other and work as a single 60A charger. I love that they have the power to quickly recharge my 560Ah battery but still do a great job of transitioning down to minimal current to top off and then go to storage. When I get to the boat to load up before I go on a cruise, I turn off the power to the chargers and then when I turn them back on, the charge cycle restarts so they bulk and absorb to bring the batteries back to 100% jSOC before I leave the dock.

I also have mine set up so that it uses tail current for absorption rather than time. This works for my battery because it has a JK BMS and the active balancing means that the cells are always in perfect balance. If I had pasive balancing, I would go for a longer time absoption.

 

[colemj]

Why does having a separate storage voltage on a charger matter? I just charge ours to 13.8V, keep it there for 30min, then float at 13.2V. Gets the batteries 100% charged and then goes straight into what is being called a "storage voltage". At the end of 30min @13.8V, the charger current is down to <5A on a 1000Ah bank. Once or twice each year I bring them to 13.8V like normal, then increase the voltage to 14.6V and measure the additional current to get them there. It is alway <10Ah, and generally <5Ah, which is why I'm comfortable stating 13.8V for 30min is fully charging the battery.

13.2V keeps the batteries at ~95%, so I wouldn't call it a storage voltage. When we are leaving the batteries to sit for a long time on a charger (marina, etc), we drop the float voltage to 13.1V, which brings them down to 60% or so and keeps them there.

We have a battery constructed from individual cells, and not a drop in. The point about needing to sit at a higher voltage for a period of time to allow the balancers to work is correct for drop in batteries.

While I balance our cells once a year for good measure, they are never more than 50mV out at 14.6V before I turn the balancer on, even though they spend a lot of time sitting at partial states of charge, and see deep cycles regularly during the time between yearly balancing.

Mark