Lifepo4 battery too cheap?

[Tony1]

7 minutes ago, MtB said:

All this chat about float charging on lithiums is asking for trouble AIUI. As Nick says, one needs to STOP charging when any one cell gets up to 3.65V.

 

For the most comprehensive seemingly knowledgable article I've ever read about LiFePO4 batteries in boats, this chap is well worth reading. The link has not been posted on this forum for a while now so it's time it had another outing. 

https://nordkyndesign.com/protection-and-management-of-marine-lithium-battery-banks/

 

Li batts in boats still strike me as immature technology, mainly because Li batts like to be cycled over a wide range (not kept well charged like LA batts) and most Li users still seem to have the LA mentality engaged and write in ways that imply they keep their Li batts constantly charged. E.g. using a charger with a 'float' setting. One really should not be doing this. Charge them, then discharge them low before re-charging almost fully. Don't put them on float so they get recharged after a small discharge. 

 

What the boating world needs is some devices that monitor the SOC somehow and keep the charge sources disconnected until it falls to a low value, then reconnects until charged to a high SOC, then disconnects, etc etc. 

 

 

 

I would personally prefer no float stage- as you say that is a lead acid procedure that has been carried over and is not needed.

I do set my float to 13.15v, but I do get the impression that even then, the chargers are periodically trying to apply a very small charge, so I might reduce my float values down to 13.0 or even less. 

One of the things I like about my SoC-based charging management is that at 85% SoC, all the chargers are switched off (no float), and I have a suspicion that this allows the battery voltage to fall more naturally than if the charger is still awake, and is periodically prodding the battery to see what voltage its at.  

 

 

[IanD]

45 minutes ago, MtB said:

All this chat about float charging on lithiums is asking for trouble AIUI. As Nick says, one needs to STOP charging when any one cell gets up to 3.65V.

 

For the most comprehensive seemingly knowledgable article I've ever read about LiFePO4 batteries in boats, this chap is well worth reading. The link has not been posted on this forum for a while now so it's time it had another outing. 

https://nordkyndesign.com/protection-and-management-of-marine-lithium-battery-banks/

 

Li batts in boats still strike me as immature technology, mainly because Li batts like to be cycled over a wide range (not kept well charged like LA batts) and most Li users still seem to have the LA mentality engaged and write in ways that imply they keep their Li batts constantly charged. E.g. using a charger with a 'float' setting. One really should not be doing this. Charge them, then discharge them low before re-charging almost fully. Don't put them on float so they get recharged after a small discharge. 

 

What the boating world needs is some devices that monitor the SOC somehow and keep the charge sources disconnected until it falls to a low value, then reconnects until charged to a high SOC, then disconnects, etc etc. 

 

 

 

The bit in bold is why you really *do* need a BMS which monitors each cell, and is capable of top-balancing the bank -- batteries with good built-in BMS do this, as do high-quality external BMS, but not all do.

 

Given how rapidly cell voltage rises around 100% SoC, if you only measure the overall battery voltage and stop charging using this (e.g. at 14.6V) then if there's any cell imbalance this could be reached with one cell well above 3.65V (e.g. 3.8V) and the others below it (e.g. 3.6V). This shouldn't happen with well-matched Grade A cells (or most good quality drop-in batteries) but is definitely a risk with a DIY system or cheap no-name drop-ins.

 

Keeping the batteries at a high float voltage for long periods (e.g. 100% SoC or 14.6V) is *very* strongly advised against if you don't want to reduce their lifetime.

 

Another excellent source of LFP advice is here:

 

https://marinehowto.com/drop-in-lifepo4-be-an-educated-consumer/

https://marinehowto.com/lifepo4-batteries-on-boats/

Edited February 19, 2023 by IanD

[MtB]

12 minutes ago, IanD said:

Another excellent source of LFP advice is here:

 

https://marinehowto.com/drop-in-lifepo4-be-an-educated-consumer/

https://marinehowto.com/lifepo4-batteries-on-boats/

 

Ah yes, that's the other guy I read end-to-end a few years ago. I see he has now written a load more, thanks. 

 

His writing style alienates a lot of people but cut him some slack if you can manage it and persevere, the knowledge is well-worth the effort. He is American, but we all have our crosses to bear...

 

 

 

 

[nicknorman]

3 hours ago, n-baj said:

Thanks Nicknorman, I think it’s going to be a case of just playing around with the voltages and see what happens. I personally cannot see myself charging at 14.6v as I would like to be a little conservative. If I don’t use say the top 40ah in a 460ah battery and the battery lasts longer then so be it, I’ve coped fine with 480ah lead acids (probably not 480ah now) I’m only thinking of going for that 460ah battery as it’s the cheapest per ah.

One of the problems with Li is that you can’t easily charge to some desired SoC such as 90% by means of controlling the voltage. A voltage as low as 13.4v will get you to 99% eventually. It will just take longer than charging at 14.6v. So if for example you charge at 14.0v all the time you are out on a day’s cruise, then you will still be 99.9%SoC and you will still have been holding the battery there for hours, which is not good. If the charger uses timing to switch from bulk to float or off, then you have a problem if you stop for lunch and then restart with batteries already at 99%.

 

All of which is why I use the BMV712 SoC to control charging - having of course synchronised it at 100% from time to time. I can’t see any other way of doing it.

[n-baj]

2 hours ago, MtB said:

All this chat about float charging on lithiums is asking for trouble AIUI. As Nick says, one needs to STOP charging when any one cell gets up to 3.65V.

 

 

 

 

I’ll read the link thanks, however with regards to a float voltage I keep seeing lithium battery retailers quote a float voltage of 13.8v and the epever mppt manual has a 13.8v float voltage for lifepo4? Conversely Renology B2B has no float voltage for lithium?

 

I understand there’s no need for a float stage. I guess there’s talk of a float stage for lithium so they can be used with legacy charging systems or any electrical demand is met by the charging system, rather than the battery?

[nicknorman]

2 hours ago, MtB said:

All this chat about float charging on lithiums is asking for trouble AIUI. As Nick says, one needs to STOP charging when any one cell gets up to 3.65V.

…

Li batts in boats still strike me as immature technology, mainly because Li batts like to be cycled over a wide range (not kept well charged like LA batts) and most Li users still seem to have the LA mentality engaged and write in ways that imply they keep their Li batts constantly charged. E.g. using a charger with a 'float' setting. One really should not be doing this. Charge them, then discharge them low before re-charging almost fully. Don't put them on float so they get recharged after a small discharge. 

 

What the boating world needs is some devices that monitor the SOC somehow and keep the charge sources disconnected until it falls to a low value, then reconnects until charged to a high SOC, then disconnects, etc etc. 

 

Well I have to say that we do float the Li. When we are away from the boat the Combi voltage is set precisely to give around 50% SoC. There is some continuous drain from the GSM transceiver (50mA ) and the Empirbus (10mA or so) plus a mA or so for the BMS. Not a lot but it is about 1.5Ah a day. If we were to be away for several months it could add up…

 

I also float the Li when we are cruising, the alternator goes to a float voltage that matches the natural voltage of the Li at one of the specified SoCs (normally 80%) such that no current flows in or out. The advantage being that the alternator will supply up to full output to power a heavy inverter load such as the electric kettle, tumble drier etc.

 

I did have a design problem in that I can only set the alternator target voltage to a resolution of 0.1v so I had to aim slightly low. This means that the battery will slowly discharge under normal loads (fridge, lights, chargers etc), and once it has dropped 1% the alternator will go back to charge mode and put that 1% back in. So there is an element of slight discharges followed by charges. Whilst this doesn’t seem to be ideal, in fact I think that because as soon as we tie up on goes the 2kw kettle, the air fryer etc etc, the batteries get a good discharge before the next day’s cruising and so I think a few hours of dodging around 80-79-80% doesn’t matter. I think it would be different if we had solar and were not using the boat.

[MtB]

9 minutes ago, n-baj said:

I’ll read the link thanks, however with regards to a float voltage I keep seeing lithium battery retailers quote a float voltage of 13.8v and the epever mppt manual has a 13.8v float voltage for lifepo4? Conversely Renology B2B has no float voltage for lithium?

 

I understand there’s no need for a float stage. I guess there’s talk of a float stage for lithium so they can be used with legacy charging systems or any electrical demand is met by the charging system, rather than the battery?

 

No, thats not right. There is a need for NO float stage. The difference is too subtle for yer average human bean to appreciate the enormity of the difference, but I can see you're not normal  so you'll get it immediately.

 

Read and understand the links (give yourself a week to do this, at least) then you'll have found the somewhat complex answers to all your other questions above. 

 

 

[BEngo]

For  a battery reseller a float charge is a good thing.  They are not going to sell as many high cycle-life batteries without it! 

 

 

In truth the battery is OK with being floated, but not for long periods as it Will more or less slowly get to overcharge.  The lower the float voltage the better.   In practice, the makers expect most users will put some load on it and reduce the charge, before it is too long on float. The important things are to keep the voltage down,  ensure  the whole charge cycle does not  re-start until the battery is sufficiently discharged and for float never to be used as a storage or stand-by set up.  

 

N

 

 

[nicknorman]

13 minutes ago, n-baj said:

I’ll read the link thanks, however with regards to a float voltage I keep seeing lithium battery retailers quote a float voltage of 13.8v and the epever mppt manual has a 13.8v float voltage for lifepo4? Conversely Renology B2B has no float voltage for lithium?

 

I understand there’s no need for a float stage. I guess there’s talk of a float stage for lithium so they can be used with legacy charging systems or any electrical demand is met by the charging system, rather than the battery?

In my opinion 13.8v is much too high a voltage for floating. Just look at a chart of voltage vs SoC for Li. As I said earlier, 13.4 gives you 99%. So that would be the absolute maximum float voltage for me. But since holding an Li at full charge is a bad idea, I’d consider 13.3v the max float voltage.

 

You have to bear in mind that the people who say 13.8v don’t make the cells, they buy cells from china and package them up with a BMS etc. they are the same people that recommend charging at 14.6v. Ignore!

[Tony1]

 

Nick mentioned above the BMV712 battery monitor device from victron.

I think it won't be long before you get one of these, or something similar. 

You enter your battery capacity etc, and then you synchronise the battery monitor by charging the battery up to 100%. 

 

The monitor then measures all the current inputs and outputs, so it keeps a pretty accurate idea of how full your battery is. 

 

The thing is that you cant really rely on the resting battery voltage to tell you what the SoC is in the battery. 

For example, at 70% full the resting voltage will be around 13.20 (probably varies slightly depending on the battery). 

By the time the SoC gets down to say 40%, the voltage will be reading 13.10v.

 

So you can see that for a lot of the range, the battery voltage doesnt change much compared to the SoC, and thus the voltage cant really be relied on to inform you accurately about  the SoC. 

 

For this reason, I agree with Nick that its a very good idea to buy a battery monitor that measures current inputs and outputs. 

The accuracy does drift a bit over time, so its not gospel. And you should resynchronise every few weeks if you want it to stay really accurate.

But the point is that on a day to day basis,  using one of these monitors to check your SoC is much easier than trying to use the voltage. 

 

The victron BMV700 and BMV712 are well over £100, but there seem to be some much cheaper units available on Amazon, that do seem to get good reviews. 

 

 

 

[ditchcrawler]

1 hour ago, nicknorman said:

Well I have to say that we do float the Li. When we are away from the boat  

I switch both charge and discharge off on my battery with the BMS when I go home as I have no idea what my cheapo solar controller may do and I don't want the battery topping up the LA's natural discharge.

[MtB]

2 hours ago, BEngo said:

For  a battery reseller a float charge is a good thing.  They are not going to sell as many high cycle-life batteries without it! 

 

 

In truth the battery is OK with being floated, but not for long periods as it Will more or less slowly get to overcharge.  The lower the float voltage the better.   In practice, the makers expect most users will put some load on it and reduce the charge, before it is too long on float. The important things are to keep the voltage down,  ensure  the whole charge cycle does not  re-start until the battery is sufficiently discharged and for float never to be used as a storage or stand-by set up.  

 

N

 

 

 

 

But isn't that just the most impossible thing? 

 

Unless you are Nick, how will you ever get to use the full useable capacity of your Li batts if you keep them on a float charge? 

 

This has cropped up before IIRC and it all depends what one actually means by 'on float charge'. If you set your flost voltage so low they don't charge, then fine but don't call it "float charge" because that's not what its doing! 

[nicknorman]

45 minutes ago, MtB said:

… but don't call it "float charge" because that's not what its doing! 

I think you have just volunteered to invent the appropriate term!

[MtB]

9 minutes ago, nicknorman said:

I think you have just volunteered to invent the appropriate term!

 

SINK charge?

 

 

[rusty69]

9 minutes ago, nicknorman said:

I think you have just volunteered to invent the appropriate term!

I think he already did. A "flost" voltage. Float +lost =flost 

[MtB]

What we trail-blazing Li users really need is for Norman Enterprises to design and make an Li interface that keeps a charge source connected until the SoC rises to (say) 90%, then disconnects it and keeps it disconnected until the SoC has fallen to (say) 10%, then reconnects it until 90% is reached, then disconnect... etc. Ad infinitum. 

 

Or summink like that....

 

 

 

 

 

[Tony1]

2 hours ago, MtB said:

What we trail-blazing Li users really need is for Norman Enterprises to design and make an Li interface that keeps a charge source connected until the SoC rises to (say) 90%, then disconnects it and keeps it disconnected until the SoC has fallen to (say) 10%, then reconnects it until 90% is reached, then disconnect... etc. Ad infinitum. 

 

Or summink like that....

,

 

We already have a bit of kit for the job- its the BMV712 (although it was very much Mr Norman's advice that allowed me to set it up).

 

I've set my BMV712 so that when the battery SoC rises to the target value (usually 85%), the internal relay on the BMV712 sends a 12v signal to all the chargers via a very small gauge wire, and that tells them to switch off safely, rather than just disconnecting the charge cable, which sounds a bit 'heavy handed'.  

When the battery SoC falls to the appropriate level, the BMV712 sends another signal, and that will restart the charging units.

The victron and sterling chargers (including the MPPTs) have a port (called BMS), where you insert the wire.

Bish bosh, as they say. 

 

(Well almost bish bosh.

My shoreline charger doesnt have an input for a BMS remote switch off, so I have to rely on setting a charge voltage, but I'm very rarely on shore power so I can live with that. ) 

 

Edited February 19, 2023 by Tony1

[nicknorman]

51 minutes ago, MtB said:

What we trail-blazing Li users really need is for Norman Enterprises to design and make an Li interface that keeps a charge source connected until the SoC rises to (say) 90%, then disconnects it and keeps it disconnected until the SoC has fallen to (say) 10%, then reconnects it until 90% is reached, then disconnect... etc. Ad infinitum. 

 

Or summink like that....

 

This could be done, of course. However you are starting from a premise that I question.

Li cycle life seems to be based on the total Ah that can be extracted over the life of the battery. So for example you could have 5000 cycles at 50% DoD, or 2500 cycles at 100% DoD. The total Ah extracted being the same. Therefore if you force cycles on a Li battery unnecessarily, you are shortening its life unnecessarily.
There is some evidence that failing to cycle Li batteries over a long period of time can generate some sort of “memory effect” but it is reversible. And I suspect quite difficult to generate.

 

So on balance I think that supplying domestic needs from generated power (solar, or alternator on a long cruise) whilst holding a fairly high but not too high SoC is better than one charge and continuous discharge. Of course the ideal for a long day’s cruise would be to retain a mid SoC for most of the day, and then charge in the afternoon such that one reaches a fairly high SoC just as one ties up. I can do that to some extent but it does require a degree of clairvoyance to know when one is going to tie up. And remembering to do it!

[rusty69]

12 hours ago, MtB said:

What we trail-blazing Li users really need is for Norman Enterprises to design and make an Li interface that keeps a charge source connected until the SoC rises to (say) 90%, then disconnects it and keeps it disconnected until the SoC has fallen to (say) 10%, then reconnects it until 90% is reached, then disconnect... etc. Ad infinitum. 

 

Or summink like that....

 

 

 

 

 

I get the impression every man and his dog has lithium batteries on their boat now. I reckon the trailblazers are those that installed them 5 years ago. 

 

You just need to look on the 12V boating Facebook page to see hundreds of people adopting the hybrid approach and relying on the BMS and a long length of cable (unfused?) to do all the work. 

[MtB]

Hmmm... I can't clearly remember but I reckon it was at least four years ago I fitted my first Li batts! 

 

 

[rusty69]

1 minute ago, MtB said:

Hmmm... I can't clearly remember but I reckon it was at least four years ago I fitted my first Li batts! 

 

 

Sorry, that only make you a trailblazer I, not a trailblazer II. 

[MtB]

1 minute ago, rusty69 said:

Sorry, that only make you a trailblazer I, not a trailblazer II. 

 

A trail smoulderer, perhaps....

 

 

[rusty69]

2 minutes ago, MtB said:

 

A trail smoulderer, perhaps....

 

 

Maybe. 

 

The real question is whether the trailblazers original batteries are still in service 

[MtB]

59 minutes ago, rusty69 said:

Maybe. 

 

The real question is whether the trailblazers original batteries are still in service 

 

And is there an imaginary question to go with the real one? 

 

But the answer in my case is no, those from four years ago are no longer in service. The bod who bought the boat weirdly perceived me as some sort of technical wizard (gawd knows why) and the lithiums were part of my mystical unfathomable machinations and he wanted all trace of them removed before he collected the boat. So I have them here in my rain room at the hovel! 

 

He seemed to like my gas lights though and elected to keep those. 

 

 

[rusty69]

19 minutes ago, MtB said:

And is there an imaginary question to go with the real one? 

I'll see if I can think of one.