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

[Maine Sail]

Originally Posted by nebster

But the worst thing of all was the mistake of putting multiple dual-bus batteries in parallel and allowing/encouraging the user to switch on or off the batteries individually. Once any one of those batteries gets out of sync with the others in terms of SOC, then the paralleled-dual-contactor design falls over: a battery going high opens its charge bus relay, but leaves its discharge relay connected. That discharge relay is paralleled with all the other discharge relays... but on the other happy batteries, their discharge relays and charge relays are still both closed. So the charger can continue to charge the battery whose BMS has tried to shut it down, by feeding back through the other batteries' busses.

Glad I am not the only one who was horrified by that system... To say I was shocked at the installation and execution would be an understatement. I tried to explain to the owner why the "ON/OFF' switches, one for each battery, were a bad idea and why it was problematic but he did not really understand it. If I had more time I would have dug into the system more but he was enroute and we had only about 6 hours for us to examine it, try to make a diagnosis and some quick tweaks. At least he went away with a better understanding of his system than even the battery manufacturer gave him. He was starving for info and yet no one could explain the magic to him. I hope the entire RV world is not like this but this was supposed to be a real "Lexus" of the RV world.



*Disclaimer: I am not an RV guy so he may have been yanking my chain..

Originally Posted by nebster

On many models, a lead-acid battery was added in parallel with the lithium batteries to try to put a stop to the BMS-based destruction of the alternators (because the regulator was not implemented/programmed correctly, as MaineSail describes). That lead acid buffer battery wreaked havoc with the UI for the power system, keeping things running when you'd expect them not to, underpowering a big inverter with a tiny battery for a few minutes at shutdown, and on and on.

He did not have the buffer battery. I tried to talk him into a simple low v-drop isolator, had a Mastervolt with me just in case, connected to the cranking battery to absorb a transient but he got nervous about that and needed time to "mull it over".

Originally Posted by nebster

Basically the system was an absolute boondoggle made only slightly better through some iterative improvements in a few of the components. It is a textbook demonstration of how Not to build a mobile power system.

I honestly felt terrible for the guy. He worked his whole life to retire and buy this supposedly high end RV, and it was a disaster. It had literally ruled his every move forcing him to essentially bounce around North America from RV dealer to RV dealer for problem solving.

This RV was billed as the be-all-end-all of RV quality and it was pretty horrific. I would not even put it in the same level as a the lowest end pontoon boat in terms of quality build especially when related to the electrical system. If that thing floated, I would not have set foot on it. It was loaded with the cheapest Chinese made no-name gear, cheap vinyl, panels that did not fit right, batteries located so they were continually kicked with road debris, sand, salt and water and on and on...

I suspect the RV industry could learn some from the marine industry and that is saying something because the marine industry is not very representative of much in the way of quality and reliability either.

With a few tweaks and changes to that battery/BMS it could be decent but not the way they executed or implemented the system design.

[Maine Sail]

Originally Posted by anthem00

I was always under the impression that the brown wire was a orderly shutdown and the power wire (red) was instantaneous. But Balmar techs said, even the power to the regulator, you need to wait 6 seconds to be safe and avoid damaging the alternator.. . Thats what I was getting at. So i've programmed my delay to be 10 seconds upon receiving a HVC before disconnecting the charge bus.

I think they were just being over cautious. Still, it's a good idea to have a delay and also to use the red wire vs. brown, if your BMS does not allow for a delay.

[JmanC]

Originally Posted by john61ct

Please don't put words in my mouth, I do not believe that.

Nope I did not put words in your mouth you are making up stuff seeing what you want to see.
I was agreeing that it's along the lines of moronic, and that further from all that I have read (online stuff mainly) i believe will cause more problems than it will solve. I sure will not be charging my dropin every cycle to balancing voltages vs occasionally, just because someone else tells me that is what they are designed for. Not without realworld longterm testing.

[JmanC]

Originally Posted by john61ct

So far I have not seen any "memory effect"; perhaps the above variations in the charge-termination setpoints prevents it. Note also that my capacity benchmark protocol **requires** going to much higher than usual voltage/SoC, a great example of the classic Heisenberg / observer effect - testing to determine the state of the system, in itself alters that state.

That is absolutely not an example of the uncertainty principle, if that is what you are saying. And when you word it like that you make it sound like the UP & observer effect are the same or similar, when they are completely utterly different things most of the time.

[john61ct]

Just an analogy.

My main point is just that, doing regular capacity testing,

which is required in order to detect any "memory effect" issues,

will likely be an effective prophylactic if done regularly, preventing any such issues from manifesting.

And I apologize if I misinterpreted what you stated you were agreeing with.

[CatNewBee]

Originally Posted by JmanC

I always thought going into the shoulders simply ages the battery slowly overtime reducing capacity. And that imbalance problems in shoulders are more from high discharge/charge rates. Maybe not an issue when charging at just 0.3C? Also ambient temps/climates may be a big factor, with people getting much longer life in cold climates.

I agree the BMS dropin balancing is going to cause more longterm damage that any good it will do, but that's life. These are built to a price for the laymen with just a few years real warranty.

No, the real problem is the cell resistance, that varies with SOC. What happens is pretty simple to explain.

Consider the cells as a series of resistors with different slightly values. The higher the resistance, the bigger the voltage drop, resulting in more heat production.

Resistance is Voltage drop divided by Current, power (heat) is Voltage * Current, since current is constant in a string of resistors, the cells with lower resistance will accept the charge better, than the cells with higher resistance, they will produce some more heat instead of charging, so they will drift, also will show a higher voltage.

When you charge partially, imbalances will be amplified over the time, no matter if you go into the shoulders or not, you simply will not notice it, because you will think, the couple of millivolt difference are acceptable. One day you will wonder why your capacity between the shoulders has gone and you may blame memory effects, in fact part of the problem is one cell is full and another is half empty. Also ageing of the cells will be different, the one that always get charged to full may age faster than the one that remains in the middle, the cells on the bottom may get damaged or age faster too due too frequent deep discharge.

Ideal is if all cells remain at the the same SOC, age the same way and die together. Then you have all the time the optimal capacity available.

That is also the reason, serious manufacturers recommend a BMS, that balances the cells and keeps them balanced with each charge.

Bottom balancing is not practical for every day use, it means always fully discharge the cells before recharging. Deep cycling shortens the life span too.

[john61ct]

Originally Posted by CatNewBee

Ideal is if all cells remain at the the same SOC, age the same way and die together. Then you have all the time the optimal capacity available.

That is only possible in reality, if EoL is defined at a still-high SoH.

Even starting with new well-matched top-notch quality cells,

once they are well worn, but **long** before "death",

a bank's cell will inevitably be at a significantly different resistance and capacity.

So yes, more frequent balancing does eventually, inevitably, become necessary.

But that does not imply "a BMS" is required.

What is required, are **the functionalities** implemented,

whether fully & well, or poorly / partially,

in various devices marketed as such.


> Bottom balancing is not practical for every day use, it means always fully discharge the cells before recharging.

I agree there are plenty of reasons to prefer top-balancing, but that specific claim is absolute balderdash & poppycock.

Bottom balancing just requires that charge termination is based on the first cell to hit the HV setpoint, rather than on the pack/bank overall voltage.

[CatNewBee]

Originally Posted by john61ct

That is only possible in reality, if EoL is defined at a still-high SoH.

Even starting with new well-matched top-notch quality cells,

once they are well worn, but **long** before "death",

a bank's cell will inevitably be at a significantly different resistance and capacity.

So yes, more frequent balancing does eventually, inevitably, become necessary.

But that does not imply "a BMS" is required.

What is required, are **the functionalities** implemented,

whether fully & well, or poorly / partially,

in various devices marketed as such.


> Bottom balancing is not practical for every day use, it means always fully discharge the cells before recharging.

I agree there are plenty of reasons to prefer top-balancing, but that specific claim is absolute balderdash & poppycock.

Bottom balancing just requires that charge termination is based on the first cell to hit the HV setpoint, rather than on the pack/bank overall voltage.

BMS is not required, you can run batteries without. You even do not need to care about SOC. Just charge, use them as long as it takes and dispose them when dead. This is how the LiPo batteries in power tools work.

[john61ct]

Originally Posted by CatNewBee

Just charge, use them as long as it takes and dispose them when dead.

My post was within the context of getting maximum longevity. That is generally the case, I have no interest in those "care free" kind of usage patterns.

That is why, if you do buy assembled LFP batteries that include "a BMS", it is important that a replacement BMS can easily be swapped out.

Not only if its limitations turn out to not be suitable for your needs, but also since they do often fail long before the cells wear out.

Originally Posted by CatNewBee

This is how the LiPo batteries in power tools work.

Actually, the toolpack batteries often have small chip-based BMS internally.

Apparently, some even have cycle loggers, record unauthorised usage to prevent warranty scammers,

and their chargers' controls can be pretty sophisticated.

Ryobi's a great source for quality 18650 type cells, e, g, Sony (actually Murata) VTC6, not LiPo but specifically LiNiMnCoO2 chemistry, aka NMC, or INR.

But none of this is relevant for House banks on a boat, much too high risk of thermal runaway.

[nebster]

Originally Posted by CatNewBee

Bottom balancing is not practical for every day use, it means always fully discharge the cells before recharging. Deep cycling shortens the life span too.

It might not be practical for you. But let's not go too far.

[evm1024]

Originally Posted by john61ct

My post was within the context of getting maximum longevity. That is generally the case, I have no interest in those "care free" kind of usage patterns.

SNIP

I think it is fair to say that the majority if not all cruisers are NOT interested in getting the theoretical maximum longevity out of their LiFePO4 house banks. (or LA bank for that matter) In short, cruisers Do have an interest in those "care free" kind of usage patterns. The discussion of getting a theoretical maximum lifetime for a house bank, which may be enjoyable to some, yet is so removed from reality, or experience that it has no practical use.

Simply put: Cruising is a maintenance intensive activity and the more "care free" my house bank is the better.

In my case I am after an acceptable cost house bank that has an acceptable life span that requires as little as reasonable of my time to keep healthy and just plain works.

If I were to choose between a care free bank that lasts 5 years or a bank that requires significant time to keep healthy and lasts 8 years you can guess my answer.

I'll take the 5 year bank any time. Oh, wait - I've got 5 years on my LiFePO4 bank already. Even with B grade cells I am happy with the banks performance lost capacity or not. Chasing theory is basically a waste of my time.

That of course is just my opinion.

[newhaul]

All I'm sure of I will not need new batteries for at least 20 years . Just need to set my solar controller to 14.45 once a month for the day to top balance my bank . And all is good .should not have any loss of capacity issues . Everything g else is just noise that clutters up the passing of knowledge.

[john61ct]

I don't think there **is** a "theoretical" maximum for cycle life, unless I suppose where calendar aging becomes the more significant factor.

Unlike most other battery market segments, the quality manufacturers commonly **understate** both shipped Ah capacity and lab-tested lifetime cycles.

Both due to their focus on high C-rate use cases as discussed above, gentler House storage being such an outlier.

Yes, if manufacturer spec'd lifetime cycles are sufficient for you, then just charge to their spec, say Absorb voltage of 3.65V, for 4S 14.6V, holding to endAmps of .01C, or whatever you think best.

Presumably then the balancing circuitry delivered by even (IMO poorly designed) standard-cheap BMSs will work every cycle.

I am committed to "the cause" of extending lifetime cycles far past mfg ratings, while still drawing down to high DoD when needed, rather than doing so by oversizing the bank.

I at least want to **know** as much as possible about how to get optimum lifespan; I think well over 10,000 cycles is achievable, until calendar life issues and factors ambient temperature, start to dominate.

I may not actually want or be able in all use cases to **implement** the necessary requirements, but I want to "not-do" so consciously, not out of ignorance.

This is the context of the "for longevity" qualifier I try to remember to use.

WRT "regular boaters" buying LFP banks, I think only packaged systems remove enough risk of total loss of the very costly required investment due to a mishap.

The "bare cells plus protective systems selected & installed by owner" approach I favour is a pretty challenging commitment to a steep and fraught learning curve.

[evm1024]

Originally Posted by john61ct

I don't think there **is** a "theoretical" maximum for cycle life, unless I suppose where calendar aging becomes the more significant factor.

SNIP %<

I'm just at a loss for where you are coming from. It appears to be a classic ELIZA response. But that is just how it appears to me.

By my understanding you stated that you were posting with the goal of the maximum longevity...

Originally Posted by john61ct

My post was within the context of getting maximum longevity.

...And not in terms of actual usage.

And again, theoretical maximum longevity discussions are just not part of my world view or my needs. But of course that is just me.

[john61ct]

Which Eliza, Pertigkiozoglou?

Of course I mean actual usage.

For example, disconnecting the bank from Floating charge sources while they continue to carry ongoing loads.

Given today's mainstream systems currently on the market, many here say "impractical" or " too hard!" In reality it is easy to do if you want to, especially with a setup where only the main protective BMS-functionality is automated.

If full "carefree" automation is desired, then a higher level of tech literacy is required to implement that goal and also retain a high level of secure reliability.

Charging to a lower than maximum setpoint, or ensuring a higher than minimum LVC are **very** easy to implement, require no special skills.

Similarly avoiding charging when batteries get below freezing.

What if someone in a cold climate were to say, gee that seems hard, I'll just take my chances?

Few BMS offer such protection, yet I would not personally consider it optional.

There isn't a sharp B&W line duality here between "I want longevity" and ¯\_(ツ)_/¯

It's all grey-scale judgement calls.

Taking a slop-jar attitude to even the critical risk factors is all fine and good, but I'm pretty sure those owners won't be using the same bank in twenty years.