Lithium Batteries installation

[GUMPY]

57 minutes ago, nicknorman said:

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.

Yes this is what I should have said.

But if you don't have the password...........

[IanD]

26 minutes ago, nicknorman said:

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!

 

 

True, but it's difficult to see what you can do better with a third-party drop-in LFP which doesn't talk to the MPPT (or alternator, or charger...) to control charging, via a controller like the Cerbo or similar -- or the same function running inside charger/inverter combos like the Multiplus/Quattro. The key is communication and having the BMS "in charge".

 

Which is of course what Victron recommend (battery BMS controls charging voltage and current) and what both my boat and yours do, because it's the optimum solution... 🙂

Edited February 16 by IanD

[nicknorman]

7 minutes ago, IanD said:

 

True, but it's difficult to see what you can do better with a third-party drop-in LFP which doesn't talk to the MPPT (or alternator!) to control charging, via a controller like the Cerbo or similar (or the same function inside charger/inverter combos like the Multiplus/Quattro).

 

Which is of course what Victron recommend (battery BMS controls charging voltage and current) and what both my boat and yours do, because it's the optimum solution... 🙂

Well it wouldn’t be too hard to link a Victron charger with something that measures battery current such as their BMV712 or Smartshunt. Then the charger would know when to stop charging (when the input to the battery fell to 5%C).

 

By the way, I checked the Fogstar recommended charge profile, they use EVE cells and have this to say about charging them - the ubiquitous 0.05C aka 5%C again.

Edited February 16 by nicknorman

[Guest]

1 hour ago, Naughty Cal said:

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.

 

Alde wet system. The Swift 'Command system was supposed to do all that remote monitoring stuff allowing you to look at what was going on with the battery, activate the heating remotely , check the fridge etc etc.

 

But it was just pants. 

Edited February 16 by MJG

[GUMPY]

18 minutes ago, nicknorman said:

Well it wouldn’t be too hard to link a Victron charger with something that measures battery current such as their BMV712 or Smartshunt. Then the charger would know when to stop charging (when the input to the battery fell to 5%C).

Problem for me is that the 75/10 mppt controller only takes voltage and temperature, over the VE smart network,  from the smart Shunt not current 😟

 

[rusty69]

1 hour ago, nicknorman said:

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.

Ok. Thanks. The absorbtion is usually set between 13.9 and 14.1 Volts for a 10 minute duration. So, if I want to use the tail current setting, it should be set to 5% of my 280Ahr LI + 100 Ahr LA bank = 19 A, or 5 % of 280Ahr = 14A? The chargers are capable of 30A each, and there are 2.

1 hour 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.

Thanks. Yes, I remember reading that just before I put my own settings in. Dunno what fogstar recommend, I don't have one of their batteries or cells (yet).

[nicknorman]

9 minutes ago, rusty69 said:

Ok. Thanks. The absorbtion is usually set between 13.9 and 14.1 Volts for a 10 minute duration. So, if I want to use the tail current setting, it should be set to 5% of my 280Ahr LI + 100 Ahr LA bank = 19 A, or 5 % of 280Ahr = 14A? The chargers are capable of 30A each, and there are 2.

Ah well here we run headlong into the problem of mixing batteries of different chemistries. The LA wants a tail current setting of 2% or less, the Li wants a tail current setting of 5%. Which is appropriate? There is only one way to find out.

 

FIGHT!

[rusty69]

2 minutes ago, nicknorman said:

Ah well here we run headlong into the problem of mixing batteries of different chemistries. The LA wants a tail current setting of 2% or less, the Li wants a tail current setting of 5%. Which is appropriate? There is only one way to find out.

 

FIGHT!

Maybe I'll just ditch the LA. Seems so much easier.

[IanD]

4 minutes ago, nicknorman said:

Ah well here we run headlong into the problem of mixing batteries of different chemistries. The LA wants a tail current setting of 2% or less, the Li wants a tail current setting of 5%. Which is appropriate? There is only one way to find out.

 

FIGHT!

Aren't the recommended absorption voltages different too? And LA voltages vary with temperature but LFP don't?

[rusty69]

1 minute ago, IanD said:

Aren't the recommended absorption voltages different too? And LA voltages vary with temperature but LFP don't?

Yes. My LA has a recommended absorbtion of 14.4V. I tend to stick it on the battery charger once a week and isolate the LI to satisfy that requirement, though understand it is less than ideal.

[rusty69]

22 hours ago, nicknorman said:

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

I'm sure you know all this, being an electronic genius, however I thought I would share it here anyway. Whilst investigating my optimum tail current termination valuation vs absorption voltage, I came across this quote from nordkyn:

 

Quote

The worst ripple voltage is produced by solar PWM charge controllers, followed by old-style transformer/rectifier battery chargers, which should not be associated with lithium batteries

 

 

From this page on tinterweb

 

https://nordkyndesign.com/charging-marine-lithium-battery-banks/

Edited February 17 by rusty69
not Rod

[nicknorman]

19 minutes ago, rusty69 said:

I'm sure you know all this, being an electronic genius, however I thought I would share it here anyway. Whilst investigating my optimum tail current termination valuation vs absorbrion voltage, I came across this quote from Rod:

 

 

 

From this page on tinterweb

 

https://nordkyndesign.com/charging-marine-lithium-battery-banks/

Yes it’s a good point. I got the Li battery in the early winter and so far, what with snow on the panel, the panel blowing over etc etc, the solar has never got even close to fully charging the battery. But in summer, it will do. Which is a good reason for getting an MPPT controller!

 

It’s actually also a good point in relation to charging with an alternator which is intrinsically fairly rippley. In our case the Combi input capacitors act to smooth out the ripples a lot, but a system with just an alternator and no large capacitors in the system, is going to have plenty of ripple. At some point I might take my ‘scope down to the boat and check out the ripple with and without the Combi in circuit. Probably the ripple won’t be that bad at lower SoC due to the very low internal resistance of the Li, but it will be interesting  see the ripple as the batteries approach 100% and the current is tapering.

[peterboat]

22 hours 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.

I have always charged by solar on my Lithiums, however I do have things running, the fan on the toilet and the fridge freezer  so this seems to keep things correct on my system. Even still I have seen my midnite controller showing no charge and the batteries at the correct voltage, maybe the quality of the controller is what counts?

[GUMPY]

Some waffle about setting MPPT controllers for lithium.

 

 

[MtB]

56 minutes ago, GUMPY said:

Some waffle about setting MPPT controllers for lithium.

 

 

 

 

37 minutes!!!!!!

 

I'm watching it at double speed and not seen anything useful yet....

 

But hark, at 2 mins 40 sec I hear "Lets get to it!" and he does! 

 

Back to watching now....