LiFePO4 battery capacity.

[Peanut]

Following from the thread on Lithium batteries, “memory”.

 

I am advised that my FLA batteries shouldn't be discharged below 50% to get the best life from them so that I have only half of the advertised capacity.
Now, I am told that the superior LiFePO4 batteries should be kept between 20% and 80% charge.  If so, then only 60% of the capacity is routinely usable.
I know that FLA's are heavy, and take an age to achieve full charge, but now I wonder whether the significant additional cost and complexity of a LiFePO4 installation would really justify the small increase in real-world capacity.

Maybe, Gel or AGM batteries would be a better investment, giving a longer life and faster charging than the FLA's, and the only a change being to the charging profile.

 

 

[MtB]

17 minutes ago, Peanut said:

Following from the thread on Lithium batteries, “memory”.

 

I am advised that my FLA batteries shouldn't be discharged below 50% to get the best life from them so that I have only half of the advertised capacity.
Now, I am told that the superior LiFePO4 batteries should be kept between 20% and 80% charge.  If so, then only 60% of the capacity is routinely usable.
I know that FLA's are heavy, and take an age to achieve full charge, but now I wonder whether the significant additional cost and complexity of a LiFePO4 installation would really justify the small increase in real-world capacity.

Maybe, Gel or AGM batteries would be a better investment, giving a longer life and faster charging than the FLA's, and the only a change being to the charging profile.

 

 

 

 

The main benefit of LiFePO4 batteries is they recharge to 80% (or whatever you decide) so quickly, whereas any of the LA battery types take many hours to recharge to the mandatory 100% for reasonable battery life. They also last effectively indefinitely is treated correctly while LAs need replacing every few years.

 

They do however need careful and intelligent management, a bit like owning a thoroughbred racehorse Vs a regular dobbin. 

 

 

[BEngo]

He advantage of Li is not just a little more useable capacity.  It is the ability to put in the  'useable' 240 Ah of 400 at  pretty well constant current. So if your power source  will hack it you can recharge in 2 1/2 hours. Li will also not mind if you stop at 50% go away for week and come back and recharge.  Try either of those on LA and you are going to be disappointed.

 

N

Edited September 15, 2022 by BEngo

[Peanut]

I hear of Gel and AGM's, when looked after, lasting ten and more years. Not the cheapest ones, of course. Compared to FLA's they require little extra maintenance, and take charge better, but not like Li batteries.

There is a significant initial cost to Li batteries, and the upgrades needed to the installation.  Not saying Li's don't have advantages, weight and fast charging, but at a cost.

[BEngo]

Like everything else in life, where there is a course, there is a horse for it.  It is of course true that  Shergar,  Dobbin or Red Rum you will find that a lot of crap comes with your horse!

 

If you are an off-grid CC liveaboard then the advantages of Li, max solar and engine backup are probably what you need.  A good Li set up is neither cheap nor simple though.

 

OTOH if you are a marina moorer with a grid connection who gets one two week holiday a year, likes to boat from dawn to dusk and has a very low power usage boat you may find that LA batteries abd engine charging will meet all your needs.  There will be many mechanics who understand at least the basics of this sort of system, and they can be relatively cheap

 

There is a range of options in between (and out to the sides too)  and only the boater's analysis can pick the right one.

 

N

Edited September 15, 2022 by BEngo

[nicknorman]

1 hour ago, Peanut said:

Following from the thread on Lithium batteries, “memory”.

 

I am advised that my FLA batteries shouldn't be discharged below 50% to get the best life from them so that I have only half of the advertised capacity.
Now, I am told that the superior LiFePO4 batteries should be kept between 20% and 80% charge.  If so, then only 60% of the capacity is routinely usable.
I know that FLA's are heavy, and take an age to achieve full charge, but now I wonder whether the significant additional cost and complexity of a LiFePO4 installation would really justify the small increase in real-world capacity.

Maybe, Gel or AGM batteries would be a better investment, giving a longer life and faster charging than the FLA's, and the only a change being to the charging profile.

 

In my opinion the 80/20% thing is a myth. Firstly, it is quite difficult to charge to 80% unless you have a reliable means to both measure the SoC and to then stop charging at that point. The battery voltage at 70%, 80%, or 90% is virtually identical so you can’t do it by voltage. If you do it using an Ah counter like a BMV712 then it drifts out of sync over time and so you need to charge to near 100% to resynchronise, say every 2 weeks to a month. Similarly, on discharge you can get below 10% before there is noticeable reduction in voltage.

 

IMO the main point is to avoid routinely going a long way “up the knee” or “down the knee”. As it happens I did a full charge last night (boat has been on shore power float at around 50% for the past month) and even at 95% SoC, the voltage was only just creeping above 13.6v (3.4v per cell). I would say you can easily use 80% capacity without going anywhere near the knee.

 

The other thing to bear in mind is that Ah is not a measure of energy. The energy from a certain number of Ah is a function of the voltage. Since Li voltage remains up at 13v at a low SoC when a LA battery would be at 12.0v, you get more energy per Ah with Li. And under heavy load the Li keeps the voltage much higher.

Edited September 15, 2022 by nicknorman

[DaveP]

I'd also add that the 20-80% regime is also based on long-term cycling, ie the battery is held below or above these limits for many weeks to kill it.  Liveaboards will be cycling on a daily basis, so a wider range can be used.  I've been using a pair on 200ah TN Power drop-ins for 2.5years now with my solar banging them to 100% most days over 9 months of the year and in winter getting down to 30% SoC.  I haven't found _any_ dimunition in capacity yet....

 

[MtB]

20 minutes ago, DaveP said:

I'd also add that the 20-80% regime is also based on long-term cycling, ie the battery is held below or above these limits for many weeks to kill it.  Liveaboards will be cycling on a daily basis, so a wider range can be used.  I've been using a pair on 200ah TN Power drop-ins for 2.5years now with my solar banging them to 100% most days over 9 months of the year and in winter getting down to 30% SoC.  I haven't found _any_ dimunition in capacity yet....

 

 

 

So how are you determining 100%, please?

 

3.4v per cell? AH counting in and out? Or something else?

 

Thanks.

 

 

[DaveP]

17 minutes ago, MtB said:

 

 

So how are you determining 100%, please?

 

3.4v per cell? AH counting in and out? Or something else?

 

Thanks.

 

 

14.4v (3.6v/cell), held for 10min by the mppt, then floated at 13.6v (3.4v).  I also have a wh counter which shows about 2% inefficiency in charging.

 

Screenshot of yesterday, look at behaviour just after 1pm when the batteries hit full...

 

Edited September 15, 2022 by DaveP

[MtB]

51 minutes ago, DaveP said:

Screenshot of yesterday, look at behaviour just after 1pm when the batteries hit full...

 

 

Very interesting, thanks! What app is generating this display? One which came with the batteries I imagine....

 

 

[DaveP]

1 minute ago, MtB said:

 

Very interesting, thanks! What app is generating this display? One which came with the batteries I imagine....

 

 

Nope; batteries have no comms.  MPPT (Epever) and shunt (pzem017) data polled over modbus, fed into a mysql database on a Pi over wifi. Grafana runs queries on that and displays on a webpage. Glued together with some Python -  also does sms alerting/reporting.

[IanD]

3 hours ago, DaveP said:

I'd also add that the 20-80% regime is also based on long-term cycling, ie the battery is held below or above these limits for many weeks to kill it.  Liveaboards will be cycling on a daily basis, so a wider range can be used.  I've been using a pair on 200ah TN Power drop-ins for 2.5years now with my solar banging them to 100% most days over 9 months of the year and in winter getting down to 30% SoC.  I haven't found _any_ dimunition in capacity yet....

 

High-quality LFP batteries with proper BMS matched to the battery (e.g. BMS LVL 15.4) have guaranteed lifetime specified in MWh (e.g. 47MWh, which is 3000 cycles from 0% to 100% or 5000 from 20% to 80%) and are tested over the SoC full range. The key is not to spend long periods continuously at 100% or 0%, but cycling out to these limits regularly is no issue.

Edited September 15, 2022 by IanD

[nicknorman]

5 hours ago, DaveP said:

Nope; batteries have no comms.  MPPT (Epever) and shunt (pzem017) data polled over modbus, fed into a mysql database on a Pi over wifi. Grafana runs queries on that and displays on a webpage. Glued together with some Python -  also does sms alerting/reporting.

@MtB Haha well you did ask!

3 hours ago, IanD said:

High-quality LFP batteries with proper BMS matched to the battery (e.g. BMS LVL 15.4) have guaranteed lifetime specified in MWh (e.g. 47MWh, which is 3000 cycles from 0% to 100% or 5000 from 20% to 80%) and are tested over the SoC full range. The key is not to spend long periods continuously at 100% or 0%, but cycling out to these limits regularly is no issue.

Of course 3000 cycles at 100% DoD is exactly the same total Wh extractable as 5000 cycles at 60% (80-20%), just in case anyone missed the point.

Edited September 15, 2022 by nicknorman

[MtB]

7 hours ago, DaveP said:

Nope; batteries have no comms.  MPPT (Epever) and shunt (pzem017) data polled over modbus, fed into a mysql database on a Pi over wifi. Grafana runs queries on that and displays on a webpage. Glued together with some Python -  also does sms alerting/reporting.

 

I knew that really....

 

But well impressed actually! Can you make me one too please? I'll buy you a pint.

[DaveP]

1 hour ago, MtB said:

 

I knew that really....

 

But well impressed actually! Can you make me one too please? I'll buy you a pint.

Too late; I left the village last week!  May (should) be back in the Spring...

 

Soz.

 

[And the software is in no way ready for release into the wild; and the hardware assembly will probably give any engineer palpitations.]

Edited September 15, 2022 by DaveP

[IanD]

5 hours ago, nicknorman said:

@MtB Haha well you did ask!

Of course 3000 cycles at 100% DoD is exactly the same total Wh extractable as 5000 cycles at 60% (80-20%), just in case anyone missed the point.

That's exactly the point, and how the batteries are specified -- the manufacturer quotes a lifetime based on total energy throughput, and they don't care how you do it -- lots of small SoC cycles, or fewer big ones. Basically LFP batteries don't much care how you treat them (depth of charge * number of cycles) so long as you don't abuse them ("floating" at 100% SoC for long periods, or sitting discharged at 0% SoC).

 

So long as you do this there really isn't any problem cyclically charging LFPs all the way up to 100% and discharging all the way down to 0% -- assuming your BMS *really* understands what "100%" and "0%" mean... 😉

 

(which is an advantage for battery manufacturers who understand how their batteries behave and do the BMS themselves, and rather more difficult for everyone else...)

Edited September 15, 2022 by IanD

[cuthound]

On 15/09/2022 at 08:31, Peanut said:

I hear of Gel and AGM's, when looked after, lasting ten and more years. Not the cheapest ones, of course. Compared to FLA's they require little extra maintenance, and take charge better, but not like Li batteries.

There is a significant initial cost to Li batteries, and the upgrades needed to the installation.  Not saying Li's don't have advantages, weight and fast charging, but at a cost.

 

The Lifeline AGM's on my boat are now 15 years old and down to about 50% of there original capacity, but still meet my needs.

 

They are not cheap however (especially since Brexit, even though they come from the USA) and mine are  6 volt, so four of these. I suspect LifePo batteries now cost about the same.

 

https://www.tayna.co.uk/marine-batteries/lifeline/?ordering=&A-8=6&A-22=220

 

[MoominPapa]

22 hours ago, IanD said:

High-quality LFP batteries with proper BMS matched to the battery (e.g. BMS LVL 15.4) have guaranteed lifetime specified in MWh (e.g. 47MWh, which is 3000 cycles from 0% to 100% or 5000 from 20% to 80%) and are tested over the SoC full range. The key is not to spend long periods continuously at 100% or 0%, but cycling out to these limits regularly is no issue.

At some point,  I can't remember exactly when, but certainly over a year ago, I added code to my BMS to keep a running total of charge and discharge. It's currently at ~30000Ah, so assuming average battery voltage of 13v, that's 0.39MWh. I think these batteries are going to last a long time.

 

Interestingly, either there's a small zero offset, or I've invented a perpetual motion machine, the exact figures are charge: 29947.02Ah and discharge: 30934.53Ah.

 

MP.

[Tony1]

 

I can't back this up with any hard data, although hopefully the lithium experts will be able to do so: 

I've found that the lithiums seem to accept solar charge more readily than LAs. So whatever the panels can produce, will go into the batteries.

It didnt feel like that was always the case with my old  LAs (although to be fair I did sort of break them in my ignorance).  

 

It could be argued that with good quality 100Ah lithiums now on the market for around £500, and with them likely to last a decade (depending on usage and care taken), maybe the price difference over a ten year period is not that great. 

 

The other thing worth a mention is that if you also go for 1000watts or more of solar panels, you can get hot water on most days during the summer, and there is a saving there in terms of engine hours, wear and tear, diesel fuel, and servicing costs. 

As an example, my engine was last serviced 9 months ago, and its done about 150 hours since then. Without the lithiums and the solar panels, those hours would probably be doubled. I sometimes see boaters running engines for 3 hours and more in the winter to recharge LA batteries, and there's a significant cost with that. 

 

 

 

[1st ade]

2 hours ago, MoominPapa said:

the exact figures are charge: 29947.02Ah and discharge: 30934.53Ah.

Rounding error somewhere? Charge rounded down (at the n'th decimal place) and discharge rounded up?

 

Apologies if you have already thought of this.

[nicknorman]

4 hours ago, cuthound said:

 

The Lifeline AGM's on my boat are now 15 years old and down to about 50% of there original capacity, but still meet my needs.

 

They are not cheap however (especially since Brexit, even though they come from the USA) and mine are  6 volt, so four of these. I suspect LifePo batteries now cost about the same.

 

https://www.tayna.co.uk/marine-batteries/lifeline/?ordering=&A-8=6&A-22=220

 

If you buy bare LiFePO4 cells from china you can get 230Ah at 12v (well, 13v really) delivered to the door for £650. So a good bit cheaper, but of course you then need all the gubbins to go with it - BMS, charge control etc.

Edited September 16, 2022 by nicknorman

[Tony1]

38 minutes ago, nicknorman said:

If you buy bare LiFePO4 cells from china you can get 230Ah at 12v (well, 13v really) delivered to the door for £650. So a good bit cheaper, but of course you then need all the gubbins to go with it - BMS, charge control etc.

 

The problem with this cost comparison thing is that its hard to compare like with like in the real world.

I say that because anyone building their own 230Ah lithium battery and seeking advice here would go looking for a BMS of about £50-100 (I think one example given here was from Daly), because they would rightly think the extra features in the dearer BMS's would be worth paying extra compared to the cheaper ones you can get. 

If I were doing it now, I would probably build my own- after all there is a wealth of knowledge and super-helpful people such as yourself on this forum.  

If you were to opt for two cheap BMS's, at say £40 each, that gives you a battery bank of 2x230 including the BMS's for about £1400, which is amazing really. 

Add on £50 for a pair of battery boxes, cable, and copper bars, and you're still under £1500 for 460Ah. 

Even if you add on a piece of 16mm sq cable as a current limiter, plus a victron battery monitor at about £130 (which I imagine will be part of most new installs), you're still in at well under two grand for the lot.

I'm surprised more people aren't tempted tbh.

 

 

Edited September 16, 2022 by Tony1

[cuthound]

36 minutes ago, nicknorman said:

If you buy bare LiFePO4 cells from china you can get 230Ah at 12v (well, 13v really) delivered to the door for £650. So a good bit cheaper, but of course you then need all the gubbins to go with it - BMS, charge control etc.

 

So £1300 for 460Ah, which leaves £700 for a BMS and charge controller.

 

I reckon by the time the capacity of my AGM's has dwindled to below what I find acceptable (we rarely stay in one place longer than overnight) I should be able to get a fully functional 460Ah battery with BMS and charge controller for less than replacing the Lifelines.

 

If I settle for 230Ah then it should be much cheaper.

Edited September 16, 2022 by cuthound
Clarification

[Tony1]

5 minutes ago, cuthound said:

 

So £1300 for 460Ah, which leaves £700 for a BMS and charge controller.

 

I reckon by the time the capacity of my AGM's has dwindled to below what I find acceptable (we rarely stay in one place longer than overnight) I should be able to get a fully functional 460Ah battery with BMS and charge controller for less than replacing the Lifelines.

 

If I settle for 230Ah then it should be much cheaper.

 

I guess another option would be 3x100Ah batteries- and they'd be easier to lug around too. 

The cheapest way would be to build your own, but those Sterling lithium batteries at £500 do look a steal at the moment, and I think the BMS on them will probably be half decent. 

 

 

[Col_T]

I don’t actually have lithiums, and am probably unlikely to ever get them, but out of curiosity a question regarding Ah counting on lithium batteries, specifically LiFePO4 batteries.

 

Possibly / probably wrong, but I thought that the Ah counting inaccuracies on LA batteries was due to their internal resistance, which meant that significantly more charge current was needed to replace the current taken by the loads. This then accounted for the ‘drift’, SoC vs voltage, seen by Ah counting devices . Given that lithium batteries have much lower internal resistance than LA batteries, which is why they charge so much more quickly(?), wouldn’t this mean that Ah counting is a viable means of determining SoC on lithium batteries?