Re: [electricboats] Cells (modules) are dying.

Peter,
Look at the charge/discharge chart for your batteries. There should be one. In addition to Will Prowse look up the Current Connected SOK rack battery manual. Very good discussion about charging, conclusion is to fully charge the bank every time.  You do need to top balance the bank. Our group of 3 guys have run solar off grid house banks exactly the same as yours for 4 years. Our biggest problem was BMS. Current favorite is Jackery, I personally made 3 Ant Bms from circuit boards from Taiwan. You can go without one if you top balance periodically with Lifepo4. All of us had cell failures like you did because of bad bms or because we manually over rid it. I recently went to server rack style because it's easier.

The top balance works. About 3.6v in parallel with small DC power supply. Might take a week to 10 days. Most exciting part is all that metal around exposed terminals. You drop a wrench once and you'll find out. Ditch the screws, get SS studs.
Jerry

On September 30, 2024, at 7:07 PM, bobkart <couch45@msn.com> wrote:

3.65V is 'full' for LFP cells.  By bringing all your cells to that voltage (usually in parallel), you're more sure they are at the same energy level (assuming capacity-balanced cells).  This approach is referred to as 'top-balancing'.

 

The problem with 3.2V is that's on the very flat part of the charge/discharge curve for LFP chemistry.  You could be at 20% SOC or 40% SOC, depending on very small voltage differences that would all read as 3.2V on a not-very-precise-or-accurate meter.

 

There is also an approach called bottom-balancing, which I've never used, that tries to achieve the same result by starting at 0% SOC (or some other very low number).  I don't like bringing cells down that low (it can be hard on them), and it's not as well-defined of a voltage (2.5V, 2.75V, ...?).  100% SOC is easy to know you're at, based on the cells not accepting further charge beyond just a trickle (C/100 say).

_._,_._,_

---

Groups.io Links:

You receive all messages sent to this group.

View/Reply Online (#32721) | Reply To Group | Reply To Sender | Mute This Topic | New Topic
Your Subscription | Contact Group Owner | Unsubscribe [newarmyguitar24@gmail.com]

_._,_._,_