LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[Dockhead]

Originally Posted by CatNewBee

I agree, but I am not sure how to use the forum software for this, I started my thread about a year ago specifically to my setup (Winston 1000Ah LiFeYPO4 battery and all electric galley) intentionally to show a working project, the thoughts behind the dessign, the circuit diagramms explained in detail, the changes to the original manufacturer wiring, and finally the use pattern and discussions about improvements.

The first 20 posts are really focussed on the details as a type of blog with very little clutter. The discussions afterwards is as always going in all directions, but the initial dessign is compact at the beginning.

You cannot change or append old posts unfortunately, so additions and fixes are done among the clutter somewhere. You need a read only blog to keep the content in context and a free discussion part about the project for all questions, opinions and off topic issues. But as far as I understand the CF plattform, there is no easy way to achive this.

On a general LFP thread like this one you compare various setups and discuss pros and cons.

When you are ready for your install, start a new thread, write down your thoughts in a text document, prepare the pictures of the circuit diagrams, the gear used etc. Then post all the stuff at once or in close sequence before going into the discussion to keep the first posts clean and complete.

I have no other work around at the moment.

I think we need a whole sub-forum on LiFePo power systems, with topics, instead of trying to carry on 20 different conversations in one monster thread.


If you guys could help with a good list of topics, I will suggest to the site owners that the topics are implemented.


Something like:


Engineering & Systems
>Electrical: Lithium Power Systems

>>LiFePo4 Installations
>>BMS & Protection Systems
>>?
>>?

[CatNewBee]

Every single project is a kind of unique and there are not many willing or able to post the details.

I would suggest a structure like

- realised DIY projects from cells
- realized projects with drop in batteries
- general topics related to LFP (charge sources, BMS, monitoring)

There are solutions from various companies, where the owners are happy with the install, but cannot discuss the solution in depth, except how well it works. Many owners even have no clue about the electric systems they have. Only DIY builds force the skippers to think in depth what they have and what they need to change.

Before I started my project I have done a 2 year research on the technology, available cells, BMS options, power circuitry and interfaces in between until I found the one I considered optimal for my needs. And I was looking only on the options available or sourcable on the European market.

On other continents the situation may be completly different.

[Dockhead]

Originally Posted by CatNewBee

. . . Before I started my project I have done a 2 year research on the technology, available cells, BMS options, power circuitry and interfaces in between until I found the one I considered optimal for my needs. . .

And I guess I am far from the only person on here, who is very grateful to you for sharing so generously the results of all that research!

[JmanC]

Why exactly does charging to higher voltages lead to needing more balancing?
I don't get it, from what I have searched online I can't see why.
Did some testers just notice this?


I still don't know when a bank needs re balancing? From what I understand you look for voltage differences of more than 100mv at least in the upper shoulders area starting at around 3.45V right?
I don't think any differences in flat region tell you anything, mine in flat region are within 5-10mv but near the top they are alot worse.

[rgleason]

Dockhead, No you are not entitled to your opinion Yes, we try to discern the source and evaluate the facts. It would be very nice to have smarter searches/filters to separate, facts, accepted practice, ideas, opinions & beliefs. Many of use are still trying to learn and understand more, so there is another set of filters: questions and answers. Those answers get refined and the questions get changed by additional posts. It gets pretty complicated.

Phyics, tries to describe the real world up to certain levels of precision, experiment and reliability are cornerstones, but the more known (regarded as true), the greater the unknowns, conversely we know more by what we know is not true. Perhaps a vote mechanism attached to each post would help, under the presumption that the majority of users have some experience with the topic.

However this would not result in any summarized or consolidated body of knowledge.

Catnewbee, I think you're working suggestion Post #6975 is useful and makes good points. Thank you for sharing your expertise.


It is too bad with 7000 posts, that we can't read it all, or even edit it down, because there must be knowledge in there, but it has become totally unwieldy, too much information spread through chaff.

[newhaul]

Originally Posted by JmanC

Why exactly does charging to higher voltages lead to needing more balancing?
I don't get it, from what I have searched online I can't see why.
Did some testers just notice this?


I still don't know when a bank needs re balancing? From what I understand you look for voltage differences of more than 100mv at least in the upper shoulders area starting at around 3.45V right?
I don't think any differences in flat region tell you anything, mine in flat region are within 5-10mv but near the top they are alot worse.

that goes back to the thread about capacity loss.
http://www.cruisersforum.com/forums/...ad-219814.html
occasionally top balancing seems to be the general consensus to help prevent/ stave off the eventual failure of a bank .
More study is of course needed which by the nature of Lfp chemistry takes years for us to get the lifecycles to know if ( like for me a monthly ) top balance will prevent some of the capacity loss .
The further out of balance the cells the less total capacity you seem to have .

[john61ct]

Originally Posted by JmanC

Why exactly does charging to higher voltages lead to needing more balancing?

Same as with higher C-rate usage, just amalgamation of experience & anecdotal reports from thousands of users across different use cases.

But cell quality, e.g. chemical purity, consistency in manufacturing process, rigor of QA processes, integrity of sellers/distribution channels

are much bigger factors IMO. As is age / cycle life / SoH.


As a practical matter, those getting truly Grade 1 brand new "fresh" output from top factories will generally have few to no balancing issues in the first few hundred maybe thousand cycles.

Especially at low C-rates and avoiding the shoulders. And any such slight imbalances if they do exist will **not cause significant problems** so could be taken care of by balancing manually say once a year as a maintenance routine.

But even the best cells may well show increasing need for more frequent / longer / higher-current balancing as they wear.

If you rely on balancing gear that requires going to higher voltages than desired, IMO best to change to use different gear.


_____

Yes you should not worry about imbalances in the middle SoC ranges, only near the (top vs bottom) voltage range where you do your balancing.

If you are top-balancing, I would recommend using a voltage range just incrementally higher than the stop-charge termination point you use for normal cycling.

If bottom-balancing, then use just below your LVC cutoff, say around 3Vpc.

_____
How much imbalance delta you want to accept will depend on the gear / methods you use.

If you have low-current balancers hooked up full-time anyway, then a 0.01V delta trigger would mean more frequent and shorter sessions. If you only balance when needed, and the process is a bit inconvenient, then waiting for a .1V delta might be appropriate, as long as that did not result in an unacceptably long session time.

[CatNewBee]

Originally Posted by JmanC

Why exactly does charging to higher voltages lead to needing more balancing?
I don't get it, from what I have searched online I can't see why.
Did some testers just notice this?


I still don't know when a bank needs re balancing? From what I understand you look for voltage differences of more than 100mv at least in the upper shoulders area starting at around 3.45V right?
I don't think any differences in flat region tell you anything, mine in flat region are within 5-10mv but near the top they are alot worse.

The cells simpli run out of balance with each cycle.

Charging to higher voltages shows the imbalances more prominent, also the inner resistance at higher SOC differs more, what leads to less equal charge distribution in serial cells.

You notice several mV in the flat region that translate to several percent SOC. This difference remains and when get to the shoulders, eithe charge or discharge, it manifests in 100mV or more. Besides this the cell impedance /resistance varies with SOC, so the small differences lead to different acceptance rates of the charge, what leads to increasing of the imballances.

The same happens with FLA btw, but keeping the battery at absorption does the top balancing without electronics. Some cells simply produce heat and boil while other still convert PbO and Pb out of PbSO4 in the electrolyte.

DISCHARGE

Negative side: Pb + SO4 -> PbSO4 + 2e-
Positive Side: PbO + SO4 + 4H+ + 2e- -> PbSO4 + 2 H2O

charge is in opposite direction.

The whole reaction is as following

Pb + PbO + H2SO4 < - - > PbSO4 + 2 H2O

Unfortunately LFP cells would runoff when overcharged that way, so an external balancer must do the job.

[Checkswrecks]

Originally Posted by Dockhead

I think we need a whole sub-forum on LiFePo power systems, with topics, instead of trying to carry on 20 different conversations in one monster thread.

If you guys could help with a good list of topics, I will suggest to the site owners that the topics are implemented.

Something like:


Engineering & Systems
>Electrical: Lithium Power Systems

>>LiFePo4 Installations
>>BMS & Protection Systems
>>?
>>?

Dockhead must be an engineer like me.


Seriously, I like the idea of grouping major topics into break-out areas.

And also do appreciate all that CatNewbee contributes.
Thank you!

[swampbush]

Originally Posted by Dockhead

I think we need a whole sub-forum on LiFePo power systems, with topics, instead of trying to carry on 20 different conversations in one monster thread.


If you guys could help with a good list of topics, I will suggest to the site owners that the topics are implemented.


Something like:


Engineering & Systems
>Electrical: Lithium Power Systems

>>LiFePo4 Installations
>>BMS & Protection Systems
>>?
>>?

Good idea. This would create a handy resource.
Perhaps also suppliers and prices by region, EU, North America, Australia,etc
Also charging methodology

[newhaul]

Originally Posted by swampbush

Good idea. This would create a handy resource.
Perhaps also suppliers and prices by region, EU, North America, Australia,etc
Also charging methodology

a lot of this already exists a couple of threads. .
http://www.cruisersforum.com/forums/...ad-219455.html

There are also several threads that address the various charging schemes just do a cruisers forum search for Lfp and lifepo4 you will find a plethora of source threads .

[swampbush]

Originally Posted by newhaul

a lot of this already exists a couple of threads. .

http://www.cruisersforum.com/forums/...ad-219455.html



There are also several threads that address the various charging schemes just do a cruisers forum search for Lfp and lifepo4 you will find a plethora of source threads .

It is covered but not structured in a way that is easy to find by browsing, to use as a reference for anyone starting to learn about LifePo4. Pretty sure I have read every word regarding LifePo4 on cruisersforum. Search on mobile and Tapatalk is very poor within cruisersforum, better in google.

[newhaul]

Originally Posted by swampbush

It is covered but not structured in a way that is easy to find by browsing, to use as a reference for anyone starting to learn about LifePo4. Pretty sure I have read every word regarding LifePo4 on cruisersforum. Search on mobile and Tapatalk is very poor within cruisersforum, better in google.

then do a cruisers forum specific Google search .

Here is a 10 second search go get you started
Lifepo4

https://www.google.com/search?q=life...w=1024&bih=768

When searching Lfp

https://www.google.com/search?client...71.8_boVghzxSQ

[swampbush]

Originally Posted by newhaul

then do a cruisers forum specific Google search .



Here is a 10 second search go get you started

Lifepo4



https://www.google.com/search?q=life...w=1024&bih=768



When searching Lfp



https://www.google.com/search?client...71.8_boVghzxSQ

Thanks but I wasn't asking how to do a search, I was agreeing with dockhead that a structured approach to the info would be handy. It is hard to search when you don't even know the terms. When I started reading up on LifePo4 some years ago the terms were confusing, the acronyms cryptic. I am trying to make it easier for those that come after to easily get the information without repeating the same questions.
My new LifePo4 are on order now, my charging sorted largely due to info from this site among others. Thanks all who have contributed.

[Recy]

I got this in a news mail from GWL the other day.
What do think is it something useful or are there better options?

https://www.ev-power.eu/_d7077.html?...-20190926#tab1

https://www.youtube.com/watch?v=Vdo9...odule-20190926