Overview of LiFePo4 batteries with "Full Charge Protection"

[Barking Sands]

I see many of the same discussions over and over regarding Full Charge Protection (FCP). Usually the conversation starts with "Why are my batteries discharging unevenly". To keep from typing a very long explanation over and over I have made this rather crappy video hoping to explain it. It also demonstrates a few other things for MOSFET based BMS's. This is especially critical when attempting direct alternator charging. Be sure to find out of the batteries you have your eye on DO NOT have FCP. It just leads to headaches. Unfortunately we are finding that more and more of the cheap Chinese brands have a BMS with FCP. Generally if you stick with a JBD BMS or JK BMS they will not have FCP. Also no Epoch batteries have FCP except the 460 V1. And if anyone has the Epoch 460V1 please contact me and I will help you remove it.

I just threw it together for discussion, but this is what I have come to understand what is going on. If anyone has anything to add or correct by all means. I think its important for everyone to understand that these batteries exist in the wild and the possible consequences they may bring.

If you have been following, Watt Cycle has attempted a fix via the app by adding a "parallel mode". They also attempted to say that this was a "design" choice. I am pretty confident it was not. The uneven discharge and see-saw effect is simply an unintended by-product of a "clever" bit of programming to add a voltage threshold>current threshold tail current> and time component to terminate the charge using other means than simple voltage thresholds from what I see. Couple that with some of the behavior of MOSFET based BMS's and you have a recipe for this odd behavior.

There are many models out there on Amazon and TEMU that have this. I have yet to see anyone disclose that a particular battery may have this. So buyer beware. Litime is one of the largest to employ this, but not all models do. Watt Cycle seems to have a fix but the jury may still be out. And many many other copies. Generally if you stay with a JBD or JK BMS they do not have this "feature".

One thing I have learned in dealing directly with Chinese Engineers is most have no idea what we do with these batteries as cruisers, boaters and RV'ers.

They see every battery and battery installation as a giant golf cart. A use case where the battery bank will be charged with something like one of those terrible golf cart chargers that terminate the charge at various parameters.

There are more and more of cheap drop in models that are being discovered to have FCP. And in the case of non-bluetooth models...you'd never even know it.

As seen in the other thread about the Arco Zues, batteries with FCP should be avoided at all cost for most cruisers and RV'ers that have a continuously cycled system. Having FCP compresses the safe operating envelope tremendously. And that is if you actually knew what the FCP criteria where. Many have not published them and it comes as a great surprise to the end user. Usually in the form of Multiplus voltage spikes or alternator damage or just simple uneven discharge of each battery in the bank.


1) Full charge protection and how it causes issues and why it happens
2) The reading and demonstrating of "ghost" bleed through voltage with the discharge mosfet off that confuses many.
3) That turning off the charge mosfet does in fact affect terminal voltage. This is true whether you manually do it or the BMS does it for "protections"

 

[CharlieJ]

Clear. Concise. Helpful.
Thank you.

 

[Delta Riverat]

I have verified this. Only happened when I used the RV charger with the Victron argofet. Never had the problem with the RV and the argodiode. The bigger voltage drop is good.

Yeah, I thought something was weird with the numbers and so I switched the battery switch from all to 1 and everything worked fine so I switched back to all and house 2 started charging at 10 amps with no charger. House 1 was in FCP for sure and loading it cleared the fault and all went back to normal.

So if your batts have this undesired feature make sure that you don't charge at "max" values.

 

[tpbrady]

Agree with Riverat’s recommendation. I charge LiTime 230AH to 95% by setting absorption to 14.1v and float to 13.5v. It never reaches FCP. Over the winter I set float to 13.2v which keeps them between 50-60% SOC.

 

[Barking Sands]

Agree with Riverat’s recommendation. I charge LiTime 230AH to 95% by setting absorption to 14.1v and float to 13.5v. It never reaches FCP. Over the winter I set float to 13.2v which keeps them between 50-60% SOC.

Yes that is the remedy. I lived with FCP batteries for over a year. Once it was known it was there and the charge settings modified appropriately its not too big of a deal.

The main problem is of course there is not a single manufacturer of batteries that contain FCP that also discloses the presence of FCP and the specific parameter to set FCP conditions. This has led to quite a bit of unnecessary wrangling and troubleshooting. And in some cases, destruction of equipment.

Watt Cycle finally has put up a blurb regarding FCP on their website, but it was after it was discovered and tons of users griped about it. Now they have a fix for it via an app setting for "parallel mode".

So this post of course is just for new buyers to try to find out if their desired batteries have FCP prior to purchases well as inform people who have FCP batteries already what to look for and how to deal with it.

 

[SteveK]

I have 8-Renogy 100Ah smart batteries. I chose them because they talk to each other via ethernet cable. They not only self balance they group balance. Or so the document say. The weak battery gets the charge while others stop accepting until they level out. They have FCP, no blue tooth, add on available. FCP that goes to float and does not accept more current, but otherwise the batteries come to life when needed.
I have an ethernet display that gives average volts, amps in/out & SOC from battery BMS, not the posts.
I compare that to my bluetooth/wifi shunt and it is the same reading. My other shunt in Parallel does not keep pace for some reason, but is right twice a day.

OK, I do not know what each cell of the battery is doing and do not care. Until switching to LFP I did not know my Magnum inverter chargers LFP program profile lets the battery determine float maintained at 13.5v. But on board I can see a load come on (Magnum remote display) and the charger supplies the needed amps for load
I look at my phone app and see 13.58v, 0.0 -1.0A changing/discharge. SOC 99-100% staying 800A most of the time when plugged to shore and away from boat.

 

[CharlieJ]

@SteveK
You are not doing your batteries a favor by keeping them at “99-100” SOC. You are reducing their service life. How much? No idea and maybe it is not a factor for you whether the batteries survive 4,000 cycles or 3,589 cycles before their C < 80% of the original C.

 

[SteveK]

@SteveK
You are not doing your batteries a favor by keeping them at “99-100” SOC. You are reducing their service life. How much? No idea and maybe it is not a factor for you whether the batteries survive 4,000 cycles or 3,589 cycles before their C < 80% of the original C.

Thanks Charlie, they only need to last my lifetime.

 

[CharlieJ]

True.

 

[ronobrien]

I see many of the same discussions over and over regarding Full Charge Protection (FCP). Usually the conversation starts with "Why are my batteries discharging unevenly". To keep from typing a very long explanation over and over I have made this rather crappy video hoping to explain it. It also demonstrates a few other things for MOSFET based BMS's. This is especially critical when attempting direct alternator charging. Be sure to find out of the batteries you have your eye on DO NOT have FCP. It just leads to headaches. Unfortunately we are finding that more and more of the cheap Chinese brands have a BMS with FCP. Generally if you stick with a JBD BMS or JK BMS they will not have FCP. Also no Epoch batteries have FCP except the 460 V1. And if anyone has the Epoch 460V1 please contact me and I will help you remove it.

I just threw it together for discussion, but this is what I have come to understand what is going on. If anyone has anything to add or correct by all means. I think its important for everyone to understand that these batteries exist in the wild and the possible consequences they may bring.

If you have been following, Watt Cycle has attempted a fix via the app by adding a "parallel mode". They also attempted to say that this was a "design" choice. I am pretty confident it was not. The uneven discharge and see-saw effect is simply an unintended by-product of a "clever" bit of programming to add a voltage threshold>current threshold tail current> and time component to terminate the charge using other means than simple voltage thresholds from what I see. Couple that with some of the behavior of MOSFET based BMS's and you have a recipe for this odd behavior.

There are many models out there on Amazon and TEMU that have this. I have yet to see anyone disclose that a particular battery may have this. So buyer beware. Litime is one of the largest to employ this, but not all models do. Watt Cycle seems to have a fix but the jury may still be out. And many many other copies. Generally if you stay with a JBD or JK BMS they do not have this "feature".

One thing I have learned in dealing directly with Chinese Engineers is most have no idea what we do with these batteries as cruisers, boaters and RV'ers.

They see every battery and battery installation as a giant golf cart. A use case where the battery bank will be charged with something like one of those terrible golf cart chargers that terminate the charge at various parameters.

There are more and more of cheap drop in models that are being discovered to have FCP. And in the case of non-bluetooth models...you'd never even know it.

As seen in the other thread about the Arco Zues, batteries with FCP should be avoided at all cost for most cruisers and RV'ers that have a continuously cycled system. Having FCP compresses the safe operating envelope tremendously. And that is if you actually knew what the FCP criteria where. Many have not published them and it comes as a great surprise to the end user. Usually in the form of Multiplus voltage spikes or alternator damage or just simple uneven discharge of each battery in the bank.


1) Full charge protection and how it causes issues and why it happens
2) The reading and demonstrating of "ghost" bleed through voltage with the discharge mosfet off that confuses many.
3) That turning off the charge mosfet does in fact affect terminal voltage. This is true whether you manually do it or the BMS does it for "protections"

I admit that I did not watch your video. I just wanted to add that I just came back from a 2 day Nigel Calder seminar in which he spoke of the battery arrangement being critical in the life/death of batteries. Some peoples issues may be that they have them "daisy chained" (if you hadn't already covered that). The seminar gets off into the weeds on some of the technology but ignoring the basics is a sure way to create problems that are then impossible to diagnose.

 

[Barking Sands]

I admit that I did not watch your video. I just wanted to add that I just came back from a 2 day Nigel Calder seminar in which he spoke of the battery arrangement being critical in the life/death of batteries. Some peoples issues may be that they have them "daisy chained" (if you hadn't already covered that). The seminar gets off into the weeds on some of the technology but ignoring the basics is a sure way to create problems that are then impossible to diagnose.

The daisy chaining can be a significant issue on load sharing. But the type of load sharing for batteries with FCP is on another level. For instance, you can have 60 amps coming out of one battery and 0 amps coming out of the one wired up in parallel right next to it. Batteries with bad daisy chained wiring will just have maybe a small % of load sharing difference depending on various factors.

 

[SteveK]

The daisy chaining can be a significant issue on load sharing. But the type of load sharing for batteries with FCP is on another level. For instance, you can have 60 amps coming out of one battery and 0 amps coming out of the one wired up in parallel right next to it. Batteries with bad daisy chained wiring will just have maybe a small % of load sharing difference depending on various factors.

OK, how do you suggest a bank should be wired?

 

[Barking Sands]

OK, how do you suggest a bank should be wired?

I think he was talking about daisy chaining batteries from nearest to farthest with the load carrying wires coming off the nearest battery. Which we all know is to be avoided.

For FCP load sharing issues it wouldn't matter how you wired it because unequal load sharing will be present in any configuration.

So I am just trying to make a distinction between two possible and unrelated causes of poor load sharing. I have seen people redo their perfectly fine wiring in an attempt to chase down an uneven load sharing issue when in fact it was FCP all along and no manner of wiring configuration would solve it.

So if you have unequal load sharing...the first step is to try to classify it to eliminate FCP as a possible cause before moving to wiring or wiring configuration. And that can generally be done just by observing the disparity and nature of the unequal load sharing. FCP load sharing is MUCH more drastic and cant be troubleshot with methods such as measuring voltage drop or resistances in the wiring circuit.

 

[Frosty]

@SteveK said:

"Ok, how do you suggest a bank should be wired"

Here is what I know. It has to do with pulling equally from all batteries. We're talking parallel connected bank here.

As @Barking Sands mentioned, what you *don't* want to do is wire all the batteries in parallel and then take the positive and negative off from the same battery (say the first one). This creates a scenario where the first battery gets used the most, the second gets less use, the third even less, etc.

With just two batteries in parallel, you can simply take the positive lead from one battery, and the negative from the other. This loads them equally.

You can still do that with a larger parallel bank, but then you are back to a certain degree of what you get in the "don't do this" example (though not as bad).

The best way (with more than two batteries in parallel) is to either have equal length positive cables all going to a bussing point (or wherever suits your installation). And then equal length negative cables (though the positive and negative sets do not have to be the same lenght). (In this method, due to placement of batteries in a bank, some cables will likely have a little coil of "extra" length in order to make them match.)

A variation on that is to have a couple of long bus bars (pos and neg) and the battery cables lead directly to those, then other cables take off from the bus bars to the rest of the system.

 

[luna]

And there I thought daisy chaining was reserved for wiring loads like light fixtures or receptacles.

Don't we use Series and Parallel when talking about battery wiring? Which of these 2 would be daisy chaining numerous batteries together?

 

[SteveK]

And there I thought daisy chaining was reserved for wiring loads like light fixtures or receptacles.

Don't we use Series and Parallel when talking about battery wiring? Which of these 2 would be daisy chaining numerous batteries together?

Series is adding voltage, parallel is keeping the voltage the same

 

[SteveK]

@SteveK said:

"Ok, how do you suggest a bank should be wired"

Here is what I know. It has to do with pulling equally from all batteries. We're talking parallel connected bank here.

As @Barking Sands mentioned, what you *don't* want to do is wire all the batteries in parallel and then take the positive and negative off from the same battery (say the first one). This creates a scenario where the first battery gets used the most, the second gets less use, the third even less, etc.

With just two batteries in parallel, you can simply take the positive lead from one battery, and the negative from the other. This loads them equally.

You can still do that with a larger parallel bank, but then you are back to a certain degree of what you get in the "don't do this" example (though not as bad).

The best way (with more than two batteries in parallel) is to either have equal length positive cables all going to a bussing point (or wherever suits your installation). And then equal length negative cables (though the positive and negative sets do not have to be the same lenght). (In this method, due to placement of batteries in a bank, some cables will likely have a little coil of "extra" length in order to make them match.)

A variation on that is to have a couple of long bus bars (pos and neg) and the battery cables lead directly to those, then other cables take off from the bus bars to the rest of the system.

OK, so not a daisy chain, equal lengths to buss bar is optimal, theoretically. But the gain according to many that have studied it is minimal compared to taking positive from one end and negative from the other, which involves daisy chain in between batteries.

 

[DDW]

If you use large cable and keep them short, the difference is quite small. Just went through that exercise on 3 parallel batteries. With two or four batteries there are cabling schemes that are theoretically perfect, but not for three (except the equal length cables to bus bars). I was considering three 300AH batteries connected with short 4/0 cables, and drawing 600A from the bank. The theoretical difference in voltage is about 0.007 volts, with positive taken from one side and negative from the other. About double that if done "wrong". Due to other uncertainties you probably cannot actually achieve that with any scheme, so I chose to ignore it.

 

[Frosty]

I did the "take from opposite ends" approach to my set of three AGM batteries wired in parallel (so theoretically the middle battery never got used as hard). Every year or two I would rotate a couple batteries so the middle battery changed. That seemed to work out fine.

I haven't had a three-battery bank setup yet with LFP, so haven't needed to decide about that. (With two have just made the wires equal length to the regular bus bars.)

@luna I think we are exclusively talking about parallel-wired banks here -- or at least I was. I don't think any of the described setups are actually "daisy chaining" (as to my mind that would = Series or you might say nose-to-tail wiring like a chain of elephants).

 

[luna]

I would agree, daisy chaining would be the equivalent of a series connection. So if it already has a name, why don't we just call it a Series connection?

 

[SteveK]

I would agree, daisy chaining would be the equivalent of a series connection. So if it already has a name, why don't we just call it a Series connection?

"Series" is already spoken for as connecting positive to negative to increase voltage like we did with 6V golf cart batteries in series/parallel to get a 12V bank

 

[luna]

Ok, fine.

Then please explain using the 2 available terminals on any battery, how you would wire a daisy chained connection.

 

[Frosty]

Ok, fine.

Then please explain using the 2 available terminals on any battery, how you would wire a daisy chained connection.

I think @ronobrien is the one who mentioned "daisy chained" in reference to a seminar comment. He hadn't watched the video that @Barking Sands made for this thread.

Perhaps this ping to him will have him come back and he can go into more detail about why he mentioned "daisy chained." That said, I think everyone else in the thread is referring to parallel wired battery banks.

 

[luna]

I'm not so sure. Here is someone else using the term.

The daisy chaining can be a significant issue on load sharing. But the type of load sharing for batteries with FCP is on another level.

All I am doing is trying to understand the meaning of the term. Is it any different than Series or Parallel or Series/Parallel? And if so how is it different? Can you provide a wiring diagram of a daisy chained battery circuit?

 

[luna]

And yet another. All in the same day.

What is this daisy chain?

But the gain according to many that have studied it is minimal compared to taking positive from one end and negative from the other, which involves daisy chain in between batteries.

 

[Barking Sands]

I dont think "daisy chain" is a technical term. I am basically talking about the practice of wiring batteries as seen here. Which is the least desirable.

 

[SteveK]

In electrical and electronic engineering, a daisy chain is a wiring scheme in which multiple devices are wired together in sequence or in a ring,[1] similar to a garland of daisy flowers.

 

[Barking Sands]

A quick search and it seems the term is used loosely on a regular basis. Apparently even things generally associated with daisy chain like comm cables tend to be parallel. I suppose for the purpose of battery discussion best keep it to parallel and series, and in this case we are just talking the various parallel configurations.

But the main gist was that uneven discharge of parallel batteries with power taken off one end, or even poor crimps and connections is minor when compared to uneven discharge of a parallel set of batteries stuck in FCP. Really when in FCP is not really uneven discharge. Its no discharge at all for a long period in most cases.

You can actually see that here in this old video, The video is queue'd up to demonstrate FCP in the first gen Epoch batteries.

 

[Frosty]

But the main gist was that uneven discharge of parallel batteries with power taken off one end, or even poor crimps and connections is minor when compared to uneven discharge of a parallel set of batteries stuck in FCP. Really when in FCP is not really uneven discharge. Its no discharge at all for a long period in most cases.

Geez, when "protection" goes bad. Glad you (and others) managed to identify that and get rid of it on the Epoch batteries + at least warn people about it with other batteries.

 

[luna]

I suppose for the purpose of battery discussion best keep it to parallel and series, and in this case we are just talking the various parallel configurations.

My sentiments exactly.