lithium battery source/price thread

[john61ct]

https://scholar.google.com/scholar?q...fetime+lifepo4

[KTP]

Perhaps the most legit paper I could find on the subject of LFP aging is this paper:

https://www.nrel.gov/docs/fy18osti/70616.pdf


It is quite a read but does seem to indicate a quite large capacity loss per year if the battery is stored at either 100% SoC or at high temperature.

Like in Figure 12 it seems to say if you store a LFP battery at 15 degrees C and 100% SoC the capacity loss is about 3% per year but if the battery is stored at 45 degrees C and 100% SoC the loss is a whopping 9% per year.

I dunno, it looks to me that something like 2% to 3% a year capacity loss is going to be the norm for LFP regardless of use unless you are storing them in Anchorage AK at 50% SoC.

[newhaul]

Originally Posted by KTP

Perhaps the most legit paper I could find on the subject of LFP aging is this paper:

https://www.nrel.gov/docs/fy18osti/70616.pdf


It is quite a read but does seem to indicate a quite large capacity loss per year if the battery is stored at either 100% SoC or at high temperature.

Like in Figure 12 it seems to say if you store a LFP battery at 15 degrees C and 100% SoC the capacity loss is about 3% per year but if the battery is stored at 45 degrees C and 100% SoC the loss is a whopping 9% per year.

I dunno, it looks to me that something like 2% to 3% a year capacity loss is going to be the norm for LFP regardless of use unless you are storing them in Anchorage AK at 50% SoC.

the best option for storage pre use is somewhere between 30 and 50% and under 80℉
The metrics seem to change considerably once they are placed into service.

[john61ct]

Originally Posted by KTP

something like 2% to 3% a year capacity loss is going to be the norm for LFP regardless of use unless you are storing them in Anchorage AK at 50% SoC.

But you'd have to pretty uninformed to allow your LFP bank to sit for any length of time at any high SoC, even while being actively cycled.

Anyone bringing up storage issues is told 40-50% is the norm, but lower is better, so long as there is no risk of dropping anywhere near say 3Vpc.

Like leaving a BMS attached, a frequent cause of banks getting murdered.

[KTP]

Which again brings up how you are going to use the batteries.

If you have a big bank that you use for propulsion, you are not going to want to show up at the marina where you have your boat docked and find it sitting at 50% SoC. This is a check in the plus column for lead acid, since having the battery at 100% SoC is the best for longevity in lead acid.

Alternatively, if you are actively using the boat and never really even bringing it up to 100% SoC, that is better for LFP longevity.

Although I really didn't want to devolve into the lead vs lithium argument, it does come up even when thinking about which lithium battery to choose.

[newhaul]

Originally Posted by KTP

Which again brings up how you are going to use the batteries.

If you have a big bank that you use for propulsion, you are not going to want to show up at the marina where you have your boat docked and find it sitting at 50% SoC. This is a check in the plus column for lead acid, since having the battery at 100% SoC is the best for longevity in lead acid.

Alternatively, if you are actively using the boat and never really even bringing it up to 100% SoC, that is better for LFP longevity.

Although I really didn't want to devolve into the lead vs lithium argument, it does come up even when thinking about which lithium battery to choose.

the storage point is more important with long term storage
ie: over the winter layup season .
For most of the season when you are expecting cycling on a weekly or so basis then the 80% point makes more sense just hit the big charger when you get to the boat to top it off while you do your pre underway stuff like filling the water tanks showing the food and other supplies . An hour or two will bep good to bring you up to near full . The Lfp batteries just don't like being kept fully charged.

[KTP]

The only slight problem is I run our 12V bilge pumps off of the 48V battery bank (through a 60 amps DC-DC) and if I am forced to leave the LFP bank in a partial state of charge during the winter (and disconnected from the shore power connected charger) then there would be the risk of a leak in the boat eventually draining the LFP bank and sinking the boat.

I could have one lead acid bank and one LFP bank and just never switch both banks on together...

[john61ct]

Originally Posted by KTP

If you have a big bank that you use for propulsion

Would be pretty silly to use lead for propulsion these days hardly anyone does extra weight is self-defeating.

With all that would be involved setting up EP on a boat, a wireless control to schedule charging to Full the night before, when the boat's only occasionally used, would not be unreasonable.

[KTP]

Originally Posted by john61ct

Would be pretty silly to use lead for propulsion these days hardly anyone does extra weight is self-defeating.

Submarines did it for a long time didn't they?

[newhaul]

Originally Posted by KTP

Submarines did it for a long time didn't they?

yes they did back when lead was the only but now the diesel electric subs use Lfp banks

[newhaul]

Originally Posted by KTP

The only slight problem is I run our 12V bilge pumps off of the 48V battery bank (through a 60 amps DC-DC) and if I am forced to leave the LFP bank in a partial state of charge during the winter (and disconnected from the shore power connected charger) then there would be the risk of a leak in the boat eventually draining the LFP bank and sinking the boat.

I could have one lead acid bank and one LFP bank and just never switch both banks on together...

why not run your bilge pump off of a small Fla battery that is topped off from your Lfp via the b2b charger and just use a small standard 12v battery charger to keep the lead battery charged during the winter isolating the Lfp .

That is similar to how I will be doing my starting battery with the b2b running the other way.

[newhaul]

Originally Posted by john61ct

Would be pretty silly to use lead for propulsion these days hardly anyone does extra weight is self-defeating.

With all that would be involved setting up EP on a boat, a wireless control to schedule charging to Full the night before, when the boat's only occasionally used, would not be unreasonable.

heck with all the connectivity stuff now days I bet you could set it up so you could turn on your charger with your phone from home.

[john61ct]

Yes, exactly what I meant.

I bet Victron controls can do so OTS

[KTP]

So I noticed this in the Trojan Trillium user guide:

"For batteries connected in series (24V to 48V systems), each of the batteries can be charged individually for best results or the batteries can be charged with a multi-bank charging system. Bulk 48V chargers may not charge all series connected batteries and may require individual battery maintenance charging at periodic intervals to fully charge the set."

Any guestimate on how in balance four of these would stay in a series string? Are we talking having to disassemble the bank and manually charge each one every 5 cycles or is this something that would rarely happen, like once every year or two?

[john61ct]

This is because their BMSs are "internal" to each 12V set and are not designed to coordinate balancing across a serial'd set.

I suppose there might be 4S balancer devices out there that could handle 12V "cells"?

Meantime as long as you monitor the at-rest voltage when a bulk charge cycle at 48V is done, and all 4 of the 12V units are within say 50-100mV that's OK.

If they drift as they say charge with precision in 12V units, basically "meta" top balancing.

I think it likely would not be required too often.

____
The proper setup to get to 48V is 16S at the topmost level, with a 16S BMS there (if you use one).

If you are paralleling cells to get to a higher Ah capacity than your cells, or for redundancy, each of those 16 3.2V groups would be a set of paralleled cells, which set needs to be broken down to check / test at the individual cell level.