Lithium Batteries installation

[rusty69]

6 minutes ago, nicknorman said:

For my caravan battery (which is left unattended without significant power drain for days or weeks at a time), I have set the solar to 13.9v with very short absorption time, and float of 13.25v hoping that that is not going to result in the battery being held “up the knee” too far every day. But it is not ideal because when I am using the caravan in summer, it will take longer to recharge at that voltage.

Shirly one would just increase the absorption voltage in the summer months, and disconnect the solar when not in use. Unless you need it for your caravan bilge pump perhaps.

[dmr]

I'm not going to contribute to this thread anymore (for a while at least) as I predict its going to vanish quite soon and my words will be wasted.

Maybe we should have a new thread where the lithium experts share their knowledge and experience without the insults.

[Guest]

16 minutes ago, nicknorman said:

For my caravan battery (which is left unattended without significant power drain for days or weeks at a time), I have set the solar to 13.9v with very short absorption time, and float of 13.25v hoping that that is not going to result in the battery being held “up the knee” too far every day. But it is not ideal because when I am using the caravan in summer, it will take longer to recharge at that voltage.

 

Out of interest what controller do you have in the 'van?

 

Ours is in no way manually adjustable, It's a Sargent that came with the 'van when new.

 

 

Edited February 16 by MJG

[IanD]

10 minutes ago, dmr said:

I'm not going to contribute to this thread anymore (for a while at least) as I predict its going to vanish quite soon and my words will be wasted.

Maybe we should have a new thread where the lithium experts share their knowledge and experience without the insults.

 

Great idea. But how do we stop the usual agents provocateurs repeating what they've done to this one, and so many others? 😞

Edited February 16 by IanD

[nicknorman]

3 minutes ago, rusty69 said:

Shirly one would just increase the absorption voltage in the summer months, and disconnect the solar when not in use. Unless you need it for your caravan bilge pump perhaps.

My point was a general one and not specifically all about me(!) - the point being that charging to a specified limit voltage (which is what solar controllers do) can result in either under or over charging. The latter being more of an issue for Li. Of course it is not an issue for LA.

 

But to continue with my particular issue I have a 100Ah Li battery and a 100W solar panel. So even in summer on a sunny day (in Scotland) it only is likely to charge at about 5%C and in winter much slower, 1%C if I’m lucky!

 

In winter I use it to run the telly and Sat box and the electric blanket for Friday evening and Saturday evening. So that probably takes out 40% of capacity. Meanwhile it may get between zero and 5% back in during the day in winter. So I leave on Sunday with it quite low and hope that when I return on Friday evening it will be replenished - otherwise I need to get the genny going. Then as we move towards spring, it gets more charge each day and at some point - varying each week according to the weather, it is going to get to 100% during the week and I am going to be using much less power of an evening. So there is a risk of it being overcharged.

 

All of which is simply to say that solar controllers are not optimised to Li charging.

[GUMPY]

21 minutes ago, nicknorman said:

Having thought about this a bit more, I can see a problem. Li doesn’t like to be overcharged. As we know, the correct way to fully charge Li is to charge to 3.65v /cell and hold that voltage until the current falls to 5%. Then disconnect.

If you hold the voltage 3.65 with the current below 5%, you are still adding charge to a battery that is already at 100% of its design capacity. Aka overcharging, which risks Li plating and accumulating permanent damage.

 

With solar, the charge rates can be very low especially in winter or if you have a large bank and small panel. Certainly less than 5%. Let’s us hypothesise at 2% charge in winter - eg 4A for a 200Ah battery.

 

If your solar controller is set to charge to 3.65v/cell (14.6v) then by the time you reach 14.6v, the battery has been overcharged just the same as if you charged at 50%C to 3.65v and then waited for the current to fall to 2%C. And of course it has been held “up the knee” for a long time. Which will shorten its life. It will probably still last many years, but not as many as if you hadn’t overcharged it.

 

So even with solar, correctly charging Li is not easy.

 

For my caravan battery (which is left unattended without significant power drain for days or weeks at a time), I have set the solar to 13.9v with very short absorption time, and float of 13.25v hoping that that is not going to result in the battery being held “up the knee” too far every day. But it is not ideal because when I am using the caravan in summer, it will take longer to recharge at that voltage.

Which is why I switched off my solar controller when the battery reached 100%  mainly because the BMS on the Fogstar doesn't recognise current below 1amp and often that's all the solar is putting out in winter. With a maximum draw of 0.5A it will be a while before it needs recharging.

[rusty69]

4 minutes ago, nicknorman said:

My point was a general one and not specifically all about me(!) - the point being that charging to a specified limit voltage (which is what solar controllers do) can result in either under or over charging. The latter being more of an issue for Li. Of course it is not an issue for LA.

 

But to continue with my particular issue I have a 100Ah Li battery and a 100W solar panel. So even in summer on a sunny day (in Scotland) it only is likely to charge at about 5%C and in winter much slower, 1%C if I’m lucky!

 

In winter I use it to run the telly and Sat box and the electric blanket for Friday evening and Saturday evening. So that probably takes out 40% of capacity. Meanwhile it may get between zero and 5% back in during the day in winter. So I leave on Sunday with it quite low and hope that when I return on Friday evening it will be replenished - otherwise I need to get the genny going. Then as we move towards spring, it gets more charge each day and at some point - varying each week according to the weather, it is going to get to 100% during the week and I am going to be using much less power of an evening. So there is a risk of it being overcharged.

 

All of which is simply to say that solar controllers are not optimised to Li charging.

What you need is a LA in parallel with a switch between.That way, you can leave the solar to charge the LA whilst isolating the partially charged lithium. When you return, charge the LI from the LA. Sorted.😂

[nicknorman]

10 minutes ago, MJG said:

 

Out of interest what controller do you have in the 'van?

 

Ours is in no way manually adjustable, It's a Sargent that came with the 'van when new.

 

 

Not totally sure, I think it is an epever PWM controller. Very cheap, but it has the interface for the MT50 display which can be used to adjust all the settings.

 

I have been thinking of getting an MPPT controller but there is not a huge advantage when the Vmp of the panel is only around 16v

[GUMPY]

14 minutes ago, MJG said:

 

Out of interest what controller do you have in the 'van?

 

Ours is in no way manually adjustable, It's a Sargent that came with the 'van when new.

 

 

I have a Victron 75/10 mppt controller

Fully programmable if you know what you are doing😉

[Guest]

10 minutes ago, GUMPY said:

I have a Victron 75/10 mppt controller

Fully programmable if you know what you are doing😉

 

I think that is why ours is what it is as most people (caravanners) don't and just leave it to 'do it's own thing', which it does. I'm also not sure how it works in conjunction with the on board charger.

 

I did once ask Sargent about swapping the unit for something more 'adjustable' and got a bit of a vague response as to whether I could swap it or not. Along the lines of 'well it might work but it also might not'.

[GUMPY]

2 minutes ago, MJG said:

 

I think that is why ours is what it is as most people (caravanners) don't and just leave it to 'do it's own thing', which it does. I'm also not sure how it works in conjunction with the on board charger.

 

I did once ask Sargent about swapping the unit for something more 'adjustable' and got a bit of a vague response as to whether I could swap it or not. Along the lines of 'well it might work but it also might not'.

My on board charger has also been replaced with a Victron. Both chargers are independently wired and the originals disconnected so they can be put back when I sell it. 

[IanD]

16 minutes ago, GUMPY said:

Which is why I switched off my solar controller when the battery reached 100%  mainly because the BMS on the Fogstar doesn't recognise current below 1amp and often that's all the solar is putting out in winter. With a maximum draw of 0.5A it will be a while before it needs recharging.

 

What voltage does the Fogstar call 100% SoC?

 

3.65V/cell (14.6V for a 12V battery) is rather higher than recommended nowadays to routinely cut off charging in day-to-day use, 3.55V (14.2V) is a more normal figure. If you ever want to top balance the cells -- which is rarely if ever needed with a bank built from matched cells -- then a slightly higher voltage is needed, some (e.g. marinehowto) recommend 3.6V/cell (14.4V), some still use 3.65V/cell (14.6V).

 

Mine (REC-BMS 48V) always turns the MPPT controllers off (100% SoC) at 3.55V/cell (56.8V), at which point all the cell voltages are the same.

[nicknorman]

3 minutes ago, IanD said:

 

What voltage does the Fogstar call 100% SoC?

 

3.65V/cell (14.6V for a 12V battery) is rather higher than recommended nowadays to routinely cut off charging in day-to-day use, 3.55V (14.2V) is a more normal figure. If you ever want to top balance the cells -- which is rarely if ever needed with a bank built from matched cells -- then a slightly higher voltage is needed, some (e.g. marinehowto) recommend 3.6V/cell (14.4V), some still use 3.65V/cell (14.6V).

 

Mine (REC-BMS 48V) always turns the MPPT controllers off (100% SoC) at 3.55V/cell (56.8V), at which point all the cell voltages are the same.

3.60v/cell I think. ie that is the BMS disconnect voltage. Which is perhaps a little cautious but probably a good thing.

[IanD]

7 minutes ago, nicknorman said:

3.60v/cell I think. ie that is the BMS disconnect voltage. Which is perhaps a little cautious but probably a good thing.

I'd have thought that 100% SoC would normally be defined as a bit lower voltage (e.g. 3.55V) than the disconnect voltage (e.g. 3.65V), if you take "100% SoC" as the point that the batteries are routinely charged to -- otherwise there's no way to do top balancing should you want to, and you don't want to take the voltage high enough to do this regularly, only occasionally when needed.

 

Maybe this is difficult to do for Fogstar since it's a drop-in and doesn't control external charging sources, but it's what I'd expect an LFP installation to do.

Edited February 16 by IanD

[rusty69]

12 minutes ago, IanD said:

I'd have thought that 100% SoC would normally be defined as a bit lower voltage (e.g. 3.55V) than the disconnect voltage (e.g. 3.65V), if you take "100% SoC" as the point that the batteries are routinely charged to -- otherwise there's no way to do top balancing should you want to, and you don't want to take the voltage high enough to do this regularly, only occasionally when needed.

 

Maybe this is difficult to do for Fogstar since it's a drop-in and doesn't control external charging sources, but it's what I'd expect an LFP installation to do.

I was under the impression the Fogstar BMS could be set with user defined parameters, so If top balancing is required, the voltage settings can be altered. Though I thought you said earlier with well matched cells that have already been properly balanced, it wouldn't need doing.

 

 

Edited February 16 by rusty69
Only one L in balanced. What a Balls up

[GUMPY]

1 minute ago, rusty69 said:

I was under the impression the Fogstar BMS could be set with user defined parameters, so If top balancing is required, the voltage settings can be altered. Though I thought you said earlier with well matched cells that have already been properly ballanced, it wouldn't need doing.

 

 

You can't change the BMS settings on the Fogstar, can't remember offhand what it actually shuts down at.

[rusty69]

Anyway, a question for you Lithium experts. I have since recently had the tail current function settings on my Victron mppt controllers set to off. I just turned it on with a 1% of nominal capacity setting of 3A.

 

Is this:

 

A}Right

B} Wrong

C} There is no right or wrong or

D} Nobody gives a shit?

 

7 minutes ago, GUMPY said:

You can't change the BMS settings on the Fogstar, can't remember offhand what it actually shuts down at.

They must have changed it since I asked the guy at fogstar then, because he said it could.That was with a JBD BMS.

 

Quote from Fogstar when I asked in 2022:

Quote

Thanks for the email - We understand the need to configure the BMS. Changing the settings will not invalidate the warranty - breaking the battery by changing the parameters may.
 
We have had customers who do not understand batteries, fiddle with the settings, and disable safety measures of the BMS. Unfortunately, we can't cover this under warranty. 
 
Kind Regards,

 

Edited February 16 by rusty69

[Naughty Cal]

43 minutes ago, MJG said:

 

I think that is why ours is what it is as most people (caravanners) don't and just leave it to 'do it's own thing', which it does. I'm also not sure how it works in conjunction with the on board charger.

 

I did once ask Sargent about swapping the unit for something more 'adjustable' and got a bit of a vague response as to whether I could swap it or not. Along the lines of 'well it might work but it also might not'.

A friend of ours has an Autotrail motorhome that it equipped with a load of Sargent gear. He has had a bit of a nightmare when trying to upgrade to Victron equipment as various parts of the system now refuse to "talk" to the Victron kit meaning parts of his control panel and systems panel now just don't work. They have yet to find a work around for this despite talking to both Sargent and Victron.

 

We have just installed a new Victron MPPT solar controller and thankfully our CBE kit will happily interact with it. Got a new Victron battery charger to fit as well in the next week or so. 

[nicknorman]

14 minutes ago, GUMPY said:

You can't change the BMS settings on the Fogstar, can't remember offhand what it actually shuts down at.

The BMS settings can be changed, but you are prevented from doing so by needing the password. I think Fogstar will give you the password but will also note that your warranty will be invalidated for anything to do with cell problems arising from over or undercharge.

[magnetman]

I still think the option of putting a resistor between alt and bat is interesting.

 

If this could somehow be made to do hot water...

Car hifi forums could be worth reading.

[nicknorman]

51 minutes ago, IanD said:

I'd have thought that 100% SoC would normally be defined as a bit lower voltage (e.g. 3.55V) than the disconnect voltage (e.g. 3.65V), if you take "100% SoC" as the point that the batteries are routinely charged to -- otherwise there's no way to do top balancing should you want to, and you don't want to take the voltage high enough to do this regularly, only occasionally when needed.

 

Maybe this is difficult to do for Fogstar since it's a drop-in and doesn't control external charging sources, but it's what I'd expect an LFP installation to do.

It might even be 3.55, I can’t remember. On the other hand since they specify 14.4v as the charge voltage, it’s probably 3.60v.

 

On my own system I use 3.65v as the start of the alarm, I think 3.70 is the disconnect voltage, but since I only charge to 14.3v for a 100% charge (and that is only done once a month) these higher voltages should never be reached. Balancing is triggered if a cell goes over 3.60v but the balancing continues for a calculated period of time regardless of what the charge voltage subsequently is - ie even if the system stops charging. However in the past year, balancing has not been triggered.

 

Again we are up against the issue of whether the BMS disconnect is used routinely as the charge control, or whether it is there as an emergency backup disconnect.

35 minutes ago, rusty69 said:

Anyway, a question for you Lithium experts. I have since recently had the tail current function settings on my Victron mppt controllers set to off. I just turned it on with a 1% of nominal capacity setting of 3A.

 

Is this:

 

A}Right

B} Wrong

C} There is no right or wrong or

D} Nobody gives a shit?

 

They must have changed it since I asked the guy at fogstar then, because he said it could.That was with a JBD BMS.

 

Quote from Fogstar when I asked in 2022:

 

Wrong. I would make it 5%. Assuming the system can charge at over 15A. Although it also depends on what voltage settings you have set.

Edited February 16 by nicknorman

[Guest]

29 minutes ago, Naughty Cal said:

A friend of ours has an Autotrail motorhome that it equipped with a load of Sargent gear. He has had a bit of a nightmare when trying to upgrade to Victron equipment as various parts of the system now refuse to "talk" to the Victron kit meaning parts of his control panel and systems panel now just don't work. They have yet to find a work around for this despite talking to both Sargent and Victron.

 

We have just installed a new Victron MPPT solar controller and thankfully our CBE kit will happily interact with it. Got a new Victron battery charger to fit as well in the next week or so. 

 

Thanks. I think I will give it a miss. I was wanting to get towards a situation where I could remotely monitor the battery without having to resort to using Swift's awful Command system which never worked properly when I did subscribe.

[IanD]

44 minutes ago, rusty69 said:

Anyway, a question for you Lithium experts. I have since recently had the tail current function settings on my Victron mppt controllers set to off. I just turned it on with a 1% of nominal capacity setting of 3A. Is this A)Right B} Wrong c} There is no right or wrong or D} Nobody gives a shit?

They must have changed it since I asked the guy at fogstar then, because he said it could.That was with a JBD BMS.

Victron don't recommend using a tail current for LFP batteries -- do Fogstar? From the MPPT manual:

 

Default settings for LiFePO4 batteries
The default absorption voltage is to 14.2V (28.4V) and the absorption time is fixed and set to 2 hours. The float voltage is
set at 13.5V (27V). Equalization is disabled. The tail current is set to 0A, this so that the full absorption time is available
for cell balancing. The temperature compensation is disabled and the low temperature cut off is set to 5. These settings are
the recommended settings for LiFePO4 batteries, but they can be adjusted if the battery manufacturer specifications advise
otherwise.

Edited February 16 by IanD

[Naughty Cal]

4 minutes ago, MJG said:

 

Thanks. I think I will give it a miss. I was wanting to get towards a situation where I could remotely monitor the battery without having to resort to using Swift's awful Command system which never worked properly when I did subscribe.

What heating system do you have?

 

Our Truma Combi 6E is hooked up to the Truma I Net system. You can remotely monitor battery voltages, van temperature, water temperature and remotely control the heating and hot water.

[nicknorman]

16 minutes ago, IanD said:

Victron don't recommend using a tail current for LFP batteries -- do Fogstar? From the MPPT manual:

 

Default settings for LiFePO4 batteries
The default absorption voltage is to 14.2V (28.4V) and the absorption time is fixed and set to 2 hours. The float voltage is
set at 13.5V (27V). Equalization is disabled. The tail current is set to 0A, this so that the full absorption time is available
for cell balancing. The temperature compensation is disabled and the low temperature cut off is set to 5. These settings are
the recommended settings for LiFePO4 batteries, but they can be adjusted if the battery manufacturer specifications advise
otherwise.

This is presumably because the charger doesn’t know the battery current. Charging to a specified voltage without regard to the current results in potentially a very large variation in final SoC depending on the relationship between charger output and battery capacity. Certainly with a 2 hour absorb time the current is going to have fallen way off so the battery will be fully charged even if charged at a high C rate, but holding the voltage up at 14.2 for about 1:45 longer than necessary is not optimal. The battery may be slightly over charged.

 

As we have said, unless there is something wrong with the cells, they do not go out of balance so even with a crappy BMS that needs the voltage to be held up whilst balancing is taking place, in practice there will be no balancing going on during the 2 hours.

 

Victron don’t make cells. They just assemble batteries. So they, like so many other people, have adapted their LA chargers to roughly suit LiFePO4. Sub optimal!

 

Edited February 16 by nicknorman