Author Topic: LiFePO4 batteries going mainstream?  (Read 314 times)

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Offline Godot

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LiFePO4 batteries going mainstream?
« on: November 13, 2020, 11:50:45 AM »
It's beginning to look like lithium (LiFePO4 most common on boats) are beginning to go mainstream. The prices are dropping to the point of being practical without breaking the bank.

100 AH SOK LiFePO4 battery available for $570. I saw a youtube review of that battery and was pretty impressed. The batteries appear well built, and are servicable (cells can be replaced if necessary). There are lots of other brands out there as well, some more expensive, others less. Battleborn is a common brand, and is a lot more expensive; but still, even there the price is coming down.

It's getting to the point where I think I'm going to be able to justify going this way when next I replace the batteries in a year or so. 200AH lithiums replacing my 200AH FLA cells would pretty much double my useful capacity.

Advertised advantages: Lighter weight than Lead Acid batteries, and the ability to take a much deeper discharge without damage. I think many battery manufacturers claim a 100% discharge rate; but my understanding is that 90% is a better point. Many batteries apparently turn themselves off when they get down to 90% DoD in order to protect themselves. They can also take a much larger charge source (apparently 50% of the rating); though I suspect most of us in small boats won't have a charge source that can provide that much juice.

Disadvantages that I'm aware of: They can't take a charge when they are below freezing without serious damage. Some batteries, at least, have a temperature disconnect to protect against this. There is also some fear of fire, although I don't think that is a big thing with LiFePO4. They are more expensive initially, although maybe that isn't true anymore if you compare usable capacity per dollar of AGMs compared to usable capacity per dollar of LiFePO4 especially if you consider charge cycles. I also understand you can fry these batteries fairly quickly if charge controllers aren't set up properly, so the cost of new chargers might need to be factored in. And lastly, I don't think you can really tell state of charge via voltage, so a battery monitor that understands lithium would probably be a good idea.

I've been trying to understand what would happen in a mixed environment. Right now I have two FLA battery banks that link together by an automatic charge relay when there is a charge source. If I were to go LiFePO4 for the house bank, and keep a smaller lead acid for the starting battery it's not clear to me if it would be OK for the two batteries to link via the ACR during charging. Actually, I'm not sure the ACR would ever disengage even when not charging given the voltage cutouts, and the two banks could be linked together most of the time which might not be good. I've been told by some folks that LA is better for starting, and by others that it would be OK to just use the house lithium bank for starting maybe allowing the removal of the starter battery.
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Offline Norman

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Re: LiFePO4 batteries going mainstream?
« Reply #1 on: November 13, 2020, 09:54:31 PM »
Thanks for the extensive over view.

The built in protection from going below 10% is vital, near zero, they can not be recharged.  I have been there with a laptop.

Charge controllers and chargers must be exactly matched to the size and nature of the bank you buy.  Lithium batteries vary in the manner in charging they will accept without damage.

Any  device that can co ordinate charging both technologies lead and lithium, from a single source would be out of sight expensive, dedicated separate is the way to go.

Tying them together temporarily would most cheaply done with a mechanical switch, returned to open as soon as possible.

I agree that the fire danger has been addressed in most designs, but  I believe that a quick disconnect system for the wires, and quick release for mechanical security would be well worth designing in to the installation.  This should make it possible to remove the battery if trouble is detected.  My understanding is that smoke is present for quite a while before fire is likely.

Certainly the power density per pound is extremely attractive, and discharge to 10% without damage allows a much smaller AH for the same service.

Offline Owly055

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Re: LiFePO4 batteries going mainstream?
« Reply #2 on: November 15, 2020, 12:38:33 PM »
I've lost several lithium batteries (cordless power tool) due to temperature extremes.... how this equates to LifePO4s I don't know, as the chemistry is different.  It seems that most lithium batteries are "intelligent" in terms of limiting charge and discharge... The technology is just too complex not to have onboard control.