Overview of LiFePo4 batteries with "Full Charge Protection"

[tpbrady]

I saw this effect with 3 LiTime batteries in parallel. However it seemed to be self correcting a short time after the batteries started discharging. When the charging source was removed one or two of the bank would start discharging and within 30 minutes the third would be discharging. Within a few hours the SOC on all three would be within a couple % of each other. Once I configured the charging sources to keep the bank out of FCP, I never saw this behavior again.

LiTime doesn’t think this is a problem. Their DC-DC chargers would always push the battery into FCP. Pushing it into FCP wasn’t a problem since once the charging source was removed a single battery would always assume the load. The problem was a parallel bank where they wouldn’t all come on line at the same time to assume the load.

Tom

 

[SteveK]

@Barking Sands Your video showed FCP. So what have you done to prevent it from occurring again? I saw 14.4V absorb, did you reduce that setting and did it avoid FCP.

ETA: How are the two batteries wired. Equal cable to buss bar or pos to pos, neg to neg and opposite end load cables?

 

[Barking Sands]

@Barking Sands Your video showed FCP. So what have you done to prevent it from occurring again? I saw 14.4V absorb, did you reduce that setting and did it avoid FCP.

ETA: How are the two batteries wired. Equal cable to buss bar or pos to pos, neg to neg and opposite end load cables?

Keep in mind that video is about 2 years old. It was on the old v1s. To Epochs credit we did share the details for FCP in the V1 and published it on the website for best practices for V1 owners. We knew that the criteria for FCP was:
-14.0 and above activation threshold
- current falling below 3.5 amps
-for 10 seconds

So everyone that had V1s was instructed to set absorption to 13.8 or 13.9 and then cycle as normal. Now on my personal V1s I was able to change the three settings to push them out of the way so FCP was no longer even activated and the battery just operated with standard voltage thresholds such as 14.7 pack and 3.7 cell limits.

For a year or so I have had the v2s. And V2s or any Epoch battery no longer have anything close to FCP. In addition, the V2 battery Victron comms just work so the SOE threshold is maintained. But in recent times it appears the number of batteries using FCP has exploded when it should have shrunk to nothing. It seems like the number of people posting about unequal discharge is just rising daily. And many times the advice given is to check your wiring. So, an enormous amount of time may be wasted with users redoing and reconfiguring their wiring when in reality the only thing they need to do is lower their absorption voltage on ALL charge sources to stay just under FCP activation threshold. That works just fine and cycling is smooth.

And as I mentioned the first step to deciding whether a person's particular issue with uneven discharge is FCP or wiring is to look at the nature of the uneven discharge. FCP should be easy to spot since its so drastic as seen in the video. In addition...the charge mosfets will remain off for the battery not discharging. This is how to spot it. From there, ruling FCP in/out as a cause will dictate the next steps.
1) if FCP set charge parameters accordingly to avoid FCP, clear FCP and then cycle as normal
2) if its not FCP, address uneven discharge via traditional troubleshooting of checking configuration, crimps. clean surfaces etc.

 

[SteveK]

I was wondering if voltage readout is accurate or internal battery FCP is below settings for bulk and absorb.
Lowering charge V below 14 is a solution to avoid being near the trip into FCP.
That makes me wonder if readout is less than expected for the many having this issue.

 

[Barking Sands]

I was wondering if voltage readout is accurate or internal battery FCP is below settings for bulk and absorb.
Lowering charge V below 14 is a solution to avoid being near the trip into FCP.
That makes me wonder if readout is less than expected for the many having this issue.

Thats a good question. And it also depends on how good the charger is. When absorption voltage is reached will the charger clamp down on voltage and current quickly or will there be some overshoot. Thats why in the case of the V1 we stated 13.8 or 13.9. Some chargers could do 13.9. In the case of Victron MMPT where you can set absorption to 2 decimals some users would even set 13.9. On other chargers such as that Heart Interface it would overshoot by a tenth and some users reported slight overshoot on various pieces of equipment. Or their system had some kind of compensation such as temp compensation that they didnt account for that would cause voltage to hit just above the set absorption voltage and thus the threshold for FCP. In those cases we would say 13.8 for additional margin.

FCP can be a pain. So those who have it need to know details to mitigate it. And those about to buy should just avoid.

 

[SteveK]

As an example I have two inverters with two remotes. One remote I noticed reads higher voltage, only 0.1-0.2V confirmed by switching remotes. So I change my preferences to accommodate that on one remote. Even then it has not been an FCP problem.

 

[Barking Sands]

It really only matters what the battery/BMS sees. So I guess a direct measurement with a good meter at battery terminals in absorption would be best. But if you arent hitting FCP then no harm. To be clear, I used FCP batteries for around 2 years without issue, running very smoothly. So if you have them its not a deal killer. You just have to do the set up accordingly.