Practical Questions about LiFePo4 Power Systems

[Dockhead]

Originally Posted by john61ct

The comparability is the fact that one easy accidental "event" can instantly turn an expensive battery into scrap.

Much harder to do with a FLA bank.

Well, requiring certain controls and safeguards, which FLA don't need.


But I think everyone knows that. It's an obvious drawback of LiFePo.


But there's another, and that's the COST of a bank-killing mistake. Do it with lead acid, and I have (!), and it costs x. Do it with LiFePo, and it costs x times pick a number.



Lead acid batteries can also be killed, but we don't worry about it as much because the cost of doing so is quite a bit less.




Nevertheless it seems to me that a reasonable BMS system can reduce the risk of killing the LiFePo bank to quite acceptable levels. If they last so much longer, than it is entirely reasonable that you spend more time and money being sure not to kill them.

[john61ct]

I was simply pointing out the comparability - yes limited - between LFP and the other LI chemistries.

[travellerw]

Originally Posted by john61ct

The comparability is the fact that one easy accidental "event" can instantly turn an expensive battery into scrap.

Much harder to do with a FLA bank.

While I agree that its harder to do with FLA. I very much disagree that a single event will always turn LiFePO4 into scrap. We know multiple LiFePO4 users that have had complete discharge (like 1V/cell) events and the cells came back. One cruiser I know had that happend 4 years ago and his bank is still going strong.

I have spent 15 years flying hobby LiPO and have puffed my share of packs. I stand by my statement that comparing a hobby LiPO to prismatic LiFePO4 cells is as different as comparing LiFePO4 to FLA.

That is the problem with people here on Cruisers Forum. Much of the information here is just a rehash of Mainsail's stuff, which is great information, but a single source. That information keeps getting passed around over and over, by people who don't even have LiFePO4 banks or no actual experience with them(ahem). So called "Internet Experts". My outlook completely changed when I talked in person with owners that had been living with them for 2, 3 and even 5 years (in a liveaboard scenario, not weekend warriors).

[Kenomac]

Dockhead,

Here’s what we decided to do two months ago given the same set of circumstances with a dead bank of wet cells.

1. Replaced our 840ah 24v Rolls wet cell bank with the same. Cost $5000 with an expected life of 10-14 years.

2. Will add 900w of Solbian solar in Italy to the bimini top. Cost including canvas work $7000.

3. Generator run time will be reduced to less than one hour every other day and the boat will be nearly 100% energy independent except for the hot water heater. Not much to go wrong., no worries.

4. We already have two 100amp Mastervolt chargers plus a spare 75amp charger.

[missourisailor]

Originally Posted by travellerw

That is the problem with people here on Cruisers Forum. Much of the information here is just a rehash of Mainsail's stuff, which is great information, but a single source. That information keeps getting passed around over and over, by people who don't even have LiFePO4 banks or no actual experience with them(ahem). So called "Internet Experts".

This 1000% true!!!!

I'm not talking about Mainesail. His stuff is fantastic and we all owe him a big "thank you" for all he has done.

I'm talking about the "Internet Experts" who repeatedly cite his work. The same ones who have no real experience on the subject/s they post about. And whom only seem to be posting to get their post numbers up.

[Dockhead]

Originally Posted by Kenomac

Dockhead,

Here’s what we decided to do two months ago given the same set of circumstances with a dead bank of wet cells.

1. Replaced our 840ah 24v Rolls wet cell bank with the same. Cost $5000 with an expected life of 10-14 years.. . . .

Well, if you have a space for 840ah x 24v (that's like 1680 at 12v!) of Rolls traction batts, then what the heck are we talking about? That's like literally a metric ton of batteries, isn't it? You could run a WWII submarine on a bank like that! Be happy, and move on to another thread!

[Kenomac]

Originally Posted by Dockhead

Well, if you have a space for 840ah x 24v (that's like 1680 at 12v!) of Rolls traction batts, then what the heck are we talking about? That's like literally a metric ton of batteries, isn't it? You could run a WWII submarine on a bank like that! Be happy, and move on to another thread!

I’m actually trying to help you explore the possibilities, as we also looked at switching to lithium batteries. If you’re designing from scratch they’re something to consider, but remember... our boat was designed to have four large batteries weighing a “metric ton” sitting low as part of the ballast. Changing over to lithium requires much more than switching out just the batteries.

[a64pilot]

I also think your incorrect about the nothing to gain if you have Solar.
I have enough Solar to pretty easily replace the AH I use each day, however I still have to run the generator in order to get enough hours of charge to get to fully, 100% charged.
If I had a Lifepo bank, I wouldn’t have to do that.
However in my case I’m still running the generator to make water and wash clothes anyway, and throw in a cloudy, Winter day every few days and you likely have to have some form of generator anyway.

I still think if I wait long enough someone will market a box, inside of this box is a Lifepo battery and a BMS, all you have to do is feed it x voltage, the BMS will take care of the rest, disconnecting from the charge or whatever is necessary to maintain the bank.
It’s not hard, I wonder why there isn’t already a drop in solution?

Note, I gave up on the Lifepo thread long ago.

[Dockhead]

Originally Posted by a64pilot

. . . I still think if I wait long enough someone will market a box, inside of this box is a Lifepo battery and a BMS, all you have to do is feed it x voltage, the BMS will take care of the rest, disconnecting from the charge or whatever is necessary to maintain the bank.
It’s not hard, I wonder why there isn’t already a drop in solution?
. . .

But there are several such solutions already! Victron, Mastervolt, and Lithonics, come to mine just for starters.


The problem is cost, which is several times more than a "home brew" system, which is already quite expensive enough. That's why most people roll their own, plain and simple.

[Dockhead]

Originally Posted by Kenomac

. . . Changing over to lithium requires much more than switching out just the batteries.

Of course, but you probably don't even care with that much capacity. No matter how cool lithium is, lead-acid WORKS, and although there are some disadvantages, has some serious advantages. I would be very happy to have a flooded lead acid bank, if it met my requirements and could be accommodated.



But I have the opposite problem from you -- I have no good way to accommodate a single bank of heavy duty batts. So LiFePo offers the only way to get the capacity I need, in the practical space I have. A banal but serious reason to choose one technology over the other.

[Dockhead]

I'm gradually immersing myself in this topic, and found this resource:


Lithium Battery Systems | Nordkyn Design


To be really useful, particularly this article:


Electrical Design For a Marine Lithium Battery Bank | | Nordkyn Design


So, it seems the questions in the OP are fairly root issues in lithium systems design.


It's much more complex than I imagined, when I started thinking about this.

[travellerw]

Originally Posted by Dockhead

I'm gradually immersing myself in this topic, and found this resource:


Lithium Battery Systems | Nordkyn Design


To be really useful, particularly this article:


Electrical Design For a Marine Lithium Battery Bank | | Nordkyn Design


So, it seems the questions in the OP are fairly root issues in lithium systems design.


It's much more complex than I imagined, when I started thinking about this.

Thanks for posting those, I actually had not come across those articles before. They are well written.

Eventually I will be writing a blog post about our LiFePO4 install. I have really worked hard to make it the least complex possible, but still provide adequate protections (no BMS, just cell level BP with temp protection). I have based it off information I got from cruisers that have been living with LiFePO4 for years. One thing that REALLY simplifies a lithium install is removing the alternator from the system. I feel like not having to worry about the alternator (either killing it with a disconnect, or cooking it with over current), removed over 1/2 the complexity of our system. We just have solar (Victron MPPTs) and a house charger as charging sources.

[john61ct]

Yes those Nordkyn resources are very widely cited.

"House charger" meaning from shore AC while at a slip?

And BP meaning cell-level active balancing? protection?

[john61ct]

The fact that, given enough amps input, any LFP bank can go from completely depleted, user-defined 0% back to completely Full in under 60 minutes of charging.

To me makes the alternator a key player in system design. Even sitting on the hook for weeks, just run your already-installed propulsion engine for an hour, a few times per week, and you've got all the power you need.

Solar becomes irrelevant, unless **you want** to never burn dino juice.

And no dedicated genny needed at all.

[john61ct]

Originally Posted by travellerw

least complex possible, but still provide adequate protections (no BMS, just cell level BP with temp protection)

Not even LVDs at the bank level?

No HVD for charging in case the sources' regulation fails?

Such devices are not expensive.