What size LiFEPO4 bank

[Mike_Thor]

As an aside I re-read the original post and I could not detect where jbinbi indicated they were fla (and still assuming this is 'flooded' cells). Simply stated an Amp Hour amount.

My simple understanding is that with 420 AH (AGM assumed) you have 420*0.4=168 AH of usable energy before starting to impact life of the battery. In order to get 168 AH in LI you would need around 336 AH.

But this is NOT the actual position. See above for all the ramifications and associated changes either needed or probably required or really should have if you go down this route. A simple change of technology is definitely only the very beginning of the discussion.

[Mike_Thor]

jbinbi,

For clarification 'marina hopping' actually means (in this context) connecting to shore power for the night. i.e. day sailing with all its associated power needs and then onto the marina and connecting shore power (in AU that is 240 VAC with around 16A max per outlet for a single phase).

Then off in daylight to again tie up and connect to shore power the following night.

[Mike_Thor]

Running an engine to generate electrical power. Caution - BIG caution.

Please do some research into longevity of engine components (e.g. exhaust mixing elbows, etc) if you regularly run a propulsion engine at low RPM for long periods simply to charge your batteries.

I know lots and lots of people do it - particularly mono hulls where space may be more restricted and getting a built in generator simply not acceptable however......

Externally regulated high power alternators also come with their own trials and tribulations not the least are the belt (pulley) requirements as flat battery implications and not the least that the 'charging profile' for LIPO is more critical than LA and must be followed. Not sure if you 'alternator' can achieve this. For your Lagoon better to have the 'generator' option installed and then a good AC battery charger with all the profiles and safety features built in and for a whole bunch of other reasons.

[john61ct]

Originally Posted by Mike_Thor

We have recently converted to Lithium or LiFePO4 (or LFP, LIPO, LP etc)

…

Some debates above but I refer to, and thoroughly recommend, using the manufacturers specs. In the case of LIPO
…

Our new LiPO technology allows for 100% down
…
(yes you will get to all of these things if you go LIoPO)

LiPo batteries have nothing at all to do with LFP/LiFePo4

Lithium LI lithium-ion is a general category, umbrella term for many dozens of widely differing chemistries.

Only LFP is being discussed here, nearly all the others are too dangerous to use on a boat.

LP is not a thing, aside from the cooking / fuel gas.

Misusing basic terminology confuses noobs and casts doubt on the credibility of all your other statements.


And yes, FLA means flooded, open cells where you can top up lost water, as opposed to the other two lead types, AGM or GEL chemistry.

[Delfin]

Originally Posted by Mike_Thor

We have recently converted to Lithium or LiFePO4 (or LFP, LIPO, LP etc). In any case the 'challenge' we have in trying to size our new house bank was more difficult than anticipated.

To set the baseline I am an electrical engineer so kidded myself that I was on top of it all.

Lets start with some boundaries. Regardless of the actual total capacity when moving from Lead Acid technology (in any form) to LiFePO4 technology (for example) you need to assess what you are moving from in terms of USABLE capacity to new USABLE capacity.

Some debates above but I refer to, and thoroughly recommend, using the manufacturers specs. In the case of LIPO as I read it from my supplier (read packaging/battery designer not cell manufacturer) and the one who under writes the warranty by the way. In my case with VICTRON Energy as I increased the Depth of Discharge (DoD) from 10%, 20% to say 60% I also increased the life cycles (i.e. life of the battery). This is one of the 'real bonuses' with LI technology as compared to Lead Acid (LA) technology which shortens as you increase and should not go beyond the nominal 40% DoD.

In other words with LA I used 60% DoD as the maximum usage drop (for normal not emergency conditions) and am using with LIPO, after consultation with tech support, a continuous partial charge/discharge cycle from 98% down to 50% (sometimes 45%).

Importantly to understand that in order to 'protect' my battery bank and to somewhat extend the life of the battery (more accurately not to significantly shorten it) I also needed to understand my usage profile and the time-of-day that I used it.

A hidden gotcha is also mentioned above - whatever you think you are using now will NOT be what you use in the future simply as stated above - you will find it so more convenient and effective (usage/effective/efficiency etc etc) that you will use more of it (or at least the crew and wife will even if you are doggedly stating that you won't).

So with our original 900 AH 12 V Lead Acid (happened to be AGM format) I was able to 'reliably' (with all caveats above) use 40% of this meaning 900*0.4=360 AH of usable energy (or power depending on how and when you measure it - lets leave that thorny issue alone).

Our new LiPO technology allows for 100% down to say 45% = 55% = 360/0.55 = 654 AH for the same available (usable) capacity. I also took the opportunity to change from 12 VDC to 24 VDC for better conversion efficiency and power density. It also made my existing wiring less lossy.

Let me also say that (for nominal 24 V system) LiPO provides 28.4-26.3 VDC not 24 so there is more power available.

Noting that all this is a 'system' issue and by moving technology you are also jumping into a big pool of related requirements. Generation and consumption generally but you should 'match' all these elements.

Having large storage capacity is like having AMEX with a million dollar limit; sooner rather than later you will have to pay it back and you will (can) push a lot of energy into LIPO but you will need both the generator AND associated charger to achieve this (efficiently).

Solar is great for our LA AGM bank but only OK to 'top up' or keep the time down for LIPO; when you actually change to LI and start to become an 'energy hog' (we all do) then this simply does not cut the cake. Wind is even further behind.

Whilst I initially tried to justify in engineering or technical terms I was simply way off in respect of cost effectiveness. But it certainly has made life simpler and more enjoyable to all who work the galley and instruments (for night sailing etc).

We ended up with a new 4.5 KVa generator (Northern Lights) and new 24/5000/120 A Victron combination inverter charger which was coupled to the remainder of the new Victron battery bank bluetooth (400AH/24V), monitoring system, controllers, new fast MPPT (blue tooth etc) and VenusGX monitoring and remote reporting. Full load monitoring and dump relays, fully sized new wiring complete with full documentation, labelling and all AUST 240 VAC electrically compliant.

Wouldn't look back but in hindsight it was a huge investment that cannot in any way be justified as cost-effective. It is purely in the realms of lifestyle. So in summary, once you have made the decision to move to LP then you will use more and you then need to revisit all your consumers and understand what the impact will be down the whole chain.

As an aside I somewhat disagree with some of the comments above about using items at 'full rating' or otherwise. I use our generator, or try to, use at its full continuous rating (i.e. 4.5 KVA). Running it at any loss is both inefficient in terms of diesel consumption but also not good for the diesel engine itself. Again I use the charger at it full continuous rating (in our case 100 A at 26.3-28.4 VDC. The charger is all automatic and shuts down the charge rating automatically when at the charge ceiling. furthermore i run my lights on full (i.e. they are on - not 'half on'); same with my electrical jug (on not sort of on); microwave (full power); coffee maker (on); Fridge, Freezer etc. They are ON.

I believe that a steady heavy load is far better than any 'cycling' or partial load. I am not talking about 'maxing out' a device but looking for its rated (design) continuous and using it.

Be aware that microwave and thermal induction cookers use a 'on-off' cycle at 'full' rating to achieve their nominated 'average' power setting so you need extra capacity in your inverter to cater for this (yes you will get to all of these things if you go LIPO).

Have fun....

Good summary....

The only things I would add is that after using our LFP bank cruising for a couple of years, I realized that rather than sizing the bank to 50% of the AGM bank it replaced, I could have reduced that further to 33 - 40%. Since we re-charge with a genset, it makes no difference if, after taking out 300 Ah per day, we run the genset for an hour once a day or two hours every other day. Same run time. I would also point out that in many use cases little change needs to be made to charging equipment, wiring or controllers. At least that was the case with us. Finally, an additional factor in cost analysis for us was reduced wear and tear, fuel consumption and maintenance costs for the genset since it runs about 30% of the time it would take to fully charge a LA bank.

So for us, the cost of replacing 1250 Ah of AGM with 600 Ah of LFP (which could have been 400 Ah) was not that much different, and with LFP being more economical if cycle life is taken into account. But cost alone does not reflect the desirability of not having to run the genset nearly as much, stable and robust voltage with virtually no sag, and much longer life. I would never go back.

[newhaul]

Originally Posted by Mike_Thor

Running an engine to generate electrical power. Caution - BIG caution.

Please do some research into longevity of engine components (e.g. exhaust mixing elbows, etc) if you regularly run a propulsion engine at low RPM for long periods simply to charge your batteries.

I know lots and lots of people do it - particularly mono hulls where space may be more restricted and getting a built in generator simply not acceptable however......

Externally regulated high power alternators also come with their own trials and tribulations not the least are the belt (pulley) requirements as flat battery implications and not the least that the 'charging profile' for LIPO is more critical than LA and must be followed. Not sure if you 'alternator' can achieve this. For your Lagoon better to have the 'generator' option installed and then a good AC battery charger with all the profiles and safety features built in and for a whole bunch of other reasons.

the issue you think there is wrt diesel engines has been discussed and debunked many times . If you have new evidence to provide please post the links .

As to battery chemistry abbreviations please be specific . Lipo is not correct it is generic covering about 10 chemistry markups that are not acceptable on boats as well as the 2 that are . For future reference please state Lfp if you are referring to lifepo4 or lifeypo4 .

The alternator charge issue has been well covered earlier in the thread .

[john61ct]

Lithium Ion, LI, is the umbrella term.

LiPo or "Li-poly" or "lithium polymer" is no indicator of specific **chemistry** either, just means the use of a gelled polymer electrolyte and flexible pouch enclosure to save weight for "RC hobby" usage, or sometimes ebikes.

Often LCO lithium cobalt oxide, LiCoO2*(LiCo), but other high power density chemistries now used, all very fire-risky.

IOW the term LiPo has no place in discussion of power on boats.

[Namoian]

We upgraded our battery bank to lithium in 2011.

The old bank, consisting of four Trojan six-volt golf car batteries were replaced with four 160 AH LiFePO batteries. The Trojans provided 450AH and their lithium replacement 640 AH. We chose 640 AH as that number of batteries fitted the battery box perfectly.

The theoretical differential increase in capacity is nearly 3X due to larger capacity as well as the increased discharge levels and charge acceptance rates. We have never probed the discharge envelope and always maintained a minimum 50% state of charge.

So far, at nearly ten years of usage, no problems (knocking on wood). The LiFePO stay cool when being charged by either 200 amp alternator (derated to 160) or solar or Mastervolt charger. Do not miss the corrosion potential and low relative capacity of the old lead acid batteries.

[john61ct]

Originally Posted by ablefollower

If you live extensively on it, you would install as much LFP as you could fit.

Same goes with PV - as much as you can fit on the rack.

For PV, windage and aesthetics are limiting factors.

For LFP capacity, would be silly to buy more than you need.

Unlike lead, adding to the bank later is NBD long as you've been caring for it properly.

And the high CAR can greatly reduce the PV panelage required, especially if ICE source is also available.

With a big enough alt or genset, just an hour couple times a week can be plenty, gives you more options, no PV needed at all if you want to keep the boat clean.

[newhaul]

Originally Posted by ablefollower

Depends how you use your boat.

If you live extensively on it, you would install as much LFP as you could fit.
Same goes with PV - as much as you can fit on the rack.

That is not actuakly correct. You need to ballance your needs aginst your charging ability. You need to be able to replace each wh that is removed from the bank . The more solar the more bank you can support. If you are using ice for primary charging its not as important .

[newhaul]

Originally Posted by ablefollower

For LiFePo4 chemistry, explain why this is paramount. Within the allowable cell voltages, why must every WH be religiously replaced ASAP?

Never said it needs to be replaced immediately or religiously.
The fact is you do need to replace what you use. Otherwise eventually you have a dead bank. You shouldnt make suppositions as to what is posted .

Btw i am running currently 100ah lfp with 200 watts solar to recharge.

[mark0978]

Originally Posted by john61ct

If trying to get by on mostly solar, I'd build in 3+ days of storage.

You get into weather patterns where the solar doesn't make much for a week, or everyday during peak charging hours you get clouds (Ocho Rios, Jamaica for example). Only having one days worth of charge is not what you want.

[newhaul]

Originally Posted by ablefollower

You haven't said anything at all then. Even a five year old knows he needs more ice cream when the bowl is empty.

Just as a frame of reference would you be willing to post your system perameters include battery bms and charging sources.

[john61ct]

Originally Posted by ablefollower

You haven't said anything at all then. Even a five year old knows he needs more ice cream when the bowl is empty.

Plenty of noobs focus on bank size, ratio to panels etc

rather than the basic principle, your average daily input must exceed your output

a larger bank just gives a wider time-shifting buffer.

You are correct the fact that LFP never needs to get to a high SoC does give greater flexibility.

But just saying "fit as much as possible" is indeed bad advice, and that was our main point.

[newhaul]

Originally Posted by mark0978

You get into weather patterns where the solar doesn't make much for a week, or everyday during peak charging hours you get clouds (Ocho Rios, Jamaica for example). Only having one days worth of charge is not what you want.

hence the alternator on the ice .
Or in my case the little 1,000 watt generator. That I have not needed in several years .