Happy 15th Birthday to my LiFePo4 Bank

[CaptainRivet]

Originally Posted by Maine Sail

What cells are you using that have been around for 20 years? As fat asI know Thndersky only began selling production LFP cells in 2007..? Their earliest cells were green and most of these went to Universities and industry for testing purposes..

Lishen Lifepo4 cells where available in 2003 through grey channels and 2005 officially.
my buddy has an NPO building commercial EVs, emergency backups and power walls in Austria and he imported the first lithium cells into Europe, same with Yinglong LTOs.

[senormechanico]

Congrats on your recovery Rod. I have read most of your website and am very grateful for all the information you have provided.
I'm a fan of LiFePo4's. Got a 200 ah bank on the boat installed 13 years ago.
It now is equipped with a Neey balancer. 100% satisfied with everything, no problems whatever.
The house has a grid tie, and a 24 volt 700 ah bank of Winstons with a Neey balancer.


Glad to have you back posting.

[CarlF]

I like the argument that LFP boat banks should not be charged over 13.8v since boats charging systems generally are not able to charge a large bank quickly. You can get to 100% charge just about as quickly at 13.8v.

But virtually all drop ins require much higher charge voltages (14.4) for balancing. Is that correct?

I have a Kilovault house bank which is spec to charge to 14.1v. Could I reduce that without balance problems and have a longer bank life?

[jcapo]

I have two 300AH Epoch drop-ins in parallel. Apparently both have well matched cells. I charge to 13.8 with 15 minute absorption and float at 13.4 volts. With these batteries the current is dropping quickly and cell imbalance is increasing when charging past 13.8 volts.

I've charged to the recommended 14.1 volts a few times and cell imbalance approaches 150mv but the cells get back in balance when the voltage drops.

So far I see no advantage to charge past 13.8. Time will tell.

[wholybee]

Originally Posted by jcapo

I have two 300AH Epoch drop-ins in parallel. Apparently both have well matched cells. I charge to 13.8 with 15 minute absorption and float at 13.4 volts. With these batteries the current is dropping quickly and cell imbalance is increasing when charging past 13.8 volts.

I've charged to the recommended 14.1 volts a few times and cell imbalance approaches 150mv but the cells get back in balance when the voltage drops.

So far I see no advantage to charge past 13.8. Time will tell.

It is impossible to know the cell balance below about 13.8V. Below that the cells will always read the same voltage. That is why to charge higher than 13.8V, to check the balance. You should charge to ~14V, and hold it there and monitor the cells. You should see the BMS begin to balance them and bring them closer together. I'm not sure how detailed the EPOCH app is, but it should tell you that it is doing this. Once they are balanced, then only do that again once in a while to check on it. If the cells are really well matched, then many cycles can pass and they will still be in balance. If they are not so well balanced, then you will need to perform that balancing operation more frequently. The worst cells need that daily, or even an active balancer, to keep them in balance.

If the cells become so out of balance that there is an over voltage event then it can be a challenge to get them back in balance. So it is best to keep them balanced to begin with.

[CaptainRivet]

Originally Posted by CarlF

I like the argument that LFP boat banks should not be charged over 13.8v since boats charging systems generally are not able to charge a large bank quickly. You can get to 100% charge just about as quickly at 13.8v.

But virtually all drop ins require much higher charge voltages (14.4) for balancing. Is that correct?

I have a Kilovault house bank which is spec to charge to 14.1v. Could I reduce that without balance problems and have a longer bank life?

This is cell and usage dependent. Especially how much c-rate you charge and discharge.
The kilovaults have only passive balancer but very good cells. You can charge to 13.8V but i would recommend to charge to 3.55 or 14.4V once every 2 month to keep or get get them to balance.

[CaptainRivet]

Originally Posted by jcapo

I have two 300AH Epoch drop-ins in parallel. Apparently both have well matched cells. I charge to 13.8 with 15 minute absorption and float at 13.4 volts. With these batteries the current is dropping quickly and cell imbalance is increasing when charging past 13.8 volts.

I've charged to the recommended 14.1 volts a few times and cell imbalance approaches 150mv but the cells get back in balance when the voltage drops.

So far I see no advantage to charge past 13.8. Time will tell.

Holy cow these epochs are way out of balance when they are at 14.1V and have 150mV.

With this chemistry you only see the balance of the cells and therfore its capacity in the upper knee from 13.8 to 14.6V. If they have 150mA at 14.1 then they have 250mv at 14.8V which is huge and need to be brought back to balance immediately before you damage them permanently (if not too late already).

You need to set temporarily till they are back in balance end the High voltage cutoff to 14.6V or 3.65V per cell. Then change the parameter of your solar to 14.4v with absorption of 8h and float at 14.2V. They need to stay in the upper knee to give your balancer the time to get them back to balance. A deviation of 15-20mV at 14.4V is acceptable so they need to be as long in the upper knee till this deviation is reached. If you get a HVC with 14.4V go first lower to 14.2V or even 14V with absorption till you get no cutoff. And then step by step raise the absorption voltage to 14.4V.

You can only charge a perfectly top balanced battery to 13.8V, if not perfectly top balanced you harm the battery more then charging to 14.4V for 30min absorption and then float at 13.5V.
to figure out if its perfectly top balanced you need to charge it to 14.8V or 3,65V and if the deviation directly after cut off is below 20mV then they are perfectly top balanced. If you don't reach that i highly recommend to charge to 14.4V with absorption and 13.4V as float to get it and keep it in balance.

Winston are always delivered perfectly matched cells and they are ultrastable till 8S configurations, so after a perfect top balance charging to 13.8V is ok as no balancing necessary. Thats different with other cells.

[s/v Jedi]

Good to see you on video again Rod

I have the same cells in a 8S setup, forgot the year I got them but never had to rebalance them yet. They are much more powerful than new LiTime batteries which must mean their internal resistance is lower.

[SaylorMade]

Originally Posted by CaptainRivet

Holy cow these epochs are way out of balance when they are at 14.1V and have 150mV.

With this chemistry you only see the balance of the cells and therfore its capacity in the upper knee from 13.8 to 14.6V. If they have 150mA at 14.1 then they have 250mv at 14.8V which is huge and need to be brought back to balance immediately before you damage them permanently (if not too late already).

Why would they be damaged?
It would just mean that some of the lower voltage cells will not get to the same SoC as the high voltage cells.
I assume here that, there is a BMS to keep any cell from getting above the set max voltage per cell.
But agree, they should be balanced to get the most capacity out of the pack.

[bgallinger]

Wow! I'm so impressed!

[rslifkin]

From what I remember, the Epoch batteries activate the passive balancer starting at something like 13.4V when charging. I'd expect that if you hold them around 14 - 14.2V for a while the imbalance should start getting smaller.

[jcapo]

Originally Posted by rslifkin

From what I remember, the Epoch batteries activate the passive balancer starting at something like 13.4V when charging. I'd expect that if you hold them around 14 - 14.2V for a while the imbalance should start getting smaller.

The balance start voltage is 13.6 and 10mv differential. I've watched to balancer work at voltages past 13.8 and the balancer doesn't seem to do much. Maybe I need to charge longer. Testing that today.

The BMS is a JBD 200A so several apps are available. I'm using the Overkill app that gives plenty of detail.

[CaptainRivet]

Originally Posted by jcapo

The balance start voltage is 13.6 and 10mv differential. I've watched to balancer work at voltages past 13.8 and the balancer doesn't seem to do much. Maybe I need to charge longer. Testing that today.

The BMS is a JBD 200A so several apps are available. I'm using the Overkill app that gives plenty of detail.

Yes to balance 250mV deviation will take days if not weeks with a passive balancer. Typically a balancer has max 200mA and 250mV deviation is typically about 1.5 till 2% of capacity means 200AH its 3 till 4AH imbalance.

You definitely need to charger higher to 14.4 and then 14.8V as the balancer need to make a proper top balance. I would also separate the 2 parallel batteries and treat each individually.
Either your battery has not been properly top balanced, you are using them.outside spec or you have a bad cell, time to find out.
I would write epoch and ask how to get them back ho balance, they know their cells best.

[jcapo]

Originally Posted by CaptainRivet

Yes to balance 250mV deviation will take days if not weeks with a passive balancer. Typically a balancer has max 200mA and 250mV deviation is typically about 1.5 till 2% of capacity means 200AH its 3 till 4AH imbalance.

You definitely need to charger higher to 14.4 and then 14.8V as the balancer need to make a proper top balance. I would also separate the 2 parallel batteries and treat each individually.
Either your battery has not been properly top balanced, you are using them.outside spec or you have a bad cell, time to find out.
I would write epoch and ask how to get them back ho balance, they know their cells best.

I charged today to 14.3 from about 50% SOC as shown by the Victron BMV. The cell voltage differential increased to 23mv on one battery and 17mv on the other with ~25A charge current to each battery. At 14.3 volts the current is less than 1A.

I must have read 15mv as 150mv a few weeks ago.

Just for grins I disabled charge and discharge and it took a bit over an hour to drop that 15mv imbalance to 5mv. The BMS uses a 150ma balance current, at least that's what the specs say.

There is a "Balance while charging" BMS setting that according to the Overkill docs when enabled balances only while charging. If disabled the balancer balances while charging and discharging. Apparently that applies only to the JBD 120A BMS. With this 200A BMS, disabling that setting balances only when there is no charge current and no discharge current. There are 'net recommendations to disable this setting but that gets you little or no balancing.

[wholybee]

Originally Posted by SaylorMade

Why would they be damaged?
It would just mean that some of the lower voltage cells will not get to the same SoC as the high voltage cells.
I assume here that, there is a BMS to keep any cell from getting above the set max voltage per cell.
But agree, they should be balanced to get the most capacity out of the pack.

You won't damage them. What will happen is that as they get further out of balance there will reach a point that one cell has an over voltage event and the BMS disconnects. There won't be damage to the cell (because the BMS protected from that) but while disconnected you will be unable to charge further, and thus won't be able to balance further. You will have to go through a long and time consuming process to balance the battery before you can use it again.

23mV is ok, but not great. Probably all you need to do is set the absorption voltage to 14.1V and use the battery as normal. After a month or so of getting to that voltage every day, it'll probably get a little better.