LiFePO4: what voltage?

[rgleason]

I don't know if this chart by MaineSail is current, but looking at it
https://marinehowto.com/wp-content/u...4-On-Boats.jpg

It looks like he starts charging at 12.95v and ends at 13.88v

Is that correct? Do you think that is his settings now?
It seems like the 12.9v is pretty high, but looking at the curve it isn't.
I have references to LVD is 11.9v / 2.98vpc and 11.60v


I am puzzled because I thought charging started at Min Voltage of 12v or 3.00vpc
I am guessing that is incorrect, after seeing this.
Can anyone confirm?

This is from his article
https://marinehowto.com/lifepo4-batteries-on-boats/
Which I had not seen. It answered a number of things that I had to dig to learn, and it added to that. Very Helpful.

I am wondering if the capacity in Ah is then about 80% of the manufacturer's Ah?
Because I'd like to see what ah will be useful.


PS| MS Article: "Approx 80% of an LFP banks capacity is fully usable, 20% DOD to 100% SOC"

[Nicholson58]

Read this. Very good tech.

https://marinehowto.com/lifepo4-batteries-on-boats/

[travellerw]

Originally Posted by rgleason

Is that correct? Do you think that is his settings now?
It seems like the 12.9v is pretty high, but looking at the curve it isn't.
I have references to LVD is 11.9v / 2.98vpc and 11.60v

While Mainsail's article is a great starting point, I think it has started to become a little dated. As more and more users begin installing LFP and reporting their experiences, the data is becoming better. There is some pretty good Facebook groups these days with actual users.

However, those numbers in his article are pretty close to what we run on our LFP bank. Our low voltage alarm is set at 12.8V. If we get to that voltage, this is the point where I will start my generator to begin dumping amp hours back in. However, its almost a non-event as our Victron Battery monitor has been pretty accurate. I watch it and usually put amp hours back in before the voltage fall off.

As to charging. We charge our bank to 13.8V, then hold that voltage until the current tails to C/100ish (about 5A for our 400Ah bank). At that point, I consider it %100 full (although in reality its probably %92-%95). However, I don't really stress about hitting this. If I know it will be nice and sunny in the days to come, I have no problem going to bed with the bank at %65.

[rgleason]

MaineSail RE: Floating?


"JUST SAY NO TO FLOAT CHARGING!!!!
If you are in a situation where charge equipment can’t be turned off and would necessitate floating the LFP bank, you need to wire in a cross-over lead acid battery to handle shore-side or unattended duration’s of alternative energy charging. For dock side or unattended uses you need to be able to discharge the LFP to 50-60% SOC and TAKE IT OFF-LINE while allowing the small lead acid bank to run DC system loads along with the shore side charger or alternative energy systems."

[rgleason]

Travellerw, Thanks, very helpful

High Kneewall 13.8v charge to 13.8 hold CV until current tails to C/100
Low kneewall start charging 12.8v

How many usable Ah in this range do you figure for your 400ah bank?
Are they Winston? Are you using a BMS? Sorry I forget some of the thread.

[travellerw]

Originally Posted by rgleason

Travellerw, Thanks, very helpful

High Kneewall 13.8v charge to 13.8 hold CV until current tails to C/100
Low kneewall start charging 12.8v

How many usable Ah in this range do you figure for your 400ah bank?
Are they Winston? Are you using a BMS? Sorry I forget some of the thread.

Yes my cells are Winston. I'm using a BMS that controls a single BlueSea ML-RBS relay (I used to have 2, one on POS and one on NEG, but have removed one). I don't have any relays controlling charging ect. Just a single cut point. Triggering the ML-RBS completely isolates the pack.

Charging to 13.8V and holding to C/100 will get Winstons charged to about %95. I personally haven't done a capacity check, but others in the Facebook groups have. %95-%98 is what multiple users found.

Other users claim I'm being way to conservative on my low voltage number. Based on my Victron Battery monitor AH counter, that is most likely true. However, I have left the alarm there as it just makes me feel better. Eventually, I will bump that down.

Now as to Mainsail's article on "not floating". I %100 agree with Mainsail that long term floating on a dock or during storage is not a good idea. In the event we ever goto a dock, we will use the ML-RBS to isolate the battery pack and power the boat on our charger (which is safe to use as a power supply).

However, when it comes to day to day usage, its a different story. The goal here is to set your solar controllers float voltage so they cover the loads, but are putting in essentially zero amps. So at least you are not throwing away your excess solar. You will often hear people say you need to charge to full and then turn off your charge sources. When really you need to charge to full and STOP (no amps going in). Turning off your solar at 2pm would be silly as you would be throwing away tons of power.

Now with that said.. LFP is a change in mindset. If we know we are going to have a very sunny day and make tons of power, then we will run high draw devices early in the day. We do laundry, plug in our laptops, even heat water. Our goal is to leave our bank depleated enough that we don't actually get to %100 and float. Its a good day if we do all that and still get the bank back to %90.

[john61ct]

Playing with dozens or hundreds of cells to create a big bank is a Science Project, fine on land, not on a boat.

I would not build a pack that I thought **required** anything at the cell level, IMO that level of complexity should always be optional.

Originally Posted by rgleason

I don't know if this chart by MaineSail is current, but looking at it
https://marinehowto.com/wp-content/u...4-On-Boats.jpg

It looks like he starts charging at 12.95v and ends at 13.88v

Testing / demo / maintenance is not day-to-day usage. If your daily cycling needs to go that low you sized the bank too small.

As per recent posts 3Vpc is his zero when load testing, and I believe he still stays well below the top shoulder as well, maybe in the 3.5Vpc range.

But I am sure he knows enough to safely vary by context, we little minds need the foolish consistency 8-)

Originally Posted by rgleason

I have references to LVD is 11.9v / 2.98vpc and 11.60v

No reason to go that low, even if it isn't intrinsically harmful, every step toward the cliff edge is that bit more dangerous.

> I am wondering if the capacity in Ah is then about 80% of the manufacturer's Ah?

No, his more recent posts have shown very low capacity sacrifices from backing well off the shoulders.

The 80% reference is either outdated, or being IMO overly cautious / conservative.

Note quality cells ship with capacity greater than rated, so if a 100AH bank load tests at 95AH staying between 3.00V and 3.45V, I would call that 95% usable,

even if pushing the shoulders by going to more destructive voltages tested at say 110AH.

[john61ct]

Originally Posted by rgleason

charge to 13.8 hold CV until current tails to C/100

There will not be any advantage at all in daily cycling holding CV / Absorb to any endAmps spec.

When precision benchmarking is required, .03C or even .05C is fine, no need to push to .01C.

Such a low endAmps spec is just holdover lead thinking.

At higher voltages pushing Absorb longer will actually increase the harm to longevity.

In normal use, just charge to your selected voltage and Stop.

That voltage can be a bit higher for high-current charge sources, at low C rates need to be more conservative.

But again, you really aren't buying anything significant doing that, just adding complexity for no benefit.

Stop means stop **charging the LFP**, either A. isolate the bank, not necessarily disable the charge source.

Can also mean B. go to a low enough Float, differences already discussed.

[travellerw]

Originally Posted by john61ct

There will not be any advantage at all in daily cycling holding CV / Absorb to any endAmps spec.

When precision benchmarking is required, .03C or even .05C is fine, no need to push to .01C.

Such a low endAmps spec is just holdover lead thinking.

At higher voltages pushing Absorb longer will actually increase the harm to longevity.

In normal use, just charge to your selected voltage and Stop.

That voltage can be a bit higher for high-current charge sources, at low C rates need to be more conservative.

But again, you really aren't buying anything significant doing that, just adding complexity for no benefit.

Stop means stop **charging the LFP**, either A. isolate the bank, not necessarily disable the charge source.

Can also mean B. go to a low enough Float, differences already discussed.

Again, John is just quoting stuff he is reading (in multiple posts to bump his post number). He has zero experience with LFP (google is your friend "John61ct Forum"). Worse, he seems to only quote one source (Mainsail). John, please prove me wrong, post your experience, pictures/details of your bank, ect.

Actually, Google really is a great resource. On top of Mainsails articles, I would suggest you Google the following "T1Terry forum lifepo4", "Pnjunction forum lifepo4". Read EVERYTHING you find (ignore Sunking). Also, Facebook is your friend. There are groups on there with people actually using LFP. They are a trove of data and quickly weed out pretenders.

The holding until C/100 actually only gives you about an extra %5 of capacity. However, there is ZERO real data showing it harms cells life, so why not get that extra %5.

[Delfin]

Originally Posted by travellerw

John, please prove me wrong, post your experience, pictures/details of your bank, ect.

Never will happen...

[john61ct]

Originally Posted by travellerw

The holding until C/100 actually only gives you about an extra %5 of capacity.

No it is a lot less than that. As Maine Sail very specific and precise posting data demonstrated in the recent thread that you yourself were participating in.

Recommending Facebook for technical info is just ridonculous.

And I have been learning from Terry at T1 Lithium for several years now, his insights and experience are very valuable, and do not conflict much at all with Rod's much more precise published test results.

[john61ct]

And why on earth would anyone care about post numbers? Most forums wouldn't even know how to look that up?

[john61ct]

Originally Posted by travellerw

The holding until C/100 actually only gives you about an extra %5 of capacity.

Direct from MS

********
Vendor / theoretical benchmark for "100%" in this case:

3.65V taper to 0A
______
Charge to 13.80V (3.45VPC) taper to 0A, gives 99.94% SOC

Charge to 13.80V (3.45VPC) taper to 5A (.06C) = 98.69% SOC
********

I get a 1.25% difference.

And I did not make any claim about "damage" from holding Absorb at lower voltages.

Please stop over-simplifying my words just to give yourself a straw man to attack.

My point, by which I still stand, is that holding Absorb in daily cycling serves no useful purpose.

Charge **to** a target voltage and Stop is safer and simpler.

As always do as you like with your stuff.

[travellerw]

Originally Posted by john61ct

As always do as you like with your stuff.

First question.
Do you have any stuff?

Again ONE SOURCE.. Mainsail.. You are simply taking his stuff and regurgitating it and claiming its your own. Acting like an expert, yet you have ZERO experience or credentials to be doing so. Did you do those tests? What size bank do you have? What proceedure did you use to confirm Mainsail's results? AGAIN, post pictures or details of your bank and experience with it. Boats you have worked on. Details of banks you helped design/install.

Saying that Facebook is ridiculous for technical data shows exactly how out of touch you really are. A Facebook group full of people with boats or RVs that are actually using LFP every day. That have been using them for years and posting their data and experience, is not ridiculous. Taking advice from someone on a forum who has read some data and acts like an expert is.

I don't need a straw man to attack, you do a fantastic job by yourself. Even your statement that you don't know how to look up post counts (hey, look to the left here and almost any other forum).

Originally Posted by john61ct

My point, by which I still stand, is that holding Absorb in daily cycling serves no useful purpose.

Please back this statement up with data that is yours, not taken from a website that has already been posted here.

My big problem with you John, is you are taking stuff you read online and interpretting it. Its very clear you have no experience and that is scary. You then take this data you interpretted and pass it off as you being an expert. I believe that users should know that they are not talking with an expert and the stuff you post is based on ZERO experience. I have no problem with you posting you opinions based on things you have read. However, acting like an expert with experience is not OK.

[tanglewood]

Originally Posted by rgleason

MaineSail RE: Floating?


"JUST SAY NO TO FLOAT CHARGING!!!!
If you are in a situation where charge equipment can’t be turned off and would necessitate floating the LFP bank, you need to wire in a cross-over lead acid battery to handle shore-side or unattended duration’s of alternative energy charging. For dock side or unattended uses you need to be able to discharge the LFP to 50-60% SOC and TAKE IT OFF-LINE while allowing the small lead acid bank to run DC system loads along with the shore side charger or alternative energy systems."

I hate to speak for someone else, but from his participation in the "float" thread, I think the statement above is in the context of chargers that continue to drive current into the battery when on float, i.e. at an elevated voltage.