Lucia 40: DIY Lithium Bank Install

[john61ct]

Best to keep the LFP bank isolated at as low SoC as possible when shore power is available. And cool if possible.

Just not so low you risk going "flat".

Cycling them unnecessarily will cost you in shortened lifetime than the shore power you're saving.

Or substitute a cheap lead batt for that purpose.

[Terbonium]

I can't argue with that logic. But we do live aboard, and do leave the dock on average weekly. Discharging to an ideal storage voltage would require some hands on time. Then isolating them and switching to a different battery with different charge requirements would require some reconfiguring. A

I could set the discharge level to 50% and disable charging. The Victron would just discharge to that level and then pull all power thru the shore. I'm not sure what it would do about the 12V system though. There is no real float voltage that can hold lithium at 50%.. Just 10% or 100%. That part would be tricky sine we have active 12V systems all the time.

I expect to get at least 6 years from the batteries with this usage pattern. Then I hope to replace them with the latest krypton powered diamond cells that offer 100x the capacity at half the weight

[john61ct]

Sorry I wasn't more clear.

LFP should not be Floated at any voltage.

As long as they're isolated, 12.1-2 should be fine for resting, self-discharge in a week or two will be negligible.

Only charge them past that point, just before when you will need to run loads off them. And no higher than say 13.8V, no Absorb time.

[Terbonium]

I didn't mean the imply float. I meant that there was no real way to hold the bank at a storage voltage and supply 12v loads from shore power.

[john61ct]

Originally Posted by Terbonium

I didn't mean the imply float. I meant that there was no real way to hold the bank at a storage voltage and supply 12v loads from shore power.

You don't hold it at a voltage, you charge to your selected point, then let it decline, which will be very slowly since it's completely isolated.

Then long before it gets critically low, you give it a bit of charge, say .1C would be plenty if you're checking few times a month.

The LFP bank should have nothing to do with supplying loads while shore power is available, that is my main point.

I'm not saying you **must** do this, just pointing out that even shallow cycles have a cost, and even more so holding LFP at a higher SoC than necessary, when they don't need to be used at all.

If changing the infrastructure is more costly than losing bank lifetime, then at least others planning their setup will benefit.

[CatNewBee]

Even no cycling and storing has a cost too.
So best would be to sell the battery when not using it and buy a new one when needed.

I guess you got the point, the LFP is there to be used and charged and to store energy. It is not just a decoration.

If you can afford a empty battery of huge size just for longuitivity, then you probably have a sizing problem.

Take a smaller bank and replace it when it dies and dont worry about keeping at low SOC. On the long run, it would be cheaper and your life may be happier without the burden to keep the battery discharged. Just saying...[emoji12] [emoji49] [emoji15]

[john61ct]

We were discussing a bank not being used for a few days or a week, say a weekend use pattern as is common for many boats.

Not long-term storage, although the ideal is similar treatment.