Lifepo4 setup

[bowring]

Hi, I am considering changing my house batteries to lifepo4 310ah 12v, which I’m told would give me 30% more capacity

the lifepo4 battery supplier is saying the below,

12.8v x 310ah x 80% dod = 3.1kw real can use output power capacity.

Your 572ah agm battery real can use capacity is 12v x 572ah x 30% dod = 2kw.

My current AGM battery supplier is wanting me to only use 20% depth of discharge cycles”[/I]

Currently I have
572 ah house AGM
Start battery (150ah AGM)
Solar charger x 2
Sterling 60 amp Charger
120 amp Alternator
Volonic Monitor
VSR

Do I need:
Dc to dc charger to replace the VSR so that the charging from the alternator can charge both start(AGM) and the lifepo4 at their correct voltage

What size and type of DC/DC Charger

Does the Shore power charger go only to the start (AGM) battery and the does the Dc to dc charge the lifepo4

Do I still need the voltonic battery monitor and disconnecting solenoid

[SOLAR SUPPORT]

If you're happy with the service life, I think stick with the AGM. Changes to be made in order to fully charge the Lifepo4 battery with the electrical installation installed on the boats and their safe operation are still being discussed. You have to invest much more money in Lithium-Lifepo4 than in AGM replacement. It is possible to use these batteries in boats, of course, but the promised service life has not been finalized yet. Voluntary experiences over time will show this.

[more]

Originally Posted by bowring

Currently I have

Start battery (150ah AGM)
Solar charger x 2
Sterling 60 amp Charger
120 amp Alternator
Volonic Monitor
VSR

Do I need:
Dc to dc charger to replace the VSR so that the charging from the alternator can charge both start(AGM) and the lifepo4 at their correct voltage

What size and type of DC/DC Charger

Does the Shore power charger go only to the start (AGM) battery and the does the Dc to dc charge the lifepo4

Do I still need the voltonic battery monitor and disconnecting solenoid

you have VP D2-55 you don't need start battery agm 150AH. for your VP manual say regular 70Ah starter battery
you don't need dc dc charger VSR is good

[MWGDVC]

Bowring,
I just installed a set up on our Pearson 385 very similar to what you are proposing for yours.
This is what I chose:
300AH LiFePo4 (12V) house bank
AGM start battery
640Wsolar charging house bank only
wind gen charging only house bank (boat had wind gen when I bought her, not sure I would install if not already there)
120A alternator, serpentine belt, with Balmar voltage regulator charging start battery
60A Renogy DC-DC charger to charge house bank
Xantrex Freedom 2500 inverter charger wired to house bank


The solar pretty quickly replenishes the house bank. We usually see 100% charge on house bank before 11:00 local time (36 degrees north latitude), running re-fridge 24/7, plus usual lights (all LED)
I have installed an on-off-on switch for the DC-DC charger, so I can choose when to use for additional house bank charging. This switch allows me to select 30 or 60 amp charge rates. At 60 amp house charge, the alternator is putting out 75Amps continuous until house bank is charged, this gets the alternator warmer than I like in summer, to I usually limit charge rate to 30A, requiring less than 40A continuous from alternator.
I have the DC-DC charger programmed for LiFePo4 profile, the Balmar voltage regulator is programmed for AGM charge profile.
I am still researching which shore power charger to replace the Xantrex Inverter charger.
It is an older unit with no LiFePo4 charging options, and the inverter is a modified sine wave unit.
I do plan to separate charger and inverter though.
The DC-DC charger effectively separates the start battery from the house bank.
My theory is this set up keeps a lead acid (AGM) battery in constant contact with the alternator, eliminating the possibility of a BMS shutdown causing a voltage spike/ current surge that may, or may not, damage alternator diodes.
For us, if we run the engine every few weeks, the start battery is quickly charged by the alternator. For longer term storage, I suppose one could attach a small automotive battery charger to maintain the start battery.
I don't regret, for one minute, the switch to LiFePo. They charge quickly, the voltage remains more constant (and higher than FLA) during most of their discharge. This means lights stay brighter, electronics are happier, electric motors run cooler and faster. (think fans and pumps).
Just do your research as the care and feeding of LiFePo is significantly different from FLA.


Sorry for the long winded reply.


Mike,
S/V Kismet.

[Captain Bill]

I just purchased a similar system for my boat to replace my AGM house bank that failed after 3.5 years. Despite what Solar Support says I was able to buy three 100 a/h batteries with built in BMSs plus a DC-DC charger for less money than replacing my two 210 a/h AGMs. The BMSs in these units are inexpensive and without low temperature cutoffs, but since I live in Florida if I ever get the batteries to 0c I'll have bigger problems than that. The 300 a/h LiFePO4 bank will give me about the same usable watt hours as my AGM bank. I plan to cycle them between 20 and 85% and hold them at about 50% when tied to the dock. I have 640 watts of solar so I will probably never actually get below 50% except in unusual circumstances. The dc-dc charger will only be used for carrying house/instrument loads on overnight motoring trips. I have a battery monitor and shunt to that I plan to keep in the system for monitoring the house bank. My shore power Inverter charger will be connected to the LiFePO4 bank and my alternators to the AGM bank.



It's interesting that your AGM supplier wants you to use only 20% depth of discharge. My supplier told me that insufficient discharge caused me to have reduced life from my AGMs. His explanation was that above 80% the internal resistance of the battery limits the amperage one is able to put in in bulk charging and that high charge rates are needed to "blow" the sulfation off of the plates. With my solar I replaced a lot of amp hours at a relatively low rate and by the time the solar was able to put out higher amperage I was already above 90% where the internal battery resistance really limited the rate of charge. He recommended occasionally discharging to 50% and hitting them with as many amps as I could produce from multiple sources. This was not a daily recommendation, but once every three to six months. I did not actually do this because it seemed contrary to other advice I had been given. But due to covid, and a mechanical issue, my house bank basically lasted only for 1 year of cruising and 2.5 years mostly at the dock doing no cycling at all. It would seem to me that people that say fully charged AGMs are happy to sit at float basically forever have never in fact done that. Maybe I should have listened to the guy.



I guess only time will tell if buying drop in LiFePO4s was a wise idea or not. Even if they only last as long as the last set of AGMs I will not be out any extra money.